CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority from U.S. provisional application number 62/866,773, filed June 26, 2019, having the same inventors and the same title, which is incorporated herein by referenced in its entirety.

FTEED OF THE DISCLOSURE

[0001] The present disclosure pertains generally to Stirling cycle engines, and more particularly to gas circuit cooler designs for Stirling cycle engines.

BACKGROUND OF THE DISCLOSURE

[0002] State of the art of external combustion Stirling Cycle engine designs for application in automotive transportation typically utilize direct drive configurations in which the engine is mechanically connected to a transmission or reduction gear. This type of configuration requires the manipulation of the internal pressures of the motive gas or working fluid. This has typically been accomplished by means of compressors, storage bottles, tanks (or cascade systems of storage bottles or tanks) or other fluid reservoirs. In particular, the working fluid is disposed in, or withdrawn from, such fluid reservoirs in order to reduce or increase the speed and torque output of the engine, respectively. Unfortunately, mean pressure controls of this type have been found to be inherently sluggish in response time as compared to state of the art internal combustion Otto Cycle engines.

[0003] The gas circuits in external combustion engines, such as Stirling Cycle or Ericsson Cycle engines, typically consist of a kinematic circuit and a compressor circuit. The kinematic circuit typically consists of a plurality of heater heads, piston cylinders, pistons-displacers, piston rod seals, thermal regenerators and gas circuit coolers. These elements impart kinetic energy to the pistons-displacers through adiabatic expansion and compression of the working fluid. Such expansion or compression may occur isothermally or isobarically, depending on the type of cycle employed. The compressor circuit typically consists of check valves, working fluid or motive gas compressors, electrically actuated valves, storage bottles or tanks for the working fluid, external refill fittings or valves, over pressure relief valves, O-rings and seals. The kinematic circuit and compressor circuit are connected only when the pressure of the working fluid within the kinematic gas circuit needs manipulation to accommodate the work demands of the engine.

[0004] The heater heads typically consist of a plurality of heater tubes arranged in combustion chamber such that the combustion takes place externally from the kinematic gas circuit. The heater tubes may have heat transfer fins fixed to the outer surfaces thereof to increase surface area so as to enhance the thermal energy transfer rates from the combustion gasses to the working fluid disposed within the heater tubes. As the working fluid is heated, it expands and is forced into the piston cylinder to impart kinetic energy to the piston-displacers. The heater tubes are typically fabricated from an alloy of steel that has both sufficient tensile and shear strength to contain the working fluid at high pressures and temperatures.

[0005] The thermal regenerators typically consist of a matrix of stainless steel wire mesh. The stainless steel has a significantly lower coefficient of thermal conductivity than hydrogen, which is commonly used as the working fluid. Additionally, stainless steel is subject to hydrogen embrittlement and permeation. This may lead to degradation of the integrity of the wire mesh in the regenerator, which may result in shedding of the wire mesh. The small fragments produced by this process may degrade the integrity of seals and O-rings, which may reduce working pressures and cause malfunctions in the check valves within the compressor gas circuit.

[0006] The gas circuit cooler is typically an array of small metal tubes through which the working fluid passes. The tubes are immersed in a water jacket to reject thermal energy. The check valves typically are typically made of stainless steel, and are spring and ball actuated. The working fluid compressor is typically a stainless steel reciprocating compressor.

[0007] During the operation of the Stirling Cycle engine or Ericsson Cycle engine, combustion takes place in the combustion chamber externally from the working fluid in the kinematic gas circuit. The heat of combustion is transferred to the working fluid through the surfaces of the heater tubes. The transfer of thermal energy to the working fluid causes it to expand, which then vents into the cylinder to impart kinetic energy to each of a plurality of piston-displacers. [0008] Each of the piston-displacers is out-of-phase with its adjacent neighbors. Ideally, this phase relationship allows for thermal energy conversion to kinetic energy in a thermodynamic system. In this system of adiabatic expansion and compression, the expansion volume leads the compression volume. The kinematic gas circuit includes the volumetric sum of the swept volumes, or displacement volumes, of the cylinders as well as the dead volume which may include the heater heads, heater tubes, regenerators, gas circuit coolers with associated fittings, conduits and manifolds.

