LH2 fuel cell aircraft with distributed system

Abstract

An aircraft includes a fuselage, a wing connected to the fuselage, an engine connected to the wing, and a liquid hydrogen tank. Each of the engines includes a nacelle, an electric motor within the nacelle, a fuel cell stack within the nacelle, and a nacelle heat exchanger within the nacelle that receives air flowing through a nacelle inlet. The liquid hydrogen tank is configured to store liquid hydrogen, wherein the liquid hydrogen tank extends along an exterior of the fuselage and above the wings and below a window in the fuselage.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 519,504, filed on August 14, 2023, entitled "Configuration of an LH2 Fuel Cell Aircraft with a Distributed System," the entire contents of which are incorporated herein by reference.

[0003] This application is related to the following U.S. patent applications: U.S. Patent Application No. 18 / 610,438, filed on the same date, entitled “Pumped Two-Phase Cooling of Aircraft Electronics”; U.S. Patent Application No. 18 / 610,580, filed on the same date, entitled “Method of Nacelle Heat Exchanger Integration for a Hydrogen Fueled Fuel Cell Powered Aircraft”; U.S. Patent Application No. 18 / 610,697, filed on the same date, entitled “Liquid Hydrogen Feed System for Fuel Cell Powered Aircraft”. U.S. Patent Application No. 18 / 610,742, filed on the same date as this application, and entitled “Start-Up of High Temperature Proton Exchange Membrane (HTPEM) Fuel Cell Aircraft with Multiple Power Generating Units”; U.S. Patent Application No. 18 / 610,816, filed on the same date as this application, and entitled “Low Temperature Proton Exchange Membrane Charge Air Heat Exchanger”; and U.S. Patent Application Serial No. 18 / 610,868, filed on the same date as this application, and entitled “Fuel Cell Aircraft Thermal Management System”; the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present disclosure relates generally to aircraft, and more particularly to aircraft using a propulsion system powered by a hydrogen-fueled fuel cell. Background Art

[0005] 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.

[0006] Additionally, electric motors are generally quieter than internal combustion engines. Therefore, noise pollution can be reduced by using these types of aircraft.

[0007] 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 typically in a liquid state and is stored at very low temperatures (e.g., -253°C).

[0008] The hydrogen in these fuel tanks can be stored as liquid hydrogen, gaseous hydrogen, or other hydrogen carriers such as methane or other hydrocarbons in liquid or gaseous form. Reformers can be used in the reforming process to remove hydrogen from hydrocarbon molecules.

[0009] The hydrogen in these tanks can then be sent to fuel cells 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

[0010] An embodiment of the present disclosure provides an aircraft, including a fuselage, wings connected to the fuselage, engines connected to the wings, and liquid hydrogen tanks. Each of the engines includes a nacelle, an electric motor in the nacelle, a fuel cell stack in the nacelle, and a nacelle heat exchanger in the nacelle that receives air flowing through the nacelle inlet. The liquid hydrogen tank is configured to store liquid hydrogen, wherein the liquid hydrogen tank extends along the outside of the fuselage and above the wing and below a window in the fuselage.

[0011] An aircraft includes a fuselage, wings connected to the fuselage, and engines connected to the wings. Each of the engines includes a nacelle, an electric motor in the nacelle, a fuel cell stack in the nacelle, and a nacelle heat exchanger in the nacelle that receives air flowing through a nacelle inlet.

[0012] Another embodiment of the present disclosure provides an aircraft, comprising: a fuselage; a wing connected to the fuselage; an engine connected to the wing; and a plurality of liquid hydrogen tanks configured to store liquid hydrogen. The plurality of liquid hydrogen tanks are located outside the fuselage and above the wing. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The novel features believed characteristic of the exemplary embodiments are set forth in the appended claims. However, the exemplary embodiments together with the preferred modes of use, further objects and features thereof will be best understood by reference to the following detailed description of exemplary 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 exemplary embodiment;

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

[0016] Figure 3 is a diagram of a nacelle layout according to an exemplary embodiment;

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

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

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

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

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

[0022] Fig. 9 is a schematic diagram of an engine having a nacelle heat exchanger according to an exemplary embodiment;

[0023] Fig.10 is a schematic diagram of an engine having a nacelle heat exchanger according to an exemplary embodiment;

[0024] Fig.11 is a schematic diagram of an engine having a nacelle heat exchanger according to an exemplary embodiment;

[0025] Fig.12 is another schematic diagram of an engine having a nacelle heat exchanger according to an exemplary embodiment;

[0026] Fig.13 is a schematic diagram of a fan configuration for use with a nacelle heat exchanger within a nacelle associated with an exemplary embodiment;

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

[0028] Fig.15 is a diagram of airflow through a nacelle to provide cooling for a fuel cell stack according to an exemplary embodiment;

[0029] Fig.16 is an illustration of a front view of a nacelle having a nacelle heat exchanger according to an exemplary embodiment;

