MONOLITHIC HEATER BODIES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority to the following U.S. Provisional

Applications, the contents of which applications are incorporated herein by reference in their entirety as if set forth verbatim: App. No. 62/850,599, filed May 21, 2019; App. No.

62/850,623, filed May 21, 2019; App. No. 62/850,678, filed May 21, 2019; App. No.

62/850,692, filed May 21, 2019; and App. No. 62/850,701, filed May 21, 2019.

FIELD

[0002] The present subject matter relates generally to energy conversion systems, power generation systems, and energy distribution systems. The present subject matter additionally relates to heat exchangers and heat exchanger systems. The present subject matter further relates to piston engine assemblies, such as closed-cycle engine systems. The present subject matter still further relates to systems and methods for control or operation of one or more systems of the present subject matter herein.

BACKGROUND

[0003] Power generation and distribution systems are challenged to provide improved power generation efficiency and/or lowered emissions. Furthermore, power generation and distribution systems are challenged to provide improved power output with lower

transmission losses. Certain power generation and distribution systems are further challenged to improve sizing, portability, or power density generally while improving power generation efficiency, power output, and emissions.

[0004] Certain engine system arrangements, such as closed cycle engines, may offer some improved efficiency over other engine system arrangements. However, closed cycle engine arrangements, such as Stirling engines, are challenged to provide relatively larger power output or power density, or improved efficiency, relative to other engine arrangements. Closed cycle engines may suffer due to inefficient combustion, inefficient heat exchangers, inefficient mass transfer, heat losses to the environment, non-ideal behavior of the working fluid(s), imperfect seals, friction, pumping losses, and/or other inefficiencies and

imperfections. As such, there is a need for improved closed cycle engines and system arrangements that may provide improved power output, improved power density, or further improved efficiency. Additionally, there is a need for an improved closed cycle engine that may be provided to improve power generation and power distribution systems.

[0005] Additionally, or alternatively, there is a general need for improved heat transfer devices, such as for heat engines, or as may be applied to power generation systems, distribution systems, propulsion systems, vehicle systems, or industrial or residential facilities.

[0006] Furthermore, there is a need for improved control system and methods for operating power generation systems as may include subsystems that collectively may provide improved power generation efficiency or reduced emissions.

BRIEF DESCRIPTION

[0007] Aspects and advantages will be set forth in part in the following description, or may be apparent from the description, or may be learned through practicing the presently disclosed subject matter.

[0008] In one aspect, the present disclosure embraces monolithic heater bodies, such as for use in connection with a closed-cycle engine. An exemplary monolithic heat exchanger body may include a plurality of heating walls and a plurality of combustion fins. The plurality of heating walls may be configured and arranged in an array of spirals or spiral arcs relative to a longitudinal axis. Adjacent portions of the plurality of heating walls may respectively define a corresponding plurality of heating fluid pathways therebetween. The plurality of combustion fins may be circumferentially spaced about a perimeter of an inlet plenum. The inlet plenum may include or fluidly communicate with a combustion chamber. The plurality of heating fluid pathways may fluidly communicate with the inlet plenum. The plurality of combustion fins may occupy a radially or concentrically inward portion of the monolithic heat exchanger body. The plurality of heating fluid pathways may have a heat transfer relationship with a heat sink disposed about a radially or concentrically outward portion of the monolithic heat exchanger body. A plurality of conduction breaks disposed radially or concentrically outward relative to the plurality of combustion fins may at least partially inhibit heat conduction from the plurality of combustion fins to the plurality of heating walls.

[0009] These and other features, aspects and advantages will become better understood with reference to the following description and appended claims. The

accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and, together with the description, serve to explain certain principles of the presently disclosed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A full and enabling disclosure including the best mode, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

[0011] FIG. 4.1.1 schematically depicts a cross-sectional view of an exemplary closed-cycle engine, which may be a regenerative heat engine and/or a Stirling engine;

[0012] FIGs. 4.1 2A and 4.1 2B schematically depict an exemplary heater bodies, which, for example, may be included in the closed-cycle engine shown in FIG. 4.1.1;

[0013] FIGs. 4.1.3 A, 4.1.3B, and 4.1.3C schematically depict a cross-sectional perspective view of an exemplary heater body, which, for example, may be included in the closed-cycle engine shown in FIG. 4.1.1;

[0014] FIG. 4.1.4 schematically depicts a top view of an exemplary heater body, which, for example, may be included in the closed-cycle engine shown in FIG. 4.1.1;

[0015] FIG. 4.1.5 shows a flowchart depicting an exemplary method of heating a closed-cycle engine, such as a regenerative heat engine;

[0016] FIGs. 4.1.6A and 4.1.6B schematically depict exemplary monolithic bodies, which may include monolithic body portions and/or monolithic body-segments;

[0017] FIG. 4.1.7 schematically depicts another exemplary monolithic heater body;

[0018] FIGs. 4.1.8A-4.1.8G schematically depict exemplary heat shields that may be included in a monolithic heater body and/or a monolithic body-segment;

[0019] FIG. 4.1.9 schematically depicts a cross-sectional view of a portion of an exemplary heater body, illustrating portions of an exemplary piston body and an exemplary heat-capture pathway;

[0020] FIG. 4.1.10 schematically depicts a cross-sectional view of an exemplary an interface between a heater body and an engine body;

[0021] FIG. 4.2.1 A shows a cross-sectional perspective view of an exemplary combustor body portion of a heater body that may be included in the heater body shown in FIG. 4.1.3B; [0022] FIG. 4.2. IB shows a cross-sectional perspective view of another exemplary combustor body portion of a heater body that may be included in the heater body shown in FIG. 4.1.3B;

[0023] FIG. 4.2.2A schematically depicts a cross-sectional view of an perspective exemplary heater body that includes multi-stage combustion;

[0024] FIG. 4.2.2B schematically depicts a cross-sectional top-view of an exemplary combustion zone occupying a radially-inward portion of a hot-side heat exchanger;

[0025] FIG. 4.2.3A schematically depicts a cross-sectional view of an exemplary combustor body that includes a venturi;

[0026] FIGs. 4.2.3B and 4.2.3C illustrate exemplary fluid velocity profiles for the combustor body shown in FIG. 4.2.3 A;

[0027] FIGs. 4.2.4A-4.2.4E schematically depict exemplary combustor vanes;

[0028] FIG. 4.2.5 A shows a flowchart depicting an exemplary method of combusting a fuel;

[0029] FIG. 4.2.5B shows a flowchart depicting another exemplary method of combusting a fuel;

[0030] FIG. 4.3.1 schematically depicts a cross sectional view of an exemplary fuel injector assembly according to an aspect of the present disclosure;

[0031] FIG. 4.3.8 schematically depicts a cross sectional view of an exemplary fuel injector assembly according to an aspect of the present disclosure;

[0032] fuel injector assembly according to an aspect of the present disclosure;

[0033] FIG. 4.4.1 A shows a top cross-sectional view of an exemplary heat exchanger body portion of a heater body, such as the heater body shown in FIG. 4.1.3 A;

[0034] FIG. 4.4. IB shows a top cross-sectional view of the exemplary heat exchanger body of FIG. 4.4.1 A, with a plurality of heat transfer regions indicated;

[0035] FIG. 4.4.2A shows a top cross-sectional view of an exemplary heat exchanger body portion of a heater body, such as the heater body shown in FIG. 4.1 3B;

[0036] FIG. 4.4.2B shows a top cross-sectional view of the exemplary heat exchanger body of FIG. 4.4.2A, with a plurality of heat transfer regions indicated;

[0037] FIG. 4.4.3A and 4.4.3B show top cross-sectional views of additional exemplary embodiments of a heat exchanger body;

[0038] FIG. 4.4.4 shows a flowchart depicting an exemplary method of heating a plurality of heat transfer regions; [0039] FIG. 4.5.2 schematically depicts a cross-sectional view of another exemplary working-fluid body that may be included in a heater body, such as the heater body shown in FIG. 4.1.3B;

[0040] FIG. 4.5.3 schematically depicts a bottom cross-sectional view of an exemplary working-fluid body;

[0041] FIGs. 4.5.5A-4.5.5D schematically depict further aspects of an exemplary heater body;

[0042] FIG. 4.5.6 shows a flowchart depicting an exemplary method of heating an engine-working fluid;

[0043] FIG. 5.1.28 provides an example computing system in accordance with an example embodiment of the present disclosure.

[0044] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present disclosure.

DETAILED DESCRIPTION

[0045] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure and not limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope of the disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. In another instance, ranges, ratios, or limits associated herein may be altered to provide further embodiments, and all such embodiments are within the scope of the present disclosure. Unless otherwise specified, in various embodiments in which a unit is provided relative to a ratio, range, or limit, units may be altered, and/or subsequently, ranges, ratios, or limits associated thereto are within the scope of the present disclosure. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0046] It is understood that terms“upstream” and“downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example,“upstream” refers to the direction from which the fluid flows, and“downstream” refers to the direction to which the fluid flows. It is also understood that terms such as“top”,“bottom”,“outward”,“inward”, and the like are words of convenience and are not to be construed as limiting terms. The term “loop” can be any suitable fluid pathway along which fluid can flow and can be either open or closed, unless stated otherwise. As used herein, the terms“first”,“second”, and“third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. The terms“a” and“an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0047] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as“about,”“substantially,” and“approximately,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value, or the precision of the methods or machines for constructing or manufacturing the components and/or systems. For example, the approximating language may refer to being within a 10 percent margin.

[0048] Here and throughout the specification and claims, range limitations are combined and interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. For example, all ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.

[0049] The heat transfer relationships described herein may include thermal communication by conduction and/or convection. A heat transfer relationship may include a thermally conductive relationship that provides heat transfer through conduction (e.g., heat diffusion) between solid bodies and/or between a solid body and a fluid. Additionally, or in the alternative, a heat transfer relationship may include a thermally convective relationship that provides heat transfer through convection (e.g., heat transfer by bulk fluid flow) between a fluid and a solid body. It will be appreciated that convection generally includes a combination of a conduction (e.g., heat diffusion) and advection (e.g., heat transfer by bulk fluid flow). As used herein, reference to a thermally conductive relationship may include conduction and/or convection; whereas reference to a thermally convective relationship includes at least some convection.

[0050] A thermally conductive relationship may include thermal communication by conduction between a first solid body and a second solid body, between a first fluid and a first solid body, between the first solid body and a second fluid, and/or between the second solid body and a second fluid. For example, such conduction may provide heat transfer from a first fluid to a first solid body and/or from the first solid body to a second fluid.

Additionally, or in the alternative, such conduction may provide heat transfer from a first fluid to a first solid body and/or through a first solid body (e.g., from one surface to another) and/or from the first solid body to a second solid body and/or through a second solid body (e.g., from one surface to another) and/or from the second solid body to a second fluid.

[0051] A thermally convective relationship may include thermal communication by convection (e.g., heat transfer by bulk fluid flow) between a first fluid and a first solid body, between the first solid body and a second fluid, and/or between a second solid body and a second fluid. For example, such convection may provide heat transfer from a first fluid to a first solid body and/or from the first solid body to a second fluid. Additionally, or in the alternative, such convection may provide heat transfer from a second solid body to a second fluid.

[0052] It will be appreciated that the terms“clockwise” and“counter-clockwise” are terms of convenience and are not to be limiting. Generally, the terms“clock-wise” and “counter-clockwise” have their ordinary meaning, and unless otherwise indicated refer to a direction with reference to a top-down or upright view. Clockwise and counter-clockwise elements may be interchanged without departing from the scope of the present disclosure.

[0053] As used herein, the terms“additively manufactured” or“additive

manufacturing techniques or processes” refer generally to manufacturing processes wherein successive layers of material(s) are provided on each other to“build-up,” layer-by-layer, a three-dimensional component. The successive layers generally fuse together to form a monolithic component which may have a variety of integral sub-components.

[0054] Although additive manufacturing technology is described herein as providing fabrication of complex objects by building objects point-by-point, layer-by-layer, typically in a vertical direction, other methods of fabrication are possible and are within the scope of the present subject matter. For example, although the discussion herein refers to the addition of material to form successive layers, one skilled in the art will appreciate that the methods and structures disclosed herein may be practiced with any additive manufacturing technique or manufacturing technology. For example, embodiments of the present disclosure may use layer-additive processes, layer-subtractive processes, or hybrid processes. As another example, embodiments of the present disclosure may include selectively depositing a binder material to chemically bind portions of the layers of powder together to form a green body article. After curing, the green body article may be pre-sintered to form a brown body article having substantially all of the binder removed, and fully sintered to form a consolidated article.

[0055] Suitable additive manufacturing techniques in accordance with the present disclosure include, for example, Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), 3D printing such as by inkjets and laseijets, Sterolithography (SLA), Direct Laser Sintering (DLS), Direct Selective Laser Sintering (DSLS), Electron Beam Sintering (EBS), Electron Beam Melting (EBM), Laser Engineered Net Shaping (LENS), Laser Net Shape Manufacturing (LNSM), Direct Metal Deposition (DMD), Digital Light Processing (DLP), Direct Laser Melting (DLM), Direct Selective Laser Melting (DSLM), Selective Laser Melting (SLM), Direct Metal Laser Melting (DMLM), Binder Jetting (BJ), and other known processes.

[0056] The additive manufacturing processes described herein may be used for forming components using any suitable material. For example, the material may be plastic, metal, concrete, ceramic, polymer, epoxy, photopolymer resin, or any other suitable material that may be in solid, liquid, powder, sheet material, wire, or any other suitable form or combinations thereof. More specifically, according to exemplary embodiments of the present subject matter, the additively manufactured components described herein may be formed in part, in whole, or in some combination of materials including but not limited to pure metals, nickel alloys, chrome alloys, titanium, titanium alloys, magnesium, magnesium alloys, aluminum, aluminum alloys, and nickel or cobalt based superalloys (e.g., those available under the name Inconel® available from Special Metals Corporation). These materials are examples of materials suitable for use in the additive manufacturing processes described herein, and may be generally referred to as“additive materials.”

[0057] In addition, one skilled in the art will appreciate that a variety of materials and methods for bonding those materials may be used and are contemplated as within the scope of the present disclosure. As used herein, references to“fusing” or“binding” may refer to any suitable process for creating a bonded layer of any of the above materials. For example, if an object is made from polymer, fusing may refer to creating a thermoset bond between polymer materials. If the object is epoxy, the bond may be formed by a crosslinking process. If the material is ceramic, the bond may be formed by a sintering process. If the material is powdered metal, the bond may be formed by a melting or sintering process, or additionally with a binder process. One skilled in the art will appreciate that other methods of fusing materials to make a component by additive manufacturing are possible, and the presently disclosed subject matter may be practiced with those methods.

[0058] In addition, the additive manufacturing process disclosed herein allows a single component to be formed from multiple materials. Thus, the components described herein may be formed from any suitable mixtures of the above materials. For example, a component may include multiple layers, segments, or parts that are formed using different materials, processes, and/or on different additive manufacturing machines. In this manner, components may be constructed which have different materials and material properties for meeting the demands of any particular application. In addition, although the components described herein are constructed entirely by additive manufacturing processes, it should be appreciated that in alternate embodiments, all or a portion of these components may be formed via casting, machining, and/or any other suitable manufacturing process. Indeed, any suitable combination of materials and manufacturing methods may be used to form these components.

[0059] An exemplary additive manufacturing process will now be described. Additive manufacturing processes fabricate components using three-dimensional (3D) information, for example a three-dimensional computer model, of the component. Accordingly, a three- dimensional design model of the component may be defined prior to manufacturing. In this regard, a model or prototype of the component may be scanned to determine the three- dimensional information of the component. As another example, a model of the component may be constructed using a suitable computer aided design (CAD) program to define the three-dimensional design model of the component.

[0060] The design model may include 3D numeric coordinates of the entire configuration of the component including both external and internal surfaces of the component. For example, the design model may define the body, the surface, and/or internal passageways such as openings, support structures, etc. In one exemplary embodiment, the three-dimensional design model is converted into a plurality of slices or segments, e.g., along a central (e.g., vertical) axis of the component or any other suitable axis. Each slice may define a thin cross section of the component for a predetermined height of the slice. The plurality of successive cross-sectional slices together form the 3D component. The component is then“built-up” slice-by-slice, or layer-by-layer, until finished. [0061] In this manner, the components described herein may be fabricated using the additive process, or more specifically each layer is successively formed, e.g., by fusing or polymerizing a plastic using laser energy or heat or by sintering or melting metal powder. For example, a particular type of additive manufacturing process may use an energy beam, for example, an electron beam or electromagnetic radiation such as a laser beam, to sinter or melt a powder material. Any suitable laser and laser parameters may be used, including

considerations with respect to power, laser beam spot size, and scanning velocity. The build material may be formed by any suitable powder or material selected for enhanced strength, durability, and useful life, particularly at high temperatures.

[0062] Each successive layer may be, for example, between about 10 pm and 200 pm, although the thickness may be selected based on any number of parameters and may be any suitable size according to alternative embodiments. Therefore, utilizing the additive formation methods described above, the components described herein may have cross sections as thin as one thickness of an associated powder layer, e.g., 10 pm, utilized during the additive formation process.

[0063] In addition, utilizing an additive process, the surface finish and features of the components may vary as need depending on the application. For example, the surface finish may be adjusted (e.g., made smoother or rougher) by selecting appropriate laser scan parameters (e.g., laser power, scan speed, laser focal spot size, etc.) during the additive process, especially in the periphery of a cross-sectional layer which corresponds to the part surface. For example, a rougher finish may be achieved by increasing laser scan speed or decreasing the size of the melt pool formed, and a smoother finish may be achieved by decreasing laser scan speed or increasing the size of the melt pool formed. The scanning pattern and/or laser power can also be changed to change the surface finish in a selected area.

[0064] After fabrication of the component is complete, various post-processing procedures may be applied to the component. For example, post processing procedures may include removal of excess powder by, for example, blowing or vacuuming. Other post processing procedures may include a stress relief process. Additionally, thermal, mechanical, and/or chemical post processing procedures can be used to finish the part to achieve a desired strength, surface finish, a decreased porosity decreasing and/or an increased density (e.g., via hot isostatic pressing), and other component properties or features.

[0065] It should be appreciated that one skilled in the art may add or modify features shown and described herein to facilitate manufacture of the system A10 provided herein without undue experimentation. For example, build features, such as trusses, grids, build surfaces, or other supporting features, or material or fluid ingress or egress ports, may be added or modified from the present geometries to facilitate manufacture of embodiments of the system A10 based at least on a desired manufacturing process or a desired particular additive manufacturing process.

[0066] Notably, in exemplary embodiments, several features of the components described herein were previously not possible due to manufacturing restraints. However, the present inventors have advantageously utilized current advances in additive manufacturing techniques to develop exemplary embodiments of such components generally in accordance with the present disclosure. While certain embodiments of the present disclosure may not be limited to the use of additive manufacturing to form these components generally, additive manufacturing does provide a variety of manufacturing advantages, including ease of manufacturing, reduced cost, greater accuracy, etc.

[0067] In this regard, utilizing additive manufacturing methods, even multi-part components may be formed as a single piece of continuous metal, and may thus include fewer sub-components and/or joints compared to prior designs. The integral formation of these multi-part components through additive manufacturing may advantageously improve the overall assembly process, reduce potential leakage, reduce thermodynamic losses, improve thermal energy transfer, or provide higher power densities. For example, the integral formation reduces the number of separate parts that must be assembled, thus reducing associated time, overall assembly costs, reduces potential leakage pathways, or reduces potential thermodynamic losses. Additionally, existing issues with, for example, leakage, may advantageously be reduced. Still further, joint quality between separate parts may be addressed or obviated by the processes described herein, such as to desirably reduce leakage, assembly, and improve overall performance.

[0068] Also, the additive manufacturing methods described above provide much more complex and intricate shapes and contours of the components described herein to be formed with a very high level of precision. For example, such components may include thin additively manufactured layers, cross sectional features, and component contours. As another example, additive manufacturing may provide heat exchanger surface areas, volumes, passages, conduits, or other features that may desirably improve heat exchanger efficiency or performance, or overall engine or system performance. In addition, the additive

manufacturing process provides the manufacture of a single component having different materials such that different portions of the component may exhibit different performance characteristics. The successive, additive steps of the manufacturing process provide the construction of these novel features. As a result, the components described herein may exhibit improved functionality and reliability.

[0069] HEATER BODIES AND METHODS OF HEATING A CLOSED-CYCLE

ENGINE

[0070] An exemplary engine c002 is shown in FIG. 4.1.1. The engine c002 may be a closed cycle engine, such as a regenerative heat engine and/or a Stirling engine; however other engines including other closed-cycle engines and/or regenerative heat engines are also contemplated and the scope of the present disclosure embraces any engine. A closed-cycle engine c002 may include a heater body clOO and an engine body c050. In the embodiment shown, a closed-cycle engine c002 may include an engine body c050 and a heater body clOO disposed on opposite sides of the engine body c050. For example, a first heater body clOO may be disposed at a first side of an engine body c050 and a second heater body clOO may be disposed at a second side of an engine body c050. In still other embodiments, a plurality of engine bodies c050 may be provided and/or a single heater body clOO or a multitude of heater bodies clOO may be provided. The closed-cycle engine c002 may include a piston assembly c090 and a load device c092 operably inserted within an engine body c050 and/or a heater body clOO.

[0071] The closed-cycle engine c002 may be provided in the form of an engine assembly that includes one or more monolithic bodies or monolithic body-segments as described herein. A monolithic body and/or a monolithic body-segment may be fabricated using an additive manufacturing technology and may be void of any seams, joints, or the like characteristic of separately fabricated components. By way of example, an exemplary closed-cycle engine c002 may be assembled from an engine assembly that includes a first heater body clOO and a first engine body c050. The first heater body may define a first portion of a first monolithic body or a first monolithic body-segment, and the first engine body may define a second portion of the first monolithic body or a second monolithic body- segment operably coupled or operably couplable to the first heater body.

[0072] Now turning to e.g., FIGs. 4.1 2A and 4.1 2B, 4.1.3 A through 4.1 3C, and

4.1.4, exemplary heater bodies clOO will be described. The presently disclosed heater bodies clOO may be used to supply heat to a closed-cycle engine c002 such as a regenerative heat engine and/or a Stirling engine. However, it will be appreciated that the presently disclosed heater bodies cl 00 may be used as a heating source in a number of other settings, all of which are within the scope of the present disclosure. In some embodiments, at least a portion of the heater body cl 00 may define at least a portion of a closed-cycle engine c002, such as a monolithic body or a monolithic body-segment of such a closed-cycle engine c002. For example, the monolithic body may be an additively manufactured monolithic body, or the monolithic body-segment may be an additively manufactured monolithic body-segment. However, in addition or as an alternative to additive manufacturing technology, it will be appreciated that the monolithic body or various monolithic body-segments of a closed-cycle engine c002 may be formed using any desired technology, all of which are within the scope of the present disclosure.

[0073] As shown, an exemplary heater body cl 00 may include a combustion chamber cl 02 and a recirculation pathway cl 04 configured to recirculate combustion gas through the combustion chamber cl02. The recirculation pathway cl04 may include a hot-side heat exchanger cl 06 configured to transfer heat from circulating combustion gas to a heat input source, such as a working-fluid body cl 08 defining a heat transfer region having a thermally conductive relationship with at least a portion of the hot-side heat exchanger cl06. For example, heat from the combustion gas may be transferred to the heat transfer region via an engine-working fluid disposed within a working-fluid pathway cl 10. The working-fluid pathway cl 10 may be defined at least in part by the hot-side heat exchanger cl06 and/or at least in part by the working-fluid body cl 08. The hot-side heat exchanger cl 06 may define a portion of the recirculation pathway cl04. The heat transfer region may define a region having a have a thermally conductive relationship with the heating fluid pathway.

[0074] The heat transfer region defined by the working-fluid body cl 08 may include a solid body and/or a fluid pathway defined at least in part by the solid body. In an exemplary embodiment, the hot-side heat exchanger cl 06 may include a plurality of heating fluid pathways that have a heat transfer relationship with a plurality of heat transfer regions. For example, the plurality of heat transfer regions have a thermally conductive relationship with a corresponding portion of the plurality of heating fluid pathways. Additionally, or in the alternative, the heat transfer regions may have a thermally convective relationship with a heating fluid flowing through the heating fluid pathways. The heat transfer regions may be circumferentially spaced about the longitudinal axis of the heater body clOO. Respective ones of the plurality of heat transfer regions may include a solid body and/or a fluid pathway defined at least in part by the solid body. [0075] The working-fluid body cl08 may include one or more portions of a closed- cycle engine c002, such as a piston chamber cl 12 (e.g., a hot piston chamber) and/or a regenerator body cl 14. A fluid pathway defined the working-fluid body cl08 may fluidly communicate with the piston chamber and the regenerator body cl 14. The engine-working fluid disposed within the working-fluid pathway cl 10 may be an engine-working fluid, such as an inert gas, which may flow in an alternating fashion between the piston chamber cl 12 and the regenerator body cl 14. The hot-side heat exchanger cl06 may be provided in the form of a heat exchanger body. The heat exchanger body may define a monolithic body portion of the heater body cl 00 or a monolithic body-segment operably coupled or operably couplable to a monolithic heater body cl 00 or to one or more other monolithic body- segments that make up the heater body clOO.

[0076] The recirculation pathway cl 04 may additionally include a recirculation eductor cl 16 configured to utilize intake air flowing through an intake air pathway cl 18 to entrain and/or accelerate combustion gas and thereby provide a mixture of intake air and recirculating combustion gas to the combustion chamber cl02. The recirculation eductor cl 16 may also include an exhaust pathway cl20 configured to discharge a portion of the combustion gas as exhaust gas. The recirculation eductor cl 16 may fluidly communicate with a downstream portion of the hot-side heat exchanger cl06. The recirculation eductor cl 16 may be provided in the form of an eductor body. The eductor body may define a monolithic body portion of the heater body cl 00 or a monolithic body-segment operably coupled or operably couplable to a monolithic heater body cl 00 or to one or more other monolithic body-segments that make up the heater body clOO.

[0077] In some embodiments, the heater body clOO may include a conditioning conduit cl 22 fluidly communicating with a downstream portion of the recirculation eductor cl 16 and an upstream portion of the combustion chamber cl02. The conditioning conduct cl22 may be configured to guide combustion gas (e.g., a mixture of intake air and

recirculating combustion gas) to the combustion chamber cl 02, and may be configured with a size and shape so as to condition one or more fluid dynamic properties of the combustion gas flowing to the combustion chamber cl22. Exemplary fluid dynamics properties that may be conditioned by the conditioning conduit cl 22 include pressure, pressure gradient, flow velocity, velocity gradient, turbulence, vorticity, curl, and so forth. The conditioning conduit cl 22 may define a conduit volume selected to provide one or more desired fluid dynamics properties of combustion gas flowing therethrough, and/or to allow for mixing of intake air with recirculating combustion gas. In some embodiments, the conditioning conduit cl 22 may be configured to swirl combustion gas flowing therethrough. For example, the conditioning conduit cl22 may establish or sustain a vortex, which may enhance combustion quality in the combustion chamber cl02. Additionally, or in the alternative, combustion gas circulating through the conditioning conduit cl 22 may cool the combustion chamber cl 02, with heat from the combustion chamber cl 02 heating the combustion gas prior to entering the combustion chamber cl 02.

[0078] The combustion chamber cl02 and the conditioning conduit cl04 may be provided in the form of a combustor body. The combustor body may define a monolithic body portion of the heater body cl 00 or a monolithic body-segment operably coupled or operably couplable to a monolithic heater body cl 00 or to one or more other monolithic body-segments that make up the heater body clOO.

[0079] The heater body clOO may additionally include a heat recuperator cl24 configured to utilize exhaust gas flowing through the exhaust pathway cl 20 to preheat intake air flowing through the intake air pathway cl 18, thereby recuperating heat from the exhaust gas. The terms preheater and recuperator may be used interchangeably; however, in some instances, the term preheater may be used with reference to preheating intake air flowing through the intake air pathway cl 18, and the term recuperator may be used with reference to recuperating heat from exhaust gas flowing through the exhaust pathway cl20. The heat recuperator cl24 may be provided in the form of a heat recuperator body. The heat recuperator body may define a monolithic body portion of the heater body clOO or a monolithic body-segment operably coupled or operably couplable to a monolithic heater body clOO or to one or more other monolithic body-segments that make up the heater body clOO. As shown in FIG. 4.1.2A, the heat recuperator cl24 may be located downstream from the recirculation eductor cl 16 relative to the exhaust gas pathway cl 20 and upstream from the recirculation eductor cl 16 relative to the intake air pathway cl 18. The heat recuperator located as shown in FIG. 4.1 2A may exchange heat between exhaust gas flowing through the exhaust gas pathway cl 20 and intake air flowing through the intake air pathway cl 18. In another embodiment, as shown in Fig. 4.1.2B, the heat recuperator cl24 may define a portion of the recirculation pathway cl04. For example, the heat recuperator cl24 may be located upstream from the recirculation eductor cl 16 relative to the recirculation pathway cl 20, while also being located upstream from the recirculation eductor cl 16 relative to the intake air pathway cl 18. The heat recuperator located as shown in FIG. 4.1 2B may exchange heat between exhaust gas flowing through the exhaust gas pathway cl 20 and intake air flowing through the intake air pathway cl 18, and/or between combustion gas flowing through the recirculating pathway cl 04 and intake air flowing through the intake air pathway cl 18.

[0080] One or more fuel nozzles cl 26 may be operably coupled to the heater body clOO. Fuel may be supplied to the combustion chamber cl02 by one or more fuel lines cl03. For example, the one or more fuel nozzles cl 26 may be operably coupled to the combustion chamber cl02. Fuel injected into the combustion chamber cl02 may combine with circulating combustion gas to provide a suitable air-to-fuel ratio. The fuel and at least a portion of the circulating combustion gas may be combusted in the combustion chamber so as to generate hot combustion gas. The combustion chamber cl 02 may fluidly communicate with an upstream portion of the hot-side heat exchanger cl 06, thereby suppling the hot combustion gas to the hot-side heat exchanger cl 06 for heating the working-fluid body cl 08. One or more intake air pathways cl 18, one or more exhaust gas pathways cl20, one or more recirculation pathways cl 04, and one or more fuel lines cl 03 may collectively define a primary flowpath cl21.

[0081] FIGs. 4.1.3A, 4.1.3B, and 4.1.3C schematically depict cross-sectional perspective views of an exemplary heater bodies clOO, while FIG. 4.1.4 schematically depicts a top view of the exemplary heater body clOO shown in FIG. 4.1.3 A. As shown, an exemplary heater body clOO may have an annular configuration, however, other

configurations are also contemplated. The heater body clOO may include a plurality of monolithic body portions that together may define a monolithic heater body clOO.

Alternatively, or in addition, the heater body cl 06 may include one or more monolithic body- segments operably coupled or operably couplable to a monolithic heater body clOO. Further, a plurality of monolithic body-segments may be operably coupled or operably couplable to one another to define at least a portion of a heater body clOO. In an exemplary embodiment, a heater body clOO may define a single monolithic body. In other embodiments, a plurality of monolithic body-segments may be operably coupled to one another, such as via welding, fusing, or the like, so as to provide an integrally formed heater body clOO.

[0082] A heater body clOO and/or various featured thereof may include a proximal portion c200 and a distal portion c202 oriented relative to a longitudinal axis c204, with a medial portion c206 disposed between the proximal portion c200 and the distal portion c202. The proximal portion c200 of the heater body clOO or a feature thereof refers to a portion, relative to a longitudinal axis c204, adjacent or relatively proximate to a working-fluid body cl08 such as one or more pistons of a closed-cycle engine c002. The distal portion c202 of the heater body cl 00 or a feature thereof refers to a portion, relative to the longitudinal axis c204, opposite from or relatively remote to the working-fluid body cl08. A proximal, distal, or medial portion c200, c202, c206 need not refer to a finite point on the heater body cl 00 or a feature thereof; rather, it will be appreciated that the terms proximal, distal, and medial c200, c202, c206 may be used generally, such as to denote the location of a portion of the heater body clOO or a feature thereof relative to the working-fluid body cl08 and/or to denote the location of various features of the heater body cl 00 relative to one another.

[0083] Referring still to FIGs. 4.1.3 A, 4.1.3B, and 4.1.3C, a heater body clOO may include a combustion chamber cl 02 and a hot-side heat exchanger cl 06 circumferentially surrounding at least a portion of the combustion chamber cl02. In some embodiments, a recirculation pathway cl 04 may circumferentially surround at least a portion of the combustion chamber cl02. A heater body clOO may additionally or alternatively include a conditioning conduit cl 22 circumferentially surrounding at least a portion of the combustion chamber cl02. For example, as shown, the hot-side heat exchanger cl06 may

circumferentially surround a proximal portion c200 of the combustion chamber cl 02 and the conditioning conduit cl22 may circumferentially surround a medial portion c206 and/or a distal portion c202 of the combustion chamber cl02. In some embodiments, the hot-side heat exchanger cl 06 may additionally circumferentially surround at least some of a medial portion c206 of the combustion chamber cl02. In some embodiments, it may be advantageous for the combustion chamber cl02 to be aligned with the longitudinal axis c204 and/or for a plurality of combustion chambers cl 02 to be circumferentially spaced (e.g., evenly distributed) about the longitudinal axis c204. For example, such alignment and/or even distribution may encourage relatively even heat distribution within the heater body clOO and/or the hot-side heat exchanger cl06. Such relatively even heat distribution may, in turn, encourage relatively even heat transfer from the hot-side heat exchanger cl06 (e.g., from a heating fluid flowing therethrough) to the plurality of heat transfer regions.

[0084] The heater body clOO may further include a recirculation eductor cl 16 circumferentially surrounding the combustion chamber cl02. When the heater body clOO includes a conditioning conduit cl 22, the recirculation eductor cl 16 may be disposed radially or concentrically outward from the conditioning conduit cl 22, for example, such that the recirculation eductor cl 16 circumferentially surrounds at least a portion of the conditioning conduit cl22. For example, the recirculation eductor cl 16 may circumferentially surround a distal portion c202 and/or a medial portion (e.g., a distally-medial portion) of the combustion chamber cl02. Additionally, when the heater body clOO includes a conditioning conduit cl 22, the recirculation eductor cl 16 may circumferentially surround a distal portion c202 and/or a medial portion (e.g., a distally-medial portion) of the conditioning conduit cl22.

The recirculation eductor cl 16 may be disposed axially adjacent to the hot-side heat exchanger cl 06, such as adjacent to a distal portion c202 of the hot-side heat exchanger cl 06 relative to the longitudinal axis c204.

[0085] In some embodiments, a heater body clOO may include a heat recuperator cl24 circumferentially surrounding the combustion chamber cl02. When the heater body clOO includes a conditioning conduit cl 22, the heat recuperator cl24 may be disposed radially or concentrically outward from the conditioning conduit cl 22, for example, such that the heat recuperator cl 24 circumferentially surrounds at least a portion of the conditioning conduit cl22. For example, the heat recuperator cl24 may circumferentially surround a distal portion c202 and/or a medial portion (e.g., a distally-medial portion) of the combustion chamber cl02. Additionally, when the heater body clOO includes a conditioning conduit cl 22, the heat recuperator cl24 may circumferentially surround a distal portion c202 and/or a medial portion (e.g., a distally-medial portion) of the conditioning conduit cl22. The heat recuperator cl24 may be disposed axially adjacent to the recirculation eductor cl 16, such as adjacent to a distal portion c202 of the recirculation eductor cl 16 relative to the longitudinal axis c204.

[0086] In some embodiments, as shown for example in FIG. 4.1 3B, a heater body clOO may include a heat shield cl27. The heat shield cl27 may be configured to insulate and/or shield one or more portions of the heater body clOO from a heat source within the heater body clOO. For example, the heat source may include a combustion flame and/or combustion gas circulating through the recirculation pathway cl04, and/or portions of the heater body clOO that become heated by the combustion flame and/or combustion gas.

Additionally, or in the alternative, the heat shield cl27 may provide a heat sink to absorb and/or dissipate heat, such as heat from a combustion flame and/or combustion gas circulating through the recirculation pathway cl04. In some embodiments, the heat shield cl 27 may include a cooling jacket cl 28 defined by an inner wall cl 30 and an outer wall cl32. The cooling jacket cl28 may fluidly communicate with the intake air annulus c216, such that intake air may flow therethrough. Additionally, or in the alternative, the cooling jacket cl28 may define a space with a vacuum or near vacuum. The cooling jacket cl28 may define one or more pathways, such as an annular pathway or a plurality of semi-annular pathways. The cooling jacket may cool hot portions of the heater body clOO, for example to maintain suitable operating temperatures and/or to shield users or surrounding equipment from hot portions of the heater body clOO.

[0087] A heater body clOO may define a single monolithic body providing a recirculation pathway cl04, an intake air pathway cl 18, and/or an exhaust pathway cl20.

For example, a plurality of monolithic body portions may together define a single monolithic body. Alternatively, a heater body clOO may include separate monolithic body-segments respectively defining a recirculation pathway cl04, an intake air pathway cl 18, and/or an exhaust pathway cl20. In some embodiments, a first monolithic body-segment may define a recirculation pathway cl 04, a second monolithic body-segment may define an intake air pathway cl 18, and a third monolithic body-segment may define an exhaust pathway cl20. Such monolithic body-segments may be coupled to one another, such as via welding, fusing, or the like, so as to provide an integrally formed heater body clOO.

[0088] A monolithic body defining a recirculation pathway cl04 may include a combustion chamber cl 02 and a hot-side heat exchanger cl 06 fluidly communicating with a proximal portion c200 of the combustion chamber cl02. Such a monolithic recirculation pathway cl 04 may additionally include a recirculation eductor cl 16 fluidly communicating with a radially or concentrically outward portion of the hot-side heat exchanger cl 06 and a conditioning conduit cl 22 having a proximal portion c200 fluidly communicating with a radially or concentrically inward portion of the recirculation eductor cl 16 and a distal portion c202 fluidly communicating with a distal portion c202 of the combustion chamber cl02.

[0089] In some embodiments, a heater body clOO may include a recirculation annulus c208. The recirculation annulus c208 may be disposed radially or concentrically outward from at least a portion of the hot-side heat exchanger cl 06 and/or at least a portion of the recirculation eductor cl 16. Additionally, or in the alternative, the recirculation annulus c208 may circumferentially surround at least a portion of the hot-side heat exchanger cl06 and/or at least a portion of the recirculation eductor cl 16. The recirculation annulus c208 may fluidly communicate with a radially or concentrically outward portion of the hot-side heat exchanger cl 06 and a radially or concentrically outward portion of the recirculation eductor cl 16 so as to define a pathway to direct at least a portion of the combustion gas discharging from the hot-side heat exchanger cl 06 into the recirculation annulus c208. [0090] In some embodiments, a heater body cl 00 may include fuel injector body c401. The fuel injector body c401 may include a combustor cap c210 providing fluid communication between a distal portion c202 of the conditioning conduit cl22 and a distal portion c202 of the combustion chamber cl02. The fuel injector body c401 may additionally or alternatively include one or more fuel nozzles c214. The fuel injector body c401 and/or the combustor cap c210 and/or one or more fuel nozzles c214 may be a separate component operably coupled or operably couplable to the heater body cl 10, such as at a distal portion c202 of the conditioning conduit cl 22 as shown. Additionally, or in the alternative, the fuel injector body c401 and/or the combustor cap c210 and/or one or more fuel nozzles c214 may be a portion of a monolithic body defining at least a portion of the heater body cl 00.

[0091] In some embodiments, one or more fuel nozzles c214 may be operably coupled to the combustor cap c210. For example, the combustor cap c210 may include one or more nozzle ports c212 respectively configured to receive a fuel nozzle c214. One or more fuel nozzles c214 may be operably coupled to corresponding nozzle ports c212 such as by mating threads or the like. The one or more fuel nozzles c214 may include a glow plug c215 operable to ignite fuel and/or combustion gas in the combustion chamber cl02. As shown, the fuel nozzle may be aligned with the longitudinal axis c204 of the heater body clOO and may be concentric with the combustion chamber cl02. Additionally, or in the alternative, one or more fuel nozzles c214 may be circumferentially spaced about the distal portion c202 of the combustion chamber. In some embodiments, it may be advantageous for a fuel nozzle c214 to be aligned with the longitudinal axis c204 and/or for a plurality of fuel nozzles c214 to be circumferentially spaced (e.g., evenly distributed) about the longitudinal axis c204. For example, such alignment and/or even distribution may encourage flame stability within the combustion chamber cl02 and/or relatively even heat distribution within the combustion chamber cl02 and/or the hot-side heat exchanger cl06.

[0092] A monolithic body defining an intake air pathway cl 18 may include an intake air body, such as an intake air annulus c216 and/or a monolithic body defining an exhaust pathway cl 20 may include an exhaust body, such as an exhaust annulus c218. The intake air annulus c216 and the exhaust annulus c218 may define portions of a single monolithic body or may be separate monolithic body-segments operably coupled or operably couplable to one another. The intake air annulus c216 and/or the exhaust annulus c218 may circumferentially surround at least a portion of the combustion chamber cl02. As shown, the intake air annulus c216 may include one or more intake ports c220 and the exhaust annulus c218 may include one or more exhaust ports c222. As shown in FIGs. 4.1.3 A and 4.1 3B, the intake air annulus c216 and the exhaust annulus c218 may be disposed axially adjacent to one another. For example, the intake air annulus c216 may be adjacent to a distal portion c202 of the exhaust annulus c218 and/or the exhaust annulus c218 may be adjacent to a proximal portion of the intake air annulus c216 relative to the longitudinal axis c204. As shown in FIG. 4.1.3C, the intake air annulus c216 and the exhaust annulus c218 may be disposed co-annularly relative to one another. For example, the intake air annulus c216 may be disposed radially or concentrically inward from the exhaust annulus c218, with the exhaust annulus c218 circumferentially surrounding the intake air annulus c216. Alternatively, the exhaust annulus c218 may be disposed radially or concentrically inward from the intake air annulus c216, with the intake air annulus c216 circumferentially surrounding the exhaust annulus c218.

[0093] The intake air annulus c216 may include a plurality of intake vanes c224 circumferentially spaced about the intake air annulus c216. The intake vanes c224 may define at least a portion of a pathway configured to direct intake air from the intake air annulus c216 to the recirculation pathway cl 04. The exhaust annulus c218 may include a plurality of exhaust vanes c226 circumferentially spaced about the exhaust annulus c218.

The exhaust vanes c226 may define at least a portion of a pathway configured to direct exhaust gas into the exhaust pathway c218.