[0009] Once the working fluid has imparted kinetic energy to the piston-displacer, the working fluid moves through the kinematic gas circuit to the thermal regenerator to reject thermal energy. The working fluid then moves into a gas circuit cooler where a portion of the waste heat is rejected by means of a water jacket. The adiabatic compression of the cooled working fluid then enters the adjacent cylinder as the piston-displacer moves toward the top dead center of the stroke. At the same time, the adjacent cylinder is out-of-phase in either an up stroke or down-stroke. On the return stroke, when the cooled working fluid absorbs thermal energy and expands, the resulting motion of the piston-displacer forces the cooled working fluid through the adjacent gas circuit cooler into the thermal regenerator to absorb the thermal energy previously stored there. Once through the thermal regenerator, the working fluid enters the heater tubes to absorb additional thermal energy from ongoing combustion within the combustion chamber. Absorption of the thermal energy expands the working fluid, which is forced into the cylinder to impart kinetic energy to the piston-displacer, thus completing the cycle.

[0010] The torque output of the engine is controlled by manipulating the working pressure of the working fluid by lowering the pressure within the kinematic gas circuit. This may be accomplished with a compressor that moves the working fluid into one or more external storage tanks, thereby reducing the speed of the engine. To increase the speed of the engine, an actuator valve opens the external storage tanks, thus increasing the pressure of the working fluid within the engine. The foregoing approach to pressure manipulation results in sluggish response times of the engine during acceleration as compared to conventional automotive drivetrains.

[0011] Previous research projects have focused on direct drive automotive drivetrains employing Stirling Cycle engines. In these projects, the engine was attached to a transmission or reduction gear system. The speed of the engine was controlled by increasing and decreasing internal pressure of the working gas within the kinematic gas circuit, which requires a complex system of gas circuitry (including compressors, actuator valves, check valves, short circuit valves, power control valves, over pressure dump valves and atmospheric vent valves) in order to accommodate the varying engine speeds necessary in a direct drive Stirling Cycle automotive drivetrain configuration.

[0012] The sluggish response time of the Stirling Cycle engine during acceleration, and the significant interval required to warm up the external combustion engine to an optimal operating temperature, are the primary reasons that direct drive configurations of the automotive Stirling Cycle engine designs have not been commercially viable.

[0013] Hybrid automotive technology has been well engineered over the past two decades. The state of the art in common practice is known as a parallel hybrid design. This design uses both electric motors and Otto Cycle engines to provide kinetic energy to the wheels of the vehicle.

[0014] The railroad industry also employs hybrid technology. However, in contrast to automotive applications, the common practice in the railroad industry is to configure diesel electric locomotives in a series hybrids design. In such a design, a diesel engine drives a generator, which then powers the electric motors to turn the wheels on the locomotive.

Conceptually, a series hybrid design is an electrically driven vehicle which carries an electrical power plant with it. This type of series hybrid design has been shown to be more fuel efficient than parallel hybrid designs.

[0015] Neither of the foregoing common practices employs Stirling Cycle engines or Ericsson Cycle engines, which have been shown to be more than twice as efficient as either the Otto Cycle engine or the Diesel Cycle engine. In both the Otto Cycle and the Diesel Cycle, combustion takes place under compression, which produces nitrogen oxides (NOx) in

combustion exhaust gases. These nitrogen oxides contribute significantly to poor air quality in every major city around the world. By contrast, combustion within the Stirling Cycle engine or Ericsson Cycle engine takes place at atmospheric pressure, which significantly reduces the production of NOx in combustion exhaust gases.

[0016] A vehicle employing either a Stirling Cycle engine or Ericsson Cycle engine in a series hybrid configuration only requires manipulation of the working pressures of the kinematic gas circuit during the starting sequence and the shutdown sequence. Once the desired operational speed and torque are achieved, the working pressure of the kinematic gas circuit is not manipulated. Both the Stirling Cycle engine and the Ericsson Cycle engine may be run at their “sweet spots” of highest thermal efficiency during operation to drive an electrical generator, thus avoiding the cumbersome and sluggish manipulation of the pressure of an internal working fluid to change the operating speed of the engine. A vehicle configured in this manner will operate as an electrically driven vehicle such that speed changes are controlled by more responsive voltage regulation and dynamic braking.

