Method and system for power generation and thermal management with combined cycle architecture

Abstract

Methods and systems related to power generation and thermal management for combined cycle architectures. In particular, methods and apparatus for cooling a surface on an aircraft and generating power are provided, the methods and apparatus including propelling the aircraft at a speed of at least 3 Mach causing the surface to heat up aerodynamically. A first working fluid is circulated through a first fluid circuit, the circulation heating the first working fluid by a heat-absorbing section that is thermally coupled to the surface, and the first working fluid is expanded in a first heat engine to generate a first work output. A second fluid circuit has a second working fluid that receives heat from the first working fluid, and a second heat engine that generates a second work output. The first and second work outputs are operatively coupled to first and second power generators, respectively, to power primary or auxiliary systems on the aircraft.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to high-speed flight vehicles, and more particularly to systems and methods for thermal management and power generation on high-speed flight vehicles. BACKGROUND

[0002] Flight vehicles traveling through the atmosphere at high speeds can experience extremely high temperatures. When traveling at speeds greater than 3 Mach, and more particularly at hypersonic speeds greater than 5 Mach, temperatures can locally exceed 1000 degrees Fahrenheit, forcing the use of high-density materials such as superalloys or expensive non-metallic materials such as ceramic matrix composites. Additionally, turbofan and turbojet engines cannot be used at speeds in excess of 3 Mach without air cooling. Moreover, as speed increases, a large portion of the total engine airflow is diverted around the turbine machinery into an augmenter, also known as a afterburner, which is essentially a ramjet. As a result, the turbine machine generates a lower amount of power, thus reducing the turbine machine's ability to generate power for the vehicle systems. SUMMARY

[0003] According to one aspect of the present invention, a method of generating power from at least one heat source associated with a flight vehicle is provided, the method comprising the step of propelling the flight vehicle at a flight speed of at least 3 Mach. The method further comprises the step of circulating a first working fluid through a first fluid circuit, the circulating step comprising, in order: compressing the first working fluid through a first compressor; heating the first working fluid through a first heat intake of the first fluid circuit, wherein the first heat intake of the first fluid circuit is thermally coupled to the at least one heat source associated with the flight vehicle; expanding the first working fluid in a first thermal engine to generate a first work output from the first thermal engine; cooling the first working fluid; and recirculating the first working fluid to the first compressor. The method further comprises the step of circulating a second working fluid through a second fluid circuit, the circulating step comprising, in order: pressurizing the second working fluid through a fluid pressurization device; exchanging heat from the first working fluid to the second working fluid through a recuperator; expanding the second working fluid in a second thermal engine to generate a second work output from the second thermal engine; cooling the second working fluid; and recirculating the second working fluid to the fluid pressurization device. Still further, the method comprises the steps of generating a first power source by work-coupling the first work output of the first thermal engine to a first generator; and generating a second power source by work-coupling the second work output of the second thermal engine to a second generator.

[0004] According to another aspect of the application, there is provided a system for generating power from at least one heat source associated with a flight vehicle traveling at a flight speed of at least 3 Mach, the system comprising: a first fluid circuit containing a first working fluid, the first fluid circuit comprising, in order: a first compressor for compressing the first working fluid; a first heat absorption section positioned in thermal coupling relationship to the at least one heat source associated with the flight vehicle, the first heat absorption section for heating the first working fluid; and a first heat engine for expanding the first working fluid and generating a first work output. The system further comprises: a second fluid circuit containing a second working fluid, the second fluid circuit comprising, in order: a fluid pressurization device for pressurizing the second working fluid; a second heat engine for expanding the second working fluid and generating a second work output; a heat exchanger for exchanging heat from a low pressure leg of the first fluid circuit between the first heat engine and the first compressor to a high pressure leg of the second fluid circuit between the fluid pressurization device and the second heat engine; and a radiator heat exchanger operatively coupled to a low pressure leg of the second fluid circuit between the second heat engine and the fluid pressurization device.