[0094] In some embodiments, the intake air annulus c216 and the exhaust annulus c218 may fluidly communicate with a heat recuperator cl24. More particularly, a preheater portion of the heat recuperator cl 24 may define at least a portion of an intake air pathway cl 18 and a recuperator portion of the heat recuperator cl 24 may define at least a portion of an exhaust pathway cl20. The heat recuperator cl24 may be part of a monolithic body defining the intake air pathway cl 18 and/or the exhaust pathway cl 20. The exhaust annulus c218 and/or the intake air annulus c216 may circumferentially surround at least a portion of the heat recuperator cl24. As shown in FIG. 4.1.2A, the exhaust annulus c218 may circumferentially surround the heat recuperator cl 24, and the intake air annulus c216 may be axially adjacent to the exhaust annulus c218, with the intake vanes c224 being axially adjacent to at least a portion of the heat recuperator cl24. For example, the intake vanes c224 may be adjacent to a distal portion c202 of the heat recuperator cl24.

[0095] The heat recuperator cl24 may include a preheater portion and a recuperator body portion having a thermally conductive relationship with one another. The preheater portion may fluidly communicate with the intake air annulus c216 and the recirculation eductor cl 16 so as to define at least a portion of the intake air pathway cl 18. The recuperator body portion may fluidly communicate with the recirculation eductor cl 16 and the exhaust annulus c218 so as to define at least a portion of the exhaust pathway cl20. In an exemplary embodiment, the exhaust pathway cl 20 from the recirculation eductor cl 16 may be upstream from the intake air pathway cl 18 to the recirculation eductor cl 16 so as to avoid intake air from the intake air pathway cl 18 flowing directly into the exhaust pathway cl 20 before combining with the recirculation pathway cl 04.

[0096] In some embodiments, a heater body cl 00 may include a motive annulus c228 providing fluid communication from the preheater portion of the recuperator cl 24 to the recirculation eductor cl 16. The heat recuperator cl24 may circumferentially surround the motive annulus c228, and the motive annulus may circumferentially surround at least a portion of the combustion chamber cl02. When the heater body clOO includes a conditioning conduit cl 22, the motive annulus c228 may be disposed radially or concentrically outward from the conditioning conduit cl 22, for example, such that the motive annulus c228 circumferentially surrounds at least a portion of the conditioning conduit cl22. For example, the motive annulus c228 may circumferentially surround a medial portion of the combustion chamber cl02 and/or a medial portion of the conditioning conduit cl22. The motive annulus c228 may be disposed axially adjacent to the recirculation eductor cl 16, such as adjacent to a distal portion of the recirculation eductor cl 16 relative to the axial axis c204.

[0097] In exemplary embodiments, the recirculation pathway cl 04, the intake air pathway cl 18 and/or the exhaust pathway cl20 may follow a generally spiral orientation. As shown in FIG. 4.1.2A, the recirculation pathway cl04 and the intake air pathway cl 18 may spiral counterclockwise, and the exhaust pathway cl20 may spiral clockwise. Alternative, the recirculation pathway cl04 and the intake air pathway cl 18 may spiral clockwise, and the exhaust pathway cl 20 may spiral counterclockwise. Such flows through the heater body clOO may transition from counterclockwise flow to clockwise flow (or from clockwise flow to counterclockwise flow) at the exhaust pathway cl20, where exhaust gas separates from combustion gas at the recirculation eductor cl 16. In this way, pressure loss from a change in flow direction may be minimized. Additionally, a pressure drop associated with a change in direction at the exhaust pathway cl 20 may at least partially favor recirculation of combustion gas through the recirculation eductor cl 16.

[0098] During operation, intake air is directed into the intake air annulus c216. In some embodiments, the intake air may be pressurized, such as via a compressor (not shown), to induce a flow of intake air into the intake air pathway cl 18. The intake air circulates counterclockwise through the intake air annulus c216, where a plurality of intake vanes c224 circumferentially spaced about the intake air annulus c216 direct the intake air in a radially or concentrically inward and axially proximal spiral having a counterclockwise orientation. The intake air flowing through the intake vanes c224 continues a radially or concentrically inward spiral flow through the heat recuperator cl 24 and into the motive annulus c228. The intake air in the motive annulus c228 enters the recirculation eductor cl 16 through a plurality of eductor slots configured to accelerate the intake air spirally into the conditioning conduit cl22. The intake air passing through the eductor slots accelerates and entrains combustion gas flowing into the recirculation eductor cl 16 from the recirculation annulus c208. The intake air and the combustion gas mix to provide fresh combustion gas while flowing helically through the conditioning conduit cl 22 in an axially distal direction. The fresh combustion gas reaches the combustion cap c210, which directs the flow of fresh combustion gas into the combustion chamber while a fuel nozzle c214 introduces a flow of fuel, which may include a liquid, gaseous fuel.

[0099] In the combustion chamber cl 02, fuel combines with the fresh combustion gas and is ignited, for example, by a glow plug or a spark plug. The combustion chamber cl 02 provides a vortex combustion pattern with a counterclockwise flow. Centripetal force of the vortex combustion pattern draw the combustion flame radially or concentrically inward while propelling unburnt combustion gas radially or concentrically outward. The combustion gas continues with a spiral counterclockwise flow out of the combustion chamber cl02 and into the hot-side heat exchanger cl06. The combustion gas flows in a radially or concentrically outward counterclockwise spiral through the hot-side heat exchanger cl06 and into the recirculation annulus c208.

[0100] The recirculation annulus c208 directs the combustion gas in an axially distal and radially or concentrically inward direction into the recirculation eductor cl 16, where a portion of the combustion gas is accelerated and entrained by intake air flowing through the eductor slots of the recirculation eductor cl 16. The remainder of the combustion gas flows in an axially distal direction through exhaust slots in the recirculation eductor cl 16. The exhaust slots in the recirculation eductor cl 16 reverse the direction of the exhaust gas flow, directing the exhaust gas in an axially distal and clockwise spiral direction into the recuperator body portion of the heat recuperator cl24. The exhaust gas flow in a clockwise spiral into the exhaust annulus c218, where the exhaust gas discharges from the heater body cl 00 through one or more exhaust ports c222.

[0101] Referring still to e.g., FIGs. 4.1.2A and 4.1.2B, and 4.1.3 A through 4.1.3C, an exemplary heater body cl 00 may include a combustion chamber cl 02 and a recirculation pathway cl 04 configured to recirculate combustion gas through the combustion chamber cl02. The heater body clOO includes an intake air pathway cl 18 and an exhaust pathway cl20 may fluidly communicate with the recirculation pathway cl04. The recirculation pathway cl04 may include a hot-side heat exchanger cl06 and a recirculation eductor cl 16. However, in some embodiments, the recirculation eductor cl 16 may be omitted and the combustion chamber cl 02 may fluidly communicate with the intake air pathway cl 18 and the exhaust pathway cl20 with combustion gas discharging from the heater body without recirculating. The exhaust pathway cl 20 may fluidly communicate with the recirculation pathway cl 04 upstream from the intake air pathway cl 18.

[0102] As shown in FIGs. 4.1.2A and 4.1.3 A, the hot-side heat exchanger cl06 may fluidly communicate with a proximal portion of the combustion chamber cl 02, and the recirculation eductor cl 16 may fluidly communicate with a downstream portion of the hot- side heat exchanger cl06 and a distal portion c202 of the combustion chamber cl02. The recirculation eductor cl 16 may be configured to entrain and/or accelerate combustion gas circulating through the recirculation pathway cl 04 using intake air, for example, from an intake air pathway cl 18 may fluidly communicate with the recirculation pathway cl04.

[0103] In some embodiments, the recirculation eductor cl 16 may define at least a portion of the exhaust pathway cl20. For example, the exhaust pathway cl20 may fluidly communicate with the recirculation pathway cl 04 at the recirculation eductor cl 16, such that the exhaust pathway cl20 discharges a portion of the combustion gas from the recirculation eductor cl 16 as exhaust gas. In another embodiment, as shown for example in FIG. 4.1.2B, the exhaust pathway cl20 may discharge exhaust gas upstream from the recirculation eductor cl 16.

[0104] When the heater body cl 00 includes a recirculation pathway cl 04, the proportion of combustion gas may be recirculated may vary depending on the operating conditions of the heater body clOO. The proportion of combustion gas may be recirculated to the proportion of fresh intake air may be utilized may be described by a recirculation ratio R, according to the following equation (1): R = I/C, where I is the flow rate if intake air flowing into the heater body clOO and T is C the flow rate of combustion gas flowing to the combustion chamber. The recirculation ratio may vary from 0% to 100% depending, for example, on the operating conditions of the heater body clOO. For example, a greater proportion of intake air may be utilized during startup, with recirculation ratio increasing as the heater body cl 00 transitions from startup conditions to steady-state conditions.

Additionally, the recirculation ratio may depend on desired combustion conditions, such as equivalence ratio. In some embodiments, the recirculation ratio may be from 0% to 90%, such as from 10% to 90%, such as from 0% to 60%, such as from about 30% to about 70%, such as from 40% to 60%. During startup conditions, the recirculation ratio may be from 0% to 50%, such as from 0% to 30% or from 0% to 10%. During steady-state conditions, the recirculation ratio may be from 10% to 90%, such as from 10% to 60%, or from 30% to 60%. The remainder of combustion gas may be discharged from the recirculation pathway cl04 as exhaust gas.

[0105] In some embodiments, the exemplary heater body clOO may include a heat recuperator cl 24 defining at least a portion of an exhaust pathway cl 20 and at least a portion of an intake air pathway cl 18. The heat recuperator cl 24 may be located upstream from a recirculation eductor cl 16 as shown in FIG. 4.1.2 A, or the heat recuperator cl24 may be located upstream from a recirculation eductor cl 16 as shown in FIG. 4.1.2B. As shown in FIG. 4.1.2A, the heat recuperator cl24 may utilize exhaust gas flowing through the exhaust pathway cl 20 to preheat intake air flowing through the intake air pathway cl 18, the exhaust pathway cl 20 having a thermally conductive relationship with the intake air pathway cl 18. The heat recuperator cl 24 may fluidly communicate with the recirculation pathway cl 04 indirectly, such as at the recirculation eductor cl 16 through the exhaust pathway cl 20 and the intake air pathway cl 18. Alternatively, the heat recuperator cl 24 may fluidly communicate with the recirculation pathway cl04 directly, as shown in FIG. 4.1.2A, such that the heat recuperator cl 24 may heat the intake using combustion gas recirculating through the recirculation pathway cl 04 to air, or a combination of exhaust gas and combustion gas.

Regardless of whether the heat recuperator cl24 utilizes exhaust gas and/or recirculating combustion gas to heat the intake air, the exhaust pathway cl 20 may be located upstream from the intake air pathway cl 18, such that exhaust gas may be removed from the

recirculation pathway cl 04 prior to intake air being introduced to the recirculation pathway cl04.

[0106] Now referring to FIG. 4.1.5 exemplary methods of heating a heat exchanger body c600 will be described. The exemplary methods of heating a heat exchanger body c600 may include, for example, methods of heating a closed-cycle engine c002. For example, exemplary methods may be performed in connection with operation of a heater body cl 00 and/or a closed-cycle engine c002 as described herein. As shown in FIG. 4.1.5, an exemplary method cl 50 may include, at block cl 52, circulating combustion gas through a combustion chamber cl 02 and a recirculation pathway cl 04 configured to recirculate combustion gas through the combustion chamber cl02. The recirculation pathway cl04 may include a hot- side heat exchanger cl06 and a recirculation eductor cl 16. The hot-side heat exchanger cl06 may fluidly communicate with a proximal portion of the combustion chamber cl02. The recirculation eductor cl 16 may fluidly communicate with a downstream portion of the hot- side heat exchanger cl06 and a proximal portion of the conditioning conduit cl22 and/or and a distal portion of the combustion chamber cl02. At block cl54, an exemplary method cl50 may include transferring heat from the combustion gas in the hot-side heat exchanger cl 06 to a plurality of heat transfer regions that respectively have a heat transfer relationship with a corresponding semiannular portion of the hot-side heat exchanger cl06. The exemplary method cl 50 may include, at block cl 56, swirling combustion gas through a conditioning conduit cl22 defining at least a portion of the recirculation pathway cl04. The conditioning conduit cl 22 may fluidly communicate with a downstream portion of the recirculation eductor cl 16 and a distal portion of the combustion chamber cl02. The exemplary method cl 50 may additionally include, at block cl 58, combusting a fuel and/or at least a portion of the combustion gas. The fuel and/or combustion gas may be combusted in the combustion chamber cl02. In some embodiments, at least a portion of the combustion may take place within the hot-side heat exchanger cl06.

[0107] In some embodiments, an exemplary method cl50 may include, at block cl60, injecting intake air into the recirculation pathway cl04. The intake air may be injected through an intake air pathway cl 18 fluidly communicating with the recirculation pathway cl04. For example, a recirculation eductor cl 16 may include a motive pathway defining at least a portion of the intake air pathway cl 18. The exemplary method may additionally include, at block cl 62, entraining and/or accelerating combustion gas circulating through the recirculation pathway cl 04 at least in part by injecting the intake air into the recirculation pathway cl04, for example, through the motive pathway of the recirculation eductor cl 16. The exemplary method may further include, at block cl64, discharging a portion of the combustion gas from the recirculation pathway cl 04 as exhaust gas. The exhaust gas may discharge through an exhaust pathway cl20, and the exhaust gas pathway cl20 may fluidly communicate with the recirculation pathway cl04. In some embodiments, the exhaust gas pathway cl20 may be defined at least in part by the recirculation eductor cl 16. The exhaust gas may be preferentially discharged from the recirculation pathway cl04 upstream from a location where the intake air pathway cl 18 fluidly communicates with the recirculation pathway cl 04.

[0108] The exemplary method may additionally include, at block cl 66, preheating intake air flowing through the intake air pathway cl 18. The intake air may be preheated at least in part using exhaust gas flowing through an exhaust pathway cl 20 by the exhaust pathway cl 20 having a thermally conductive relationship with the intake air pathway cl 18. For example, in some embodiments, the intake air may be preheated at least in part using a heat recuperator cl24. The heat recuperator cl24 may define at least a portion of the intake air pathway cl 18 and at least a portion of the exhaust pathway cl 20, thereby providing a thermally conductive relationship between the exhaust gas pathway cl 20 and the intake air pathway cl 18. Additionally, or in the alternative, the intake air may be preheated at least in part using combustion gas flowing through a recirculation pathway cl 04 by the recirculation pathway cl 04 having a thermally conductive relationship with the intake air pathway cl 18. With the heat recuperator cl 24 fluidly communicating with the recirculation eductor cl 16, the exemplary methodcl50 may include flowing combustion gas from the recirculation pathway cl 04 into the heat recuperator cl 24 at the recirculation eductor cl 16 through the exhaust pathway cl 20, and flowing intake air from the intake air pathway cl 18 into the recirculation eductor cl 16 at the heat recuperator cl24. The exhaust pathway cl20 may preferably be located upstream from the intake air pathway cl 18.

[0109] In an exemplary embodiment, transferring heat from the combustion gas in the hot-side heat exchanger cl 06 at block cl 54 may include transferring heat to a working-fluid body cl08. The working-fluid body cl08 may include a solid body and/or fluid in a fluid pathway defined at least in part by the solid body. The heat transferring to the working-fluid body cl 08 may come from combustion gas flowing through a plurality of heating fluid pathways defined at least in part by the hot-side heat exchanger cl06. The heat may be transferred to respective ones of a plurality of heat transfer regions that have a thermally conductive relationship with a corresponding portion of the plurality of heating fluid pathways. The working-fluid body cl08 may include a plurality of working-fluid pathways, and the exemplary method cl 50 may include flowing fluid through the working-fluid pathways as heat transfers thereto from the hot-side heat exchanger cl06. In some embodiments, the working-fluid pathways may fluidly communicate with a piston chamber and a regenerator of a closed-cycle engine c002, and the exemplary method may include flowing fluid through the working-fluid pathways alternatingly between the regenerator and the piston chamber.

[0110] In an exemplary embodiment, combusting a fuel and/or at least a portion of the combustion gas at block cl 58 may include combusting fuel and at least a portion of the combustion gas in the combustion chamber cl02 and/or in the heating fluid pathways of the hot-side heat exchanger cl 06. The fuel may be supplied by a fuel nozzle fluidly

communicating with the combustion chamber cl02. The combustion gas circulating through the combustion chamber cl02 and/or the recirculation pathway cl04 at block cl52 may be from 10% to 90% of the total combustion gas flowing into the combustion chamber cl 02, and the remainder of the combustion gas may be discharged from the recirculation pathway cl04 as exhaust gas through the exhaust pathway cl20. It will be appreciated that the proportion of combustion gas being recirculated may vary depending on operating conditions and/or configuration of the heater body clOO. For example, the proportion of combustion gas being recirculated may vary as between startup and steady-state conditions. Also, in some embodiments, the heater body cl 00 may not have a recirculation pathway or the recirculation pathway may be closed so as to carry out combustion of the fuel utilizing 100% intake air.

[0111] Now referring to FIGs. 4.1.6A and 4.1.6B exemplary monolithic bodies defining at least a portion of a heater body cl 00 will be described. Exemplary monolithic bodies may be formed as one single monolithic body. Various portions of a monolithic body are sometimes referred to as monolithic body portions. Additionally, or in the alternative, exemplary monolithic bodies may include a plurality of segments combinable to form a monolithic body. Such segments are sometimes referred to herein as monolithic body- segments. As shown in FIGs. 4.1 6A and 4.1 6B, an exemplary heater body clOO may include a combustor body c400, a fuel injector body c401, a hot-side heat exchanger body c600, an eductor body c300, a heat recuperator body c500, and/or a working-fluid body cl08. The combustor body c400, the fuel injector body c401, the hot-side heat exchanger body c600, the eductor body c300, the heat recuperator body c500, and/or the working-fluid body cl08 may respectively define monolithic body portions of the heater body clOO and/or monolithic body-segments of the heater body clOO.

[0112] An exemplary heater body clOO may include a combustor body c400. The combustor body c400 may include a combustion chamber body c402 defining at least a portion of a combustion chamber cl02. The combustion chamber body c402 and/or the combustion chamber cl 02 may be disposed annularly about an axis c204. The combustor body c400 may additionally include a conditioning conduit body c404 defining at least a portion of a conditioning conduit cl 22 circumferentially surrounding the combustion chamber cl02. The combustion chamber body c402 and the conditioning conduit body c404 may be monolithically integrated with the heater body clOO at a distal portion of the heater body cl 00 such that the conditioning conduit may fluidly communicate with the combustion chamber cl02 at a distal portion of the combustion chamber cl02. For example, the conditioning conduit body c404 may be monolithically integrated with the combustion chamber body c402. Alternatively, the combustion chamber body c402 and the conditioning conduit body c404 may define monolithic body-segments operably couplable to one another and/or to the heater body clOO or another monolithic body-segment thereof so as to provide an integrally formed combustor body c400.

[0113] An exemplary heater body clOO may additionally or alternatively include a fuel injector body c401. The fuel injector body c401 may be monolithically integrated with the heater body clOO at a distal portion c202 of the heater body clOO, such as at a distal portion c202 of the combustion chamber cl02. For example, the fuel injector body c401 may be monolithically integrated with the combustor body c400 (e.g., with the combustion chamber body c402 and/or the conditioning conduit body c404). Alternatively, the fuel injector body c401 and the combustor body c400 (e.g., the combustion chamber body c402 and/or the conditioning conduit body c404) may define monolithic body-segments operably couplable to one another and/or to the heater body clOO or another monolithic body-segment thereof.

[0114] An exemplary heater body clOO may additionally or alternatively include a hot-side heat exchanger body c600. The hot-side heat exchanger body c600 may include a plurality of heating fluid pathways and a plurality of heat transfer regions. The plurality of heating fluid pathways may be circumferentially spaced about an inlet plenum fluidly communicating with the plurality of heating fluid pathways. In some embodiments, respective ones of the plurality of heating fluid pathways may define a spiral pathway.

Respective ones of the plurality of heat transfer regions may have a heat transfer relationship with a corresponding semiannular portion of the plurality of heating fluid pathways.

[0115] The hot-side heat exchanger body c600 may be monolithically integrated with the heater body clOO at a proximal portion c200 of the heater body clOO such that the combustion chamber cl 02 may fluidly communicate with the plurality of heating fluid pathways at a proximal portion c200 of the combustion chamber cl02. For example, the hot- side heat exchanger body c600 may be monolithically integrated with the combustor body c400 (e.g., with the combustion chamber body c402 and/or the conditioning conduit body c404). Alternatively, the hot-side heat exchanger body c600 and the combustor body c400 (e.g., the combustion chamber body c402 and/or the conditioning conduit body c404) may define monolithic body-segments operably couplable to one another and/or to the heater body cl 00 or another monolithic body-segment thereof.

[0116] An exemplary heater body cl 00 may additionally or alternatively include an eductor body c300. The eductor body c300 may be monolithically integrated with the hot- side heat exchanger body c600 and/or the combustor body c400 (e.g., the conditioning conduit body c404) such that the plurality of heating fluid pathways may fluidly

communicate with a radially or concentrically outward portion of the an eduction pathway defined by the eductor body c300. In some embodiments, the exemplary heater body clOO may include a recirculation annulus body c302 configured to provide fluid communication between the plurality of heating fluid pathways of the hot-side heat exchanger body c600 and the combustor body c400 (e.g., the conditioning conduit body c404).

[0117] An exemplary heater body cl 00 may additionally or alternatively include a heat recuperator body c500. The heat recuperator body c500 may be monolithically integrated with the eductor body c300. In some embodiments, the exemplary heater body clOO may include an intake annulus body c502, an exhaust annulus body c504, and/or a motive annulus body c506. The intake annulus body c502 may be monolithically integrated with the heat recuperator body c500 such that the intake annulus body c502 and the heat recuperator body c500 define at least a portion of an intake air pathway cl 18. The exhaust annulus body c504 may be monolithically integrated the heat recuperator body c500 such that the exhaust annulus body c504 and the heat recuperator body c500 define at least a portion of the exhaust pathway cl20. The motive annulus body c502 may be monolithically integrated with the heat recuperator body c500 and the eductor body c300 such that the motive annulus body defines at least a portion of the intake air pathway cl 18 between the heat recuperator body c500 and the eductor body c300.

[0118] An exemplary heater body clOO may additionally or alternatively include a working-fluid body cl 08. A working-fluid body cl 08 may include any one or more bodies that receive a heat input from the hot-side heat exchanger body c600. An exemplary working-fluid body cl08 may include one or more piston bodies c700 and/or one or more regenerator bodies c800. An exemplary working-fluid body cl 08 may additionally or alternatively include one or more working-fluid pathways cl 10, such as one or more working-fluid pathways cl 10 fluidly communicating with at least one piston body c700 and/or at least one regenerator body c800. A working-fluid body cl08 may be monolithically integrated with the hot-side heat exchanger body c600. In some embodiments, the working- fluid body cl 08 may define at least a portion of a plurality of working-fluid pathways.

Additionally, or in the alternative, in some embodiments the hot-side heat exchanger body c600 may define at least a portion of the plurality of working-fluid pathways.

[0119] As shown in FIG. 4.1 6B, an exemplary monolithic body may include a plurality of monolithic body-segments. A heater body cl 00 may include any one or more of the elements described with reference to FIG. 4.1.6A provided as a monolithic body portion or as a monolithic body-segment. An exemplary heater body cl 00 may include an arrangement of monolithic body-segments as shown in FIG. 4.1.6B; however, other combinations and arrangements are contemplated and any combination or arrangement of monolithic body-segments is within the scope of the present disclosure. As shown in FIG.

4.1 6B, a heater body clOO may include a first monolithic body-segment c056, a second monolithic body-segment c058, and a third monolithic body-segment c060.

[0120] The first monolithic body-segment c056 may include a combustor body c400.

Additionally, or in the alternative, the first monolithic body-segment c056 may include a fuel injector body c401. The second monolithic body-segment c058 may include an eductor body c300 defining a first monolithic body portion of the second monolithic body-segment c058, a heat recuperator body c500 defining a second monolithic body portion of the second monolithic body-segment c058, a recirculation annulus body c302 defining a third monolithic body portion of the second monolithic body-segment c058, an intake annulus body c502 defining a fourth monolithic body portion of the second monolithic body-segment c058, an exhaust annulus body c506 defining a fifth monolithic body portion of the second monolithic body-segment c058, and/or a motive annulus body c506 defining a sixth monolithic body portion of the second monolithic body-segment c058, as well as subcombinations of these.

[0121] The third monolithic body-segment c060 may include a hot-side heat exchanger body c600 defining a second monolithic body portion of the third monolithic body-segment c060, and a working-fluid body cl 08 defining a second monolithic body portion of the third monolithic body-segment c060. In other embodiments, the first monolithic body-segment c056, the second monolithic body-segment c058, and/or the third monolithic body-segment c058 may respectively include any subcombination of the foregoing monolithic body portions, respectively provided as monolithic body portions of a respective monolithic body-segment or as separate monolithic body-segments.

[0122] Now referring to FIGs. 4.1.7, 4.1.8A-4.1.8G, 4.1.9, and 4.1.10, further exemplary embodiments will be described that pertain to a heater body cl 00, such as a monolithic heater body cl 00, and/or to one or more monolithic body-segments that make up the heater body clOO. A heater body clOO and/or a monolithic body-segment may include one or more features that allow the heater body clOO to operate at a relatively elevated temperature. For example, such features may include one or more heat shields cl 27, one or more heat-capture pathways cl33, and/or one or more thermal expansion joints cl35, as respectively described herein. Such features may allow for a closed cycle engine such as a Sterling engine to operate at with an improved temperature ratio

(THot,engine/TCold, ambient) and/or with an improved Carnot efficiency. For example, in some embodiments, a closed cycle engine that includes a heater body clOO configured in accordance with the present disclosure may exhibit a temperature ratio of from about 2 to about 4, such as at least about 2, such as at least about 3, or such as at least about 3.5.

Additionally, or in the alternative, a closed cycle engine that includes a heater body clOO configured in accordance with the present disclosure may exhibit an improved Carnot efficiency, such as a Carnot efficiency 40% to about 60%, such as from about 50% to about 70%, such as from about 60% to about 70%, such as from about 60% to about 80%; such as at least about 50%, such as at least about 60%, such as at least about 65%. Such improved temperature ratio and/or improved Carnot efficiency may be attributable at least in part to the heater body clOO being configured according to the present disclosure. By way of example, the one or more heat shields cl27, the one or more heat-capture pathways cl33, and/or the one or more thermal expansion joints cl35, may allow the heater body clOO to operate at an elevated temperature, thereby increasing the temperature difference between a hot side and a cold side of a heat engine, and corresponding conversation of heat energy to mechanical work, effective to impart such temperature ratio and/or such Carnot efficiency.

[0123] In some embodiments, a one or more portions of a monolithic heater body clOO, and/or to one or more monolithic body-segments that make up the heater body clOO, may include a heat shield cl27. The heat shield cl27 may be configured to insulate and/or shield one or more portions of the heater body clOO from a heat source within the heater body clOO. For example, the heat source may include a combustion flame and/or combustion gas circulating through the recirculation pathway cl 04, and/or portions of the heater body cl 00 that become heated by the combustion flame and/or combustion gas. Additionally, or in the alternative, the heat shield cl27 may provide a heat sink to absorb and/or dissipate heat, such as heat from a combustion flame and/or combustion gas circulating through the recirculation pathway cl04. FIG. 4.1.7 shows a variety of exemplary locations for a heat shield cl27.

[0124] As shown, in some embodiments, a heat shield cl27 may be disposed about an exterior region of a heater body clOO. For example, a first heat shield cl27A may

circumferentially surround at least a portion of a hot-side heat exchanger cl06 and/or at least a portion of a working-fluid body cl 08, such as an outward portion of a hot-side heat exchanger cl06 and/or an outward portion of a working-fluid body cl08. The first heat shield cl27A may be disposed about an annular or semi-annular portion of the hot-side heat exchanger cl06, and/or an annular or semi-annular portion of the working-fluid body cl08.

[0125] Additionally, or in the alternative, a second heat shield cl27B may be disposed about an inward portion of a heater body clOO, such as an inward annular portion of a heater body clOO or an inward semi-annular portion of a heater body clOO. As shown, the second heat shield cl27B may be disposed about an inward annular or semiannular portion of a hot-side heat exchanger cl06 and/or working-fluid body cl08. The second heat shield cl27B may be additionally or alternatively disposed about a radial portion of the hot-side heat exchanger cl06 and/or working-fluid body cl08, such as an upper radial portion (as shown) and/or a lower radial portion. The second heat shield cl27B may follow a contour or profile of the hot-side heat exchanger cl06 and/or working-fluid body cl08. The second heat shield cl27C may be disposed between the hot-side heat exchanger cl06 and a recirculation eductor cl 16.

[0126] In addition, or in the alternative, to the first heat shield cl 27 A and the second heat shield C127B, a heater body clOO may include a third heat shield cl27C disposed about at least a portion of a combustor body c400. For example, the third heat shield cl27 may circumferentially surround at least a portion of the combustion chamber cl 02, such as a proximal portion c200 of the combustion chamber cl02.

[0127] It will be appreciated that the locations of the heat shields cl 27 shown in FIG.

4.1.7 are provided by way of example and are not to be limiting. In fact, a heat shield cl27 may be provided at any desirable location of a heater body clOO. Other exemplary location for a heat shield cl27 may include an exhaust body c504, a heat recuperation body c500, a motive annulus body c506, a conditioning conduit body c404, an eductor body c300, a regenerator body c800, a piston body c700, and/or a recirculation annulus body c302.

[0128] As discussed with reference to FIG. 4.1 3B, a heat shield may include a cooling jacket cl28 through which air may flow, such as from an intake air annulus c216. Additionally, or in the alternative, in some embodiments a heat shield cl 27 may include an insulating material cl29, such as shown in FIGs. 4.1.8A-4.1.8G. In an exemplary

embodiment, the insulating material cl 29 may be formed of an additive manufacturing material, such as the same material as, or a different material from that, used to additively manufacture the heater body cl 00 or the monolithic body-segments that includes the insulating material cl29. During operation of exemplary heater bodies clOO, radiative heat may represent a significant source of heat transfer. An insulating material cl29 may reduce the view factor of the heat shield cl 27, for example, as compared to an air gap between an inner wall cl30 and an outer wall cl32. However, in some embodiments, a heat shield cl27 may include an insulating material cl29 and an air jacket cl28, which may also provide an improved view factor. For example, as shown in FIG. 4.1.7, the first heat shield cl27A may include an insulating material cl29 and an air jacket cl28. Exemplary insulating materials cl 29 provide a view factor of zero as between opposite portions of the heater body cl 00, such as between an inner wall cl30 and an outer wall cl32.

[0129] In some embodiments, as shown in FIGs. 4.1.8A, and 4.1.8C-4.1.8G, an insulating material cl 29 of a heat shield cl 27 may include a radiative-heat shield cl 29 A.

The radiative-heat shield cl 29 A may include any additively printed structure configured to shield the outer wall cl32 from radiative heat from the inner wall cl30, or vice versa. In some embodiments, as shown for example in FIG. 4.1.8A, three-dimensional unit cells, such as a three-dimensional array of unit cells. Such unit cells may have any desired shape, including polyhedral unit cells, conical unit cells, spherical unit cells, and/or cylindrical unit cells. The unit cells in a radiative-heat shield cl29 may include open cells and/or closed cells. As shown in FIGs. 4.1.8D-4.1.8G, the radiant heat shield may include elongate shield elements that are formed as substantially independent additive structures, such as slanted elongate additive structures (FIG. 4.1.8D), horizontal elongate additive structures (FIG. 4.1.8E), and/or vertical additive structures (FIGs. 4.1.8F and 4.1.8G). As shown, a radiative- heat shield Cl 29 A may include one or more elongate shield elements, including less than five (5) elongate shield elements (FIGs. 4.1.8F) and/or less than two (2) elongate shield elements (FIG. 4.1.8G). [0130] The radiative-heat shield cl29A may be disposed within any portion of a heater body clOO, such as between an inner wall cl30 and an outer wall cl32. The radiative- heat shield cl 29 A may be an additively manufactured structure, which may be formed as part of the additive manufacturing process used to form a heater body cl 00 or a monolithic body- segment that defines a portion of the heater body clOO. The radiative-heat shield cl29A may be integrally formed with adjacent material of the heater body clOO. In an exemplary embodiment, the radiative-heat shield cl 29 may provide a view factor of zero as between opposite portions of the heater body clOO, such as between an inner wall cl 30 and an outer wall cl32.

[0131] In some embodiments, the radiative-heat shield cl 29 A may have a cross- sectional thickness of about 100 micrometers to about 5,000 micrometers, such as from about 750 micrometers to about 2,000 micrometers, such as from about 1,000 micrometers to about 1,500 micrometers. In some embodiments, the radiative-heat shield cl29A may include unit cells with walls that have a thickness of from about 50 micrometers to about 500

micrometers, such as from about to about 125 micrometers to about 250 micrometers.

[0132] Heat conduction posts cl31 may monolithically connect the radiative-heat shield cl 29 A with an adjacent portion of the heater body clOO, such as with an inner wall cl30 and an outer wall cl32 as shown. The conduction posts cl31 may additionally or alternatively provide separation between the radiative-heat shield and adjacent portions of the heater body clOO. The dimensions and/or quantity of the heat conduction posts cl31 may be selected at least in part to augment a rate of conductive heat transfer between the radiative- heat shield cl29A and an adjacent body clOO. For example, relatively small, infrequently spaced, conduction posts cl31 may be positioned on a hot-side of the radiative-heat shield cl 29 A. Additionally, or in the alternative, relatively large, regularly spaced, conduction posts cl31 may be positioned at least in part to conductively transport heat from the radiative-heat shield cl29A to a desired portion of the heater body clOO. For example, such conduction posts cl 31 may be configured and arranged so as to transport heat from a radiative-heat shield cl 29 A to a recirculation eductor cl 16, where the heat may be advantageously utilized to preheat intake air and/or reheat combustion gas circulating through the recirculation pathway cl04.

[0133] In some embodiments, as shown in FIG. 4.1.8B, an insulating material cl29 may include a powder material cl29B, such as an additive manufacturing powder material. The powder material cl29B may be the same as that utilized to additively manufacture the heater body clOO and/or a monolithic body-segment thereof. The powder material cl29B may be unsintered or partially sintered. The powder material cl29B may exhibit a lower thermal conductivity relative to solidified material of the heater body clOO. In some embodiments, as shown in FIG. 4.1.8C, an insulating material cl29 may include a combined powder-radiative-heat shield cl29C made up of a radiative-heat shield (e.g., a three- dimensional array of unit cells) cl29A and a powder material (an additive manufacturing powder material) cl29B disposed interstitially about the radiative-heat shield cl29A. In some embodiments, closed cells of the radiative-heat shield cl29 may include a powder material cl29B, defining a powder-radiative-heat shield cl29C. Additionally, or in the alternative, open cells of a radiative-heat shield cl29A may include powder material cl29B, defining a powder-radiative-heat shield cl29C.

[0134] The powder-radiative-heat shield cl29 may be configured and arranged at least in part to augment a rate of heat transfer between the powder-radiative-heat shield cl29C and an adjacent body clOO. For example, closed cells may be utilized to provide a conductive heat transfer modality, and/or open cells may be utilized to provide a radiative heat transfer modality. The powder-radiative-heat shield cl29C may be configured and arranged at least in part to transport heat from the powder-radiative-heat shield cl29C to a desired portion of the heater body clOO. For example, a powder-radiative-heat shield cl29C may be configured and arranged so as to transport heat from a hot-side heat exchanger cl 06 to a working-fluid body cl 08, or vice versa. Additionally, or in the alternative, a powder- radiative-heat shield cl29C may be configured and arranged so as to transport heat from a hot-side heat exchanger cl06 and/or a working-fluid body cl08 to a recirculation eductor cl 16, where the heat may be advantageously utilized to preheat intake air and/or reheat combustion gas circulating through the recirculation pathway cl04.

[0135] Referring now to FIGs. 4.1.7 and 4.1.9, in some embodiments, an heater body clOO may include one or more heat-capture pathways cl 33. The one or more heat-capture pathways cl33 may be defined by the monolithic structure of the heater body clOO and/or by the monolithic structure of one or more monolithic body segments that make up the heater body clOO. A heat-capture pathway cl33 may be provided at any desired location of the heater body clOO. The heat-capture pathway cl33 may be configured to transport a heat- capture fluid. As used herein, the term“heat-capture fluid” includes any suitable fluid transported through a heat-capture pathway cl 33 that, during operation of the heater body clOO, has a temperature that is lower than a portion of the heater body clOO intended to be cooled by the fluid in the heat-capture pathway cl 33.

[0136] A heat-capture pathway cl 33 may capture heat from one or more regions of a heater body clOO. In some embodiments, a heat-capture pathway cl33 may include a flowpath configured to flow a fluid disposed within the heat-capture pathway cl33 to a relatively hotter region of the heater body clOO, such as from a radially or concentrically outward portion of the heater body clOO to a radially or concentrically inward portion of the heater body clOO, and/or from a distal portion of the heater body clOO to a proximal portion of the heater body clOO. By way of example, a heat-capture pathway cl33 may include a flowpath configured to flow a fluid to the combustion chamber cl02 and/or an upstream portion of a hot-side heater body cl06. Additionally, or in the alternative, a heat-capture pathway cl 33 may cool hot portions of the heater body clOO, for example to maintain suitable operating temperatures and/or to shield users or surrounding equipment from hot portions of the heater body clOO.

[0137] In an exemplary embodiment, the heat-capture fluid may include a process fluid derived from a fluid pathway located elsewhere in the heater body clOO, such as a fluid extracted from a primary flowpath cl21 of the heater body clOO. For example, the heat- capture fluid may include a process gas, such as intake air, exhaust gas, combustion gas, and/or a fuel. Such combustion gas may include a combination of intake air, fuel, uncombusted or partially combusted combustion gas c428, and/or exhaust gas. Intake air may be supplied from an intake air pathway cl 18 to a heat-capture pathway cl 33 fluidly communicating with the intake air pathway cl 18. Exhaust gas may be supplied from an exhaust pathway cl 20 to a heat-capture pathway cl 33 fluidly communicating with the exhaust pathway cl20. Combustion gas may be supplied from a recirculation pathway cl04 to a heat-capture pathway cl33 fluidly communicating with the recirculation pathway cl04. Fuel may be supplied from a fuel supply line to a heat-capture pathway cl 33 fluidly communicating with the fuel supply line.

[0138] In some embodiments, the heat-capture pathway cl 33 may be configured to discharge a cooling fluid to a fluid pathway located elsewhere in the heater body clOO after having been utilized to provide cooling to a location of the heater body clOO. For example, a heat-capture pathway cl33 may be configured to discharge a cooling fluid to a location along a primary flowpath cl21 of the heater body clOO, such as to an intake air pathway cl 18, an exhaust gas pathway cl20, a recirculation pathway cl04, and/or a fuel line cl03. The heat- capture pathway cl33 may discharge cooling fluid to a fluid pathway of the primary flowpath cl21 that is the same or different from the fluid pathway of the primary flowpath cl21 from which the cooling fluid is obtained. For example, a heat-capture pathway cl33 that utilizes intake air for cooling may discharge to an intake air pathway cl 18. Additionally, or in the alternative, a heat-capture pathway cl33 that utilizes intake air for cooling may discharge to an exhaust gas pathway cl 20, to a recirculation pathway cl 04, and/or to a fuel line cl 03. A heat-capture pathway cl33 that utilizes combustion gas, fuel, and/or exhaust gas, may discharge to an intake air pathway cl 18, an exhaust gas pathway cl20, a recirculation pathway cl04, and/or a fuel line cl03. In some embodiments, a heat-capture pathway cl33 may include a cooling jacket cl 28. Additionally, or in the alternative, a heat-capture pathway cl 33 may fluidly communicate with a cooling jacket cl 28.

[0139] As used herein, the term“heat-capture pathway” includes any fluid pathway configured to capture heat from a location of the heater body clOO, and/or to provide cooling to a location of the heater body cl 00, apart from heat transfer that occurs along the primary flowpath cl21. A heat-capture pathway cl 33 that utilizes a fluid from the primary flowpath cl21 may be differentiated from the primary flowpath cl21 by the heat-capture pathway cl 33 having an intended purpose of capturing heat from one or more portions of the heater body clOO, and/or providing cooling to one or more portions of the heater body clOO, separate and apart from a respective intended purpose of the primary flowpath cl21, even though portions of the primary flowpath cl21inherently provide heat capture and/or cooling with respect to portions of the heater body clOO. By way of example, a heat-capture pathway cl33 that utilizes fluid from the primary flowpath cl21 may transects a portion of the heater body clOO that differs from that of the primary flowpath cl21, thereby capturing heat from a portion of the heater body clOO located elsewhere relative to the primary flowpath cl21and/or providing cooling to a portion of the heater body clOO located elsewhere relative to the primary flowpath cl21. Additionally, or in the alternative, a heat-capture pathway cl33 that utilizes fluid from the primary flowpath cl21 may have an inlet and an outlet that fluidly

communicate with respectively different portions of the primary flowpath cl21. A heat- capture pathway cl 33 that utilizes fluid from the primary flowpath cl21 may additionally or alternatively have a heat transfer relationship with a location of the heater body clOO where, during operation of the heater body clOO, at least one location of the heater body clOO has a heat transfer relationship with respect to the fluid in the heat-capture pathway cl 33 that includes a temperature gradient that is greater than the temperature gradient of a heat transfer relationship between such location of the heater body clOO and the primary flowpath cl21.

By way of contrasting illustration, the respective flowpaths of the recirculation eductor cl 16 and/or of the heat recuperator cl24 flow to their respective locations along the recirculation pathway cl 04 or the exhaust gas pathway cl 20, and are thereby differentiated from a heat- capture pathway cl 33.

[0140] In some embodiments, a heat-capture pathway cl 33 may utilize a cooling fluid that remains fluidly separate from the primary flowpath cl31. For example, a heat-capture pathway cl33 may utilize a chiller working fluid (e.g., a refrigerant), such as from a chiller assembly A40, as described herein. Additionally, or in the alternative, a heat-capture pathway cl 33 may utilize an engine-working fluid, such as from a working-fluid pathway cl 10, as described herein.

[0141] FIGs. 4.1.7 and 4.1.9 show an exemplary heat-capture pathway cl33. As shown, a heat-capture pathway cl 33 may provide cooling to an interface between a heater body clOO and another portion an engine assembly 900. The heat-capture pathway cl33 may provide cooling to a portion of the heater body clOO that includes a working-fluid body cl 08, a piston body c700, and/or a regenerator body c800. The heat-capture pathway cl33 may additionally or alternatively provide cooling to a portion of the heater body clOO that interfaces with a working-fluid body cl08, a piston body c700, and/or a regenerator body c800. The heat-capture pathway cl33 may also return heat to the heater body clOO, such as to an interior heater body-portion clOOA of the heater body, such as a combustor body c400. As shown, the heat-capture pathway cl 33 may provide cooling to an interface between the heater body clOO and an engine body c050. In some embodiments, the heat-capture pathway cl33 may provide cooling to a portion of the heater body clOO that interfaces with the engine body c050, such as to a working-fluid body cl08, a piston body c700, and/or a regenerator body c800. As shown in FIG. 4.1.7, the heat-capture pathway cl33 may fluidly communicate with an intake pathway cl 18, and may utilize intake air from the intake air pathway cl 18. Additionally, or in the alternative, the heat-capture pathway cl 33 may fluidly communicate with a cooling jacket cl 28 and may utilize a fluid such as intake air from the cooling jacket cl28.