[0030] Fig.17 is a diagram of a nacelle heat exchanger according to an exemplary embodiment;

[0031] Fig.18 is a diagram of airflow through a nacelle heat exchanger according to an exemplary embodiment;

[0032] Fig.19 is a diagram showing a block diagram of a starting system for an aircraft according to an exemplary 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 according to an exemplary embodiment;

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

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

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

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

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

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

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

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

[0044] Fig.31 is an illustration of a block diagram of an aircraft management system according to an exemplary embodiment;

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

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

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

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

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

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

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

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

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

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

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

[0059] Fig.46 is an illustration of a flow chart of a process for cooling a heat load according to an exemplary embodiment;

[0060] Fig.47 is an illustration of a flow chart of a process for cooling a heat load according to an exemplary embodiment;

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

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

[0063] Fig.50 is a diagram of a pumped two-phase (P2P) cooling loop with waste heat recovery according to an exemplary 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 problems with aircraft operating using liquid hydrogen fuel. The problems recognized by the different illustrative embodiments are described herein.

[0066] The exemplary 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, there are design challenges 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 exemplary 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 the tanks in a safe manner while keeping the added weight and wetted area as small as possible. In one exemplary example, six engine 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 occur 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 exemplary embodiment can use a high temperature proton exchange membrane fuel cell instead of a low temperature proton exchange membrane. The use of a high temperature proton exchange membrane fuel cell helps to reduce the size of the heat exchanger and a heat exchanger with microchannel flow passing through it, which further reduces the size. In the exemplary embodiment, systems such as these systems are optional.

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

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

[0072] In this exemplary embodiment, aircraft 100 is an example of a liquid hydrogen fuel cell vehicle. Aircraft 100 is an aircraft that can carry various 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 exemplary embodiments, aircraft 100 may 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, and 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) may 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 may also be connected to the second component using a third component. The first component may 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 may 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 liquid hydrogen tanks 108 is located above wing 105, and liquid hydrogen tank 131 of liquid hydrogen tanks 108 is located above wing 104. The locations of liquid hydrogen tanks 108 are selected to provide desired center of gravity (CG) characteristics for aircraft 100. As depicted in this example, liquid hydrogen tanks 108 are located below windows 138 in fuselage 102. As depicted in this example, window 138 is located along window line 139 on fuselage 102.

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

[0078] Furthermore, the location of the liquid hydrogen tanks 108 protects these components from a hard landing. Furthermore, the location of the liquid hydrogen tanks protects these tanks from damage due to impact with the ground.

[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 engine 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 for higher lift at lower speeds, 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] Furthermore, by using six engines instead of two or four, there is increased redundancy. As the number of engines increases, the electric motors can have a smaller size and power requirements. In a similar manner, the size of the heat exchangers for the engines within the nacelle 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 vented from the liquid hydrogen tank 108 through a conduit to a vent system. The vent system may vent the gaseous hydrogen away from and above passengers, crew, and ground personnel, such as the vertical tail 110.

[0083] Figure 2 1 is an illustration of a front view of liquid hydrogen tank locations according to an exemplary embodiment. In this figure, a front view of aircraft 100 provides additional views of the locations of liquid hydrogen tank 130 above wing 105 and 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 one exemplary example and is not meant to limit the manner in which other exemplary examples may be implemented. For example, although liquid hydrogen tanks 108 are shown as including two liquid hydrogen tanks, other exemplary 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 a nacelle layout according to an exemplary embodiment. The engine 300 is Figure 1 and Figure 2300. In this example, engine 300 includes nacelle 302, electric motor 304, fuel cell stack 305, and heat exchanger 308. In this illustrative example, nacelle 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 nacelle 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 a block diagram of a liquid hydrogen fuel cell aircraft according to an exemplary embodiment. In this exemplary embodiment, as Figure 1 , Figure 2 and Figure 3 The aircraft 100 and the components of the aircraft 100 shown are examples of implementations of the aircraft 400. In this example, the aircraft 400 takes the form of a liquid hydrogen fuel cell aircraft 457 with 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 group of liquid hydrogen tanks 408. As used herein, when used with reference to an item, a "group" refers to one or more items. For example, a group 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. These 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, group of liquid hydrogen tanks 408 is coupled to fuselage 402 . Stabilizer 412 is coupled to tail 410 of fuselage 402 .

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

[0093] The nacelle 420 is a housing that contains the components of 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 exemplary embodiment, the nacelle heat exchanger receives air 430 flowing through an inlet 431 in the nacelle 420. The nacelle heat exchanger 423 provides cooling for the fuel cell stack 422 in the nacelle 420. This cooling may be provided in a high temperature cooling circuit (such as the following Fig.34 It is implemented in the high temperature circuit 3401).

[0095] For example, the piping system 424 is fluidly connected to the nacelle 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, conduits, tubes, or other suitable structures. The piping system 424 can also include a valve that can control the flow of coolant within the pipe. In addition, the piping system 424 can include a pump to move the fluid.

