Patent Publication Number: US-2023144917-A1

Title: Fuel heater and energy conversion system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional application claiming the benefit of priority under 35 U.S.C. § 119(e) to U.S. Non-Provisional application Ser. No. 17/166,245, filed Feb. 3, 2021, which is hereby incorporated by reference in its entirety. 
     FIELD 
     The present subject matter relates generally to systems for energy conversion and systems for thermal management for propulsion systems and vehicles. The present subject matter relates to thermal management and energy conversion systems for aircraft and propulsion systems. 
     BACKGROUND 
     Propulsion systems, such gas turbine engines, are challenged with thermal management of increasingly higher thermal loads and energy conversion. The increasingly higher thermal loads and energy requirements are due to increasing electrification of propulsion systems and vehicles such as aircraft, greater electric loads, and the need for improved thermal efficiency at fuel systems, oil systems, and cooling fluids. 
     Conventional systems that generate auxiliary power to meet increased power requirements are limited by the power output of the propulsion system. Low power and part-power conditions may insufficiently generate heat for thermal management and energy conversion systems. 
     As such, there is a need for energy conversion systems that meet increased vehicle and propulsion system power generation requirements without limits from power outputs from the propulsion system. Additionally, there is a need for energy conversion and thermal management systems that can meet the challenges associated with increased thermal loads. 
     BRIEF DESCRIPTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     An aspect of the present disclosure is directed to a system for energy conversion. The system for energy conversion includes a propulsion system including a compressor section, a heat addition system, and an expansion section in serial flow arrangement. A fuel circuit is in fluid communication from a fuel tank to a fuel flow control device. The fuel flow control device separates a flow of fuel from the fuel tank into a first portion of fuel and a second portion of fuel. The fuel circuit is configured to provide the first portion of fuel to the heat addition system. A combustion device is configured to receive a flow of oxidizer from the compressor section via a fluid circuit. The fuel circuit is in fluid communication to provide the second portion of fuel to the combustion device. The combustion device is configured to generate combustion gases from the second portion of fuel and the flow of oxidizer. The fluid circuit is in fluid communication from the combustion device to flow the combustion gases to the propulsion system. A turbine configured to receive the combustion gases from the combustion device via the fluid circuit. A load device is operably coupled to the turbine via a driveshaft. The load device is configured to receive an output torque from the driveshaft via expansion of the combustion gases through the turbine. 
     These and other features, aspects and advantages of the present invention 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 embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG.  1    is an exemplary embodiment of a vehicle including a propulsion system and energy conversion system according to aspects of the present disclosure; 
         FIG.  2    is an exemplary schematic embodiment of an energy conversion system including a propulsion system in accordance with aspects of the present disclosure; 
         FIG.  3    is an exemplary schematic embodiment of an energy conversion system in accordance with aspects of the present disclosure; and 
         FIGS.  4 - 7    are exemplary schematic embodiments of an energy conversion and thermal management system in accordance with aspects of the present disclosure. 
     
    
    
     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 invention. 
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     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 “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. 
     Embodiments of a propulsion system, vehicle, and energy conversion system are provided herein that may improve overall system and vehicle efficiency, such as through utilizing relatively small amounts of bleed air or other oxidizer from a propulsion system or auxiliary power unit to generate combustion gases from a combustion system separate from a combustion system at the propulsion system or auxiliary power unit. The combustion gases then expand through a power turbine to generate an output torque for a load device. A fuel-air heat exchanger is positioned in thermal communication with at least a portion of the flow of fuel. The combustion gases generated via the dedicated combustion system, separate from the propulsion system combustion system, allow for heat generation and release that is substantially de-coupled from power output or engine speed from the propulsion system. Certain embodiments include receiving a flow of oxidizer from the propulsion system and generating and expanding combustion gases at the combustion device and turbine separate from the propulsion system. Still certain embodiments include thermal communication of the combustion gases with one or more heat exchangers. 
     Embodiments of the energy conversion and thermal management system provided herein allow for weight-advantaged systems and methods for fuel heating and controlling fuel temperature independent of engine speed from the propulsion system. Embodiments of the systems may include unexpectedly beneficial results from having a combustion system and turbine separate from the propulsion system to generate fuel heating and power generation for a load device, such as an electric machine, an accessory gear assembly, pumps, mechanical loads generally, or other systems conventionally powered mechanically, electrically, or pneumatically by propulsion system. 