[0017] Information disclosed in this Background of the Invention section is only for enhanced and detailed understanding of the general background of the invention. It should not be taken as an acknowledgement, or any form of suggestion, that this information forms prior art to anything disclosed herein.

SUMMARY OF THE DISCLOSURE

[0018] In one aspect, an external combustion engine is provided which comprises (a) a plurality of cylinders, wherein each cylinder has a movable piston disposed therein; (b) a kinematic gas circuit which includes said plurality of cylinders, wherein said kinematic gas circuit imparts kinetic energy to the piston in each of said plurality of cylinders through the expansion and compression of a working fluid disposed therein, and wherein said working fluid has an operating pressure; (c) a compressor gas circuit which modifies the operating pressure of the working fluid in the kinematic gas circuit; and (d) at least one valve which is transformable between a first state in which the kinematic gas circuit is isolated from the compressor gas circuit, and a second state in which the kinematic gas circuit is in fluidic communication with said compressor gas circuit.

BRIEF DESCRIPTION OF THU DRAWINGS

[0019] FIG. l is a diagrammatic cut away view representation of an embodiment of the kinematic portion of a gas circuit in accordance with the teachings herein.

[0020] FIG. 2 is a diagrammatic representation of the compressor portion of an embodiment of the compressor portion of a gas circuit in accordance with the teachings herein. PET ATT, ED DESCRIPTION OF THE DISCLOSURE

[0021] Preferred embodiments of the systems and methodologies disclosed herein are designed to improve the operation of an external combustion Stirling Cycle engine or Ericsson Cycle engine for automotive or industrial application in a series hybrid vehicle drivetrain. The improvements upon the prior art make advantageous use of techniques and materials which are novel in the field of external combustion heat engine designs. These improvements may overcome the problems of lengthy time intervals for engine warm-up to operating temperatures, and the sluggish and cumbersome responsiveness of the vehicle drivetrain during acceleration, as have been encountered in previously tested automotive designs of external combustion heat engine drivetrains.

[0022] The Stirling Cycle engine and the Ericsson Cycle engine are external combustion heat engines which employ similar adiabatic closed circuit expansion and compression of a working fluid to derive kinetic energy from the internal piston-displacers. These two cycles differ in that the Stirling Cycle is isothermal, and the Ericsson Cycle is isobaric. Some of the improvements upon the prior art disclosed herein focus on increasing thermal energy transfer rates, reducing friction loses, reducing parasitic heat loses, improving seal life and integrity, and reducing the number of moving (for example, by simplifying the gas circuit pressure controls, check valves, actuator valves and the plurality of other components within the kinematic gas circuit and the compressor gas circuit).

[0023] The temperature difference between the hot side of the engine and the cold side of the engine may be increased by improving thermal energy transfer rates and reducing parasitic heat loses, thereby improving the overall thermal efficiency of the external combustion heat engine. This may be accomplished by (a) utilizing materials with higher coefficients of thermal conductivity; (b) increasing the surface area to mass ratios of various components within the kinematic gas circuit to improve the thermal energy transfer rates, and (c) the application of thermal barrier coatings to reduce parasitic heat losses. Additional improvements upon the prior art may be realized through the application of low friction coatings and materials which will improve seal integrity and longevity. The reliability of the engine may also be enhanced by simplifying the pressure controls, check valves and a plurality of other components, while additionally making the engine more compatible with modem mass production methodologies.

In the aggregate, these improvements may result in the engine being simpler to operate, and achieving higher fuel efficiency, thus allowing the engine to be more commercially viable for mass production.