[0142] As shown in FIG. 4.1.9, a heat-capture pathway cl33 may circumferentially surround at least a portion of a piston chamber cl 12. A first heat-capture pathway-portion cl33A of the heat-capture pathway cl33 may flow circumferentially around a first semiannular piston chamber-portion cl 12A of the piston chamber cl 12. A second heat- capture pathway-portion cl33B may flow circumferentially around a second semiannular piston chamber-portion cl 12B. The first heat-capture pathway-portion cl33A and the second heat-capture pathway-portion cl33B may reunite and/or fluidly communicate at an inward perimeter piston chamber-portion cl 12C of the piston chamber cl 12. As shown, the first heat-capture pathway-portion cl33A and the second heat-capture pathway-portion cl33B first heat-capture pathway-portion cl33A and the second heat-capture pathway-portion cl33B reunite, without fluidly communicating, at the inward perimeter piston chamber- portion cl 12C. In some embodiments, the heat-capture pathway cl33 (e.g., the first heat- capture pathway-portion cl33A and/or the second heat-capture pathway-portion cl33A) may have a heat transfer relationship with a thermal expansion joint cl35. For example, as shown, the heat-capture pathway cl 33 may include a hairpin cl33D that follows a perimeter of the thermal expansion joint cl35.

[0143] In some embodiments, a fluid flowing through the heat-capture pathway cl 33 may fluidly communicate with the primary flowpath cl21, and fluid flowing through the heat-capture pathway cl33 may be discharged from the heat-capture pathway cl33 to the primary flowpath cl21. As shown, the heat-capture pathway cl 33 may fluidly communicate with the recirculation pathway cl04, such as at the combustion chamber cl04. In some embodiments, fluid in the heat-capture pathway cl 33 may discharge into the combustion chamber cl04 through a distal portion of the combustion chamber cl02. The distal portion of the combustion chamber cl 04 may include a plurality of openings providing fluid

communication with the heat-capture pathway cl 33. The plurality of openings may include a plurality of pore-like openings cl37A (FIG. 4.5.5D ) circumferentially surrounding the vortex conditioner cl37 and/or disposed about the vortex conditioner cl37. The heat-capture pathway cl 33 may transect at least some of the distal portion of the combustion chamber C102A, thereby providing cooling to the combustion chamber cl02. In some embodiments, the heat-capture pathway cl 33 may include a plurality of spiral-heat-capture pathways cl33E disposed about the distal portion of the combustion chamber C102A (FIG. 4.5.5D). In some embodiments, heat-capture fluid in the heat-capture pathway cl 33 may have a heat transfer relationship with a portion a heater body cl 00 that would be capable of exceeding a threshold temperature during operations, such as a threshold temperature determined in relation to a melting temperature, whereas the heat-capture fluid operates to maintain such portion of the heater body clOO below such threshold temperature during operations. [0144] Now referring to FIG. 4.1.10, in some embodiments, an interface between a heater body clOO and an engine body c050 may include an engine-to-heater coupling cl37.

In some embodiments, the engine-to-heater coupling cl 39 may include a fitting cl41, such as a tri-clamp fitting or any other suitable fitting, configured to couple a heater body-flange cl43 and an engine body-flange cl45 to one another. A gasket cl47 may be disposed between the heater body-flange cl 43 and the engine body-flange cl 45. A heat-capture pathway cl 33 may capture heat from a region of the heater body cl 00 that includes the heater body-flange cl43, and/or provide cooling to a region of the heater body clOO that includes the heater body-flange cl 43. Heat captured from such region of the heater body clOO may be returned to another portion of the heater body, thereby preventing the heat from being lost to the engine body c050, which may include a cold-side of a closed-cycle engine. While the embodiment shown in FIG. 4.1.10 depicts a fitting cl41, other types of fittings are also contemplated. A fitting cl41 may allow for thermal expansion as a result of heat from the heater body clOO, as well as differences in temperature as between the heater body clOO and the engine body c050.

[0145] In some embodiments, an engine-to-heater coupling cl37 may include a gasket cl 47 formed at least in part from a polymeric material, such as silicone, fluorosilicone, fluorocarbon, nitrile rubber, polytetrafluoroethylene (PTFE), ethylene propylene diene monomer rubber (EPDM), polyamides, aramid fiber-polymeric laminates, carbon fiber polymeric laminates, graphite-polymeric laminates, or the like. Such gaskets formed of a polymeric material may advantageously have a relatively low thermal conductivity, which may reduce heat loss from the heater body clOO to the engine body c050. Additionally, or in the alternative, an engine-to-heater coupling cl 37 may utilize a gasket cl 47 that includes of a non-polymeric material, such as a ceramic or metallic material. For example, a gasket cl 47 may include metal alloys, ceramics, vermiculite, woven or compressed graphite, ceramic fiber, fiberglass, or the like.

[0146] In some embodiments, cooling provided by a heat-capture pathway cl 33 may allow for temperatures existing at the interface between the heater body clOO and the engine body c050 to remain within a range suitable for using a gasket cl47 formed at least in part of a polymeric material. In some embodiments, at least a portion of the heater body clOO may exceed a maximum operating temperature of a gasket cl 47 while a region of the heater body clOO that includes the heater body -flange cl 43 may be within the maximum operating temperature of the gasket cl47. The region of the heater body clOO that includes the heater body-flange cl 43 may be maintained below the maximum operating temperature of the gasket cl 47 at least in part by cooling provided by the heat-capture pathway cl 33. In some embodiments, such polymeric materials would be unsuitable for use at the engine-to-heater coupling cl 37, if not for the cooling provided by the heat-capture pathway cl 33, at least in part due to the temperature of the heater body clOO otherwise exceeding the maximum operating temperature of the gasket cl47. Such maximum operating temperature may be specified by a manufacturer of the gasket and/or by an industry standards organization such as ASTM. Such polymeric materials may also provide for a degree of flexibility and vibration absorption at the interface between the heater body clOO and the engine body c050.

[0147] By way of example, in some embodiments at least a portion of a heater body clOO may exhibit an operating temperature in excess of about 400C, such as at least about 500C, such as at least about 600C, such as at least about 700C, or such as at least about 800C. Meanwhile, while at least a portion of the heater body exhibits an aforementioned operating temperature, in some embodiments, a region of the heater body clOO that includes the heater body-flange cl 43 may exhibit an operating temperature of at least less than 600C, such as at least less than 500C, such as at least less than 400C, such as at least less than 300C, or such as at least less than 200C.

[0148] In some embodiments a region of the heater body clOO that includes the heater body-flange cl43 may exhibit an operating temperature of at least about 50C cooler than another region of the heater body clOO, such as the working-fluid body cl 08. For example, the region of the heater body clOO that includes the heater body-flange cl 43 may be at least about 50C cooler than a portion of the heater body clOO that includes the working-fluid body cl08, such as at least about 75C cooler, such as at least about lOOC cooler, such as at least about 200C cooler, such as at least about 300C cooler, or such as at least about 400C cooler, than such region of the heater body clOO that includes the working-fluid body cl 08. Such temperature difference in operating temperature may be attributable at least in part to cooling provided by a cooling fluid in a heat-capture pathway cl 33.

[0149] Now referring to FIGs. 4.2.1 A and 4.2. IB, and 4.2.2A and 4.2.2B, exemplary combustor bodies c400 will be described. The presently disclosed combustor bodies c400 may define part of a heater body clOO and/or a closed-cycle engine c002. For example, a combustor body c400 may define at least a portion of a monolithic body or a monolithic body-segment. Such monolithic body or monolithic body-segment may define at least a portion of the heater body clOO and/or the closed-cycle engine c002. Additionally, or in the alternative, the presently disclosed combustor bodies c400 may be provided as a separate component, whether for use in connection with a heater body cl 00, a closed-cycle engine c002, or any other setting whether related or unrelated to a heater body cl 00 or a closed-cycle engine c002. At least a portion of the combustor body c400 may define a combustion chamber cl02 and/or a conditioning conduit cl22. While the heater bodies clOO depicted in the figures may show one combustor body c400 and/or one combustion chamber cl02 and/or one conditioning conduit cl 22, it will be appreciated that a heater body cl 00 may include a plurality of combustor bodies c400 and/or a plurality of combustion chambers cl 02 and/or a plurality of conditioning conduits cl22. For example, a heater body clOO may include one or more combustor bodies c400, and/or a combustor body c400 may include one or more combustion chambers cl02 and/or one or more conditioning conduits cl22. Exemplary heater bodies clOO and/or combustor bodies c400 may be configured for single-stage combustion and/or multi-stage combustion. A heater body clOO and/or a combustor body c400 configured for multi-stage combustion may include two, three, four, or more

combustion zones.

[0150] As shown, an exemplary combustor body c400 may include a combustion chamber cl 02 and a conditioning conduit cl 22 circumferentially surrounding at least a portion of the combustion chamber cl 02. The combustion chamber cl 02 may be disposed annularly about an axis c204, or the combustion chamber may be off-center from the axis c204. In some embodiments, a plurality of combustion chambers cl02 may be

circumferentially spaced about the axis c204. The combustion chamber cl02 may include an annular combustion chamber wall c406. An inward portion of the annular combustion chamber wall c406 may define at least a portion of the combustion chamber cl02. The conditioning conduit cl 22 may include an outward annular conditioning conduit wall c408 circumferentially surrounding the combustion chamber cl 22, and an inward annular conditioning conduit wall c410 circumferentially surrounding the outward annular conditioning conduit wall c408. An outward portion of the annular combustion chamber wall c406 may define at least a portion of the inward annular conditioning conduit wall c410. The inward portion of the annular combustion chamber wall c406 and the outward portion of the annular combustion chamber wall c406 may adjoin one another at a distal end c202 of the combustion chamber cl 02.

[0151] The combustion chamber cl02 may include a combustion chamber outlet c412 disposed about a proximal portion c202 of the combustion chamber cl02. For example, the combustion chamber outlet c412 may be disposed about a proximal portion of an annular combustion chamber wall c406. A combustion chamber cl02 may include a single combustion chamber outlet c412 or a plurality of combustion chamber outlets c412, and the combustion chamber outlet or outlets c412 may be oblique to the combustion chamber cl02. For example, a plurality of combustion chamber outlets c412 may be circumferentially spaced about a proximal portion c202 of the combustion chamber cl 02, such as about a proximal portion c202 of the annular combustion chamber wall c406.

[0152] The conditioning conduit cl 22 may fluidly communicate with the combustion chamber cl02 at a distal portion of the combustion chamber cl02. The conditioning conduit cl22 may include a conditioning conduit inlet c414 disposed about a proximal portion c202 of the conditioning conduit cl22. For example, the conditioning conduit inlet c414 may be disposed about a proximal portion of the outward annular conditioning conduit wall c408. A conditioning conduit cl 22 may include a single conditioning conduit inlet c414 or a plurality of conditioning conduit inlets c414, and the conditioning conduit inlet or inlets c414 may be oblique to the conditioning conduit cl20. For example, a plurality of conditioning conduit inlets c414 may be circumferentially spaced about a proximal portion c202 of the

conditioning conduit cl 22, such as about a proximal portion c202 of the outward annular conditioning conduit wall c408.

[0153] The inward annular conditioning conduit wall c410 may be defined at least in part by the annular combustion chamber wall c406. In some embodiments, a portion of the inward annular conditioning conduit wall c410 may be separated from the annular combustion chamber wall c406, such that the inward annular conditioning conduit wall c410 and the annular combustion chamber wall c406 define an insulating space therebetween (not shown). For example, a medial portion of the inward annular conditioning conduit wall c410 may be separated from the annular combustion chamber wall c406 so as to define such an insulating space.

[0154] As shown in FIGs. 4.2.1A and 4.2. IB, the conditioning conduit cl22 may define at least a portion of the recirculation pathway cl04. The portion of the recirculation pathway cl 04 defined by the conditioning conduit cl 22 may sometimes be referred to as a conditioning conduit pathway c416. The conditioning conduit pathway c416 may be defined at least in part by the inward annular conditioning conduit wall c410 and the outward annular conditioning conduit wall c408. [0155] In exemplary embodiments, the one or more conditioning conduit inlets c414 may be disposed about a proximal portion c200 of the conditioning conduit cl22 and oriented oblique to the conditioning conduit cl22. For example, the one or more conditioning conduit inlets c414 may be oblique to the outward annular conditioning conduit wall c408 and/or the inward annular conditioning conduit wall c410. The one or more conditioning conduit inlets c414 may respectively include a motive pathway c418 and an eduction pathway c420 fluidly communicating with the conditioning conduit cl22. As shown in FIGs. 4.2.1 A and 4.2. IB, a plurality of conditioning conduit inlets c412 may include a plurality of motive pathways c418 and a plurality of eduction pathways c420 circumferentially spaced about the conditioning conduit cl 22.

[0156] The motive pathway c418 (or plurality of motive pathways c418) and the eduction pathway c420 (or plurality of eduction pathway c420) may be defined at least in part by an eductor body c300. The motive pathway c418 or plurality of motive pathways define a portion of an intake air pathway and the eduction pathway or plurality of eduction pathways define a portion of a recirculation pathway. The eduction pathway c420 and the motive pathway c418 may be adjacent to one another, such that intake air flowing through the motive pathway c418 may accelerate and entrain combustion gas from the eduction pathway c420 so as to move circulating combustion gas into the conditioning conduit cl22. The motive pathway c418 and the eduction pathway c420 are preferably oriented oblique to the conditioning conduit cl22 (e.g., oblique to the outward annular conditioning conduit wall c408 and/or the inward annular conditioning conduit wall c410), such that intake air and combustion gas flowing into the conditioning conduit may readily establish a helical flow pattern through the conditioning conduit cl22.

[0157] In exemplary embodiments, the one or more combustion chamber outlets c412 may be disposed about a proximal portion c200 of the combustion chamber cl02 and oriented oblique to the combustion chamber cl02. For example, the one or more combustion chamber outlets c412 may be oblique to the annular combustion chamber wall c406. The one or more combustion chamber outlets c412 may fluidly communicate with a corresponding plurality of combustion-gas pathways c422 circumferentially spaced about the combustion chamber cl02. The plurality of combustion-gas pathways c422 may fluidly communicate with a respective portion of the combustion chamber cl02. Respective combustion-gas pathways c422 may extend in a radial, circumferential, and/or tangential direction relative to the combustion chamber cl02. For example, the respective combustion-gas pathways c422 may concentrically spiral radially or circumferentially outward from the combustion chamber.

The respective combustion-gas pathways c422 may extend annularly or semi-annularly along a spiral or spiral arc relative to the combustion chamber and/or the longitudinal axis c204 thereof. As shown in FIGs. 4.2.1 A and 4.2. IB, the plurality of combustion-gas pathways c422 define at least a portion of a hot-side heat exchanger body c600. The oblique orientation of the one or more conditioning conduit inlets c414 and/or of the one or more combustion chamber outlets c412 may cause combustion gas to swirl through the

conditioning conduit cl 22, for example, from a proximal portion of the conditioning conduit cl22 to a distal portion of the conditioning conduit cl22 and through the combustion chamber cl02 from a distal portion of the combustion chamber cl02 to a proximal portion of the combustion chamber 102.

[0158] The swirling combustion gas may provide a bidirectional coaxial vortex flow field. When the combustor body c400 includes a conditioning conduit cl 22, the conditioning conduit cl 22 provides separation between an outward portion of the bidirectional coaxial vortex flow field and an inward portion of the bidirectional coaxial vortex flow field, the conditioning conduit defining a pathway for the outward portion of the bidirectional coaxial vortex flow field and the combustion chamber defining a pathway for the inward portion of the bidirectional coaxial vortex flow field. Such separation of the bidirectional coaxial vortex flow field provided by the conditioning conduit cl 22 may enhance combustion dynamics, for example, by reducing shear between the outward and inward portions of the bidirectional coaxial vortex flow field.

[0159] In some embodiments, the annular combustion chamber wall c406 may have a

Coanda surface c424 disposed at a distal end thereof defining a transition between an inner annular portion and an outer annular portion of the annular combustion chamber wall c406. The Coanda surface c424 may be operable at least in part to draw combustion gas from the conditioning conduit cl22 into the combustion chamber cl02. A“Coanda surface” refers to a curved surface that creates a zone of reduced pressure in the immediate proximity of such curved surface. This pressure drop entrains and accelerates fluid along the contour of the surface, which is sometimes referred to as the“Coanda effect.” The Coanda effect is the phenomena in which a flow attaches itself to a nearby surface and remains attached even though the surface curves away from the initial direction of flow. Characteristic of the Coanda effect, fluid tends to flow over the surface closely, seemingly“clinging to” or “hugging” the surface. As such, the Coanda effect can be used to change the direction of the combustion gas swirling through the conditioning conduit cl 22 and into the combustion chamber cl22. In doing so, a combustion flame c426 may be surrounded by a flow of cooler, uncombusted or partially combusted combustion gas c428, thereby form a boundary layer separating the flame c426 from the annular combustion chamber wall c406.

[0160] In some embodiments, the combustor body c400 may include a combustor cap c210 disposed axially adjacent to a distal portion of the conditioning conduit cl22. The combustor cap c210 may be operably coupled to the combustor body c400, for example, using bolts (not shown) insertable into bolt holes c430. Alternatively, the combustor cap c210 may define a portion of a monolithic body or a monolithic body-segment that includes at least a portion of the combustor body c400. As yet another alternative, the combustor cap c210 may be integrally formed with at least a portion of the combustor body c400. In an exemplary embodiment, the combustor cap c210 may be operably coupled to the

conditioning conduit body c404, or the combustor cap c210 may define a portion of the conditioning conduit body c404 or may be integrally formed with the conditioning conduit body c404.

[0161] As shown in FIGs. 4.2.1 A and 4.2. IB, the combustor cap c210 includes an inward combustor cap wall c432 defining a portion of the recirculation pathway cl04. The portion of the recirculating pathway cl04 including the inward combustor cap wall c432 may provide fluid communication between the conditioning conduit cl 22 and the combustion chamber cl02 at a distal portion of the combustion chamber cl02, and the combustor cap c210 may be operable at least in part to direct combustion gas from the conditioning conduit cl22 to the combustion chamber cl02. The combustor cap c210 may be disposed axially adjacent to a distal portion c202 of the conditioning conduit cl22 and/or the combustion chamber cl 02.

[0162] The combustion chamber cl 02 and the conditioning conduit cl 22 may have any desired shape. In various embodiments, the combustion chamber cl 02 may have a shape including a cylinder and/or a frustum, and the conditioning conduit cl 22 may have a shape including a cylinder and/or a frustum. As shown in FIGs. 4.2.1 A and 4.2. IB, the combustion chamber cl 02 and the conditioning conduit cl 22 respectively have a cylindrical shape. In other embodiments, a portion of the combustion chamber cl 02 having a cylinder shape may be circumferentially surrounded by a portion of the conditioning conduit cl 22 having a cylinder shape and/or a portion of the conditioning conduit cl22 having a frustum shape. Additionally, or in the alternative, a portion of the combustion chamber cl 02 having a frustum shape may be circumferentially surrounded by a portion of the conditioning conduit cl22 having a cylinder shape and/or a portion of the conditioning conduit cl22 having a frustum shape. Such a frustum shape of the combustion chamber cl02 and/or of the conditioning conduit cl22 may converge proximally and/or diverge proximally.

[0163] By way of example, a first portion of a combustion chamber cl 02 may have a first shape that includes a cylinder, and the first portion of the combustion chamber cl 02 may be circumferentially surrounded by a second portion of the conditioning conduit cl 22 having a second shape that includes a cylinder and/or a frustum. Additionally, or in the alternative, a third portion of the combustion chamber cl 02 may have a third shape that includes a cylinder and/or a frustum, and the third portion of the combustion chamber cl02 may be

circumferentially surrounded by a fourth portion of the conditioning conduit cl 22 having a fourth shape that includes a cylinder. Further in addition or in the alternative, a fifth portion of the combustion chamber cl 02 may have a fifth shape that includes a frustum diverging proximally, and the fifth portion of the combustion chamber cl 02 may be circumferentially surrounded by a sixth portion of the conditioning conduit cl 22 having a sixth shape that includes a frustum converging proximally and/or a frustum diverging proximally. Still further in addition or in the alternative, a seventh portion of the combustion chamber cl 02 may have a seventh shape that includes a frustum diverging proximally, and the seventh portion of the combustion chamber cl 02 may be circumferentially surrounded by an eighth portion of the conditioning conduit having an eighth shape that includes a frustum converging proximally and/or a frustum diverging proximally.

[0164] Referring now to FIG. 4.2. IB, in some embodiments, a combustor body c400 may include one or more aerodynamic features c434. The one or more aerodynamic features c434 may be disposed about at least a portion of the combustion chamber cl02 and/or at least a portion of the conditioning conduit cl 22, such as the annular combustion chamber wall c406 (e.g. an inward surface and/or an outward surface thereof), the outward annular conditioning conduit wall c408, and/or the inward annular conditioning conduit wall c410. The one or more aerodynamic features c434 may be configured to condition the flow of combustion gas c428 flowing through the conditioning conduit cl 22, such as by swirling the flow of combustion gas c428. Additionally, or in the alternative, the one or more

aerodynamic features c434 may be configured to condition the flow of combustion gas c428 or the flame c426 flowing through the combustion chamber cl 02, such as by swirling the flow of combustion gas c428 and/or flame c426. For example, the one or more aerodynamic features c434 may include a fin, a ridge, a groove, a contour, and/or the like disposed about the combustion chamber cl02 and/or the conditioning conduit cl22.

[0165] The one or more aerodynamic features c434 may followed a helical orientation along the combustion chamber cl02 and/or the conditioning conduit cl22. The helical orientation of the one or more aerodynamic features c434 may help condition the flow of combustion gas c428 and/or the flame c426 in a helical path. For example, the combustion gas c428 and/or the flame c426 may follow a helical path that depends at least in part on the slope of the helical orientation of the one or more aerodynamic features c434. Additionally, or in the alternative, such helical path of the combustion gas c428 and/or the flame c426 may depend on the size, number, and/or spacing of the one or more aerodynamic features c434. In an exemplary embodiment, the one or more one or more aerodynamic features c434 may provide a bidirectional coaxial vortex flow field, which may enhance heat transfer of the flame c426 to the hot-side heater body cl06 and/or may protect the combustion chamber wall c406 from receiving excessive heat from the flame c426.

[0166] As shown in FIG. 4.2. IB, the one or more aerodynamic features c434 may include a first helical conditioning ridge c436 be disposed about the annular combustion chamber wall c406 (e.g. an outward surface thereof). Additionally, or in the alternative, the one or more aerodynamic features c434 may include a second helical conditioning ridge c438 disposed about the inward annular conditioning conduit wall c410 and/or a third helical conditioning ridge c440 disposed about the outward annular conditioning conduit wall c408.

[0167] Still referring to FIGs. 4.2.1 A and 4.2. IB, the combustor body c400 and/or the combustion chamber cl 02 may have an axial length selected based at least in part on a desired flame length and/or a corresponding combustion time. In some embodiments, the combustion time may be from 1 to 10 milliseconds, such as from 2 to 4 milliseconds. The combustion time may be at least 1 millisecond, at least 2 milliseconds, or at least 5 milliseconds. The combustion time may be less than 10 milliseconds, less than 7

milliseconds, or less than 3 milliseconds.

[0168] The flame c426 may have an axial length extending all or a portion of the combustion chamber cl 02. In some embodiments, the flame c426 may extend though one or more combustion chamber outlets c412 and into the hot-side heat exchanger cl06. The hot- side heat exchanger cl 06 may include working-fluid pathways cl 10; however, in some embodiments, the working-fluid pathways cl 10 may be omitted from a radially or concentrically inward portion of the hot-side heat exchanger cl 06 so as to facilitate the flame c426 flowing into the hot-side heat exchanger cl06. Such a radially-inward portion of the hot-side heat exchanger cl 06 may define a combustion zone where combustion may occur in the hot-side heat exchanger cl06. The combustion that occurs in the hot-side heat exchanger may represent an extension of combustion that occurs in the combustion chamber cl 02, such as in the case of a flame that extends from the combustion chamber into the hot-side heat exchanger cl06. The radially-inward portion of the hot-side heat exchanger cl06 may additionally/or alternatively support stable combustion separate and distinct from the combustion that occurs in the combustion chamber clO. For example, a first flame c426 in the combustion chamber may quench upstream from the hot-side heat exchanger cl 06, and a second flame c426 may be established and stabilize in the radially-inward portion of the hot- side heat exchanger cl06.

[0169] The radially-inward portion of the hot-side heat exchanger cl 06 may sometimes be referred to as a second combustion chamber c448, in which case, the combustion chamber cl02 may be referred to as a first combustion chamber cl02. In some embodiments, the flame c426 may extend into the combustion chamber c448. Additionally, or alternatively, a second flame c426 may exist in the second combustion chamber c448, defining a combustion zone that is separate from a combustion zone in the second combustion chamber c448 may include a plurality of combustion fins c450 circumferentially spaced about the combustion chamber cl 02. The combustion fins c450 may occupy a region of the hot-side heat exchanger cl 06 configured for stable combustion to occur. Combustion may occur in the region of the hot-side heat exchanger cl 06 where the combustion fins c450 are located at least in part by the combustion fins c450 being heated to a sufficiently high temperature during operation to prevent flame quenching and/or promote an extended flame length.

[0170] The plurality of combustion fins c450 may spiral concentrically relative to the combustion chamber cl 02 and/or the longitudinal axis c204 thereof. The plurality of combustion fins c450 may be configured and arranged as spirals or spiral arcs, disposed annularly or semi-annularly, relative to the combustion chamber cl02 and/or the longitudinal axis c204 thereof. The combustion fins c450 may be concentrically nested with one another. Concentrically nested combustion fins c450 may be configured as an array of substantially concentric spirals and/or an array of substantially concentric spiral arcs. By way of example, a spiral or spiral arc, such as in an array of substantially concentric spirals or spiral arcs, may correspond to at least a portion of an Archimedean spiral, a Cornu spiral, a Fermat’s spiral, a hyperbolic spiral, a logarithmic spiral, a Fibonacchi spiral, an involute, or a squircular spiral, as well as combinations of these.

[0171] Upstream portions of the respective combustion-gas pathways c422 may fluidly communicate with the combustion chamber cl 02 at respective circumferential locations about the perimeter of the combustion chamber cl 02. Downstream portion of the respective combustion-gas pathways c422 may fluidly communicating with corresponding heating fluid pathways c602 of the hot-side heat exchanger cl06 (e.g. FIGs. 4.4.2A, 4.4.2B, 4.4.3A, and 4.4.3B). Such combustion fins c450 may concurrently define at least a portion of the second combustion chamber c448 and at least a portion of the hot-side heat exchanger cl06. The combustion fins c450 may become red-hot, encouraging a sustained combustion flame within the second combustion chamber c448. The second combustion chamber c448 may allow combustion to take place at an air-to-fuel ratio closer to the stoichiometric air-to- fuel ratio.

[0172] The combustor body c400 may include one or more features of the combustion chamber cl 02 and/or one or more features of the conditioning conduit cl 22 configured to burn fuel in a lean combustion environment. For example, the conditioning conduit cl22 may include one or more conditioning conduit inlets c414 dimensionally configured to provide sufficient combustion gas flow for a lean combustion environment. Additionally, or in the alternative, the one or more features of the combustion chamber cl 02 may include one or more combustion chamber outlets dimensionally configured to provide sufficient combustion gas flow for a lean combustion environment. The combustor body c400 may include one or more fuel nozzles, and the one or more fuel nozzles may be configured to provide a fuel flow sufficient for a lean combustion environment.

[0173] With respect to the one or more conditioning conduit inlets c414, the lean combustion environment may be provided by one or more motive pathways c418 and/or one or more eduction pathways c420. The one or more motive pathways c418 may be dimensionally configured to supply the conditioning conduit cl22 and/or the combustion chamber cl 02 with sufficient intake air to from the intake air pathway cl 18 to provide a lean combustion environment. Additionally, or in the alternative, the one or more motive pathways c418 may be dimensionally configured to accelerate and entrain sufficient combustion gas from the recirculation pathway cl 04 to provide a lean combustion environment. The one or more eduction pathways c420 may be dimensionally configured to recirculate sufficient combustion gas from the recirculation pathway cl 04 to provide a lean combustion environment.

[0174] A lean combustion environment may be characterized by an equivalence ratio, which is the ratio of the actual fuel-to-air ratio to the stoichiometric fuel-to-air ratio. An exemplary lean combustion environment may include an equivalence ratio of 0.6 to 1.0, such as an equivalence ratio of 0.7 to 0.8. The equivalence ratio may be at least 0.6, such as at least 0.8. The equivalence ratio may be less than 1.0, such as less than 0.7. An exemplary lean combustion environment may include an air-to-fuel ratio of from 40: 1 to 90: 1 by mass, or from 55: 1 to 75: 1 by mass. The air-to-fuel ratio may be at least 40: 1 by mass, such as at least 55: 1 by mass. The air-to-fuel ratio may be less than 90: 1 by mass, such as less than 75: 1 by mass.

[0175] The combustor body c400 may include one or more features of the combustion chamber cl 02 and/or one or more features of the conditioning conduit cl 22 configured to circulate at least a portion of the combustion gas by volume and to introduce a balance of the combustion gas as intake air. For example, the conditioning conduit cl 22 may include one or more conditioning conduit inlets c414 dimensionally configured to circulate at least a portion of the combustion gas by volume and to introduce a balance of the combustion gas as intake air. Additionally, or in the alternative, the one or more features of the combustion chamber cl 02 may include one or more combustion chamber outlets dimensionally configured to circulate from at least a portion the combustion gas by volume and to introduce a balance of the combustion gas as intake air.

[0176] The volume of circulating combustion gas may be from about 10% to about

90% of the combustion gas, such as from about 30% to about 70% of the combustion gas, such as from about 40% to about 60% of the combustion, with the balance of the combustion gas as being intake air. The volume of intake air included in the combustion gas may be from about 10% to about 90% of the combustion gas, such as from about 30% to about 70% of the combustion gas, such as from about 40% to about 60% of the combustion, with the balance being circulated combustion gas. However, in some embodiments the combustor body c400 may utilize 100% intake air and/or 100% circulating combustion gas.

[0177] In some embodiments, a cooling jacket c442 disposed within the at least a portion of the combustor body c400. The cooling jacket may define a pathway for a cooling fluid to flow within the combustor body c400. The flow of fluid cooling fluid may provide cooling to the combustor body c400. The cooling jacket c442 may fluidly communicate with the intake air pathway cl 18, the recirculation pathway cl 04, and/or the working-fluid pathway cl 10. By way of example, as shown in FIG. 4.1.1 A, a cooling jacket c442 may be disposed between at least a portion of the inward portion of the annular combustion chamber wall c406 and the outward portion of the annular combustion chamber wall c406, with the cooling jacket c442 fluidly communicating with at least one of the one or more motive pathways c418. Additionally, or in the alternative, the cooling jacket c442 shown in FIG.

4.1.1 A may fluidly communicate with at least one of the one or more eduction pathways c420. When the cooling fluid for the cooling jacket includes intake air and/or combustion gas, the combustor body c400 may include one or more cooling-jacket outlets c444, allowing the cooling fluid to flow into the conditioning conduct cl22 and/or the combustion chamber cl02.

[0178] Referring again to FIG. 4.1. IB, in some embodiments, a combustor body c400 may include a plurality of conditioning pathways c446 traversing the annular combustion chamber wall c406. The conditioning pathways may be disposed about a proximal, medial, and/or axial portion of the combustion chamber cl02, for example, traversing a proximal, medial, and/or axial portion of the annular combustion chamber wall c406 and providing fluid communication between the combustion chamber cl 02 and the conditioning conduit cl22.

[0179] Now referring to FIGs. 4.2.2A and 4.2.2B, an exemplary heater body cl 00 and/or combustor body c400 configured for multi-stage combustion will be described. A combustor body c400 configured for multi-stage combustion may sometimes be referred to as a multi-stage combustor c403. As used herein, the term“multi-stage combustion” refers to a combustion regime that includes at least two combustion zones oriented in serial flow relationship. As used herein, the term“combustion zone” refers to a portion of a combustion gas and/or fuel flowpath configured to support a stable flame c426 under one or more operating conditions. In some embodiments, a combustion zone may include a fuel injection point. For example, a multi-stage combustor may include a plurality of fuel injection points in serial flow relationship that are respectively configured to support a stable flame c426. Additionally, or in the alternative, a multi-stage combustor may include a combustion zone that is configured to support a stable flame c426 by combusting a fuel and/or combustion gas c428 introduced into the flowpath at an upstream combustion zone. For example, a fuel-rich environment may allow for a reburn combustion regime in which fuel injected at a first combustion zone is partially combusted at the first combustion zone and then further combusted at a second combustion zone.

[0180] An exemplary multi-stage combustor c403 may include a primary combustion zone and a secondary combustion zone. In some embodiments, a multi-stage combustor may include a tertiary combustion zone. The primary combustion zone may be situated upstream and/or downstream from a secondary combustion zone. A tertiary combustion zone may be located upstream or downstream from a primary combustion zone, and/or upstream or downstream from a secondary combustion zone. As used herein, the term“primary combustion zone” refers to a combustion zone that generates a larger proportion of heat during steady-state operation relative to one or more other combustion zones, such as relative to a secondary combustion zone and/or relative to a secondary and tertiary combustion zone. As used herein, the term“secondary combustion zone” refers to a combustion zone that generates a lesser proportion of heat during steady-state operation relative to another combustion zone, such as relative to a primary combustion zone. The term“tertiary combustion zone” refers to a combustion zone that generates a lesser proportion of heat during steady-state operation relative to a plurality of other combustion zones, such as relative to a primary combustion zone and a secondary combustion zone.

[0181] In an exemplary embodiment, a heater body cl 00 that includes a multi-stage combustor c403 may include a first combustion zone c405 and a second combustion zone c407. The first combustion zone c405 may occupy a distal or medial position relative to the longitudinal axis c204 of the combustion chamber cl 02. The second combustion zone c407 may occupy a proximal position relative to the longitudinal axis c204 of the combustion chamber cl02. The first combustion zone c405 may occupy a radially or concentrically inward position relative to the longitudinal axis c204 of the combustion chamber cl02. The second combustion zone c407 may occupy a radially or concentrically outward position relative to the longitudinal axis c204 of the combustion chamber cl 02 and/or relative to the radially or concentrically inward position of the first combustion zone c405. In some embodiments, the first combustion zone c405 may occupy at least a portion of a vortex flow field, such as a bidirectional vortex flow field. For example, the first combustion zone c405 may occupy at least part of an inward portion of a bidirectional coaxial vortex flow field.

The second combustion zone c407 may occupy at least part of a proximal region of the combustion chamber cl02. Additionally, or in the alternative, the second combustion zone c407 may occupy at least part of a radially-inward portion of the hot-side heat exchanger cl06. For example, the hot-side heat exchanger cl06 may define a second combustion chamber c448, and the second combustion zone c407 may occupy at least a portion of the second combustion chamber c448.

[0182] The first combustion zone c405 may be located upstream from a heat sink c409 a sufficient distance to allow combustion in the first combustion zone c405 to start, warm up, and stabilize. For example, the heat sink c409 may include at least a portion of the working-fluid bodies cl08 and/or at least a portion of the hot-side heat exchanger cl06. The working-fluid bodies cl 08 may have a heat transfer relationship with the hot-side heat exchanger cl06. The heat sink c409 may include a plurality of working-fluid pathways cl 10 that have a heat transfer relationship with the hot-side heat exchanger cl08 and/or the plurality of combustion-gas pathways c422. The plurality of heating walls c616 may define at least a portion of the hot-side heat exchanger cl06. The hot-side heat exchanger cl06 may include a plurality of working-fluid pathways monolithically formed within the plurality of heating walls c616.

[0183] Combustion in the second combustion zone c407 may be initiated

concurrently with and/or subsequently to initiation of combustion the first combustion zone c405. In some embodiments, combustion in the second combustion zone c407 may be initiated after combustion in the first combustion zone c405 has started, and/or after combustion in the first combustion zone c405 at least partially heated at least a portion of the combustor body c400 proximate to the second combustion zone c407. Additionally, or in the alternative, combustion in the second combustion zone c407 may be initiated after combustion in the first combustion zone c405 has stabilized.

[0184] Combustion in the first combustion zone c405 may be operated or sustained as a primary combustion zone. Additionally, or in the alternative, combustion in the first combustion zone c405 may be operated or sustained as a secondary combustion zone, or even as a tertiary combustion zone. In some embodiments, combustion in the first combustion zone c405 may be initially operated or sustained as a primary combustion zone, such as during a warm-up period. After an initial operating period, such as the warm-up period, combustion in the first combustion zone may transition to operation as a secondary combustion zone or a tertiary combustion zone. Combustion in the second combustion zone c407 may be operated or sustained as a primary combustion zone and/or a secondary combustion zone. For example, combustion in the second combustion zone c407 may be operated or sustained as a primary combustion zone after combustion in the first combustion zone c405 has sufficiently heated at least a portion of the combustor body c400 proximate to the second combustion zone c407. As combustion in the first combustion zone c405 transitions to operation as a secondary combustion zone, combustion in the second combustion zone c407 may transition to operation as a primary combustion zone. In some embodiments, combustion in the first combustion zone may be throttled back to a nominal proportion of combustion. For example, combustion in the first combustion zone c405 may operate at a nominal level sufficient to sustain steady combustion at the secondary

combustion zone c407.

[0185] During operation, such as during steady state operation, combustion in the first combustion zone c405 may support combustion in the second combustion zone c407 by maintaining a supply of heat sufficient to sustain at least a portion of the combustor body c400 proximate to the second combustion zone c407 at a temperature that exceeds a threshold suitable for good combustion and flame characteristics at the second combustion zone c407. Such support from the first combustion zone c405 may advantageously allow the second combustion zone c407 to operate as a primary combustion zone, thereby introducing heat closer to a heat sink such as a working-fluid body cl08 and/or a hot-side heat exchanger cl06. In some embodiments, a hot-side heat exchanger cl06 and/or a working-fluid body cl 08 may provide an improve heating efficiency with the second combustion zone c407 operating as the primary combustion zone.

[0186] As mentioned, in some embodiments, a combustor body c400 may include a plurality of combustion fins c450 circumferentially spaced about the perimeter of the combustion chamber cl 02 and/or the longitudinal axis c204. The plurality of combustion fins c450 may define a radially or concentrically inward portion of the plurality of combustion-gas pathways c422. The term“combustion-gas pathway” may refer to the portion of a heating fluid pathway c 602 defined by the combustion fins c450. The combustion-gas pathways c422 may be configured and arranged as spirals or spiral arcs, and may be oriented concentrically about the combustion chamber cl02 and/or the longitudinal axis c204. The combustion-gas pathways c422 may fluidly communicating with a corresponding plurality of spiral pathways of the hot-side heat exchanger cl06. The plurality of combustion fins c450 may respectively define a portion of a corresponding plurality of heating walls c616. Such combustion fins c450 may concurrently define at least a portion of the second combustion chamber c448 and at least a portion of the hot-side heat exchanger cl06. The second combustion zone c407 may occupy at least part of the radially or concentrically inward portion of the plurality of combustion-gas pathways c422 defined by the plurality of combustion fins c450.

[0187] Regardless of whether the secondary combustion zone c407 includes combustion fins c450, at least a portion of the combustor body c400 proximate to the secondary combustion zone c407 may become red-hot, encouraging a sustained combustion flame within the secondary combustion zone c407. Combustion in the secondary combustion zone c407 may take place at an air-to-fuel ratio closer to the stoichiometric air-to-fuel ratio, with or without secondary combustion support from the first combustion zone c405.

[0188] A heater body clOO that includes a multi-stage combustor c403 may include a cool-zone fuel injector c411 and a hot-zone fuel injector c413. However, in some embodiments, a multi-stage combustor c403 may be configured to sustain combustion in a plurality of combustion zones with only a single fuel injector, such as a cool -zone fuel injector c411 or a hot-zone fuel injector c413. The cool -zone fuel injector c411 may occupy a distal position relative to the longitudinal axis c204 of the combustion chamber cl02. The cool-zone fuel injector c411 may occupy a radially or concentrically inward position relative to the longitudinal axis c204 of the combustion chamber cl 02. In some embodiments, a hot- zone fuel injector c413 may occupy a proximal position relative to the longitudinal axis c204 of the combustion chamber cl 02. The hot-zone fuel injector c413 may occupy a radially or concentrically outward position relative to the longitudinal axis c204 of the combustion chamber cl02 and/or relative to the radially or concentrically inward position of the cool- zone fuel injector c411. The cool-zone fuel injector c411 may coincide with the first combustion zone c405. Additionally, or in the alternative, the first fuel injector may be located upstream from the first combustion zone c405. For example, the cool-zone fuel injector c411 may be operably coupled to a combustor cap c210, such as at a nozzle port c212. The hot-zone fuel injector c413 may coincide with the second combustion zone c407. Additionally, or in the alternative, the hot-zone fuel injector c413 may be located upstream from the second combustion zone c407.

[0189] In some embodiments, a heater body clOO and/or a combustor body c400 may include one or more fuel injectors monolithically integrated with a distal portion of the combustor body c400 and/or a radially or concentrically inward portion of the combustor body c400. The one or more fuel injectors may be monolithically integrated with a radially or concentrically inward portion of the hot-side heat exchanger cl06. For example, a plurality of a hot-zone fuel injectors c413 may be monolithically integrated with a distal portion of the combustor body c400 and/or a radially or concentrically inward portion of the plurality of combustion-gas pathways c616 of the hot-side heat exchanger cl06. The one or more fuel injectors may be monolithically integrated with the plurality of heating walls c616 and/or the plurality of combustion fins c450. Such plurality of hot-zone fuel injectors c413 may operate as a collective unit and may be referred to collectively as a hot-zone fuel injector c413. Additionally, or in the alternative, such plurality of hot-zone fuel injectors c413 may operate independently from one another and may be referred to individually as a hot-zone fuel injector c413.

[0190] One or more hot-zone fuel pathways c415 may be monolithically integrated with at least part of a distal portion of the combustor body c400 and/or a radially or concentrically inward portion of the hot-side heat exchanger cl 06. The one or more hot-zone fuel pathways c415 may be configured to supply fuel for combustion at the second combustion zone c407. For example, as shown in FIGs. 4.2.2A and 4.2.2.B, a plurality of hot-zone fuel pathways c415 may be defined within respective ones of a plurality of heating walls c616 of a hot-side heat exchanger cl06. Additionally, or in the alternative, one or more hot-zone fuel pathways c415 may be defined within a distal portion of the combustor body c400.