     Referring now to the drawings, in  FIG.  1   , an exemplary embodiment of a vehicle  100  including a propulsion system  10  and an energy conversion system  200  according to aspects of the present disclosure is provided. In an embodiment, the vehicle  100  is an aircraft including an aircraft structure or airframe  105 . The airframe  105  includes a fuselage  110  to which wings  120  and an empennage  130  are attached. The propulsion system  10  according to aspects of the present disclosure is attached to one or more portions of the airframe. In certain embodiments, the vehicle  100  includes an auxiliary power unit (APU)  15 . The APU  15  may form a gas turbine engine including a compressor section, a heat addition system, an expansion section, and an exhaust section such as further described herein. In various embodiments, the energy conversion system  200  is a system configured to desirably distribute thermal loads, such as to add or remove heat from one or more fluids or structures, such as, but not limited to, oxidizer at the propulsion system, fuel, lubricant, hydraulic fluid, pneumatic fluid, or cooling fluid for an electric machine, electronics, computing system, environmental control system, gear assembly, or other system or structure. 
     In certain instances, the propulsion system  10  is attached to an aft portion of the fuselage  110 . In certain other instances, the propulsion system  10  is attached underneath, above, or through the wing  120  and/or portion of the empennage  130 . In various embodiments, the propulsion system  10  is attached to the airframe  105  via a pylon or other mounting structure. In still other embodiments, the propulsion system  10  is housed within the airframe, such as may be exemplified in certain supersonic military or commercial aircraft. 
     Various embodiments of the vehicle  100  include a computing system  140 , such as avionics or other electronics or computing devices configured to control the vehicle  100  or the propulsion system  10 . The vehicle  100  may further include an environmental control system (ECS)  150 , such as to provide thermally conditioned air to a cabin of the vehicle, the computing system  140 , a vehicle surface anti-icing system  160 , a propulsion system anti-icing system, or other system of the vehicle  100  or propulsion system  10 . In various embodiments such as described herein, the energy conversion system  200  may be configured to provide energy to one or more subsystems of the vehicle or propulsion system, such as described above and further herein. Further embodiments of the energy conversion system may be configured to provide thermally conditioned fluid to one or more of the systems described herein. 
     Referring now to  FIG.  2   , an exemplary schematic embodiment of an engine  13  for the propulsion system  10  or the APU  15  ( FIG.  1   ) operably coupled to the energy conversion system  200  is provided. Particular embodiments of the propulsion system  10  may be configured as a turbomachine, a ramjet engine, or a scramjet engine. Still particular embodiments of the propulsion system  10  may include a turbomachine configured as a turbofan, turboprop, turbojet, turboshaft, propfan, or open rotor engine. In  FIG.  2   , the propulsion system  10  is configured as a three-stream engine including a fan bypass stream  14 , a core flowpath  70 , and a core bypass or third stream  71 . Certain embodiments of the propulsion system  10  include a fan section  12 , a compressor section  20 , a combustion section or heat addition system  26 , an expansion section  30 , and an exhaust section  36  in serial flow arrangement. In various embodiments, the heat addition system  26  may be configured as a deflagrative combustion system or a detonative combustion system. The heat addition system  26  may include any suitable type of system for receiving a flow of liquid and/or gaseous fuel and generating hot gases, including, but not limited to, annular, can-annular, can, trapped vortex, volute or scroll, rotating detonation, pulse detonation, subsonic or supersonic combustion systems. The fan section  12  includes one or more stages of rotors and blades  121 . Certain embodiments further include one or more stages of vanes that are stationary relative to a centerline axis of the propulsion system  10 . 
     The compressor section  20 , the heat addition system  26 , and the expansion section  30  are positioned in serial aerodynamic flow arrangement. The compressor section  20 , the heat addition system  26 , and the expansion section  30  may together define a core engine or gas generator of the propulsion system  10 . In certain embodiments, such as described herein, the compressor section  20  includes a high pressure compressor  24  positioned in direct serial flow arrangement with the heat addition system  26  and a high pressure turbine  32  of the expansion section  30 . A low pressure turbine  34  of the expansion section  30  may be operably coupled to the fan section  12  to drive the one or more stages of the fan section  12 . In certain embodiments, the propulsion system  10  may include a low pressure compressor or an intermediate pressure compressor  24  positioned aerodynamically between the fan section  12  and the high pressure compressor  24 . In still further embodiments, an intermediate press turbine may be positioned aerodynamically between the high pressure turbine  32  and the low pressure turbine  34 . 