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

[0097] In this example, the nacelle heat exchanger 423 and the piping 424 form a thermal management system 425. The thermal management system 425 cools the fuel cell stack 422. HTPEM (high temperature proton exchange membrane) fuel cells require a coolant temperature that is too high to be used as a coolant for other engine components. Another low temperature coolant loop is needed to cool engine components other than the fuel cell stack 422. The low temperature coolant loop uses its own ram air radiator or cools the coolant in another heat exchanger or cooling method. The vehicle cools its low temperature coolant as part of its pressure control system for the tanks, which require heating and recirculating hydrogen.

[0098] In this illustrative example, the 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 set 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 set 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 vent system 440. Vent system 440 is connected to a set of liquid hydrogen tanks 408. Vent system 440 operates to vent gaseous hydrogen 434 from liquid hydrogen tanks 408.

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

[0102] Therefore, in these examples, as the number of engines 106 increases, different 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 the 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 exemplary embodiments. For example, distribution of the propulsion power, thermal management and fuel cell systems over 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 broken down 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 an example of an embodiment of an aircraft and is not meant to imply physical or architectural limitations to the manner in which the exemplary 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, blocks are presented to illustrate some functional components. When implemented in the exemplary embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

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

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

[0107] 2. Nacelle heat exchanger integration method for hydrogen fuel cell powered aircraft

[0108] The illustrative examples recognize and take into account that hydrogen powered aircraft may use fuel cells to drive electric motor driven propellers. 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 both generate a significant amount of heat compared to the power generated. This heat is exhausted from the engine into the ambient air. During flight phases such as taxiing, takeoff, and climb, heat removal is more difficult. During these phases, the amount of ambient air is not always available in the desired amount to provide the desired cooling. In addition, during these flight phases, the temperature difference between the ambient air and the fuel cell coolant is generally lower than the temperature difference during 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 frontal area may lead to problems related to the packaging of the heat exchanger within the nacelle.

[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. The size of the heat exchanger currently required is considered large due to the large amount of heat to be removed and the small temperature difference between the coolant and the ambient air.

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

[0114] The temperature difference between the coolant and the ambient air can be as low as 20 degrees Celsius in the case of a low temperature proton exchange membrane (PEM) fuel cell, and as low as 70 degrees Celsius in the case of a high temperature PEM fuel cell. The present disclosure addresses the problems associated with mounting a nacelle heat exchanger with minimal drag penalty, as well as the options associated with getting ambient cooling air in and out of the heat exchanger and potentially other problems.

[0115] Exemplary examples provide fuel cell-based electric aircraft using hydrogen as fuel. In these examples, the fuel cell stack is composed of fuel cells. These fuel cell stacks can be located with the aircraft's engine. In other words, the fuel cell stack is located in the same nacelle containing the engine. The fuel cell stack is cooled by various options and must be cooled using a coolant to an ambient air heat exchanger located in the nacelle to discharge heat from the fuel cell stack to the ambient air.

[0116] Additionally, a fan system may be included in each nacelle. The electric fan system may include multiple fans that may vary in speed depending on the cooling required. In this example, the fan system increases airflow through the heat exchanger. The increased airflow using the fan system may reduce the size of the heat exchanger within the nacelle.

[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 from the entire cooling system in all phases of flight.

[0118] The exemplary embodiment provides that these heat exchangers are integrated into the nacelle instead of into the fuselage.

[0119] In one illustrative example, a fuel cell-based electric aircraft using hydrogen as fuel is described. In these examples, a fuel cell stack is composed of fuel cells. The fuel cell stack can be located with the engine of the aircraft. In other words, the fuel cell stack can be located in the same nacelle containing the engine. The fuel cell stack is cooled by various options, and the heat from the fuel cell stack must be discharged to the ambient air using a coolant to ambient air heat exchanger.

[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. Furthermore, the fixed area nozzles may enable useful thrust recovery from ambient ram air. In this example, ambient air is the air surrounding or around the aircraft. Further, in the exemplary example, increasing the area of ​​the nacelle heat exchanger may reduce ram drag.

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

[0122] Thus, the exemplary examples may also provide at least one of reduced drag or thrust generation. In these examples, the phrase "at least one," when used with a list of items, indicates that different combinations of one or more of the listed items may be used, and only one of each item in the list may be required. In other words, "at least one" means that any combination of items and multiple items in the list may be used, but not all items in the list are required. An item may be a specific object, thing, or category.