[0191] As shown, a plurality of heating walls c616 may include a heat sink c409, such as a hot-side heat exchanger cl06 and/or a working-fluid body cl08. The plurality of heating walls c616 may occupy a radially concentrically outward position relative to the combustion chamber cl02. The plurality of heating walls c616 may define a corresponding plurality of combustion-gas pathways c422, such as spiral pathway or a spiral arc pathway, fluidly communicating with the combustion chamber c402 at circumferentially spaced locations about the combustion chamber c402. The combustion-gas pathways c422 may fluidly communicate with a proximal portion c200 of the combustion chamber cl02. The plurality of combustion-gas pathways c422 may follow an annular or semiannular spiral trajectory relative to the combustion chamber cl02 and/or the longitudinal axis c204 thereof.

[0192] The hot-zone fuel pathways c415 may fluidly communicate with respective ones of a plurality of combustion-gas pathways c422 of the hot-side heat exchanger cl 06, such as at respective ones of a plurality of heating walls c616 and/or combustion fins c450. The plurality of heating walls c616 and/or combustion fins c450 may have a plurality of openings c451 (e.g., pore-like openings) that fluidly communicate with the plurality of combustion-gas pathways c422 of the hot-side heat exchanger cl 06 and define the hot-zone fuel injectors c413.

[0193] In some embodiments, at least a portion of the hot-zone fuel pathways c415 may define a vaporization heat exchanger c417 that provides a heat transfer relationship between a combustion flame c426 and fuel within the hot-zone fuel pathways c415, and or between hot combustion gas c426 fuel within the hot-zone fuel pathways c415. The vaporization heat exchanger c417 may be effective to vaporize fuel (e.g., liquid fuel), such as when the fuel is within the hot-zone fuel pathways c415 and/or the hot-zone fuel injectors c413, or as the fuel is discharged from the openings (e.g., the pore-like openings) of the hot- zone fuel injectors c413.

[0194] During operation, heat from the first combustion zone c405 may heat the hot- zone fuel injectors c413 and/or at least a portion of the second combustion zone c407 to a sufficiently high temperature to allow fuel flowing out of the hot-zone fuel injectors c413 to auto-ignite. For example, a distal portion of the combustion chamber cl02, and/or a radially or concentrically inward portion of the hot-side heat exchanger cl 06 (e.g., the combustion fins c450 and/or a radially or concentrically inward portion of the heating walls c616) may operate at a sufficiently high temperature to allow fuel flowing out of the hot-zone fuel injectors c413 to auto-ignite. The flame c426 and/or hot combustion gas c428 may have a temperature of from about 300C to about 900C, such as from about 350C to about 800C, such as from about 425C to about 750C, such as from about 500C to 600C. Once the fuel flowing out of the hot-zone fuel injectors c413 auto-ignites, the flame provided by cool-zone fuel injector c411 may be reduced to a minimal length sufficient to support combustion at the second combustion zone c407. In this way, the flame from the cool-zone fuel injector c411 may operate as a pilot burner configured to provide a pilot flame, or ignition source, for combustion in the second combustion zone c407. The pilot flame, or ignition source, provided by the cool -zone fuel injector c411 may support auto-ignition and good combustion of combustion gas c428 and/or fuel c426 flowing from the first combustion zone c405 to the second combustion zone c407, for example, providing a reburn combustion regime.

Additionally, or in the alternative, such pilot flame, or ignition source may support auto ignition and good combustion of fuel supplied by the hot-zone fuel injectors c413.

[0195] In some embodiments, the first combustion zone c405 may exhibit a rich combustion environment attributable at least in part to the fuel-to-air ratio resulting from fuel from the cool-zone fuel injector c411. The second combustion zone c407 may exhibit a lean combustion environment attributable at least in part to the fuel-to-air ratio resulting from the rich combustion environment of the first combustion zone c405 and/or fuel from the hot-zone fuel injectors c413. In some embodiments, the first combustion zone c405 may exhibit a lean combustion environment prior to auto-ignition at the second combustion zone c407. Upon auto-ignition at the second combustion zone c407, the first combustion zone c405 may transition to a rich combustion environment. The second combustion zone c407 may thereafter exhibit a lean combustion environment while the first combustion zone c405 may exhibit a rich combustion environment.

[0196] As mentioned, a lean combustion environment may be characterized by an equivalence ratio, which is the ratio of the actual fuel-to-air ratio to the stoichiometric fuel-to- air ratio. A rich combustion environment may similarly be characterized by an equivalence ratio. An exemplary lean combustion environment may include an equivalence ratio of from about 0.5 to about 1.0, such as from about 0.6 to about 0.9, or from about 0.7 to about 0.8 An exemplary rich combustion environment may include an equivalence ratio of from less than about 0.1 to about 0.5, such as from less than about 0.1 to about 0.2. By way of example, the first combustion zone c405 may exhibit an aforementioned“lean” equivalence ratio prior to auto-ignition at the second combustion zone c407, such as from about 0.5 to about 1.0, or any other suitable lean equivalence ratio. Upon auto-ignition at the second combustion zone c407, the first combustion zone c405 may transition to a“rich” equivalence ratio, such as from less than about 0.1 to about 0.5, or any other suitable rich equivalence ratio. The second combustion zone, meanwhile, may exhibit a“lean” equivalence ratio, such as from about 0.5 to 1.0, or any other suitable lean equivalence ratio. In exemplary embodiments, fuel may be supplied to the cool-zone fuel injector without pre-mix air, for example, to provide a rich combustion environment.

[0197] As shown in FIG. 4.2.2B, in some embodiments, the second combustion zone c407 may occupy one or more regions of the plurality of combustion-gas pathways c422 of the hot-side heat exchanger cl06. For example, respective combustion-gas pathways c422 may include a respective second combustion zone-segment c407A.

[0198] In some embodiments, the combustion-gas pathways c422 may include a burner zone c419 configured to support combustion and/or flame stabilization within the second combustion zone c407 and/or within the respective combustion zone-segments c407A. The burner zone c419 may be defined by a plurality of burner gap, GB, c421 defined in the respective heating walls c616 and oriented along the flowpath of the respective combustion-gas pathways c422. The burner gaps c421 may be located downstream from the hot-zone fuel injectors c413, such as between respective combustion fins c450 and corresponding downstream portions of the heating walls c616. A burner gap c421 may define a gap between a combustion fin c450 and a corresponding heating wall c616. The burner gaps c421 may include an open space, a mesh, a three-dimensional lattice, a porous medium, or the like. The burner zone c419 may coincide with at least a portion of the second combustion zone c407. Additionally, or in the alternative, the second combustion zone c407 may at least partially coincide with the plurality of burner gaps c421.

[0199] In some embodiments, a combustion chamber cl 04 may include a vortex conditioner cl37, as shown, for example, in FIGs. 4.1.7, 4.2.2A, 4.5.5A, 4.5.5C, and 4.5.5D. The vortex conditioner cl 37 may be monolithically integrated with a proximal portion of the combustion chamber cl02. The vortex conditioner cl37 may be configured at least in part to establish and/or sustain a vortex flow field that includes the combustion gas c428 and/or the flame c426. For example, the vortex conditioner cl37 may be configured at least in part to establish and/or sustain a bidirectional coaxial vortex flow field, which may enhance heat transfer of the flame c426 to the hot-side heater body cl 06 and/or may protect the

combustion chamber wall c406 from receiving excessive heat from the flame c426. The second combustion zone c407 may occupy a radially or concentrically outward position relative to the vortex conditioner cl37. As shown, the vortex conditioner cl37 may have a conical or frustoconical shape projecting into the combustion chamber cl02, such as along the longitudinal axis c204; however, other shapes are also envisioned. In some embodiments, a conical or frustoconical shape of the vortex conditioner cl37, and/or the location and/or dimensions thereof, may at least partially contribute to the vortex flow field (e.g., the bidirectional coaxial vortex flow field) of the combustion gas c428 and/or the flame c426. A vortex conditioner cl37 may be included with a heater body clOO and/or a combustor body c400 configured for single-stage and/or multi-stage combustion.

[0200] Now referring to FIGs. 4.2.3 A-4.2.3C, further exemplary combustor bodies c400 will be described. As shown in FIG. 4.2.3 A, an exemplary combustor body c400 may include a venturi c423 in the conditioning conduit pathway c416, such as at a distal portion c202 of the conditioning conduit cl22. The combustor body c400 may have a frustoconical configuration. For example, the conditioning conduit cl22 may have a frustoconical configuration. Additionally, or in the alternative, the combustion chamber cl02 may have a frustoconical configuration. The venturi c423 may be effective to improve mixing and/or reduce pressure drop in fluid flow through the conditioning conduit pathway c416 as the flow transitions form the conditioning conduit pathway c416 to the combustion chamber cl02.

The venturi c423 may additionally or alternatively induce turbulence, providing a mixing zone for fuel entering the combustion chamber cl 02 from a fuel nozzle cl 26, such as a cool- zone fuel injector cl 11. The venturi c423 may additionally or alternatively accelerate flow into the combustion chamber, such as into the first combustion zone c405. Such improved mixing, reduced pressure drop, and/or flow acceleration may increase combustion efficiency and/or heating efficiency of the heater body clOO.

[0201] As shown in FIG. 4.2.3B, the venturi provides an increase in velocity as the flow of combustion gas and/or intake air along the conditioning conduit pathway c416 transitions form zone“A” to zone“B” at the transition from the conditioning conduit cl 22 to the combustion chamber cl02. The velocity of the flow decreases as the flow advances towards zone“C” within the combustion chamber cl 02. The venturi c423 may work in cooperation with a Coanda surface c424 to condition flow into the combustion chamber cl02. A smoothly converging and diverging flowpath may be effective to reduce pressure drop across the venturi c423.

[0202] As shown in FIG. 4.2.3C, in some embodiments, the flow of combustion gas and/or intake air in the conditioning conduit pathway c416 may exhibit a tangential velocity gradient that increases from a radially or concentrically inward portion to a radially or concentrically outward portion of the conditioning conduit pathway c416. The tangential velocity gradient may increase as the radius of the conditioning conduit pathway c416 decreases, for example, as the conditioning conduit pathway c416 approaches the venturi c423. Such increase in velocity attributable to the tangential velocity gradient may further enhance mixing at zone“B,” shown in FIG. 4.2.3 A and 4.2.3B, such as at the venturi c423.

[0203] The frustoconical configuration and arrangement of the combustor body c400, including the configuration and arrangement of the conditioning conduit cl 22 and/or the combustion chamber cl 02, may be selected at least in part to provide a desired reduction in pressure drop, fluid flow rate, and/or size of the combustor body. For example, pressure drop may be reduced by providing a small convergence angle, Q c425. By contrast, a small convergence angle may correspond to a taller combustor body c400, increasing material cost. Conversely, a large convergence angle, Q c425 may allow for a shorter combustor body c400 but increased pressure drop. These factors may be balanced to determine a suitable frustoconical configuration and arrangement for the combustor body c400. [0204] Now turning to FIGs. 4.2.4A-4.2.4E, in some embodiments, a combustor body c400 may include one or more combustor vanes c427. The combustor vanes c427 may be configured to condition a flow of combustion gas and/or intake air into the combustion chamber. In some embodiments, the combustor vanes c427 may be configured to induce a vortex or turbulent flow in combustion gas and/or intake air entering the combustion chamber. Such vortex or turbulent flow may improve mixing, for example, providing a mixing zone for fuel entering the combustion chamber 102 from a fuel nozzle cl 26, such as a cool-zone fuel injector cl 11. The combustor vanes c427 may be fixed to the combustor cap c210. For example, the combustor vanes c427 may define a monolithic portion of the combustor cap c210. Additionally, or in the alternative, a combustion chamber cl 02 may include one or more combustor vanes c427, for example, defining a monolithic portion of the combustion chamber cl 02.

[0205] In some embodiments, a plurality of vane rows may be provided. For example, as shown, a combustor body c400 and/or a combustor cap c210 may include three vane rows. As shown in FIG. 4.2.4A, a combustor cap c210 may include a first vane row c429A, a second vane row c429B, and/or a third vane row c429C. The respective vane rows may include one or more vanes. The vane rows may be oriented coannularly relative to a longitudinal axis of the combustor body c204.

[0206] The first vane row c429A may define a shield flowpath along the wall of the combustion chamber cl 02. The shield flowpath may provide cooling to the combustion chamber wall. The second vane row c429B may provide a main flowpath. The main flowpath may provide the bulk flow for combustion. The third vane row c429C may provide a premixing flowpath. The premixing flowpath may provide oxygen to mix with fuel prior to combustion.

[0207] The respective combustor vanes c427 may have any desired configuration. A combustor vane c427 may have any desired height extending from an inward combustor cap- surface c431. A combustor vane c427 may have a height that runs parallel to the inward combustor cap-surface c431. Additionally, or in the alternative, a combustor vane c427 may have a height that is sloped relative to the inward combustor cap-surface 431. By way of example, FIG. 4.2.4B shows an individual combustor vane c427 that has a sloped height relative to the inward combustor cap surface c431.

[0208] By way of example, FIGs. 4.2.4C-4.2.4E show exemplary configurations of combustor vanes c427. The configurations shown are provided by way of example and not to be limiting. As shown in FIG. 4.2.4C, a plurality of combustor vanes c427 may have an airfoil-type configuration. Additionally, or in the alternative, a plurality of combustor vanes c427 may have a baffle-type configuration. A plurality of rows of airfoil-type combustor vanes c427 and/or baffle-type combustor vanes c427 may be provided, such as three rows, as shown. A plurality of combustor vanes c427 may additionally or alternatively have a spiral configuration, as shown, for example, in FIG. 4.2.4E.

[0209] Now turning to FIG. 4.2.5 A and 4.2.5B, exemplary methods of combusting a fuel will be described. Exemplary methods may be performed in connection with operation of a combustor body c400, a heater body clOO, and/or a closed-cycle engine c002 as described herein. As shown in FIG. 4.2.5A, an exemplary method c470 may include, at block c472, swirling combustion gas through a conditioning conduit cl 22, with the combustion gas flowing from a proximal portion of the conditioning conduit cl22 to a distal portion of the conditioning conduit cl 22 while swirling. At block c474, the exemplary method c470 may include swirling the combustion gas through a combustion chamber cl02. In the exemplary method c470, the conditioning conduit cl22 may circumferentially surround the combustion chamber cl 02 with the conditioning conduit cl 22 providing fluid

communication with the combustion chamber cl02 at a distal portion of the combustion chamber cl02. The combustion gas may flow from the distal portion of the conditioning conduit cl22 to the distal portion of the combustion chamber cl02 and from the distal portion of the combustion chamber cl02 to a proximal portion of the combustion chamber cl02. At block c476, the exemplary method c470 may include combusting a fuel c426 in the combustion chamber cl 02. The fuel may be supplied at least in part from the combustion gas flowing from the conditioning conduit cl22 to the combustion chamber cl02.

[0210] The exemplary method c470 may additionally or alternatively include, at block 478, supplying at least a portion of the fuel to the combustion chamber cl02 through a fuel nozzle c214 fluidly communicating with a distal portion of the combustion chamber cl02. Additionally, or in the alternative, the exemplary method c470 may include supplying at least a portion of the fuel to the combustion chamber through the conditioning conduit.

For example, the exemplary method c470 may include, circulating at least a portion of the combustion gas through one or more conditioning conduit inlets c414 disposed about a proximal portion of the conditioning conduit.

[0211] At block c480, the exemplary method c470 may include circulating at least a portion of the combustion gas through a recirculation pathway cl 04, with the recirculation pathway cl 04 providing fluid communication from a proximal portion of the combustion chamber cl02 to a proximal portion of the conditioning conduit cl22. The recirculation pathway cl04 may include a hot-side heat exchanger cl06 and a recirculation eductor cl 16. The hot-side heat exchanger cl 06 may fluidly communicate with a proximal portion of the combustion chamber cl 02 and the recirculation eductor cl 16 may fluidly communicate with a downstream portion of the hot-side heat exchanger cl 06 and a proximal portion of the conditioning conduit cl22 and/or and a distal portion of the combustion chamber cl02. The exemplary method may include combusting at least a portion of the combustion gas circulating through the recirculation pathway cl04.

[0212] At least a portion of the fuel may be supplied to the combustion chamber cl 02 through one or more conditioning conduit inlets c414 disposed about a proximal portion of the conditioning conduit cl22. Supplying fuel through the one or more conditioning conduit inlets c414 may include supplying fuel through one or more motive pathways c418 and/or one or more eduction pathways c420. The one or more conditioning conduit inlets c414 may be oblique to the conditioning conduit cl 22, for example, to facilitate swirling of the combustion gas and/or fuel.

[0213] Now referring to FIG. 4.2.5B, another exemplary method c471 of combusting a fuel will be described. As shown, an exemplary method c471 may include, at block c473, combusting a fuel at a first combustion zone c405; at a block c475, heating a second combustion zone c407; and, at block c477, combusting a fuel at the second combustion zone c407. In some embodiments, an exemplary method c471 may include, at block c479, auto- igniting fuel at the second combustion zone c407. Combusting the fuel at a first combustion zone c405 may include, at block c481, combusting fuel from a cool-zone fuel injector c411 at the first combustion zone c405. Auto-igniting fuel at the second combustion zone c407 may include, at block c483, auto-igniting fuel from the cool -zone fuel injector c411 from a hot- zone fuel injector c413 at the second combustion zone c407. Combusting the fuel at the second combustion zone c407 may include, at block c485, combusting fuel from the cool- zone fuel injector c411 and/or from the hot-zone fuel injector c413 at the second combustion zone c407. Heating the second combustion zone c407 may include, at block c487 vaporizing fuel in a vaporization heat exchanger c417.

[0214] In some embodiments, combusting fuel at the first combustion zone c405 may include, at block c489, combusting fuel at the first combustion zone c405 in a lean combustion environment and/or a rich combustion environment. At block c491, combusting fuel at the second combustion zone c407 may include combusting fuel at the second combustion zone c407 in a rich combustion environment. In some embodiments, an exemplary method c471 may include, at bock c493A, combusting fuel at the first combustion zone in a lean combustion environment, and, at block c493B, combusting fuel at the first combustion zone in a rich combustion environment upon having auto-ignited fuel at the second combustion zone. At block c491C, an exemplary method c471 may include combusting fuel at the second combustion zone in a lean combustion environment while combusting fuel at the first combustion zone in a rich combustion environment.

[0215] Any one or more parameters may be utilized to control one or more operations of a combustor body c400, a heater body clOO, and/or a closed-cycle engine c002 as described herein, including one or more operations in connection with methods of

combustion a fuel such as the exemplary methods described herein with reference to FIGs. 4.2.5A and 4.2.5B. By way of example, an exemplary method of combustion a fuel c470, c471 may include controlling one or more of: a fuel flow (e.g., a fuel flow to a cool-zone fuel injector c411 and/or a hot-zone fuel injector c413), an air flow (e.g., an intake airflow, an exhaust flow, and/or a combustion gas flow).

[0216] Now referring to FIGs. 4.3.1 and 4.3.8, fuel injectors for relatively small or compact apparatuses such as external or internal combustion engines for automotive vehicles, watercraft, or light aircraft, or power units, are limited in spaced such as to inhibit provision of dual-fuel systems. As such, there is a need for fuel injector assemblies that provide dual fuel systems for relatively small or compact apparatuses.

[0217] Embodiments of a fuel injector assembly are provided that may improve atomization and ignition of two or more fuels flowed from the fuel injector assembly. The embodiments shown and described provide a second fuel circuit, through which a liquid or gaseous fuel flows, surrounded at a downstream end by one or more gaseous fluid circuits, such as to provide cooling at the second fuel circuit to mitigate coking and fuel injector deterioration. The fuel injector assembly provided herein provides a compact assembly that may provide dual-fuel combustion for automotive, marine, auxiliary power unit, rotary or fixed wing aircraft, or other vehicles necessitating smaller combustion assemblies.

[0218] Referring now to FIG. 4.3.1, a cross sectional view of an exemplary embodiment of a fuel injector assembly dlOO (“fuel injector dlOO”) is generally provided.

The body dl 10 of the fuel injector dl 10 is extended along a lateral direction L between an upstream end d99 and a downstream end d98. A reference fuel injector centerline axis dl3 is defined through a cylindrical portion dl 16 of the body dl 10. The cylindrical portion dl 16 of the body dl 10 is defined circumferentially relative to the reference centerline axis dl3 and extended along the lateral direction L. The body dl 10 further includes a frustoconical portion dl 17 at the downstream end d98.

[0219] The fuel injector dlOO includes a first fuel circuit di l l and a second fuel circuit dl 12 each defined within the body dl 10. The first fuel circuit di l l and the second fuel circuit dl 12 are each extended along the lateral direction L from the upstream end d99 to the downstream end d98.

[0220] Referring still to FIG. 4.3.1, in various embodiments, the first fuel circuit di l l and the second fuel circuit dl 12 each extend along a lateral distance dl20 of the body dl 10. The lateral distance dl20 of the body dl 10 is extended from the downstream end d98 (i.e., at a tip corresponding to an output port dl05) to the upstream end d99 (i.e., corresponding to an inlet port dl08). For a portion of the lateral distance dl20, such as depicted at reference dimension dl21 extended from the downstream end d98, the first fuel circuit di l l is extended annularly within the body dl 10. For another portion of the lateral distance dl20, such as depicted at reference dimension dl22 extended from the downstream end d98, the second fuel circuit dl 12 is extended annularly within the body dl 10. In various

embodiments, the portion dl21 of the lateral distance dl20 for which the first fuel circuit di l l is extended circumferentially through the body dl 10 is greater than the portion dl22 of the lateral distance dl20 for which the second fuel circuit dl 12 is extended circumferentially through the body dl 10. In one embodiment, the portion dl22 is 90% or less of the portion dl21. In another embodiment, the portion dl22 is 75% or less of the portion dl21. In still another embodiment, the portion dl22 is 50% or less of the portion dl21. In various embodiments, the portion dl22 is 33% or greater of the portion dl21.

[0221] Referring now to FIG. 4.3.8, another cross sectional view of an exemplary embodiment of the fuel injector dlOO is provided. In FIG. 4.3.8, the fuel injector dlOO further includes an igniter dl40 extended through an outlet port dl05 through the

downstream end d98 of the body dl 10. In various embodiments, the outlet port dl05 is extended through the body dl 10 concentric to the reference centerline axis dl3. The igniter dl40 may be extended through a cavity dl33 radially or concentrically inward of the fuel circuits dl 11, dl 12 and extended laterally within the body dl 10. In particular embodiments, the igniter dl40 may extend through the cavity dl33 from the upstream end d99 of the body dl 10 through an inlet port d 108 to admit the igniter dl40 into the cavity dl33 and protrude from the downstream end d98 of the body dl 10 into a combustion chamber. The igniter dl40 extends through the outlet port dl05 such as to dispose the downstream end d98 of the igniter d 140 to one or more of the flows of fuel dlOl, dl02 egressed from their respective fuel circuits di l l, dl 12.

[0222] In various embodiments, the igniter dl40 provides an energy source to ignite and combust the flows of fuel dlOl, dl02 egressed from their respective fuel circuits di l l, dl 12. In one embodiment, the igniter dl40 defines a glow plug such as to provide a source of thermal energy such that when one or more flows of fuel dlOl, dl02 are exposed to heat generated from the igniter dl40 causes the fuel dlOl, dl02 to ignite. In particular

embodiments, the second flow of fuel dl02 defining a liquid fuel is exposed to heat generated from the igniter d 140 to cause the fuel d 102 to ignite.

[0223] A method for operation of the fuel injector dlOO is provided herein in which a relatively low pressure second flow of fuel dl02 is provided through a second fuel inlet opening dl07 (FIGs. 4.3.1 and 4.3.8) to the second fuel circuit dl 12. The relatively low pressure second flow of fuel dl02 egresses from the body dl 10 of the fuel injector dlOO via the second fuel injection opening dl25. As the egressed fuel dl02 flows closer to or touches the igniter dl40, it is initially ignited (e.g., light-off) and may further ignite the first flow of fuel dlOl egressed from the plurality of first fuel injection apertures dl 15. Following light- off, the pressure may increase such as to improve atomization and desirably alter combustion and heat release characteristics, such as to improve operability, performance, and reduce emissions output (e.g., smoke, unburned hydrocarbons, oxides of nitrogen, etc.).

[0224] The igniter dl40 included through the body dl 10 of the fuel injector dlOO may provide and/or improve providing dual fuel (i.e., the first and second flows of fuel dlOl, dl02) operation of the fuel injector dlOO at relatively small engine apparatuses, such as those for external or internal combustion engines, including those for automotive, personal or light water craft, or auxiliary power unit applications.

[0225] In still various embodiments, during operation of the fuel injector dlOO, the first flow of fuel dlOl defining a gaseous fuel is provided through a first inlet opening dl06 (FIGs. 4.3.1 and 4.3.8) to the first fuel circuit dl l l. The fuel dlOl egresses from the body dl 10 through the plurality of first fuel injection apertures dl 15 for combustion.

[0226] Embodiments of the fuel injector dlOO shown and depicted herein in regard to

FIGs. 4.3.1 and 4.3.8 may be constructed via one or more manufacturing processes known in the art. In various embodiments, the fuel injector dlOO may be constructed as a single, unitary construction. In another embodiment, the body dl 10 may be constructed as a single, unitary construction separate from the igniter dl40. Manufacturing processes for

constructing the fuel injector dlOO may include one or more processes generally referred to as additive manufacturing or 3D printing. Additionally, or alternatively, manufacturing processes for constructing the fuel injector dlOO may include one or more machining processes or other material removal processes, material additive processes such as welding, brazing, soldering, or bonding processes generally, or one or more casting or forming processes.

[0227] In still various embodiments, the fuel injector dlOO may include one or more materials appropriate for fuel injection to a combustion chamber, such as, but not limited to, iron or iron-based materials, aluminum, magnesium, nickel, titanium, ceramic or metal matrix composites, or alloys or combinations thereof, or other materials appropriate for combustion systems. Furthermore, the fuel injector dlOO may include one or materials appropriate for heat engines generally, or external or internal combustion engines, closed-cycle engines, Stirling cycle, Rankine cycle, or Brayton cycle machines more specifically.

[0228] Embodiments of the fuel injector dlOO provided herein may be configured to receive and desirably inject a plurality of types of fuels through the first circuit di l l and the second circuit dl 12. Exemplary fuels include, but are not limited to, propane, ethane, coke oven gas, natural gas, synthesis gas, liquid fuel such as diesel fuel, gasoline, synthetic fuel, or a plurality of specifications of kerosene or jet fuel (e.g., Jet A, JP-8, etc.), or mixtures of gaseous and/or liquid fuels thereof.

[0229] A method for operation of the fuel injector dlOO provides for selectively relatively low pressure/flow output and high pressure/flow output of fuel through each circuit dl 11, dl 12, dl 13 of the fuel injector dlOO. The fuel injector dlOO provides for a relatively low pressure/flow operation of the fuel injector dlOO for a first flow of fuel to egress from the fuel injector dlOO and touch the hot igniter dl40, such as defining glow plug, to ignite the fuel. The fuel injector dlOO further provides for a relatively high pressure/flow operation of the fuel injector dlOO for the first flow of fuel, or additionally or alternatively, a second flow of fuel, to egress the fuel injector dlOO such as to avoid touching the igniter dl40. As such, the relatively high pressure/flow operation of the fuel injector dlOO prevents undesired burn- up, wear, or other deterioration of the igniter dl40. The high pressure/flow operation of the fuel injector dlOO may additionally, or alternatively, provide the second flow of fuel (e.g., via the second circuit dl 12) to generate a buffer, such as a fluid and/or thermal break, between the first flow of fuel from the first circuit di l l and the igniter dl40. In still various embodiments, the first flow of fuel from the first circuit di l l defines a liquid fuel. The second flow of fuel from the second circuit dl 12 may define a liquid and/or gaseous fuel. In still other embodiments, one or more other fluids, such as a non-fuel fluid, may be provided through the first circuit dl 11, the second circuit dl 12, and/or the third circuit dl 13. In one embodiment, the fluid provided through the fuel injector dlOO includes an inert gas, urea, or other substance such as to desirably control emissions, provide a thermal or fluid barrier, or clean one or more circuits or passages of the fuel injector dlOO. For example, urea may be added to the fuel such as to decrease emissions associated with diesel fuels or similar.

[0230] In still various embodiments, the fuel injector dlOO provides a structure and method for operation at which the vane structure dl30 provides or generating a

circumferential swirl to the fuel through second circuit dl 12, such as described herein. In one embodiment, the method for operation includes providing a circumferential swirl to a liquid fluid or fuel via the vane structure dl30 within the second circuit dl 12. The liquid fuel then egresses the fuel injector dlOO via the respective opening(s) with at least a partial circumferential velocity component, such as depicted in regard to FIG. 4.3.1.

[0231] In another embodiment, the structure and method for operation includes providing or generating a substantially no-swirl or axial flow of fuel through the second circuit dl 12 via the vane structure dl30 such as described herein. In one embodiment, the method for operation includes providing the gaseous fluid or fuel through a first upstream vane structure dl30 relative to a second downstream vane structure dl30. The second downstream vane structure dl30 defines at least one opening circumferentially offset from an opening defined at the first upstream vane structure dl30. In one embodiment, the method may include providing a single opening at the first upstream vane structure dl30 and a single opening at the second downstream vane structure dl30. The vane structure dl30 may further provide for retarding a circumferential flow component of the fluid via the circumferentially offset opening defined at each vane structure dl30. The method may further include egressing the flow of fuel via respective opening(s) with a substantially no-swirl or non- circumferential flow component. The substantially non-swirl flow of gaseous fluid may provide improved thermal and/or fluid barrier between the igniter dl40 and the combustion gases radially or concentrically outward or surrounding the igniter dl40.

[0232] Embodiments of the fuel injector dlOO provided herein may provide relatively low pressure supply of the fuels dlOl, dl02 through the fuel injector dlOO for egress through the plurality of first fuel injection apertures dl 15 and second fuel injection opening dl25 and combustion at a combustion chamber. In one embodiment, the fuel injector dlOO provided herein may provide the second flow of fuel dl02 defining a liquid fuel to be provided through the fuel injector dlOO without a fuel pump. For example, the fuel injector dlOO may receive the second flow of fuel dl02 via header pressure from a fuel tank providing the second flow of fuel dl02. Generally, as the fuel injector dlOO provided herein may operate with relatively low pressure fuel sources, dual -fuel fuel injectors dlOO may be provided to apparatuses typically too small or compact for dual-fuel systems, such as, but not limited to, external or internal combustion engines for automotive vehicles, personal or commercial marine vehicles, personal watercraft, light aircraft, including short takeoff and vertical landing (STOVL) vehicles, rotary or fixed wing aircraft, or auxiliary power units.

[0233] Now referring to FIGs. 4.4.1 A and 4.4. IB, 4.4.2A and 4.4.2B, and 4.4.3 A and

4.4.3B, exemplary heat exchanger bodies c600 (e.g., hot-side heat exchanger bodies c600) will be described. The presently disclosed hot-side heat exchanger bodies c600 may define part of a heater body clOO and/or a closed-cycle engine c002. For example, a hot-side heat exchanger body c600 may define at least a portion of a monolithic body or a monolithic body-segment. Such monolithic body or monolithic body-segment may define at least a portion of the heater body clOO and/or the closed-cycle engine c002. Additionally, or in the alternative, the presently disclosed hot-side heat exchanger bodies c600 may be provided as a separate component, whether for use in connection with a heater body clOO, a closed-cycle engine c002, or any other setting whether related or unrelated to a heater body clOO or a closed-cycle engine c002. At least a portion of the hot-side heat exchanger body c600 may define a hot-side heat exchanger cl06. While the heater bodies clOO depicted in the figures may show one hot-side heat exchanger body c600 and/or one hot-side heat exchanger cl06, it will be appreciated that a heater body clOO may include a plurality of hot-side heat exchanger bodies c600 and/or a plurality of hot-side heat exchangers cl06. For example, a heater body clOO may include one or more hot-side heat exchanger bodies c600, and/or a hot-side heat exchanger body c600 may include one or more hot-side heat exchangers cl06.

[0234] As shown, a hot-side heat exchanger body c600 and/or a hot-side heat exchanger cl 06 may include a plurality of heating walls c616. The plurality of heating wall c616 may be configured and arranged as an array of heating walls c616. The heating walls c616 may be radially or concentrically adjacent to one another. The heating walls c616 may be configured and arranged as a spiral or a spiral arc, and may be disposed annularly or semi- annularly relative to the combustion chamber cl 02 and/or the longitudinal axis c204 thereof. The heating wall c616 may be concentrically nested with one another. The heating wall c616 may be configured and arranged as an array of substantially concentric spirals and/or an array of substantially concentric spiral arcs. By way of example, a spiral or spiral arc, such as in an array of substantially concentric spirals or spiral arcs, may correspond to at least a portion of an Archimedean spiral, a Cornu spiral, a Fermat’s spiral, a hyperbolic spiral, a logarithmic spiral, a Fibonacchi spiral, an involute, or a squircular spiral, as well as combinations of these.

[0235] The heating walls c616 define a plurality of heating fluid pathways c602. The heating fluid pathways c602 may make up a portion of the hot-side heat exchanger body c600 and/or a hot-side heat exchanger cl06, defining a pathway through which a heating fluid such as circulating combustion gas may flow. The heating fluid pathways c602 may fluidly communicate with an inlet plenum c604. The inlet plenum may include a combustion chamber c602. The heating fluid pathways c602 may be configured and arranged as an array of heating fluid pathways c602. The heating fluid pathways c602 may be radially or concentrically adjacent to one another with a heating wall c616 disposed between respective adjacent heating fluid pathways c602. The heating walls c616 may be radially or

concentrically adjacent to one another with a heating fluid pathway c602 disposed between respective adjacent heating walls c616. The heating walls c616 may be configured and arranged as a spiral or a spiral arc, and may be disposed annularly or semi-annularly relative to the combustion chamber cl02 and/or the longitudinal axis c204 thereof. The heating fluid pathways c602 may be concentrically nested with one another. The heating fluid pathways c602 may be configured and arranged as an array of substantially concentric spirals and/or an array of substantially concentric spiral arcs. The hot-side heat exchanger body c600 may include an array of alternating heating walls c616 and heating fluid pathways c602.

[0236] Upstream ends of the heating walls c616 may be circumferentially spaced about an inlet plenum c604, such as a combustion chamber. Upstream ends of the heating fluid pathways c602 may respectively define an inlet c606, which may be circumferentially spaced about the inlet plenum c604, such as the combustion chamber cl02. At least some of the inlets c606 may be oriented oblique to the inlet plenum c604. At least some of the plurality of heating fluid pathways c602 may define a spiral pathway.

[0237] The inlet plenum c604, such as the combustion chamber cl 02, may fluidly communicate with the plurality of heating fluid pathways c602. The plurality of heating fluid pathways c604 may respectively define an inlet c606 circumferentially spaced about the inlet plenum c604 (and/or disposed radially about the inlet plenum c604). Respective ones of the plurality of heating fluid pathways c604 may define respective ones of a plurality of inlets c606. The plurality of inlets c604 may be circumferentially spaced about the inlet plenum c604 (and/or disposed radially about the inlet plenum c604). For example, the plurality of inlets c604 may be circumferentially spaced about the combustion chamber cl02 (and/or disposed radially about the combustion chamber cl 02). In some embodiments, respective ones of the plurality of inlets may define respective ones of a plurality of combustion chamber outlets c412. Additionally, or in the alternative, the inlet plenum c604 may define a plurality of inlets c606 fluidly communicating with respective ones of the plurality of heating fluid pathways c602. For example, the combustion chamber cl02 may define a plurality of combustion chamber outlets c412 and/or a plurality of inlets c606 fluidly communicating with respective ones of the plurality of heating fluid pathways c602.

[0238] The plurality of heating fluid pathways c602 may additionally or alternatively fluidly communicate with one or more outlet plenum c608, such as a recirculation annulus c208. The fluid communication between the plurality of heating fluid pathways c602 and the one or more outlet plenum c608, such as a recirculation annulus c208 may be at a

downstream portion of respective ones of the plurality of heating fluid pathways c602. The outlet plenum c608 or recirculation annulus c208 may circumferentially surround at least a portion of the hot-side heat exchanger body c600 and/or the hot-side heat exchanger cl06.

For example, the outlet plenum c608 or recirculation annulus c208 may circumferentially surround at least a portion of the plurality of heating fluid pathways c602.

[0239] As shown, for example, in FIGs. 4.4. IB and 4.4.2B, the hot-side heat exchanger body c600 and/or a working-fluid body cl 08 may define a plurality of heat transfer regions c612. The plurality of heat transfer regions c612 may correspond to respective portions of a working-fluid body cl 08. A respective heat transfer region c612 may encompass a portion of the hot-side heat exchanger body c600 and/or a portion of the working-fluid body cl08. Respective ones of the plurality of heat transfer regions c612 have a thermally conductive relationship with a corresponding portion c614 of the plurality of heating fluid pathways c602, such as a semiannular portion c614 of the plurality of heating fluid pathways c602. Respective ones of the plurality of heat transfer regions c612 may include a heat input region, at least one heat extraction region, and a plurality of working- fluid pathways cl 10. The heat input region may include a piston body c700 and the heat extraction region may include a regenerator body c800.

[0240] In some embodiments, a heat transfer region c612 may include at last a portion of a working-fluid body cl 08. For example, a heat transfer region c612 may include at least a portion of a piston body c700 and/or at least a portion of a regenerator body c800.

Additionally, or in the alternative, a heat transfer region c612 include one or more working- fluid pathways cl 10 that have a thermally conductive relationship with a corresponding portion c614 (e.g., a semiannular portion) of at least some of the plurality of heating fluid pathways c602. For example, the heat transfer region c612 may include one or more working-fluid pathways cl 10 defined at least in part within a corresponding one or more heating wall c616 of a hot-side heat exchanger cl06. Such working-fluid pathways cl 10 may define a pathway for an engine-working fluid to flow through the hot-side heat exchanger cl06, such as through the one or more heating walls c616 thereof. Where a working-fluid pathway cl 10 flows through a hot-side heat exchanger cl 06, the heat transfer region c612 may include a portion of the working-fluid pathway within or defined by the hot-side heat exchanger cl 06, such as within a region of one or more heating wall c616 of the hot-side heat exchanger cl06 corresponding to the heat transfer region c612.

[0241] The hot-side heat exchanger body c600 may include a plurality of working- fluid pathways cl 10 monolithically formed within the plurality of heating walls c616. The plurality of working-fluid pathways may be grouped into an array of working-fluid pathways cl 10 and/or a plurality of arrays of working fluid-pathways cl 10. An array of working-fluid pathways cl 10 may define a heat transfer region c612. A plurality of arrays of working-fluid pathways cl 10 may define a corresponding plurality of heat transfer regions c612.

Respective ones of the plurality of arrays of working-fluid pathways cl 10 may be

circumferentially spaced about the hot-side heat exchanger body c600. Respective ones of the plurality of heat transfer regions c600 may be circumferentially spaced about the hot-side heat exchanger body c600.

[0242] As shown, for example, in FIGs. 4.4.2A and 4.4.2B, at least some of the working-fluid pathways cl 10 may be radially or concentrically adjacent to one another. Additionally, or in the alternative, as also shown, at least some of the working-fluid pathways cl 10 may be semiannular to one another. The working-fluid pathways cl 10 may fluidly communicate between the heat input region and the at least one heat extraction region. The plurality of heating fluid pathways c602 may be disposed radially or concentrically adjacent to corresponding respective ones of the plurality of working-fluid pathways cl 10, such as radially or concentrically adjacent to respective ones of a plurality of semiannular working- fluid pathways cl 10. Respective ones of the plurality of heating fluid pathways c602 may have a thermally conductive relationship with corresponding respective ones of the plurality of working-fluid pathways cl 10.

[0243] The plurality of heat transfer regions c612 may be circumferentially spaced about the hot-side heat exchanger body c600. The semiannular portion c614 of the plurality of heating fluid pathways c602 corresponding to a respective heat transfer region c612 may correspond to a radial position of the respective heat transfer region c612. For example, the plurality of heating fluid pathways c602 may define a spiral pathway, spiraling annularly or semi-annularly around a longitudinal axis, A, c214. The portion c614 of the plurality of heading fluid pathways c602 passing the radial position of a respective heat transfer region c612 may define the semiannular portion c614 of the plurality of heating fluid pathways c602 corresponding to the respective heat transfer region c612.

[0244] In some embodiments, the plurality of heating fluid pathways c602 may pass adjacent to at least some of the plurality of heat transfer regions c612 in circumferential series. For example, the plurality of heating fluid pathways c602 may have a thermally conductive relationship with the at least some of the plurality of heat transfer regions c612, and the particular heat transfer region c612 with which a respective portion c614 of the plurality of heating fluid pathways c604 has a thermally conductive relationship may transition radially from one heat transfer region c612 to and adjacent heat transfer region c612. The circumferential series of a respective one of the plurality of heating fluid pathways c602 may have a sequence depending at least in part on a circumferential location of an inlet c606 to the respective one of the plurality of heating fluid pathways c602.

[0245] By way of example, a first heating fluid pathway c618 may pass adjacent to at least some of the plurality of heat transfer regions c612 in a first circumferential series that includes a first heat transfer region c620 followed by a second heat transfer region c622. The first circumferential series may additionally or alternatively include the second heat transfer region c622 followed by a third heat transfer region c624 and/or a fourth heat transfer region c626. For example, the fourth heat transfer region c626 may be preceded by the third heat transfer region c624. A second heating fluid pathway c628 may pass adjacent to at least some of the plurality of heat transfer regions c612 in a second circumferential series. The second circumferential series may include the second heat transfer region c622 followed by the third heat transfer region c624. The second circumferential series may additionally or alternatively include the third heat transfer region c624 followed by the fourth heat transfer region c626 and/or the first heat transfer region c620. For example, the first heat transfer region c620 may be preceded by the fourth heat transfer region c626. A third heating fluid pathway c630 may pass adjacent to at least some of the plurality of heat transfer regions c612 in a third circumferential series. The third circumferential series may include the third heat transfer region c624 followed by the fourth heat transfer region c626. The third

circumferential series may additionally or alternatively include the fourth heat transfer region c626 followed by the first heat transfer region c620 and/or the second heat transfer region c622. For example, the second heat transfer region c622 may be preceded by the first heat transfer region c620. A fourth heating fluid pathway c632 may pass adjacent to at least some of the plurality of heat transfer regions c612 in a fourth circumferential series. The fourth circumferential series may include the fourth heat transfer region c626 followed by the first heat transfer region c620. The fourth circumferential series may additionally or alternatively include the first heat transfer region c620 followed by the second heat transfer region c622 and/or the third heat transfer region c624. For example, the third heat transfer region c624 may be preceded by the second heat transfer region c622.