     The core flowpath  70  is extended through at least the high pressure compressor  24 , the heat addition system  26 , and the high pressure turbine  32 . The core bypass or third stream flowpath  71  is extended from downstream of the intermediate or low pressure compressor  22  and bypasses the core flowpath  70  at the high pressure compressor  24 . In certain embodiments, the third stream flowpath  71  is in fluid communication with the fan bypass stream  14  downstream of the vanes  122 . 
     The third stream flowpath  71  is an air stream configured to recover fluid energy to produce a portion of total thrust of the propulsion system  10 . In one embodiment, the portion of total thrust produced through the third stream flowpath  71  may include a dedicated exhaust nozzle at an outlet end. In another embodiment, the portion of total thrust produced through the third stream flowpath  71  may be mixed with the fan bypass stream  14 . In still another embodiment, the portion of total thrust produced through the third stream flowpath  71  may be mixed with the core flowpath  70  downstream of the heat addition system  26 , and egressed through the exhaust section  36 . Various embodiments of the third stream flowpath  71  are configured to generate less than 50% of the total thrust of the propulsion system  10 . 
     It should be appreciated by those skilled in the art that the third stream flowpath  71  is extended from the core flowpath  70  upstream of the heat addition system  26  and downstream of the fan section  12 , and is further configured to allow the flow of air to egress the propulsion system  10  to generate a portion of the total thrust of the propulsion system  10 . The operating temperature of the air through the third stream flowpath  71  may generally correspond to a range of air temperatures as egressed from the intermediate or low pressure compressor  22 . 
     Referring now to  FIGS.  3 - 7   , the energy conversion system  200  includes a pipe, manifold, or other walled conduit forming a fluid circuit  210  providing fluid communication of a flow of oxidizer  201 , or air specifically, extracted from the compressor section  20  of the engine  13 . In particular embodiments, the flow of oxidizer  201  is bled or otherwise directed from a portion of the oxidizer compressed by a compressor assembly  220 . In a particular embodiment, the flow of oxidizer  201  is extracted from one or more stages of the high pressure compressor  24  of the engine  13  ( FIG.  2   ). However, it should be appreciated that certain embodiments of the system  200  may receive the flow of oxidizer from the intermediate pressure compressor or low pressure compressor  22  ( FIG.  2   ). Still further embodiments may receive the flow of oxidizer  201  from a dedicated compressor separate from the compressor section  20  of the propulsion system  10 . A flow control device  205 , such as a valve or other appropriate control mechanism, may desirably adjust or modulate an amount or magnitude of flow of oxidizer extracted from the compressor section  20 . 
     The fluid circuit  210  is configured to provide fluid communication of the flow of oxidizer  201  from the compressor section  20  to a combustion device  230 . The combustion device  230  may be any appropriate type of deflagrative or detonative combustion device configuration. Embodiments may include, but are not limited to, an annular combustor, a can combustor, a can-annular combustor, a trapped vortex combustor (TVC), an involute or scroll combustor, a rich burn combustor, a lean burn combustor, a pulse detonation combustor, a rotating detonation combustor, or combinations thereof, or other appropriate type of deflagrative or detonative combustion system. 
     In a particular embodiment, the flow control device  205  may limit, regulate, or control the flow of oxidizer  201  received by the combustion device  230  such that the flow is steady or otherwise within a particular or desired parameter range. The desired parameter range may be a particular flow rate or pressure, or combinations thereof, of oxidizer  201  provided to the combustion device  230 . The flow control device  205  may generally allow for combustion within desired operational limits. Such limits may include emissions or greenhouse gases (e.g., oxides of nitrogen, smoke, unburned hydrocarbons, carbon dioxide, carbon monoxide, etc.). Limits may additionally, or alternatively, include those associated with lean blow out, rich blow out, re-light, combustion stability, pressure oscillations, acoustics, or other performance or operability parameters for combustion systems. 