[0024] The systems and methodologies disclosed herein may be further understood with reference to FIG. 1, which is a diagrammatic cut away view of the kinematic portion of the gas circuit of a particular, non-limiting embodiment of an external combustion engine of the type disclosed herein. As seen therein, the kinematic portion of the gas circuit comprises a plurality of cylinders 6, each of which is equipped on the exterior thereof with a manifold 9, a heater tube 1, a regenerator 2 and a gas cooler 3. A first end of the heater tube 1 is connected to the manifold 9, and a second end of the heater tube 1 is connected to the regenerator 2. Below the regenerator is the gas cooler 3, which is equipped with tubes arranged in a quasi-spiral helix to increase surface area thereof.

[0025] The kinematic gas circuit is interconnected with adjacent cylinders. A displacer- piston 4 is disposed within each cylinder 6. Each of the displacer-pistons 4 has a plurality of piston rings 5 disposed thereon. The base of each displacer-piston 4 is attached to a piston rod 7. A pumping Leningrad seal 8 is disposed about the piston rod 7 to maintain the pressure within the kinematic gas circuit as the displacer-pistons 4 move.

[0026] FIG. 2 is a diagrammatic representation of the compressor portion of the gas circuit of a particular, non-limiting embodiment of an external combustion engine of the type disclosed herein. A plurality of solenoid valves 10 are disposed within the compressor portion of the gas circuit to allow the compressor portion of the gas circuit to reduce or increase pressure of the working fluid within the kinematic gas circuit during the shutdown or startup sequence, respectively. A series of isolation check valves 11 is provided to minimize the dead volume of the kinematic gas circuit. The compressor 12 within the compressor gas circuit may be a reciprocating type compressor, a screw type compression or a wobble plate type of compressor, and may operate to draw down the working gas pressure from the engine to be stored in the external storage tank 18.

[0027] One or more filters 13 are provided within the gas lines of the compressor portion of the gas circuit to remove particulates from the circuit. Additionally, a gas cooler 14 may be employed to reject heat from the compressed working fluid. One or more pressure transducers 15 may be incorporated into the circuit to ensure that optimal pressures are maintained. Over pressure relief valves 16 are provided in the circuit to prevent tank rupture. The external storage tank 18 may be equipped with a tank valve 17 to allow safe removal thereof. An external fill valve fitting 19 may also be provided for the occasional addition of working fluid to compensate for leakage or other loss.

[0028] The gas circuits disclosed herein may be utilized in various external combustion engines such as, for example, Stirling Cycle engine types of Alpha, Beta or Gamma designs, or Ericsson Cycle engines for automotive applications.

[0029] The kinematic gas circuit and compressor gas circuit may be interconnected. The kinematic gas circuit is involved in the adiabatic expansion and compression of the working fluid to impart kinetic energy to the piston-displacers. The compressor gas circuit is employed to reduce or increase the operating pressure of the working fluid during the startup sequence and shutdown sequence. In all other modes of operation of the external combustion heat engine, the two gas circuits are preferably isolated one from the other.

[0030] The kinematic circuit may comprise various components which may include, but are not limited to, a plurality of heater heads consisting of a plurality of heater tubes, a plurality of thermal regenerators, a plurality of working fluid coolers, a plurality of piston cylinders and a plurality of piston-displacers. The compressor gas circuits may be comprised of a plurality of check valves and/or Tesla valvular conduits or diode valves, a plurality of electrically controlled actuator valves, a plurality of working fluid expansion chambers, a plurality of working fluid compressors, a plurality of power control valves, a plurality of external high pressure working fluid storage tanks, a plurality of external low pressure working fluid tanks, compressor bypass valves, tank solenoid valves, tank shut-off valves, pressure transducers, tank over pressure relief valves, atmospheric vent valves, working fluid filters, and external working fluid refill valves or fittings.

[0031] The kinematic gas circuit may be configured with a plurality of heater heads which may include an array of a plurality of tubes through which a working fluid may flow in response to expansion or compression. These tubes are preferably configured in parallel and equidistant from the center of combustion within a combustion chamber enclosure of the external combustion heat engine. In one possible embodiment, the plurality of heater tubes may be arranged to surround the outer margin of the combustion chamber enclosure such that the thermal energy of combustion may be absorbed by the heater tubes, either by radiation, convection or conduction, and preferably at uniform rates. The tubes may be connected to the kinematic gas circuit with one end venting via a manifold into the piston-displacer cylinders and the other end may be vented into one or more thermal regenerators via a manifold. To improve the surface area to mass ratio, the plurality of heater tubes surfaces may be threaded or corrugated along the surfaces closest to the center of combustion in the combustion chamber.