[0005] According to another aspect of the application, there is provided a system for generating power from at least one heat source associated with a flight vehicle traveling at a flight speed of at least 3 Mach, the system comprising: a first fluid circuit containing a first working fluid, the first fluid circuit comprising in order: a first compressor for compressing the first working fluid; a first heat sink positioned in thermal coupling relationship to the at least one heat source associated with the flight vehicle, the first heat sink for heating the first working fluid; and a first heat engine for expanding the first working fluid and generating a first work output. The system further comprises: a second fluid circuit containing a second working fluid, the second fluid circuit comprising in order: a fluid pressurization device for pressurizing the second working fluid; a second heat engine for expanding the second working fluid and generating a second work output; a heat exchanger for exchanging heat from a low pressure leg of the first fluid circuit between the first heat engine and the first compressor to a high pressure leg of the second fluid circuit between the fluid pressurization device and the second heat engine; and a radiator heat exchanger operatively coupled to a low pressure leg of the second fluid circuit between the second heat engine and the fluid pressurization device. A first generator is operatively coupled to the first heat engine and configured to receive at least a portion of the first work output and generate a first electrical power source. A second generator is operatively coupled to the second heat engine and configured to receive at least a portion of the second work output and generate a second electrical power source. A controller is operatively coupled to the first compressor and the fluid pressurization device, wherein the controller is programmed to perform a method comprising the step of starting operation of the first compressor and the fluid pressurization device when the flight speed of the flight vehicle is above 3 Mach.

[0006] The features, functions, and advantages that have been discussed can be implemented independently in various examples, or can be combined in yet other examples, further details of which can be appreciated throughout the description and drawings herein. BRIEF DESCRIPTION OF DRAWINGS

[0007] The novel features of the exemplary examples are set forth with

[0008] Figure 1 is a perspective view of a high speed flight vehicle having an integrated cooling and power generation system according to the present application.

[0009] Figure 2 is a schematic illustration of an integrated cooling and power generation system.

[0010] Figure 3 is a plot illustrating exemplary supercritical fluids for use in an integrated cooling and power generation system.

[0011] Figure 4 is a block diagram illustrating a method of cooling a surface of a high-speed flight vehicle in the context of simultaneous power generation. Figure 1 DETAILED DESCRIPTION

[0012] The accompanying drawings and the following description illustrate specific examples of the claimed subject matter. Accordingly, it will be apparent to those of ordinary skill in the art that various arrangements can be constructed without departing on the scope of the subject matter as defined by the appended claims and equivalents thereof. Furthermore, the examples described herein are intended to help illustrate the principles of the disclosed subject matter and are not intended to limit the scope of the subject matter to the specific examples described. As such, the present subject matter is not intended to be limited to the specific examples described below, but rather is intended to include all variations commensurate with the principles of the subject matter. It is therefore intended that the scope of the subject matter covered by the appended claims and their equivalents be limited only to the extent necessary to preserve the fair rights of others.

[0013] Examples of the integrated cooling and power generation system described herein simultaneously cool a surface of a high-speed flight vehicle and generate power by circulating working fluids through separate fluid circuits of a combined cycle architecture. For example, a first working fluid, such as a supercritical working fluid, is circulated through a first fluid circuit having a compressor and a dedicated heat engine, which in an exemplary implementation has a Brayton cycle architecture. A second working fluid, which can be a low temperature working fluid such as water, is circulated through a second fluid circuit having a fluid pressurization device and a dedicated heat engine, which in an exemplary implementation has a Rankine cycle architecture. A portion of the surface of the flight vehicle can reach 650 degrees Fahrenheit or more when the flight vehicle is traveling above Mach 3. At Mach 5, the surface of the flight vehicle can reach 1000 degrees Fahrenheit or more. The supercritical working fluid in the first fluid circuit absorbs heat from the surface of the flight vehicle, thereby eliminating hot spots and allowing the use of lighter and / or less expensive materials. In addition, the heat absorbed by the first working fluid can be used to generate power for the flight vehicle. The second fluid circuit is thermally coupled to the first fluid circuit, such as through a heat exchanger, to cause the heat engine in the second circuit to generate additional power. Thus, the combined cycle architecture more efficiently generates electrical power from waste heat associated with a high-speed flight vehicle.

[0014] Figure 1 ​Examples of a high-speed flight vehicle 102 are illustrated. The flight vehicle 102 can be piloted or unpiloted as desired. The flight vehicle 102 is merely one configuration of a flight vehicle capable of traveling at speeds of at least 3 Mach, and other configurations not shown can be implemented as desired. For example, the flight vehicle 102 can have different shapes, sizes, aspect ratios, etc. as desired. Thus, the flight vehicle 102 is shown in a particular configuration for purposes of discussion only.

[0015] In this example, the flight vehicle 102 has a surface 104 that is exposed to aerodynamic heating. In some examples, the surface 104 is disposed on a leading surface of the flight vehicle 102, such as a wing 106, a tail 108, a nose cap 110, or an inlet duct 112 (e.g., an inlet air duct). The surface 104 is aerodynamically heated during operation of the flight vehicle 102 above 3 Mach, or in hypersonic flight (e.g., the flight vehicle 102 moves at hypersonic speeds of 5 Mach and above). For example, the temperature of the surface 104 can exceed 1000 degrees Fahrenheit.

