Fuel cell aircraft thermal management system

Abstract

An aircraft thermal management system includes a high temperature circuit and a low temperature circuit. The high temperature loop is configured to manage a temperature of a fuel cell stack in the engine compartment using the engine compartment heat exchanger. The cryogenic circuit is configured to cool a plurality of thermal loads in the engine compartment using the thermal capacity of the liquid hydrogen.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 519,480, filed on August 14, 2023, and entitled “Fuel Cell Aircraft Thermal Management System,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to aircraft, and more particularly to aircraft using a propulsion system that uses hydrogen-fueled fuel cells for power. Background Art

[0004] Aircraft with electric propulsion systems are an emerging trend that can provide many benefits to the aviation industry. Electric aircraft can provide many environmental benefits. For example, electric aircraft produce zero emissions during flight, which can reduce their carbon footprint.

[0005] Additionally, electric motors are generally quieter than internal combustion engines. Therefore, noise pollution can be reduced by using these types of aircraft.

[0006] Electric aircraft have electric propulsion systems that can be powered by hydrogen. The hydrogen can be stored in tanks. The hydrogen stored in these tanks is usually in a liquid state and stored at very low temperatures, such as -253°C.

[0007] The hydrogen in these fuel storage tanks may be stored as liquid hydrogen, gaseous hydrogen, or other hydrogen carriers such as methane or other hydrocarbons in liquid or gaseous state. Reformers may be used in the reforming process to remove hydrogen from hydrocarbon molecules.

[0008] The hydrogen in these tanks can then be sent to multiple fuel cells to be used to generate electricity to power the propulsion and other systems in the aircraft. These fuel cells are electrochemical devices that convert hydrogen and oxygen obtained from the air into electricity to power the propulsion systems in the aircraft. These types of cells operate with high efficiency and minimal emissions, with water vapor as a byproduct. Summary of the invention

[0009] An embodiment of the present disclosure provides an aircraft thermal management system including a high temperature circuit and a low temperature circuit. The high temperature circuit is configured to manage the temperature of a fuel cell stack in the engine compartment using a nacelle heat exchanger. The low temperature circuit is configured to use the heat capacity of liquid hydrogen to cool multiple heat loads in the engine compartment.

[0010] Another embodiment of the present disclosure provides an aircraft thermal management system, comprising: a ram air cooler in an engine compartment, a fuel cell stack in the engine compartment, and a duct system configured to carry a coolant. The ram air cooler in the engine compartment includes an engine compartment heat exchanger and a set of fans configured to increase air flow through the engine compartment heat exchanger. The duct system includes a high temperature loop and a low temperature loop. The high temperature loop is configured to remove heat from the fuel cell stack and transfer the heat removed from the fuel cell stack to the ambient air as part of the exhaust gas leaving the engine compartment. The low temperature loop is configured to use the heat capacity of liquid hydrogen to remove heat from a set of components in the engine compartment.

[0011] Yet another embodiment of the present disclosure provides an aircraft, comprising: a fuselage; a first wing and a second wing connected to the fuselage; an engine connected to the first wing and the second wing; a liquid hydrogen tank; a piping system; a high temperature loop; and a low temperature loop. The liquid hydrogen tank is configured to store liquid hydrogen. The liquid hydrogen tank extends along the exterior of the fuselage. Each of the engines includes: an engine compartment; an electric motor in the engine compartment; a fuel cell stack in the engine compartment; and a ram air radiator in the engine compartment. The ram air radiator is configured to receive air flowing through an inlet in the engine compartment. The high temperature loop is configured to manage the temperature of the fuel cell stack using an engine compartment heat exchanger. The low temperature loop is configured to cool multiple heat loads in the engine compartment using a fuel system heat exchanger, which uses the heat capacity of liquid hydrogen to cool the coolant.

[0012] Another embodiment of the present disclosure provides a method for thermal management. A fuel cell stack temperature in an engine compartment is managed using an engine compartment heat exchanger in a high temperature loop. Multiple heat loads in the engine compartment are cooled in a low temperature loop that uses the heat capacity of liquid hydrogen to cool the multiple heat loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The novel features believed to characterize the illustrative embodiments are set forth in the appended claims. However, these illustrative embodiments and preferred modes of use, as well as further objects and features thereof, will be best understood by reference to the following detailed description of illustrative embodiments of the disclosure when read in conjunction with the accompanying drawings, in which:

[0014] Figure 1 is a diagram of a hydrogen fuel cell vehicle having a distributed propulsion system according to an illustrative embodiment;

[0015] Figure 2 is an illustration of a front view of a liquid hydrogen tank location according to an illustrative embodiment;

[0016] Figure 3 is a diagram of an engine compartment layout according to an illustrative embodiment;

[0017] Figure 4 is an illustration of a block diagram of a liquid hydrogen fuel cell aircraft according to an illustrative embodiment;

[0018] Figure 5 is an illustration of a block diagram of a heat exchanger system for an aircraft according to an illustrative embodiment;

[0019] Figure 6 is a cross-sectional view of a portion of an engine compartment having a heat exchanger according to an illustrative embodiment;

[0020] Figure 7 is another illustration of a cross-sectional view of a portion of an engine compartment having an engine compartment heat exchanger according to an illustrative embodiment;

[0021] Figure 8 is another illustration of a cross-sectional view of a portion of an engine compartment having an engine compartment heat exchanger according to an illustrative embodiment;

[0022] Fig. 9 is a perspective illustration of an engine having an underhood heat exchanger according to an illustrative embodiment;

[0023] Fig.10 is a perspective illustration of an engine having an underhood heat exchanger according to an illustrative embodiment;

[0024] Fig.11 is a perspective illustration of an engine having an underhood heat exchanger according to an illustrative embodiment;

[0025] Fig.12 is another perspective illustration of an engine having an underhood heat exchanger according to an illustrative embodiment;

[0026] Fig.13 is a schematic illustration of a fan configuration for use with a nacelle heat exchanger within an engine compartment according to an illustrative embodiment;

[0027] Fig.14 is a cross-sectional view of an engine compartment having an engine compartment heat exchanger according to an illustrative embodiment;

[0028] Fig.15 is a diagram of air flow through an engine compartment to provide cooling for a fuel cell stack according to an illustrative embodiment;

[0029] Fig.16 is an illustration of a front view of an engine compartment with an engine compartment heat exchanger according to an illustrative embodiment;

[0030] Fig.17 is a diagram of an engine compartment heat exchanger according to an illustrative embodiment;

[0031] Fig.18 is a graphical representation of air flow through an engine compartment heat exchanger according to an illustrative embodiment;

[0032] Fig.19 is an illustration of a block diagram of a startup system for an aircraft according to an illustrative embodiment;

[0033] Fig. 20 is an illustration of a flow chart of a process for managing startup and operation of a fuel cell stack of an aircraft in accordance with an illustrative embodiment;

[0034] Fig.21 is an illustration of a flow chart of a process for heating a fuel cell stack according to an illustrative embodiment;

[0035] Fig. 22 is an illustration of a flow chart of a process for managing startup and operation of a fuel cell stack of an aircraft in accordance with an illustrative embodiment;

[0036] Fig.23 is an illustration of a flow chart of a process for circulating heated coolant according to an illustrative embodiment;

[0037] Fig.24 is an illustration of a flow chart of a process for delivering power to a fuel cell stack according to an illustrative embodiment;

[0038] Fig.25 is an illustration of a flow chart of a process for stopping heating of a coolant according to an illustrative embodiment;

[0039] Fig.26 is a diagram of an aircraft having a propulsion and power system according to an illustrative embodiment;

[0040] Fig. 27 is a diagram of an integrated power and propulsion unit according to an illustrative embodiment;

[0041] Fig.28 is an illustration of a schematic diagram of a fuel cell stack startup system according to an illustrative embodiment;

[0042] Fig.29 is an illustration of a schematic diagram of a fuel cell stack startup system in a thermal management system according to an illustrative embodiment;

[0043] Fig.30 is an illustration of a schematic diagram of a fuel cell stack startup system in a thermal management system according to an illustrative embodiment;

[0044] Fig.31 is an illustration of a block diagram of an aircraft management system in accordance with an illustrative embodiment;

[0045] Fig.32is an illustration of a flow chart of a process for air management according to an illustrative embodiment;

[0046] Fig.33 is an illustration of a schematic diagram of an aircraft air management system for a fuel cell stack according to an illustrative embodiment;

[0047] Fig.34 is an illustration of a block diagram of an aircraft thermal management system according to an illustrative embodiment;

[0048] Fig.35 is an illustration of a flow chart of a process for thermal management according to an illustrative embodiment;

[0049] Fig.36 is an illustration of a flow chart of a process for managing the temperature of a fuel cell stack according to an illustrative embodiment;

[0050] Fig.37 is a diagram of a thermal management system having a low temperature loop and a high temperature loop according to an illustrative embodiment;

[0051] Fig.38 is a diagram of a hydrogen recycling system according to an illustrative embodiment;

[0052] Fig.39 is an illustration of a flow chart of a process for recycling hydrogen according to an illustrative embodiment;

[0053] Fig.40 is an illustration of a flow chart of a process for recycling hydrogen according to an illustrative embodiment;

[0054] Fig.41 is an illustration of a flow chart of a process for recycling hydrogen according to an illustrative embodiment;

[0055] Fig.42 is a diagram of a liquid hydrogen recirculation system for tank pressure control according to an illustrative embodiment;

[0056] Fig.43 is a diagram of a venting system for gaseous hydrogen according to an illustrative embodiment;

[0057] Fig.44 is a diagram of a system for recycling gaseous hydrogen for tank pressure control according to an illustrative embodiment;

[0058] Fig.45 is an illustration of a block diagram of an aircraft cooling system according to an illustrative embodiment;

[0059] Fig.46 is an illustration of a flow chart of a process for cooling a heat load in accordance with an illustrative embodiment;

[0060] Fig.47is an illustration of a flow chart of a process for cooling a heat load in accordance with an illustrative embodiment;

[0061] Fig.48 is a diagram of a pumped two-phase (P2P) cooling circuit according to an illustrative embodiment;

[0062] Fig.49 is a diagram of a hybrid two-phase (P2P) cooling circuit according to an illustrative embodiment; and

[0063] Fig.50 is a diagram of a pumped two-phase (P2P) cooling loop with waste heat recovery in accordance with an illustrative embodiment. DETAILED DESCRIPTION

[0064] 1. Configuration of LH2 fuel cell aircraft with distributed systems

[0065] The illustrative embodiments recognize and take into account a number of different issues with aircraft operating on liquid hydrogen fuel. These issues recognized by the different illustrative embodiments are described herein.

[0066] The illustrative embodiments recognize and take into account that integrating a liquid hydrogen (LH2) system into an airliner, such as the 50, can be challenging. For example, design challenges arise in determining where to safely locate large liquid hydrogen tanks and how to package thermal management and fuel cell stack systems, both of which have large volume requirements.

[0067] In these illustrative examples, the location of the fuel tanks terminates above the wings and along the sides of the fuselage. This type of configuration allows for the integration of these tanks in a safe manner while keeping the added weight and wetted area as small as possible. In one illustrative example, six nacelles are used to increase redundancy and enable the packaging of the thermal management and fuel cell systems in a manner that uses the smallest possible volume in each nacelle while also reducing the electric motor power requirements.

[0068] Increased redundancy can be achieved by increasing the number of engines. As used herein, when used with reference to an item, "plurality" means one or more items. For example, a plurality of engines is one or more engines.

[0069] In addition, the illustrative examples can use high temperature proton exchange membrane fuel cells instead of low temperature proton exchange membranes. Using high temperature proton exchange membrane fuel cells helps reduce the size of heat exchangers and using heat exchangers with microchannel flow paths helps further reduce the size. In multiple illustrative examples, systems such as these systems are optional.

[0070] A plurality of additional ducts leading from the liquid hydrogen tank to the top of the vertical tail may be implemented in the duct system. During flight, these ducts may be used to provide venting to release excess pressure in the liquid hydrogen tank. In various illustrative examples, the duct system may also be referred to as a pipe or duct system.

[0071] See also Figure 1 , depicts a diagram of a hydrogen fuel cell vehicle with a distributed propulsion system according to an illustrative embodiment. In different illustrative examples, the same reference numeral may be used in more than one figure. Such reuse of reference numerals in different figures represents the same element in the different figures.

[0072] In this illustrative example, aircraft 100 is an example of a liquid hydrogen fuel cell vehicle. Aircraft 100 is an aircraft that can carry different numbers of passengers. For example, aircraft 100 is an aircraft designed to carry 50 passengers, 100 passengers, 130 passengers, or some other number of passengers. In other illustrative examples, aircraft 100 can be a cargo aircraft or a cargo and passenger aircraft.

[0073] As depicted in this example, aircraft 100 includes fuselage 102 having wing 104 and wing 105. In this example, engines 106 and liquid hydrogen tanks 108 are located on wings 104 and 105. As depicted, engine 106 includes six engines. Engine 111, engine 112, engine 113 are connected to wing 104, and engine 114, engine 115, and engine 116 are connected to wing 105.

[0074] In this example, when one component is "connected" to another component, the connection is a physical connection. For example, a first component (such as an engine) can be considered to be physically connected to a second component (such as a wing) by at least one of being fixed to the second component, bonded to the second component, mounted to the second component, welded to the second component, fastened to the second component, or connected to the second component in some other suitable manner. The first component can also be connected to the second component using a third component. The first component can also be considered to be physically connected to the second component by being formed as a part of the second component, an extension of the second component, or both. In some examples, the first component can be physically connected to the second component by being located within the second component.

[0075] In this example, liquid hydrogen tanks 108 are connected to the fuselage 102. These liquid hydrogen tanks are located above the wings 104 along the sides of the fuselage 102. These liquid hydrogen tanks have a substantially cylindrical shape. The liquid hydrogen tanks may also have other shapes, such as an annular shape, a rounded rectangular prism, a teardrop shape, or other suitable shapes. In this example, the liquid hydrogen tanks 108 are cryogenic tanks that carry liquid hydrogen.

[0076] In this example, liquid hydrogen tank 130 of the plurality of liquid hydrogen tanks 108 is located above wing 105, and liquid hydrogen tank 131 of the plurality of liquid hydrogen tanks 108 is located above wing 104. The locations of the liquid hydrogen tanks 108 are selected to provide a desired center of gravity (CG) characteristic for the aircraft 100. As depicted in this example, the liquid hydrogen tanks 108 are located below a plurality of windows 138 in the fuselage 102. As depicted in this example, the windows 138 are located along a window line 139 on the fuselage 102.

[0077] The location of the two liquid hydrogen tanks reduces the wetted area by placing the fuel tanks against certain surfaces of the aircraft 100. In other words, the surface area of ​​the fuselage 102 in contact with the air during flight is reduced around the liquid hydrogen tanks 108 compared to other locations that may be selected on the aircraft 100. By reducing the wetted area of ​​the fuselage 102 around the liquid hydrogen tanks 108, improved aerodynamic performance may be achieved.

[0078] In addition, the location of the liquid hydrogen tanks 108 can protect these components from a hard landing. Moreover, the location of the liquid hydrogen tanks can protect these tanks from damage due to ground impact.

[0079] Furthermore, in this example, six engines are used for aircraft 100. Increasing the number of engines may allow for greater distribution of different components of the thermal management system and other components in the engines into smaller components. These components may be located within the nacelle volume of each engine.

[0080] This distribution also provides the ability to use blown wings at lower speeds for higher lift, increased redundancy, and lower power requirements for the electric motors. In addition, by increasing the number of engines, the size of the fuel cell stack in each engine can be smaller.

[0081] Additionally, there is increased redundancy by using six engines instead of two or four engines. As the number of engines increases, the electric motors can have smaller size and power requirements. In a similar manner, the size of the heat exchangers for the engines within the engine compartment can also be smaller. In a similar manner, the multiple fuel cells in the fuel cell stack can be smaller in size, making it easier to package and integrate these components into the aircraft 100.

[0082] In this example, gaseous hydrogen (GH2) may be exhausted from the liquid hydrogen tank 108 through a pipeline to an exhaust system. The exhaust system may exhaust the gaseous hydrogen from an area away from and above passengers, crew, and ground personnel, such as a vertical tail 110.

[0083] Figure 21 is an illustration of a front view of liquid hydrogen tank locations in accordance with an illustrative embodiment. In this figure, a front view of aircraft 100 provides additional views of the location of liquid hydrogen tank 130 above wing 105 and the location of liquid hydrogen tank 131 above wing 104. As depicted, liquid hydrogen tank 131 is located above wing 104 and liquid hydrogen tank 130 is located above wing 105 on the side of fuselage 102 of aircraft 100.

[0084] These locations of the liquid hydrogen tanks 108 can reduce trim issues and hydrogen entrapment in the fuselage. In addition, lower drag and weight of the integrated liquid hydrogen tanks can be achieved through easier integration compared to liquid hydrogen tanks used under the wings of the aircraft. Additional tanks can be used to reduce liquid sloshing and increase redundancy.

[0085] Figure 1 and Figure 2 The illustration of aircraft 100 in FIG. 1 is provided as an illustrative example and is not meant to be limiting of the manner in which other illustrative examples may be implemented. For example, although liquid hydrogen tanks 108 are shown as including two liquid hydrogen tanks, other illustrative examples may have other numbers of hydrogen fuel tanks. For example, the liquid hydrogen tanks may include four liquid hydrogen tanks, with two liquid hydrogen tanks located above the wing and below the windows on either side of aircraft 100.

[0086] Next go to Figure 3 , depicts a diagram of an engine compartment layout according to an illustrative embodiment. The engine 300 is Figure 1 and Figure 2 300. In this example, engine 300 includes engine compartment 302, electric motor 304, fuel cell stack 305, and heat exchanger 308. In this illustrative example, engine compartment 302 is a structure that encloses electric motor 304, fuel cell stack 305, and heat exchanger 308.