[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] In addition, 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 frontal area relative to the inlet of the nacelle. The frontal area may be substantially perpendicular to the inlet. The heat exchanger may also include a fan system, such as an electrically driven shaft fan or a radial blower, to provide a desired level of airflow 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 exemplary embodiment. In this exemplary example, heat exchanger system 500 is located in nacelle 502. Nacelle 502 is a Figure 4 4 and nacelle 420 of aircraft 400. In this illustrative example, nacelle heat exchanger 520 may be oriented substantially parallel to flight direction 547 of the aircraft. For example, nacelle heat exchanger 520 may have a length greater than a width or thickness, and this 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 an inlet 504 and an 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 nacelle heat exchanger 520 . In some illustrative examples, heat exchanger system 500 may also include fan system 522 .

[0129] The nacelle heat exchanger uses air 530 in airflow 532 to transfer heat from the coolant 526 to the nacelle heat exchanger 520 .

[0130] In this illustrative example, airflow 532 to nacelle heat exchanger 520 may take one or more different forms. For example, airflow 532 may move over a surface of nacelle heat exchanger 520, move through nacelle heat exchanger 520, or some combination thereof. For example, nacelle heat exchanger 520 may have a solid surface through which air 530 flows in airflow 532. In another example, nacelle heat exchanger 520 may have ducts, channels, or openings through which air 530 in airflow 532 travels.

[0131] The nacelle heat exchanger 520 may be constructed of a variety of different types of materials. For example, the nacelle heat exchanger 520 may be constructed of 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 material.

[0132] The nacelle heat exchanger 520 may take a variety of different forms. For example, the nacelle heat exchanger 520 may include a hollow geometric duct 550 having a channel 551. In this example, the airflow 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 may be, for example, a cylinder, a rectangular prism, an ellipsoid, or some other suitable form.

[0133] In another exemplary example, the nacelle heat exchanger 520 may include concentric cylinders 552 positioned in the nacelle 502. In yet another exemplary example, the nacelle heat exchanger 520 may include a solid geometric post 553 positioned within the nacelle 502. For this example, the airflow 532 passes over the exterior of the solid geometric post 553 positioned within the nacelle, wherein the airflow passes over the exterior of the solid geometric post 553.

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

[0135] When used in the heat exchanger system 500, the fan system 522 operates to increase the airflow 532 to the nacelle heat exchanger 520. This increased airflow can reduce the size of the nacelle heat exchanger 520 while still providing the 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 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] The coolant 526 may be used within the piping system 540 to cool various components within the nacelle 502. For example, the coolant 526 may be located in the piping system 540. The piping system 540 includes pipes 541, which are conduits or pipes through which a fluid may travel. In addition, the piping system 540 may also include valves 542 to control the flow of fluid through the piping system 540. In this example, the piping system 540 may include a pump 543 for moving the fluid.

[0139] Piping system 540 is a hardware system that includes one or more pipes. These pipes may be conduits, tubes, or other structures through which coolant 526 may flow between nacelle heat exchanger 520 and other components 525 in nacelle 502. Piping system 540 is thermally connected to nacelle heat exchanger 520 and other components 525 in nacelle 502. In these illustrative examples, thermal connection means that heat transfer can occur between the 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 use coolant 526 to cool at least one of the fuel cell stack, the electric motor, or the electronic system in other components 525. Furthermore, in these illustrative examples, one or more other components 525 may be located at different locations relative to nacelle heat exchanger 520. For example, when nacelle heat exchanger 520 takes the form of a hollow geometry duct 550, a component such as a fuel cell stack may be located within a channel 551 in hollow geometry duct 550.

[0142] In one exemplary example, the inlet 504 may have a fixed area 560. For this example, a variable area nozzle 561 may be positioned between the fan system 522 and the outlet 505. Variable area means that the area of ​​the cross section of the variable area nozzle 561 may vary. The airflow 532 through the variable area nozzle 561 may result in an exhaust velocity 563 of the exhaust air 554 leaving the outlet 505 that is greater than the free stream velocity.

[0143] Figure 5 The block diagram illustration of the heat exchanger system 500 in the example is not meant to imply physical or structural limitations on the manner in which the exemplary embodiments may be implemented. Other components in addition to or in place of the 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 exemplary embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0144] For example, the nacelle heat exchanger 520 may add other shapes, such as a prism or other suitable shapes. Furthermore, one or more nacelle heat exchangers may be used in addition to or in place of the nacelle 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 exemplary example, the nacelle heat exchanger may be used in a dedicated nacelle that provides cooling. In yet another exemplary example, a tip-driven fan may be used in the fan system. In other exemplary examples, the heat exchanger with the air inlet and fan system may be located elsewhere in the aircraft, such as the fuselage, in addition to or in place of the nacelle of the engine. In addition, the heat exchanger may have flow turning features, such as guide vanes, to ensure that airflow enters and leaves the heat exchanger in a desired orientation.

[0146] See now Figures 6 to 18, depicts a diagram of a nacelle heat exchanger configuration according to an exemplary 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 a nacelle.

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

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

[0149] As depicted, the fan 604 is located aft of the nacelle heat exchanger 600. In other examples, the fan 604 may be located forward of the nacelle heat exchanger 600.