[0016] The flight vehicle 102 includes a system 100 for generating power from the heated surface 104. Drawing heat from the surface 104 also cools the surface 104, which can enable the surface 104 to be formed from materials that do not need to be rated for excessively high temperatures, thereby reducing material costs and reducing material weight. As Figure 2 Best shown, the system 100 includes a first fluid circuit 120 through which a first working fluid 122 is circulated. In the illustrated example, the first fluid circuit 120 is formed as a closed loop having a Brayton cycle architecture. When the flight vehicle 102 is operated at speeds above 3 Mach, heat from the surface 104 is conducted to the first working fluid 122 in the first fluid circuit 120, thereby maintaining the first working fluid 122 at a temperature and pressure above its critical point. Figure 3 The critical point of a substance is illustrated graphically, where temperatures and pressures above the critical point will result in a supercritical state. In some examples, the first working fluid is supercritical carbon dioxide.

[0017] The system 100 includes components disposed in the first fluid circuit 120 that perform a sequence of thermodynamic processes involving the transfer of heat and work into and out of the system 100 while changing the temperature and pressure of the first working fluid 122 within the system. As Figure 2As schematically illustrated, the system 100 includes a first compressor 130 for compressing the first working fluid 122 to an increased pressure. The system 100 also includes a first heat sink 140 that absorbs heat from a source external to the first fluid circuit 120 to heat the first working fluid 122. In the illustrated example, the external source can be the surface 104 of the flight vehicle 102, and the first heat sink 140 is a segment of the first fluid circuit 120 positioned in a thermally coupled relationship to the surface 104. Additionally or alternatively, the external source can be incoming air diverted from the inlet duct 112 of the flight vehicle 102, and an inlet air heat exchanger 256 is provided to conduct heat from the incoming air to the first working fluid 122. In Figure 2 In the illustrated example, the inlet air line 253 passes through the inlet air heat exchanger 256. An upstream end of the inlet air line 253 is fluidly coupled to the inlet duct 112. A high temperature air system 255 on the flight vehicle 102 is directly fluidly coupled to the inlet duct 112, thereby bypassing the inlet air heat exchanger 256. A low temperature air system 257 is fluidly coupled to a downstream end of the inlet air line 253.

[0018] A first heat engine 150 is provided in the first fluid circuit 120 for extracting a first work output 152 from the first working fluid 122 by expanding the first working fluid 122 to a reduced pressure. Although Figure 2 The first heat engine 150 is schematically illustrated as a turbine, although other types of heat engines that are capable of extracting a work output from a heated and pressurized working fluid can be used. In the illustrated example, the first work output 152 takes the form of a rotating output shaft of the turbine that is mechanically coupled to the first compressor 130 through a shaft 154, thereby causing the first compressor 130 to operate. In alternative examples, the first compressor 130 can operate electrically, in which case the first work output 152 is mechanically coupled to an electric generator that converts mechanical energy to electrical power to drive the first compressor 130. As discussed in greater detail below, this electrical power can also be used to power other vehicle systems. Additionally, it should be appreciated that the first compressor 130 and the first heat engine 150 generally divide the first fluid circuit 120 into a low pressure leg 124 that extends downstream of the first heat engine 150 to an inlet of the first compressor 130, and a high pressure leg 126 that extends upstream of the first heat engine 150 to an outlet of the first compressor 130.

[0019] The system 100 also includes a second fluid circuit 250 through which a second working fluid 252 is circulated. In the illustrated example, the second fluid circuit 250 is formed as a closed loop having a Rankine cycle architecture. The second fluid circuit 250 extracts heat from the first fluid circuit 120 and uses the heat to generate additional electrical power. In some examples, the second working fluid 252 can be a low temperature working fluid such as water.

[0020] The system 100 includes components disposed in the second fluid circuit 250 for performing a sequence of thermodynamic processes involving the transfer of heat and work into and out of the system 100 while changing the temperature and pressure of the second working fluid 252 within the system. As Figure 2 As schematically illustrated in FIG. 2, the system 100 includes a fluid pressurization device 254 for pressurizing the second working fluid 252. The fluid pressurization device 254 can be a pump, a second compressor, or any other device capable of increasing the pressure of the second working fluid 252 in the second fluid circuit 250.

