CONTROL

BACKGROUND

[0001] The subject matter disclosed herein relates to compression ignition engines, and more particularly to homogeneous charge compression ignition (HCCI) and pre-mixed charge compression ignition (PCCI) engines utilizing a charged oxidant flow.

[0002] An internal combustion engine (e.g., reciprocating engine such as a diesel, gasoline, or gas engine) combusts fuel with an oxidant (e.g., air) to generate hot combustion gases, which in turn drive an engine member (e.g., piston, rotor, blade). The engine member may be coupled to a shaft that rotates to power a load. Traditional industrial engines can operate under a variety of operating conditions (e.g., temperature, pressure, air-fuel mixture) for a particular load condition. However, suitable operating conditions for HCCI and PCCI engines may vary greatly based on the load conditions.

[0003] In HCCI engines, the fuel and air mixture may be premixed. In HCCI and PCCI engines, auto-ignition and rates of combustion are largely affected by the composition, temperature, and/or pressure of a charged oxidant flow during the compression stroke.

However, dynamic load conditions on the HCCI and PCCI engines affects the desired composition, pressure, and temperature of the fuel and air mixture, thereby complicating the control of HCCI and PCCI engines.

BRIEF DESCRIPTION

[0004] Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

[0005] In one embodiment, a system includes a compressed air system configured to couple to an engine. The compressed air system includes a compression device configured to compress an air flow, a heat exchanger configured to exchange heat with the air flow along a first flow path, and a bypass system configured to flow the air along a second flow path that bypasses the heat exchanger. The compressed air system may be configured to selectively flow the airflow along the first flow path, the second flow path, or a combination thereof, to the engine.

[0006] In one embodiment, a system may include a controller configured to control a temperature of a compressed air flow provided to an engine. The controller may be configured to control the temperature via control of an oxidant ratio and a coolant ratio. The oxidant ratio may include a first ratio between a bypass air flow that bypasses a heat exchanger and the compressed air flow provided to the engine, and the coolant ratio comprises a second ratio between a bypass coolant flow that bypasses the heat exchanger and a remainder coolant flow through the heat exchanger.

[0007] In one embodiment, a method may include compressing an air flow to form a compressed air flow to be provided to an engine, and controlling the temperature of the compressed air flow provided to the engine. Controlling the temperature of the compressed air flow may include cooling a portion of the compressed air flow via a heat exchanger, controlling a bypass air flo that bypasses the heat exchanger, and providing the portion of the compressed air flow and the bypass air flow to the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0009] FIG. 1 is a block diagram of an embodiment of a system having a compressed oxidant system coupled to an engine with a bypass line and a controller:

[0010] FIG. 2 is a block diagram of an embodiment of a system having a compressed oxidant system coupled to an engine and a heat exchanger bypass line;

[0011] FIG. 3 is a block diagram of an embodiment of a system having a compressed oxidant system coupled to an engine with a bypass line and a heat exchanger bypass line; and [0012] FIG. 4 is a block diagram of an embodiment of a system having a compressed oxidant system coupled to an engine with a two stage heat exchanger.