[0246] During operation, heating fluid such as combustion gas flowing through the plurality of heating fluid pathways c602 may transfer heat to any one or more of the plurality of heat transfer regions c612. The rate or quantity of heat transferring from the heating fluid to a heat transfer region c612 may vary as between respective ones of the heat transfer pathways c602 and/or as between respective ones of the heat transfer regions c612. For example, the rate or quantity of heat transferring from the heating fluid to a heat transfer region c612 may depend at least in part on a temperature gradient between the heating fluid and the heat transfer region, such as a temperature gradient between the heating fluid and the engine-working fluid. In some embodiments, however, the heating fluid within the plurality of heating fluid pathways c602 may exhibit a temperature that differs as between at least two portion c614 (e.g., at least two semiannular portion) corresponding to respective heat transfer regions c612 and/or as between at least two heating fluid pathways c602 within a given portion c614 (e.g., within a semiannular portion) corresponding to a given heat transfer regions c612. Additionally, or in the alternative, the plurality of heat transfer regions c612 may exhibit a temperature that differs as between at least two heat transfer regions c612. For example, the engine-working fluid within the plurality of working-fluid pathways cl 10 corresponding to respective ones of the heat transfer regions c612 may exhibit a temperature that differ as between at least two heat transfer regions c612 and/or as between at least two working-fluid pathways cl 10 within a given heat transfer region c612.

[0247] In some embodiments, the temperature of a heating fluid such as a combustion gas may decrease as the heating fluid flows through the plurality of heating fluid pathways c602 and heat transfers from the heating fluid to the heat transfer regions c612 of the working-fluid body cl 08, such as from the heating fluid to engine-working fluid in the working-fluid pathways cl 10. However, with the plurality of heating fluid pathways c602 defining a spiral pathway, as shown for example in FIGs. 4.4.1 A through 4.4.2B, respective ones of the plurality of heating fluid pathways c602 may encounter the respective ones of the plurality of heat transfer regions c612 in a differing sequence, which may depend at least in part on a circumferential location of an inlet c606 to the respective one of the plurality of heating fluid pathways c602.

[0248] For example, a first heating fluid pathway c618 may initially encounter the first heat transfer region c620, such as according to a first circumferential series, while a second heating fluid pathway c628 may encounter the first heat transfer region c620 last, such as according to a second circumferential series. Additionally, or in the alternative, a third heating fluid pathway c630 may encounter the first heat transfer region c620 third in series, such as according to a third circumferential series, and/or a fourth heating fluid pathway c632 may encounter the first heat transfer region c620 second in series, such as according to a fourth circumferential series.

[0249] As another example, the second heat transfer region c622 may have a thermally conductive relationship with the first heating fluid pathway c618 occurring second, such as according to the first circumferential series. The second heat transfer region c622 may have a thermally conductive relationship with the second heating fluid pathway c628 occurring first, such as according to the second circumferential series. The second heat transfer region c622 may have a thermally conductive relationship with the third heating fluid pathway c630 occurring last, such as according to the third circumferential series. The second heat transfer region c622 may have a thermally conductive relationship with the fourth heating fluid pathway c632 occurring third, such as according to the third

circumferential series.

[0250] In some embodiments, a heat transfer region c622 may include a piston body c700 and/or a regenerator body c800, and/or a plurality of working-fluid pathways cl 10 fluidly communicating between the piston body c700 and/or the regenerator body c800.

When a closed-cycle engine c002 includes a plurality of piston bodies, the piston assemblies may have a staggered or offset stroke cycle, such that a first piston and a second piston may be located at different points in respective stroke cycles upon least one point of the stroke cycle. For example, the first piston may be at a top point of the stroke cycle and the second piston may be at a bottom point of the stroke cycle. As another example, the first piston may be at a midpoint of the stroke cycle and the second piston may be at the top point or the bottom point of the stroke cycle. In some embodiments, engine-working fluid flowing from a piston body c700 (e.g., from a piston chamber cl 12) to a regenerator body c800 may exhibit a temperature that differs from engine-working fluid flowing in the opposite direction, from the regenerator body c800 to the piston body c700 (e.g., to the piston chamber cl 12).

[0251] The engine-working fluid flowing through the working-fluid pathways cl 10 may exhibit a temperature that depends at least in part on whether the engine-working fluid is flowing towards the regenerator body c800 (e.g., from the piston body c700) or towards the piston body c700 (e.g., from the regenerator body c800). For example, the temperature of the engine-working fluid may exhibit a first temperature when flowing towards the regenerator body c800 (e.g., from the piston body c700) and a second temperature when flowing towards the piston body c700 (e.g., from the regenerator body c800). In some embodiments the first temperature may be greater than the second temperature.

[0252] In some embodiments, the heating fluid such as combustion gas and the engine-working fluid may exhibit a temperature gradient that depends at least in part on whether the engine-working fluid is flowing towards the regenerator body c800 (e.g., from the piston body c700) or towards the piston body c700 (e.g., from the regenerator body c800). For example, a first temperature gradient may correspond to engine-working fluid flowing towards the regenerator body c800 (e.g., from the piston body c700) and a second

temperature gradient may correspond to engine-working fluid flowing towards the piston body c700 (e.g., from the regenerator body c800). In some embodiments the first

temperature gradient may be smaller than the second temperature gradient. In some embodiments the second temperature gradient may be greater than the first temperature gradient. For example, the first temperature gradient may be smaller than the second temperature gradient at least in part because of the temperature of the engine-working fluid flowing towards the regenerator body c800 (e.g., from the piston body c700) being greater than the temperature of engine-working fluid flowing towards the piston body c700 (e.g., from the regenerator body c800).

[0253] In some embodiments, the rate and/or quantity of heat transfer from the heating fluid to the engine-working fluid may depend on whether the engine-working fluid is flowing towards the regenerator body c800 (e.g., from the piston body c700) or towards the piston body c700 (e.g., from the regenerator body c800). For example, a first rate and/or quantity of heat transfer from the heating fluid to the engine-working fluid may correspond to engine-working fluid flowing towards the regenerator body c800 (e.g., from the piston body c700) and a second rate and/or quantity of heat transfer from the heating fluid to the engine working fluid may correspond to engine-working fluid flowing towards the piston body c700 (e.g., from the regenerator body c800). In some embodiments the first rate and/or quantity of heat transfer may be smaller than the second rate and/or quantity of heat transfer. In other words, the second rate and/or quantity of heat transfer may be greater than the first rate and/or quantity of heat transfer. For example, the first rate and/or quantity of heat transfer may be smaller than the second rate and/or quantity of heat transfer at least in part because of the first temperature gradient corresponding to engine-working fluid flowing towards the regenerator body c800 (e.g., from the piston body c700) being smaller than the second temperature gradient corresponding to engine-working fluid flowing towards the piston body c700 (e.g., from the regenerator body c800).

[0254] In some embodiments, the heating efficiency of the heater body cl 00 may be enhanced at least in part by the second rate and/or quantity of heat transfer corresponding to engine-working fluid flowing towards the piston body c700 (e.g., from the regenerator body c800) being greater than the first rate and/or quantity of heat transfer corresponding to engine-working fluid flowing towards the regenerator body c800 (e.g., from the piston body c700). For example, in this way, a relatively larger proportion of the heat input by the heater body cl 00 may be applied to the engine-working fluid as the engine-working fluid flows towards the piston body c700 and thereby drives the piston downward, performing the downstroke portion of a stroke cycle. The heat input to the engine-working fluid during the downstroke may contribute to the downstroke (e.g., directly) by further heating and thereby further expanding the engine-working fluid. During the upstroke portion of the stroke cycle, a relatively smaller proportion of the heat input by the heater body cl 00 may be applied to the engine-working fluid, which may reduce or mitigate a potential for heat input to the engine-working fluid to counteract the upstroke by further heating and thereby expanding the engine-working fluid, providing an additional or alternative efficiency enhancement. With a relatively smaller proportion of the heat input by the heater body cl 00 applied to the engine working fluid during the upstroke, a smaller portion of the heat input may be transferred to the regenerator body c800. While the regenerator body c800 may be configured to retain heat, at least some heat transferring to the regenerator body c800 may be lost. By transferring a larger proportion of the heat input of the heater body cl 00 to the engine-working fluid when flowing towards the piston body c700 (e.g., from the regenerator body c800), less heat energy may be lost to the regenerator body c800, thereby providing yet another additional or alternative efficiency enhancement.

[0255] In some embodiments, at least a portion of the heater body clOO (e.g., the hot- side heat exchanger body c600 and/or the working-fluid body cl08) may be configured such that the temperature gradient between the temperature gradient between the heating fluid and the engine-working fluid is relatively small when the engine-working fluid is flowing towards the regenerator body c800. For example, the temperature gradient between the heating fluid and the engine-working fluid may be minimal when the engine-working fluid is flowing towards the regenerator body c800. With a relatively small and/or minimal temperature gradient, the rate and/or quantity of heat transfer to the engine-working fluid when flowing towards the regenerator body c800 may be minimal or nominal. Additionally, or in the alternative, at least a portion of the heater body clOO (e.g., the hot-side heat exchanger body c600 and/or the working-fluid body cl 08) may be configured such that the temperature gradient between the temperature gradient between the heating fluid and the engine-working fluid is relatively large when the engine-working fluid is flowing towards the piston body c700. For example, the temperature gradient between the heating fluid and the engine working fluid may be maximal when the engine-working fluid is flowing towards the piston body c700. With a relatively large and/or maximal temperature gradient, the rate and/or quantity of heat transfer to the engine-working fluid when flowing towards the regenerator body c800 may be maximized.

[0256] In some embodiments, the rate and/or quantity of heat transferred from the heating fluid to the engine-working fluid may exhibit a ratio of heat transfer when flowing towards the piston body c700 to heat transfer when flowing towards the regenerator body c800 of from about 1 : 1 to about 100:1, such as from about 2: 1 to about 100: 1, such as from about 2: 1 to about 10: 1, such as from about 10: 1 to about 20: 1, such as from about 20: 1 to about 50: 1, or such as from about 50:1 to about 100: 1. The ratio may be at least 1 : 1, such as at least 2: 1, such as at least 10: 1, such as at least 20: 1, such as at least 50: 1, or such as at least 90: 1. The ratio may be less than 100:1, such as less than 90: 1, such as less than 50: 1, such as less than 20: 1, such as less than 10: 1, or such as less than 2: 1.

[0257] As the heating fluid flows through the plurality of heating fluid pathways c602, heat may preferentially transfer to heat transfer regions c612 where the temperature gradient is larger or largest, thereby preferentially providing heat to the heat transfer regions where heat is needed more or most, for example, in favor of other heat transfer regions c612 with a lower or lowest temperature gradient. In some embodiments, heat may preferentially transfer to heat transfer regions (e.g., to engine-working fluid flowing through working-fluid pathways cl 10 therein) corresponding to a piston during a downstroke portion of the stroke cycle relative to heat transfer regions corresponding to a piston during an upstroke portion of the stoke cycle. Such preferential heat transfer may be accomplished at least in part by providing a relatively greater temperature gradient during the downstroke portion of the stroke cycle as described. With the plurality of heating fluid pathways c602 defining a spiral pathway, as shown for example in FIGs. 4.4.1 A through 4.4.2B, the plurality of heating fluid pathways c602 may encounter all or a portion of the heat transfer regions c612, thereby allowing for preferential heat transfer to the heat transfer regions c612 where the temperature gradient is larger or largest.

[0258] In some embodiments, a hot-side heat exchanger body c600 may include a combustion chamber cl02 disposed annularly about an axis c204. A hot-side heat exchanger body c600 may additionally include a conditioning conduit cl 22 circumferentially surrounding the combustion chamber cl02. The conditioning conduit cl22 may fluidly communicate with the combustion chamber cl 02 at a distal portion c202 of the combustion chamber cl 02.

[0259] In some embodiments, as shown for example in FIGs. 4.4.2A and 4.4.2B, and

4.4.3 A and 4.4.3B, a hot-side heat exchanger body c600 may include a plurality of combustion fins c450 circumferentially spaced about the perimeter of the combustion chamber cl02 (and/or disposed radially about the perimeter of the combustion chamber cl02). The plurality of combustion fins c450 may occupy a radially or concentrically inward portion of the hot-side heat exchanger body c600. In some embodiments, a portion of the hot-side heat exchanger body c600 may define a second combustion chamber c448. The second combustion chamber c448 may include a plurality of combustion fins c450 circumferentially spaced about the perimeter of the combustion chamber cl02 (and/or disposed radially about the perimeter of the combustion chamber cl02). The plurality of combustion fins c450 may define at least a portion of the plurality of heating fluid pathways c602. Additionally, or in the alternative, the plurality of combustion fins c450 may define a plurality of combustion-gas pathways c422 fluidly communicating upstream with the combustion chamber cl 02 and downstream with a corresponding plurality of heating fluid pathways c602. Such combustion-gas pathways c422 may concurrently define at least a portion of the second combustion chamber c448 and at least a portion of the plurality of heating fluid pathways c602. The second combustion chamber c448 may allow combustion to take place at an air-to-fuel ratio closer to the stoichiometric air-to-fuel ratio.

[0260] The plurality of combustion fins c450 may be monolithically integrated with corresponding ones of a plurality of heating walls c616 that respectively define the plurality of heating fluid pathways c602. Additionally, or in the alternative, the combustion fins c450 and the heating walls c616 may be spaced apart from one another, such as with a gap or pathway between an upstream end of the heating walls c602 and a downstream end of the combustion fins c450. The portion of a heating fluid pathways c602 defined by the combustion fins c450 may be referred to as combustion-gas pathways c422. The

combustion-gas pathways c422 may at least partially occupy the region of the hot-side heat exchanger cl06 where combustion is configured to occur. Combustion may occur in the combustion-gas pathways c42 at least in part by the combustion fins c450 being heated to a sufficiently high temperature during operation to prevent flame quenching.

[0261] The plurality of heating fluid pathways c602 may fluidly communicate with the outlet plenum c608 at a corresponding plurality of circumferential locations about the hot- side heat exchanger body c600. By way of example, a first heating fluid pathway c618 may fluidly communicate with an outlet plenum c608 at a first circumferential location c634 about a circumferential axis of the hot-side heat exchanger cl06. The first circumferential location c634 may be from about 0 to 30 degrees about the circumferential axis , such as from about 0 to 15 degrees on the circumferential axis. A second heating fluid pathway c628 may fluidly communicate with an outlet plenum c608 at a second circumferential location c636 about the circumferential axis. The second circumferential location c636 may be from about 90 to 120 degrees about the circumferential axis, such as from about 90 to 105 degrees about the circumferential axis. A third heating fluid pathway c630 may fluidly communicate with an outlet plenum c608 at a third circumferential location c638 about the circumferential axis.

The third circumferential location c638 may be from about 180 to 210 degrees about the circumferential axis, such as from about 180 to 195 degrees about the circumferential axis c205. A fourth heating fluid pathway c632 may fluidly communicate with an outlet plenum c608 at a fourth circumferential location c640 about the circumferential axis c205. The fourth circumferential location c640 may be from about 270 to 300 degrees about the circumferential axis c205, such as from about 270 to 285 degrees about the circumferential axis c205.

[0262] A hot-side heat exchanger body c600 and/or a working-fluid body cl08 may define any number of heat transfer regions c612. For example, heat exchanger body c600 and/or a working-fluid body cl08 may define from 1 to 10 heat transfer regions c612, such as from 2 to 8 heat transfer regions c612, such as from 3 to 5 heat transfer regions. A plurality of heat transfer regions c612 may be circumferentially spaced about the hot-side heat exchanger body, such as at respective circumferential regions about the circumferential axis c205. As shown, four heat transfer regions c612 may be circumferentially spaced about the hot-side heat exchanger body c600. By way of example, a first heat transfer region c620 may be disposed about a first circumferential segment or sector about the circumferential axis c205 of the hot-side heat exchanger cl06. The first circumferential segment or sector may be from about 270 to about 360 degrees about the circumferential axis c205 . A second heat transfer region c622 may be disposed about a second circumferential segment or sector about the circumferential axis c205. The second circumferential segment or sector may be from about 180 to about 270 degrees about the circumferential axis c205. A third heat transfer region c624 may be disposed about a third circumferential segment or sector about the circumferential axis c205. The third heat transfer region c624 may be from about 90 to about 180 degrees about the circumferential axis c205. A fourth heat transfer region c626 may be disposed about a fourth circumferential segment or sector about the circumferential axis c205. The fourth circumferential segment or sector may be from about 0 to about 90 degrees about the circumferential axis c205.

[0263] A hot-side heat exchanger body c600 and/or a hot-side heat exchanger cl06 may include any number of heating fluid pathways c602. For example, a hot-side heat exchanger body c600 and/or a hot-side heat exchanger cl 06 may include from 1 to 96 heating fluid pathways c602, such as from 1 to 48 heating fluid pathways c602, such as from 4 to 32 heating fluid pathways c602, such as from 8 to 24 heating fluid pathways c602, such as from 12 to 20 heating fluid pathways c602, such as from 4 to 16 heating fluid pathways c602, such as from 4 to 8 heating fluid pathways c602, such as at least 4, at least 8, at least 16, or at least 32 heating fluid pathways c602.

[0264] In some embodiments, at least some of the plurality of heating fluid pathways c602 may have a substantially uniform cross-sectional width and/or a substantially uniform cross-sectional area. The substantially uniform cross-sectional width and/or a substantially uniform cross-sectional area of a heating fluid pathway c602 may be present along at least a portion of a length of the heating fluid pathway c602.

[0265] At least some of the heating fluid pathways c602 may define a spiral pathway spiraling annularly or semi-annularly around a longitudinal axis A 214. A spiral pathway may follow a spiral arc having any desired curvature. The spiral arc may continue along all or a portion of the spiral pathway defined by the heating fluid pathway c602. By way of example, a spiral and/or a spiral arc, such as in a spiral pathway, may correspond to at least a portion of an Archimedean spiral, a Cornu spiral, a Fermat’s spiral, a hyperbolic spiral, a logarithmic spiral, a Fibonacchi spiral, an involute, or a squircular spiral, as well as combinations of these. As shown, in some embodiments the plurality of heating fluid pathways c602 may define a squircular spiral. At least a portion of a squircular spiral may include an arc corresponding to a squircle. The plurality of heating fluid pathways c602 may have an arc length of from 180 degrees to 1260 degrees, such as from 180 degrees to 450 degrees, such as from 315 degrees to 765 degrees, such as from 675 degrees to 1260 degrees.

[0266] In some embodiments, the plurality of heating fluid pathways c602 may include radially or concentrically adjacent pathways. Additionally, or in the alternative, the plurality of heating fluid pathways c602 may include one or more inverse pairs. For example, an inverse pair may include a pair of heating fluid pathways c602 fluidly communicating with the inlet plenum c604 (e.g., the combustion chamber cl02) at opposite sides thereof. Additionally, or in the alternative, an inverse pair may include a pair of heating fluid pathways c602 fluidly communicating with the outlet plenum c608 (e.g., the

recirculation annulus c208) at opposite sides thereof. By way of example, a first heating fluid pathway c618 and a third heating fluid pathway c630 may define an inverse pair. As another example, a second heating fluid pathway c628 and a fourth heating fluid pathway c632 may define an inverse pair. The inverse pair may follow a spiral arc having any desired curvature, such as a spiral arc inverse pair. For example, the heating fluid pathways c602 may define a plurality of spiral arc inverse pairs. In some embodiments, an inverse pair may include a parabolic spiral. [0267] Now referring to FIG. 4.4.3A and 4.4.3B, further exemplary embodiments of a hot-side heat exchanger body c600 will be described. As shown, in some embodiments, a hot-side heat exchanger body c600 may have a plurality of heating walls c616 and/or combustion fins c450 that respectively include a plurality of conduction breaks c605. The conduction breaks c605 may be disposed radially or concentrically outward relative to the plurality of combustion fins c450, and/or radially or concentrically inward relative to the plurality of heating walls c616. The conduction breaks c605 may at least partially inhibit heat conduction from the plurality of combustion fins c450 to the plurality of heating walls c616. The conduction breaks c605 may impart a decrease in thermal conductivity relative to the thermal conductivity of the plurality of heating walls c616 and/or the plurality of combustion fins c450. The plurality of heating walls c616 may be configured an arranged in a spiral array or spiral arc, such as an annular or semiannular spiral array or spiral arc.

Additionally, or in the alternative, the plurality of combustion fins c450 may be configured an arranged in a spiral array or spiral arc, such as an annular or semiannular spiral array or spiral arc. A combustion fins c450 and a corresponding heating wall c616 may follow a common trajectory. Additionally, or in the alternative, one or more combustion fins c450 may be staggered or offset from one or more heating walls c616. The condition breaks c605 may be configured to reduce heat conduction along the plurality of heating walls c616, such as along a radial axis or a circumferential axis. For example, the conduction breaks c450 may reduce heat conduction from a downstream portion of the combustion fins c450 to an upstream portion of the heating walls c616, and/or from an upstream portion of the plurality of heating walls c616 to a downstream portion of the plurality of heating walls c616. During operation, the combustion fins c450 may operate at a relatively higher temperature at least in part because of the reduced heat conduction attributable to the conduction breaks.

[0268] In some embodiments, a portion of the heating wall c616 upstream from a conduction break c605 may define a combustion fin c450. Additionally, or in the alternative, at least a portion of the heating wall c616 downstream from a conduction break c605 may define a heat transfer fin c607. The plurality of heating walls c616 may be formed of one or more materials, and/or may exhibit one or more material properties and/or structures. For example, the heat transfer fins c607 and the combustion fins c450 may differ from one another in respect of material composition, material properties, and/or material structure. In some embodiments, the heat transfer fins c607 may exhibit a greater thermal conductivity relative to the combustion fins c450. Additionally, or in the alternative, the combustion fins c450 may exhibit a greater heat capacity relative to the heat transfer fins c607. A desired thermal conductivity and/or heat capacity may be imparted to the combustion fins c450 and/or the heat transfer fins c607 at least in part by augmenting the material properties and/or structure during additive manufacturing. For example, the density and/or porosity may be augmented by modifying additive manufacturing parameters to impart desired

thermodynamic properties, such as heat capacity properties and/or thermal conductivity properties. Density and/or porosity may be augmented by modifying the degree of consolidation of powder material, and/or by providing regions of unsintered or partially sintered regions of powder material. Additionally, or in the alternative, material structure may be augmented to impart desired thermodynamic properties. For example, a lattice structure, a porous medium, a cellular structure, or the like may be provided to impart desired heat capacity properties and/or thermal conductivity properties to the combustion fins c450 and/or the heat transfer fins c607.

[0269] The plurality of condition breaks c605 may be disposed circumferentially adjacent to one another at the respective ones of the plurality of heating walls c616. The location of the conduction breaks c605 at the respective heating walls c616 may define a circumferential array of conduction breaks c605. A plurality of combustion fins c450 may occupy a radially or concentrically inward position of the hot-side heat exchanger body c600 relative to the circumferential array of conduction breaks c605. At least a portion of the plurality of heating walls c616 may define a corresponding plurality of heat transfer fins c607. The heat transfer fins c616 may occupy a radially or concentrically outward position of the hot-side heat exchanger body c600 relative to the circumferential array of conduction breaks c605. For example, the radially or concentrically outward portion of the heating walls c616 may define the heat transfer fins c607.

[0270] The plurality of combustion fins c450 may define a corresponding plurality of combustion-gas pathways c422. The plurality of combustion fins c450 and/or the plurality of combustion-gas pathways c422 may be configured an arranged in a spiral array, such as a semiannular spiral array. The plurality of combustion fins c450 may spiral concentrically outward from a combustion chamber outlet c412 towards the corresponding conduction break c605. The plurality of combustion fins c450 may be arranged in an array of annular or semiannular substantially concentric spirals and/or substantially concentric spiral arcs relative to the longitudinal axis c204. The circumferential array of conduction breaks c605 may define a radially or concentrically outward perimeter of the plurality of combustion fins c450. [0271] The plurality of heat transfer fins c607 may define a corresponding plurality of heating fluid pathways c602. The plurality of heat transfer fins c607 and/or the plurality of heating fluid pathways c602 may be configured an arranged in a spiral array, such as an annular or semiannular spiral array. The plurality of heat transfer fins c607 may spiral concentrically outward from the corresponding conduction breaks, transecting respective ones of the plurality of heat transfer regions c612. The circumferential array of conduction breaks c605 may define a radially or concentrically inward perimeter of the plurality of heating walls c616. Additionally, or alternatively, the circumferential array of conduction breaks c605 may define a radially or concentrically inward perimeter of the plurality of heat transfer regions c612. For example, the plurality of working-fluid bodies cl08 and/or the plurality of working-fluid pathways cl 10 may occupy a region of the hot-side heat exchanger body c600 disposed radially or concentrically outward from the circumferential array of conduction breaks c605. Additionally, or in the alternative, the portion of the heat transfer fins c607 and/or the heating walls c616 that include working-fluid pathways cl 10

monolithically defined therein may occupy a region of the hot-side heat exchanger body c600 disposed radially or concentrically outward from the circumferential array of conduction breaks c605.

[0272] The plurality of heat transfer regions c612 may respectively include an array of working-fluid pathways cl 10, such as a plurality of arrays of working fluid pathways cl 10. The array of working fluid pathways cl 10 may be monolithically defined within respective ones of the plurality of heating walls c616 (e.g., within respective ones of the plurality of heat transfer fins c607). The circumferential array of conduction breaks c605 may define a radially or concentrically inward perimeter of the plurality of working-fluid pathways cl 10. Respective ones of the plurality of arrays of working-fluid pathways cl 10 may be disposed circumferentially adjacent to one another about the hot-side heat exchanger body c600. Respective ones of the plurality of arrays of working-fluid pathways cl 10 may define at least a portion of a working-fluid body cl 08. A plurality of working-fluid bodies cl08 may be disposed circumferentially adjacent to one another about the hot-side heat exchanger body c600. The circumferential array of conduction breaks c605 may define a radially or concentrically inward perimeter of the plurality of working-fluid bodies cl 08.

[0273] In some embodiments, at least a portion of fuel combustion may take place within the plurality of combustion-gas pathways c422. Combustion that takes place within the combustion-gas pathways c422 may be attributable at least in part to the reduced heat conduction along the heating walls c616 provided by the conduction breaks c605. In some embodiments, the conduction breaks c605 may prevent or reduce a possibility that combustion may quenching prematurely. During operation, the combustion fins c450 may reach a sufficiently high temperature for stable combustion to take place within the plurality of combustion-gas pathways c422 without being prematurely quenched, such as by conductive heat transfer along the heating walls c616 and into the working-fluid bodies cl08. The reduction in heat conduction provided by the conduction breaks c605 may reduce the potential that heat transfer to the working fluid-pathways c610 may decrease the temperature of the heating walls c616 to a level that prematurely quenches combustion.

[0274] The conduction breaks c605 may allow the combustion fins to remain at a sufficiently high temperature to allow fuel combustion to approach complete combustion within the plurality of combustion-gas pathways c422. The circumferential array of conduction breaks c605 may be located at a distance along the combustion-gas pathways c422 selected to allow sufficient time for complete combustion upon the combustion gas having encountered the conduction breaks c605. In this way, the conduction breaks may provide for reduced emissions attributable to complete combustion and a corresponding reduction of unbumt combustion products in exhaust gas. The plurality of heat transfer regions c612 and/or the arrays of working-fluid pathways cl 10 may be located substantially immediately downstream from the circumferential array of conduction breaks c605, thereby allowing the hot combustion gas to begin heating the working fluid in the working-fluid pathways substantially immediately upon complete combustion.

[0275] As used herein, the term“complete combustion” refers to a state of fuel combustion that yields carbon dioxide and water as the combustion products with an absence of hydrocarbons. Complete combustion may yield carbon monoxide as a combustion product on the order of parts-per-million, such as single-digit parts-per-million (ppm). For example, with complete combustion, carbon monoxide may be present as a combustion product in an amount of less than 10 ppm, such as less than 5 ppm, or such as less than 1 ppm. In some embodiments, complete combustion may be qualitatively characterized by a blue flame, whereas incomplete combustion may be qualitatively characterized by an orange flame.

[0276] In some embodiments, a heater body cl 00 may be configured to burn fuel in a lean combustion environment. As mentioned, a lean combustion environment may be characterized by an equivalence ratio (i.e., the ratio of the actual fuel-to-air ratio to the stoichiometric fuel-to-air ratio), such as an equivalence ratio of from about 0.5 to about 1.0, such as from about 0.6 to about 0.9, or from about 0.7 to about 0.8. A lean combustion environment may generate a relatively longer flame length, which may otherwise point to a relatively larger combustion zone as an approach for reducing the potential for premature quenching and/or to allow for complete combustion.

[0277] In some embodiments, a heater body cl 00 configured to allow combustion to take place within the combustion-gas pathways c422 not only allows for complete combustion; but additionally, or in the alternative, a heater body cl 00 configured to allow fuel combustion within the plurality of combustion-gas pathways c422 may allow a heater body cl 00 to be operated at a higher equivalence ratio, thereby improving fuel efficiency and/or heating efficiency, while reducing emissions. Additionally, or in the alternative, the heater body cl 00 may be configured with a relatively smaller combustion chamber cl 02, thereby reducing material costs and weight.

[0278] In some embodiments, a combustion zone may occupy a position that includes the combustion-gas pathways c422. For example, the combustion-gas pathways c422 may define at least a portion of a second combustion zone c407 as described herein. The circumferential array of conduction breaks c605 may define a radially or concentrically outward perimeter of the second combustion zone c407. In some embodiments, the array of conduction breaks c605 may define an array of burner gaps c421. Such burner gaps may be configured as described herein. Additionally, or in the alternative, a hot-side heat exchanger body c600 may include both an array of conduction breaks c605 and an array of burner gaps c421.

[0279] The combustion fins c450 may be spatially separated from the heating walls c616 (e.g., the heat transfer fins c607), such that a conduction break c605 may include a physical gap or space defined by the spatial separation between a combustion fin c450 and heating wall c616 (e.g., a heat transfer fin c607). Additionally, or in the alternative, a conduction break c605 may include a change in a material property, a change in material composition, and/or a change in structure relative to the combustion fin c450 and/or the heat transfer fin c607 that provides a reduction in heat conduction relative to the combustion fin c450 and/or the heat transfer fin c607. For example, a conduction break c605 may include a structure such as a mesh, a three-dimensional lattice, a porous medium, or unsintered or partially sintered powder material, as well as combinations of these.

[0280] As shown in FIG. 4.4.3B, The plurality of heating walls c616 and/or combustion fins c450 may have a plurality of openings c451 (e.g., pore-like openings) that fluidly communicate with the plurality of combustion-gas pathways c422 of the hot-side heat exchanger cl 06 and define the hot-zone fuel injectors c413. In some embodiments, at least a portion of the hot-zone fuel pathways c415 may define a vaporization heat exchanger c417 that provides a heat transfer relationship between a combustion flame c426 and fuel within the hot-zone fuel pathways c415, and or between hot combustion gas c426 fuel within the hot-zone fuel pathways c415. The vaporization heat exchanger c417 may be effective to vaporize fuel (e.g., liquid fuel), such as when the fuel is within the hot-zone fuel pathways c415 and/or the hot-zone fuel injectors c413, or as the fuel is discharged from the openings (e.g., the pore-like openings) of the hot-zone fuel injectors c413.

[0281] Now referring to FIG. 4.4.4, exemplary methods of heating a plurality of heat transfer regions will be described. The exemplary methods of heating a plurality of heat transfer regions may include, for example, methods of heating one or more working-fluid bodies cl 08. For example, exemplary methods may be performed in connection with operation of a hot-side heat exchanger body c600, a working-fluid body cl 08, a heater body clOO, and/or a closed-cycle engine c002 as described herein. As shown in FIG. 4.4.4, an exemplary method c650 may include, at block c652, flowing a first heat transfer fluid through a plurality of heating fluid pathways c602 fluidly communicating with an inlet plenum c604. Respective ones of the plurality of heating fluid pathways c602 may define a spiral pathway. The exemplary method c650 may include, at block c654, transferring heat from the first heat transfer fluid to a plurality of heat transfer regions c612. Respective ones of the plurality of heat transfer regions c612 may have a heat transfer relationship with a corresponding semiannular portion of the plurality of heating fluid pathways c602.

[0282] In some embodiments, transferring heat from the first heat transfer fluid to the plurality of heat transfer regions, at block 654, may include transferring heat from the plurality of heating fluid pathways c602 to at least some of the plurality of heat transfer regions c612 in circumferential series. The circumferential series of a respective one of the plurality of heating fluid pathways c612 may have a sequence depending at least in part on a circumferential location of an inlet c606 to the respective one of the plurality of heating fluid pathways c602.

[0283] Now referring to FIGs. 4.5.2 and 4.5.3, exemplary working-fluid bodies cl08 will be described. The presently disclosed working-fluid bodies cl08 may define part of a heater body clOO and/or a closed-cycle engine c002. For example, a working-fluid body cl 08 may define at least a portion of a monolithic body or a monolithic body-segment. Such monolithic body or monolithic body-segment may define at least a portion of the heater body clOO and/or the closed-cycle engine c002. Additionally, or in the alternative, the presently disclosed working-fluid bodies cl08 may be provided as a separate component, whether for use in connection with a heater body cl 00, a closed-cycle engine c002, or any other setting whether related or unrelated to a heater body clOO or a closed-cycle engine c002. At least a portion of the working-fluid bodies cl08 may define a one or more piston bodies c700, one or more regenerator bodies c800, and/or one or more working-fluid pathway cl 10. It will be appreciated that a heater body clOO may include any desired number of working-fluid bodies cl08, including any desired number of piston bodies c700, regenerator bodies c800, and/or working-fluid pathways cl 10. For example, a heater body clOO may include one or more working-fluid bodies cl 08, and/or a working-fluid body cl 08 may include one or more piston bodies c700, regenerator bodies c800, and/or working-fluid pathways cl 10.

[0284] A working-fluid body cl 08 may define a first portion of a monolithic body and the piston body c700 may defines a second portion of the monolithic body.

Alternatively, the piston body c700 may define a monolithic body-segment operably coupled or operably couplable to the working-fluid body cl 08. Additionally, or in the alternative, a regenerator body c800 may a second portion of the monolithic body, or the regenerator body c800 may define a second monolithic body-segment operably coupled or operably couplable to the piston body 700 and/or the working-fluid body cl08.

[0285] As shown, an exemplary working-fluid body cl08 may include a plurality of heat transfer regions c612. Respective ones of the plurality of heat transfer regions may include a plurality of working-fluid pathways cl 10 fluidly communicating between a heat input region and a heat extraction region. The heat input region may include a piston body c700 and the heat extraction region may include a regenerator body c800.

[0286] At least some of the plurality of working-fluid pathways cl 10 may be radially or concentrically adjacent and/or axially adjacent to one another. In some embodiments, a heating fluid pathway c602 may be disposed between radially or concentrically adjacent and/or axially adjacent working-fluid pathways cl 10. Additionally, or in the alternative, at least some of the working-fluid pathways cl 10 may be semiannular to one another. For example, a working-fluid body cl 08 may include a plurality of radially or concentrically adjacent semiannular spiral pathways and/or a plurality of axially adjacent semiannular spiral pathways. [0287] The plurality of working-fluid pathways cl 10 may be disposed axially adjacent to corresponding respective ones of the plurality of heating fluid pathways c602, such as radially or concentrically adjacent spiral heating fluid pathways c602. Respective ones of the plurality of working-fluid pathways cl 10 may have a thermally conductive relationship with corresponding respective ones of the plurality of heating fluid pathways c602.

[0288] An exemplary working-fluid body cl08 may include a first heat transfer region c620, a second heat transfer region c622, a third heat transfer region c624, and/or a fourth heat transfer region c626. The first heat transfer region c620 may include a first plurality of working-fluid pathways c701. The first plurality of working-fluid pathways c701 may include semiannular radially or concentrically adjacent and/or axially adjacent spiral pathways. The second heat transfer region c622 may include a second plurality of working- fluid pathways c702. The second plurality of working-fluid pathways c702 may include semiannular radially or concentrically adjacent and/or axially adjacent spiral pathways. The third heat transfer region c624 may include a third plurality of working-fluid pathways c703. The third plurality of working-fluid pathways c703 may include semiannular radially or concentrically adjacent and/or axially adjacent spiral pathways. The fourth heat transfer region c626 may include a fourth plurality of working-fluid pathways c704. The fourth plurality of working-fluid pathways c704 may include semiannular radially or concentrically adjacent and/or axially adjacent spiral pathways.

[0289] The first heat transfer region c620 may be circumferentially adjacent to the second heat transfer region c622. The second heat transfer region c622 may be

circumferentially adjacent to the third heat transfer region c624. The third heat transfer region c624 may be circumferentially adjacent to the fourth heat transfer region c626. The fourth heat transfer region c626 may be circumferentially adjacent to the first heat transfer region c620.

[0290] The first plurality of working-fluid pathways c701 may be circumferentially adjacent to the second plurality of working-fluid pathways c702. The second plurality of working-fluid pathways c702 may be circumferentially adjacent to the third plurality of working-fluid pathways c703. The third plurality of working-fluid pathways c703 may be circumferentially adjacent to the fourth plurality of working-fluid pathways c704. The fourth plurality of working-fluid pathways c704 may be circumferentially adjacent to the first plurality of working-fluid pathways c701. [0291] In some embodiments, respective ones of the plurality of working-fluid pathways cl 10 may include circumferentially adjacent working-fluid pathways cl 10. The circumferentially adjacent working-fluid pathways may circumferentially initiate and/or circumferentially terminate a spiral array c706 of working-fluid pathways cl 10. The spiral array c706 may diverge radially or concentrically outward. The spiral array c706 may transition from radially or concentrically inward to radially or concentrically midward and/or from radially or concentrically midward to radially or concentrically outward, as the spiral array c706 passes from one heat transfer region to the next.

[0292] At least some of the working-fluid pathways cl 10 may define a spiral pathway spiraling annularly or semi-annularly around a longitudinal axis A 214. A spiral pathway may follow a spiral arc having any desired curvature. The spiral arc may continue along all or a portion of the spiral pathway defined by the working-fluid pathways cl 10. By way of example, the spiral or spiral arc may correspond to at least a portion of an Archimedean spiral, a Cornu spiral, a Fermat’s spiral, a hyperbolic spiral, a logarithmic spiral, a Fibonacchi spiral, an involute, or a squircular spiral, as well as combinations of these. As shown, in some embodiments the plurality of working-fluid pathways cl 10 may define a squircular spiral. At least a portion of a squircular spiral may include an arc corresponding to a squircle. The plurality of working-fluid pathways cl 10 may have an arc length of from 180 degrees to 1260 degrees, such as from 180 degrees to 450 degrees, such as from 315 degrees to 765 degrees, such as from 675 degrees to 1260 degrees.

[0293] In some embodiments, the plurality of working-fluid pathways cl 10 may include radially or concentrically adjacent pathways. Additionally, or in the alternative, the plurality of working-fluid pathways cl 10 may include one or more inverse pairs. For example, an inverse pair may include a pair of working-fluid pathways cl 10 respectively fluidly communicating with a corresponding heat extraction region (e.g., a regenerator body c800) at opposite sides of the working-fluid body cl 08. Additionally, or in the alternative, an inverse pair may include a pair of working-fluid pathways cl 10 respectively fluidly communicating with a corresponding heat input region (e.g., a piston body c700) at opposite sides of the working-fluid body cl 08. The inverse pair may follow a spiral arc having any desired curvature, such as a spiral arc inverse pair. For example, the heating fluid pathways c602 may define a plurality of spiral arc inverse pairs. In some embodiments, an inverse pair may include a parabolic spiral. [0294] Referring again to FIG. 4.5.2, a working-fluid body cl08 may include a plurality of working-fluid pathways cl 10 interleaved with a plurality of heating fluid pathways c602 of a hot-side heat exchanger body c600, such as to provide a thermally conductive relationship therebetween. Respective ones of the plurality of working-fluid pathways cl 10 may be disposed alternatingly adjacent to respective ones of the plurality of heating fluid pathways c602. In some embodiments, a portion of the working-fluid body cl08 defining at least some of the working-fluid pathways cl 10 may protrude into adjacent respective ones of the plurality of heating fluid pathways c602. Additionally, or in the alternative, at least a portion of the hot-side heat exchanger body c600 defining at least some of the heating fluid pathways c602 may protrude into adjacent respective ones of the plurality of working-fluid pathways cl 10. For example, a portion of the working-fluid body cl08 and/or a portion of the hot-side heat exchanger body c600 defining alternatingly adjacent working-fluid pathways cl 10 and heating fluid pathways c602 may protrude into such working-fluid pathways cl 10 and/or heating fluid pathways c602. The protruding portion of the working-fluid body cl08 and/or hot-side heat exchanger body c600 may protrude in any direction towards an adjacent working-fluid pathways cl 10 and/or heating fluid pathways c602. For example, the working-fluid body cl08 and/or hot-side heat exchanger body c600 may protrude radially or concentrically inward and/or radially or concentrically outward.

[0295] The protruding portions of the working-fluid body cl08 and/or a portion of the hot-side heat exchanger body c600 may define conduction-enhancing protuberances c728.

The conduction-enhancing protuberances c728 may enhance conduction between the heating fluid and the engine-working fluid, for example, by disrupting a boundary layer between the heating fluid and the heating fluid pathways c602 and/or by a disrupting boundary layer between the engine-working fluid and the working-fluid pathways cl 10. Respective ones of the plurality of conduction-enhancing protuberances c728 may be defined at least in part by a portion of the working-fluid body cl 08 corresponding to respective ones of a plurality of working-fluid pathways cl 10 protruding into adjacent respective ones of a plurality of heating fluid pathways c602. Additionally, or in the alternative, respective ones of the plurality of conduction-enhancing protuberances c728 may be defined at least in part by a portion of the hot-side heat exchanger body c600 corresponding to respective ones of a plurality of heating fluid pathways c602 protruding into adjacent respective ones of the plurality of working-fluid pathways cl 10. [0296] Exemplary conduction-enhancing protuberances may include any one or more of a combination of protuberant features having a variety of shapes and configurations, including nodules, loops, hooks, bumps, burls, clots, lumps, knobs, projections, protrusions, swells, enlargements, outgrowths, accretions, blisters, juts, and the like. These conduction attenuating protuberances c728 occur in an ordered, semi-ordered, random, or semi-random fashion. However, the particular configuration, arrangement, or orientation of the

conduction-enhancing protuberances c728 may be selectively controlled or modified by adjusting the configuration or arrangement of at least a portion of the working-fluid body cl08 and/or hot-side heat exchanger body c600, such as the configuration or arrangement of at least a portion of the working-fluid pathways cl 10 and/or heating fluid pathways c602.