[0150] Fan 604 operates to increase airflow through nacelle heat exchanger 600. This type of airflow 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 exemplary 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 channel 705.

[0152] As depicted, the fan 704 is located aft of the nacelle heat exchanger 700. In other examples, the fan 704 may be located forward of the nacelle heat exchanger 700. In this example, the fan 704 is located aft of the nacelle heat exchanger 700. Figure 6 Other components 707 are shown as being further located within channel 705 of nacelle heat exchanger 700 compared to other components 602 in FIG.

[0153] refer to Figure 8 , depicts another illustration of a cross-sectional view of a nacelle with a nacelle heat exchanger according to an exemplary 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 aft of 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 nacelle heat exchanger 800 at a shallow angle reduces the exposed forward nacelle area and reduces the degree to which the airflow turns when passing through the nacelle heat exchanger 800 to maintain a low pressure drop across the heat exchanger.

[0156] In this example, fan 802 is shown positioned aft of heat exchanger 800. In other examples, fan 802 may be located forward of nacelle heat exchanger 800.

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

[0158] See also Fig. 9 , depicts a schematic diagram of an engine with a nacelle heat exchanger according to an exemplary 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 shown in phantom.

[0159] In this view, it can be seen that nacelle heat exchanger 904 is at a shallow angle relative to inlet 906 in nacelle 902. In this illustrative example, the shallow angle is an angle of up to 45 degrees. Also depicted is ductwork 908 connected to heat exchanger 904. Ductwork 908 may circulate a fluid such as a gas or liquid for cooling in response to air passing through inlet 906 in nacelle 902 through nacelle heat exchanger 904. Air flowing to nacelle heat exchanger 904 through inlet 906 may reduce the temperature of a coolant flowing within ductwork 908.

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

[0161] See also Fig.10 , depicts a schematic diagram of an engine with a nacelle heat exchanger according to an exemplary embodiment. In this example, Fig. 9 The 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 exemplary examples, fan system 910 may be located in front of or in front of nacelle heat exchanger 904. In other exemplary 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 schematic diagram of an engine with a nacelle heat exchanger according to an exemplary embodiment. In this exemplary example, engine 1100 is shown in a side view. Engine 1100 includes a nacelle 1102 that houses 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 to illustrate other components within engine 1100 .

[0165] As depicted, nacelle heat exchanger 1104 is located within nacelle 1102. In this illustrative example, nacelle heat exchanger 1104 is an annular cylindrical shape and has passages 1110.

[0166] The nacelle heat exchanger 1104 is positioned within the nacelle 1102 such that components may be positioned within a passage 1110 in the nacelle heat exchanger 1104. Additionally, in this view, a fan 1106 is located in front of the nacelle heat exchanger 1104. In the example depicted here, the fan 1106 is a ring fan.

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

[0168] exist Fig.12 , another schematic diagram of an engine with a nacelle heat exchanger according to an exemplary embodiment is depicted. 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. The nacelle heat exchanger 1104 is shown as two concentric cylinders 1200. In this example, cylinder 1202 is located inside another cylinder.

[0169] Next in Fig.13 , a schematic diagram of a fan configuration for use with a nacelle heat exchanger within a nacelle is depicted in accordance with an exemplary embodiment. As depicted, fans 1300 are arranged in a 360 degree ring 1302. This fan arrangement 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 with a nacelle heat exchanger according to an exemplary embodiment. In this example, a cross-sectional view of a nacelle 1400 with an inlet 1407 and an outlet 1409 is depicted. For example, nacelle 1400 is a dedicated nacelle for a nacelle heat exchanger 1402.

[0171] Nacelle heat exchanger 1402 is also shown in cross-section within nacelle 1400. In this example, nacelle heat exchanger 1402 has a tapered annular shape. In other words, nacelle heat exchanger 1402 can be a hollow geometric duct having a channel. For this example, air flow 1406 passes through at least one of the following: through a surface in the channel or a surface on the exterior of the hollow geometric duct. In an exemplary example, nacelle heat exchanger 1402 can also be a frustoconical cone shape.

[0172] Additionally, in this example, fan 1404 is shown as being located aft of nacelle heat exchanger 1402. In various examples, aft mount fan 1404 is located aft of nacelle heat exchanger 1402 relative to air flow 1406 entering inlet 1407 and air flow 1406 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. Achieving this higher exhaust velocity relative to the free stream speed of the aircraft results in 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 airflow through a nacelle to provide cooling for a fuel cell stack according to an exemplary embodiment. As depicted, arrows 1500 show airflow entering a generally rectangular inlet at the bottom of a nacelle 1502. In this example, this airflow enters the nacelle 1502 through an inlet 1551, passes through the front of a nacelle heat exchanger 1504, and exits the rear of the nacelle heat exchanger 1504. The air then passes through a fan 1506 before exiting a nozzle 1554 in an outlet 1552 of the nacelle 1502.