DETAILED DESCRIPTION

[0013] One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a de velopment effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[ 0014] When introducing elements of various embodiments of the present invention, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0015] The system and methods described herein control the temperature of a charged oxidant flow supplied to a homogeneous charge compression ignition (HCCI) or pre-mixed charge compression ignition (PCCI) operating engines in response to varying loads. Active control of the temperature of the charged oxidant system enables faster, more accurate transitions between varying loads on the engine. In some embodiments, the flow rate, composition, and pressure of the charged oxidant system may also be controlled. A compressed air system may be configured to couple to an engine, and the compressed air system may include a compression device to compress an air flow, a heat exchanger configured to exchange heat with the air flow along a first flow path, and a bypass system configured to flow air along a second flow path that bypasses the heat exchanger. The compressed air system may be configured to selectively flow the air flow along the first flow path, the second flow path, or a combination thereof, to the engine. The charged oxidant (e.g., compressed air) system may include a first coolant circuit and a second coolant circuit connected to a radiator that has a high pressure and a low pressure stage. The high pressure stage is coupled to the first coolant circuit, and the low pressure stage is coupled to the second coolant circuit. A heat exchanger (e.g., intercooler) may be coupled to a first coolant circuit, such that the heat exchanger is configured to transfer heat from a portion of the compressed air flow to a first water flow through the first coolant circuit. The low pressure stage is configured to transfer heat from the portion of the compressed air flow to a second water flow through the second coolant circuit. Bypass lines may be present in the compressed air system so that a bypass line of the compressed air flow may remain at a wanner temperature compared to the portion of the compressed air flow that is cooled via the heat exchanger. Additionally, or in the alternative a heat exchanger bypass line may be present to enable a bypass portion of the heat exchanger flow (e.g., water) to bypass the heat exchanger, such that the bypass portion may remain at higher temperatures. Both the bypass line and the heat exchanger bypass line may be independently controlled to control the temperature, flow rate, pressure, and/or composition of the compressed air flow such that the ignition timing for the HCCI and/or PCCI engines may be quickly adjusted to correspond with various loadings. The bypass portion and the heat exchanger bypass portion may be independently controlled during a start-up sequence of the engine, during steady-state operation (e.g., driving a load, operating in a simple cycle or combined cycle power plant), during shutdown of the engine, or any combination thereof, thereby enabling rapid ignition timing adjustments for varying (e.g., dynamic) loads during operation of the engine.

[0016] FIG. 1 is a block diagram of an embodiment of a system. 10 having a compressed oxidant system 12 coupled to an engine 14 with a bypass line 30 and a controller 56. In certain embodiments, the engine 14 is coupled to a load 21, such as a generator, a mechanical drive, or machinery. The engine 14 receives fuel 19 (e.g., diesel, natural gas, coal seam gases, associated petroleum gas, etc.) or a mixture of both the fuel 19 and a charged oxidant flow or compressed air flow 16 (e.g., air, oxygen, oxygen-enriched air, or any combination thereof). Although the following discussion refers to the charged oxidant flow 16 as air, any suitable oxidant (e.g., oxygen, oxygen-enriched air, exhaust gas, oxygen-enriched exhaust gas) may be utilized with the disclosed embodiments. In some embodiments, the compressed air flow 16 may be mixed with exhaust gas recirculation (EGR) gases 15. The EGR gases 15 may be introduced and mixed with the compressed air flow 16 upstream and/or downstream of the bypass line 30. [0017] The engine 14 may be a reciprocating or piston engine (e.g., internal combustion engine). The engine 14 may be a compression-ignition engine. The engine 14 may be a natural gas engine, gasoline engine, diesel engine, or dual fuel engine. The engine 14 may be a two-stroke engine, three-stroke engine, four-stroke engine, five-stroke engine, or six-stroke engine. The engine 14 may also include any number of cylinders (e.g., 1-24 cylinders or any other number of cylinders) and associated piston and liners. In some such cases, the cylinders and/or the pistons may have a diameter of between approximately 13.5 - 34 centimeters (cm). In some embodiments, the cylinders and/or the pistons may have a diameter of between approximately 10-40 cm, 15-25 cm, or about 15 cm. The system 10 may generate power ranging from 10 kVV to 10 MW. In some embodiments, the engine 14 may operate at less than approximately 1800 revolutions per minute (RPM). In some embodiments, the engine 14 may operate at less than approximately 2000 RPM, 1900 RPM, 1700 RPM, 1600 RPM, 1500 RPM, 1400 RPM, 1300 RPM, 1200 RPM, 1000 RPM, 900 RPM, or 750 RPM. In some embodiments, the engine 14 may operate between

approximately 750-2000 RPM, 900-1800 RPM, or 1000-1600 RPM. In some embodiments, the engine 14 may operate at approximaiely 1800 RPM, 1500 RPM, 1200 RPM, 1000 RPM, or 900 RPM. Exemplary engines 14 may include General Electric Company ^' s Jenbacher Engines (e.g., Jenbacher Type 2, Type 3, Type 4, Type 6 or J920 FleXtra) or Waukesha Engines (e.g., Waukesha VGF, VHP, APG, 275GL), for example.