[0297] Now referring to FIG. 4.5.3, another exemplary cross-sectional view of a working-fluid body cl08 will be described. As shown in FIG. 4.5.3, a plurality of piston bodies c700 and a plurality of regenerator bodies c800 may be circumferentially spaced about a longitudinal axis c204 of the working-fluid body cl08. The plurality of piston bodies c700 and regenerator bodies c800 may be paired with one another, for example, with a plurality of working-fluid pathways cl 10 fluidly communication between respective piston body c700 and regenerator body c800 pairs. For example, a first plurality of working-fluid pathways c701 may fluidly communicate between a first piston chamber cl 12 defined by a first piston body c700 and a first regenerator chamber c802 defined by a first regenerator body c800. A second plurality of working-fluid pathways c702 may fluidly communicate between a second piston chamber cl 12 defined by a second piston body c700 and a second regenerator chamber c802 defined by a second regenerator body c800. A third plurality of working-fluid pathways c703 may fluidly communicate between a third piston chamber cl 12 defined by a third piston body c700 and a third regenerator chamber c802 defined by a third regenerator body c800. A fourth plurality of working-fluid pathways c704 may fluidly communicate between a fourth piston chamber cl 12 defined by a fourth piston body c700 and a fourth regenerator chamber c802 defined by a fourth regenerator body c800.

[0298] A flow direction of engine-working fluid flowing through a plurality of working-fluid pathways cl 10 may be counter-current or co-current relative to a flow direction c732 of heating fluid flowing through the heating fluid pathways c602 adjacent to such working-fluid pathways cl 10. For example, as shown, engine-working fluid flowing from a piston chamber cl 12 towards a regenerator chamber c802 may be counter-current to the flow direction c732 of the heating fluid flowing through adjacent heating fluid pathways c602. Engine-working fluid flowing from a regenerator chamber c802 towards a piston chamber cl 12 may be co-current to the flow direction c732 of the heating fluid flowing through adjacent heating fluid pathways c602. Alternatively, in other embodiments, engine working fluid may be counter-current to the flow direction c732 of the heating fluid when flowing from a piston chamber cl 12 towards a regenerator chamber c802 and co-current when flowing from a regenerator chamber c802 towards a piston chamber cl 12.

[0299] In a general sense, heat transfer from a hot fluid to a cold fluid may be greater during counter-current flow relative to co-current flow. For example, with co-current flow, the temperature of the cold fluid may be always less than the temperature of the hot fluid, and as such, heat transfer may be restricted by the discharge temperature of the cold fluid.

Conversely, with counter-currently flow, heat transfer is not restricted by the discharge temperature of the cold fluid, which may allow for a greater quantity of heat transfer. On the other hand, with co-current flow, the temperature gradient between a hot fluid and a cold fluid may be greater at an initial zone of heat transfer prior to achieving thermal equilibrium, relative to the temperature gradient at an initial zone of heat transfer with counter-current flow. As such, faster heat transfer may be achieved during non-equilibrium conditions during co-current flow.

[0300] In some embodiments, it may be advantageous for heating fluid to flow co- currently relative to engine-working fluid when the engine-working fluid flows from the regenerator body c800 to the piston body c700. For example, the temperature gradient between the engine-working fluid and the heating fluid may be greater when the engine working fluid flows from the regenerator body c800 towards the piston body c700 relative to engine-working fluid flowing in the opposite direction. Such temperature gradient may be greater, for example, because of heat losses as heat transfers from the engine-working fluid to the regenerator body c800 and back to the engine-working fluid. With a greater temperature gradient existing when engine-working fluid flows from the regenerator body c800 towards the piston body c700, such temperature gradient may facilitate a more rapid heat transfer from the heating fluid to the engine-working fluid. In particular, such temperature gradient may facilitate a more rapid heat transfer to the engine-working fluid as the engine-working fluid flows into the piston body c800, thereby further expanding the engine-working fluid and contributing to the downstroke (e.g., directly) of the piston within the piston chamber.

Additionally, or in the alternative, with heating fluid flowing counter-current relative to engine-working fluid flowing from the piston body c700 to the regenerator body c800, the rate of heat transfer from the heating fluid to the engine-working fluid may be less than when the engine-working fluid flows in the opposite direction. As such, relatively less heat transfer may be imparted to the engine-working fluid when flowing into the regenerator body c800 the engine-working fluid flows from the regenerator body c800, further contributing to efficiency of the heater body cl 00, such as when inputting heat to the closed-cycle engine c002.

[0301] Any suitable engine-working fluid may be utilized in accordance with the present disclosure. In exemplary embodiments, the engine-working fluid may include a gas, such as an inert gas. For example, a noble gas, such as helium may be utilized as an engine working fluid. Exemplary engine-working fluids preferably are inert, such that they generally do not participate in chemical reactions such as oxidation within the environment of the working-fluid body cl 08. Exemplary noble gasses include monoatomic gases such as helium, neon, argon, krypton, or xenon, as well as combinations of these. In some embodiments, an engine-working fluid may include air, oxygen, nitrogen, or carbon dioxide, as well as combinations of these.

[0302] Now turning to FIGs. 4.5.5A-4.5.5D, exemplary thermal expansion joints cl 35 of a heater body cl 00 will be described. A heater body cl 00 may include one or more thermal expansion joints cl35 at any one or more desired locations of the heater body clOO.

A thermal expansion joint cl 35 may include an expansion gap cl 49 configured to allow for thermal expansion, and/or a difference in thermal expansion, as between respective sides of the thermal expansion joint cl35. In some embodiments, a thermal expansion joint cl 35 may include an expansion gap cl 49 that provides for a hairpin configuration, as shown, for example, in FIG. 4.5.5B. Such hairpin configuration may provide an extended thermal conduction pathway as between respective sides of the thermal expansion joint cl35. In some embodiments, the expansion gap cl 47 may include an insulating material cl 29, such as a radiative-heat shield radiative-heat shield cl29A (FIGs. 4.1.8A-4.1.8G), to provide an improved view factor and corresponding reduction in radiative heat transfer as between respective sides of the thermal expansion joint cl35.

[0303] As shown, in some embodiments, a heater body cl 00 may include one or more combustor-thermal expansion joints cl 35 A. A combustor-thermal expansion joint cl35A may allow for thermal expansion, and/or a difference in thermal expansion, as between at least a portion of a combustor body c400 and one or more adjacent regions of the heater body clOO. For example, a combustor-thermal expansion joint cl35A may allow for thermal expansion, and/or a difference in thermal expansion, as between a combustor body c400 and a hot-side heat exchanger body c600 (such as between a combustion chamber cl 02 and a hot-side heat exchanger cl 06). Additionally, or in the alternative, a combustor-thermal expansion joint cl35A may allow for thermal expansion, and/or a difference in thermal expansion, as between a combustor body c400 and a working-fluid body cl 08 (such as between a combustion chamber cl02 and an array of working-fluid pathways cl 10).

[0304] A combustor-thermal expansion joint cl35A may be oriented concentric with a combustion chamber cl02 and/or a longitudinal axis c204 of the heater body clOO, as shown, for example in FIGs. 4.5.5A, 4.5.5C and 4.5.5D. The combustor-thermal expansion joint cl35A may circumferentially surround at least a portion of the combustor body c400. For example, as shown in FIGs. 4.5.5A and 4.5.5B, an expansion gap cl49 may be disposed within at least a portion of a hot-side heater body c600. Additionally, or in the alternative, the combustor-thermal expansion joint cl35A may be at least partially axially offset from the combustion chamber cl 02, as shown. Such axial offset may be configured to provide an extended thermal conductive pathway as between the combustor body c400 and the hot-side heat exchanger body c600.

[0305] In some embodiments, a heater body clOO may include one or more heat transfer region-thermal expansion joints cl35B. A heat transfer region-thermal expansion joint cl35B may allow for thermal expansion, and/or a difference in thermal expansion, as between respective heat transfer regions c612 of a heater body clOO. For example, a heat transfer region-thermal expansion joint cl35B may allow for thermal expansion, and/or a difference in thermal expansion, as between a working-fluid body cl 08 and a regenerator body c800, and/or as between a piston body c700 and a regenerator body c800. As shown in FIGs. 4.5.5C and 4.5.5D, a heat transfer region-thermal expansion joint cl35B may be disposed between a regenerator body c800 of a first heat transfer region c620 and a working- fluid body cl 08 of a second heat transfer region c622 (and/or between a regenerator body c800 of a first heat transfer region c620 and a piston body c700 of a second heat transfer region c622).

[0306] Additionally, or in the alternative, a heat transfer region-thermal expansion joint cl35B may be disposed between a heat input region c601 of a working-fluid body cl08 and a heat extraction region c603 of a working fluid body cl 08, such as between a heat input region c601 of a first heat transfer region c620, and a heat extraction region c603 of a second heat transfer region c622. Such as heat input region c601 includes working-fluid pathways cl 10 on a side of the working-fluid body cl08 proximal to the piston body c700, such as including a portion of the working-fluid pathways cl 10 proximal to corresponding piston chamber apertures cl 11. Such a heat extraction region c603 includes working-fluid pathways cl 10 on a side of the working-fluid body proximal to the regenerator body c800, such as including a portion of the working-fluid pathways cl 10 proximal to corresponding regenerator apertures cl 13.

[0307] Now referring to FIG. 4.5.6 exemplary methods of heating an engine-working fluid will be described. The exemplary methods of heating an engine-working fluid may include, for example, methods of heating one or more working-fluid bodies cl08. For example, exemplary methods may be performed in connection with operation of a hot-side heat exchanger body c600, a working-fluid body cl08, a heater body clOO, and/or a closed- cycle engine c002 as described herein. As shown, an exemplary method c750 may include, at block c752 flowing an engine-working fluid across respective ones of a plurality of heat transfer regions c612. The plurality of heat transfer regions c612 may include a plurality of working-fluid pathways cl 10 fluidly communicating between a heat input region such as a piston body c700 and a heat extraction region such as a regenerator c800. The engine working fluid may flow through the plurality of working-fluid pathways cl 10, such as alternatingly between the heat input region such as the piston body c700 and the heat extraction region such as the regenerator c800. At block c754, the exemplary method may include transferring heat from a heating source to the engine-working fluid. The plurality of working-fluid pathways cl 10 may have a heat transfer relationship with the heating source. The heating source may be a heating fluid, such as combustion gas, which may be heated using a heater body clOO.

[0308] An exemplary method c750 may include alternatingly flowing the engine working fluid from the heat input region to the heat extraction region, and from the heat extraction region to the heat input region. For example, the method c750 may include alternatingly flowing through a first plurality of working-fluid pathways c701, a first portion of the engine-working fluid from the heat input region to the heat extraction region and from the heat extraction region to the heat input region. In some embodiments, the first portion of the engine-working fluid may alternatingly flow from the heat input region to a first heat extraction region and from the first heat extraction region to the heat input region.

Additionally, or in the alternative, the method c750 may include alternatingly flowing through a second plurality of working-fluid pathways c702, a second portion of the engine- working fluid from the heat input region to the heat extraction region and from the heat extraction region to the heat input region. In some embodiments, the second portion of the engine-working fluid may altematingly flow from the heat input region to a second heat extraction region and from the second heat extraction region to the heat input region. In another embodiment, the first portion of the engine-working fluid may altematingly flow between a first heat input region and a first heat extraction region and the second portion of the engine-working fluid may altematingly flow between a second heat input region to a second heat extraction region.

[0309] Control systems and methods of controlling various systems disclosed herein will now be provided. A control system generates control commands that are provided to one or more controllable devices of the system. The controllable devices execute control actions in accordance with the control commands. Accordingly, the desired output of the system can be achieved.

[0310] FIG. 5.1.28 provides an example computing system in accordance with an example embodiment of the present disclosure. The one or more controllers, computing devices, or other control devices described herein can include various components and perform various functions of the one or more computing devices of the computing system b2000 described below.

[0311] As shown in FIG. 5.1.28, the computing system b2000 can include one or more computing device(s) b2002. The computing device(s) b2002 can include one or more processor(s) b2004 and one or more memory device(s) b2006. The one or more processor(s) b2004 can include any suitable processing device, such as a microprocessor, microcontroller, integrated circuit, logic device, and/or other suitable processing device. The one or more memory device(s) b2006 can include one or more computer-readable media, including, but not limited to, non-transitory computer-readable media, RAM, ROM, hard drives, flash drives, and/or other memory devices.

[0312] The one or more memory device(s) b2006 can store information accessible by the one or more processor(s) b2004, including computer-readable instructions b2008 that can be executed by the one or more processor(s) b2004. The instructions b2008 can be any set of instructions that when executed by the one or more processor(s) b2004, cause the one or more processor(s) b2004 to perform operations. In some embodiments, the instructions b2008 can be executed by the one or more processor(s) b2004 to cause the one or more processor(s) b2004 to perform operations, such as any of the operations and functions for which the computing system b2000 and/or the computing device(s) b2002 are configured, such as e.g., operations for controlling certain aspects of power generation systems and/or controlling one or more closed cycle engines as described herein. For instance, the methods described herein can be implemented in whole or in part by the computing system b2000. Accordingly, the method can be at least partially a computer-implemented method such that at least some of the steps of the method are performed by one or more computing devices, such as the exemplary computing device(s) b2002 of the computing system b2000. The instructions b2008 can be software written in any suitable programming language or can be implemented in hardware. Additionally, and/or alternatively, the instructions b2008 can be executed in logically and/or virtually separate threads on processor(s) b2004. The memory device(s) b2006 can further store data b2010 that can be accessed by the processor(s) b2004. For example, the data b2010 can include models, databases, etc.

[0313] The computing device(s) b2002 can also include a network interface b2012 used to communicate, for example, with the other components of system (e.g., via a network). The network interface b2012 can include any suitable components for interfacing with one or more network(s), including for example, transmitters, receivers, ports, controllers b 1510, antennas, and/or other suitable components. One or more controllable devices b 1534 and other controllers b 1510 can be configured to receive one or more commands or data from the computing device(s) b2002 or provide one or more commands or data to the computing device(s) b2002.

[0314] The technology discussed herein makes reference to computer-based systems and actions taken by and information sent to and from computer-based systems. One of ordinary skill in the art will recognize that the inherent flexibility of computer-based systems allows for a great variety of possible configurations, combinations, and divisions of tasks and functionality between and among components. For instance, processes discussed herein can be implemented using a single computing device or multiple computing devices working in combination. Databases, memory, instructions, and applications can be implemented on a single system or distributed across multiple systems. Distributed components can operate sequentially or in parallel.

[0315] Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the present disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. [0316] With respect to a heater body, such as a monolithic heater body, further aspects of the invention are provided by the subject matter of the following clauses:

[0317] 1. A monolithic heater body, comprising: a combustor body defining a combustion chamber and a conditioning conduit circumferentially surrounding the combustion chamber, the conditioning conduit fluidly communicating with the combustion chamber at a distal portion of the combustion chamber; a hot-side heat exchanger body defining a hot-side heat exchanger comprising a heating fluid pathway fluidly communicating with a proximal portion of the combustion chamber; and an eductor body defining an eduction pathway fluidly communicating with a downstream portion of the heating fluid pathway and a proximal portion of the conditioning conduit.

[0318] 2. The monolithic heater body of any clause herein, wherein the combustion chamber, the heating fluid pathway, the eduction pathway, and the conditioning conduit together define at least a portion of a recirculation pathway configured to recirculate combustion gas through the combustion chamber.

[0319] 3. The monolithic heater body of any clause herein, comprising: a fuel injector body defining a portion of the monolithic heater body or operably coupled to the monolithic heater body, the fuel injector body comprising a combustor cap defining a nozzle port configured to receive a fuel nozzle, the combustor cap disposed axially adjacent to a distal portion of the conditioning conduit.

[0320] 4. The monolithic heater body of any clause herein, wherein the combustor cap defines at least a portion of a recirculation pathway configured to recirculate combustion gas through the combustion chamber.

[0321] 5. The monolithic heater body of any clause herein, wherein the hot-side heat exchanger body defines a plurality of heating fluid pathways fluidly communicating with the proximal portion of the combustion chamber, the plurality of heating fluid pathways concentrically spiraling about a perimeter of the combustion chamber.

[0322] 6. The monolithic heater body of any clause herein, wherein respective ones of the plurality of heating fluid pathways comprise a spiral pathway.

[0323] 7. The monolithic heater body of any clause herein, wherein the hot-side heat exchanger body comprises a heat transfer region having a heat transfer relationship with the plurality of heating fluid pathways.

[0324] 8. The monolithic heater body of any clause herein, wherein the hot-side heat exchanger body comprises a plurality of heat transfer regions respectively disposed about a semiannular portion of the hot-side heat exchanger body, wherein respective ones of the plurality of heat transfer regions have a heat transfer relationship with a corresponding semiannular portion of the plurality of heating fluid pathways.

[0325] 9. The monolithic heater body of any clause herein, comprising: a working- fluid body defining a working-fluid pathway fluidly communicating between a heat input region and a heat extraction region.

[0326] 10. The monolithic heater body of any clause herein, wherein the working- fluid body defines a plurality of heat transfer regions, respective ones of the plurality of heat transfer regions comprising a plurality of working-fluid pathways fluidly communicating between a respective one of a plurality of heat input regions and a respective one of a plurality of heat extraction regions.

[0327] 11. The monolithic heater body of any clause herein, wherein the hot-side heat exchanger body comprises a heat transfer region having a heat transfer relationship with a working-fluid body, the working-fluid body defining a working-fluid pathway fluidly communicating between a heat input region and a heat extraction region.

[0328] 12. The monolithic heater body of any clause herein, wherein the heat input region comprises a piston body defining a piston chamber and/or wherein the heat extraction region comprises a regenerator body defining a regenerator conduit.

[0329] 13. The monolithic heater body of any clause herein, wherein the eductor body defines a motive pathway fluidly communicating with the proximal portion of the conditioning conduit.

[0330] 14. The monolithic heater body of any clause herein, comprising: an intake air body defining an intake air pathway fluidly communicating with a motive pathway defined by the eductor body, the motive pathway fluidly communicating with the proximal portion of the conditioning conduit.

[0331] 15. The monolithic heater body of any clause herein, comprising: a heat recuperator body defining at least a portion of an exhaust pathway and at least a portion of an intake air pathway, the exhaust pathway having a heat transfer relationship with the intake air pathway.

[0332] 16. The monolithic heater body of any clause herein, wherein the monolithic heater body has an annular configuration.

[0333] 17. The monolithic heater body of any clause herein, comprising: an inner wall and an outer wall; and a cooling jacket defined between the inner wall and the outer wall; wherein the cooling jacket fluidly communicates with an intake air pathway and a proximal portion of the combustion chamber.

[0334] 18. The monolithic heater body of any clause herein, comprising: a thermal expansion joint disposed annularly or semi-annularly about a longitudinal axis of the combustion chamber.

[0335] 19. The monolithic heater body of any clause herein, wherein the monolithic heater body defines at least a portion of an additively manufactured monolithic body or an additively manufactured monolithic body-segment.

[0336] 20. The monolithic heater body of any clause herein, wherein the monolithic heater body defines at least a portion of a closed-cycle engine.

[0337] 21. A heater body, comprising: a combustion chamber and a recirculation pathway configured to recirculate combustion gas through the combustion chamber, the recirculation pathway comprising a hot-side heat exchanger and a recirculation eductor, the hot-side heat exchanger fluidly communicating with a proximal portion of the combustion chamber and the recirculation eductor fluidly communicating with a downstream portion of the hot-side heat exchanger and a distal portion of the combustion chamber.

[0338] 22. The heater body of any clause herein, wherein the recirculation eductor comprises an intake air pathway fluidly communicating with the recirculation pathway, the intake air pathway configured to entrain and/or accelerate combustion gas circulating through the recirculation pathway; and/or wherein the recirculation eductor comprises an exhaust pathway fluidly communicating with the recirculation pathway, the exhaust pathway configured to discharge a portion of the combustion gas as exhaust gas.

[0339] 23. The heater body of any clause herein, comprising: the exhaust pathway fluidly communicating with the recirculation pathway upstream from the intake air pathway.

[0340] 24. The heater body of any clause herein, wherein the recirculation pathway comprises a conditioning conduit fluidly communicating with a downstream portion of the recirculation eductor and a distal portion of the combustion chamber, the conditioning conduit configured to swirl combustion gas flowing therethrough.

[0341] 25. The heater body of any clause herein, comprising: a heat recuperator defining at least a portion of an exhaust pathway and at least a portion of an intake air pathway, the heat recuperator configured to utilize exhaust gas flowing through the exhaust pathway to preheat intake air flowing through the intake air pathway, the exhaust pathway having a thermally conductive relationship with the intake air pathway. [0342] 26. The heater body of any clause herein, comprising: the heat recuperator fluidly communicating with the recirculation pathway at the recirculation eductor through the exhaust pathway and the intake air pathway, the exhaust pathway being upstream from the intake air pathway.

[0343] 27. The heater body of any clause herein, wherein the hot-side heat exchanger comprises: a heating fluid pathway; and a heat transfer region having a thermally conductive relationship with the heating fluid pathway.

[0344] 28. The heater body of any clause herein, wherein the heat transfer region comprises a solid body and/or a fluid pathway defined at least in part by the solid body.

[0345] 29. The heater body of any clause herein, wherein the hot-side heat exchanger comprises: a plurality of heating fluid pathways; and a plurality of heat transfer regions, wherein respective ones of the plurality of heat transfer regions have a thermally conductive relationship with a corresponding portion of the heating fluid pathways.

[0346] 30. The heater body of any clause herein, wherein respective ones of the plurality of heat transfer regions comprise a solid body and/or a fluid pathway defined at least in part by the solid body.

[0347] 31. The heater body of any clause herein, comprising the fluid pathway defined at least in part by the solid body fluidly communicating with a regenerator and/or a piston chamber.

[0348] 32. The heater body of any clause herein, wherein the heater body defines a portion of a closed-cycle engine, wherein the closed-cycle engine comprises a regenerative heat engine and/or a Stirling engine.

[0349] 33. The heater body of any clause herein, the heater body having an annular configuration.

[0350] 34. The heater body of any clause herein, comprising: the hot-side heat exchanger circumferentially surrounding at least a portion of the combustion chamber; and/or a conditioning conduit circumferentially surrounding at least a portion of the combustion chamber.

[0351] 35. The heater body of any clause herein, comprising: the hot-side heat exchanger circumferentially surrounding a proximal portion of the combustion chamber; and/or the conditioning conduit circumferentially surrounding a medial portion and/or a distal portion of the combustion chamber. [0352] 36. The heater body of any clause herein, comprising: a recirculation eductor circumferentially surrounding the combustion chamber.

[0353] 37. The heater body of any clause herein, comprising: a conditioning conduit, and a recirculation eductor, the recirculation eductor circumferentially surrounding at least a portion of the conditioning conduit.

[0354] 38. The heater body of any clause herein, comprising: the recirculation eductor disposed adjacent to a distal portion of the hot-side heat exchanger.

[0355] 39. The heater body of any clause herein, comprising: the recirculation pathway circumferentially surrounding at least a portion of the combustion chamber.

[0356] 40. The heater body of any clause herein, comprising: an intake air pathway and/or an exhaust pathway circumferentially surrounding at least a portion of the combustion chamber.

[0357] 41. The heater body of any clause herein, comprising: a fuel nozzle operably coupled to the heater body.

[0358] 42. The heater body of any clause herein, comprising a combustor body configured according to any clause herein.

[0359] 43. The heater body of any clause herein, comprising a hot-side heat exchanger body configured to any clause herein.

[0360] 44. The heater body of any clause herein, comprising an eductor body configured according to any clause herein.

[0361] 45. The heater body of any clause herein, comprising: an eductor body, the eductor body comprising: an eduction pathway fluidly communicating with an annulus, the eduction pathway oriented oblique to the annulus; and a motive pathway fluidly

communicating with the annulus, the motive pathway being adjacent to the eduction pathway and oriented oblique to the annulus.

[0362] 46. The heater body of any clause herein, comprising a heat recuperator body configured according to any clause herein.

[0363] 47. The heater body of any clause herein, comprising a working-fluid body configured according to any clause herein.

[0364] 48. The heater body of any clause herein, wherein the heater body defines at least a portion of an engine assembly, the engine assembly configured according to any clause herein. [0365] 49. The heater body of any clause herein, wherein the heater body comprises a regenerator body configured according to any clause herein.

[0366] 50. A heater body, comprising: an intake annulus; an exhaust annulus; and/or a recirculation annulus.

[0367] 51. The heater body of any clause herein, wherein the heater body is a monolithic heater body, the monolithic heater body configured according to any clause herein.

[0368] 52. The heater body of any clause herein, wherein the heater body is configured to perform the method of any clause herein.

[0369] 53. The heater body of any clause herein, comprising: a heat shield configured to insulate and/or shield one or more portions of the heater body from a heat source within the heater body; and/or to provide a heat sink to absorb and/or dissipate heat from the heat source.

[0370] 54. The heater body of any clause herein, wherein the heat source comprises a combustion flame and/or combustion gas circulating through a recirculation pathway.

[0371] 55. The heater body of any clause herein, wherein the heat shield comprises a cooling jacket.

[0372] 56. The heater body of any clause herein, comprising: one or more heat shields, one or more heat-capture pathways, and/or one or more thermal expansion joints.

[0373] 57. The heater body of any clause herein, wherein the heater body defines a portion of a closed cycle engine, and wherein the closed cycle engine exhibits an improved Carnot efficiency, such as a Carnot efficiency of from about 40% to about 60%, such as from about 50% to about 70%, such as from about 60% to about 70%, such as from about 60% to 80%; with the Carnot efficiency being attributable at least in part to the heater body comprising one or more heat shields, one or more heat-capture pathways, and/or one or more thermal expansion joints, that allow the heater body to operate at an elevated temperature effective to impart such Carnot efficiency.

[0374] 58. The heater body of any clause herein, comprising: a heat shield circumferentially surrounding at least a portion of a hot-side heat exchanger and/or at least a portion of a working-fluid body.

[0375] 59. The heater body of any clause herein, comprising: a heat shield disposed about an inward annular or semiannular portion of a hot-side heat exchanger and/or working- fluid body. [0376] 60. The heater body of any clause herein, comprising: a heat shield disposed about at least a portion of a combustor body.

[0377] 61. The heater body of any clause herein comprising: a first heat shield circumferentially surrounding at least a portion of a hot-side heat exchanger and/or at least a portion of a working-fluid body; a second heat shield disposed about an inward annular or semiannular portion of a hot-side heat exchanger and/or working-fluid body; and a third heat shield disposed about at least a portion of a combustor body.

[0378] 62. The heater body of any clause herein, wherein the heat shield comprises an insulating material formed of an additive manufacturing material.

[0379] 63. The heater body of any clause herein, wherein the insulating material comprises a radiative-heat shield.

[0380] 64. The heater body of any clause herein, wherein the insulation material is integrally formed with adjacent material of the heater body.

[0381] 65. The heater body of any clause herein, wherein the radiative-heat shield has a cross-sectional thickness of from 100 micrometers to 5,000 micrometers.

[0382] 66. The heater body of any clause herein, wherein the radiative-heat shield comprises unit cells with walls that have a thickness of from 50 micrometers to 500 micrometers.

[0383] 67. The heater body of any clause herein, wherein the insulating material is monolithically connected to an adjacent portion of the heater body by a plurality of conduction posts, the conduction posts providing separation between such insulating material and such adjacent portions of the heater body.

[0384] 68. The heater body of any clause herein, wherein the insulating material comprises an additive manufacturing powder material, the additive manufacturing powder material being sintered and/or unsintered.

[0385] 69. The heater body of any clause herein, wherein the insulating material comprises a powder-radiative-heat shield, the powder-radiative-heat shield comprising a three-dimensional array of unit cells and an additive manufacturing powder material disposed interstitially about the three-dimensional array of unit cells.

[0386] 70. The heater body of any clause herein, comprising: one or more heat- capture pathways configured to transport a heat-capture fluid.

[0387] 71. The heater body of any clause herein, wherein the heat-capture fluid comprises intake air, exhaust gas, combustion gas, and/or a fuel. [0388] 72. The heater body of any clause herein, wherein the heat-capture pathway is configured to discharge cooling fluid to a primary flowpath of the heater body.

[0389] 73. The heater body of any clause herein, wherein the cooling fluid comprises a chiller working fluid or an engine-working fluid.

[0390] 74. The heater body of any clause herein, comprising: a heat-capture pathway configured to provide cooling to a working-fluid body, a piston body, and/or a regenerator body.

[0391] 75. The heater body of any clause herein, wherein the heat-capture pathway is configured to return heat to an interior heater body -portion.

[0392] 76. The heater body of any clause herein, wherein the interior heater body- portion comprises a combustor body.

[0393] 77. The heater body of any clause herein, wherein the heat-capture pathway is configured to provide cooling to a portion of the heater body that interfaces with an engine body.

[0394] 78. The heater body of any clause herein, wherein the heat-capture pathway circumferentially surrounds at least a portion of a piston chamber.

[0395] 79. The heater body of any clause herein, wherein the heat-capture pathway is configured to discharge cooling fluid into the combustion chamber through a distal portion of the combustion chamber.

[0396] 80. The heater body of any clause herein, wherein the combustion chamber comprises a vortex conditioner, and wherein the heat-capture pathway is configured to discharge cooling fluid into the combustion chamber through a plurality of pore-like openings circumferentially surrounding the vortex conditioner and/or disposed about the vortex conditioner.

[0397] 81. The heater body of any clause herein, wherein the vortex conditioner is configured at least in part to establish and/or sustain a vortex flow field that includes a combustion gas and/or a flame.

[0398] 82. The heater body of any clause herein, wherein the vortex flow field comprises a bidirectional coaxial vortex flow field.

[0399] 83. The heater body of any clause herein, wherein the vortex conditioner has a conical or frustoconical shape. [0400] 84. The heater body of any clause herein, wherein the heat-capture pathway comprises a plurality of spiral-heat-capture pathways disposed about a distal portion of the combustion chamber.

[0401] 85. The heater body of any clause herein, comprising: an engine-to-heater coupling, the engine-to-heater coupling configured to provide an interface between the heater body and an engine body.

[0402] 86. The heater body of any clause herein, wherein the engine-to-heater coupling comprises a fitting configured to couple a heater body-flange and an engine body- flange to one another.

[0403] 87. The heater body of any clause herein, comprising: a gasket disposed between the heater body-flange and the engine body-flange.

[0404] 88. The heater body of any clause herein, comprising: a heat-capture pathway configured to provide cooling to a region of the heater body that includes the heater body- flange.

[0405] 89. The heater body of any clause herein, wherein the gasket is formed at least in part from a polymeric material or a non-polymeric material.

[0406] 90. The heater body of any clause herein, wherein the polymeric material comprises at least one of: silicone, fluorosilicone, fluorocarbon, nitrile rubber,

polytetrafluoroethylene (PTFE), ethylene propylene diene monomer rubber (EPDM), polyamides, aramid fiber-polymeric laminates, carbon fiber-polymeric laminates, or graphite polymeric laminates.

[0407] 91. The heater body of any clause herein, wherein the non-polymeric material comprises a ceramic or metallic material.

[0408] 92. The heater body of any clause herein, wherein at least a portion of the heater body exhibits an operating temperatures of at least 400C, such as at least 500C, such as at least 600C, such as at least 700C, or such as at least 800C; and/or wherein a region of the heater body that includes the heater body-flange exhibits an operating temperature of at least less than 600C, such as at least less than 500C, such as at least less than 400C, such as at least less than 300C, or such as at least less than 200C.

[0409] 93. The heater body of any clause herein, wherein a region of the heater body that includes the heater body-flange exhibits an operating temperature of at least 50C cooler than a portion of the heater body that includes the working-fluid body cl 08, such as at least 75C cooler, such as at least lOOC cooler, such as at least 200C cooler, such as at least 300C cooler, or such as at least 400C cooler.

[0410] 94. The heater body of any clause herein, wherein such difference in operating temperature is attributable at least in part to cooling provided by cooling fluid in a heat-capture pathway.

[0411] 95. The heater body of any clause herein, comprising a thermal expansion joint, the thermal expansion joint having a hairpin configuration comprising an expansion gap-

[0412] 96. The heater body of any clause herein, wherein the expansion gap comprises an insulating material.

[0413] 97. The heater body of any clause herein, comprising: a combustor-thermal expansion joint.

[0414] 98. The heater body of any clause herein, wherein the combustor-thermal expansion joint is configured to allow for thermal expansion, and/or a difference in thermal expansion, as between a combustor body and a hot-side heat exchanger body.

[0415] 99. The heater body of any clause herein, wherein the combustor-thermal expansion joint is configured to allow for thermal expansion, and/or a difference in thermal expansion, as between a combustor body and a working-fluid body.

[0416] 100. The heater body of any clause herein, wherein the combustor-thermal expansion joint is oriented concentric with a combustion chamber and/or a longitudinal axis of the heater body.

[0417] 101. The heater body of any clause herein, wherein the combustor-thermal expansion joint circumferentially surrounds at least a portion of the combustor body.

[0418] 102. The heater body of any clause herein, wherein the combustor-thermal expansion joint comprises an expansion gap disposed within at least a portion of a hot-side heater body.

[0419] 103. The heater body of any clause herein, wherein the combustor-thermal expansion joint is at least partially axially offset from the combustion chamber.

[0420] 104. The heater body of any clause herein, comprising: one or more heat transfer region-thermal expansion joints.

[0421] 105. The heater body of any clause herein, wherein the one or more heat transfer region-thermal expansion joints are configured at least in part to allow for thermal expansion, and/or a difference in thermal expansion, as between respective heat transfer regions of the heater body.

[0422] 106. The heater body of any clause herein, comprising: a heat transfer region- thermal expansion joint configured at least in part to allow for thermal expansion, and/or a difference in thermal expansion, as between a working-fluid body and a regenerator body, and/or as between a piston body and a regenerator body.

[0423] 107. The heater body of any clause herein, comprising: a heat transfer region- thermal expansion joint disposed between a regenerator body of a first heat transfer region and a working-fluid body of a second heat transfer region.

[0424] 108. The heater body of any clause herein, comprising: a heat transfer region- thermal expansion joint disposed between a regenerator body of a first heat transfer region and a piston body of a second heat transfer region.

[0425] 109. The heater body of any clause herein, comprising: a heat transfer region- thermal expansion joint disposed between a heat input region of a working-fluid body and a heat extraction region of a working fluid body.

[0426] 110. The heater body of any clause herein, comprising: a heat transfer region- thermal expansion joint disposed between a heat input region of a first heat transfer region, and a heat extraction region of a second heat transfer region.

[0427] 111. A heater body, comprising: a combustor body, the combustor body comprising: a combustion chamber disposed annularly about an axis; and a conditioning conduit circumferentially surrounding the combustion chamber, the conditioning conduit fluidly communicating with the combustion chamber at a distal portion of the combustion chamber.

[0428] With respect to a method of heating a closed-cycle engine, further aspects of the invention are provided by the subject matter of the following clauses:

[0429] 1. A method of heating a closed-cycle engine, the method comprising:

circulating combustion gas through a combustion chamber and a recirculation pathway configured to recirculate combustion gas through the combustion chamber, the recirculation pathway comprising a hot-side heat exchanger and a recirculation eductor, the hot-side heat exchanger fluidly communicating with a proximal portion of the combustion chamber and the recirculation eductor fluidly communicating with a downstream portion of the hot-side heat exchanger and a distal portion of the combustion chamber; and transferring heat from the combustion gas in the hot-side heat exchanger to a plurality of heat transfer regions, wherein respective ones of the plurality of heat transfer regions have a heat transfer relationship with a corresponding semiannular portion of the hot-side heat exchanger.

[0430] 2. The method of any clause herein, comprising: injecting into the

recirculation pathway intake air through an intake air pathway fluidly communicating with the recirculation pathway, the intake air pathway defined at least in part by the recirculation eductor.

[0431] 3. The method of any clause herein, comprising: entraining and/or accelerating combustion gas circulating through the recirculation pathway at least in part by injecting the intake air into the recirculation pathway.

[0432] 4. The method of any clause herein, comprising: discharging from the recirculation pathway a portion of the combustion gas as exhaust gas, the exhaust gas discharging through an exhaust pathway fluidly communicating with the recirculation pathway, the exhaust gas pathway defined at least in part by the recirculation eductor.

[0433] 5. The method of any clause herein, comprising: discharging the portion of the combustion gas as exhaust gas from the recirculation pathway upstream from the intake air pathway fluidly communicating with the recirculation pathway.

[0434] 6. The method of any clause herein, comprising: swirling combustion gas through a conditioning conduit defining at least a portion of the recirculation pathway, the conditioning conduit fluidly communicating with a downstream portion of the recirculation eductor and a distal portion of the combustion chamber.

[0435] 7. The method of any clause herein, comprising: preheating intake air flowing through an intake air pathway at least in part using exhaust gas flowing through an exhaust pathway, the exhaust pathway having a thermally conductive relationship with the intake air pathway.

[0436] 8. The method of any clause herein, comprising: preheating the intake air at least in part using a heat recuperator, the heat recuperator defining at least a portion of the intake air pathway and at least a portion of the exhaust pathway.

[0437] 9. The method of any clause herein, comprising: flowing combustion gas from the recirculation pathway into the heat recuperator at the recirculation eductor through the exhaust pathway; and flowing intake air from the intake air pathway into the recirculation eductor at the heat recuperator, the exhaust pathway being upstream from the intake air pathway. [0438] 10. The method of any clause herein, comprising: transferring heat from a recirculation pathway defined at least in part by the hot-side heat exchanger to a heat transfer region having a thermally conductive relationship with the heating fluid pathway.

[0439] 11. The method of any clause herein, wherein transferring heat from the recirculation pathway to the heat transfer region comprises: transferring heat to a solid body; and/or transferring heat to a fluid in a fluid pathway defined at least in part by the solid body.

[0440] 12. The method of any clause herein, comprising: transferring heat from a plurality of heating fluid pathways defined at least in part by the hot-side heat exchanger to respective ones of a plurality of heat transfer regions, wherein the respective ones of the plurality of heat transfer regions have a thermally conductive relationship with a

corresponding portion of the plurality of heating fluid pathways.

[0441] 13. The method of any clause herein, wherein transferring heat from the plurality of heating fluid pathways to a respective one of the plurality of heat transfer regions comprises: transferring heat to a solid body; and/or transferring heat to a fluid in a fluid pathway defined at least in part by the solid body.

[0442] 14. The method of any clause herein, comprising: flowing fluid through the fluid pathway defined at least in part by the solid body fluidly alternatingly between a regenerator and a piston chamber.

[0443] 15. The method of any clause herein, comprising: combusting fuel and at least a portion of the combustion gas in the combustion chamber, the fuel supplied by a fuel nozzle fluidly communicating with the combustion chamber.

[0444] 16. The method of any clause herein, comprising: circulating from about 10% to about 90% of the combustion gas through the combustion chamber, a remainder of the combustion gas being discharged from the recirculation pathway as exhaust gas through the exhaust pathway.

[0445] 17. The method of any clause herein, comprising: circulating from about 30% to about 70% of the combustion gas through the combustion chamber.

[0446] 18. The method of any clause herein, comprising: circulating from about 40% to about 60% of the combustion gas through the combustion chamber.

[0447] 19. The method of any clause herein, wherein the remainder of the

combustion gas being discharged from the recirculation pathway as exhaust gas comprises from about 10% to about 90%, or from about 30% to about 70%, or from about 40% to about 60%. [0448] 20. The method of any clause herein, comprising: combusting a fuel according to the method of any clause herein.

[0449] 21. The method of any clause herein, comprising: heating a plurality of heat transfer regions according to the method of any clause herein.

[0450] 22. The method of any clause herein, comprising: circulating fluid according to the method of any clause herein; or circulating combustion gas according to the method of any clause herein.

[0451] 23. The method of any clause herein, comprising: transferring heat between fluid streams according to the method of any clause herein.

[0452] 24. The method of any clause herein, comprising: recuperating heat from exhaust gas according to the method of any clause herein.

[0453] 25. The method of any clause herein, comprising: heating an engine-working fluid according to the method of any clause herein.

[0454] 26. The method of any clause herein, comprising: regenerating heat in an engine-working fluid according to the method of any clause herein.

[0455] 27. The method of any clause herein, comprising: performing the method at least in part using the heater body of any clause herein.

[0456] 28. The method of any clause herein, comprising the method of any subsequent clause.

[0457] With respect to a combustor body, further aspects of the invention are provided by the subject matter of the following clauses:

[0458] 1. A combustor body, comprising: a combustion chamber disposed annularly about an axis; and a conditioning conduit circumferentially surrounding at least a portion of the combustion chamber, the conditioning conduit fluidly communicating with the combustion chamber at a distal portion of the combustion chamber.

[0459] 2. The combustor body of any clause herein, wherein the combustion chamber comprises an annular combustion chamber wall.

[0460] 3. The combustor body of any clause herein, wherein the conditioning conduit comprises an outward annular conditioning conduit wall circumferentially surrounding the combustion chamber.

[0461] 4. The combustor body of any clause herein, comprising: a conditioning conduit inlet disposed about a proximal portion of the conditioning conduit, the conditioning conduit inlet being oblique to the conditioning conduit. [0462] 5. The combustor body of any clause herein, comprising: the conditioning conduit inlet disposed about a proximal portion of the outward annular conditioning conduit wall.

[0463] 6. The combustor body of any clause herein, comprising: a combustion chamber outlet disposed about a proximal portion of the combustion chamber, the combustion chamber outlet being oblique to the combustion chamber.

[0464] 7. The combustor body of any clause herein, comprising: the combustion chamber outlet disposed about a proximal portion of the annular combustion chamber wall.

[0465] 8. The combustor body of any clause herein, comprising: a plurality of conditioning conduit inlets circumferentially spaced about a proximal portion of the conditioning conduit.

[0466] 9. The combustor body of any clause herein, comprising: an outward annular conditioning conduit wall circumferentially surrounding the combustion chamber; and the plurality of conditioning conduit inlets circumferentially spaced about a proximal portion of the outward annular conditioning conduit wall.

[0467] 10. The combustor body of any clause herein, comprising: a plurality of combustion chamber outlets circumferentially spaced about a proximal portion of the combustion chamber.

[0468] 11. The combustor body of any clause herein, comprising: an annular combustion chamber wall; and the plurality of combustion chamber outlets circumferentially spaced about a proximal portion of the annular combustion chamber wall.

[0469] 12. The combustor body of any clause herein, wherein the conditioning conduit comprises an inward annular conditioning conduit wall and an outward annular conditioning conduit wall.

[0470] 13. he combustor body of any clause herein, wherein the conditioning conduit comprises a conditioning conduit pathway defined at least in part by the inward annular conditioning conduit wall and the outward annular conditioning conduit wall.

[0471] 14. The combustor body of any clause herein, comprising: a combustor cap, the combustor cap disposed axially adjacent to a distal portion of the conditioning conduit.

[0472] 15. The combustor body of any clause herein, comprising: the combustor cap being operably coupled to the conditioning conduit; or the combustor cap defining a portion of a monolithic body or a monolithic body-segment comprising at least a portion of the combustor body; or the combustor cap being integrally formed with at least a portion of the combustor body.