[0087] In this example, the heat exchanger 308 has a rectangular shape and is positioned obliquely relative to the opening of the inlet 310. This inclination may have an acute angle of less than 90 degrees. This shape and positioning of the heat exchanger 308 can reduce the front area of ​​the engine compartment 302. As the number of engines increases, a reduction in the size of the electric motor 304, the fuel cell stack 305, and the heat exchanger 308 can be achieved.

[0088] See next Figure 4 , depicts an illustration of a block diagram of a liquid hydrogen fuel cell aircraft according to an illustrative embodiment. In this illustrative example, as Figure 1 , Figure 2 and Figure 3The depicted aircraft 100 and the various components of the aircraft 100 are examples of embodiments of the aircraft 400. In this example, the aircraft 400 takes the form of a liquid hydrogen fuel cell aircraft 457 having a distributed system. The aircraft 400 can be selected from a group including an unmanned aircraft, a manned aircraft, a remotely piloted aircraft, a passenger aircraft, a cargo aircraft, a commercial aircraft, an autonomous aircraft, or other types of aircraft. In one example, the aircraft 400 can be a passenger aircraft, such as a 50 passenger aircraft.

[0089] In this example, aircraft 400 has a number of different components. As depicted, aircraft 400 includes fuselage 402, wings 404, engines 406, stabilizers 412, and a set of liquid hydrogen tanks 408. As used herein, when used with reference to an item, a "set" refers to one or more items. For example, a set of liquid hydrogen tanks is one or more liquid hydrogen tanks.

[0090] In this illustrative example, wings 404 include first wing 403 and second wing 405. The wings are connected to fuselage 402. Engines 406 are connected to first wing 403 and second wing 405. In one example, engines 406 may be four engines, six engines, ten engines, or some other suitable number of engines.

[0091] In this illustrative example, set of liquid hydrogen tanks 408 is connected to fuselage 402. Stabilizer 412 is connected to tail 410 of fuselage 402.

[0092] In this example, each engine includes multiple components. For example, engine 415 in multiple engines 406 includes engine compartment 420, electric motor 421, fuel cell stack 422, and engine compartment heat exchanger 423. In this example, electric motor 421, fuel cell stack 422, and engine compartment heat exchanger 423 are located in engine compartment 420.

[0093] The nacelle 420 is a housing that contains various components for the engine 415. This housing can provide aerodynamic properties. The nacelle 420 can also provide structural support for the components in the engine 415.

[0094] Further, in this illustrative example, the engine compartment heat exchanger receives air 430 flowing through an inlet 431 in the engine compartment 420. The engine compartment heat exchanger 423 provides cooling for the fuel cell stack 422 in the engine compartment 420. This cooling can be in a high temperature cooling circuit (such as Fig.34 It is implemented in the high temperature circuit 3401).

[0095] For example, the piping system 424 is fluidly connected to the engine compartment heat exchanger 423 and the fuel cell stack 422. The piping system 424 includes one or more pipes that carry a coolant that can be used to cool the fuel cell stack 422. These pipes can be, for example, pipes, tubes, or other suitable structures. The piping system 424 can also include a valve that can control the coolant flow in the pipe. In addition, the piping system 424 can include multiple pumps to move the fluid.

[0096] In this way, the coolant flow can be controlled to flow to or through a plurality of components. In addition, these valves can be used to control the coolant flow to form different circuits for cooling or heating components.

[0097] In this example, the engine compartment heat exchanger 423 and the ductwork 424 form a thermal management system 425. The thermal management system 425 cools the fuel cell stack 422. The temperature of the coolant required by the HTPEM fuel cells is too high to be used as a coolant for other engine components. Another low temperature coolant loop is required to cool engine components other than the fuel cell stack 422. The low temperature coolant loop either uses its own ram air radiator or uses another heat exchanger or cooling method to cool the coolant. The vehicle cools its low temperature coolant as part of its pressure control system for the tank, which requires heating and recirculation of hydrogen.

[0098] In this illustrative example, set of liquid hydrogen tanks 408 are located outside of fuselage 402. The liquid hydrogen tanks store liquid hydrogen 433, which is used in fuel cell stack 422 to generate electricity to power electric motor 421.

[0099] Furthermore, in this example, the liquid hydrogen tanks extend along the exterior of the fuselage 402 above the wings 404. Furthermore, the bank of liquid hydrogen tanks 408 may be located below windows 427 in the fuselage 402. In this example, the windows 427 are arranged along a line on either side of the fuselage 402. In this example, the bank of liquid hydrogen tanks 408 extend along multiple sides of the fuselage 402. The liquid hydrogen tanks 408 are cryogenic tanks.

[0100] In this illustrative example, aircraft 400 also includes exhaust system 440. Exhaust system 440 is connected to set of liquid hydrogen tanks 408. Exhaust system 440 operates to exhaust gaseous hydrogen 434 from liquid hydrogen tanks 408.

[0101] In one illustrative example, exhaust system 440 extends through fuselage 402 to vertical fin 441 in stabilizer 412. Vertical fin 441 is connected to tail 410 of fuselage 402. For this example, exhaust system 440 exhausts gaseous hydrogen 434 through vertical fin 441.

[0102] Therefore, in these examples, as the number of engines 106 increases, different multiple components can be further distributed across these engines. This distribution can provide an increase in redundancy. In addition, as the number of engines 406 increases, the size of multiple components within the engine can be reduced.

[0103] The arrangement of liquid hydrogen tanks and reducing the size of packaging for thermal management and fuel cell systems are examples of one or more features resulting from various illustrative examples. For example, distributing the propulsion power, thermal management and fuel cell systems across a greater number of nacelles may enable electric motors in those nacelles to have smaller power requirements and enable heat exchangers and fuel cells to be divided into smaller sizes that are easier to manufacture and integrate into an aircraft.

[0104] Figure 4 A block diagram of the aircraft 400 and Figure 1 and Figure 2 The illustration of aircraft 100 in FIG. 1 is a multiple example for implementing an aircraft and is not meant to imply physical or structural limitations on the manner in which the illustrative embodiments may be implemented. A plurality of other components may be used in addition to or in place of the plurality of components illustrated. Some components may be unnecessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the illustrative embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0105] In another illustrative example, different liquid hydrogen tank locations can be used, rather than on the top of the wing and on the side of the fuselage. In addition, in another illustrative example, other numbers of fuel cell stacks can be used in the engine, such as 2, 3, or some other number of fuel cell stacks. In addition, other features can be implemented to reduce the volume required for the thermal management system or fuel cell stack to further assist packaging. Features such as high temperature proton exchange membrane fuel cells in microchannel heat exchangers or fuel cell stacks can be used.

[0106] As another example, hydrogen can be stored in other forms other than liquid hydrogen. For example, different hydrogen carriers such as liquid or gaseous methane or other hydrocarbon molecules. For this example, reforming can be used to process these types of hydrocarbon fuels to separate hydrogen for use in a fuel cell stack. In other words, in addition to liquid hydrogen tank 408, other types of storage tanks can be used to store other types of hydrocarbon fuels, which can be processed to obtain gaseous hydrogen 434 for use in a fuel cell stack to generate electricity.

[0107] 2. Engine compartment heat exchanger integration method for hydrogen fueled fuel cell powered aircraft

[0108] The illustrative examples recognize and take into account that hydrogen powered aircraft can use fuel cells to drive electric motor driven propulsion. Fuel cells typically generate a large amount of waste heat. This waste heat is removed from the fuel cells and dissipated into the ambient air during aircraft operation.

[0109] For example, fuel cell stacks using high temperature proton exchange membrane (HTPEM) fuel cells and low temperature proton exchange membrane (LTPEM) fuel cells generate a significant amount of heat compared to the power generated. This heat is discharged from the engine into the ambient air. During flight phases such as taxiing, takeoff, and climb, heat discharge is more difficult. During these phases, the desired amount of ambient air is not always available to provide the desired cooling. In addition, during these flight phases, the temperature difference between the ambient air and the fuel cell coolant is typically lower than when cruising.

[0110] This heat removal may also be referred to as heat rejection. This heat rejection may result in significant ram drag, especially during takeoff and climb phases. When sufficient ram air is not available and the temperature difference between the ambient air and the fuel cell coolant is also low, significant ram drag may exist.

[0111] One solution may involve using a large inlet area and a variable exhaust system. However, increasing the size of the front area may lead to problems associated with packaging of the heat exchanger within the engine compartment.

[0112] Ram drag is the difference in momentum change between the exit and the inlet of a system. It can be positive, which means thrust is produced, or negative, which is a drag on the aircraft. Due to the larger amount of heat to be removed and the smaller temperature difference between the coolant and the ambient air, the size of the heat exchanger currently required is considered larger.

[0113] Typical fuel cells operate at efficiencies in the 40% to 60% range. Typical power required based on aircraft size can be hundreds to thousands of kilowatts. This operation means that the amount of heat emitted by the fuel cells in a fuel cell stack can be of the same order of magnitude as the power generated by the aircraft.

[0114] In the case of a low temperature proton exchange membrane (PEM) fuel cell, the temperature difference between the coolant and the ambient air can be as low as 20 degrees Celsius, and in the case of a high temperature PEM fuel cell can be as low as 70 degrees Celsius. The present disclosure addresses problems related to mounting an engine compartment heat exchanger with minimal drag losses and solutions related to getting ambient cooling air in and out of the heat exchanger, as well as potential other problems.

[0115] Illustrative examples provide an electric aircraft based on a fuel cell using hydrogen as a fuel. In these examples, a fuel cell stack includes a fuel cell. These fuel cell stacks can be located with multiple engines of the aircraft. In other words, the fuel cell stack is located in the same engine compartment that houses the engines. The fuel cell stack is cooled by a variety of schemes, and the heat from the fuel cell stack must be sent to an ambient air heat exchanger also located in the engine compartment using a coolant to be discharged to the ambient air.

[0116] In addition, a fan system may be included in each engine compartment. The electric fan system may include multiple fans that can change speed depending on the required cooling. In this example, the fan system increases the air flow through the multiple heat exchangers. The increased air flow using the fan system can reduce the size of the heat exchangers in the engine compartment.

[0117] Furthermore, fixed area nozzles enable useful thrust recovery through ram air. The use of variable area nozzles can optimize the power required by the fan system and increase the thrust contribution of the entire cooling system in multiple phases of flight.

[0118] The illustrative examples provide for the heat exchangers to be integrated into the nacelle rather than within the fuselage.

[0119] In one illustrative example, a fuel cell-based electric aircraft using hydrogen as fuel is depicted. In these examples, a fuel cell stack includes a plurality of fuel cells. These fuel cell stacks can be located with the engine of the aircraft. In other words, the fuel cell stack can be located in the same engine compartment that houses the engine. The fuel cell stack is cooled by a variety of schemes, and the heat from the fuel cell stack must be sent to an ambient air heat exchanger using a coolant to be discharged into the ambient air.

[0120] In addition, an electric fan system may be included in each nacelle. The electric fan system may include a plurality of variable speed fans that may vary speed depending on the cooling required. Moreover, the fixed area nozzles may enable useful thrust recovery from ambient ram air. In this example, ambient air is the air surrounding or surrounding the aircraft. Further, in the illustrative example, increasing the area of ​​the nacelle heat exchanger may reduce ram drag.

[0121] Therefore, a heat exchanger and a fan system may be used within the nacelle of the engine to deliver a desired cooling air flow.The heat exchanger may be positioned within the nacelle substantially parallel to the direction of flight of the aircraft.

[0122] Thus, the illustrative examples may also provide at least one of reducing drag or generating thrust. In these examples, the phrase "at least one" when used with a list of items means that one item or different multiple combinations of multiple items in the list of items may be used, and only one of each item in the list of items may be required. In other words, "at least one" means that any combination of multiple items in the list of items and multiple items in the list of items may be used, but not all items in the list of items are required. Items may be specific objects, things, or categories.

[0123] For example, but not limited to, "at least one of item A, item B, or item C" may include item A, item A and item B, or item B. This example may also include item A, item B, and item C, or item B and item C. Of course, there may be any combination of these items. In some illustrative examples, "at least one" may be, for example, but not limited to, two items A; one item B; and ten items C; four items B and seven items C; or other suitable combinations.

[0124] Moreover, variable area nozzles can be used to reduce fan power. In this example, variable area means that the cross-sectional area of ​​the nozzle can be adjusted during operation. This area change can change the exhaust velocity. Fixed area means that the cross-sectional area of ​​the nozzle remains fixed and does not change.

[0125] In different examples, the heat exchanger may have different shapes to reduce the front area relative to the inlet of the nacelle. The front area may be substantially perpendicular to the inlet. The heat exchanger may also include a fan system, such as an electrically driven axial fan or a radial blower, to provide a desired level of air flow during different phases of flight, including when the aircraft is on the ground.

[0126] See next Figure 5 , depicts a block diagram of a heat exchanger system for an aircraft according to an illustrative embodiment. In this illustrative example, heat exchanger system 500 is located in engine compartment 502. Engine compartment 502 is Figure 4 4 and nacelle 420 for aircraft 400. In this illustrative example, nacelle heat exchanger 520 may be oriented substantially parallel to aircraft flight direction 547. For example, nacelle heat exchanger 520 may have a length greater than a width or thickness, and the longer dimension of nacelle heat exchanger 520 may be oriented substantially parallel to flight direction 547. Heat exchanger system 500 may also be referred to as a ram air radiator.

[0127] In this illustrative example, nacelle 502 has inlet 504 and outlet 505. Air 530 flows into nacelle 502 through inlet 504 and flows out of nacelle 502 through outlet 505.

[0128] In this illustrative example, heat exchanger system 500 includes underhood heat exchanger 520 . In some illustrative examples, heat exchanger system 500 may also include fan system 522 .

[0129] Underhood heat exchanger uses air 530 in air flow 532 to transfer heat from coolant 526 to underhood heat exchanger 520 .

[0130] In this illustrative example, air flow 532 flowing to underhood heat exchanger 520 can take one or more different forms. For example, air flow 532 can move over a surface of underhood heat exchanger 520, through underhood heat exchanger 520, or some combination thereof. For example, underhood heat exchanger 520 can have a solid surface through which air 530 in air flow 532 flows. In another example, underhood heat exchanger 520 can have a duct, channel, or opening through which air 530 in air flow 532 travels.

[0131] The underhood heat exchanger 520 may include a variety of different types of materials. For example, the underhood heat exchanger 520 may include a variety of materials selected from at least one of aluminum, copper, copper alloys, aluminum alloys, titanium, titanium alloys, composite materials, or some other suitable materials.

[0132] The underhood heat exchanger 520 can take a variety of different forms. For example, the underhood heat exchanger 520 can include a hollow geometric duct 550 having a channel 551. In this example, the air flow 532 passes through at least one of a surface in the channel 551 or a surface on the exterior of the hollow geometric duct 550. The hollow geometric duct 550 can be, for example, a cylinder, a rectangular prism, an ellipsoid, or some other suitable form.

[0133] In another illustrative example, the engine compartment heat exchanger 520 may include concentric cylinders 552 positioned in the engine compartment 502. In yet another illustrative example, the engine compartment heat exchanger 520 may include a solid geometric cylinder 553 positioned within the engine compartment 502. For this example, the air flow 532 passes outside of the solid geometric cylinder 553 positioned within the engine compartment where the air flow passes outside of the solid geometric cylinder 553.

[0134] In yet another example, the underhood heat exchanger 520 may include a rectangular shaped heat exchanger 555 positioned at an angle to the air flow 532. The rectangular shaped heat exchanger may have the shape of a rectangular prism or a cuboid.

[0135] When used in heat exchanger system 500, fan system 522 operates to increase air flow 532 to underhood heat exchanger 520. This increased air flow may reduce the size of underhood heat exchanger 520 while still providing a desired level of cooling.

[0136] In this illustrative example, fan system 522 is a hardware system and includes a plurality of fans 523. A plurality of fans 523 may be located at least one of in front of nacelle heat exchanger 520 or behind nacelle heat exchanger 520. As another example, fans 523 and fan system 522 may be arranged in a ring within nacelle 502.

[0137] In this example, the front of the nacelle heat exchanger 520 is closer to the inlet 504 than to the outlet 505. The fan 523 may be selected from at least one of an axial fan, a ring fan, a radial blower, a rim-driven fan, or some other suitable type of fan.

[0138] Coolant 526 can be used within piping system 540 to cool various components within engine compartment 502. For example, coolant 526 can be located in piping system 540. Piping system 540 includes pipes 541, which are tubes or pipes through which fluid can travel. In addition, piping system 540 can also include valves 542 to control the flow of fluid through piping system 540. In this example, piping system 540 can include pumps 543 to move the fluid.

[0139] Piping system 540 is a hardware system that includes one or more pipes. These pipes may be tubes, pipes, or other structures through which coolant 526 can flow between engine compartment heat exchanger 520 and other components 525 in engine compartment 502. Piping system 540 is thermally connected to engine compartment heat exchanger 520 and other components 525 in engine compartment 502. In these illustrative examples, thermal connection means that heat transfer can occur between two components.

[0140] For example, the pipes in pipe system 540 may be in contact with or very close to the heat load. In other illustrative examples, the pipes may be connected to the heat load such that coolant 526 may flow from pipe system 540 through the heat load.

[0141] In this example, duct system 540 may utilize coolant 526 to cool at least one of a fuel cell stack, a motor, or an electronic system in other components 525. Furthermore, in these illustrative examples, one or more of other components 525 may be located at different locations relative to underhood heat exchanger 520. For example, when underhood heat exchanger 520 takes the form of hollow geometry duct 550, a component such as a fuel cell stack may be located within channel 551 in hollow geometry duct 550.