[0018] In the illustrated embodiment, the compressed oxidant system 12 includes a compressed air flow 16. The compressed air flow 16 is discharged from a compression device 18. The compression device 18 may include, but is not limited to, a compressor, a supercharger, or a turbocharger, or any combination thereof. The compression device 18 may be coupled to a cleaner 20 (e.g., scrubber, particulate matter filter) disposed upstream of the compression device 18 which receives a fluid (e.g., oxidant, air, oxygen-enriched air). The cleaner 20 may be utilized to remove particulates from a fluid input 11. In certain embodiments, the fluid input 11 (e.g., oxidant) is received from a downstream process 13 (e.g., exhaust gas recirculation conduit), or the fluid input 1 1 may be provided to the compression device 18 from the ambient environment 17.

[0019] As discussed in further detail below, the embodiments of the compressed oxidant system 12 are configured to bypass various areas of the system 10 to facilitate rapid control of an oxidant temperature to enable an engine 14 to efficiently drive different loads 21. As described above, varying the load 21 may affect the desired temperature of the compressed air flow 16 to aid the timing of homogeneous charge compression ignition (HCC1) and pre- mixed charged compression ignition (PCCI) of the engine 14.

[0020] In some embodiments, the system 10 may not include all of the components illustrated in FIG. 1. In addition, the system 10 may include additional components such as an exhaust stack, silencer, control components, and/or heat recovery components. The system 10 may generate power ranging from 10 kW to 10 MW or greater. Besides power generation, the system 10 may be utilized in other applications such as those that recover heat and utilize the heat (e.g., combined heat and power applications), combined heat, power, and cooling applications, applications that also recover exhaust components (e.g., carbon dioxide) for further utilization, gas compression applications, and mechanical drive applications. Embodiments of the present disclosure include a compressed oxidant system 12 coupled to a engine 14 and configured to decrease the response time and improve control of an oxidant temperature to enable the engine 14 to operate efficiently at varying loads 21. In some embodiments, a controller 56 may enable precise control of one or more properties (e.g., temperature, pressure, composition) of the compressed air flow 16. As may be appreciated, varying (e.g., dynamic) loads on the engine 14 may correspond to different desired temperatures of the compressed air flo 16 supplied to the HCCI and/or PCCI for proper ignition timing.

[0021] The compressed oxidant system 12 provides the compressed air flow 16 to the engine 14. The compressed oxidant system 12 includes a heat exchanger 26 (e.g., an intercooler) disposed downstream, of the compression device 18 between the compression device 18 and the engine 14. The heat exchanger 26 is configured to receive and cool at least a portion 28 of the compressed air flow 16. The compressed oxidant system 12 may include the bypass line 30 that directs a bypass portion 34 of the compressed air flow 16 to bypass the heat exchanger 26. The bypass line 30 is disposed between the engine 14 and a bypass port 32 that is upstream of the heat exchanger 26. That is, the bypass port 32 is disposed between the heat exchanger 26 and the compression device 18. A bypass control valve 36 that controls (e.g., divides) the compressed air flow 16 into the portion 28 and the bypass portion 34 may be disposed along the compressed air flow 16 upstream or downstream of the heat exchanger 26. As discussed herein, the bypass portion 34 may be defined as the compressed air flow 16 minus the portion 28, which is cooled by the heat exchanger 26. Accordingly, the bypass portion 34 may include approximately 1/8, 1/4, 1/3, 3/8, 1/2, 5/8, 2/3, 3/4, 7/8, or more of the compressed air flow 16, in some embodiments, the bypass line 30 may not be utilized, resulting in approximately none of the compressed air flow 16 being directed as the bypass portion 34. In other embodiments, the approximately entire amount of the compressed air flow 16 may be directed to the bypass Sine 30 as the bypass portion 34. In some embodiments, the heat exchanger 26 is configured to transfer heat from the portion 28 of the compressed air flow 16 to another system or medium (e.g., coolant system 50, ambient environment). The cooiant system 50 circulates a coolant, which may include but is not limited to water, alcohol, or oil, or any combination thereof. The heat exchanger 26 may transfer heat from the portion 28 to a first coolant circuit 38. The first coolant circuit 38 may be disposed between and coupled to the engine 14 and a radiator 40. In some embodiments, the temperature of engine coolant 42 of the first coolant circuit 38 may range from approximately 80 to 130 ^° C, or 90 to 120 ^° C, or 110 to 1 10 C, and all subranges

therebetween. In some embodiments, the engine coolant 42 may be configured to discharge from the engine 14 via the first coolant circuit 38 to be recei ved by the radiator 40. In some embodiments, a portion 44 of the first coolant circuit 38 may be directed back to the engine 14 after bypassing the radiator 40 via valve 39. In some embodiments the portion 44 of the first coolant circuit 38 that bypasses the radiator 40 includes approximately 1/8, 1/4, 1/3, 3/8, or 1/2 of the first cooiant circuit 38 flow. The portion 44 that bypasses the radiator 40 may pass through the heat exchanger 26 prior to returning to the engine 14.