This approach increases the surface area of the tubes without lengthening the tubes themselves. The tube surfaces farthest from the center of combustion may be fixed with heat transfer fins and/or heat transfer pins for an additional increase in surface area for thermal energy transfer to the working fluid from the combustion gases. The heater head tubes and manifold preferably comprise a metal, metal alloy, metal composite, ceramic or ceramic composite. Preferably, the materials chosen for construction of the heater tubes or manifold have high coefficients of thermal conductivity, high shear strength and high tensile strength.

[0032] In order to reduce the overall volumetric dimensions of the heater heads and thereby achieve a reduction of the total volume of the combustion chamber, the heater tubes may be arranged in an alternating pattern, with half of the tubes being slightly longer and configured such that the longer tubes bridge over the shorter tubes in a nested pattern under the longer tubes. The tubes may be tilted or inclined over at an angel of 30° to 45 ⁰ to reduce the overall height of the heater heads within the combustion chamber of the external combustion engine.

[0033] The tubes vent the working fluid into the plurality of piston-displacers cylinders by means of heater head manifold into which the plurality of tubes are fixed. As the working fluid vents from the heater head manifold into the piston-displacer cylinder, the adiabatic expansion of the working fluid imparts kinetic energy to the plurality of pistons-displacers. At the point of maximum expansion, the working fluid may pass from the piston-displacer cylinder into a thermal regenerator.

[0034] The cylinder wall may be coated with a low friction ceramic coating that may be comprised of a compound of Aluminum, Magnesium, Boron and Titanium (AlMgB14 - TiB2) (also known as“BAM”) and/or equivalent heat tolerant low friction substances. [0035] One or more thermal regenerators may be disposed within the kinematic gas circuit. The thermal regenerators preferably include a matrix comprising a wire mesh or beads with high coefficients of thermal conductivity. The porosity and permeability of aggregation of the beads or wire mesh forming the matrix of the thermal regenerator may be 50% or greater.

[0036] In some embodiments, ceramic beads may be utilized in place of steel wire mesh in thermal regenerator devices. Ceramic beads may comprise a variety of materials that have inherently high coefficients of thermal conductivity. These properties are more compatible with the coefficient of thermal conductivity of the working fluid without suffering material degradation in a pure hydrogen environment (due, for example, to chemical reactions such as hydrogen embrittlement and permeation). Materials that may be incorporated into the matrix of a ceramic beads may include cubic boron nitride (c-BN), zirconium-diboride (ZrB2), or other materials of a similar thermal conductivity, phase stability and material integrity at 900°C. The beads may be of a sufficient size such that near 100% thermal saturation may be achieved as the pressure wave passes through the regenerator at the optimal operating speed of the external combustion heat engine.

[0037] The kinematic gas circuit thermal regenerator may be canister type or annular type in configuration. The external surfaces of the thermal regenerator may be coated with a thermal barrier coating such as zirconium-dioxide (ZrCk) or similar materials. The thermal barrier coating may reduce parasitic heat losses, thus improving the overall thermal efficiency of the external combustion heat engine.

[0038] The working fluid passes from the thermal regenerator to the kinematic gas circuit cooler. The plurality of gas coolers within the kinematic gas circuit may comprise an array of tubes made out of stainless steel or similar substances with high tensile and shear strength and with inherently high coefficients of thermal conductivity. The array of tubes may be immersed in a water jacket to reject heat. The configuration of the tubes may be inclined in a quasi-spiral helix at an angle to increase the overall length of the tubes without increasing the volumetric dimensions of the plurality of the individual gas coolers. The surfaces of each tube may be threaded or corrugated to increase the surface area to mass ratio for improved thermal energy transfer rates. The configuration of the gas coolers may be either canister or annular. [0039] The kinematic gas circuit may include conduit tubing. Such tubing may conduct the pressure waves of the working fluid within the kinematic gas circuit such that the propagation of the pressure wave sustains a Stirling Cycle or an Ericsson Cycle.