[0176] As depicted, fan 1506 can increase the airflow indicated by arrow 1500 during different flight phases to provide the desired airflow for cooling. For example, increased airflow can be achieved when the aircraft is stationary or taxiing before takeoff. In this example, duct system 1508 is present and connected to the front end of heat exchanger 1504 and provides cooling for fuel cell stack 1510. Duct system 1508 can provide coolant flow through nacelle heat exchanger 1504, where the coolant is cooled by the airflow 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 exemplary embodiment. As shown, the nacelle heat exchanger 1600 is visible at the inlet 1630 of the nacelle 1631. In this example, coolant enters through the coolant inlet 1612 and exits through the coolant outlet 1610. The coolant may be cooled by the heat exchanger 1600. The coolant may be cooled by airflow entering the inlet 1630 of the nacelle 1631 and passing through the nacelle heat exchanger 1600.

[0178] Next in Fig.17 , a diagram of a nacelle heat exchanger according to an exemplary embodiment is depicted. In this example, a top view of a heat exchanger 1600 is shown. Nacelle heat exchanger 1600 is a rectangular heat exchanger. As depicted, coolant enters nacelle 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 airflow through a nacelle heat exchanger is depicted according to an exemplary embodiment. In the figure, arrows 1840 show the flow of coolant in an enlarged view of a portion 1704 of a nacelle heat exchanger 1600. In the enlarged view, the coolant flows through multiple rows of tubes 1830 stacked on top of each other, forming a panel 1814 for the heat exchanger 1600. The coolant is cooled by the airflow traveling through the fins 1831 in the heat exchanger 1600.

[0180] exist Figures 6 to 18 Different views of the heat exchanger system implemented in the nacelle are presented in Figure 5 5. In other exemplary embodiments, these diagrams are not meant to limit the manner in which other heat exchanger systems may be implemented. In other exemplary embodiments, other heat exchanger shapes and locations of components may exist. In another example, two heat exchangers may be implemented in one exemplary embodiment.

[0181] In these examples, a single inlet and a single outlet for the nacelle are shown. In other examples, the nacelle may have more than one inlet and more than one outlet. For example, there may be one inlet and one outlet in the nacelle for the main airflow to the fuel cell. There is another inlet and another outlet for the cooling airflow to the heat exchanger that cools other components, such as the motor and motor controller. In these examples, a unique arrangement may be used where there are multiple inlets for, for example, Fig.14 A dedicated nacelle for the nacelle heat exchanger in FIG. 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] High temperature proton exchange membrane (HTPEM) fuel cells (having a higher operating temperature) provide a significant improvement in thermal driving potential compared to conventional low temperature proton exchange membrane (LTPEM) technology, allowing for significant miniaturization of fuel cell aircraft thermal management systems (TMS). However, with a much higher minimum operating temperature of about 120°C, when using high temperature proton exchange membrane (HTPEM) fuel cells in a fuel cell stack, the startup process can be a time and energy intensive process. In these instances, the startup process is a process in which the fuel cell stack is brought to a minimum operating temperature and then fuel and oxidant are supplied to allow the fuel cell stack to begin independently generating electricity.

[0184] The illustrative examples recognize and take into account that it is desirable to reduce the amount of time and 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 stacks are started up, since no electricity can be obtained from these fuel cell stacks before operating temperature. 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 exemplary embodiments recognize and take into account that there are no existing solutions for aerospace applications. An alternative solution may be used for ground 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 areas inside the fuel cell stack through the outside of the stack. This type of heating uses a more resistant heat flow path, resulting in a large amount of waste heat to the surrounding environment and a slower time for the fuel cell stack internal components to reach operating temperature. This situation is particularly prominent for fuel cell stack geometries with large cross-sectional areas and can produce 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 has poor effective thermal conductivity between the heating fluid (air) and the stack media compared to coolant.

[0190] Another solution may employ heating the fuel cell stack via a cooling fluid as described in the various exemplary embodiments. 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 6 engines located in 6 nacelles, there are three fuel cell power units per wing. With this configuration, the energy usage can be tripled compared to starting only one fuel cell stack size per wing before starting the other fuel cell stacks with the electricity they generate.

[0192] Therefore, an exemplary embodiment provides a method, apparatus and system to minimize the total energy and time required to complete the startup of multiple HTPEM fuel cell stacks contained in a fuel cell powered aircraft. In an exemplary embodiment, 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 the total number of fuel cell stacks on the aircraft. After these fuel cell stacks reach operating temperature and begin to generate electricity, the electricity can be used to start the remaining fuel cell stacks.

[0193] This feature involves a unique configuration of the coolant heating architecture in the exemplary embodiment. The exemplary embodiment uses an electric coolant heater. The heater can be integrated into the piping for the coolant system so that the existing cooling pump will be used to circulate the coolant through the stack and start the heater. Some bypasses will also be included in the architecture to allow the coolant to skip the heater in normal operation after startup, and the bypass allows the coolant to skip the heat exchanger during startup to avoid the need to heat the heat exchanger in addition to the stack - minimizing startup time and energy required.