[0022] The radiator 40 may include a high pressure stage 46, a low pressure stage 48, or any combination thereof. The high pressure stage 46 may be coupled to the first coolant circuit 38 and may operate between approximately 600 to 1,200 kPa, or 650 to 1 ,050 kPa, or 700 kPa to 900 kPa, and all subranges therebetween. Hie first coolant circuit 38 is configured to receive (e.g., absorb) heat from the portion 28 of the compressed air flow 16 into a first coolant flow 42 (e.g., water) through the first coolant circuit 38. In some embodiments, the low pressure stage 48 is coupled to a second coolant circuit 52. The second cooiant circuit 52 is configured to receive (e.g., absorb) heat from the portion 28 of the compressed air flow 16 into a second coolant flow 53 (e.g., water, engine coolant 42) through the second coolant circuit 52. The low pressure stage 48 of the radiator 40 may operate between approximately 300 to 750 kPa, or 350 to 700 kPa, or 400 to 600 kPa, and all subranges therebetween. In some embodiments, an engine cooling system 50 may include the radiator 40 coupled to the engine 14 and the heat exchanger 26. In some embodiments, the first coolant circuit 38 may be coupled to the radiator 40, the engine 14, and the heat exchanger 26. The second coolant circuit 52 may be coupled to the radiator 40 and the heat exchanger 26. In some embodiments, the second coolant circuit 52 may operate at a lower temperature than the first coolant circuit 38. For example, the temperature of the second coolant 53 of the second coolant circuit 52 may operate from approximately 60 to 90 C, or 65 to 85 ^° C, or 70 to 75 ^° C, and all subranges therebetween. The coolants (e.g., engine coolant 42, second coolant 53) in the first coolant circuit 38 and the second coolant circuit 52 may flow between the high pressure stage 46 and the low pressure stage 48. In some embodiments, a water pump 54 may control the pressure and the temperature of the second coolant circuit 52. The water pump 54 may be controlled by the controller 56.

[0023] Presently contemplated embodiments may include the controller 56 coupled to the compressed oxidant system 12. The controller 56 may be coupled via control lines 62 to at least one valve assembly 58. The controller 56 may be configured to open and close the valves 60 to control the flow of the compressed air flow 16 through the valve assembly 58. Additionally, or in the alternative, the controller 56 may be configured to adjust valves 39 that control the flow of one or more coolant flows 42, 53 through the coolant system 50. In certain embodiments, the controller 56 may include a memory 64 to store instructions and a processor 66 configured to the process the instructions. The controller 56 may include an operator interface 68 to display various readings taken from sensors 70 disposed about the coolant system 50. Also, the operator interface 68 may display positioning of the valves 36, 39, 60 of the compressed oxidant system 12 and coolant system 50. The controller 56 may receive input, such as a desired operating load 21 , temperature of the compressed air flow 16, pressure of the compressed air flow 16, or any other condition affecting homogeneous charge compression ignition (HCCT) or pre-mixed charged compression ignition (PCC1) of the engine 14.