     It should further be appreciated that the flow control device  205  may allow for stable operation of the combustion device  230  configured as a detonation combustor. The flow control device  205  may provide the flow of oxidizer  201  within ranges of pressure and/or flow rate particular for operation of the combustion device  230  as a detonation combustor. The combustion device  230  configured as a detonation combustor may further provide improvements to energy and thermal efficiency over deflagrative combustor configurations. Additionally, the combustion device  230  may be configured within operational ranges suitable for driving a turbine  240  different from operation of the heat addition system  26  and the expansion section  30  at the propulsion system  10 . For instance, the system  200  may be configured to operate the combustion device  230  within operational ranges or steady state that are more narrow than those for the propulsion system  10 . In another instance, propulsion systems  10 , such as for aircraft, are generally configured for ranges of operating conditions corresponding to a landing-takeoff cycle for an aircraft. In contrast, the flow control device  205  may be configured to provide the flow of oxidizer  201  to the combustion device  230  within operational ranges that obviate issues related to transient operation or differences from relatively low power output (e.g., light-off, idle) to relatively high power output (e.g., takeoff). Additionally, or alternatively, the compressor assembly  220  may be of the APU  15 . The APU  15  may generally be configured to operate at relatively steady-state operation, such as described above. Still other embodiments may receive the flow of oxidizer  201  from a compressor or pump separate from the aerodynamic or thermodynamic flowpath of the propulsion system  10  or the APU  15 . Such embodiments include the compressor section forming an air compressor driven by an electric machine. 
     The system  200  further includes a pipes, manifolds, or walled conduits forming a fuel circuit  310  extended in fluid communication from a fuel tank  300 . The fuel tank  300  contains a liquid and/or gaseous fuel for mixing and combustion/detonation at the combustion device  230 . The fuel circuit  310  is configured to provide a flow of fuel, depicted schematically via arrows  302 , to the combustion device  230 . In a particular embodiment, the fuel tank  300  is furthermore in fluid communication with the heat addition system  26  of the engine  13  to provide a flow of liquid and/or gaseous fuel, depicted schematically via arrows  305 , for generating combustion gases to expand at the expansion section  30 . 
     In certain embodiments, the system  200  includes a fuel flow control device  307  configured to provide a first portion of fuel, depicted schematically via lines  303 , toward the heat addition system  26  of the engine  13 , and a second portion of fuel, depicted schematically via lines  304 , toward the combustion device  230 . The fuel flow control device  307  may form a valve, a flow divider, or other appropriate mechanism for separating the flow of fuel  301  into the first portion  303  and the second portion  304 . In some embodiments, a fuel control device  307  is configured to control an amount or quantity of the second portion of fuel  304  provided to the combustion device  230 . In certain embodiments, the fuel control device  307  at least partially determines an output energy of the of the combustion gases  202  to the turbine  240 , such as by adjusting or modulating the amount of fuel provided to and combusted/detonated at the combustion device  230 . In a particular embodiment, the flow control device  205  ( FIG.  2   ) furthermore determines an output energy of the combustion gases  202  to the turbine  240 , such as by adjusting or modulating the amount of oxidizer provided to and mixed with the fuel  302  for combustion/detonation at the combustion device  230 . 
     During operation, the combustion device  230  generates combustion gases  202  and provides the combustion gases  202  to drive the turbine  240 . The turbine  240  is operably coupled to a load device  270  via a driveshaft  241 . During operation, as the combustion gases  202  expand through the turbine  240 , the turbine generates an output torque and provides power to the load device  270  via transmission through the driveshaft  241 . The load device  270  may include one or more fuel pumps, electric machines (e.g., motors and/or generators, constant frequency or variable frequency machines, hybrid powertrains, etc.), lubricant pumps, hydraulic pumps, air compressors, engine starter, sensor drives (e.g., one or more sensor devices, instrumentation sensors, or telemetry, including, but not limited to, transducers, capacitors, slip rings, thermocouples, electronic measurement devices, or computing systems), and auxiliary gearbox drives, or combinations thereof. 
     The expanded combustion gases, depicted schematically via lines  203 , egress from the turbine  240  are provided to the engine  13 . Referring to  FIGS.  2 - 3   , in certain embodiments, the combustion gases provided to the engine  13  are particularly provided to the core flowpath  70 . In one embodiment, the combustion gases are provided from the turbine  240  to the core flowpath  70  at the exhaust section  36  of the engine  13 . In another embodiment, the combustion gases are provided from the turbine  240  to the core flowpath  70  at the expansion section  30  of the engine  13 . In a still particular embodiment, the combustion gases are provided from the turbine  240  to the core flowpath at the intermediate pressure turbine or low pressure turbine  34  at the expansion section  30  of the engine  13 . In still other embodiments, the flow of combustion gases  204  is provided to one or more of the fan stream  14  or the third stream flowpath  71 . 