[0040] Within the compressor gas circuit, the plurality of expansion chambers may be configured as cylinders and inserted into the engine block. The volume of the cylinders may be manipulated by electrically driven pistons or hydraulically driven pistons. The cylinders may have electrically controlled actuator valves which may be opened or closed when there is a need to change the operating pressure of the working fluid within the gas circuit.

[0041] The walls of the expansion chamber cylinders may be coated with a low friction ceramic coating that may comprise a compound of aluminum, magnesium, boron and titanium (AlMgBi4 - T1B2) (also known as“BAM”) or equivalent low friction substances to minimize friction losses. The plurality of cylinders, comprising both high pressure chambers and low pressure chambers, may be fully expanded when the engine is in the warm-up and starting sequence of operation to reduce the amount of torque needed to start a sustained external combustion cycle.

[0042] Upon the establishment of a sustained Stirling Cycle, or a sustained Ericsson Cycle, the electrically controlled actuator valve will open and the expansion chamber pistons will reduce the volume within the expansion chamber, thus forcing working fluid into the kinematic gas circuit volume of the engine to bring the operating pressure of the working fluid to an optimal operating pressure within the engine. The volume of the expansion chamber cylinders may be expanded during the shutdown procedure of the external combustion heat engine to assist with thermal energy rejection to preserve the material integrity of the seals and O-rings. When the volume of the plurality of the expansion chamber cylinders are not being manipulated the electrically controlled actuator valve, they may remain closed to eliminate dead volume.

[0043] In the compressor gas circuit, the working fluid compressors may be employed in conjunction with the expansion chamber cylinders or independent of the expansion chambers to increase the operating pressure to an optimal working pressure within the kinematic gas circuit of the engine. An electrically controlled actuator valve will open when the compressor is in operation to bring the pressure of the active circuit to a predetermined operating pressure. [0044] When the compressor is not in operation, the electrically controlled actuator valve will remain closed to eliminate dead volume within the kinematic circuit. When the compressor is in operation, it may draw working fluid from the kinematic gas circuit to compress into one or more external storage tanks, thereby bringing the operating pressure of the working fluid to a predetermined optimal working pressure for the desired engine speed and torque. A plurality of gas circuit filters and gas circuit coolers may be provided downstream from the compressors within the compressor gas circuit.

[0045] A plurality of external storage tanks may be provided within the compressor gas circuit for working fluid. Preferably, half of these storage tanks are utilized for the low pressure side of the compressor gas circuit, and the other half are utilized for the high pressure side of the compressor gas circuit of the engine (depending upon design specifications). A plurality of electrically controlled actuator valves, tank solenoid valves and/or tank shut-off valves may be provided which may be open when the compressor is drawing working fluid from the kinematic gas circuit, thereby compressing the working fluid into the storage tanks of the compressor gas circuit and decreasing pressure within the kinematic gas circuit of the engine. Conversely, when pressure is increased in the kinematic gas circuit, actuator valves may be utilized to open the storage tanks, thereby allowing the tanks to feed directly into the kinematic gas circuit.

[0046] The plurality of electrically controlled actuator valves, tank solenoid valves, and/or tank shut-off valves may be closed when the external storage tanks and compressors are not in use. This manipulates the pressure of the kinematic gas circuit of the engine, thereby isolating the compressor gas circuit from the kinematic gas circuit to minimize dead volume. A plurality of tank over pressure relief valves are preferably provided in the compressor gas circuit.

[0047] A plurality of short circuit dump valves may be provided in the kinematic gas circuit. These dump valves may be electrically actuated to vent to the atmosphere as necessary to prevent a runaway Stirling Cycle, prevent seal or fitting failure, or prevent rupture of a tank or gas circuit line. A refill valve or fitting connection may be provided within the compressor gas circuit to provide for the occasional addition of working fluid, as some leakage of the working fluid may occur over time.