10024] In some embodiments, the controller 56 may control the flow of the compressed air flow 16 based in part on a result of a signal received from the one or more sensors 70. The sensors 70 may be configured to measure various properties of the system 10, including but not limited to temperature, pressure, composition (e.g., oxygen concentration), vibration, flow rate, or any combination thereof. The sensors 70 may be disposed along the compressed oxidant system 12, including within or adjacent (e.g., downstream) of the compression device 18, within or adjacent to the engine 14, along the compressed air flow 16, the first coolant circuit 38, the second coolant circuit 52, within or adjacent to (e.g., upstream, downstream) the heat exchanger 26, or any other place suitable for measuring a system property as described above. The sensors 70 can include, but are not limited to, temperature sensors (e.g., thermocouples, thermoresistors, RTD), fluid level sensors, pressure sensors, composition sensors (e.g., lambda sensors), motion sensors (e.g., accelerometers), or any other sensors suitable for determining or measuring an operating condition affecting the compressed oxidant system 12. In some embodiments, a bypass control valve 36 may be coupled to the bypass line 30 such that the bypass control valve 36 is configured to control a ratio of the bypass portion 34 to the relatively cool compressed air flow portion 28 (e.g., remainder) that flows through the heat exchanger 26. In some embodiments, the bypass portion 34 is approximately 1/8, 1/4, 1/3, 3/8, or 1 /2, or more of the first coolant circuit 38 flow. Through control of the bypass control valve 32, the controller 56 may adjust the temperature of the compressed air flow 16 provided to the engine 14 by adjusting the ratio of the bypass portion 34 to the relatively cool compressed air flow portion 28 (e.g., remainder). When the bypass portion 34 is increased, the portion 28 is decreased, thereby enabling the temperature of the compressed air flow 16 to maintain a hotter temperature than w hen the bypass portion 34 is decreased. When the bypass portion 34 is decreased, the portion 28 is increased, thereby decreasing the temperature of the compressed air flow 16.

10025] In some embodiments, the controller 56 is configured to control the bypass control valve 32 to control the temperature and/or pressure of the compressed air flow 16 provided to the engine 14 based at least in part on the load 21 coupled to the engine 14. By controlling the temperature, pressure, flow rate, and/or composition of the compressed air flow 16 precisely by utilizing the charged oxidant system 12, the engine 14 may be utilized in cold weather conditions such that the engine 14 does not need cold weather protection and is not coupled to a cold weather package. Through use of the charged oxidant system 12, cold weather packages may be eliminated in some instances because temperature control of the compressed air flow 16 can be achieved as described above, enabling rapid heating of the compressed air flow 16. [0026] FIG. 2 is a block diagram of an embodiment of a system 10 having a compressed oxidant system 12 coupled to an engine 14 and a heat exchanger bypass line 72. In some embodiments, a coolant circuit (e.g., tlie second coolant circuit 52) may include a heat exchanger bypass line 72 to control the temperature of the second coolant circuit 52 such that the temperature of the coolant fluid 53 of the second coolant circuit 52 decreases (e.g., is lower) when the coolant fluid 53 (e.g., water) bypasses the heat exchanger 26. When the remainder coolant 51 (e.g., the portion of the coolant flowing through the heat exchanger 26) is increased, the bypass coolant portion 80 is decreased, thereby decreasing the temperature of the compressed air flow 16. When the remainder coolant 51 is decreased, the bypass coolant portion 80 is increased, thereby enabling the temperature of the compressed air flow 16 to remain hotter than w hen the remainder coolant 51 is increased.

[0027] A heat exchanger bypass valve 76 may be disposed between the water pump 54 of the second coolant circuit 52 and the radiator 40 such that the heat exchanger bypass line 72 is configured to receive a bypass coolant portion 80 of the second coolant 53. The heat exchanger bypass valve 76 may be disposed upstream or downstream of the heat exchanger 26. The bypass coolant portion 80 may include the coolant flow 53 of the second coolant circuit 52, less a portion 82 of the second coolant 53 received by the heat exchanger 2,6. In some embodiments, the controller 56 may be configured to open and close the heat exchanger bypass valve 76 to control the flow of the heat exchanger bypass line 72. The controller 56 may be configured to receive signals from one or more sensors 70 disposed along the second coolant circuit 52, the heat exchanger bypass line 72, upstream or downstream from the heat exchanger bypass valve 76, within or adjacent (e.g. downstream) of the compression device 18, within or adjacent to tlie engine 14, or any other place suitable for measuring an operating condition of the charged oxidant system 12. The controller 56 may utilize one or more valves 60 to control various flow rates in the charged oxidant system 12. In some embodiments, the controller 56 may be configured to adjust the flow rate of the second coolant 53 through the heat exchanger bypass line 72. The heat exchanger bypass line 72 may include