     In a particular embodiment, the second portion of fuel, depicted schematically via lines  304 , is provided into thermal communication with the flow of combustion gases  203  egressed from the turbine  240  via a fuel-air heat exchanger  250 . The fluid is generally an oxidizer, such as the flow of air through the propulsion system  10 . In one embodiment, the fuel-air heat exchanger  250  is configured to transmit heat or thermal energy from the flow of combustion gases  203  downstream of the turbine  240  to the flow of fuel  304  upstream of the heat addition system  26 . The cooled flow of combustion gases, depicted schematically via lines  204 , is provided from the fuel-air heat exchanger  250  to the engine  13 , such as described above. The heated flow of fuel, depicted schematically via lines  305 , is provided from the fuel-air heat exchanger  250  to the heat addition system  26  of the engine  13 . 
     In certain embodiments, a deoxygenator  320  is positioned in flow arrangement along the fuel circuit  310 . The deoxygenator  320  is configured to remove oxygen from the second portion of fuel  303 . In an embodiment, the deoxygenator  320  receives energy or motive force from the load device  270 . The energy may be provided from the load device  270  via a shaft, electric energy, or other appropriate method for energy transmission. The deoxygenated flow of fuel is provided downstream to the fuel-air heat exchanger  250 . 
     Referring now to  FIG.  4   , the system  200  is configured substantially similarly as depicted and described in  FIGS.  2 - 3   . In the embodiment depicted in  FIG.  4   , the energy conversion system  200  further includes a thermal management system  400  including a walled conduit forming a heat transfer fluid circuit  410  configured to provide a heat transfer fluid in thermal communication with the flow of combustion gases  203  egressed from the turbine  240 . In  FIG.  4   , the fuel-air heat exchanger  250  provides the combustion gases  203  received from the turbine  240  in thermal communication with a flow of heat transfer fluid, depicted schematically via lines  401 , received from a heat transfer fluid flow device  405 . In various embodiments, the flow device  405  is operably coupled to and driven by the load device  270 , such as described with regard to the deoxygenator  320 . 
     The thermal management system  400  is further configured to provide the heat transfer fluid, depicted schematically via lines  402 , in thermal communication with the second portion of fuel  304  via a first thermal bus heat exchanger  410 . The heat exchanger  410  is configured to heat the flow of fuel  304  by receiving heat or thermal energy from the flow of heat transfer fluid  402 . The flow of heat transfer fluid  402  receives heat or thermal energy from the flow of combustion gases  203  egressed from the turbine  240 . 
     In various embodiments, the heat transfer fluid is a lubricant (e.g., oil, oil-based fluid, synthetic oil, polyalphaolefin, polyalphaolefin-based fluids, etc., or combinations thereof), a liquid and/or gaseous fuel (e.g., hydrocarbon fuels, fuel oils, aviation turbine fuels, or other appropriate propulsion system fuels), a supercritical fluid (e.g., supercritical carbon dioxide, water, methane, ethane, propane, ethylene, propylene, methanol, ethanol, acetone, nitrous oxide, or other appropriate substance at a temperature and pressure above its end point of a phase equilibrium curve), a silicone or silicone-based heat transfer fluid (e.g., a polydimethylsiloxane-based fluid, such as Syltherm™, or similar fluid), or other appropriate heat transfer fluid. 
     In some embodiments, the system  200  further includes a second thermal bus heat exchanger  420  positioned in thermal communication with the heat transfer fluid, such as depicted schematically via lines  403 . The second heat exchanger  420  provides thermal communication between the flow of heat transfer fluid  403  and a flow of cooling fluid  501  provided by an engine cooling flow  500 . The engine cooling flow  500  is a flow of relatively cool oxidizer from the engine  13 , such as a flow of oxidizer at the fan stream  14  or the third stream flowpath  71  ( FIG.  2   ). The second heat exchanger  420  is configured to remove thermal energy or heat from the flow of heat transfer fluid  403  and transmit the heat or thermal energy to the flow of cooling fluid  501 . The cooled flow of heat transfer fluid, depicted schematically via lines  404 , is provided to the fuel-air heat exchanger  250 , such as to provide cooling to the flow of combustion gases  203 . The cooled flow of combustion gases  204  is provided to the engine  13 , such as for cooling one or more components of the intermediate pressure turbine or low pressure turbine  34 , or as an active clearance control system. 