[0473] 16. The combustor body of any clause herein, comprising: the combustor cap defining a portion of the conditioning conduit.

[0474] 17. The combustor body of any clause herein, comprising: the combustor cap defining a portion of a recirculation pathway comprising the conditioning conduit fluidly communicating with the combustion chamber at a distal portion of the combustion chamber, the combustor cap operable at least in part to direct combustion gas from the conditioning conduit to the combustion chamber.

[0475] 18. The combustor body of any clause herein, wherein the combustion chamber comprises an annular combustion chamber wall, the annular combustion chamber wall having a Coanda surface disposed at a distal end thereof, the Coanda surface operable at least in part to draw combustion gas from the conditioning conduit into the combustion chamber.

[0476] 19. The combustor body of any clause herein, wherein the combustion chamber comprises an annular combustion chamber wall, an inward portion of the annular combustion chamber wall at least in part defining the combustion chamber, and an outward portion of the annular combustion chamber wall defining an inward annular conditioning conduit wall.

[0477] 20. The combustor body of any clause herein, comprising: the inward portion of the annular combustion chamber wall adjoining the outward portion of the annular combustion chamber wall at a distal end of the combustion chamber.

[0478] 21. The combustor body of any clause herein, comprising: a cooling jacket disposed between at least a portion of the inward portion of the annular combustion chamber wall and the outward portion of the annular combustion chamber wall, the cooling jacket configured to receive a cooling fluid operable to cool the combustion chamber.

[0479] 22. The combustor body of any clause herein, comprising: the cooling jacket fluidly communicating with an intake air pathway; the cooling jacket fluidly communicating with a recirculation pathway; or the cooling jacket fluidly communicating with a working- fluid pathway.

[0480] 23. The combustor body of any clause herein, comprising: a plurality of conditioning pathways disposed about a proximal, medial, and/or axial portion of the combustion chamber, the conditioning pathways providing fluid communication between the combustion chamber and the conditioning conduit.

[0481] 24. The combustor body of any clause herein, comprising: a plurality of conditioning conduit inlets disposed about a proximal portion of the conditioning conduit, the plurality of conditioning conduit inlets oriented oblique to the conditioning conduit.

[0482] 25. The combustor body of any clause herein, wherein the plurality of conditioning conduit inlets comprise: a motive pathway fluidly communicating with the conditioning conduit, the motive pathway oriented oblique to the conditioning conduit; and an eduction pathway fluidly communicating with the conditioning conduit, the eduction pathway being adjacent to the motive pathway and oriented oblique to the conditioning conduit.

[0483] 26. The combustor body of any clause herein, wherein the plurality of conditioning conduit inlets comprise a plurality of motive pathways circumferentially spaced about the conditioning conduit and a plurality of eduction pathways circumferentially spaced about the conditioning conduit, the plurality of motive pathways and the plurality of eduction pathways oriented oblique to the conditioning conduit.

[0484] 27. The combustor body of any clause herein, wherein the motive pathway or plurality of motive pathways define a portion of an intake air pathway and the eduction pathway or plurality of eduction pathways define a portion of a recirculation pathway.

[0485] 28. The combustor body of any clause herein, comprising: a plurality of combustion chamber outlets disposed about a proximal portion of the combustion chamber, the plurality of combustion chamber outlets oriented oblique to the combustion chamber.

[0486] 29. The combustor body of any clause herein, comprising: the plurality of combustion chamber outlets fluidly communicating with a corresponding plurality of spiral pathways circumferentially spaced about the combustion chamber.

[0487] 30. The combustor body of any clause herein, wherein the plurality of spiral pathways define at least a portion of a hot-side heat exchanger body.

[0488] 31. The combustor body of any clause herein, wherein at least a portion of the combustion chamber has a shape comprising a cylinder and/or a frustum, at least a portion of the frustum converging proximally and/or at least a portion of the frustum diverging proximally.

[0489] 32. The combustor body of any clause herein, wherein at least a portion of the conditioning conduit has a shape comprising a cylinder and/or a frustum, at least a portion of the frustum converging proximally and/or at least a portion of the frustum diverging proximally.

[0490] 33. The combustor body of any clause herein, comprising: a first portion of the combustion chamber having a first shape comprising a cylinder circumferentially surrounded by a second portion of the conditioning conduit having a second shape comprising a cylinder and/or a frustum, at least a portion of the frustum converging proximally and/or at least a portion of the frustum diverging proximally.

[0491] 34. The combustor body of any clause herein, comprising: a third portion of the combustion chamber having a third shape comprising a cylinder and/or a frustum circumferentially surrounded by a fourth portion of the conditioning conduit having a fourth shape comprising a cylinder, at least a portion of the frustum converging proximally and/or at least a portion of the frustum diverging proximally.

[0492] 35. The combustor body of any clause herein, comprising: a fifth portion of the combustion chamber having a fifth shape comprising a frustum converging proximally circumferentially surrounded by a sixth portion of the conditioning conduit having a sixth shape comprising a frustum converging proximally and/or a frustum diverging proximally.

[0493] 36. The combustor body of any clause herein, comprising: a seventh portion of the combustion chamber having a seventh shape comprising a frustum diverging proximally and circumferentially surrounded by an eighth portion of the conditioning conduit having an eighth shape comprising a frustum converging proximally and/or a frustum diverging proximally.

[0494] 37. The combustor body of any clause herein, the combustor body configured and arranged so as to swirl combustion gas through the conditioning conduit from a proximal portion of the conditioning conduit to a distal portion of the conditioning conduit and through the combustion chamber from a distal portion of the combustion chamber to a proximal portion of the combustion chamber.

[0495] 38. The combustor body of any clause herein, the combustor body configured and arranged so as to provide a bidirectional coaxial vortex flow field.

[0496] 39. The combustor body of any clause herein, comprising: the combustion chamber operable to separate an outward portion of the bidirectional coaxial vortex flow field from an inward portion of the bidirectional coaxial vortex flow field, the conditioning conduit defining a pathway for the outward portion of the bidirectional coaxial vortex flow field and the combustion chamber defining a pathway for the inward portion of the bidirectional coaxial vortex flow field.

[0497] 40. The combustor body of any clause herein, comprising: one or more aerodynamic features disposed about at least a portion of the conditioning conduit and/or at least a portion of the combustion chamber.

[0498] 41. The combustor body of any clause herein, comprising: an annular combustion chamber wall and one or more aerodynamic features disposed about at least a portion of the annular combustion chamber wall.

[0499] 42. The combustor body of any clause herein, comprising: an inward annular conditioning conduit wall and one or more aerodynamic features disposed about at least a portion of the inward annular conditioning conduit wall; and/or an outward annular conditioning conduit wall and one or more aerodynamic features disposed about at least a portion of the outward annular conditioning conduit wall.

[0500] 43. The combustor body of any clause herein, wherein the one or more aerodynamic features comprises, a fin, a ridge, and/or a groove configured and arranged to condition a flow of combustion gas flowing through the conditioning conduit and/or the combustion chamber.

[0501] 44. The combustor body of any clause herein, wherein condition the flow of combustion gas comprises swirling the combustion gas.

[0502] 45. The combustor body of any clause herein, wherein condition the flow of combustion gas comprises providing a bidirectional coaxial vortex flow field.

[0503] 46. The combustor body of any clause herein, wherein the one or more aerodynamic features comprises, a helical fin, a helical ridge, and/or a helical groove.

[0504] 47. The combustor body of any clause herein, comprising: a combustor cap, the combustor cap disposed axially adjacent to a distal portion of the conditioning conduit, the combustor cap comprising a nozzle port configured to receive a fuel nozzle.

[0505] 48. The combustor body of any clause herein, comprising: the fuel nozzle operably coupled to the nozzle port of the combustor cap.

[0506] 49. The combustor body of any clause herein, wherein the fuel nozzle comprises a glow plug operable to ignite fuel and/or combustion gas in the combustion chamber. [0507] 50. The combustor body of any clause herein, the combustor body and/or the combustion chamber having an axial length selected based at least in part on a desired flame length and/or a corresponding combustion time.

[0508] 51. The combustor body of any clause herein, wherein the combustion time is from 1 to 10 milliseconds, or wherein the combustion time is from 2 to 4 milliseconds.

[0509] 53. The combustor body of any clause herein, comprising one or more features of the combustion chamber and/or one or more features of the conditioning conduit configured to provide a lean combustion environment.

[0510] 54. The combustor body of any clause herein, wherein the one or more features of the conditioning conduit comprise one or more conditioning conduit inlets and/or wherein the one or more features of the combustion chamber comprise one or more combustion chamber outlets.

[0511] 55. The combustor body of any clause herein, comprising a fuel nozzle operably configured to provide a lean combustion environment.

[0512] 56. The combustor body of any clause herein, the lean combustion environment comprising an equivalence ratio of 0.6 to 1.0 or an equivalence ratio of 0.7 to 0 8

[0513] 57. The combustor body of any clause herein, the lean combustion environment comprising an air to fuel ratio of from 40: 1 to 90: 1 by mass, or from 55: 1 to 75: 1 by mass.

[0514] 58. The combustor body of any clause herein, comprising one or more features of the combustion chamber and/or one or more features of the conditioning conduit dimensionally configured to circulate from about 10% to about 90% of the combustion gas and to introduce a balance of the combustion gas as intake air.

[0515] 59. The combustor body of any clause herein, wherein the one or more features of the conditioning conduit comprise one or more conditioning conduit inlets, and/or wherein the one or more features of the combustion chamber comprise one or more combustion chamber outlets.

[0516] 60. The combustor body of any clause herein, comprising the one or more features of the combustion chamber and/or the one or more features of the conditioning conduit dimensionally configured to circulate from about 30% to about 70% of the combustion gas or from about 40% to about 60% of the combustion gas and to introduce a balance of the combustion gas as intake air. [0517] 61. The combustor body of any clause herein, wherein the intake air comprises from about 10% to about 90% of the combustion gas.

[0518] 62. The combustor body of any clause herein, wherein the intake air comprises from about 30% to about 70% of the combustion gas or from about 40% to about 60% of the combustion gas.

[0519] 63. The combustor body of any clause herein, comprising: a secondary combustion chamber, the secondary combustion chamber comprising a plurality of combustion fins, the plurality of combustion fins circumferentially spaced about a perimeter of the combustion chamber.

[0520] 64. The combustor body of any clause herein, wherein the plurality of combustion fins define a plurality of spiral pathways fluidly communicating with a corresponding plurality of spiral pathways defined by the hot-side heat exchanger.

[0521] 65. The combustor body of any clause herein, comprising the plurality of combustion fins concurrently defining at least a portion of the secondary combustion chamber and at least a portion of the hot-side heat exchanger.

[0522] 66. The combustor body of any clause herein, comprising a monolithic combustor body configured to provide multi-stage combustion, wherein the combustor body is configured according to any subsequent clause.

[0523] 67. A monolithic combustor body configured to provide multi-stage combustion, the combustor body comprising: a combustion chamber body disposed annularly about a longitudinal axis and defining a combustion chamber; a plurality of heating walls comprising a heat sink, the plurality of heating walls occupying a radially or concentrically outward position relative to the combustion chamber and defining a corresponding plurality of combustion-gas pathways fluidly communicating with at least a proximal portion of the combustion chamber; wherein during operation, the combustor body exhibits multi-stage combustion, the multi-stage combustion comprising: a first combustion zone occupying a distal or medial position of the combustion chamber relative to the longitudinal axis; and a second combustion zone occupying a proximal position relative to the first combustion zone, and a radially or concentrically outward position of the combustion chamber and/or a radially or concentrically inward position of the plurality of combustion-gas pathways.

[0524] 68. The monolithic combustor body of any clause herein, wherein the second combustion zone occupies at least part of a proximal region of the combustion chamber. [0525] 69. The monolithic combustor body of any clause herein, wherein the heat sink comprises a plurality of working-fluid pathways, the plurality of working fluid pathways having a heat transfer relationship with the plurality of combustion-gas pathways.

[0526] 70. The monolithic combustor body of any clause herein, wherein the plurality of heating walls comprise the plurality of working-fluid pathways monolithically formed within at least a portion of the plurality of heating walls.

[0527] 71. The monolithic combustor body of any clause herein, comprising: a plurality of combustion fins circumferentially spaced about a perimeter of the combustion chamber, the plurality of combustion fins defining a radially or concentrically inward portion of the plurality of combustion-gas pathways.

[0528] 72. The monolithic combustor body of any clause herein, wherein the plurality of combustion fins define a portion of respective ones of the plurality of heating walls.

[0529] 73. The monolithic combustor body of any clause herein, wherein the second combustion zone occupies at least part of the radially or concentrically inward portion of the plurality of combustion-gas pathways defined by the plurality of combustion fins.

[0530] 74. The monolithic combustor body of any clause herein, wherein the plurality of combustion fins and/or the plurality of heating walls are configured to support auto-ignition at the second combustion zone when heated by combustion at the first combustion zone.

[0531] 75. The monolithic combustor body of any clause herein, wherein the second combustion zone occupies at least part of a proximal region of the combustion chamber.

[0532] 76. The monolithic combustor body of any clause herein, comprising: one or more fuel pathways monolithically integrated with a proximal portion of the combustion chamber body and/or a radially or concentrically inward portion of the plurality of combustion-gas pathways.

[0533] 77. The monolithic combustor body of any clause herein, comprising: a plurality of combustion fins circumferentially spaced about a perimeter of the combustion chamber, the plurality of combustion fins defining a radially or concentrically inward portion of the plurality of combustion-gas pathways; wherein the one or more fuel pathways fluidly communicate with the plurality of combustion-gas pathways through a plurality of pore-like openings in the plurality of combustion fins. [0534] 78. The monolithic combustor body of any clause herein, comprising: one or more fuel injectors monolithically integrated with a proximal portion of the combustor body and/or a radially or concentrically inward portion of the plurality of combustion-gas pathways.

[0535] 79. The monolithic combustor body of any clause herein, wherein the one or more fuel injectors are monolithically integrated with the plurality of heating walls and/or with a plurality of combustion fins circumferentially spaced about a perimeter of the combustion chamber, the plurality of combustion fins defining a radially or concentrically inward portion of the plurality of combustion-gas pathways.

[0536] 80. The monolithic combustion body of any clause herein, comprising: a plurality of burner gaps, respective ones of the plurality of burner gaps defined in respective ones of the plurality of heating walls, the second combustion zone at least partially coinciding with the plurality of burner gaps; wherein the plurality of burner gap comprises one or more of: an open space, a mesh, a three-dimensional lattice, or a porous medium.

[0537] 81. The monolithic combustor body of any clause herein, comprising a pilot burner configured to provide a pilot flame occupying the first combustion zone, wherein the pilot flame provides an ignition source for combustion in the second combustion zone.

[0538] 82. The monolithic combustor body of any clause herein, comprising: a conditioning conduit body circumferentially surrounding at least a portion of the combustion chamber body, the conditioning conduit body and the combustion chamber body defining a conditioning conduit fluidly communicating with the combustion chamber at a distal portion of the combustion chamber.

[0539] 83. The monolithic combustor body of any clause herein, wherein the plurality of combustion-gas pathways follow an annular or semiannular spiral trajectory relative to the combustion chamber and/or the longitudinal axis.

[0540] 84. The monolithic combustor body of any clause herein, comprising: a downstream portion of the plurality of combustion-gas pathways fluidly communicating with a proximal portion of a conditioning conduit defined by the combustor body; and a distal portion of the conditioning conduit fluidly communicating with a distal portion of the combustion chamber.

[0541] 85. The monolithic combustor body of any clause herein, comprising: a vortex conditioner monolithically integrated with a proximal portion of the combustion chamber, the vortex conditioner having a conical or frustoconical shape projecting into the combustion chamber along the longitudinal axis.

[0542] 86. The monolithic combustor body of any clause herein, wherein the second combustion zone occupies a radially or concentrically outward position relative to the vortex conditioner.

[0543] 87. The monolithic combustor body of any clause herein, comprising: one or more heat-capture pathways monolithically integrated with a proximal portion of the combustor body, the one or more heat-capture pathways fluidly communicating with the combustion chamber at a plurality of openings circumferentially surrounding the vortex conditioner and/or disposed about the vortex conditioner.

[0544] 88. The combustor body of any clause herein, wherein the combustor body defines a multi-stage combustor.

[0545] 89. The combustor body of any clause herein, wherein the combustor body defines at least a portion of a heater body.

[0546] 90. The combustor body of any clause herein, wherein the combustor body comprises an additively manufactured monolithic body or an additively manufactured monolithic body-segment.

[0547] 91. The combustor body of any clause herein, comprising: an eductor body configured according to any clause herein.

[0548] 92. The combustor body of any clause herein, wherein the combustor body comprises a hot-side heat exchanger body configured according to any clause herein.

[0549] 93. The combustor body of any clause herein, comprising a heat recuperator body configured according to any clause herein.

[0550] 94. The combustor body of any clause herein, comprising: a working-fluid body configured according to any clause herein.

[0551] 95. The combustor body of any clause herein, comprising a regenerator body configured according to any clause herein.

[0552] 96. The combustor body of any clause herein, wherein the combustor body defines at least a portion of an engine assembly configured according to any clause herein.

[0553] 97. The combustor body of any clause herein, wherein the combustor body defines at least a portion of the heater body configured according to any clause herein.

[0554] 98. The combustor body of any clause herein, wherein the combustor body defines at least a portion of a closed-cycle engine. [0555] 99. The combustor body of any clause herein, wherein the combustor body is configured to perform a method of any clause herein.

[0556] 100. The combustor body of any clause herein, comprising: an eduction pathway fluidly communicating with an annulus, the eduction pathway oriented oblique to the annulus; and a motive pathway fluidly communicating with the annulus, the motive pathway being adjacent to the eduction pathway and oriented oblique to the annulus.

[0557] 101. The combustor body of any clause herein, comprising: an intake air pathway fluidly communicating with a conditioning conduit, the intake air pathway oriented oblique to the conditioning conduit; and a recirculation pathway fluidly communicating with the conditioning conduit, the recirculation pathway being adjacent to the intake air pathway and oriented oblique to the conditioning conduit.

[0558] 102. The combustor body of any clause herein, comprising: a plurality of heating fluid pathways circumferentially spaced (and/or disposed radially about) an inlet plenum, respective ones of the plurality of heating fluid pathways defining a spiral pathway and the inlet plenum fluidly communicating with the plurality of heating fluid pathways; and a plurality of heat transfer regions, wherein respective ones of the plurality of heat transfer regions have a heat transfer relationship with a corresponding semiannular portion of the plurality of heating fluid pathways.

[0559] 103. The combustor body of any clause herein, comprising: a heat recuperator body, the heat recuperator body comprising: a first intake annulus disposed annularly about an axis, a first discharge annulus disposed annularly about the axis, and a plurality of first pathways spiraling annularly about the axis, the plurality of first pathways comprising: a plurality of first pathway-inlets fluidly communicating annularly about the first intake annulus, and a plurality of first pathway-outlets fluidly communicating annularly about the first discharge annulus; and a second intake annulus disposed annularly about the axis, a second discharge annulus disposed annularly about the axis, and a plurality of second pathways spiraling annularly about the axis, respective ones of the plurality of second pathways altematingly adjacent to respective ones of the plurality of first pathways, the plurality of second pathways comprising: a plurality of second pathway -inlets fluidly communicating annularly about the second intake annulus, and a plurality of second pathway-outlets fluidly communicating annularly about the second discharge annulus.

[0560] 104. The combustor body of any clause herein, comprising: a regenerator conduit; and a plurality of fin arrays adjacently disposed within the regenerator conduit and respectively supported by the regenerator conduit in spaced relation to one another, the spaced relation of the plurality of fin arrays defining a gap longitudinally separating adjacent ones of the plurality of fin arrays.

[0561] With respect to a method of combusting a fuel, further aspects of the invention are provided by the subject matter of the following clauses:

[0562] 1. A method of combusting a fuel, the method comprising: swirling combustion gas through a conditioning conduit, the combustion gas flowing from a proximal portion of the conditioning conduit to a distal portion of the conditioning conduit while swirling; swirling the combustion gas through a combustion chamber, the conditioning conduit circumferentially surrounding the combustion chamber and providing fluid communication with the combustion chamber at a distal portion of the combustion chamber, the combustion gas flowing from the distal portion of the conditioning conduit to the distal portion of the combustion chamber and from the distal portion of the combustion chamber to a proximal portion of the combustion chamber; and combusting a fuel in the combustion chamber, the fuel supplied at least in part from the combustion gas flowing from the conditioning conduit to the combustion chamber.

[0563] 2. The method of any clause herein, comprising: supplying at least a portion of the fuel to the combustion chamber through a fuel nozzle fluidly communicating with a distal portion of the combustion chamber.

[0564] 3. The method of any clause herein, comprising: supplying at least a portion of the fuel to the combustion chamber through the conditioning conduit.

[0565] 4. The method of any clause herein, comprising: supplying at least a portion of the fuel to the combustion chamber through a conditioning conduit inlet disposed about a proximal portion of the conditioning conduit, the conditioning conduit inlet being oblique to the conditioning conduit.

[0566] 5. The method of any clause herein, comprising: circulating at least a portion of the combustion gas through a conditioning conduit inlet disposed about a proximal portion of the conditioning conduit, the conditioning conduit inlet being oblique to the conditioning conduit.

[0567] 6. The method of any clause herein, comprising: circulating at least a portion of the combustion gas through a recirculation pathway, the recirculation pathway providing fluid communication from a proximal portion of the combustion chamber to a proximal portion of the conditioning conduit. [0568] 7. The method of any clause herein, wherein the recirculation pathway comprises a hot-side heat exchanger and a recirculation eductor, the hot-side heat exchanger fluidly communicating with a proximal portion of the combustion chamber and the recirculation eductor fluidly communicating with a downstream portion of the hot-side heat exchanger and a proximal portion of the conditioning conduit and/or a distal portion of the combustion chamber.

[0569] 8. The method of any clause herein, comprising: combusting at least a portion of the combustion gas circulating through the recirculation pathway.

[0570] 9. The method of any clause herein, comprising: circulating from about 10% to about 90% of the combustion gas through the conditioning conduit and/or the combustion chamber; and introducing a balance of the combustion gas as intake air through an intake air pathway.

[0571] 10. The method of any clause herein, comprising: discharging a remainder of the combustion gas from the recirculation pathway as exhaust gas through the exhaust pathway fluidly communicating with the recirculation pathway upstream from the intake air pathway.

[0572] 11. The method of any clause herein, wherein the remainder of the combustion gas being discharged from the recirculation pathway as exhaust gas comprises from about 10% to about 90% of the combustion gas, or from about 30% to about 70% of the combustion gas, or from about 40% to about 60% of the combustion gas.

[0573] 12. The method of any clause herein, comprising: circulating from about 30% to about 70% of the combustion gas through the conditioning conduit and/or the combustion chamber, or circulating from about 40% to about 60% of the combustion gas through the conditioning conduit and/or the combustion chamber.

[0574] 13. The method of any clause herein, wherein the intake air being introduced through an intake air pathway comprises from about 10% to about 90% of the combustion gas.

[0575] 14. The method of any clause herein, comprising: supplying a cooling fluid to a cooling jacket disposed within an annular combustion chamber wall, the cooling fluid cooling the combustion chamber.

[0576] 15. The method of any clause herein, comprising: the cooling jacket fluidly communicating with an intake air pathway and the cooling fluid comprising intake air; the cooling jacket fluidly communicating with a recirculation pathway and the cooling fluid comprising combustion gas; or the cooling jacket fluidly communicating with a working- fluid pathway and the cooling fluid comprising an engine-working fluid.

[0577] 16. The method of any clause herein, comprising: supplying combustion gas and/or intake air to the combustion chamber at least in part through a plurality of

conditioning pathways disposed about a proximal, medial, and/or axial portion of the combustion chamber, the conditioning pathways providing fluid communication between the combustion chamber and the conditioning conduit.

[0578] 17. The method of any clause herein, comprising: swirling combustion gas and/or intake air into the conditioning conduit through a plurality of conditioning conduit inlets disposed about a proximal portion of the conditioning conduit, the plurality of conditioning conduit inlets oriented oblique to the conditioning conduit.

[0579] 18. The method of any clause herein, comprising: swirling intake air into the conditioning conduit through a motive pathway fluidly communicating with the conditioning conduit, the motive pathway oriented oblique to the conditioning conduit; and swirling combustion gas into the conditioning conduit through an eduction pathway fluidly

communicating with the conditioning conduit, the eduction pathway being adjacent to the motive pathway and oriented oblique to the conditioning conduit.

[0580] 19. The method of any clause herein, comprising: swirling into the

conditioning conduit, intake air through a plurality of motive pathways and combustion gas through a plurality of eduction pathways, the plurality of motive pathways and the plurality of eduction pathways configured and arranged as eductive pathway couplets

circumferentially spaced about the conditioning conduit, the plurality of eductive pathway couplets oriented oblique to the conditioning conduit.

[0581] 20. The method of any clause herein, comprising: discharging combustion gas through a plurality of combustion chamber outlets disposed about a proximal portion of the combustion chamber, the plurality of combustion chamber outlets oriented oblique to the combustion chamber.

[0582] 21. The method of any clause herein, wherein swirling combustion gas through the conditioning conduit and swirling the combustion gas through the combustion chamber comprises providing a bidirectional coaxial vortex flow field.

[0583] 22. The method of any clause herein, wherein providing a bidirectional coaxial vortex flow field comprises: separating with the combustion chamber, an outward portion of the bidirectional coaxial vortex flow field from an inward portion of the bidirectional coaxial vortex flow field, the conditioning conduit defining a pathway for the outward portion of the bidirectional coaxial vortex flow field and the combustion chamber defining a pathway for the inward portion of the bidirectional coaxial vortex flow field.

[0584] 23. The method of any clause herein, comprising: conditioning a flow of combustion gas flowing through the conditioning conduit and/or the combustion chamber, the conditioning provided at least in part by one or more aerodynamic features disposed about at least a portion of an annular combustion chamber wall, an inward annular conditioning conduit wall, and/or an outward annular conditioning conduit wall.

[0585] 24. The method of any clause herein, wherein the one or more aerodynamic features comprises, a fin, a ridge, and/or a groove.

[0586] 25. The method of any clause herein, wherein conditioning the flow of combustion gas comprises swirling the combustion gas.

[0587] 26. The method of any clause herein, wherein conditioning the flow of combustion gas comprises providing a bidirectional coaxial vortex flow field.

[0588] 27. The method of any clause herein, wherein the one or more aerodynamic features comprises, a helical fin, a helical ridge, and/or a helical groove.

[0589] 28. The method of any clause herein, comprising: supplying fuel to the combustion chamber at least in part using one or more the fuel nozzles.

[0590] 29. The method of any clause herein, comprising: igniting fuel and/or combustion gas in the combustion chamber using a glow plug.

[0591] 30. The method of any clause herein, comprising: supplying fuel to the combustion chamber at least in part using one or more the fuel nozzles and igniting the supplied using the one or more fuel nozzles using a glow plug.

[0592] 31. The method of any clause herein, wherein combusting the fuel comprises a combustion time from 1 to 10 milliseconds or from 2 to 4 milliseconds.

[0593] 32. The method of any clause herein, wherein combusting the fuel comprises providing a lean combustion environment.

[0594] 33. The method of any clause herein, wherein the lean combustion

environment comprises an equivalence ratio of 0.6 to 1.0 or an equivalence ratio of 0.7 to 0.8.

[0595] 34. The method of any clause herein, wherein the lean combustion

environment comprises an air to fuel ratio of from 40: 1 to 90: 1 by mass, or from 55: 1 to 75: 1 by mass. [0596] 35. The method of any clause herein, wherein swirling the combustion gas through the conditioning conduit comprises providing a helical vortex and/or a spiral vortex, the spiral vortex converging proximally and/or the spiral vortex diverging proximally.

[0597] 36. The method of any clause herein, wherein swirling the combustion gas through the combustion chamber comprises providing a helical vortex and/or a spiral vortex, the spiral vortex converging proximally and/or the spiral vortex diverging proximally.

[0598] 37. The method of any clause herein, comprising: providing a flame and swirling the flame in the combustion chamber, the swirling generating a centripetal force, the centripetal force drawing the flame radially or concentrically inward and providing an annular combustion gas buffer circumferentially surrounding the flame, the annular combustion gas buffer disposed annularly between the flame and a combustion chamber wall.

[0599] 38. The method of any clause herein, wherein swirling the combustion gas through the combustion chamber comprises: providing a flame comprising a helical vortex and/or a spiral vortex, the spiral vortex converging proximally and/or the spiral vortex diverging proximally; and providing an annular combustion gas buffer circumferentially surrounding the flame, the annular combustion gas buffer comprising a helical vortex and/or a spiral vortex, the spiral vortex converging proximally and/or the spiral vortex diverging proximally.

[0600] 39. The method of any clause herein, comprising: heating a plurality of heat transfer regions according to the method of any clause herein.

[0601] 40. The method of any clause herein, comprising: circulating fluid according to the method of any clause herein ; or circulating combustion gas according to the method of any clause herein.

[0602] 41. The method of any clause herein, comprising: transferring heat between fluid streams according to the method of any clause herein.

[0603] 42. The method of any clause herein, comprising: recuperating heat from exhaust gas according to the method of any clause herein.

[0604] 43. The method of any clause herein, comprising: heating an engine-working fluid according to the method of any clause herein.

[0605] 44. The method of any clause herein, comprising: performing the method at least in part using the combustor body of any clause herein; and/or comprising: performing the method at least in part using the heater body of any clause herein. [0606] With respect to a fuel injector assembly, further aspects of the invention are provided by the subject matter of the following clauses:

[0607] 1. A fuel injector assembly, the fuel nozzle assembly defining an upstream end from which fuel enters and a downstream end through which fuel egresses, and further defining a reference centerline axis, the fuel nozzle assembly comprising: a body extended along a lateral direction from the upstream end to the downstream end, wherein a first fuel circuit is defined within the body, the first fuel circuit extended from the upstream end to the downstream end, and further wherein a second fuel circuit is extended within the body from the upstream end to the downstream end, the first fuel circuit and the second fuel circuit each separated along a circumferential direction relative to the reference centerline axis, and wherein the first fuel circuit is extended annularly within the body at the downstream end of the body, and further wherein the second fuel circuit is extended annularly within the body at the downstream end, wherein the second fuel circuit is spaced apart radially or concentrically inward of the first fuel circuit.

[0608] 2. The fuel injector assembly of any clause herein, wherein the first fuel circuit is extended annularly within the body at the downstream end and surrounding the second fuel circuit extended annularly at the downstream end.

[0609] 3. The fuel injector assembly of any clause herein, wherein the fuel injector assembly defines a lateral distance of the body extended from the downstream end to the upstream end, and wherein a portion of the lateral distance for which the first fuel circuit is extended annularly through the body and surrounding the second fuel circuit is greater than a portion of the later distance of the second fuel circuit extended annularly through the body.

[0610] 4. The fuel injector assembly of any clause herein, wherein the portion of the lateral distance for which the second fuel circuit is extended annularly through the downstream end of the body is 90% or less than the portion of the lateral distance of the body for which the first fuel circuit is extended annularly through the body at the downstream end.

[0611] 5. The fuel injector assembly of any clause herein, wherein the portion of the lateral distance for which the second fuel circuit is extended annularly through the downstream end of the body is 33% or greater than the portion of the lateral distance of the body for which the first fuel circuit is extended annularly through the body at the downstream end. [0612] 6. The fuel injector assembly of any clause herein, wherein the first fuel circuit and the second fuel circuit are each extended partly annularly through the body for a non-annular portion upstream of the downstream end of the body.

[0613] 7. The fuel injector assembly of any clause herein, wherein the first fuel circuit and the second fuel circuit each define a single passage through the body, wherein the passage is partly annular from the upstream end to a portion of the body at the downstream end.

[0614] 8. The fuel injector assembly of any clause herein, wherein the body defines a cylindrical portion, and further wherein the body defines a frustoconical portion at the downstream end.

[0615] 9. The fuel injector assembly of any clause herein, wherein the cylindrical portion defines a plurality of threads at an outside surface of the body.

[0616] 10. The fuel injector assembly of any clause herein, wherein the body further defines a plurality of fuel injection apertures at the frustoconical portion of the body, wherein the plurality of fuel injection apertures are in fluid communication with the first fuel circuit to provide a first flow of fuel therethrough.

[0617] 11. The fuel injector assembly of any clause herein, wherein the plurality of fuel injection apertures defines a jet-in-crossflow arrangement through the frustoconical portion of the body.

[0618] 12. The fuel injector assembly of any clause herein, wherein the body defines the plurality of fuel injection apertures as a plurality of individual orifices through which individual streams of the first flow of fuel egress the body.

[0619] 13. The fuel injector assembly of any clause herein, wherein the body further defines an annular fuel injection opening through the body in fluid communication with the second fuel circuit to provide a second flow of fuel therethrough.

[0620] 14. The fuel injector assembly of any clause herein, wherein the fuel injection opening is defined through the downstream end of the body radially or concentrically inward of the plurality of fuel injection apertures.

[0621] 15. The fuel injector assembly of any clause herein, wherein the body defines a converging portion at a portion of the downstream end of the body at which the second fuel circuit is extended annularly therethrough, wherein the second fuel circuit converges toward the reference centerline axis. [0622] 16. The fuel injector assembly of any clause herein, wherein the body defines a diverging portion downstream of the converging portion.

[0623] 17. The fuel injector assembly of any clause herein, wherein the body further defines a vane structure at the downstream end portion of body at which the second fuel circuit is defined annularly therethrough.

[0624] 18. The fuel injector assembly of any clause herein, further comprising an igniter extended through the body, and protruding therefrom at the downstream end of the body.

[0625] 19. The fuel injector assembly of any clause herein, wherein the body defines an outlet port concentric to the reference centerline axis, and further wherein a cavity is defined extended from the upstream end of the body to the downstream end of the body radially or concentrically inward of the first fuel circuit and the second fuel circuit, and wherein the igniter is disposed through the body via the cavity and the outlet port.

[0626] 20. The fuel injector assembly of any clause herein, wherein the body further defines a third circuit extended radially or concentrically inward of the second fuel circuit.

[0627] 21. The fuel injector assembly of any clause herein, wherein the body further defines a plurality of apertures radially or concentrically inward of the fuel injection opening, and further wherein the plurality of apertures is in fluid communication with the third circuit.

[0628] 22. The fuel injector assembly of any clause herein, wherein the body further defines a fluid inlet opening through a cavity defined inward of the first fuel circuit and the second fuel circuit, wherein the fluid inlet opening is in fluid communication with the third circuit to provide a flow of fluid therethrough.

[0629] 23. The fuel injector assembly of any clause herein, wherein the fuel injector assembly is configured to receive a first flow fuel through the first fuel circuit and a second flow of fuel through the second fuel circuit, and wherein the first flow of fuel defines a gaseous fuel, and wherein the second flow of fuel defines a liquid or gaseous fuel.

[0630] 24. The fuel injector assembly of any clause herein, wherein the fuel injector assembly is configured to egress a flow of fluid through a plurality of apertures defined through the body radially between the fuel injection opening and an igniter extended therethrough, and wherein the flow of fluid provides a film of fluid at the igniter.

[0631] 25. The fuel injector assembly of any clause herein, wherein the body defines a fastening port extended co-directional to the reference centerline axis, wherein the fastening port disposes the fuel injector assembly co-axial to a combustion chamber centerline. [0632] With respect to a hot-side heat exchanger body, further aspects of the invention are provided by the subject matter of the following clauses:

[0633] 1. A hot-side heat exchanger body, comprising: a plurality of heating fluid pathways concentrically spiraling about an inlet plenum, respective ones of the plurality of heating fluid pathways comprising a spiral pathway and the inlet plenum fluidly

communicating with the plurality of heating fluid pathways; and a plurality of heat transfer regions, wherein respective ones of the plurality of heat transfer regions have a heat transfer relationship with a corresponding semiannular portion of the plurality of heating fluid pathways.

[0634] 2. The hot-side heat exchanger body of any clause herein, wherein the plurality of heating fluid pathways respectively comprise an inlet disposed at a respective circumferential position about the inlet plenum.

[0635] 3. The hot-side heat exchanger body of any clause herein, comprising: an outlet plenum fluidly communicating with the plurality of heating fluid pathways.

[0636] 4. The hot-side heat exchanger body of any clause herein, wherein the plurality of heating fluid pathways respectively comprise a plurality of outlets disposed at a respective circumferential position about the outlet plenum.

[0637] 5. The hot-side heat exchanger body of any clause herein, wherein the plurality of heat transfer regions are circumferentially spaced about the hot-side heat exchanger body.

[0638] 6. The hot-side heat exchanger body of any clause herein, wherein the plurality of heating fluid pathways pass adjacent to at least some of the plurality of heat transfer regions in circumferential series, the plurality of heating fluid pathways having a thermally conductive relationship with the at least some of the plurality of heat transfer regions, the circumferential series of a respective one of the plurality of heating fluid pathways having a sequence depending at least in part on a circumferential location of an inlet to the respective one of the plurality of heating fluid pathways.

[0639] 7. The hot-side heat exchanger body of any clause herein, comprising: a first heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a first circumferential series, the first circumferential series comprising a first heat transfer region followed by a second heat transfer region followed by a third heat transfer region. [0640] 8. The hot-side heat exchanger body of any clause herein, the first

circumferential series comprising a fourth heat transfer region preceded by the third heat transfer region.

[0641] 9. The hot-side heat exchanger body of any clause herein, comprising: a second heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a second circumferential series, the second circumferential series comprising the second heat transfer region followed by the third heat transfer region followed by the fourth heat transfer region.

[0642] 10. The hot-side heat exchanger body of any clause herein, the second circumferential series comprising the first heat transfer region preceded by the fourth heat transfer region.

[0643] 11. The hot-side heat exchanger body of any clause herein, comprising: a third heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a third circumferential series, the third circumferential series comprising the third heat transfer region followed by the fourth heat transfer region followed by the first heat transfer region.

[0644] 12. The hot-side heat exchanger body of any clause herein, the third circumferential series comprising the second heat transfer region preceded by the first heat transfer region.

[0645] 13. The hot-side heat exchanger body of any clause herein, comprising: a fourth heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a fourth circumferential series, the fourth circumferential series comprising the fourth heat transfer region followed by the first heat transfer region followed by the second heat transfer region.

[0646] 14. The hot-side heat exchanger body of any clause herein, the fourth circumferential series comprising the third heat transfer region preceded by the second heat transfer region.

[0647] 15. The hot-side heat exchanger body of any clause herein, comprising a first heating fluid pathway fluidly communicating with an outlet plenum at a first circumferential location of from about 0 to 30 degrees about a circumferential axis of the hot-side heat exchanger. [0648] 16. The hot-side heat exchanger body of any clause herein, comprising a second heating fluid pathway fluidly communicating with an outlet plenum at a second circumferential location of from about 90 to 120 degrees about the circumferential axis.

[0649] 17. The hot-side heat exchanger body of any clause herein, comprising a third heating fluid pathway fluidly communicating with an outlet plenum at a third circumferential location of from about 180 to 210 degrees about the circumferential axis.

[0650] 18. The hot-side heat exchanger body of any clause herein, comprising a fourth heating fluid pathway fluidly communicating with an outlet plenum at a fourth circumferential location of from about 270 to 300 degrees about the circumferential axis.

[0651] 19. The hot-side heat exchanger body of any clause herein, comprising a first heat transfer region disposed about a first circumferential segment or sector of the plurality of heating fluid pathways, the first circumferential segment or sector being from about 270 to about 360 degrees about the circumferential axis.

[0652] 20. The hot-side heat exchanger body of any clause herein, comprising a second heat transfer region disposed about a second circumferential segment or sector of the plurality of heating fluid pathways, the second circumferential segment or sector being from about 180 to about 270 degrees about the circumferential axis.

[0653] 21. The hot-side heat exchanger body of any clause herein, comprising a third heat transfer region disposed about a third circumferential segment or sector of the plurality of heating fluid pathways, the third circumferential segment or sector being from about 90 to about 180 degrees about the circumferential axis.

[0654] 22. The hot-side heat exchanger body of any clause herein, comprising a fourth heat transfer region disposed about a fourth circumferential segment or sector of the plurality of heating fluid pathways, the fourth circumferential segment or sector being from about 0 to about 90 degrees about the circumferential axis.

[0655] 23. The hot-side heat exchanger body of any clause herein, comprising from 4 to 32 heating fluid pathways, or from 8 to 24 heating fluid pathways, or from 12 to 20 heating fluid pathways, or 16 heating fluid pathways.

[0656] 24. The hot-side heat exchanger body of any clause herein, comprising from 2 to 8 heat transfer regions circumferentially spaced about the hot-side heat exchanger body, or comprising four heat transfer regions circumferentially spaced about the hot-side heat exchanger body. [0657] 25. The hot-side heat exchanger body of any clause herein, comprising: an outlet plenum circumferentially surrounding the plurality of heating fluid pathways, the outlet plenum fluidly communicating with the plurality of heating fluid pathways; and/or an inlet plenum circumferentially surrounded by the plurality of heating fluid pathways, the inlet plenum fluidly communicating with the plurality of heating fluid pathways.

[0658] 26. The hot-side heat exchanger body of any clause herein, comprising at least some of the plurality of heating fluid pathways having a substantially uniform cross- sectional width and/or a substantially uniform cross-sectional area along at least a portion of a length of respective ones of the at least some of the plurality of heating fluid pathways.

[0659] 27. The hot-side heat exchanger body of any clause herein, wherein a respective one of the plurality of heating fluid pathways comprises a spiral arc, the spiral arc corresponding to at least a portion of an Archimedean spiral, a Cornu spiral, a Fermat’s spiral, a hyperbolic spiral, a logarithmic spiral, a Fibonacchi Spiral, an involute, and/or a squircular spiral.

[0660] 28. The hot-side heat exchanger body of any clause herein, wherein the plurality of heating fluid pathways comprises a plurality of spiral arc inverse pairs, respective ones of the spiral arc inverse pairs comprising a parabolic spiral.

[0661] 29. The hot-side heat exchanger body of any clause herein, wherein the plurality of heating fluid pathways comprise a squircular spiral.

[0662] 30. The hot-side heat exchanger body of any clause herein, wherein at least a portion of the squircular spiral comprises an arc corresponding to a squircle.

[0663] 31. The hot-side heat exchanger body of any clause herein, wherein a respective one of the plurality of heating fluid pathways has an arc length of from 180 degrees to 1260 degrees.

[0664] 32. The hot-side heat exchanger body of any clause herein, wherein the respective one of the plurality of heating fluid pathways has an arc length of from 180 degrees to 450 degrees, or from 315 degrees to 765 degrees.

[0665] 33. The hot-side heat exchanger body of any clause herein, wherein the respective one of the plurality of heating fluid pathways has an arc length of from 675 degrees to 1260 degrees.