[0142] In one illustrative example, the inlet 504 can have a fixed area 560. For this example, a variable area nozzle 561 can be positioned between the fan system 522 and the outlet 505. The variable area refers to the area of ​​the cross section of the variable area nozzle 561 that can be changed. The air flow 532 through the variable area nozzle 561 can cause the exhaust gas 554 leaving the outlet 505 to have a discharge velocity 563 greater than the free stream velocity.

[0143] Figure 5 The block diagram illustration of the heat exchanger system 500 in the illustrative embodiment is not meant to imply physical or structural limitations on the manner in which the illustrative embodiments may be implemented. Other multiple components in addition to or in place of the multiple components described may be used. Some components may be unnecessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the illustrative embodiments, one or more of these blocks may be combined, divided, or combined and divided into different multiple blocks.

[0144] For example, the underhood heat exchanger 520 may have other shapes added, such as a prismatic shape or other suitable shapes. Furthermore, one or more underhood heat exchangers may be used in addition to or in place of the underhood heat exchanger 520 in the heat exchanger system 500. The heat exchanger system may also be referred to as a ram air radiator.

[0145] In another illustrative example, the nacelle heat exchanger can be used in a dedicated nacelle that provides cooling. In yet another illustrative example, a tip-driven fan can be used in the fan system. In other illustrative examples, the heat exchanger with the air inlet and fan system can be located at other locations in the aircraft, such as the fuselage, in addition to or instead of being used in the nacelle of the engine. In addition, the heat exchanger can have flow turning features, such as guide vanes, to ensure that the air flow enters and leaves the heat exchanger in a desired orientation.

[0146] See now Figures 6 to 18 , depicts a diagram of an engine compartment heat exchanger configuration in accordance with an illustrative embodiment. In this example, different layouts are shown in cross-section as examples of configurations that may be used when implementing a heat exchanger in an engine compartment of an engine.

[0147] Steering Figure 6 , depicts a cross-sectional view of a portion of a nacelle having a nacelle heat exchanger according to an illustrative embodiment. In this illustrative example, nacelle heat exchanger 600 is located in nacelle 610 having an inlet 611 and an outlet 612. As depicted, nacelle heat exchanger 600 is a hollow geometric conduit in the form of a cylinder 620 having a channel 621. The hollow geometry may also take the form of an elliptical cylinder, annular cone, polygonal prism, or other shapes.

[0148] As depicted, a plurality of components 602 are located at least forward of or partially within a passage 621 in a nacelle heat exchanger (HEX) 600. These components may be, for example, a fuel cell power system, a fuel cell stack, an electric motor, a controller, a shaft, a propeller, or other components for an aircraft engine.

[0149] As depicted, fan 604 is located behind underhood heat exchanger 600 . In other examples, fan 604 may be located in front of underhood heat exchanger 600 .

[0150] Fan 604 operates to increase air flow across nacelle heat exchanger 600. This type of air flow may be useful when the aircraft is operating on the ground, or at altitudes and speeds that do not provide the desired level of airflow or heat removal required to cool the fuel cells.

[0151] Next go to Figure 7 , depicts another illustration of a cross-sectional view of a portion of a nacelle having a nacelle heat exchanger according to an illustrative embodiment. In this example, a nacelle heat exchanger (HEX) 700 is located in a nacelle 710 having an inlet 711 and an outlet 712. In this example, the nacelle heat exchanger (HEX) 700 is annular with a passage 705.

[0152] As depicted, fan 704 is located behind underhood heat exchanger 700. In other examples, fan 704 may be located in front of underhood heat exchanger 700. Figure 6 Other components 707 are shown as being located more within channel 705 of underhood heat exchanger 700 than other components 602 in FIG.

[0153] refer to Figure 8 , depicts another illustration of a cross-sectional view of a nacelle having a nacelle heat exchanger in accordance with an illustrative embodiment. In this example, a heat exchanger 800 is located in a nacelle 801 having an inlet 811 and an outlet 812 .

[0154] As depicted, the nacelle heat exchanger 800 has a rectangular shape and is positioned within the nacelle 801 at a shallow angle, with the fan 802 located behind the heat exchanger 800. This angle is considered a shallow angle. In this example, a shallow angle is an angle of 45° or less.

[0155] The location of the underhood heat exchanger 800 at a shallow angle reduces the exposed front area of ​​the underhood and reduces the degree to which the air flow is turned when passing through the underhood heat exchanger 800 to maintain a low pressure drop across the heat exchanger.

[0156] In this example, fan 802 is shown positioned behind heat exchanger 800. In other examples, fan 802 may be located in front of underhood heat exchanger 800.

[0157] Figures 6 to 8 The schematic diagram of the layout of the heat exchanger shown is not meant to limit the manner in which the heat exchanger design in the engine compartment is implemented. For example, one or more fans may be used in addition to the fan depicted in these examples.

[0158] See also Fig. 9 , depicts a perspective view of an engine with a nacelle heat exchanger according to an illustrative embodiment. As depicted in the example, a side view of an engine 900 is shown within a nacelle 902, which is shown in an exposed view and partially in phantom.

[0159] In this view, it can be seen that the engine compartment heat exchanger 904 is at a shallow angle relative to the inlet 906 in the engine compartment 902. In this illustrative example, the shallow angle is an angle of no more than 45 degrees. Also depicted is a duct system 908 connected to the heat exchanger 904. The duct system 908 can circulate a fluid (such as a gas or liquid) for cooling in response to air flowing through the engine compartment heat exchanger 904 via the inlet 906 in the engine compartment 902. The air flowing to the engine compartment heat exchanger 904 through the inlet 906 can reduce the temperature of the coolant flowing within the duct system 908.

[0160] In this example, fan system 910 is located behind nacelle heat exchanger 904. Fan system 910 may be used to induce or increase air flow through inlet 906 and through nacelle heat exchanger 904. Fan system 910 may be used to generate or increase air flow to nacelle heat exchanger 904 when the aircraft is stationary or moving at a lower speed.

[0161] See also Fig.10 , depicts a perspective view of an engine with an engine compartment heat exchanger according to an illustrative embodiment. In this example, Fig. 9The engine 900 is shown in a perspective view.

[0162] As shown in this view, fan system 910 includes fan 1001, fan 1002, and fan 1003. In some illustrative examples, fan system 910 may be located in front of or in front of engine compartment heat exchanger 904. In other illustrative examples, other numbers of fans may be present in fan system 910. For example, fan system 910 may have one fan, five fans, or some other number of fans.

[0163] Steering Fig.11 , depicts a perspective view of an engine with a nacelle heat exchanger according to an illustrative embodiment. In this illustrative example, engine 1100 is shown from a side view. Engine 1100 includes nacelle 1102 that houses various components of engine 1100. Nacelle 1102 has an inlet 1131 and an outlet 1132.

[0164] A portion of nacelle 1102 is shown in phantom, while another portion of nacelle 1102 is shown in cross-section so that other components within engine 1100 are shown.

[0165] As depicted, underhood heat exchanger 1104 is located within underhood 1102. In this illustrative example, underhood heat exchanger 1104 is in the shape of an annular cylinder and has passages 1110.

[0166] The engine compartment heat exchanger 1104 is positioned within the engine compartment 1102 so that the components can be positioned within the passage 1110 in the engine compartment heat exchanger 1104. In addition, in this view, the fan 1106 is located in front of the engine compartment heat exchanger 1104. In this depicted example, the fan 1106 is a ring fan.

[0167] Also, in this example, an electric motor 1108 is located within the channel 1110 of the underhood heat exchanger 1104, which can be seen in this exposed view of the underhood heat exchanger 1104. Additionally, a portion of a fuel cell stack 1112 can also be seen located within the channel 1110 of the underhood heat exchanger 1104.

[0168] exist Fig.12 , another perspective view of an engine with an underhood heat exchanger is depicted in accordance with an illustrative embodiment. In this figure, a perspective view of an engine 1100 is shown. In this figure, a cross-sectional view of a heat exchanger 1104 is shown. Underhood heat exchanger 1104 is shown as two concentric cylinders 1200. In this example, cylinder 1202 is located within cylinder 1204.

[0169] Next in Fig.13, a schematic diagram of a fan configuration for use with an engine compartment heat exchanger in an engine compartment is depicted in accordance with an illustrative embodiment. As depicted, fans 1300 are arranged in a 360 degree ring 1302. This arrangement of fans may be used in place of Fig.11 and Fig.12 Ring fan in the.

[0170] See now Fig.14 , depicts a cross-sectional view of a nacelle having a nacelle heat exchanger according to an illustrative embodiment. In this example, a cross-sectional view of a nacelle 1400 having an inlet 1407 and an outlet 1409 is depicted. For example, nacelle 1400 is a dedicated nacelle for nacelle heat exchanger 1402.

[0171] The engine compartment heat exchanger 1402 is also shown in a cross-section within the engine compartment 1400. In this example, the engine compartment heat exchanger 1402 has a tapered ring shape. In other words, the engine compartment heat exchanger 1402 can be a hollow geometric duct with a channel. For this example, the air flow 1406 passes through at least one of a surface in the channel or a surface on the exterior of the hollow geometric duct. In an illustrative example, the engine compartment heat exchanger 1402 can also be a pyramidal shape.

[0172] Additionally, in this example, fan 1404 is shown as being located behind underhood heat exchanger 1402. In a different example, rear device fan 1404 is located behind underhood heat exchanger 1402 relative to air flow 1406 entering inlet 1407 and air flow 1406 passing through outlet 1409 as exhaust 1408.

[0173] Furthermore, in this example, outlet 1409 takes the form of nozzle 1412. Depending on the specific implementation, the nozzle may be a fixed area nozzle or a variable area nozzle. The nozzle may increase the exhaust velocity of air 1406 exiting nacelle 1400 as exhaust 1408. A higher exhaust velocity is achieved relative to the free stream speed of the aircraft, thereby causing thrust recovery through the system.

[0174] In some illustrative examples, a fan system having one or more fans may be located in front of or in front of the heat exchanger. Also visible in these views are ductwork, a fuel cell stack, and other components for the electric engine.

[0175] Now turn to Fig.15, shows a diagram of air flow through the engine compartment to provide cooling for the fuel cell stack according to an illustrative embodiment. As depicted, arrows 1500 show that the air flow enters the generally rectangular inlet at the bottom of the engine compartment 1502. In this example, the air flow enters the engine compartment 1502 through the inlet 1551, passes through the front of the engine compartment heat exchanger 1504, and exits from the rear of the engine compartment heat exchanger 1504. The air then passes through the fan 1506 before exiting the nozzle 1554 in the outlet 1552 of the engine compartment 1502.

[0176] As depicted, fan 1506 can increase the air flow indicated by arrow 1500 during different flight phases to provide the desired air flow for cooling. For example, increased air flow can be achieved when the aircraft is stationary or taxiing before takeoff. In this example, ductwork 1508 is present and connected to the front end of heat exchanger 1504 and provides cooling for fuel cell stack 1510. Ductwork 1508 can provide a coolant flow through nacelle heat exchanger 1504, wherein the coolant is cooled by the air flow through heat exchanger 1504.

[0177] Steering Fig.16 , depicts an illustration of a front view of a nacelle with a nacelle heat exchanger according to an illustrative embodiment. As depicted, nacelle heat exchanger 1600 is seen located in inlet 1630 of nacelle 1631. In this example, coolant enters through coolant inlet 1612 and exits through coolant outlet 1610. The coolant may be cooled by heat exchanger 1600. The coolant may be cooled by air flow entering inlet 1630 of nacelle 1631 and passing through nacelle heat exchanger 1600.

[0178] Next in Fig.17 , a diagram of an underhood heat exchanger according to an illustrative embodiment is depicted. In this example, a top view of heat exchanger 1600 is shown. Underhood heat exchanger 1600 is a rectangular heat exchanger. As depicted, coolant enters underhood heat exchanger 1600 through coolant inlet 1612, flows through heat exchanger 1600, and exits through coolant outlet 1610.

[0179] Next in Fig.18, a diagram of air flow through an underhood heat exchanger according to an illustrative embodiment is described. In this figure, a plurality of arrows 1840 show the flow of coolant in an enlarged view of section 1704 of underhood heat exchanger 1600. In this enlarged view, the coolant flows through multiple rows of tubes 1830 stacked on top of each other (the multiple rows of tubes forming panels 1814 for heat exchanger 1600). The coolant is cooled by the air flow traveling through fins 1831 in heat exchanger 1600.

[0180] exist Figures 6 to 18 Different illustrations of a heat exchanger system implemented in an engine compartment are presented in FIG. Figure 5 Some embodiments of the heat exchanger system 500 in FIG. These illustrations are not meant to limit the manner in which other heat exchanger systems can be implemented in other illustrative examples. Other heat exchanger shapes and locations of components can exist in other illustrative examples. In another example, two heat exchangers can be implemented in one illustrative example.

[0181] In these examples, a single inlet and a single outlet are shown for the nacelle. In other examples, the nacelle may have more than one inlet and more than one outlet. For example, there may be one inlet and outlet in the nacelle for the main air flow to the fuel cell. There may be another inlet and another outlet for the cooling air flow to the heat exchanger (which cools other components, such as the electric motor and motor controller). In these examples, a unique installation may be used where there are multiple inlets for, for example, Fig.14 A dedicated nacelle for a nacelle heat exchanger in the example. In this example, only one inlet and outlet are used for the cooling air flow.

[0182] 3. Launch of a high temperature proton exchange membrane (HTPEM) fuel cell aircraft with multiple power generation units

[0183] Compared to conventional low temperature proton exchange membrane (LTPEM) technology, high temperature proton exchange membrane (HTPEM) fuel cells with higher operating temperatures provide significant improvements in thermal drive potential to allow for significant miniaturization of fuel cell aircraft thermal management systems (TMS). However, when using high temperature proton exchange membrane (HTPEM) fuel cells in a fuel cell stack, the startup process can be a time-consuming and energy-intensive process due to the much higher minimum operating temperature of about 120°C. In these instances, the startup process is a process in which the fuel cell stack reaches the minimum operating temperature and then fuel and oxidant are supplied to allow the fuel cell stack to begin generating power on its own.

[0184] The illustrative examples recognize and take into account that it is desirable to reduce the time and amount of electrical energy required to start up a HTPEM fuel cell stack. This time element can be critical because startup time is allocated as downtime in the conceptual operation of fuel cell aircraft (CONOPS). Downtime is an undesirable expense for airlines to operate aircraft.

[0185] Energy elements are required before the fuel cell stack is started up, since no power can be drawn from these fuel cell stacks until the operating temperature is reached. Therefore, the energy consumed for start-up comes from another source.

[0186] Batteries are one solution for this starting energy. However, batteries have an undesirable weight. In addition, batteries also have a low gravimetric energy density (Wh / kg). Therefore, minimizing the starting energy from batteries is useful in reducing aircraft weight and improving performance in operating these types of aircraft.

[0187] The illustrative embodiments recognize and take into account that there are no existing solutions for aerospace applications. An alternative solution may be used for terrestrial applications of HTPEM fuel cells. The solution may involve heating the stack via resistive "blankets" or "pads" around the edges of the stack or resistive heaters embedded in the stack end plates.

[0188] This solution relies on heat reaching the active area inside the fuel cell stack through the outside of the stack. This type of heating uses a heat flow path with greater thermal resistance, which results in a large amount of heat being wasted to the surrounding environment and a slower rate of reaching operating temperature for components inside the fuel cell stack. This situation is particularly likely to occur in fuel cell stack geometries with large cross-sectional areas and can generate non-uniform temperature gradients within the stack.

[0189] Another alternative approach can use an air management system (AMS) for the fuel cell stack to push heated air through the fuel cell stack. This approach wastes heat by exhausting the hot air through the fuel cell stack outlet, and the effective heat transfer rate between the heating fluid (air) and the stack media is poor compared to the coolant.

[0190] Another solution may employ heating the fuel cell stack via a cooling fluid as described in the various illustrative examples. This approach may operate to heat all fuel cell stacks simultaneously, but uses significantly more energy.

[0191] For example, in the case of an aircraft configuration with six engines located in six nacelles, there are three fuel cell power units per wing. For this configuration, three times the total energy can be used before starting the other fuel cell stacks with the power they generate, compared to starting only one fuel cell stack per wing.

[0192] Therefore, an illustrative example provides a method, apparatus and system to minimize the total energy and time required to complete the startup of multiple HTPEM fuel cell stacks included in a fuel cell powered aircraft. In an illustrative example, a coolant heater and an existing thermal management system are used to start the HTPEM fuel cell stack by heating and circulating the fuel cell stack coolant. In this example, the coolant is first used to heat a subset of all fuel cell stacks on the aircraft. After these fuel cell stacks reach operating temperature and begin to generate power, the power can be used to start the remaining multiple fuel cell stacks.

[0193] In the illustrative examples, this feature involves a unique configuration of the coolant heating structure. One illustrative example uses an electric coolant heater. The heater can be integrated into the piping for the coolant system so that the existing cooling pump can be used to circulate the coolant through the stack and start the heater. Also included in the structure are bypasses that allow the coolant to skip the heater that is in normal operation after startup; and a bypass that allows the coolant to skip the heat exchanger during startup to avoid the need to heat the heat exchanger in addition to heating the stack, i.e., minimizing startup time and required energy.

[0194] Another feature in the illustrative example implements a startup process that generates the amount of energy required to start the fuel cell stack. In a configuration with multiple fuel cell stacks on an aircraft, a subset of all fuel cell stacks can be started first using an onboard battery that is sized to start only that subset of fuel cell stacks.