     Referring now to  FIG.  5   , the system  200  is configured substantially similarly as described in regard to  FIG.  4   . In  FIG.  5   , the system  200  further includes a combustion gases flow control device  207  configured to divide the flow of combustion gases  202  into a first portion  202   a  provided to the turbine  240  and a second portion  202   b  bypassing the turbine  240 . The first portion of combustion gases  202   a  expands through the turbine  240 . As energy is released through the turbine  240 , the expanded combustion gases  203  are cooler relative to the combustion gases  202 . The relatively cooler, expanded combustion gases  203  are provided to one or more appropriate modules, components, or subsystems at the engine  13 , such as may utilize a relatively low pressure cooling fluid. 
     The bypassed flow of combustion gases  202   b  provides a relatively higher pressure flow in contrast to the flow of combustion gases  203  egressed from the turbine  240 . The bypassed flow of combustion gases  202   b  is provided in thermal communication with the fuel-air heat exchanger  250 , such as described above. The cooled flow of combustion gases  204  is provided to one or more portions of the expansion section  30  such as described above. 
     In particular embodiments, the flow control device  207  and the turbine  240  are integrated as a variable area turbine nozzle (VATN). The flow control device  207  and the turbine  240  together defining the VATN are together configured to control mass flow into or through the turbine  240 . In one embodiment, the flow control device  207  is a variable area structure, such as a variable area nozzle, at an inlet of the turbine  240 . However, in other embodiments, the flow control device  207  is a separate flow control structure configured to adjust or modulate mass flow through the turbine  240 . In certain embodiments, the turbine  240  is downstream of the flow control device  207 . 
     Referring now to  FIG.  6   , the embodiments of the system  200  provided are configured substantially similarly as described with regard to  FIGS.  1 - 4   . In  FIG.  6   , the turbine  240  is further connected to a compressor  245  via a driveshaft  242 . The flow of oxidizer  201  is received from the compressor section  220  such as described above. The compressor  245  further compresses or energizes the flow of oxidizer  201  before providing the compressed flow of oxidizer, depicted schematically via arrows  201   a , to the combustion device  230 . In such embodiments, the compressor  245  operably coupled to the turbine  240  allows for a relatively lower pressure flow of oxidizer to be pulled from the compressor section  20  of the engine  13 , such as from an intermediate or low pressure compressor  22 , or from one or more forward or upstream stages of the high pressure compressor  24 , in contrast to the high pressure compressor  24  generally, or one or more aft stages thereof. In other embodiments, the compressor  245  allows for a relatively low pressure flow of oxidizer to be received from a relatively lower pressure compressor or pump device. 
     Embodiments of the energy conversion system  200 , propulsion system  10 , or vehicle  100  provided herein may provide improved overall propulsion system and vehicle efficiency through improved systems, structures, or methods for energy conversion or thermal management such as provided herein. Embodiments provided herein include particular positioning, placement, and serial flows of fluids configured to improve overall system performance. One or more elements of the system, such as, but not limited to, the heat exchangers, circuits, conduits, flow devices, combustion devices, turbines, or compressors provided herein may be produced via one or more additive manufacturing methods described below. Still further, such systems may not have been possible without flowpaths, conduits, circuits, structures, or other details allowed by additive manufacturing methods. Furthermore, certain arrangements provided herein may produce beneficial and unexpected results via the transmission of heat or thermal energy to various fluids at particular junctions or serial flows such as provided herein. 