[0666] 34. The hot-side heat exchanger body of any clause herein, wherein the plurality of heating fluid pathways comprise circumferentially adjacent pathways. [0667] 35. The hot-side heat exchanger body of any clause herein, wherein a respective one of the plurality of heating fluid pathways comprises a heating fluid pathway- inlet oriented oblique to the inlet plenum.

[0668] 36. The hot-side heat exchanger body of any clause herein, wherein respective ones of the plurality of heat transfer regions comprise a heat input region, at least one heat extraction region, and a plurality of radially or concentrically adjacent semiannular working-fluid pathways fluidly communicating between the heat input region and the at least one heat extraction region.

[0669] 37. The hot-side heat exchanger body of any clause herein, comprising respective ones of the plurality of heating fluid pathways disposed axially adjacent to corresponding respective ones of the plurality of radially or concentrically adjacent semiannular working-fluid pathways, respective ones of the plurality of heating fluid pathways having a thermally conductive relationship with corresponding respective ones of the plurality of radially or concentrically adjacent semiannular working-fluid pathways.

[0670] 38. The hot-side heat exchanger body of any clause herein, configured according to the working-fluid body of any clause herein.

[0671] 39. The hot-side heat exchanger body of any clause herein, wherein the inlet plenum comprises a combustion chamber.

[0672] 40. The hot-side heat exchanger body of any clause herein, wherein respective ones of the plurality of heating fluid pathways define respective ones of a plurality of inlets, the plurality of inlets circumferentially spaced about a perimeter of the combustion chamber, respective ones of the plurality of inlets defining respective ones of a plurality of combustion chamber outlets.

[0673] 41. The hot-side heat exchanger body of any clause herein, comprising: an outlet plenum fluidly communicating with the plurality of heating fluid pathways, the outlet plenum comprising a recirculation annulus.

[0674] 42. The hot-side heat exchanger body of any clause herein, wherein the hot- side heat exchanger body comprises an additively manufactured monolithic body or an additively manufactured monolithic body-segment.

[0675] 43. The hot-side heat exchanger body of any clause herein, comprising a combustor body configured according to any clause herein.

[0676] 44. The hot-side heat exchanger body of any clause herein, comprising: an eductor body of any clause herein. [0677] 45. The hot-side heat exchanger body of any clause herein, comprising: a heat recuperator body configured according to any clause herein.

[0678] 46. The hot-side heat exchanger body of any clause herein, comprising: a working-fluid body configured according to any clause herein.

[0679] 47. The hot-side heat exchanger body of any clause herein, comprising: a regenerator body configured according to any clause herein.

[0680] 48. The hot-side heat exchanger body of any clause herein, wherein the hot- side heat exchanger body defines at least a portion of an engine assembly of any clause herein.

[0681] 49. The hot-side heat exchanger body of any clause herein, wherein the hot- side heat exchanger body defines at least a portion of a combustor body of any clause herein.

[0682] 50. The hot-side heat exchanger body of any clause herein, wherein the hot- side heat exchanger body defines at least a portion of a heater body of any clause herein.

[0683] 51. The hot-side heat exchange body of any clause herein, wherein the hot- side heat exchanger body defines at least a portion of a closed-cycle engine.

[0684] 52. The hot-side heat exchanger body of any clause herein, wherein the hot- side heat exchanger body is configured to perform a method of any clause herein.

[0685] 53. The hot-side heat exchanger body of any clause herein, comprising a monolithic heat exchanger body configured according to any subsequent clause.

[0686] 54. A monolithic heat exchanger body, comprising: a plurality of heating walls configured and arranged in an array of spirals or spiral arcs relative to a longitudinal axis, wherein adjacent portions of the plurality of heating walls respectively define a corresponding plurality of heating fluid pathways therebetween; and a plurality of combustion fins circumferentially spaced about a perimeter of an inlet plenum, wherein the inlet plenum comprises or fluidly communicates with a combustion chamber and the plurality of heating fluid pathways fluidly communicate with the inlet plenum; wherein the plurality of combustion fins occupy a radially or concentrically inward portion of the monolithic heat exchanger body, and wherein the plurality of heating fluid pathways have a heat transfer relationship with a heat sink disposed about a radially or concentrically outward portion of the monolithic heat exchanger body; and wherein a plurality of conduction breaks disposed radially or concentrically outward relative to the plurality of combustion fins at least partially inhibit heat conduction from the plurality of combustion fins to the plurality of heating walls. [0687] 55. The monolithic heat exchanger body of any clause herein, wherein at least a portion of the plurality of conduction breaks are defined by respective downstream portions of the plurality of combustion fins being configured and arranged in spatial separation from corresponding upstream portions of the plurality of heating walls.

[0688] 56. The monolithic heat exchanger body of any clause herein, wherein the plurality of conduction breaks respectively comprise a gap or space between a combustion fin and corresponding heating wall.

[0689] 57. The monolithic heat exchanger body of any clause herein, wherein the plurality of conduction breaks respectively comprise a difference in a material property, a material composition, and/or a material structure, relative to the plurality of combustion fins and/or the plurality of heating walls.

[0690] 58. The monolithic heat exchanger body of any clause herein, wherein the plurality of conduction breaks comprise one or more of: a mesh structure, a three-dimensional lattice structure, or a porous medium structure.

[0691] 59. The monolithic heat exchanger body of any clause herein, wherein the plurality of conduction breaks comprise respective regions of the heating walls having unsintered or partially sintered powder material resulting from an additive manufacturing process used to form the monolithic heat exchanger body.

[0692] 60. The monolithic heat exchanger body of any clause herein, wherein the plurality of combustion fins are configured and arranged in an array of spirals or spiral arcs relative to the longitudinal axis.

[0693] 61. The monolithic heat exchanger body of any clause herein, wherein the plurality of combustion fins are monolithically integrated with corresponding ones of the plurality of heating walls.

[0694] 62. The monolithic heat exchanger body of any clause herein, wherein the heat sink comprises a plurality of working-fluid bodies, the plurality of working-fluid bodies comprising a plurality of working-fluid pathways that have a heat transfer relationship with the plurality of heating fluid pathways.

[0695] 63. The monolithic heat exchanger body of any clause herein, wherein the heat sink comprises a plurality of heat transfer regions circumferentially spaced about the monolithic heat exchanger body. [0696] 64. The monolithic heat exchanger body of any clause herein, comprising from 2 to 8 heat transfer regions circumferentially spaced about the monolithic heat exchanger body.

[0697] 65. The monolithic heat exchanger body of any clause herein, wherein the plurality of heating fluid pathways are configured and arranged to pass adjacent to at least some of the plurality of heat transfer regions in a circumferential series, the circumferential series of a respective one of the plurality of heating fluid pathways having a sequence depending at least in part on a circumferential location at which the respective one of the plurality of heating fluid pathways fluidly communicated with the inlet plenum.

[0698] 66. The monolithic heat exchanger body of any clause herein, comprising: a first heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a first circumferential series, the first circumferential series beginning with a first heat transfer region, and followed by a second heat transfer region, and followed by a third heat transfer region; and a second heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a second circumferential series, the second circumferential series beginning with the second heat transfer region, and followed by the third heat transfer region, and followed by a fourth heat transfer region.

[0699] 67. The monolithic heat exchanger body of any clause herein, wherein the plurality of heat transfer regions occupy a region of the monolithic heat exchanger body disposed radially or concentrically outward from the plurality of conduction breaks.

[0700] 68. The monolithic heat exchanger body of any clause herein, wherein the plurality of heat transfer regions respectively comprise an array of working-fluid pathways that have a heat transfer relationship with the plurality of heating fluid pathways.

[0701] 69. The monolithic heat exchanger body of any clause herein, wherein at least a portion of the working-fluid pathways are monolithically defined within respective ones of the plurality of heating walls.

[0702] 70. The monolithic heat exchanger body of any clause herein, wherein:

[0703] the combustion fins are configured and arranged to operate at a sufficiently high temperature for stable combustion within the portion of the heating fluid pathways disposed upstream from the conduction breaks.

[0704] 71. The monolithic heat exchanger body of any clause herein, wherein the conduction breaks are configured and arranged to reduce heat conduction from the combustion fins by an amount sufficient for the conduction fins to remain at a sufficiently high temperature to for fuel combustion to approach complete combustion within the portion of the heating fluid pathways disposed upstream from the conduction breaks.

[0705] 72. The monolithic heat exchanger body of any clause herein, wherein the conduction breaks are located at a distance along the heating fluid pathways to allow for fuel combustion to approach complete combustion within the portion of the heating fluid pathways disposed upstream from the conduction breaks.

[0706] 73. The monolithic heat exchanger body of any clause herein, wherein the plurality of heating walls, and/or the plurality of combustion fins, have a configuration and arrangement corresponding to at least a portion of one or more of the following: an

Archimedean spiral, a Cornu spiral, a Fermat’s spiral, a hyperbolic spiral, a logarithmic spiral, a Fibonacchi spiral, an involute, or a squircular spiral.

[0707] 74. The monolithic heat exchanger body of any clause herein, comprising: a combustion chamber disposed annularly about an axis; and a conditioning conduit circumferentially surrounding the combustion chamber, the conditioning conduit fluidly communicating with the combustion chamber at a distal portion of the combustion chamber.

[0708] 75. The monolithic heat exchanger body of any clause herein, comprising: an eduction pathway fluidly communicating with an annulus, the eduction pathway oriented oblique to the annulus; and a motive pathway fluidly communicating with the annulus, the motive pathway being adjacent to the eduction pathway and oriented oblique to the annulus.

[0709] 76. The monolithic heat exchanger body of any clause herein, comprising: an intake air pathway fluidly communicating with a conditioning conduit, the intake air pathway oriented oblique to the conditioning conduit; and a recirculation pathway fluidly

communicating with the conditioning conduit, the recirculation pathway being adjacent to the intake air pathway and oriented oblique to the conditioning conduit.

[0710] 77. The monolithic heat exchanger body of any clause herein, comprising: a heat recuperator body, the heat recuperator body comprising: a first intake annulus disposed annularly about an axis, a first discharge annulus disposed annularly about the axis, and a plurality of first pathways spiraling annularly about the axis, the plurality of first pathways comprising: a plurality of first pathway-inlets fluidly communicating annularly about the first intake annulus, and a plurality of first pathway-outlets fluidly communicating annularly about the first discharge annulus; and a second intake annulus disposed annularly about the axis, a second discharge annulus disposed annularly about the axis, and a plurality of second pathways spiraling annularly about the axis, respective ones of the plurality of second pathways altematingly adjacent to respective ones of the plurality of first pathways, the plurality of second pathways comprising: a plurality of second pathway -inlets fluidly communicating annularly about the second intake annulus, and a plurality of second pathway-outlets fluidly communicating annularly about the second discharge annulus.

[0711] 78. The monolithic heat exchanger body of any clause herein, comprising: a plurality of heat transfer regions, respective ones of the plurality of heat transfer regions comprising a plurality of working-fluid pathways fluidly communicating between a heat input region and a heat extraction region.

[0712] 79. The monolithic heat exchanger body of any clause herein, comprising: comprising: a regenerator conduit; and a plurality of fin arrays adjacently disposed within the regenerator conduit and respectively supported by the regenerator conduit in spaced relation to one another, the spaced relation of the plurality of fin arrays defining a gap longitudinally separating adjacent ones of the plurality of fin arrays.

[0713] With respect to a method of heating a plurality of heat transfer regions, further aspects of the invention are provided by the subject matter of the following clauses:

[0714] 1. A method of heating a plurality of heat transfer regions, the method comprising: flowing a first heat transfer fluid through a plurality of heating fluid pathways concentrically spiraling about an inlet plenum, respective ones of the plurality of heating fluid pathways defining a spiral pathway; and transferring heat from the first heat transfer fluid to a plurality of heat transfer regions, wherein respective ones of the plurality of heat transfer regions have a heat transfer relationship with a corresponding semiannular portion of the plurality of heating fluid pathways.

[0715] 2. The method of any clause herein, wherein transferring heat from the first heat transfer fluid to a plurality of heat transfer regions comprises: transferring heat from the plurality of heating fluid pathways to at least some of the plurality of heat transfer regions in circumferential series, the circumferential series of a respective one of the plurality of heating fluid pathways having a sequence depending at least in part on a circumferential location of an inlet to the respective one of the plurality of heating fluid pathways.

[0716] 3. The method of any clause herein, wherein transferring heat from the first heat transfer fluid to a plurality of heat transfer regions comprises: transferring heat from the first heat transfer fluid flowing through a first heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a first circumferential series, the first circumferential series comprising a first heat transfer region followed by a second heat transfer region followed by a third heat transfer region.

[0717] 4. The method of any clause herein, the first circumferential series comprising a fourth heat transfer region preceded by the third heat transfer region.

[0718] 5. The method of any clause herein, wherein transferring heat from the first heat transfer fluid to a plurality of heat transfer regions comprises: transferring heat from the first heat transfer fluid flowing through a second heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a second circumferential series, the second circumferential series comprising the second heat transfer region followed by the third heat transfer region followed by the first heat transfer region.

[0719] 6. The method of any clause herein, the second circumferential series comprising a fourth heat transfer region preceded by the third heat transfer region and followed by the first heat transfer region.

[0720] 7. The method of any clause herein, wherein transferring heat from the first heat transfer fluid to a plurality of heat transfer regions comprises: transferring heat from the first heat transfer fluid flowing through a third heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a third circumferential series, the third circumferential series comprising the third heat transfer region followed by the first heat transfer region followed by the second heat transfer region.

[0721] 8. The method of any clause herein, the third circumferential series comprising a fourth heat transfer region preceded by the third heat transfer region and followed by the first heat transfer region.

[0722] 9. The method of any clause herein, wherein transferring heat from the first heat transfer fluid to a plurality of heat transfer regions comprises: transferring heat from the first heat transfer fluid flowing through a fourth heating fluid pathway passing adjacent to at least some of the plurality of heat transfer regions in a fourth circumferential series, the fourth circumferential series comprising a fourth heat transfer region followed by the first heat transfer region followed by the second heat transfer region.

[0723] 10. The method of any clause herein, the fourth circumferential series comprising the third heat transfer region preceded by the second heat transfer region and followed by the fourth heat transfer region.

[0724] 11. The method of any clause herein, comprising: discharging the first heat transfer from the first heating fluid pathway to an outlet plenum, the first heating fluid pathway fluidly communicating obliquely with the outlet plenum at a first circumferential location of from about 0 to 30 degrees about the circumferential axis of the hot-side heat exchanger.

[0725] 12. The method of any clause herein, comprising: discharging the first heat transfer from the second heating fluid pathway to an outlet plenum, the second heating fluid pathway fluidly communicating obliquely with the outlet plenum at a second circumferential location of from about 90 to 120 degrees about the circumferential axis.

[0726] 13. The method of any clause herein, comprising: discharging the first heat transfer from the third heating fluid pathway to an outlet plenum, the third heating fluid pathway fluidly communicating obliquely with the outlet plenum at a third circumferential location of from about 180 to 210 degrees about the circumferential axis.

[0727] 14. The method of any clause herein, comprising: discharging the first heat transfer from a fourth heating fluid pathway to an outlet plenum, the fourth heating fluid pathway fluidly communicating obliquely with the outlet plenum at a fourth circumferential location of from about 270 to 300 degrees about the circumferential axis.

[0728] 15. The method of any clause herein, comprising: transferring heat from the first heat transfer fluid to the first heat transfer region, the first heat transfer region disposed at a first circumferential location of from about 270 to about 360 degrees about the circumferential axis.

[0729] 16. The method of any clause herein, comprising: transferring heat from the first heat transfer fluid to the second heat transfer region, the second heat transfer region disposed at a second circumferential location of from about 180 to about 270 degrees about the circumferential axis.

[0730] 17. The method of any clause herein, comprising: transferring heat from the first heat transfer fluid to the third heat transfer region, the third heat transfer region disposed at a third circumferential location of from about 90 to about 180 degrees.

[0731] 18. The method of any clause herein, comprising: transferring heat from the first heat transfer fluid to a fourth heat transfer region, the fourth heat transfer region disposed at a fourth circumferential location of from about 0 to about 90 degrees about the

circumferential axis.

[0732] 19. The method of any clause herein, comprising: flowing the first heat transfer fluid through from 4 to 32 heating fluid pathways, or from 8 to 24 heating fluid pathways, or from 12 to 20 heating fluid pathways, or 16 heating fluid pathways. [0733] 20. The method of any clause herein, comprising: transferring heat from the first heat transfer fluid to from 2 to 8 heat transfer regions circumferentially spaced about the hot-side heat exchanger body; or transferring heat from the first heat transfer fluid to four heat transfer regions circumferentially spaced about the hot-side heat exchanger body.

[0734] 21. The method of any clause herein, comprising: discharging the first heat transfer fluid to an outlet plenum circumferentially surrounding the plurality of heating fluid pathways, the outlet plenum fluidly communicating with the plurality of heating fluid pathways.

[0735] 22. The method of any clause herein, wherein respective ones of the plurality of heat transfer regions comprise a heat input region, at least one heat extraction region, and a plurality of radially or concentrically adjacent semiannular working-fluid pathways fluidly communicating between the heat input region and the at least one heat extraction region.

[0736] 23. The method of any clause herein, comprising: transferring heat from the first heat transfer fluid to a second heat transfer fluid, the second heat transfer fluid being in the plurality of radially or concentrically adjacent semiannular working-fluid pathways corresponding to respective ones of the plurality of heat transfer regions, respective ones of the plurality of radially or concentrically adjacent semiannular working-fluid pathways having a thermally conductive relationship with a semiannular portion of corresponding respective ones of the plurality of heating fluid pathways, the semiannular portion

corresponding to the respective heat transfer region.

[0737] 24. The method of any clause herein, comprising respective ones of the plurality of heating fluid pathways disposed axially adjacent to corresponding respective ones of the plurality of radially or concentrically adjacent semiannular working-fluid pathways.

[0738] 25. The method of any clause herein, comprising heating a plurality of heat transfer regions according to the method of any clause herein.

[0739] 26. The method of any clause herein, wherein the inlet plenum comprises a combustion chamber and the first heat transfer fluid comprises combustion gas.

[0740] 27. The method of any clause herein, comprising: flowing combustion gas through the plurality of heating fluid pathways, the combustion gas passing into the plurality of heating fluid pathways through a plurality of inlets circumferentially spaced about the combustion chamber, the plurality of inlets comprising combustion chamber outlets.

[0741] 28. The method of any clause herein, comprising: discharging the first heat transfer fluid to an outlet plenum fluidly communicating with the plurality of heating fluid pathways, the outlet plenum comprising a recirculation annulus and the first heat transfer fluid comprising a combustion gas.

[0742] 29. The method of any clause herein, comprising: combusting a fuel in a combustor body, the combusting providing combustion gas.

[0743] 30. The method of any clause herein, comprising: combusting the fuel according to the method of any clause herein.

[0744] 31. The method of any clause herein, comprising: circulating fluid according to the method of any clause herein; or circulating combustion gas according to the method of any clause herein.

[0745] 32. The method of any clause herein, comprising: transferring heat between fluid streams according to the method of any clause herein.

[0746] 33. The method of any clause herein, comprising: recuperating heat from exhaust gas according to the method of any clause herein.

[0747] 34. The method of any clause herein, comprising: heating an engine-working fluid according to the method of any clause herein.

[0748] 35. The method of any clause herein, comprising: regenerating heat in an engine-working fluid according to the method of any clause herein.

[0749] 36. The method of any clause herein, comprising: performing the method at least in part using the hot-side heat exchanger body of any clause herein; and/or comprising: performing the method at least in part using the heater body of any clause herein.

[0750] With respect to a working-fluid body, further aspects of the invention are provided by the subject matter of the following clauses:

[0751] 1. A working-fluid body, comprising: a plurality of heat transfer regions, respective ones of the plurality of heat transfer regions comprising a plurality of working- fluid pathways fluidly communicating between a heat input region and a heat extraction region.

[0752] 2. The working-fluid body of any clause herein, wherein the plurality of working-fluid pathways comprise a plurality of radially or concentrically adjacent semiannular spiral pathways.

[0753] 3. The working-fluid body of any clause herein, wherein the plurality of working-fluid pathways comprise a plurality of axially adjacent semiannular spiral pathways.

[0754] 4. The working-fluid body of any clause herein, comprising: the heat input region and the heat extraction region. [0755] 5. The working-fluid body of any clause herein, wherein the heat extraction region comprises a first heat extraction region and a second heat extraction region.

[0756] 6. The working-fluid body of any clause herein, comprising: the heat extraction region circumferentially surrounding the heat input region.

[0757] 7. The working-fluid body of any clause herein, comprising: the heat extraction region circumferentially adjacent to the heat input region.

[0758] 8. The working-fluid body of any clause herein, wherein the plurality of working-fluid pathways comprise: a first plurality of working-fluid pathways fluidly communicating between the heat input region and a first heat extraction region; and a second plurality of working-fluid pathways fluidly communicating between the heat input region and a second heat extraction region.

[0759] 9. The working-fluid body of any clause herein, comprising: a first heat transfer region, the first heat transfer region comprising a first plurality of working-fluid pathways, the first plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; a second heat transfer region, the second heat transfer region comprising a second plurality of working-fluid pathways, the second plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; wherein respective ones of the first plurality of working-fluid pathways are circumferentially adjacent to respective ones of the second plurality of working-fluid pathways.

[0760] 10. The working-fluid body of any clause herein, comprising: a radially or concentrically inward working-fluid pathway and a radially midward working-fluid pathway, the radially or concentrically inward working-fluid pathway being circumferentially adjacent to the radially midward working-fluid pathway.

[0761] 11. The working-fluid body of any clause herein, comprising: a radially or concentrically outward working-fluid pathway and a radially or concentrically midward working-fluid pathway, the radially or concentrically outward working-fluid pathway being circumferentially adjacent to the radially or concentrically midward working-fluid pathway.

[0762] 12. The working-fluid body of any clause herein, comprising: a radially or concentrically outward one of the first plurality of working-fluid pathways, the radially or concentrically outward one of the first plurality of working-fluid pathways circumferentially terminating a spiral array of working-fluid pathways, the spiral array of working-fluid pathways defined by at least some of the plurality of working-fluid pathways, the spiral array of working-fluid pathways diverging radially or concentrically outward.

[0763] 13. The working-fluid body of any clause herein, comprising: a radially or concentrically inward one of the first plurality of working-fluid pathways, the radially or concentrically inward one of the first plurality of working-fluid pathways circumferentially initiating a spiral array of working-fluid pathways defined by at least some of the plurality of working-fluid pathways, the spiral array of working-fluid pathways diverging radially or concentrically outward.

[0764] 14. The working-fluid body of any clause herein, comprising: a first heat transfer region, the first heat transfer region comprising a first plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways, the first plurality of working-fluid pathways comprising: a first plurality of counter-current working-fluid pathways and a first plurality of co-current working-fluid pathways, respective ones of the first plurality of counter-current working-fluid pathways being circumferentially adjacent to respective ones of the first plurality of co-current working-fluid pathways.

[0765] 15. The working-fluid body of any clause herein, comprising: a first heat transfer region, the first heat transfer region comprising a first plurality of working-fluid pathways, the first plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; a second heat transfer region circumferentially adjacent to the first heat transfer region, the second heat transfer region comprising a second plurality of working-fluid pathways, the second plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; a third heat transfer region circumferentially adjacent to the second heat transfer region, the third heat transfer region comprising a third plurality of working-fluid pathways, the third plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; and/or a fourth heat transfer region circumferentially adjacent to the third heat transfer region, the fourth heat transfer region comprising a fourth plurality of working-fluid pathways, the fourth plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways.

[0766] 16. The working-fluid body of any clause herein, comprising: the fourth heat transfer region circumferentially adjacent to the first heat transfer region.

[0767] 17. The working-fluid body of any clause herein, comprising: the first plurality of working-fluid pathways circumferentially adjacent to the second plurality of working-fluid pathways; the second plurality of working-fluid pathways circumferentially adjacent to the third plurality of working-fluid pathways; and/or the third plurality of working-fluid pathways circumferentially adjacent to the fourth plurality of working-fluid pathways.

[0768] 18. The working-fluid body of any clause herein, comprising: the fourth plurality of working-fluid pathways circumferentially adjacent to the first plurality of working-fluid pathways.

[0769] 19. The working-fluid body of any clause herein, wherein the plurality of working-fluid pathways comprise circumferentially adjacent working-fluid pathways defining a spiral, the spiral diverging radially or concentrically outward.

[0770] 20. The working-fluid body of any clause herein, wherein the plurality of working-fluid pathways comprise circumferentially adjacent working-fluid pathways, the circumferentially adjacent working-fluid pathways comprising an array of alternating counter-current pathways and co-current pathways.

[0771] 21. The working-fluid body of any clause herein, comprising the plurality of spiral pathways having a uniform cross-sectional with and/or a uniform cross-sectional area across a length of respective ones of the plurality of spiral pathways.

[0772] 22. The working-fluid body of any clause herein, wherein a respective one of the plurality of spiral pathways comprises a spiral arc, the spiral arc corresponding to at least a portion of an Archimedean spiral, a Cornu spiral, a Fermat’s spiral, a hyperbolic spiral, a logarithmic spiral, a Fibonacchi Spiral, an involute, and/or a squircular spiral.

[0773] 23. The working-fluid body of any clause herein, wherein the plurality of spiral pathways comprises a plurality of spiral arc inverse pairs, respective ones of the spiral arc inverse pairs comprising a parabolic spiral.

[0774] 24. The working-fluid body of any clause herein, wherein the plurality of spiral pathways comprise a squircular spiral.

[0775] 25. The working-fluid body of any clause herein, wherein at least a portion of the squircular spiral comprises an arc corresponding to a squircle.

[0776] 26. The working-fluid body of any clause herein, wherein a respective one of the plurality of spiral pathways has an arc length of from 180 degrees to 1260 degrees.

[0777] 27. The working-fluid body of any clause herein, wherein the respective one of the plurality of spiral pathways has an arc length of from 180 degrees to 450 degrees, or from 315 degrees to 765 degrees. [0778] 28. The working-fluid body of any clause herein, wherein the respective one of the plurality of spiral pathways has an arc length of from 675 degrees to 1260 degrees.

[0779] 29. The working-fluid body of any clause herein, wherein the plurality of spiral pathways comprise circumferentially adjacent pathways.

[0780] 30. The working-fluid body of any clause herein, comprising: a plurality of heating fluid pathways concentrically spiraling about an inlet plenum, respective ones of the plurality of heating fluid pathways defining a spiral pathway and the inlet plenum fluidly communicating with the plurality of heating fluid pathways, respective ones of the plurality of working-fluid pathways being altematingly adjacent to respective ones of the plurality of heating fluid pathways, the respective ones of the plurality of working-fluid pathways having a thermally conductive relationship with altematingly adjacent respective ones of the plurality of heating fluid pathways.

[0781] 31. The working-fluid body of any clause herein, comprising: at least a portion of the working-fluid body defining at least some of the plurality of working-fluid pathways protruding into adjacent respective ones of the plurality of heating fluid pathways; and/or at least a portion of the hot-side heat exchanger body defining at least some of the plurality of heating fluid pathways protruding into adjacent respective ones of the plurality of working-fluid pathways.

[0782] 32. The working-fluid body of any clause herein, comprising: the plurality of heating fluid pathways comprising a plurality of conduction-enhancing protuberances, respective ones of the plurality of conduction-enhancing protuberances defined at least in part by a portion of the working-fluid body corresponding to respective ones of the plurality of working-fluid pathways protruding into adjacent respective ones of the plurality of heating fluid pathways.

[0783] 33. The working-fluid body of any clause herein, comprising: the plurality of working-fluid fluid pathways comprising a plurality of conduction-enhancing protuberances, respective ones of the plurality of conduction-enhancing protuberances defined at least in part by a portion of the hot-side heat exchanger body corresponding to respective ones of the plurality of heating fluid pathways protruding into adjacent respective ones of the plurality of working-fluid pathways.

[0784] 34. The working-fluid body of any clause herein, comprising: a piston body, wherein the working-fluid body defines a first portion of a monolithic body and the piston body defines a second portion of the monolithic body, or wherein the piston body defines a first monolithic body-segment operably coupled or operably couplable to the working-fluid body.

[0785] 35. The working-fluid body of any clause herein, wherein the heat input region comprises the piston body.

[0786] 36. The working-fluid body of any clause herein, comprising: a regenerator body, the regenerator body defining a second portion of the monolithic body or a second monolithic body-segment operably coupled or operably couplable to the piston body and/or the working-fluid body.

[0787] 37. The working-fluid body of any clause herein, wherein the heat extraction region comprises the regenerator body.

[0788] 38. The working-fluid body of any clause herein, comprising: The plurality of working-fluid pathways fluidly communicating between the piston body and the regenerator body.

[0789] 39. The working-fluid body of any clause herein, comprising: a heating chamber body, the heating chamber body surrounding at least a portion of the plurality of working-fluid pathways.

[0790] 40. The working-fluid body of any clause herein, wherein at least a portion of the plurality of working-fluid pathways defining a tube array, the tube array disposed within the heating chamber body and the heating chamber body surrounding the tube array.

[0791] 41. The working-fluid body of any clause herein, comprising: the heating chamber body fluidly communicating with a heating fluid inlet and a heating fluid outlet.

[0792] 42. The working-fluid body of any clause herein, comprising: the heating chamber body defining at least a portion of a recirculation pathway.

[0793] 43. The working-fluid body of any clause herein, comprising: the heating chamber body comprising a heating fluid inlet fluidly communicating with a combustion chamber and a heating fluid outlet fluidly communicating with a recirculation annulus.

[0794] 44. The working-fluid body of any clause herein, comprising: working fluid disposed within the working-fluid pathway.

[0795] 45. The working-fluid body of any clause herein, wherein the engine-working fluid comprises a gas.

[0796] 46. The working-fluid body of any clause herein, wherein the engine-working fluid comprises an inert gas. [0797] 47. The working-fluid body of any clause herein, wherein the engine-working fluid comprises a noble gas.

[0798] 48. The working-fluid body of any clause herein, wherein the noble gas comprises helium.

[0799] 49. The working-fluid body of any clause herein, wherein the working-fluid body comprises an additively manufactured monolithic body or an additively manufactured monolithic body-segment.

[0800]

[0801] 50. The working-fluid body of any clause herein, comprising: a combustor body configured according to any preceding or subsequent clause.

[0802] 51. The working-fluid body of any clause herein, comprising: a hot-side heat exchanger body configured according to any clause herein.

[0803] 52. The working-fluid body of any clause herein, comprising: an eductor body configured according to any clause herein.

[0804] 53. The working-fluid body of any clause herein, comprising: a heat recuperator body configured according to any clause herein.

[0805] 54. The working-fluid body of any clause herein, comprising: a regenerator body of any clause herein.

[0806] 55. The working-fluid body of any clause herein, wherein the working-fluid body defines at least a portion of an engine assembly of any clause herein.

[0807] 56. The working-fluid body of any clause herein, wherein the working-fluid body defines at least a portion of the heater body of any clause herein.

[0808] 57. The working-fluid body of any clause herein, wherein the working-fluid body defines at least a portion of a closed-cycle engine.

[0809] 58. The working-fluid body of any clause herein, wherein the working-fluid body is configured to perform a method of any clause herein.

[0810] 59. The working-fluid body of any clause herein, comprising: a combustion chamber disposed annularly about an axis; and a conditioning conduit circumferentially surrounding the combustion chamber, the conditioning conduit fluidly communicating with the combustion chamber at a distal portion of the combustion chamber.

[0811] 60. The working-fluid body of any clause herein, comprising: a plurality of heating fluid pathways circumferentially spaced (and/or disposed radially about) an inlet plenum, respective ones of the plurality of heating fluid pathways defining a spiral pathway and the inlet plenum fluidly communicating with the plurality of heating fluid pathways; and a plurality of heat transfer regions, wherein respective ones of the plurality of heat transfer regions have a heat transfer relationship with a corresponding semiannular portion of the plurality of heating fluid pathways.

[0812] 61. The working-fluid body of any clause herein, comprising: an eduction pathway fluidly communicating with an annulus, the eduction pathway oriented oblique to the annulus; and a motive pathway fluidly communicating with the annulus, the motive pathway being adjacent to the eduction pathway and oriented oblique to the annulus.

[0813] 62. The working-fluid body of any clause herein, comprising: an intake air pathway fluidly communicating with a conditioning conduit, the intake air pathway oriented oblique to the conditioning conduit; and a recirculation pathway fluidly communicating with the conditioning conduit, the recirculation pathway being adjacent to the intake air pathway and oriented oblique to the conditioning conduit.

[0814] 63. The working-fluid body of any clause herein, comprising: a heat recuperator body, the heat recuperator body comprising: a first intake annulus disposed annularly about an axis, a first discharge annulus disposed annularly about the axis, and a plurality of first pathways spiraling annularly about the axis, the plurality of first pathways comprising: a plurality of first pathway-inlets fluidly communicating annularly about the first intake annulus, and a plurality of first pathway-outlets fluidly communicating annularly about the first discharge annulus; and a second intake annulus disposed annularly about the axis, a second discharge annulus disposed annularly about the axis, and a plurality of second pathways spiraling annularly about the axis, respective ones of the plurality of second pathways altematingly adjacent to respective ones of the plurality of first pathways, the plurality of second pathways comprising: a plurality of second pathway -inlets fluidly communicating annularly about the second intake annulus, and a plurality of second pathway-outlets fluidly communicating annularly about the second discharge annulus.

[0815] 64. The working-fluid body of any clause herein, comprising: comprising: a regenerator conduit; and a plurality of fin arrays adjacently disposed within the regenerator conduit and respectively supported by the regenerator conduit in spaced relation to one another, the spaced relation of the plurality of fin arrays defining a gap longitudinally separating adjacent ones of the plurality of fin arrays.

[0816] With respect to a method of heating an engine-working fluid, further aspects of the invention are provided by the subject matter of the following clauses: [0817] 1. A method of heating an engine-working fluid, the method comprising: flowing an engine-working fluid across respective ones of a plurality of heat transfer regions, respective ones of the plurality of heat transfer regions comprising a plurality of working- fluid pathways fluidly communicating between a heat input region and a heat extraction region, the engine-working fluid flowing through the plurality of working-fluid pathways; and transferring heat from a heating source to the engine-working fluid, the plurality of working-fluid pathways having a heat transfer relationship with the heating source.

[0818] 2. The method of any clause herein, wherein the plurality of working-fluid pathways comprise a plurality of radially or concentrically adjacent semiannular spiral pathways.

[0819] 3. The method of any clause herein, wherein the plurality of working-fluid pathways comprise a plurality of axially adjacent semiannular spiral pathways.

[0820] 4. The method of any clause herein, comprising: alternatingly flowing the engine-working fluid from the heat input region to the heat extraction region and from the heat extraction region to the heat input region.

[0821] 5. The method of any clause herein, comprising: alternatingly flowing through a first plurality of working-fluid pathways, a first portion of the engine-working fluid from the heat input region to the heat extraction region and from the heat extraction region to the heat input region; and alternatingly flowing through a second plurality of working-fluid pathways, a second portion of the engine-working fluid from the heat input region to the heat extraction region and from the heat extraction region to the heat input region.

[0822] 6. The method of any clause herein, comprising: alternatingly flowing the engine-working fluid from the heat input region to the heat extraction region, the heat extraction region circumferentially surrounding the heat input region.

[0823] 7. The method of any clause herein, comprising: alternatingly flowing the engine-working fluid from the heat input region to the heat extraction region, the heat extraction region circumferentially adjacent to the heat input region.

[0824] 8. The method of any clause herein, wherein the plurality of working-fluid pathways comprise: alternatingly flowing through a first plurality of working-fluid pathways, a first portion of the engine-working fluid from the heat input region to a first heat extraction region and from the first heat extraction region to the heat input region, the first plurality of working-fluid pathways fluidly communicating between the heat input region and the first heat extraction region; and alternatingly flowing through a second plurality of working-fluid pathways, a second portion of the engine-working fluid from the heat input region to a second heat extraction region and from the second heat extraction region to the heat input region, the second plurality of working-fluid pathways fluidly communicating between the heat input region and the second heat extraction region.

[0825] 9. The method of any clause herein, comprising: flowing a first volume of engine-working fluid across a first heat transfer region, the first heat transfer region comprising a first plurality of working-fluid pathways fluidly communicating between a first heat input region and a first heat extraction region and the first volume of engine-working fluid flowing through the first plurality of working-fluid pathways, the first plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; flowing a second volume of engine-working fluid across a second heat transfer region, the second heat transfer region comprising a second plurality of working-fluid pathways fluidly communicating between a second heat input region and a second heat extraction region and the second volume of engine-working fluid flowing through the second plurality of working-fluid pathways, the second plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; wherein respective ones of the first plurality of working-fluid pathways are circumferentially adjacent to respective ones of the second plurality of working-fluid pathways.

[0826] 10. The method of any clause herein, comprising: a radially or concentrically inward one of the first plurality of working-fluid pathways, the radially or concentrically inward one of the first plurality of working-fluid pathways circumferentially adjacent to a radially midward one of the second plurality of working-fluid pathways.

[0827] 11. The method of any clause herein, comprising: a radially or concentrically outward one of the second plurality of working-fluid pathways, the radially or concentrically outward one of the second plurality of working-fluid pathways circumferentially adjacent to a radially midward one of the first plurality of working-fluid pathways.

[0828] 12. The method body of any clause herein, comprising: a radially or concentrically outward one of the first plurality of working-fluid pathways, the radially or concentrically outward one of the first plurality of working-fluid pathways circumferentially terminating a spiral defined by at least some of the plurality of working-fluid pathways, the spiral diverging radially or concentrically outward.

[0829] 13. The method of any clause herein, comprising: a radially or concentrically inward one of the first plurality of working-fluid pathways, the radially or concentrically inward one of the first plurality of working-fluid pathways circumferentially initiating a spiral defined by at least some of the plurality of working-fluid pathways, the spiral diverging radially or concentrically outward.

[0830] 14. The method of any clause herein, comprising: alternatingly flowing a first volume of engine-working fluid across a first heat transfer region, the first heat transfer region comprising a first plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways and the first volume of engine-working fluid alternatingly flowing through the first plurality of working-fluid pathways, the first plurality of working-fluid pathways comprising: a first plurality of counter-current working-fluid pathways, a first portion of the first volume of engine-working fluid flowing in a counter- current direction through the first plurality of counter-current working-fluid pathways; and a first plurality of co-current working-fluid pathways, a second portion of the first volume of engine-working fluid flowing in a counter-current direction through the first plurality of counter-current working-fluid pathways; wherein respective ones of the first plurality of counter-current working-fluid pathways are circumferentially adjacent to respective ones of the first plurality of co-current working-fluid pathways.

[0831] 15. The method of any clause herein, comprising: alternatingly flowing a first volume of engine-working fluid across a first heat transfer region, the first heat transfer region comprising a first plurality of working-fluid pathways, the first plurality of working- fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; alternatingly flowing a second volume of engine-working fluid across a second heat transfer region circumferentially adjacent to the first heat transfer region, the second heat transfer region comprising a second plurality of working-fluid pathways, the second plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; alternatingly flowing a third volume of engine-working fluid across a third heat transfer region circumferentially adjacent to the second heat transfer region, the third heat transfer region comprising a third plurality of working-fluid pathways, the third plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways; alternatingly flowing a fourth volume of engine-working fluid across a fourth heat transfer region circumferentially adjacent to the third heat transfer region, the fourth heat transfer region comprising a fourth plurality of working-fluid pathways, the fourth plurality of working-fluid pathways comprising semiannular radially or concentrically adjacent spiral pathways. [0832] 16. The method of any clause herein, wherein the fourth heat transfer region is circumferentially adjacent to the first heat transfer region.

[0833] 17. The method of any clause herein, comprising: alternatingly flowing respective volumes of the engine-working fluid through the plurality of working-fluid pathways, the plurality of working-fluid pathways comprising circumferentially adjacent working-fluid pathways defining a spiral, the spiral diverging radially or concentrically outward.

[0834] 18. The method of any clause herein, comprising: flowing a heating fluid from an inlet plenum through a plurality of heating fluid pathways concentrically spiraling about the inlet plenum, respective ones of the plurality of heating fluid pathways defining a spiral pathway and the inlet plenum fluidly communicating with the plurality of heating fluid pathways, respective ones of the plurality of working-fluid pathways being alternatingly adjacent to respective ones of the plurality of heating fluid pathways; and transferring heat from the heating fluid to the engine-working fluid, the respective ones of the plurality of working-fluid pathways having a thermally conductive relationship with alternatingly adjacent respective ones of the plurality of heating fluid pathways.

[0835] 19. The method of any clause herein, wherein respective ones of the plurality of working-fluid pathways protrude radially or concentrically inward and/or radially or concentrically outward into alternatingly adjacent respective ones of the plurality of heating fluid pathways.

[0836] 20. The method of any clause herein, wherein the plurality of heating fluid pathways comprise a plurality of conduction-enhancing protuberances, respective ones of the plurality of conduction-enhancing protuberances defined at least in part by a portion of the working-fluid body corresponding to respective ones of the plurality of working-fluid pathways protruding into adjacent respective ones of the plurality of heating fluid pathways.

[0837] 21. The method of any clause herein, wherein the plurality of heating fluid pathways comprise a plurality of conduction-enhancing protuberances, respective ones of the plurality of conduction-enhancing protuberances defined at least in part by a portion of the hot-side heat exchanger body corresponding to respective ones of the plurality of heating fluid pathways protruding into adjacent respective ones of the plurality of working-fluid pathways.

[0838] 22. The method of any clause herein, wherein the engine-working fluid comprises engine-working fluid. [0839] 23. The method of any clause herein, wherein the engine-working fluid comprises an inert gas.

[0840] 24. The method of any clause herein, wherein the engine-working fluid comprises a noble gas.

[0841] 25. The method of any clause herein, wherein the noble gas comprises helium.

[0842] 26. The method of any clause herein, comprising: combusting a fuel in a combustor body, the combusting providing combustion gas.

[0843] 27. The method of any clause herein, comprising: combusting a fuel according to the method of any clause herein.

[0844] 28. The method of any clause herein, comprising: heating a plurality of heat transfer regions according to the method of any clause herein.

[0845] 29. The method of any clause herein, comprising: circulating fluid according to the method of any clause herein; or circulating combustion gas according to the method of any clause herein.

[0846] 30. The method of any clause herein, comprising: transferring heat between fluid streams according to the method of any clause herein.

[0847] 31. The method of any clause herein, comprising: recuperating heat from exhaust gas according to the method of any clause herein.

[0848] 32. The method of any clause herein, comprising: regenerating heat in an engine-working fluid according to the method of any clause herein.

[0849] 33. The method of any clause herein, comprising: performing the method at least in part using the working-fluid body of any clause herein; and/or comprising:

performing the method at least in part using the heater body of any clause herein.

[0850] This written description uses examples to describe the presently disclosed subject matter, including the best mode, and also to provide any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the presently disclosed subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.