[0195] After the subset of fuel cell stacks is started, the power generated by the subset of fuel cell power units now operating can be used to start the remaining fuel cell stacks. In addition, when the fuel cell stack reaches the minimum operating temperature required for electrochemical activity, fuel and air can be supplied to the fuel cell stack while applying a moderate power consumption to the fuel cell stack so that the fuel cell stack operates to generate enough heat to heat itself more quickly.

[0196] Thus, the illustrative example can achieve direct heating of the coolant while using a subset of the fuel cell stacks activated by this type of heating to heat other fuel cell stacks.This type of feature is achieved by using a coolant heater and a configuration of conduits for supplying heated coolant to the fuel cell stacks.

[0197] The electrical cross-connects may be used to allow the initially heated and operational fuel cell power unit to power the coolant heaters and air management systems (AMSs) of other fuel cell stacks that have not yet been started to start those fuel cell stacks. This type of start-up of the fuel cell stacks may be performed for any aircraft system having multiple fuel cell stacks.

[0198] In another example, a combustion based coolant heater utilizing fuel, hydrogen or otherwise may be used to heat the coolant and bring the fuel cell stack up to temperature.

[0199] Further, in some examples, a ground power connection may be implemented. When the aircraft is on the ground near an available ground power connection, such a ground power connection may be utilized to start all stacks in unison.

[0200] This feature enables the onboard batteries to be sized to start only an initial subset of the fuel cell power units, keeping the system light but allowing faster start-up when a ground power connection is available and without the operator having to rely on the energy contained in the batteries.

[0201] Next reference Fig.19 , depicts an illustration of a block diagram of a starting system for an aircraft according to an illustrative embodiment. In this illustrative example, a fuel cell stack starting system 1900 may be used Figure 4 400 of the aircraft were used to start Figure 4 Operation of the fuel cell stack in the engine 406 .

[0202] In this illustrative example, fuel cell stack startup system 1900 is configured to start operation of fuel cell stack 1920. Each fuel cell stack of plurality of fuel cell stacks 1920 may be located in an engine compartment of an engine. In this example, fuel cell stack 1920 is a high temperature proton exchange membrane (HTPEM) fuel cell stack.

[0203] The fuel cell stack startup system 1900 is configured to assist or enable the fuel cell stack 1920 to reach an operating temperature 1925. The operating temperature 1925 is one or more temperatures for the fuel cell stack 1920 to generate electricity. The electricity can be used to provide power for at least one of the motors or other multiple components located in the engine or elsewhere in the aircraft. The operating temperature is the temperature required to maintain the reaction in the fuel cell stack to generate electricity from hydrogen and oxygen.

[0204] For example, the fuel cell stack startup system 1900 circulates heated coolant 1916 to a subset of fuel cell stacks 1920 in a fuel cell system 1921 so that the subset of fuel cell stacks 1920 reaches an operating temperature 1925, and generates power to heat coolant 1917 to start other fuel cell stacks in the plurality of fuel cell stacks 1920 in the fuel cell system 1921. In this example, the power is electrical power.

[0205] In this illustrative example, fuel cell stack startup system 1900 includes a number of different components. As depicted in this example, fuel cell stack startup system 1900 includes heater system 1901 , piping system 1902 , pump system 1904 , and controller 1905 .

[0206] In this example, heater system 1901 operates to heat coolant 1917. Heater system 1901 may include a plurality of heaters 1915. In one example, a heater in plurality of heaters 1915 and a fuel cell stack in plurality of fuel cell stacks 1920 may be present in each engine compartment.

[0207] The heater system 1901 can include an electric heater 1930 connected to a battery system 1931. In another example, the heater system 1901 includes a combustion heater 1933 that generates heat using hydrogen gas to a heated coolant 1916. For this example, the combustion heater 1933 can be a pipe or radiator that is thermally connected to a component that burns hydrogen fuel. The hydrogen fuel can be delivered to the burner component as a gas.

[0208] The piping system 1902 is thermally coupled to the heater system 1901 and the fuel cell stack 1920. The pump system 1904 is configured to circulate the heated coolant 1916 through the piping system 1902 to the fuel cell stack 1920.

[0209] In this illustrative example, the controller 1905 is a hardware system that may include software. When software is used, the operations performed by the controller 1905 may be implemented by program instructions configured to run on hardware (such as a processor unit). When firmware is used, the operations performed by the controller 1905 may be implemented by program instructions and data and stored in a persistent memory to run on a processor unit. When hardware is employed, the hardware may include circuits that operate to perform the operations in the controller 1905.

[0210] In an illustrative example, the hardware of the controller 1905 can be selected from at least one of a circuit system, an integrated circuit, an application specific integrated circuit (ASIC), a programmable logic device, or some other suitable type of hardware configured to perform multiple operations. Using a programmable logic device, the device can be configured to perform multiple operations. The device can be reconfigured later or can be permanently configured to perform multiple operations. Programmable logic devices include, for example, programmable logic arrays, programmable array logic, field programmable logic arrays, field programmable gate arrays, and other suitable hardware devices. In addition, the process can be implemented in organic components integrated with inorganic components, and can be completely composed of organic components other than humans. For example, the method can be implemented as a circuit in an organic semiconductor. The controller 1905 can also be selected from at least one of a single-core processor, a dual-core processor, a multi-core processor, a general-purpose central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), or some other type of processor unit.

[0211] In this illustrative example, controller 1905 can control heater system 1901 to heat coolant 1917 to form heated coolant 1916. Controller 1905 can control pump system 1904 to circulate heated coolant 1916 through piping system 1902. In addition, controller 1905 can control piping system 1902 to circulate heated coolant 1917 to a subset of fuel cell stack 1920. In this example, heated coolant 1916 brings the subset of fuel cell stack 1920 to an operating temperature 1925. In this example, operating temperature 1925 is a minimum operating temperature 1923 required for the subset of fuel cell stack 1920 to begin generating electricity.

[0212] In this illustrative example, the controller 1905 can control the piping system 1902 to circulate the heated coolant 1916 to all fuel cell stacks 1920 in response to a subset of the fuel cell stacks 1920 reaching an operating temperature 1925. In this example, the heated coolant 1916 is heated by the subset of fuel cell stacks 1920 that generate power. The remaining fuel cell stacks reach the operating temperature 1925 with the help of the heated coolant 1916 heated by the subset of fuel cell stacks 1920. In this example, the heated coolant 1916 is heated by the subset of fuel cell stacks 1920. The heater system 1901 no longer needs to heat the coolant 1917.

[0213] In one example, the heater system 1901 includes a heater 1915, and in this example, each fuel cell stack in the plurality of fuel cell stacks 1920 and each heater in the plurality of heaters 1915 are located in the engine compartment. Further, in this example, each fuel cell stack is thermally connected to a heater in the plurality of heaters 1915 via a conduit system 1902. For this example, the controller 1905 sends power generated by a subset of the fuel cell stacks 1920 to the heaters 1915 for other fuel cell stacks that are not generating power.

[0214] Furthermore, in this example, the controller 1905 controls the piping system 1902 to bypass the heater system 1901 after the fuel cell stack 1920 is started. With the fuel cell stack 1920 now operating at the operating temperature 1925, it is no longer necessary to heat the coolant 1917 by the heater system 1901. For example, in response to a subset of the fuel cell stack 1920 generating power, the controller 1905 stops heating the coolant 1917 by the heater 1915 in the heater system 1901 for the subset of the fuel cell stack 1920 generating power.

[0215] During this startup process, controller 1905 controls piping system 1902 to bypass engine compartment heat exchanger 1960 during startup of the fuel cell stack. Bypassing engine compartment heat exchanger 1960 avoids cooling of heated coolant 1916 by engine compartment heat exchanger 1960. In this example, an engine compartment heat exchanger in the plurality of engine compartment heat exchangers 1960 and a fuel cell stack in the plurality of fuel cell stacks 1920 are present in each engine compartment.

[0216] In one illustrative example, the controller 1905 controls the piping system 1902 to circulate the heated coolant to the plurality of fuel cell stacks, wherein the heated coolant brings the plurality of fuel cell stacks to an operating temperature 1925 of the plurality of fuel cell stacks 1920, wherein the heated coolant brings the plurality of fuel cell stacks 1920 to an operating temperature 1925. In this example, the plurality of fuel cell stacks 1920 are selected from the group consisting of all fuel cell stacks 1920 and a subset of the fuel cell stacks 1920. In other words, the heated coolant may be circulated to all or a portion of the fuel cell stacks in the plurality of fuel cell stacks 1920.

[0217] Moreover, in this example, piping system 1902 and pump system 1904 operate to circulate coolant 1917 to nacelle heat exchanger 1960 during operation of an electric engine for an aircraft.

[0218] Fig.19The block diagram illustration of the fuel cell stack startup system 1900 in the illustrative embodiments is not meant to imply physical or structural limitations on the manner in which the illustrative embodiments may be implemented. Other components in addition to or in place of the components illustrated may be used. Some components may be unnecessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the illustrative embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0219] For example, although not shown, the piping system 1902 includes pipes. The piping system 1902 may also include valves, pumps, or some combination thereof.

[0220] Next turn Fig. 20 , an illustration of a flowchart of a process for managing startup and operation of multiple fuel cell stacks for an aircraft is depicted in accordance with an illustrative embodiment. Fig. 20 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.19 The fuel cell stack startup system 1900 is implemented.

[0221] The process heats a subset of fuel cell stacks in the aircraft so that the fuel cell stacks reach an operating temperature to generate power (operation 2000 ). The process terminates thereafter.

[0222] Next, refer to Fig.21 , depicts an illustration of a flow chart of a process for heating a fuel cell stack according to an illustrative embodiment. The process in the flow chart is performed Fig. 20 An instance of an additional operation for the operations in .

[0223] The process uses heat generated from the power generated by the subset of the fuel cell stacks to heat the remaining fuel cell stacks to an operating temperature (operation 2100 ). The process terminates thereafter.

[0224] Next turn Fig. 22 , an illustration of a flowchart of a process for managing startup and operation of a fuel cell stack of an aircraft is depicted in accordance with an illustrative embodiment. Fig. 22 The processes in may be implemented in hardware, software, or both. When implemented in software, the processes may take the form of program instructions executed by one of a plurality of processor units in one or more hardware devices in one or more computer systems. For example, the processes may be implemented in Fig.19 The fuel cell stack startup system 1900 is implemented.

[0225] The process begins by heating the coolant by a heater to form heated coolant in a piping system connected to the fuel cell stack (operation 2200). In operation 2200, the heater may be selected from at least one of an electric heater connected to the battery system or a combustion heater that uses hydrogen to generate heat to heat the coolant.

[0226] The process controls the piping system to circulate the heated coolant to the subset of the fuel cell stacks, wherein the heated coolant brings the subset of the fuel cell stacks to an operating temperature (operation 2202). The process terminates thereafter.

[0227] See now Fig.23 , depicts an illustration of a flow chart of a process for circulating a heated coolant in accordance with an illustrative embodiment. The process may be Fig. 22 An instance of an additional operation to be performed together with the operations in .

[0228] In response to the subset of fuel cell stacks reaching operating temperature, the process circulates heated coolant to all fuel cell stacks that have not yet reached operating temperature (operation 2300 ). The process terminates thereafter.

[0229] Next in Fig.24 In the figure, an illustration of a flow chart of a process for delivering power to a fuel cell stack according to an illustrative embodiment is depicted. The operations in the flow chart are performed Fig.24 An example of additional operations of the operations in the example. In this example, each of the plurality of fuel cell stacks and each of the plurality of heaters are located in the engine compartment. In addition, each fuel cell stack is thermally connected to the heater. Such thermal connection can be formed using the piping system.

[0230] The process delivers power generated by a subset of the fuel cell stacks to heaters for other fuel cell stacks that are not generating power (operation 2400 ). The process terminates thereafter.

[0231] Now turn to Fig.25 , depicts an illustration of a flow chart of a process for stopping the heating of a coolant according to an illustrative embodiment. The process in the flow chart is a process that can be used with Fig. 22 An instance of an attached operation that performs multiple operations together.

[0232] In response to the subset of the fuel cell stack generating power, the process stops heating of the coolant by the heating system for the subset of the fuel cell stack generating power (operation 2500 ). The process terminates thereafter.

[0233] The flow charts and block diagrams in the different depicted embodiments show the structure, function and operation of some possible implementations of the equipment and method in the illustrative embodiments. In this respect, each frame in the flow chart or block diagram can represent at least one of a module, section, function or operation or a part of a step. For example, one or more frames in these frames can be implemented as a combination of program instructions, hardware or program instructions and hardware. When implemented with hardware, the hardware can, for example, take the form of an integrated circuit that manufactures or is configured to perform one or more operations in the flow chart or block diagram. When implemented as a combination of program instructions and hardware, an embodiment can take the form of firmware. Each frame in the flow chart or block diagram can be implemented using a combination of a dedicated hardware system or dedicated hardware that performs different operations and a program instruction run by dedicated hardware.

[0234] In some alternative embodiments of the illustrative embodiments, one or more functions indicated in the blocks may not occur in the order indicated in the figure. For example, in some cases, two blocks shown in succession may be performed substantially simultaneously, or the blocks may sometimes be performed in reverse order, depending on the functions involved. In addition, other blocks may be added in addition to the blocks shown in the flowchart or block diagram.

[0235] refer to Fig.26 , an illustration of an aircraft with propulsion and power systems is depicted in accordance with an illustrative embodiment. Fig.19 The fuel cell stack starting system 1900 may be implemented in the aircraft 2600 .

[0236] In this illustrative example, aircraft 2600 is an airplane that includes fuselage 2630, first wing 2632 and second wing 2634, and a propulsion and power system in the form of engines 2601 and liquid hydrogen tank 2602. The engines are electric engines.

[0237] As depicted, liquid hydrogen tank 2602 includes liquid hydrogen tank 2651, liquid hydrogen tank 2652, liquid hydrogen tank 2653, and liquid hydrogen tank 2654. In this illustrative example, two liquid hydrogen tanks are located above the wings on either side of aircraft 2600.

[0238] As depicted in the figure, engines 2601 include engines 2611, 2612, and 2613 connected to first wing 2632. Engines 2601 also include engines 2614, 2615, and 2616 connected to second wing 2634. In this example, these engines are all electric engines.

[0239] In this example, each of these engines includes an engine compartment that includes a fuel cell stack, an air management system, a thermal management system, a motor, and a controller.

[0240] As depicted, there are two starting batteries. Starting battery 2603 is connected to engine 2613, and starting battery 2604 is connected to engine 2614. Starting battery 2603 can be used to start the fuel cell stack in engine 2613. Starting battery 2604 can be used to start the fuel cell stack in engine 2614. In this example, there is one starting battery on each side of aircraft 2600.

[0241] In this illustrative example, two starting batteries are depicted. In other illustrative examples, other numbers of starting batteries may be used. For example, additional starting batteries may be connected to engine 2612. In yet another illustrative example, a starting battery may be connected to engine 2616. In yet another illustrative example, a starting battery may be connected to more than one engine.

[0242] Next in Fig. 27 , an illustration of an integrated power and propulsion unit according to an illustrative embodiment is depicted. An exposed view of an engine 2700 without a nacelle is depicted. In this illustrative example, engine 2700 is an integrated power and propulsion unit (IPPU) and is Fig.26 An example of an engine without an engine nacelle is shown in multiple engines 2601.

[0243] Engine 2700 is an example of an engine that can implement a fuel cell starting system. Engine 2700 includes a number of different components.

[0244] In this illustrative example, heat exchanger 2701 is a rectangular heat exchanger and operates to remove heat from the fuel cell stack coolant and reject the heat to the ambient air. Fan system 2702 operates to increase air flow through heat exchanger 2701. This fan system can be used when the speed and temperature of the ambient air moving through the inlet of the engine compartment are not sufficient to reject heat from the coolant used to cool the various components in engine 2700.

[0245] Fuel cell stack 2703 converts hydrogen and oxygen reactants into electricity. In this example, the hydrogen is gaseous hydrogen and the oxygen is oxygen from air. Heat and water also result from using the hydrogen and oxygen reactants to generate electricity.

[0246] The motor 2704 and the controller 2705 convert the electricity generated by the fuel cell stack 2703 into rotational mechanical energy. The rotational mechanical energy is used to rotate the propeller. The controller 2705 controls the operation of the motor 2704.

[0247] Compressor 2706 compresses ambient air to provide sufficient oxygen reactant to the fuel cell stack cathode manifold. The compressor also operates to maintain cathode pressure for increased fuel cell stack performance. Turbine 2707 recovers energy from air leaving the fuel cell stack 2703 from the fuel cell stack cathode outlet.

[0248] The hydrogen (H2) recirculation blower 2708 operates to recirculate excess unreacted hydrogen fuel flowing out of the fuel cell stack 2703 from the fuel cell anode outlet back into the fuel cell stack 2703 through the fuel cell anode inlet. In this example, the heater is a startup heater that heats the fuel cell stack 2703 to bring the fuel cell stack 2703 to an operating temperature. The operating temperature is a temperature required to maintain a reaction that generates electricity from hydrogen and oxygen.

[0249] In this example, a high temperature coolant pump 2710 circulates coolant to remove heat from the fuel cell stack 2703 and transfers the heat to the heat exchanger 2701 for exhaust to the air. A low temperature coolant pump 2711 circulates coolant to remove heat from low temperature components. These low temperature components require a lower level of cooling than the fuel cell stack 2703. The low temperature components may be, for example, the motor 2704 and the controller 2705. The heat is transferred to the low temperature heat exchanger, which is not shown because it is located inside the wing closer to the LH2 tank.

[0250] Also depicted is an air management system (AMS) intake 2731. This intake receives air for the air management system which conditions air for the fuel cell stack 2703. The air management system includes a compressor 2706 and a charge air heat exchanger 2714.