     One or more components of the propulsion system  10  and energy conversion system  200  described herein may be manufactured or formed using any suitable process, such as an additive manufacturing process, such as a 3-D printing process. The use of such a process may allow such components to be formed integrally, as a single monolithic component, or as any suitable number of sub-components, or at scales and intricacies not previously allowed or conceived in the art. In particular, the additive manufacturing process may allow such component to be integrally formed and include a variety of features not possible when using prior manufacturing methods. For example, the additive manufacturing methods described herein may allow for the manufacture of the combustion device  230  or one or more heat exchangers to a size, scale, and intricacy not previously conceived in the art. As another example, the additive manufacturing methods described herein may allow for the manufacture of the turbine  240  and a flow control device as a single, integral component. In further embodiments, the additive manufacturing methods described herein allow for the manufacture of the turbine, the flow control device(s), the combustion device, or circuits having unique features, configurations, thicknesses, materials, densities, fluid passageways, headers, and mounting structures that may not have been possible or practical using prior manufacturing methods. Additive manufacturing may allow for combinations of such structures, and their particular flow and thermal arrangements, that may allow for improved thermal efficiency, improved energy conversion, and improved overall propulsion system or vehicle efficiency or operability despite the addition of an additional combustion system, turbine, compressor, or heat exchangers. 
     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, laser jets, and binder jets, Stereolithography (SLA), 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 Selective Laser Melting (DSLM), Selective Laser Melting (SLM), Direct Metal Laser Melting (DMLM), and other known processes. Suitable powder materials for the manufacture of the structures provided herein as integral, unitary, structures, or at scales and intricacies provided herein, include metallic alloy, polymer, or ceramic powders. Exemplary metallic powder materials are stainless steel alloys, cobalt-chrome, aluminum alloys, titanium alloys, nickel based superalloys, and cobalt based superalloys. In addition, suitable alloys may include those that have been engineered to have good oxidation resistance, known as “superalloys” which have acceptable strength at the elevated temperatures of operation in a gas turbine engine, e.g. Hastelloy, Inconel alloys (e.g., IN 738, IN 792, IN 939), Rene alloys (e.g., Rene N4, Rene N5, Rene 80, Rene 142, Rene 195), Haynes alloys, Mar M, CM 247, CM 247 LC, C263, 718, X-850, ECY 768, 282, X45, PWA 1483 and CMSX (e.g. CMSX-4) single crystal alloys. The manufactured objects of the present disclosure may be formed with one or more selected crystalline microstructures, such as directionally solidified (“DS”) or single-crystal (“SX”). 
     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 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. 
     Further aspects of the invention are provided by the subject matter of the following clauses: 
     1. A system for energy conversion, the system including a propulsion system including a compressor section, a heat addition system, and an expansion section in serial flow arrangement; a fuel circuit in fluid communication from a fuel tank to a fuel flow control device, wherein the fuel flow control device separates a flow of fuel from the fuel tank into a first portion of fuel and a second portion of fuel, wherein the fuel circuit is configured to provide the first portion of fuel to the heat addition system; a combustion device configured to receive a flow of oxidizer from the compressor section via a fluid circuit, wherein the fuel circuit is extended in fluid communication to provide the second portion of fuel to the combustion device, and wherein the combustion device is configured to generate combustion gases from the second portion of fuel and the flow of oxidizer, and further wherein the fluid circuit is in fluid communication from the combustion device to flow the combustion gases to the propulsion system; a turbine configured to receive the combustion gases from the combustion device via the fluid circuit; and a load device operably coupled to the turbine via a driveshaft, wherein the load device is configured to receive an output torque from the driveshaft via expansion of the combustion gases through the turbine. 
     2. The system of any one or more clauses herein, wherein the fluid circuit is in fluid communication from the combustion device to flow the combustion gases to the expansion section of the propulsion system. 
     3. The system of any one or more clauses herein, wherein the fluid circuit is in fluid communication from the combustion device to flow the combustion gases to a low pressure turbine of the expansion section of the propulsion system. 
     4. The system of any one or more clauses herein, the system including a fuel-air heat exchanger positioned along the fuel circuit in thermal communication with the first portion of fuel. 
     5. The system of any one or more clauses herein, wherein the fuel-air heat exchanger is positioned along the fluid circuit, wherein the fuel-air heat exchanger is configured to provide heat transfer between the combustion gases and the first portion of fuel. 
     6. The system of any one or more clauses herein, the system including a heat transfer fluid circuit configured to provide a flow of heat transfer fluid in thermal communication with the fuel-air heat exchanger, wherein the fuel-air heat exchanger is configured to provide heat transfer between the first portion of fuel and the heat transfer fluid. 
     7. The system of any one or more clauses herein, the system including a first thermal bus heat exchanger configured to provide heat transfer between the heat transfer fluid and the combustion gases. 
     8. The system of any one or more clauses herein, the system including a second thermal bus heat exchanger configured to provide heat transfer between the heat transfer fluid and a flow of cooling fluid. 