approximately 1 /8, 1/4, 1/3, 3/8, 1/2, 5/8, 2/3, 3/4, 7/8, or more of the second coolant 53 of the second coolant circuit 52. In some embodiments, the heat exchanger bypass line 72 may not be utilized, resulting in approximately none of tlie second coolant 53 being directed to tlie heat exchanger bypass line 72. In other embodiments, the entire amount of the flow of the second coolant 53 may be directed to the heat exchanger bypass line 72. The controller 56 may be configured to control the temperature of the compressed air flow 16 provided to the engine 14 via control of an oxidant ratio and a coolant ratio. The oxidant ratio is defined as a first ratio between a bypass oxidant flow 34 that bypasses the heat exchanger 26 and the compressed air flow 16 provided to the engine 14. The coolant ratio is defined as a second ratio between a bypass coolant flow 72 that bypasses the heat exchanger 26 and a remainder coolant flow through the heat exchanger 26. In some embodiments, the controller 56 may be configured to control the temperature of the compressed air flow 16 based at least in part on the load 21 driven by the engine 14. By controlling the oxidant ratio and the coolant ratio to controi the temperature of the compressed air flow 16, the engine 14 may be utilized in cold weather conditions such that the engine 14 is not coupled to a cold weather package. That is, the charged oxidant system 12 described herein enables rapid heating and temperature controi of the compressed air flow 16.

[0028] FIG. 3 is a block diagram of an embodiment of a system. 10 having a compressed oxidant system 12 coupled to an engine 14 with a bypass line 30 and a heat exchanger bypass line 72. As may be appreciated, the compressed oxidant system 12 of FIG. 3 has a bypass tine 3 similar to FIG. I, and a heat exchanger bypass line 72 similar to FIG. 2. The bypass portion 34 may be controlled by the controller 56, as described above with FIG. 1. The bypass portion 34 may be defined as the compressed air flow 16 minus the portion 28 which is cooled by the heat exchanger 26. In some embodiments, the bypass portion 34 may include approximately 1/8, 1/4, 1/3, 3/8, 1/2, 5/8, 2/3, 3/4, 7/8, or more of the compressed air flow 16. In some embodiments, the bypass portion 34 may not be utilized resulting in approximately none of the compressed air flow 16 being directed to bypass line 30. In other embodiments, the entire amount of the compressed air flow 16 may be directed to the bypass line 30. When a bypass portion 34 is increased, the portion 28 is decreased, resulting in the compressed air flow 16 remaining hotter than when the bypass portion 34 is decreased. When the bypass portion 34 is decreased, the portion 28 is increased, thereby cooling the compressed air flow 16. As such, adjusting the ratio of the bypass portion 34 to the portion 28 enables rapid temperature control of the compressed air flow 16.

[0029] In some embodiments, a heat exchanger bypass valve 76 may be disposed between the water pump 54 of the second coolant circuit 52 and the radiator 40 such that the heat exchanger bypass line 72 is configured to receive a bypass coolant portion 80 of the second coolant circuit 52. The bypass coolant portion 80 may include the coolant flow 53 of the second coolant circuit 52 less a portion 82 of the second coolant circuit 52 received by the heat exchanger 26. As described above, the controller 56 may be configured to open and close the heat exchanger bypass valve 76 to control the flow of the heat exchanger bypass line 72. In some embodiments, the controller 56 may be configured to adjust the flow rate of the coolant flow 53 of the bypass coolant portion 80. In some embodiments, the bypass coolant portion 80 may include approximately 1/8, 1/4, 1/3, 3/8, 1/2, 5/8, 2/3, 3/4, 7/8, or more of the flow of the heat exchanger bypass line 72. When a bypass coolant portion 80 is increased, the remainder coolant 51 is decreased, enabling the compressed air flow 16 to remain hotter than when the bypass coolant portion 80 is decreased. When the bypass coolant portion 80 is decreased, the remainder coolant 51 is increased, thereby cooling the compressed air flow 16.