[0194] Another feature in the exemplary embodiment 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 the total number of fuel cell stacks may be initially started using an onboard battery that is sized to start only the subset of fuel cell stacks.

[0195] Once a subset of the fuel cell stacks are started, the electricity generated by the now operational subset of fuel cell power units 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 a modest power draw is applied to the fuel cell stack operation, which generates enough heat to heat itself more quickly.

[0196] Thus, the exemplary embodiment 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 crossover can be used to allow an initially warmed up and operational fuel cell power unit to power the coolant heater and other air management systems (AMS) of fuel cell stacks that have not yet been started to start those fuel cell stacks. This fuel cell stack startup can be performed for any aircraft system with multiple fuel cell stacks.

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

[0199] Further, a ground power hook may be implemented in some instances. When the aircraft is on the ground approaching an available ground power hook, the ground power hook can be used 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 weight light but allowing even faster start-up when ground power hook-up is available and the operator does not need to rely on the energy contained within the batteries.

[0201] Next reference Fig.19 , depicts a diagram of a starting system for an aircraft according to an exemplary embodiment. In this exemplary embodiment, a fuel cell stack starting system 1900 may be used Figure 4 400 of the aircraft were launched Figure 4 Operation of the fuel cell stack in 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 in fuel cell stack 1920 may be located in a nacelle 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 cause the fuel cell stack 1920 to reach an operating temperature 1925. The operating temperature 1925 is one or more temperatures at which the fuel cell stack 1920 generates electricity. The power can be used to provide electricity to at least one of the motors or engines or other components 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 the fuel cell stacks 1920 of the fuel cell system 1921, bringing the subset to an operating temperature 1925, and generates power to heat the coolant 1917, thereby starting other fuel cell stacks in the fuel cell stacks 1920 of the fuel cell system 1921. In this example, the power is electricity.

[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 a heater system 1901 , a piping system 1902 , a pump system 1904 , and a 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, one heater in plurality of heaters 1915 and one fuel cell stack in fuel cell stack 1920 may be present in each nacelle.

[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 uses hydrogen gas to generate heat for the 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 assembly 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 exemplary embodiment, 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 in 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 in 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 exemplary embodiment, the hardware of the controller 1905 can take the form of at least one selected from the following: 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 an organic component integrated with an inorganic component, and can be completely composed of organic components other than humans. For example, these processes can be implemented as circuits in organic semiconductors. The controller 1905 can also be selected from at least one of the following: a single-core processor, a dual-core processor, a multi-processor core, 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 may control heater system 1901 to heat coolant 1917 to form heated coolant 1916. Controller 1905 may control pump system 1904 to circulate heated coolant 1916 through piping system 1902. In addition, controller 1905 may control piping system 1902 to circulate heated coolant 1916 to a subset of fuel cell stack 1920. In this example, heated coolant 1916 causes the subset of fuel cell stack 1920 to reach 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, controller 1905 may control piping system 1902 to circulate heated coolant 1916 to all fuel cell stacks 1920 in response to a subset of fuel cell stacks 1920 reaching operating temperature 1925. In this example, heated coolant 1916 is heated by a subset of fuel cell stacks 1920 generating electricity. The remaining fuel cell stacks reach operating temperature 1925 from heated coolant 1916 heated by a subset of fuel cell stacks 1920. In this example, heated coolant 1916 is heated by a subset of fuel cell stacks 1920. Heater system 1901 is no longer required to heat coolant 1917.

[0213] In one example, the heater system 1901 includes a heater 1915, and in this example, each of the fuel cell stacks 1920 and each of the heaters 1915 are located in a nacelle. Further, in this example, each fuel cell stack is thermally connected to one of the heaters 1915 via a piping system 1902. With 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, after the fuel cell stack 1920 is started, the controller 1905 controls the piping system 1902 to bypass the heater system 1901. 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 electricity, 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 electricity.

[0215] During this startup process, the controller 1905 controls the piping system 1902 to bypass the nacelle heat exchanger 1960 during startup of the fuel cell stack. The bypassing of the nacelle heat exchanger 1960 avoids the nacelle heat exchanger 1960 from cooling the heated coolant 1916. In this example, one of the nacelle heat exchangers 1960 and one of the fuel cell stacks 1920 are present in each nacelle.

[0216] In an exemplary example, the controller 1905 controls the piping system 1902 to circulate the heated coolant to the plurality of fuel cell stacks, wherein the plurality of fuel cell stacks to which the heated coolant causes the operating temperature 1925 are the plurality of fuel cell stacks 1925, wherein the heated coolant causes the plurality of fuel cell stacks 1920 to reach the 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 fuel cell stacks 1920. In other words, the circulation of the heated coolant may be to all or a portion of the 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 electric engine operation of the aircraft.