     9. The system of any one or more clauses herein, wherein the flow of cooling fluid is a flow of compressed oxidizer generated by the compressor section of the propulsion system. 
     10. The system of any one or more clauses herein, the system including a deoxygenator positioned along the fuel circuit to receive the first portion of fuel. 
     11. The system of any one or more clauses herein, the system including an oxidizer flow control device positioned at the fluid circuit downstream of the compressor section and upstream of the combustion device, wherein the oxidizer flow control device is configured to modulate an amount of the flow of oxidizer provided to the combustion device. 
     12. The system of any one or more clauses herein, wherein the load device is one or more of a fuel pump, an electric machine, a lubricant pump, a hydraulic pump, an air compressor, an engine starter, a sensor drive, an auxiliary gearbox drive, or combinations thereof. 
     13. The system of any one or more clauses herein, wherein the combustion device is configured as a deflagrative combustion device. 
     14. The system of any one or more clauses herein, wherein the combustion device is configured as a detonative combustion device. 
     15. The system of any one or more clauses herein, the system comprising a fuel flow control device at the fuel circuit, wherein the fuel flow control device is configured to modulate the second portion of fuel provided to the combustion device. 
     16. The system of any one or more clauses herein, the system including a combustion gases flow control device positioned at the fluid circuit downstream of the combustion device, wherein the combustion gases flow control device separates the flow of combustion gases into a first portion of combustion gases in fluid communication with the turbine and a second portion of combustion gases in fluid communication with a thermal bus heat exchanger. 
     17. The system of any one or more clauses herein, wherein the thermal bus heat exchanger provides the second portion of combustion gases in thermal communication with heat transfer fluid at a heat transfer fluid circuit. 
     18. The system of any one or more clauses herein, wherein the second portion of combustion gases bypasses the turbine. 
     19. The system of any one or more clauses herein, wherein the combustion gases flow control device is integrated to the turbine as a variable area turbine nozzle. 
     20. The system of any one or more clauses herein, the system including a compressor operably coupled to the turbine via the driveshaft, wherein the compressor is configured to receive the flow of oxidizer from the compressor section upstream of the combustion device. 
     21. A system for energy conversion, the system including a propulsion system including a compressor section, a heat addition system, and an expansion section in serial flow arrangement; a fuel circuit in fluid communication from a fuel tank to a fuel flow control device, wherein the fuel flow control device separates a flow of fuel from the fuel tank into a first portion of fuel and a second portion of fuel, wherein the fuel circuit is configured to provide the first portion of fuel to the heat addition system; a combustion device configured to receive a flow of oxidizer directly from the compressor section via a fluid circuit, wherein the fuel circuit is in fluid communication to provide the second portion of fuel to the combustion device, and wherein the combustion device is configured to generate combustion gases from the second portion of fuel and the flow of oxidizer, and further wherein the fluid circuit is in fluid communication from the combustion device to flow the combustion gases to the propulsion system; a turbine configured to receive the combustion gases from the combustion device via the fluid circuit; and a load device operably coupled to the turbine via a driveshaft, wherein the load device is configured to receive an output torque from the driveshaft via expansion of the combustion gases through the turbine. 
     22. A system for energy conversion, the system including a propulsion system including a compressor section, a heat addition system, and an expansion section in serial flow arrangement; a fuel circuit in fluid communication from a fuel tank to a fuel flow control device, wherein the fuel flow control device separates a flow of fuel from the fuel tank into a first portion of fuel and a second portion of fuel, wherein the fuel circuit is configured to provide the first portion of fuel to the heat addition system; a combustion device configured to receive a flow of oxidizer from the compressor section via a fluid circuit, wherein the fuel circuit is in fluid communication to provide the second portion of fuel to the combustion device, and wherein the combustion device is configured to generate combustion gases from the second portion of fuel and the flow of oxidizer, and further wherein the fluid circuit is in fluid communication from the combustion device to flow the combustion gases to the propulsion system; a turbine configured to receive the combustion gases from the combustion device via the fluid circuit; and a load device operably coupled to the turbine via a driveshaft, wherein the load device is configured to receive an output torque from the driveshaft via expansion of the combustion gases through the turbine; and a fuel-air heat exchanger positioned along the fuel circuit in thermal communication with the first portion of fuel.