[0021] A second heat engine 258 is disposed in the second fluid circuit 250 for extracting a second work output 260 from the second working fluid 252 by expanding the second working fluid 252 to a reduced pressure. Although Figure 2 The second heat engine 258 is schematically illustrated as a turbine, although other types of heat engines capable of extracting a work output from a heated and pressurized working fluid can be used. In the illustrated example, the second work output 260 takes the form of a rotating output shaft of a turbine that is mechanically coupled to an electrical power generator. In alternative examples, the fluid pressurization device 254 can be electrically powered, in which case the second work output 260 is mechanically coupled to an electrical generator that converts mechanical energy to electrical power to drive the fluid pressurization device 254. As discussed in more detail below, this electrical power can also be used to power other vehicle systems. In addition, it will be appreciated that the fluid pressurization device 254 and the second heat engine 258 generally divide the second fluid circuit 250 into a low pressure leg 262 that extends downstream of the second heat engine 258 to an inlet of the fluid pressurization device 254 and a high pressure leg 263 that extends upstream of the second heat engine 258 to an outlet of the fluid pressurization device 254.

[0022] The heat exchanger 160 exchanges heat from the first working fluid 122 in the first fluid circuit 120 to the second working fluid 252 in the second fluid circuit 250. As Figure 2 As shown, the heat exchanger 160 thermally couples the low pressure leg 124 of the first fluid circuit 120 to the high pressure leg 263 of the second fluid circuit. The heat exchanger 160 can be any structure that allows for fluid-to-fluid exchange of heat.

[0023] In Figure 2 In the illustrated example, the system 100 also includes a radiator heat exchanger 190 for rejecting excess heat from the second working fluid 252. The radiator heat exchanger 190 is disposed in the low pressure branch 262 in the second fluid circuit 250 between the second heat engine 258 and the fluid pressurization device 254. By rejecting heat from the second working fluid 252, the radiator heat exchanger 190 ensures that the temperature of the second working fluid 252 does not exceed the rated operating temperature range of the fluid pressurization device 254. Additionally, the excess heat can be rejected to the ambient atmosphere or conducted to an auxiliary fluid in another system on the flight vehicle 102. In the illustrated example, the radiator heat exchanger 190 also includes a radiator line 191 that passes through the radiator heat exchanger 190. An upstream end of the radiator line 191 is in fluid communication with one or more radiator fluid tanks 192 that carry a radiator fluid (e.g., fuel, water, or other fluid carried on the flight vehicle 102). The upstream end of the radiator line 191 can also be in communication with a sub-system thermal load 194, such as a thermal energy storage device. A downstream end of the radiator line 191 can be in fluid communication with other vehicle systems 196 that can use the heated radiator fluid.

[0024] The system 100 is configured to generate a first power source 172 and a second power source 173. As Figure 2 Illustratively, the system 100 can include a first generator 170 that is mechanically coupled to the first heat engine 150. The first generator 170 receives at least a portion of the work output 152 from the first heat engine 150 and generates the first power source 172. Additionally, a second generator 261 is mechanically coupled to the second heat engine 258 and is configured to receive at least a portion of the second work output 260 and generate the second power source 173. In this example, an auxiliary load 180 is operatively coupled to the first generator 170 and the second generator 261 and is configured to operate using the first power source 172 and the second power source 173. The auxiliary load 180 can be an environmental control system (ECS), one or more flight control devices (e.g., actuators), avionics systems, a payload, or other device or system that requires power. Still further, the first power source 172 and the second power source 173 can also be used to power components of the integrated cooling and power system 100, such as the first compressor 130 and the fluid pressurization device 254.

[0025] In the illustrated example, a controller 200 is provided to control the operation of the system 100. InFigure 2 In some examples, the controller 200 is operatively coupled to the first compressor 130 and the fluid pressurization device 254, and the controller is programmed to perform a method that includes the step of initiating operation of the first compressor 130 and the fluid pressurization device 254 when one or more operating conditions of the flight vehicle 102 exceed a predetermined threshold that indicates favorable conditions for maintaining the first working fluid 122 in a supercritical state. In some examples, the operating condition is a temperature of the surface 104, in which case the controller 200 receives feedback from a sensor 202 configured to detect the temperature of the surface 104, and the controller is programmed to initiate the first compressor 130 and the fluid pressurization device 254 when the surface 104 of the flight vehicle 102 exceeds a threshold temperature. Exemplary threshold temperatures include, but are not limited to, 500 degrees Fahrenheit, 600 degrees Fahrenheit, 700 degrees Fahrenheit, 800 degrees Fahrenheit, 900 degrees Fahrenheit, and 1000 degrees Fahrenheit. In other examples, the operating condition is a flight speed of the flight vehicle 102, which is indicative of the temperature of the surface 104. In these examples, the controller 200 receives an indication of the flight speed, such as from an input command or a sensor 202 configured to determine the flight speed, and the controller is programmed to initiate the first compressor 130 and the fluid pressurization device 254 when the flight vehicle 102 reaches a threshold flight speed. Exemplary threshold flight speeds include, but are not limited to, 3 Mach, 3.5 Mach, 4 Mach, and hypersonic. Additionally, the controller 200 can be operatively coupled to the first heat engine 150 and the second heat engine 258.