[0251] In addition, in this example, the exhaust port 2713 is a location for discharging dirty and humid air from the fuel cell stack cathode outlet of the fuel cell stack 2703 to the ambient air. The charge air heat exchanger 2714 heat regulates the air compressor outlet air before the air compressor outlet air enters the fuel cell stack. In these examples, the charge air heat exchanger 2714 is a charge air that provides heat exchange for the compressed air. The regulation can include raising or lowering the temperature of the air so that the fuel cell stack 2703 is at an operating temperature. The fuel cell air supply pipe 2715 guides the compressed air from the outlet of the compressor 2706 to the fuel cell stack cathode inlet of the fuel cell stack 2703. The heater 2709 can heat the coolant in the high temperature loop as part of the startup process of heating the fuel cell stack 2703 to the operating temperature.

[0252] Fig.26 2600 aircraft and Fig. 27The perspective illustration of engine 2700 in is provided as an illustration of an aircraft in which a starting system may be implemented in its engine. This illustration is not meant to limit the manner in which other illustrative examples may be implemented. For example, the aircraft may have six engines or some other number of engines other than the six engines depicted for aircraft 2600. In another illustrative example, the starting batteries are three starting batteries, which may be used in place of the two batteries shown for aircraft 2600. Other illustrative examples may omit fan system 2702. In other illustrative examples, fan system 2702 may be located forward of heat exchanger 2701. In other illustrative examples, heater 2709 may be omitted from engine 2700.

[0253] Next, refer to Fig.28 , depicts an illustration of a schematic diagram of a fuel cell stack startup system according to an illustrative embodiment. In this illustrative example, the fuel cell stack startup system 2800 is Fig.19 An example of a simplified embodiment of a fuel cell stack startup system 1900 in FIG.

[0254] As depicted, the fuel cell stack startup system 2800 includes a startup heater 2802 and a piping system 2803. These two components are used to start the operation of a high temperature proton exchange membrane (HTPEM) fuel cell stack 2801. The HTPEM fuel cell stack 2801 is Fig.19 In an example of a fuel cell stack in a plurality of fuel cell stacks 1920, the start-up heater 2802 is Fig.19 An example of a heater in the plurality of heaters 1915 in the heater system 1901, and the piping system 2803 is Fig.19 28. As depicted, piping system 2803 includes pipe 2810, valve 2811, and valve 2812. In another illustrative example, these two valves can be replaced with three-way valves.

[0255] At startup, the HTPEM fuel cell stack 2801 is warmed up to operating temperature. As depicted, valve 2811 is in a closed position and valve 2812 is in an open position. This positioning of the valves allows air to flow through the startup heater 2802 instead of the ram air radiator 2815.

[0256] As part of the process of heating the HTPEM fuel cell stack 2801 to operating temperature, air is heated by the startup heater 2802 and directed to the HTPEM fuel cell stack 2801. When the HTPEM fuel cell stack 2801 is at operating temperature, valve 2811 moves to an open position and valve 2812 moves to a closed position so that coolant now flows through the ram air radiator 2815 instead of the startup heater 2802. The ram air radiator 2815 now operates to provide cooling to maintain the HTPEM fuel cell stack 2801 at operating temperature.

[0257] Next turn Fig.29 , depicts an illustration of a schematic diagram of a fuel cell stack startup system in a thermal management system according to an illustrative embodiment. The fuel cell stack startup system 2997 in the thermal management system 2996 is Fig.19 1900 in the fuel cell stack startup system 2997 depicts multiple components that can be implemented in a single wing having three engine nacelles. For example, the wing can be Fig.26 2632 of first wing 2632 of aircraft 2600 in FIG. In this example, components for nacelle 2950, ​​nacelle 2952, and nacelle 2954 are shown. Each of the plurality of nacelles may include, for example, Fig.28 Components shown in fuel cell stack startup system 2800.

[0258] In this illustrative example, piping system 2990 is used to facilitate the flow of fluid between components in these engine compartments. Piping system 2990 includes pipes, such as pipes and tubing. The flow through these pipes can be controlled by valves to generate different flows through the piping system to heat load 2933. In addition, the piping system can include a pump for moving the fluid. Piping system 2990 is connected to different components. These connections can be thermal connections where the fluid is not exchanging components. In other examples, these connections can include introducing or receiving fluids from components.

[0259] As depicted, the HTPEM fuel cell stack 2920 is located in the nacelle 2950. Other components in the nacelle include a start-up heater 2910, a pump 2911, a charge air heat exchanger (HX) 2912, a high temperature and low temperature loop heat exchanger (HT-LT HX) 2914, and a ram air radiator 2927. In this example, a liquid hydrogen heat exchanger (LH2 LX) 2913 is positioned closer to the LH2 tank 2971, for example in the wing. In some examples, this component may be present in each of the three nacelles or in only one of the nacelles. The nacelle also includes heat loads 2933. These heat loads may include controllers, tanks, electric motors, and other multiple components that generate heat. A pump 2925 is used to move coolant to these heat loads.

[0260] In the depicted example, a HTPEM fuel cell stack 2921 is located in a nacelle 2952. Other components in the nacelle include a start-up heater 2930, a pump 2931, a charge air heat exchanger (HX) 2932, and a ram air radiator 2937. The nacelle also includes heat loads 2934. A pump 2935 is used to move coolant to these heat loads.

[0261] The HTPEM fuel cell stack 2922 is located in the engine compartment 2954. Other components in the engine compartment include a start-up heater 2960, a pump 2961, a charge air heat exchanger (HX) 2966, and a ram air radiator 2967. The engine compartment also includes heat loads 2945. The pump 2965 is used to move coolant to these heat loads.

[0262] In this configuration, the high temperature (HT) cooling circuit in each nacelle is isolated from the other nacelles. Isolation between cooling circuits can be performed by closing valves 2981 , 2982 and 2983.

[0263] In this example, a startup process is performed on HTPEM fuel cell (FC) stack 2920, HTPEM fuel cell (FC) stack 2921, and HTPEM fuel cell (FC) stack 2922. The startup process includes starting a subset of these HTPEM fuel cell stacks. In this example, the subset of HTPEM fuel cell stacks is the HTPEM fuel cell stack 2920 in the engine compartment 2950.

[0264] The operation of starting up the HTPEM FC stack 2920 in this configuration may be performed as follows:

[0265] 1. Use a starting battery to power the starting heater 2910 and coolant pump 2911. The starting battery can be Fig.26 Battery 2603 in.

[0266] 2. Open bypass valve 2973 to allow coolant to bypass ram air radiator 2927 to ensure that ram air radiator 2927 is not heated. At this point, it is used to heat the coolant to bring the fuel cell stack up to operating temperature. Therefore, no heat needs to be rejected.

[0267] As depicted, flow path 2995 is a loop that enables startup heater 2910 to heat coolant to form heated coolant for heating HTPEM fuel cell stack 2920. As depicted in this flow path, coolant flows from charge air HX 2912 to startup heater 2910, which heats the coolant. The heated coolant flows to HTPEM FC stack 2920 and then returns to charge air HX 2912. In this example, pump 2911 operates to move coolant in this flow path.

[0268] In this example, the heated coolant flow flows through a subset of the fuel cell stacks, which is HTPEMFC stack 2920. Furthermore, in this example, the flow flows to HTPEM fuel cell stack 2920, but not to the other fuel cell stacks (HTPEM fuel cell stack 2921 and HTPEM fuel cell stack 2922).

[0269] 3. After the HTPEM FC stack 2920 reaches the minimum operating temperature for electrochemical activity, air (via power to the air management system) and fuel can be supplied to the stack so that the HTPEM FC stack 2920 can begin to generate power on its own. Additionally, applying power consumption to the HTPEM FC stack 2920 at this time will help the HTPEM FC stack heat itself due to the inefficiency of operation at this initial operating temperature.

[0270] At this point, the electricity generated by the HTPEM FC stack 2920 can be used to power the startup heater of the adjacent engine compartment to begin heating those HTPEM fuel cell stacks. After these HTPEM fuel cell stacks reach operating temperature, air (via a single startup stack that powers its air management system) and fuel can be supplied to the remaining fuel cell stacks so that these fuel cell stacks can also begin generating power on their own.

[0271] For example, the high temperature (HT) coolant loops in each engine compartment can be connected to each other to form a single loop. This connection can be performed in response to the HTPEM FC stack 2920 reaching operating temperature. In other words, the coolant from this fuel cell stack can be used to heat other fuel cell stacks. This heating can be performed in addition to or instead of using the startup heaters in other engine compartments. This connection can be performed by placing valves 2981, 2982, and 2983 in the open position.

[0272] Thus, the heated coolant from the HTPEM FC stack 2920 can be exchanged with coolant in other HT coolant loops of other nacelles to start heating those fuel cell stacks. Thus, the heat generated by the fuel cell stacks that have reached operating temperature can be used to heat other fuel cell stacks in other nacelles to initiate operation of those fuel cell stacks. In addition, this type of heating can also achieve lighting purposes for start-up heaters in other nacelles. Thus, the number of heaters can be reduced, thereby reducing the weight of the aircraft.

[0273] In another illustrative example, this type of heating can be performed in conjunction with an electrical heating method using a startup trigger. Thus, the use of a startup heater and exchanging coolant with other engine compartments can increase the speed at which the fuel cell stack reaches operating temperature and begins generating electricity.

[0274] Next turn Fig.30 , an illustration of a schematic diagram of a fuel cell stack startup system in a thermal management system in accordance with an illustrative embodiment is depicted. Fig.30 A configuration of a fuel cell stack startup system 2997 is depicted in which high temperature cooling circuits are isolated from each other by a configuration of piping 2990. There are no multiple pipes that can exchange high temperature coolant between fuel cell stacks in different engine compartments.

[0275] In this example, in response to the startup heater 2910 generating heat so that the HTPEM fuel cell (FC) stack 2920 reaches an operating temperature, the startup of the HTPEM fuel cell (FC) stack 2921 and the HTPEM fuel cell (FC) stack 2922 is initiated by power delivered from the HTPEM fuel cell (FC) stack 2920 to the startup heaters 2930 and 2960. In this example, coolant is not exchanged between different engine compartments for starting different HTPEM fuel cell stacks.

[0276] Fig.29 and Fig.30 A schematic diagram of the fuel cell stack startup system 2997 is presented as Fig.191900 . This illustration is not meant to limit the manner in which other fuel cell stack systems may be implemented in other examples. For example, a single starting heater may be used in other fuel cell stack starting systems. In another illustrative example, the battery may be included in the engine compartment.

[0277] 4. Low temperature proton exchange membrane charge air heat exchanger

[0278] Low temperature proton exchange membrane (LTPEM) fuel cells provide a zero emission and high efficiency way to generate at least one of propulsion power or system power for an aircraft. When using oxygen as one of the two reactants, LTPEM fuel cell systems often use compressors to maintain adequate reactant supply and increase performance via increased cathode side pressure. In this example, the other reactant is gaseous hydrogen (H2).

[0279] However, this compression may heat the inlet air above the operating temperature of the fuel cell stack. In this case, to avoid overheating, a cooling stage may be used.

[0280] In the illustrative example, cooling load and efficiency are factors in the cooling design system. It is desirable to reduce the overall cooling load and increase the efficiency of the cooling system.

[0281] Existing low temperature proton exchange membrane (LTPEM) fuel cell systems require a compressor to fully pressurize ambient air and supply one of the two reactants, usually oxygen from the air, to the fuel cell stack. In the process of compressing the air, heat is also added. Depending on the degree of compression, the air can be cooled before entering the fuel cell stack to avoid overheating and drying out the fuel cell stack membranes.

[0282] This cooling can be done using an air-to-liquid intercooler. However, this cooling approach places the burden of cooling the air on the stack cooling system. In addition, current systems do not fully exploit energy recovery opportunities.

[0283] The illustrative examples provide a method, apparatus, and system for cooling incoming compressed air while allowing for the capture of significant energy to improve overall system efficiency.

[0284] In one illustrative example, a charge air heat exchanger is used. This component uses the cooled air coming out of the stack to cool the hot compressed compressor outlet air. This type of cooling is twice as effective. This component cools the compressed air to enable the reduction of air-to-liquid intercoolers compared to not performing this type of cooling. In addition, the use of a charge air heat exchanger enables the heating of the stack exhaust to increase the energy recovery of the air management system (AMS) expander to increase the overall system efficiency.

[0285] Cooling of the compressor outlet air is currently performed using a charge air intercooler. In ground vehicle fuel cell systems, due to the relatively low pressure ratio between the stack and ambient pressure, less heat is rejected to the air during compression. Therefore, for the same reason, less energy recovery is available through expansion.

[0286] A charge air heat exchanger is a heat exchanger that provides heat exchange to compressed air. The heat exchanger can cool the compressed air. In these examples, a charge air intercooler is an intercooler that provides cooling to the compressed air.

[0287] The illustrative examples recognize and take into account that systems used in ground vehicles typically do not have inlet air cooling or simply use a single air-to-liquid intercooler. Likewise, current systems in vehicles typically do not include an expander for energy recovery.

[0288] The illustrative examples recognize and take into account that current cooling in ground vehicle systems does not take into account the manner in which aircraft operate at greatly different altitudes compared to ground targets. For aircraft operating at different altitudes, the need to cool the compressed air and have energy available for recovery at the stack outlet increases. The illustrative examples use a heat exchanger in addition to the intercooler to reduce the cooling load and increase energy recovery of the expander. In some illustrative examples, a charge air heat exchanger may replace the charge air intercooler, rather than simply reducing the size of the charge air intercooler.

[0289] Next reference Fig.31 , depicts an illustration of a block diagram of an aircraft management system in accordance with an illustrative embodiment. In this illustrative example, aircraft air management system 3100 may be configured to: Figure 4 implemented in the aircraft 400 to manage Figure 4 406 to generate electricity to operate the engine 406. In this example, the aircraft air management system 3100 manages the temperature of the air delivered to the fuel cell stack 3105 for use with gaseous hydrogen to generate electricity for operating the electric motors in the aircraft. In this example, the fuel cell stack 3105 includes a low temperature proton exchange membrane fuel cell 3113.

[0290] In one illustrative example, aircraft air management system 3100 has a number of different components. As depicted, aircraft air management system 3100 includes air heat exchanger 3102 , intercooler 3103 , and ductwork 3104 .

[0291] In this example, the duct system 3104 is connected to the air heat exchanger 3102, the intercooler 3103, and the fuel cell stack 3105. The heated air 3120 flows to the air heat exchanger 3102 through the duct system 3104. The air heat exchanger 3102 cools the heated air 3120 to form cooler air 3122. In this example, the cooler air 3122 flows from the air heat exchanger 3102 to the intercooler 3103 through the duct system. The intercooler 3103 further cools the cooler air 3122 to form cooled air 3124. The cooled air 3124 flows from the intercooler 3103 to the fuel cell stack 3105 through the duct system 3104. In this example, the cooled air 3124 is at an operating temperature 3125 for the fuel cell stack 3105.

[0292] In one illustrative example, air heat exchanger 3102 , intercooler 3103 , ductwork 3104 , and fuel cell stack 3105 are located in nacelle 3130 of engine 3132 of aircraft 3127 .

[0293] Furthermore, the aircraft air management system 3100 comprises a compressor 3107 . The compressor 3107 is connected to the duct system 3104 and generates heated air 3120 which flows through the air heat exchanger 3102 .

[0294] In this example, heated air 3120 , cooler air 3122 , and cooled air 3124 are compressed air 3126 .

[0295] In addition, the duct system 3104 can also direct gaseous hydrogen 3140 from the fuel system 3142 to the fuel cell stack 3105. The gaseous hydrogen 3140 can be used with the cooled air 3124 to generate electricity to power the engine 3132 of the aircraft 3127. This directing is performed using separate ducts so that the gaseous hydrogen 3140 is separated from the air flowing in the duct system 3104. In other words, the first portion 3111 of the duct system 3104 can be used to direct air, while the second portion 3112 of the duct system 3104 can be used to direct gaseous hydrogen 3140. The two portions are separated from each other so that the air and hydrogen do not mix within the duct system 3104.

[0296] In this example, a second portion 3112 of the piping system 3104 directs heated air 3120 from the intercooler 3103 to a fuel system heat exchanger 3141, which heats liquid hydrogen 3143 to form gaseous hydrogen 3140. This second portion of the piping system 3104 directs the gaseous hydrogen 3140 from the fuel system heat exchanger 3141 to the fuel cell stack 3105. The fuel cell stack 3105 generates electricity using the gaseous hydrogen 3140 and the oxygen in the cooled air 3124. In this example, the air is cooled to an operating temperature 3125.

[0297] Fig.31 The block diagram illustration of aircraft air management system 3100 in FIG. 1 is not meant to imply physical or architectural limitations to the manner in which the illustrative embodiments may be implemented. Other components in addition to or in place of the components illustrated may be used. Some components may be unnecessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the illustrative embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0298] For example, in other illustrative examples, the nacelle may have more than one fuel cell stack. As another example, piping is present in piping system 3104. Additionally, valves and pumps may also be present in piping system 3104. Although not shown in the block diagram, aircraft 3127 may include other engines in addition to engine 3132.

[0299] In addition, the aircraft air management system 3100 can also heat the compressed air 3126 to heat or cool the heated air 3120 from the compressor 3107 according to the temperature of the compressed air relative to the coolant flowing through the air heat exchanger 3102. In this way, the compressed air 3126 can be managed for use in the fuel cell stack 3105 by heating and cooling the compressed air 3126 according to the temperature of the compressed air 3126 relative to the coolant in the air heat exchanger 3102. In this way, the temperature of the compressed air 3126 reaching the fuel cell stack 3105 can be managed to have a temperature close enough to the temperature of the fuel cell stack 3105, which enables the desired level of power generation. This type of management is performed on the compressed air 3126 reaching the fuel cell stack 3105 to avoid an increase in temperature gradient (an increase in temperature gradient will reduce power generation efficiency). Therefore, the compressed air 3126 that can be heated will be cooled to have a temperature related to the operating temperature of the fuel cell stack 3105, which provides a desired level of power generation.