[0030] FIG. 4 is a block diagram of an embodiment of a system. 10 having a compressed oxidant system 12 coupled to an engine 14 with a two stage heat exchanger 94 (e.g., first stage 98, second stage 100). The system 10 may include more than one heat exchanger 94. As described in further detail below, the compressed oxidant system 12 may include multiple bypass lines 30 (e.g., a first bypass line 102, a second bypass line 106, a third bypass line 108). In some embodiments, the first bypass line 102 may be disposed between a first stage 98 and a second stage 100 of the heat exchanger 94, such that a bypass oxidant flow 96 (e.g., bypass air) may bypass the second stage 100 of the heat exchanger 94. The first bypass line 102 may be coupled to the controller 56 such that the flow rate of the bypass oxidant 96 (e.g., bypass air) through primary port 118 disposed on the first bypass line 102 may be controlled via a primary bypass valve 104. In some embodiments, the second bypass line 106 may bypass only the fi rst stage 98 of the heat exchanger 94 and be disposed between the first stage 98 and the second stage 1 0 of the heat exchanger 94. The bypass oxidant 96 (e.g., bypass air) may bypass the first stage 98 of the heat exchanger, and the controller 56 may control the flow rate of the bypass oxidant 96 (e.g., bypass air) through secondary port 116 which passes through the second stage 100 of the heat exchanger 94. The controller 56 may utilize a secondaiy bypass valve 110 to control the flow of the bypass oxidant 96 (e.g., bypass air). A third bypass line 108 may bypass the first stage 98 and the second stage 100 of the heat exchanger 94 completely. The controller 56 may control the flow rate of the bypass oxidant 96 (e.g., bypass air) through a tertiary port 114 via a tertiary bypass valve 112. In some embodiments, the compressed air flow 16 is directed through both the first stage 98 and the second stage 100 of the heat exchanger 94, such that none of the bypass lines (e.g., first bypass line 102, second bypass line 106, third bypass line 108) are utilized. The controller 56 may receive signals from one or more sensors 70. As described above, the controller 56 may be configured to control the flow of the compressed air flow 16 as a result of a signal recei ved from one or more sensors 70.

[0031 ] Presently contemplated embodiments may include a method of compressing an air flow to form the compressed air flow 16 to be provided to the engine 14, and controlling the temperature of the compressed air flow 16 provided to the engine 14. Controlling the temperature of the compressed air flow 16 includes cooling a portion 28 of the compressed air flow 16 via the heat exchanger 26. When the bypass portion 34 is increased, the portion 38 is decreased, resulting in the compressed air flow 16 remaining hotter than when the bypass portion 34 is decreased. When the bypass portion 34 is decreased, the portion 28 is increased, thereby cooling the compressed air flow 16. The method may also include controlling the bypass coolant portion 80 that bypasses the heat exchanger 26. When the bypass coolant portion 80 is increased, the remainder coolant 51 is decreased, enabling the compressed air flow 16 to remain hotter than when the bypass coolant portion 80 is decreased. When the bypass coolant portion 80 is decreased, the remainder coolant 51 is increased, thereby cooling the compressed air flow 16. The heat exchanger 26 may be coupled to the engine cooling system to cool the engine via circulation of a coolant (e.g., water) flow. The method may include controlling the temperature of the compressed air flow 16 provided to the engine 14 based at least in part on a load 21 driven by the engine.

[0032] Technical effects of the invention include active control of the temperature of a charged oxidant (e.g., compressed air) provided to HCCI or PCCT engines at var ing loads. Active control of the temperature of the charged oxidant enables faster, more accurate transitions between varying loads, thereby improving efficiency of HCCI and PCCI engines. The flow rate, composition, and pressure of the charged oxidant may also be controlled. Various combinations of heat exchangers and bypass lines can be arranged in the compressed oxidant system to enable rapid temperature control of the compressed air. Bypass lines enable the temperature of the compressed air flow to be controlled by adjusting bypass ratios. When a bypass portion is increased, the portion is decreased, resulting in the compressed air i j> flow remaining hotter than when the bypass portion is decreased. When the bypass portion is decreased, the portion is increased, thereby cooling the compressed air flow. When a bypass coolant portion is increased, the remainder coolant is decreased, enabling the compressed air flow to remain hotter than when the bypass coolant port is decreased. When the bypass coolant portion is decreased, the remainder coolant is increased, thereby cooling the compressed air flow. Both the bypass line and the heat exchanger bypass line may be independently controlled to control the temperature of the compressed air fl ow such that HCCI and/or PCCI engine loads can be met to enable rapid adjustments between dynamic loads.

[0033] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claim s, 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 have 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.