[0026] In Figure 2 In the illustrated examples, the controller 200 is also operatively coupled to the first generator 170 and the second generator 261, as well as the auxiliary load 180, to control operation or other aspects of those components. As a result of the thermal efficiency, compact size, and reduced weight provided by using a supercritical working fluid as the first working fluid 122, as well as the increased power generation efficiency provided by the second fluid circuit 250, the integrated cooling and power generation system 100 achieves a weight and volume power density that is an order of magnitude greater than a battery or other conventional power source.

[0027] While the particular hardware implementation of controller 200 is subject to design choices, one particular example includes one or more processors coupled with the current driver. The one or more processors can include any electronic and / or optical circuitry capable of executing the functionality described herein. For example, the processor can perform any of the functionality described herein for controller 200. The processor can include one or more central processing units (CPUs), microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable logic devices (PLDs), control circuitry, etc. Some examples of processors include: CORE TM processor, advanced reduced instruction set computing (RISC) machine processor, etc.

[0028] System 100 is configured to maintain first working fluid 122 in a supercritical state throughout the thermodynamic cycle, thereby enabling the use of lighter and more compact turbomachinery. For example, when first working fluid 122 is carbon dioxide, the critical temperature is approximately 88 degrees Fahrenheit and the critical pressure is approximately 74 bar. The aerodynamic heating of surface 104 increases with the speed of flight vehicle 102. For example, at a speed of 3.5 Mach, localized portions of surface 104 reach 750 degrees Fahrenheit or more, which is sufficient to maintain first working fluid 122 in a supercritical state. At supersonic speeds in excess of 5 Mach, localized portions of surface 104 can reach 1000 degrees Fahrenheit. The thermodynamic efficiency of system 100 increases with the increase in the temperature of surface 104. In addition, first compressor 130 is sized to maintain the pressure of first working fluid 122 above the critical pressure throughout the thermodynamic cycle. Because first working fluid 122 is in a supercritical state, first compressor 130 and first engine 150 can have reduced size and weight, thereby making system 100 practical for use on flight vehicle 102. In addition, the illustrated system 100 is a closed loop system provided independent of the propulsion system of flight vehicle 102.

[0029] Figure 4is a block diagram illustrating a method 300 of cooling a surface 104 of a high-speed flying vehicle 102 and generating power on the flying vehicle 102. The method 300 begins at block 302 by propelling the flying vehicle 102 at a flight speed of at least 3 Mach, where the surface 104 of the flying vehicle 102 obtains heat. At block 304, a first working fluid 122 is circulated through a first fluid circuit 120. The step of circulating the first working fluid 122 through the first fluid circuit 120 includes, in order: compressing the first working fluid 122 by a first compressor 130, as shown at block 306; heating the first working fluid 122 passing through a first heat sink 140 of the first fluid circuit 120, where the first heat sink 140 of the first fluid circuit 120 is thermally coupled to the surface 104 of the flying vehicle 102, at block 308; and expanding the first working fluid 122 in a first heat engine 150, generating a first work output 152 from the first heat engine 150, at block 310. The step of circulating the first working fluid 122 through the first fluid circuit 120 also includes: cooling the first working fluid 122, at block 312; and recirculating the first working fluid 122 to the first compressor 130, at block 314.

[0030] The method 300 can also continue at block 330 by circulating a second working fluid 252 through a second fluid circuit 250. The step of circulating the second working fluid 252 through the second fluid circuit 250 includes, in order: pressurizing the second working fluid 252 by a fluid pressurizing device 254, as shown at block 332; exchanging heat from the first working fluid 122 to the second working fluid 252 by a heat exchanger 160, at block 334; expanding the second working fluid 252 in a second heat engine 258, generating a second work output 260 from the second heat engine 258, as shown at block 336; cooling the second working fluid 252, as shown at block 338; and recirculating the second working fluid 252 to the fluid pressurizing device 254, as shown at block 340.