[0300] Next go to Fig.32 , an illustration of a flowchart of a process for air management is depicted in accordance with an illustrative embodiment. Fig.32The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.19 The fuel cell stack startup system 1900 is implemented in the fuel cell stack startup system 1900.

[0301] The process begins by receiving heated air (operation 3200). The process cools the heated air using an air heat exchanger to form cooler compressed air (operation 3202).

[0302] The process cools the cooler air with an intercooler to form cooled compressed air (operation 3204). The process delivers the cooled air to the fuel cell stack (operation 3206). The process terminates thereafter.

[0303] exist Fig.32 In the invention, an air heat exchanger, an intercooler and a fuel cell stack are located in the nacelle of an engine for an aircraft. Ambient air is directed via the nacelle inlet into a compressor where the pressure is increased. The air, now at a higher pressure and temperature, is delivered to the charge air heat exchanger where it is conditioned to near the fuel cell stack temperature by heat exchange with the fuel cell stack cathode outlet.

[0304] The temperature of the air is then further regulated towards the fuel cell stack temperature via heat exchange with the fuel cell stack coolant in the charge air intercooler before being delivered to the fuel cell stack. Within the fuel cell stack, the oxygen in the air reacts with the hydrogen as the air moves through the individual fuel cells. The foul air also removes some amount of water products as it leaves the stack to prevent flooding of the fuel cell stack.

[0305] After being discharged from the stack, the air passes through the charge air heat exchanger. The air then passes through the turbine where it expands to recover the energy used in the compression process and finally, leaves the engine compartment as exhaust gas.

[0306] See now Fig.33 , depicts an illustration of a schematic diagram of an aircraft air management system in accordance with an illustrative embodiment. The air management system 3301 operates to cool a fuel cell stack 3304. In this example, the air management system 3301 includes a charge air heat exchanger (HX) 3300 and a charge air intercooler 3302, as well as a duct system 3303. The air management system 3301 also includes a compressor (C) 3305, a turbine (T) 3311, a motor 3341, and a controller 3342.

[0307] In this example, the compressor (C) 3305 receives inlet air 3317 entering the engine compartment and generates compressed air 3318 having a higher pressure than the inlet air 3317. In this example, the compressor 3305 is operated by a motor 3341 under the control of a controller 3342. In addition, the compressed air 3318 has a higher temperature that may be higher than the desired temperature for use in the fuel cell stack 3304. The compressed air can be cooled using a charge air heat exchanger (HX) 3300 and a charge air intercooler 3302 to form cooled compressed air 3319. The charge air heat exchanger (HX) 3300 initially cools the compressed air 3318 to form cooler air 3321. The cooler compressed air can be further cooled by the charge air intercooler 3302, which provides further cooling, to form cooled compressed air 3319. Therefore, the cooled compressed air 3319 is compressed air that can have a desired temperature for the fuel cell stack 3304.

[0308] The cooled compressed air 3319 can be used with gaseous hydrogen received from the hydrogen (H2) fuel system 3320 in the fuel cell stack 3304 to generate electricity, which is used to power components such as motor 3330 and controller 3331. The motor 3330 in turn provides mechanical energy for rotating the propeller 3362. The hydrogen fuel system 3320 can include a liquid hydrogen tank, a recirculation system, a cooling system, and other components. In this example, the liquid hydrogen heat exchanger converts the liquid hydrogen into gaseous hydrogen for use in the fuel cell stack 3304.

[0309] In this example, compressed air 3323 flowing through the fuel cell stack 3304 is directed to the charge air heat exchanger 3300, which heats the air as part of the process of cooling the compressed air received from the compressor 3305 to form heated air 3326. The heated air is used to turn the turbine 3311. In this way, some energy recovery can be performed using the turbine 3311. Air 3328 from the turbine 3311 is then directed and exits the engine as exhaust 3313.

[0310] The thermal management system operates to remove heat from the fuel cell stack 3304, motor 3330, and controller 3331, while the ram air radiator 3350 rejects this heat to the ambient air. The thermal management system utilizes a liquid hydrogen heat exchanger (LH2 HX) 3335 for use in the fuel cell stack 3304 to heat and vaporize the liquid hydrogen fuel.

[0311] 5. Fuel cell aircraft thermal management system

[0312] Both low temperature proton exchange membrane (LTPEM) fuel cells and high temperature proton exchange membrane (HTPEM) fuel cells offer zero carbon emission methods for powering aircraft. In addition, these types of fuel cells can also provide a highly efficient way to generate at least one of propulsion or electrical power for aircraft systems.

[0313] Lower operating temperatures compared to conventional turbomachinery make thermal management system (TMS) designs large and heavy.Illustrative examples provide features for managing and exhausting heat generated by a fuel cell propulsion system on an aircraft while reducing undesirable effects on performance.

[0314] High temperature proton exchange membrane (HTPEM) technology can be used to provide a higher thermal drive potential, which enables the thermal management system to be significantly reduced in size. In this example, the thermal drive potential is the temperature difference between the ambient air and the coolant leaving the fuel cell. However, other electric propulsion components (such as motors, their controllers, and other power electronics) typically operate at temperatures closer to the LTPEM fuel cell. Therefore, HTPEM fuel cell powered aircraft can use different thermal management methods other than having a single shared system for all electric propulsion components.

[0315] In this illustrative example, a dual-circuit structure is used to maintain separate temperature control of the HTPEM fuel cell stack and the cryogenic motors and controllers in the engine compartment (the cryogenic motors and controllers are used for the fuel cell air management system, cooling fans, and propulsion devices). In other words, one circuit can be used for the HTPEM fuel cell stack and the other circuit can be used for heat generating components other than the fuel cell stack. These heat generating components can be motors, controllers, and power electronics in the engine compartment.

[0316] In one example, a low temperature (LT) cooling loop includes coolant that cools multiple heat generating components. These heat generating components are also referred to as heat loads. The coolant in this loop is cooled by the heat capacity of the onboard liquid hydrogen fuel. This type of cooling enables sufficient heat to be obtained to gasify the liquid hydrogen of the fuel cell stack. This type of cooling can also eliminate the need for a dedicated engine compartment heat exchanger for the lower temperature liquid cooled components within the engine compartment.

[0317] The high temperature (HT) loop includes a coolant for managing the temperature of the fuel cell stack. The temperature management may include at least one of heating and cooling the fuel cell stack to maintain the fuel cell stack at an operating temperature. In these examples, there may be a range of operating temperatures.

[0318] In this example, the high temperature loop includes an underhood heat exchanger. This heat exchanger is a different heat exchanger than that used in the low temperature loop in the underhood of the engine. Separate low temperature (LT) cooling loops and high temperature (HT) cooling loops are used to cool the fuel cell stack and lower temperature heat loads. Lower temperature heat loads are heat loads that have a lower temperature than the temperature of the fuel cell stack. These separate cooling loops eliminate the need for a separate low temperature heat exchanger to increase the efficiency and effectiveness of cooling components by reducing the mass and drag caused by the thermal management system.

[0319] Next go to Fig.34 , depicts an illustration of a block diagram of an aircraft thermal management system in accordance with an illustrative embodiment. In this illustrative example, the aircraft thermal management system 3400 may be Figure 4 In the aircraft 400, the Figure 4 406 and other components that generate heat in the engine 406. In this example, the aircraft thermal management system 3400 provides cooling for the fuel cell stack 3405 and a plurality of heat loads 3416. In this example, the fuel cell stack 3405 includes a high temperature proton exchange membrane fuel cell. The plurality of heat loads 3416 include at least one of an electric motor, a power circuit, a controller, a power electronic device, or some other component that generates heat.

[0320] In this illustrative example, aircraft thermal management system 3400 includes high temperature circuit 3401 and low temperature circuit 3402. High temperature circuit 3401 and low temperature circuit 3402 are located in piping system 3403.

[0321] The high temperature loop 3401 is configured to manage the temperature 3410 of the fuel cell stack 3405 in the engine compartment 3406 using the engine compartment heat exchanger 3421. When managing the temperature 3410 of the fuel cell stack 3405, the high temperature loop 3401 is configured to maintain the fuel cell stack 3405 at an operating temperature 3411. Maintaining the temperature 3410 may include at least one of cooling or heating the fuel cell stack 3405. The operating temperature 3411 may be one or more temperatures, and may be a temperature range within an operating temperature limit 3419. In this example, the operating temperature limit 3419 is the maximum or minimum temperature at which the fuel cell stack 3405 can operate.

[0322] In this example, the high temperature loop 3401 can remove heat from the fuel cell stack 3405 using a coolant 3430 in the high temperature loop 3401. The coolant 3430 can be cooled using a nacelle heat exchanger 3421 to a temperature sufficient to cool or heat the fuel cell stack 3405 so that a temperature 3410 of the fuel cell stack 3405 is an operating temperature 3411 within the operating temperature limit 3419 of the fuel cell stack 3405.

[0323] In this example, heat is removed in response to the operating temperature 3411 being greater than the operating temperature limit 3419. For this example, the coolant 3430 has a temperature lower than the operating temperature 3411. In this case, heat is removed from the fuel cell stack 3405 and transferred to the ambient air as part of the exhaust gas exiting the engine compartment 3406. In response to the operating temperature 3411 being lower than the operating temperature limit 3419, heat can be added to the fuel cell stack 3405. In other words, the coolant 3430 can be hotter than the operating temperature limit 3419. For example, during startup of the fuel cell stack, the coolant 3430 can be hotter than the operating temperature limit 3419.

[0324] The cryogenic circuit 3402 is configured to utilize the heat capacity 3407 of the liquid hydrogen 3408 to cool the plurality of heat loads 3416 in the engine compartment 3406. In this example, the heat capacity 3407 of the liquid hydrogen 3408 can cool the coolant 3430 in the cryogenic circuit 3402 for cooling the plurality of heat loads 3416.

[0325] The heat capacity of liquid hydrogen 3408 is the energy required to convert liquid hydrogen 3408 into gaseous hydrogen 3445. Converting liquid hydrogen 3408 into gaseous hydrogen 3445 cools the coolant. Therefore, the cooled coolant can be used to cool multiple heat loads 3416.

[0326] In this illustrative example, heated compressed air 3440 generated by compressor 3441 may be conditioned by charge air heat exchanger 3420 in ductwork 3403 to form compressed air at approximately operating temperature 3411 when using charge air heat exchanger 3420 to add heat to or remove heat from fuel cell stack 3405 exhaust. The compressed air is transmitted to fuel cell stack 3405 for use with gaseous hydrogen 3445 to generate electricity.

[0327] In one illustrative example, there may also be an air intercooler 3460. For this example, the air intercooler 3460 may receive cooled compressed air 3444 from the charge air heat exchanger 3420 via the ductwork 3403 and further condition the cooled compressed air 3444 and transmit the cooled compressed air 3444 close to the operating temperature 3411 to the fuel cell stack 3405. The cooled compressed air 3444 reacts with the gaseous hydrogen 3445 in the fuel cell stack 3405 to generate electricity.

[0328] In this illustrative example, heated compressed air 3440 may be based on temperature 3410 of fuel cell stack 3405. If the air of heated compressed air 3440 is too high above the operating temperature 3411 of fuel cell stack 3405, then heated compressed air 3440 is cooled. If the air of heated compressed air 3440 is too low below the operating temperature 3411 of fuel cell stack 3405, then compressed air 3440 is heated. Thresholds may be used to determine when the temperature is too low or too high.

[0329] The ability to heat or cool the heated compressed air 3440 can be controlled by the coolant temperature. The coolant temperature can be controlled by at least one of the coolant pump speed or by varying the amount of air flow through the engine compartment heat exchanger 3421.

[0330] Thus, in this illustrative example, high temperature loop 3401 operates to cool fuel cell stack 3405. In some cases, this loop may heat fuel cell stack 3405, for example, during startup of fuel cell stack 3405. In a separate loop, low temperature loop 3402 operates to cool a set of heat loads 3416. Thus, the two loops may provide the flexibility to cool different components that may require different levels of cooling.

[0331] In addition, the illustrative example enables conditioning of air for use with gaseous hydrogen 3445 in the fuel cell stack 3405 to generate electricity. Such conditioning of the air from the compressor 3441 may include at least one of heating or cooling depending on the temperature of the heated compressed air 3440 and the temperature 3410 of the fuel cell stack 3405.

[0332] Fig.34 The block diagram illustration of aircraft thermal management system 3400 in FIG. 1 is not meant to imply physical or architectural limitations to the manner in which the illustrative embodiments may be implemented. Other components in addition to or in place of the components illustrated may be used. Some components may be unnecessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the illustrative embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0333] For example, in another illustrative example, engine compartment 3406 may include one or more fuel cell stacks in addition to fuel cell stack 3405. In another example, another heat exchanger (eg, an intercooler) may be used with boost heat exchanger 3422 to further cool heated compressed air 3440.

[0334] Next go to Fig.35 , an illustration of a flowchart of a process for thermal management is depicted in accordance with an illustrative embodiment. Fig.35 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.34 The aircraft thermal management system 3400 is implemented in the aircraft thermal management system 3400.

[0335] The process begins by managing the temperature of a fuel cell stack in an engine compartment using an engine compartment heat exchanger in a high temperature loop (operation 3500 ).

[0336] The process cools a plurality of heat loads in the engine compartment using a cryogenic circuit that uses the heat capacity of liquid hydrogen to cool the plurality of heat loads (operation 3502 ). The process terminates thereafter.

[0337] See now Fig.36 , depicts an illustration of a flow chart of a process for managing the temperature of a fuel cell stack in accordance with an illustrative embodiment. The process in this figure is Fig.35 An example of an implementation of operation 3500 in .

[0338] The process maintains the fuel cell stack at an operating temperature (operation 3600). The process terminates thereafter. In operation 3600, the air is heated by the coolant so that the fuel cell stack is maintained at an operating temperature. The operating temperature may be a temperature range at which the fuel cell stack 3405 operates to generate electricity. In addition, the operating temperature may be a temperature that provides a desired level of electricity generation. In other words, there may be other temperatures at which the fuel cell stack 3405 can generate electricity but not at a desired level of electricity.

[0339] See now Fig.37 , depicts a diagram of a thermal management system having a high temperature loop 3781 and a low temperature loop 3782 according to an illustrative embodiment. The figure shows the layout of the hardware housed within a single engine compartment for a high temperature proton exchange membrane (HTPEM) configuration. The fuel cell stack in this example is supplied with air from an air management system and hydrogen from a fuel system and in turn generates power. The power is used to supply power to an electric motor via a controller for the electric motor, which in turn rotates the propeller.

[0340] As depicted, thermal management system 3700 is located in the engine compartment of the engine. The system has a high temperature circuit 3781 and a low temperature circuit 3782. High temperature circuit 3781 uses ram air radiator 3702 to remove heat from fuel cell stack 3710.

[0341] Low temperature loop 3782 uses the heat capacity of liquid hydrogen in hydrogen fuel system 3711 to cool heat loads having lower heat generation than fuel cell stack 3710. In other words, low temperature loop 3780 cools coolant heated by these heat loads as part of the process to generate gaseous hydrogen from liquid hydrogen in hydrogen fuel system 3711.

[0342] As depicted, inlet air 3701 passes through ram air radiator 3702 to cool the coolant, which is part of the high temperature cooling circuit. In this example, the coolant is used to cool the fuel cell stack 3710. The result of this cooling is exhaust gas 3703, which has an increased temperature compared to the inlet air 3701.

[0343] As depicted, air management system 3704 includes compressor 3705, turbine 3706, motor 3707, and controller 3708. The air management system can be used to generate compressed air for use in fuel cell stack 3710. The air can be used with gaseous hydrogen from hydrogen (H2) fuel system 3711 to generate electricity. Liquid hydrogen from hydrogen fuel system 3711 is converted into gaseous hydrogen using liquid hydrogen heat exchanger (LH2 HX) 3712.

[0344] In this example, inlet air 3701 is received as ambient air at the nacelle inlet and is directed to compressor 3705 and ram air radiator 3702 .

[0345] At the compressor 3705, the air pressure of the air is increased to form compressed air. The compressed air also has a higher temperature. The compressed air is transmitted to the charge air intercooler 3720, in which the compressed air is conditioned toward the fuel cell stack temperature by heat exchange with the high temperature HT coolant. The air can be conditioned by heating or cooling the air according to the temperature of the compressed air. Such conditioning may include at least one of heating or cooling through the charge air intercooler 3720. The heating or cooling is based on the temperature of the coolant relative to the temperature of the compressed air.

[0346] The conditioned air is delivered to the fuel cell stack 3710. Within the fuel cell stack 3710, the oxygen in the conditioned air reacts with the gaseous hydrogen as it moves through the various fuel cells in the fuel cell stack 3710.

[0347] The air leaves the fuel cell stack 3710. The air is dirty and may include a certain amount of water product to prevent flooding of the fuel cell stack 3710. The air passes through a turbine 3706 after being discharged from the fuel cell stack 3710. The air expands to recover energy for use in the compression process and is discharged as exhaust gas 3703.

[0348] Ram air radiator 3702 removes heat from the high temperature coolant in high temperature loop 3781 and heats the air before it is discharged as exhaust gas 3703.

[0349] Hydrogen is stored in liquid form in tanks of the hydrogen fuel system 3711. The liquid hydrogen is distributed to the LH2 HX 3712 via fuel lines. This component heats the liquid hydrogen to form gaseous hydrogen. The heating of the gaseous hydrogen is performed using heat exchange with the cryogenic coolant in the cryogenic loop 3782. The gaseous hydrogen can then be transferred to the fuel cell stack 3710.