[0048] The kinematic gas circuit may comprise heater tubes though which thermal energy is absorbed to expand the working fluid. The expanded working fluid then vents into the plurality of piston cylinders to impart kinetic energy to the plurality of piston-displacers. The outer surfaces of the plurality of piston-displacers may be coated with a thermal barrier coating such as zirconium-dioxide (Zr0 ₂ ) or similar materials to minimize parasitic heat losses. The interior surfaces of the plurality of cylinders may be coated with a low friction coating which m ay comprise a compound of aluminum, magnesium, boron and titanium (AlMgBi4 - TiB ₂ ) (also known as“BAM”) or equivalent low friction substances.

[0049] The plurality of piston rings are preferably engineered with lower tolerance with respect to the diameter of the cylinders than the high compression pistons typically found in an internal combustion engine. These lower tolerances result in minimizing the wear on the surfaces of the plurality of cylinders. The plurality of piston rings may comprise polycrystalline alumina or other equivalent materials such as steel, steel alloys, steel composites, ceramics and ceramic composites to further reduce wear along the plurality of cylinder walls.

[0050] The surfaces of the plurality of the piston rods may be coated with a low friction coating comprising BAM or other suitable low friction substances to reduce the friction between the piston rod and the Pumping Leningrad seal (PL seal). The PL seal may have within the matrix of the material lubricious heat tolerant compounds such as hexagonal Boron-Nitride (h- BN), Talc (Mg3Si40io(OH) ₂ ) or equivalent substances to further reduce friction between the plurality of piston rods and the plurality of PL seals.

[0051] Once the working fluid has imparted kinetic energy to the plurality of the piston- displacers, it is forced into the plurality of the gas circuit regenerators of the kinematic gas circuit on the adiabatic expansion stroke. The gas circuit regenerators may comprise a variety of materials which may include compressed wire mesh or ceramic beads possessing a high coefficient of thermal conductivity (such as, for example, ceramics containing a significant percentage of cubic boron-nitride (c-BN), zirconium di-boride (ZrB ₂ ) or equivalent materials). The porosity and permeability of the plurality of gas circuit regenerators may be in excess of 50%. The plurality of the gas circuit regenerators may be configured in an annular geometry or a canister geometry depending on the design specifications. The outer surfaces of the gas circuit regenerators may be coated with a thermal barrier material such as Zirconium-Dioxide (Zr0 ₂ ) or similar materials to minimize parasitic heat losses through the outer surfaces of the plurality of the gas circuit regenerators. [0052] The plurality of gas circuit regenerators may be connected within the kinematic gas circuit to a plurality of gas circuit coolers so that the working fluid may be cooled and adiabatically compressed before entering the adjacent piston cylinders. The plurality of the gas circuit coolers may be configured such that a plurality of small diameter tubes may be threaded or corrugated to increase the surface area to mass ratio without increasing the overall length. Additionally, the plurality of small diameter tubes within the gas cooler may be inclined at an angle to form a quasi-spiral helix configuration, thereby increasing the surface area to mass ratio without increasing the overall volumetric size of the plurality of the gas circuit cooler devices. The plurality of the gas circuit coolers may be configured in a canister geometry or an annular geometry. The plurality of gas circuit coolers may be immersed in a circulating water jacket or other cooling fluid to expel thermal energy from the working fluid and to assist with the adiabatic compression of the working gas or motive fluid.

[0053] The working fluid is forced from the plurality of gas circuit coolers into the plurality of adjacent cylinders through the cold duct during the expansion stroke of the adjacent cylinder. Upon the adiabatic expansion stroke, the working fluid is then forced back through the gas circuit cooler, into the gas circuit thermal regenerator and then into the heater tubes to absorb the thermal energy from combustion in sequential phase order of 90° to 70° between the adjacent piston-displacers. This oscillation of the working fluid maintains a dynamic pressure wave within the gas circuit moving between pairs, or plurality of pairs, of the piston-displacers of the external combustion heat engine.

[0054] The above description of the present invention is illustrative, and is not intended to be limiting. It will thus be appreciated that various additions, substitutions and modifications may be made to the above described embodiments without departing from the scope of the present invention. Accordingly, the scope of the present invention should be construed in reference to the appended claims.