[0031] The method 300 also includes a step of generating power. For example, as shown at block 342, the first work output 152 and the second work output 260 can be combined to generate power. Figure 4As shown schematically, the method 300 includes the steps of generating a first power supply 172 by mechanically coupling the first work output 152 of the first heat engine 150 to the first electric generator 170 at block 318, and generating a second power supply 173 by mechanically coupling the second work output 260 of the second heat engine 258 to the second electric generator 261 at block 342. The first power supply 172 from the first electric generator 170 and the second power supply 173 from the second electric generator 261 can be used to operate the first compressor 130 and the fluid booster 254 when these components are driven by electric power. Additionally or alternatively, as shown at block 320, the first power supply 172 and the second power supply 173 can be used to power the auxiliary loads 180.

[0032] Still further, the method 300 can optionally include the additional step of reducing the temperature of the second working fluid 252 prior to recirculating the second working fluid back to the fluid booster 254. In particular, the method 300 can include the step of rejecting heat from the second working fluid 252 using a radiator heat exchanger 190 as shown at block 322.

[0033] Furthermore, the present disclosure includes the following examples, whereby the scope of protection is provided by the claims.

[0034] Example 1. A method of generating electric power from at least one heat source associated with a flight vehicle, the method comprising the steps of propelling the flight vehicle at a flight speed of at least 3 Mach; circulating a first working fluid through a first fluid circuit, the circulating step comprising in order: compressing the first working fluid by a first compressor; heating the first working fluid through a first heat sink of the first fluid circuit, wherein the first heat sink of the first fluid circuit is thermally coupled to the at least one heat source associated with the flight vehicle; expanding the first working fluid in a first heat engine to generate a first work output from the first heat engine; cooling the first working fluid; and recirculating the first working fluid to the first compressor; circulating a second working fluid through a second fluid circuit, the circulating step comprising in order: pressurizing the second working fluid by a fluid booster; exchanging heat from the first working fluid to the second working fluid by a heat exchanger; expanding the second working fluid in a second heat engine to generate a second work output from the second heat engine; cooling the second working fluid; and recirculating the second working fluid to the fluid booster; generating a first power supply by operatively coupling the first work output of the first heat engine to a first electric generator; and generating a second power supply by operatively coupling the second work output of the second heat engine to a second electric generator.

[0035] Example 2. The method of Example 1, wherein the at least one heat source associated with the flight vehicle comprises a first surface of the flight vehicle.

[0036] Example 3. The method of any of Examples 1-2, wherein the at least one heat source associated with the flight vehicle comprises heated air from an inlet duct of the flight vehicle.

[0037] Example 4. The method of any of Examples 1-3, wherein the first compressor comprises an electrically driven compressor operatively coupled to the first generator.

[0038] Example 5. The method of Example 4, wherein the fluid pressurization device comprises an electrically driven fluid pressurization device operatively coupled to the second generator.

[0039] Example 6. The method of any of Examples 1-5, further comprising the step of using the first generator and the second generator to power auxiliary loads.

[0040] Example 7. The method of any of Examples 1-6, further comprising the step of rejecting heat from the second working fluid via a radiator heat exchanger prior to recirculating the second working fluid to the fluid pressurization device.

[0041] Example 8. The method of any of Examples 1-7, wherein the first working fluid comprises a first supercritical working fluid, and wherein the second working fluid comprises a cryogenic working fluid.

[0042] Example 9. A system for generating power from at least one heat source associated with a flight vehicle, the flight vehicle traveling at a flight speed of at least 3 Mach, the system comprising: a first fluid circuit containing a first working fluid, the first fluid circuit comprising, in order: a first compressor for compressing the first working fluid; a first heat sink positioned in a thermally coupled relationship to the at least one heat source associated with the flight vehicle, the first heat sink for heating the first working fluid; and a first heat engine for expanding the first working fluid and generating a first work output; and a second fluid circuit containing a second working fluid, the second fluid circuit comprising, in order: a fluid pressurization device for pressurizing the second working fluid; a second heat engine for expanding the second working fluid and generating a second work output; a heat exchanger for exchanging heat from a low pressure leg of the first fluid circuit between the first heat engine and the first compressor to a high pressure leg of the second fluid circuit between the fluid pressurization device and the second heat engine; and a radiator heat exchanger operatively coupled to a low pressure leg of the second fluid circuit between the second heat engine and the fluid pressurization device.

[0043] Example 10. The system of Example 9, further comprising: a first electric power generator operatively coupled to the first heat engine and configured to receive at least a portion of the first work output and generate a first electric power source.