[0350] In this example, a high temperature (HT) loop 3781 removes heat generated during the fuel cell reactions using liquid coolant flowing through the fuel cell stack 3710. The heated coolant is transferred to the ram air radiator 3702 where the heat in the coolant is rejected to the ambient air passing through the ram air radiator 3702.

[0351] The cryogenic loop 3782 uses a liquid coolant to remove heat from a plurality of cryogenic heat loads. For example, these heat loads may be the motor 3750, the controller 3751, and other power electronics such as a DC to DC (DC / DC) converter 3752. The heat in the coolant may be transferred to the liquid hydrogen at the LH2 HX 3712 to vaporize the liquid hydrogen.

[0352] In this example, motor 3750 turns propeller 3795. High power bus 3786 connects fuel cell stack 3710 to other electrical components.

[0353] In some cases, these heat loads do not generate enough heat to vaporize a sufficient amount of hydrogen fuel. In this case, a high temperature to low temperature heat exchanger (HT-LT HX) 3731 can perform supplemental heating of the hydrogen. In this example, the HT-LTHX 3731 can transfer heat from the high temperature coolant to the low temperature coolant to avoid insufficient liquid hydrogen vaporization and subsequently avoid damage to the fuel cell stack from thermal shock.

[0354] The high temperature loop 3781 in the thermal management system 3700 operates to remove heat from the fuel cell, while the ram air radiator 3702 rejects this heat to the ambient air.

[0355] The LH2 HX 3712 operates to remove heat from the low temperature coolant and low temperature loop 3782, and in turn cools heat loads such as the motor 3750 and controller 3751, while also heating and vaporizing the hydrogen fuel before it enters the fuel cell stack 3710. When the lower heat loads do not provide sufficient heat, the HT-LT HX 3731 operates to supply additional heat for heating the hydrogen fuel. In one illustrative example, this feature can be implemented in the innermost nacelle of each wing.

[0356] 6. Liquid hydrogen supply system for fuel cell powered aircraft (23-1368-US-PSP)

[0357] In this illustrative example, hydrogen for a fuel cell powered aircraft stores hydrogen as a liquid. The hydrogen can be stored as a liquid at about -424°F. The storage tank is a liquid hydrogen tank, such as a cryogenic tank that stores hydrogen under pressure. Different techniques can be used to maintain pressure in the liquid hydrogen tank, ensure that venting can be performed safely without freezing the vent outlet, and direct the vented gas away from the aircraft. This venting of gas avoids undesirable tank over-pressurization.

[0358] Maintaining pressure in the fuel tanks can be accomplished by venting liquid hydrogen from a common feed line, running it through a heat exchanger, then compressing it to 5 psi and pumping it back to the top of the tanks. The system can be turned on and off based on a set of pressure sensors operated with voting logic (most of the pressure sensors must be below the boost system turn-on point).

[0359] Liquid hydrogen tanks may use a vent system to prevent overpressure due to leakage of ambient hot heat. Due to the high flammability of hydrogen, the vent system may include a flame arrester at the end to prevent flashback in the vent line if the vented hydrogen is ignited. The flame arrester design works by trapping water in a narrow passage. If a pulse of hot hydrogen is vented before the pressure relief valve is opened, this action will push the water out of the flame arrester. This process is done to avoid the low temperature of the vented hydrogen freezing the water in the flame arrester and blocking the flow through the flame arrester.

[0360] In addition to pushing water, heaters can be added to the flame arrester to prevent ice accumulation when ambient temperatures might cause freezing.

[0361] The illustrative examples recognize that the problem of safely venting hydrogen is to vent the gas in such a way that the hydrogen does not impinge on the aircraft and become trapped beneath the aircraft while the aircraft is on the ground. Impingement on the aircraft is undesirable because if the vented gas ignites, damage to the aircraft skin that it contacts can occur.

[0362] In the illustrative example, by venting the hydrogen out of the tops of the vertical stabilizers, the vented gases will not impact any aircraft surfaces and will warm to a point less dense than air, causing the vented gases to rise when the aircraft is on the ground.

[0363] Due to the temperature of liquid hydrogen, there are only two known substances that will remain gases. These substances are hydrogen (at or above the vapor pressure of liquid hydrogen) and helium.

[0364] With respect to the ability to vent hydrogen, the first step involves performing a pressure cycle of warmed hydrogen to bring the system to approximately -320° F. At this temperature, nitrogen can be safely used to complete the warming and inerting of the system.

[0365] Next reference Fig.38 , depicts a diagram of a hydrogen recycling system according to an illustrative embodiment. In this illustrative example, the hydrogen recycling system 3800 may be Figure 4 implemented in the aircraft 400 so that Figure 4 Hydrogen recycling of a group of liquid hydrogen tanks 408 in the embodiment. In this example, liquid hydrogen 3807 is stored in the group of liquid hydrogen tanks 3810.

[0366] In this illustrative example, hydrogen recirculation system 3800 includes piping 3801 and controller 3802. In this example, piping 3801 is connected to a set of liquid hydrogen tanks 3810 for aircraft 3855. Piping system 3801 includes piping 3803 and valve 3804.

[0367] The piping system 3801 includes pipes and valves. These valves can be controlled by a controller 3802 to direct fluids along different routes or circuits. The controller 3802 is a hardware system and may include software.

[0368] In one illustrative example, controller 3802 can control piping system 3801 to remove gaseous hydrogen 3811 from the set of liquid hydrogen tanks 3810. In one illustrative example, controller 3802 controls piping system 3801 to perform a number of different operations. For example, controller 3802 transfers gaseous hydrogen 3811 to tank heat exchanger 3820. Gaseous hydrogen 3811 is heated by tank heat exchanger 3820 to form heated gaseous hydrogen 3823. The tank heat exchanger can be, for example, Fig.37 The controller 3802 transmits a first portion of the heated gaseous hydrogen to the fuel cell stack 3822. The controller 3802 returns a second portion of the heated gaseous hydrogen 3823 to the set of liquid hydrogen tanks 3810.

[0369] In this example, the second portion of the heated gaseous hydrogen 3823 is an amount of heated gaseous hydrogen 3823 that maintains a pressure level in the set of liquid hydrogen tanks 3810 that enables liquid hydrogen 3807 to flow to the fuel cell stack 3822. This flow of liquid hydrogen 3807 includes liquid hydrogen 3807 flowing out of the set of liquid hydrogen tanks 3810 and being converted into gaseous hydrogen 3811 and heated for use in the fuel cell stack 3822. This type of flow may be used when the second portion of the heated gaseous hydrogen 3823 is not present in sufficient amount for use in the fuel cell stack 3822.

[0370] In addition, the controller 3802 can control the pressure in the liquid hydrogen tanks 3810. For example, the controller 3802 can transfer the gaseous hydrogen 3811 in the group of liquid hydrogen tanks 3810 to the vent 3860 through the piping system 3801 in response to the pressure in the group of liquid hydrogen tanks 3810 being greater than a certain tolerance. In this example, the vent 3860 is considered to be part of the hydrogen recycling system 3800. Therefore, in this example, in response to the pressure in the group of liquid hydrogen tanks 3810 being greater than the tolerance, excess gaseous hydrogen is transferred from the group of liquid hydrogen tanks 3810 to the vent 3860 in the aircraft 3855.

[0371] The vent 3860 may be located at various locations on the aircraft 3855. For example, the vent 3860 may be located in an empennage 3861 of a fuselage 3862 of the aircraft 3855. For example, the vent 3860 may be located in a vertical empennage 3865 on the empennage 3861 of the fuselage 3862. The vertical empennage 3865 is a vertical stabilizer connected to the empennage 3861 of the fuselage 3862.

[0372] In another illustrative example, controller 3802 may perform similar operations with liquid hydrogen 3807 stored in the set of liquid hydrogen tanks 3810. Liquid hydrogen 3807 may be used to maintain a desired pressure level in the set of liquid hydrogen tanks 3810. Such use of liquid hydrogen 3807 may be used in lieu of, or in conjunction with, operating with gaseous hydrogen 3811 to maintain a desired pressure level.

[0373] In this example, the controller 3802 can control the piping system 3801 to perform operations. For example, the controller 3802 removes liquid hydrogen 3807 from the set of liquid hydrogen tanks 3810 and transmits the liquid hydrogen 3807 to the tank heat exchanger 3820 to form heated gaseous hydrogen 3823. The controller 3802 can transmit a first portion of the heated gaseous hydrogen 3823 to the fuel cell stack 3822 and return a second portion of the heated gaseous hydrogen 3823 to the set of liquid hydrogen tanks 3810.

[0374] For example, vent 3860 may be located in another location. In another illustrative example, vent 3860 may be located in another stabilizer in vertical tail 3865. In yet another illustrative example, vent may be located on a wing of aircraft 3855.

[0375] Fig.38 The block diagram illustration of the hydrogen recycling system 3800 in the illustrative embodiments is not meant to imply physical or structural limitations on the manner in which the illustrative embodiments may be implemented. Other components in addition to or in place of the components illustrated may be used. Some components may be unnecessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the illustrative embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0376] refer to Fig.39 , depicts an illustration of a flow diagram of a process for recycling hydrogen in accordance with an illustrative embodiment. Fig.39 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.38 The hydrogen recycling system 3800 is implemented in the present invention. The process can be used to manage liquid hydrogen in the liquid hydrogen tank of the aircraft.

[0377] The process begins by extracting gaseous hydrogen from a bank of liquid hydrogen tanks connected to an aircraft (operation 3900). The process passes the gaseous hydrogen extracted from the bank of liquid hydrogen tanks through a tank heat exchanger in an engine compartment of an engine for the aircraft to form heated gaseous hydrogen (operation 3902).

[0378] The process transmits a first portion of the heated gaseous hydrogen to a fuel cell stack in an engine of the aircraft (operation 3904). The process returns a second portion of the heated gaseous hydrogen to the set of liquid hydrogen tanks (operation 3906). The process terminates thereafter.

[0379] refer to Fig.40 , depicts an illustration of a flow diagram of a process for recycling hydrogen in accordance with an illustrative embodiment. Fig.40 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.38 The hydrogen recycling system 3800 is implemented in the present invention. The process can be used to manage liquid hydrogen in the liquid hydrogen tank of the aircraft.

[0380] The process removes liquid hydrogen from the set of liquid hydrogen tanks (operation 4000). The process transfers the liquid hydrogen to a tank heat exchanger to form heated gaseous hydrogen (operation 4002).

[0381] The process transmits a first portion of the heated gaseous hydrogen to the fuel cell stack (operation 4004). The process returns a second portion of the heated gaseous hydrogen to the set of liquid hydrogen tanks (operation 4006). The process terminates thereafter.

[0382] refer to Fig.41 , depicts an illustration of a flow diagram of a process for recycling hydrogen in accordance with an illustrative embodiment. Fig.41 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.38 The hydrogen recycling system 3800 is implemented in the present invention. The process can be used to manage liquid hydrogen in the liquid hydrogen tank of the aircraft.

[0383] In response to the pressure in the group of liquid hydrogen tanks being greater than a specified tolerance, the process routes gaseous hydrogen in the group of liquid hydrogen tanks through the piping system to a vent (operation 4100 ). The process terminates thereafter.

[0384] Next turn Fig.42 , depicts a diagram of a recirculation system for liquid hydrogen for tank pressure control in accordance with an illustrative embodiment. As shown in this example, a recirculation system 4200 for recirculating gaseous hydrogen (GH2) may be implemented to control the temperature within liquid hydrogen tanks 4251 and 4252.

[0385] The process may include pumping gaseous hydrogen from the top of a liquid hydrogen tank and then passing the gaseous hydrogen through a heat exchanger 4201 as it travels downward toward the wing. The heat exchanger 4201 has heat from a cryogenic coolant line 4203 from the engine.

[0386] The gaseous hydrogen is divided into two parts at the flow control valve 4202 after the heat exchanger 4201. In this example, most of the gaseous hydrogen flows to the fuel cell stack through the pipeline 4204, and some of the gaseous hydrogen is pumped back to the liquid hydrogen tank by the gaseous hydrogen pump 4206 and the gaseous hydrogen pump 4207 through the return pipeline 4205. Returning the heated gaseous hydrogen to the liquid hydrogen tank affects how much liquid hydrogen (LH2) in the liquid hydrogen tank is evaporated and affects the tank pressure. In this example, more evaporation leads to a greater pressure increase.

[0387] In one example, the process may proceed as follows:

[0388] 1. Extract gaseous hydrogen from the liquid hydrogen tank.

[0389] 2. Gaseous hydrogen is conveyed through heat exchanger 4205 along with heated coolant from the fuel cell stack as the heating fluid. The hot coolant can be heated by multiple heat loads in the low temperature loop.

[0390] 3. Output the heated gaseous hydrogen from the heat exchanger 4205.

[0391] 4. The gaseous hydrogen is split at the flow control valve 4202, wherein a portion of the gaseous hydrogen is directed for recirculation in the liquid hydrogen tank, and another portion of the gaseous hydrogen is transmitted to the fuel cell stack.

[0392] 5. Directing the portion of the gaseous hydrogen to recirculate to gaseous hydrogen pump 4206 and gaseous hydrogen pump 4207 to return to the liquid hydrogen tank

[0393] 6. Returning gaseous hydrogen to the liquid hydrogen tank and bubbling through the liquid hydrogen to maintain the pressure in the cryogenic tank;

[0394] exist Fig.43 , a diagram of a vent system for gaseous hydrogen is depicted in accordance with an illustrative embodiment. Ventilation system 4300 provides the ability to vent gaseous hydrogen (GH2) in response to excess pressure. The vent system is capable of releasing gaseous hydrogen from liquid hydrogen tank 4310 and removing gaseous hydrogen from the aircraft. During flight, such venting can occur through vent 4304 in vertical tail 4306. In this example, vent 4304 is connected to liquid hydrogen tank 4310 via ductwork 4312.

[0395] Next reference Fig.44 , depicts a diagram of a system for recycling gaseous hydrogen for tank pressure control according to an illustrative embodiment. In illustrative examples, the same reference numeral may be used in more than one figure. Such reuse of reference numerals in different figures represents the same element in the different figures. This figure is Fig.43 A more detailed view of the components in section 4350.

[0396] In addition to the components for recycling gaseous hydrogen, this view also shows components that can be used to recycle liquid hydrogen (LH2). In this example, liquid hydrogen is extracted from the bottom of the liquid hydrogen tank 4310. Some of the liquid hydrogen is transmitted to the engine and some of the liquid hydrogen travels through the heat exchanger 4401 to warm up and change phase to gaseous hydrogen (GH2). The heat exchanger 4401 has heat from the low-temperature coolant line 4402 of the engine. The liquid hydrogen is then pumped back into the liquid hydrogen tank 4310. The heated GH2 added back to the liquid hydrogen tank 4310 affects how much liquid hydrogen in the liquid hydrogen tank 4310 is evaporated and affects the liquid hydrogen tank pressure.

[0397] With regard to recycling the liquid hydrogen, the process can be carried out as follows:

[0398] 1. Extracting liquid hydrogen from liquid hydrogen tank 4310;

[0399] 2. Liquid hydrogen is fed through heat exchanger 4401 with heated coolant from multiple heat loads (such as engines) as a heating fluid;

[0400] 3. Outputting gaseous hydrogen from heat exchanger 4401;

[0401] 4. Splitting the gaseous hydrogen at flow control valve 4407, wherein a portion of the gaseous hydrogen is directed for recirculation in the liquid hydrogen tank via refill line 4408, which leads to a fuel refill port of the liquid hydrogen tank 4310, and another portion of the gaseous hydrogen is transmitted to the fuel cell stack via fuel cell stack line 4415;

[0402] 5. delivering gaseous hydrogen for recycling to gaseous hydrogen (GH2) pump 4405 and gaseous hydrogen pump 4406; and

[0403] 6. The portion of gaseous hydrogen for recycling is returned to the liquid hydrogen tank 4310 and bubbles are generated through the liquid hydrogen to maintain the pressure in the liquid hydrogen tank 4310.

[0404] Alternatively, GH2 instead of liquid hydrogen may be drawn from the liquid hydrogen tank 4310 and a similar process performed on gaseous hydrogen.

[0405] In addition, pressure relief valve 4420 can be opened to release gaseous hydrogen to achieve pressure relief. When the pressure is greater than a selected threshold, the valve can be opened. The gaseous hydrogen can then flow to Fig.43 Vent 4304 in vertical tail wing 4306.

[0406] 7. Pumped two-phase cooling of aircraft electronics

[0407] Conventional single-phase cooling systems are unable to thermally manage electrified propulsion systems within an acceptable size, weight, and power (SWaP) envelope for use in aircraft, such as liquid hydrogen powered aircraft.

[0408] The current solution is to pump liquid in a cooling loop using a ram air radiator. Ram air radiators for electrified propulsion systems and high-power electronics are large in size and weight and require a large amount of cooling air flow. This situation leads to packaging challenges and potential aerodynamic drag penalties.

[0409] The solutions currently used in aircraft are single-phase liquid or gaseous cooling solutions for aircraft components such as power electronics, fuel cells, batteries, and electric motors and drives. These solutions are ineffective in handling the large amounts of heat from these types of electronic components that typically operate below 100 degrees Celsius.

[0410] In one or more illustrative examples, a series of components including a liquid pump, an evaporator, a condenser, and a reservoir may be used to provide the desired cooling using a pumped two-phase cooling loop.

[0411] In the illustrative example, a fluid is used that undergoes a phase change at a temperature and pressure suitable for thermal management of aircraft electronics and power systems.The heat source and heat sink may be designed to operate as an evaporator and condenser, respectively.