[0044] Example 11. The system of Example 10, further comprising: a second electric power generator operatively coupled to the second heat engine and configured to receive at least a portion of the second work output and generate a second electric power source.

[0045] Example 12. The system of Example 11, further comprising: a controller operatively coupled to the first compressor and the fluid pressurization device, wherein the controller is programmed to perform a method comprising the step of initiating operation of the first compressor and the fluid pressurization device when an operating condition of the flight vehicle exceeds a predetermined threshold.

[0046] Example 13. The system of Example 12, wherein the operating condition of the flight vehicle comprises a flight speed of the flight vehicle.

[0047] Example 14. The method of any one of examples 9 to 13, wherein the at least one heat source associated with the flight vehicle comprises a first surface of the flight vehicle.

[0048] Example 15. The method of any one of examples 9 to 14, wherein the at least one heat source associated with the flight vehicle comprises heated air from an inlet duct of the flight vehicle.

[0049] Example 16. The method of any one of examples 9 to 15, wherein the first working fluid comprises a first supercritical working fluid, and wherein the second working fluid comprises a cryogenic working fluid.

[0050] Example 17. A system for generating power from at least one heat source associated with a flight vehicle traveling at a flight speed of at least 3 Mach, the system comprising: a first fluid circuit containing a first working fluid, the first fluid circuit comprising, in order: a first compressor for compressing the first working fluid; a first heat sink positioned in a thermally coupled relationship to the at least one heat source associated with the flight vehicle, the first heat sink for heating the first working fluid; and a first heat engine for expanding the first working fluid and generating a first work output; and a second fluid circuit containing a second working fluid, the second fluid circuit comprising, in order: a fluid pressurization device for pressurizing the second working fluid; a second heat engine for expanding the second working fluid and generating a second work output; a heat exchanger for exchanging heat from a low pressure leg of the first fluid circuit between the first heat engine and the first compressor to a high pressure leg of the second fluid circuit between the fluid pressurization device and the second heat engine; and a radiator heat exchanger operatively coupled to a low pressure leg of the second fluid circuit between the second heat engine and the fluid pressurization device; a first power generator operatively coupled to the first heat engine and configured to receive at least a portion of the first work output and generate a first electrical power source; a second power generator operatively coupled to the second heat engine and configured to receive at least a portion of the second work output and generate a second electrical power source; and a controller operatively coupled to the first compressor and the fluid pressurization device, wherein the controller is programmed to perform a method comprising the step of initiating operation of the first compressor and the fluid pressurization device when the flight speed of the flight vehicle is above 3 Mach.

[0051] Example 18. The system of Example 17, wherein the at least one heat source associated with the flight vehicle comprises a first surface of the flight vehicle.

[0052] Example 19. The system of any of Examples 17-18, further comprising: an auxiliary load operatively coupled to each of the first generator and the second generator.

[0053] Example 20. The system of Example 19, wherein the radiator heat exchanger comprises a radiator fluid or a thermal storage device.

[0054] As used herein, the term "in sequence" generally refers to elements (e.g., unit operations) in an order. Such an order can refer to a process order, for example, as the order in which a working fluid flows from one component to another. In an example, a compressor, a thermal storage unit, and a turbine are in sequence: the compressor upstream of the thermal storage unit and the thermal storage unit upstream of the turbine. In such a case, a working fluid can flow from the compressor to the thermal storage unit and from the thermal storage unit to the turbine. A working fluid flowing through unit operations in sequence can flow through the unit operations sequentially. A component sequence can include one or more intermediate components. For example, a system including a compressor, a thermal storage unit, and a turbine in sequence can include an auxiliary tank between the compressor and the thermal storage unit. A component sequence can be cyclic.

[0055] Any of the various elements shown in the figures or described herein can be implemented as hardware, software, firmware, or some combination of these. For example, an element can be implemented as dedicated hardware. A dedicated hardware element can be referred to as a "processor," "controller," or some similar terminology. Where a processor is provided, it can be a single shared processor, a single dedicated processor, or a plurality of individual processors, some of which can be shared or distributed. Also, the term "processor" or "controller" should not be construed to refer exclusively to hardware capable of executing software, but can implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), or other circuitry, field- programmable gate array (FPGA), read-only memory (ROM) for storing software, random access memory (RAM), nonvolatile storage, logic, or some other physical hardware component or module.

[0056] Moreover, an element can be implemented as instructions executable by a processor or a computer to perform the functions of that element. Some examples of instructions are software, program code, and firmware. The instructions are operational when executed by the processor to direct the processor to perform the functions of the element. The instructions can be stored in storage devices, which are readable by the processor. Some examples of storage devices are digital or solid-state memories, magnetic storage media such as disks and tape, hard drives, or optically readable digital data storage media.

[0057] Although specific examples were described herein, the scope is not limited to those specific examples. Instead, the scope is defined by the following claims and their equivalents.

Claims

1. A method of generating power from at least one heat source associated with a flight vehicle, the method comprising the steps of: propelling the flight vehicle at a flight speed of at least 3 Mach; circulating a first working fluid through a first fluid circuit, the steps of the circulation comprising in order: compressing the first working fluid by a first compressor; heating the first working fluid through a first heat sink of the first fluid circuit, wherein the first heat sink of the first fluid circuit is thermally coupled to the at least one heat source associated with the flight vehicle; expanding the first working fluid in a first heat engine to generate a first work output from the first heat engine; cooling the first working fluid; and recirculating the first working fluid to the first compressor; circulating a second working fluid through a second fluid circuit, the steps of the circulation comprising in order: pressurizing the second working fluid by a fluid pressurizing device; exchanging heat from the first working fluid to the second working fluid by a heat exchanger; expanding the second working fluid in a second heat engine to generate a second work output from the second heat engine; cooling the second working fluid; and recirculating the second working fluid to the fluid pressurizing device, generating a first power source by operatively coupling the first work output of the first heat engine to a first generator; and generating a second power source by operatively coupling the second work output of the second heat engine to a second generator.

2. The method of claim 1, wherein, The at least one heat source associated with the flight vehicle includes a first surface of the flight vehicle.

3. The method of claim 1 or 2, wherein, The at least one heat source associated with the flight vehicle includes heated air from an inlet duct of the flight vehicle.

4. The method of claim 1 or 2, wherein, The first compressor includes an electrically driven compressor operatively coupled to the first generator.

5. The method of claim 4, wherein, The fluid pressurizing device includes an electrically driven fluid pressurizing device operatively coupled to the second generator.

6. The method of claim 1 or 2, further comprising at least one of the following steps: using the first generator and the second generator to power an auxiliary load; rejecting heat from the second working fluid via a radiator heat exchanger prior to recirculating the second working fluid to the fluid pressurizing device.

7. The method of claim 1 or 2, wherein, The first working fluid includes a first supercritical working fluid, and wherein the second working fluid includes water.

8. A system for generating power from at least one heat source associated with a flight vehicle, the flight vehicle traveling at a flight speed of at least 3 Mach, the system comprising: a first fluid circuit containing a first working fluid, the first fluid circuit comprising in order: a first compressor for compressing the first working fluid; a first heat sink positioned in thermal coupling relationship to the at least one heat source associated with the flight vehicle for heating the first working fluid; and a first heat engine for expanding the first working fluid and generating a first work output; and a first generator operatively coupled to the first work output of the first heat engine. a second fluid circuit containing a second working fluid, the second fluid circuit comprising, in order: a fluid pressurization device for pressurizing the second working fluid; a second heat engine for expanding the second working fluid and generating a second work output; a heat exchanger for exchanging heat from a low-pressure leg of the first fluid circuit between the first heat engine and the first compressor to a high-pressure leg of the second fluid circuit between the fluid pressurization device and the second heat engine; and a radiator heat exchanger operatively coupled to a low-pressure leg of the second fluid circuit between the second heat engine and the fluid pressurization device.

9. The system of claim 8, further comprising a first electric generator operatively coupled to the first heat engine and configured to receive at least a portion of the first work output and generate a first electrical power source.

10. The system of claim 9, further comprising a second electric generator operatively coupled to the second heat engine and configured to receive at least a portion of the second work output and generate a second electrical power source.

11. The system of claim 10, further comprising a controller operatively coupled to the first compressor and the fluid pressurization device, wherein, the controller is programmed to perform a method comprising initiating operation of the first compressor and the fluid pressurization device when a condition of the flight vehicle exceeds a predetermined threshold.

12. The system of claim 11, wherein, the condition of the flight vehicle comprises a flight speed of the flight vehicle.

13. The system of any one of claims 8 to 12, wherein, the at least one heat source associated with the flight vehicle comprises a first surface of the flight vehicle.

14. The system of any one of claims 8 to 12, wherein, the at least one heat source associated with the flight vehicle comprises heated air from an inlet duct of the flight vehicle.

15. The system of any one of claims 8 to 12, wherein, the first working fluid comprises a first supercritical working fluid, and wherein the second working fluid comprises water.

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