[0412] In a different illustrative example, a waste heat recovery (WHR) system may be added to the thermal management system downstream of the evaporator. In another illustrative example, a system that generates thrust from ram air heated by the condenser may also be used.

[0413] refer to Fig.45 , depicts an illustration of a block diagram of an aircraft cooling system according to an illustrative embodiment. In this illustrative example, aircraft cooling system 4500 may be Figure 4 45. Aircraft cooling system 4500 may be implemented in aircraft 400 to cool multiple heat loads 4501. Aircraft cooling system 4500 may be located in an engine compartment of an engine of the aircraft.

[0414] The heat load 4501 can take a variety of different forms. For example, the heat load 4501 can be selected from at least one of a fuel cell, a fuel cell stack, a power circuit, an electric motor, a computer system, an electronics housing, a laser, or some other component that generates heat.

[0415] Aircraft cooling system 4500 can take many different forms. In one illustrative example, aircraft cooling system 4500 includes evaporator 4511, condenser 4512, reservoir 4513, pump system 4514, and piping system 4515. Fluids (such as liquid 4516 and vapor 4519) flow between these various components through piping system 4515.

[0416] The piping system 4515 includes a pipe 4527 and may also include a valve 4517. The piping system 4515 is connected to the evaporator 4511, the condenser 4512, the reservoir 4513, and the pump system 4514.

[0417] In this example, evaporator 4511 is thermally coupled to a set of heat loads 4501 and can cool the set of heat loads 4501 in aircraft 4502 using liquid 4516. Liquid 4516 forms vapor 4519 in response to cooling the set of heat loads 4501.

[0418] Condenser 4512 is a hardware component that cools vapor 4519 to form liquid 4516. In one example, condenser 4512 can be a ram air condenser that uses air entering the inlet of the engine compartment or a condenser that does not use ram air. Condenser 4512 receives vapor 4519 and cools vapor 4519, where it is cooled to form liquid 4516. Furthermore, in this example, condenser 4512 rejects heat from vapor 4519 into the engine compartment air flow. The engine compartment air flow is the air flowing through the engine compartment, which leaves the engine compartment at the outlet of the engine compartment.

[0419] In this example, the reservoir 4513 receives the liquid 4516 from the condenser 4512 and stores the liquid 4516. The pump system is a physical system including one or more pumps. The pump system 4514 pumps the liquid 4516 stored in the reservoir 4513 to the evaporator 4511.

[0420] In addition, in this example, aircraft cooling system 4500 may also include generator 4530 and turbine 4531. In this example, turbine 4531 is connected to the generator and to piping system 4515. Turbine 4531 is physically connected to generator 4530 and can rotate generator 4530 to generate electrical power. Turbine 4531 is connected to piping system 4515 so that steam 4519 flows through turbine 4531 to rotate turbine 4531.

[0421] The turbine 4531 rotates in response to receiving the vapor 4519 from the evaporator 4511 and causes the generator 4530 to generate power, and wherein the condenser 4512 receives the vapor 4519 from the turbine 4531 .

[0422] In another illustrative example, aircraft cooling system 4500 includes condenser 4512, evaporator 4511, and pump system 4514. For this example, two liquids flow within piping system 4515, namely, first liquid 4541 and second liquid 4542. The two liquids flow separately from each other within piping system 4515. In other words, the liquids do not mix. In this example, first pump 4544 in pump system 4514 pumps first liquid 4541, and second pump 4545 in pump system 4514 pumps second liquid 4542.

[0423] In this example, a first pump 4544 pumps a first liquid 4541 in a liquid loop 4550 to a set of heat loads 4501. The set of heat loads 4501 heats the first liquid 4541, where the heating of the first liquid 4541 forms a heated liquid 4546.

[0424] The evaporator 4511 is a separate or partitioned evaporator in which both the first liquid 4541 (heated liquid 4546) and the second liquid 4542 can flow through the component without mixing with each other. In this example, the evaporator 4511 receives the heated liquid 4546 and cools the heated liquid 454. The cooling of the heated liquid 4546 causes the second liquid 4542 in the liquid-vapor loop 4551 to form vapor 4552.

[0425] Furthermore, in this example, condenser 4512 receives vapor 4552 and cools vapor 4552. Cooling vapor 4552 forms second liquid 4542. Second pump 4545 pumps second liquid 4542 from condenser 4512 to evaporator 4511.

[0426] Fig.45 The block diagram illustration of aircraft cooling system 4500 in FIG. 4 is not meant to imply physical or structural limitations on the manner in which the illustrative embodiments may be implemented. Other components may be used in addition to or in place of the components illustrated. Some components may be unnecessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the illustrative embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0427] Next reference Fig.46 , an illustration of a flowchart of a process for cooling a thermal load is depicted in accordance with an illustrative embodiment. Fig.46 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.45 The process may be implemented in an aircraft cooling system 4500. The process may be used to cool heat loads in an aircraft.

[0428] The process cools a set of heat loads in an aircraft using a liquid in an evaporator, wherein the liquid forms a vapor when cooling the set of heat loads (operation 4600). The process cools the vapor with a condenser to form a liquid (operation 4602).

[0429] The process receives liquid from the condenser (operation 4604). The process stores the liquid in a reservoir (operation 4606).

[0430] The process pumps the liquid stored in the reservoir to the evaporator (operation 4608). The process terminates thereafter.

[0431] Next in Fig.47 In the drawings, an illustration of a flowchart of a process for cooling a heat load is depicted in accordance with an illustrative embodiment. Fig.47 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.45The process may be implemented in an aircraft cooling system 4500. The process may be used for heat loads in an aircraft.

[0432] The process pumps a first liquid to a set of heat loads where heating the first liquid forms a heated liquid (operation 4700). The process cools the heated liquid in an evaporator where cooling the heated liquid forms a vapor from a second liquid in the evaporator (operation 4702).

[0433] The process transfers the vapor to a condenser (operation 4704). The process cools the vapor in the condenser to form a second liquid (operation 4706). The process pumps the second liquid from the condenser to an evaporator (operation 4708). The process terminates thereafter.

[0434] Next reference Fig.48 , depicts a schematic diagram of a pumped two-phase (P2P) cooling loop according to an illustrative embodiment. As depicted, a pumped two-phase cooling loop 4800 includes a pump 4802, an evaporator 4804, a condenser 4806, and a reservoir 4808. In this example, the reservoir 4808 is a liquid reservoir that stores a liquid. The pump 4802 can pump the liquid from the reservoir 4808 to the evaporator 4804. The evaporator 4804 cools a group of heat loads 4805 in the aircraft. The group of heat loads 4805 in the aircraft is selected from at least one of a fuel cell, a fuel cell stack, an electric motor, a computer system, an electronic device housing, or a laser. The group of heat loads may include a fuel cell, a fuel cell stack, an electric motor, an electronic device housing, a computer system, a laser, or other suitable types of components that generate heat.

[0435] When cooling these heat loads, the evaporator 4804 generates vapor from the liquid coolant, which is transmitted to the condenser 4806. The condenser 4806 operates via air flow moving through the condenser 4806 to cool the vapor from the evaporator 4804. The cooled vapor becomes a liquid stored in the reservoir 4808, which can be recirculated by the pump 4802 to perform further cooling in the pumped two-phase cooling loop 4800.

[0436] Next in Fig.49 , a diagram of a hybrid two-phase (P2P) cooling loop is depicted in accordance with an illustrative embodiment. In this example, a hybrid two-phase (P2P) cooling loop 4900 includes a pump 1 4902 , a pump 2 4904 , an evaporator 4906 , and a condenser 4908 .

[0437] In this example, pump 1 4902 pumps the first liquid condensed by evaporator 4906 to heat load 4910 in liquid loop 4901. In this example, heat load 4910 heats the first liquid. The heated liquid flows to evaporator 4906, where it is cooled for use by pump 1 4902.

[0438] This liquid flow forms the liquid loop 4901 in the hybrid two-phase (P2P) cooling loop 4900. In this case, the evaporator 4906 can be located at a location separate from the heat load 4910. For example, the evaporator 4906 can be located closer to the condenser 4908.

[0439] For this example, the second liquid in the evaporator 4906 is heated to form a vapor 4903 in a two-phase (P2P) loop 4915. The vapor is transmitted to the condenser 4908. This type of configuration may be desirable when the second liquid is more volatile or more difficult to handle. This configuration using two liquids can minimize the use of potentially volatile working fluids. Moreover, this configuration can also be used for heat loads that cannot be in direct contact with a liquid used as a coolant or refrigerant.

[0440] The vapor 4903 is transferred to a condenser 4908 which cools the vapor to form a second liquid. Pump 2 4904 pumps the second liquid back to the evaporator 4906. The heat exchange in the evaporator 4906 cools the first liquid in the liquid loop 4901.

[0441] Next turn Fig.50 , depicts a diagram of a pumped two-phase (P2P) cooling loop with waste heat recovery, according to an illustrative embodiment. As depicted, the pumped two-phase cooling loop 5000 includes a pump 5002 , an evaporator 5004 , a condenser 5006 , and a reservoir 5008 .

[0442] In this example, turbine 5010 is located between evaporator 5004 and condenser 5006. Liquid delivered to the evaporator by pump 5002 cools heat load 5011. For this example, vapor 5031 generated by evaporator 5004 cooling heat load 5011 can be used to rotate turbine 5010. Turbine 5010 is connected to generator 5012, which generates power in response to turbine 5010 using vapor 5031. Vapor 5031 then flows to condenser 5006 for condensation into liquid 5032 stored in reservoir 5008. As depicted, waste heat recovery system 5050 includes turbine 5010 and generator 5012.

[0443] Thus, one or more illustrative examples may use this type of cooling system in place of other cooling systems that use a single-phase liquid.A liquid may be selected that will evaporate when cooling a heat load.

[0444] In addition, the vapor 5031 produced by the evaporator 5004 can be a superheated gas. Similarly, the liquid 5032 produced by the condenser 5006 can be subcooled. The terms superheating and subcooling refer to increasing or decreasing the temperature of a fluid above the saturation temperature, respectively.

[0445] Some features of the illustrative examples described herein are described in the following clauses. These clauses are examples of features and are not intended to limit other illustrative examples.

[0446] Descriptions of different multiple illustrative embodiments have been presented for the purpose of illustration and description, and are not intended to be exhaustive or limited to embodiments of the disclosed form. Different illustrative examples describe components that perform actions or operations. In illustrative embodiments, components may be configured to perform the described actions or operations. For example, components may have such a structural configuration or design that provides the component with the ability to perform the actions or operations described as being performed by components in the illustrative examples. In addition, in the context of using the terms "include", "comprise", "have", "contain" and variations thereof in this article, these terms are intended to be inclusive in a manner similar to the term "comprise" as an open transition word, without excluding any additional or other elements.

[0447] Many modifications and variations will be apparent to those of ordinary skill in the art. In addition, different illustrative embodiments may provide different features than other desired embodiments. The selected one or more embodiments are selected and described in order to best explain the principles and practical applications of the embodiments and to enable those skilled in the art to understand the various other embodiments of the present disclosure and various modifications suitable for the specific use contemplated.

Claims

1. An aircraft thermal management system (3400, 3700), comprising: a high temperature circuit (3401, 3781) configured to manage the temperature (3410) of a fuel cell stack (4505, 3710) in an engine compartment (3406) using an engine compartment heat exchanger (3421); and A cryogenic circuit (3402, 3782) is configured to use the heat capacity (3407) of liquid hydrogen to cool a plurality of heat loads (3416) in the engine compartment (3406).

2. The aircraft thermal management system (3400, 3700) according to claim 1, wherein: The fuel cell stack (4505, 3710) includes a high temperature proton exchange membrane fuel cell.

3. The aircraft thermal management system (3400, 3700) according to claim 1, wherein When managing the temperature (3410) of the fuel cell stack (4505, 3710), the high temperature circuit (3401, 3781) is configured to maintain the fuel cell stack (4505, 3710) at an operating temperature (3411).

4. The aircraft thermal management system (3400, 3700) according to claim 1, further comprising: A piping system (3403), wherein the high temperature circuit (3401, 3781) and the low temperature circuit (3402, 3782) are located in the piping system (3403).

5. The aircraft thermal management system (3400, 3700) according to claim 1, wherein: The plurality of thermal loads (3416) include at least one of an electric motor, a power circuit, power electronics, and a controller.

6. The aircraft thermal management system (3400, 3700) according to claim 1, further comprising: A compressor (3411, 3705) configured to generate heated compressed air (3440); Charge air intercooler (3720), configured as: receiving the heated compressed air (3440) from the compressor (3411, 3705); and The heated compressed air (3440) is cooled to form cooled compressed air (3444), which is transmitted to the fuel cell stack (4505, 3710).

7. The aircraft thermal management system (3400, 3700) according to claim 6, wherein: The cooled compressed air (3444) reacts with gaseous hydrogen (3445) in the fuel cell stack (4505, 3710) to generate electricity.

8. An aircraft thermal management system (3400, 3700), comprising: A ram air radiator (3702) in an engine compartment (3406), the ram air radiator comprising: Engine compartment heat exchanger (3421); a set of fans configured to increase air flow through the engine compartment heat exchanger (3421); A fuel cell stack (4505, 3710) in the engine compartment (3406); A piping system (3403) configured to carry a coolant (3431), wherein the piping system (3403) comprises: A high temperature circuit (3401, 3781), wherein the high temperature circuit is configured as follows: removing heat from the fuel cell stack (4505, 3710); and delivering heat removed from the fuel cell stack (4505, 3710) to ambient air as part of exhaust gases exiting the engine compartment (3406); and A low temperature circuit (3402, 3782), wherein the low temperature circuit is configured as follows: Heat is removed from a set of components in the nacelle (3406) using the heat capacity (3407) of liquid hydrogen.

9. The aircraft thermal management system (3400, 3700) according to claim 8, wherein: The fuel cell stack (4505, 3710) includes a high temperature proton exchange membrane fuel cell.

10. The aircraft thermal management system (3400, 3700) according to claim 8, wherein: The high temperature circuit (3401, 3781) is configured to maintain the fuel cell stack (4505, 3710) at an operating temperature (3411) while removing heat from the fuel cell stack (4505, 3710).

11. The aircraft thermal management system (3400, 3700) according to claim 8, wherein: The low temperature circuit (3402, 3782) is also configured as: Heat is removed from at least one of the electric motor, the power circuit, and the controller.

12. The aircraft thermal management system (3400, 3700) according to claim 8, wherein: The ram air radiator (3702) includes a nacelle heat exchanger (3421) in a nacelle (3406), the nacelle heat exchanger positioned to receive air flowing through an inlet in the nacelle (3406).

13. An aircraft (199, 400, 3127, 3855, 4502), comprising: Body (102, 402, 2630, 3140, 3862); A first wing (403, 2632) and a second wing (405, 2634) connected to the fuselage (102, 402, 2630, 3140, 3862); A liquid hydrogen tank (108, 408, 2602, 3810, 4310) configured to store liquid hydrogen, wherein the liquid hydrogen tank (108, 408, 2602, 3810, 4310) extends along the exterior of the fuselage (102, 402, 2630, 3140, 3862); An engine (106, 406, 2601) connected to the first wing (403, 2632) and the second wing (405, 2634), wherein each of the engines (106, 406, 2601) comprises: Engine compartment (3406); an electric motor within said engine compartment (3406); a fuel cell stack (4505, 3710) within the engine compartment (3406); and a ram air radiator (3702) within the engine compartment (3406), wherein the ram air radiator (3702) is configured to receive air flowing through an inlet in the engine compartment (3406); Pipeline system (3403); A high temperature circuit (3401, 3781) in the piping system (3403), wherein the high temperature circuit (3401, 3781) is configured as follows: managing the temperature (3410) of the fuel cell stack (4505, 3710) using a nacelle heat exchanger (3421); and A low temperature circuit (3402, 3782) in the piping system (3403), wherein the low temperature circuit (3402, 3782) is configured as follows: A plurality of heat loads (3416) in the engine compartment (3406) is cooled using a fuel system heat exchanger that uses the heat capacity of liquid hydrogen (3407) to cool a coolant (3431).

14. The aircraft (199, 400, 3127, 3855, 4502) according to claim 13, wherein: The ram air radiator (3702) includes a nacelle heat exchanger (3421) in the nacelle (3406).

15. The aircraft (199, 400, 3127, 3855, 4502) of claim 14, wherein: The ram air radiator (3702) also includes a fan system (522, 910, 2702) positioned to increase air flow through the engine compartment heat exchanger (3421).

16. The aircraft (199, 400, 3127, 3855, 4502) of claim 13, wherein: The plurality of thermal loads (3416) include at least one of an electric motor, a power circuit, power electronics, and a controller.

17. A method for thermal management, the method comprising: managing (3500) the temperature (3410) of a fuel cell stack (4505, 3710) in an engine compartment (3406) with a high temperature circuit (3401, 3781) that uses an engine compartment heat exchanger (3421) to manage the temperature (3410) of the fuel cell stack (4505, 3710); and A plurality of heat loads (3416) in the engine compartment (3406) is cooled (3502) using a cryogenic circuit (3402, 3782), the cryogenic circuit using the heat capacity (3407) of liquid hydrogen to cool the plurality of heat loads (3416).

18. The method according to claim 17, wherein: The fuel cell stack (4505, 3710) includes a high temperature proton exchange membrane fuel cell.

19. The method according to claim 17, wherein: Managing the temperature (3410) of the fuel cell stack (4505, 3710) includes: The fuel cell stack (4505, 3710) is maintained (3600) at an operating temperature (3411).

20. The method according to claim 17, wherein: The high temperature circuit (3401, 3781) and the low temperature circuit (3402, 3782) are located in a piping system (3403).

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