[0218] Fig.19 The block diagram illustration of the fuel cell stack startup system 1900 in the example is not meant to imply physical or structural limitations on the manner in which the exemplary embodiment can be implemented. Other components in addition to or in place of the 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 exemplary embodiment, 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 flow chart of a process for managing startup and operation of a fuel cell stack of an aircraft, according to 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 electricity (operation 2000 ). The process terminates thereafter.

[0222] Next reference Fig.21 , depicts a diagram of a flow chart of a process for heating a fuel cell stack according to an exemplary embodiment. The process in the flow chart is performed Fig. 20 An example of additional operations for the operations in .

[0223] The process uses heat generated from the electricity 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 flow chart of a process for managing startup and operation of a fuel cell stack of an aircraft, according to 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 or more 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 with 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 generates heat to heat the coolant using hydrogen.

[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 , a diagram showing a flow chart of an exemplary process for circulating a heated coolant. The process may be used Fig. 22 An example of additional operations performed by 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 , depicts a diagram of a flow chart of a process for delivering power to a fuel cell stack according to an exemplary embodiment. The operations in the flow chart are performed Fig.24 An example of additional operations of the operations in FIG. In this example, each of the fuel cell stacks and each of the heaters are located in a nacelle. 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 transfers the power generated by the subset of 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 a diagram of a flow chart of a process for stopping heating a coolant according to an exemplary embodiment. The process in the flow chart may be utilized Fig. 22 An example of additional operations performed by the operations in .

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

[0233] The flow chart and block diagram in the embodiment not depicted show the architecture, function and operation of some possible implementations of the device and method in the exemplary embodiment.In this respect, each square block in the flow chart or block diagram can represent at least one of a part of a module, a section, a function or an operation or a step.For example, one or more square blocks can be implemented as a combination of program instructions, hardware or program instructions and hardware.When implemented in hardware, the hardware can, for example, take the form of an integrated circuit manufactured or configured to perform one or more operations in the flow chart or block diagram.When implemented as a combination of program instructions and hardware, the implementation can take the form of firmware.Each square block in the flow chart or block diagram can be implemented using a combination of a dedicated hardware system or dedicated hardware performing different operations and a program instruction run by dedicated hardware.

[0234] In some alternative implementations of the exemplary 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 flow chart or block diagram.

[0235] refer to Fig.26 , depicts a diagram of an aircraft having a propulsion and power system 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 aircraft 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 shown in the figure, engine 2601 includes engine 2611, engine 2612, and engine 2613 connected to first wing 2632. Engine 2601 also includes engine 2614, engine 2615, and engine 2616 connected to second wing 2634. In this example, these engines are all electric engines.

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

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

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

[0242] Next in Fig. 27 , a diagram of an integrated power and propulsion unit according to an exemplary embodiment is depicted. An exposed view of engine 2700 without a nacelle is depicted. In this exemplary example, engine 2700 is an integrated power and propulsion unit (IPPU) and is Fig.26 An example of an engine without a nacelle is shown in engine 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 airflow through heat exchanger 2701. This fan system may be used when the velocity and temperature of the ambient air moving through the inlet of the nacelle is insufficient 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 in the air. Heat and water also result from the generation of electricity using the hydrogen and oxygen reactants.

[0246] The motor 2704 and the controller 2705 convert the electric power 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 the 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 the 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 into 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 and closer to the LH2 tank 2712.

[0250] Also depicted is an air management system (AMS) intake 2731. This intake receives air for the air management system used to condition 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 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 compressed air. The regulation may 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 delivers compressed air from the outlet of the compressor 2706 to the fuel cell stack cathode inlet of the fuel cell stack 2703. As part of the startup process of heating the fuel cell stack 2703 to be at an operating temperature, the heater 2709 can heat the coolant in the high temperature loop.

[0252] Fig.26 2600 aircraft and Fig. 27 The schematic diagram of engine 2700 in is provided as an illustration of an aircraft in which the engine starting system may be implemented. This illustration is not meant to limit the manner in which other illustrative examples may be implemented. For example, the aircraft may have four engines or some other number of engines in addition to the six engines described for aircraft 2600. In another illustrative example, one starter battery or three starter batteries may be used in place of the two 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 exhausted from engine 2700.

[0253] Next reference Fig.28 , depicts a schematic diagram of a fuel cell stack startup system according to an exemplary embodiment. In this exemplary embodiment, the fuel cell stack startup system 2800 is Fig.19 An example of a simplified implementation 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 the example of the fuel cell stack in the fuel cell stack 1920, the start-up heater 2802 is Fig.19 The heater system 1901 in the example of the heater 1915, and the pipe system 2803 is Fig.192803. As depicted, piping system 2803 includes pipe 2810, valve 2811, and valve 2812. In another exemplary embodiment, 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 causes 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 , a diagram showing a schematic diagram of a fuel cell stack startup system in a thermal management system according to an exemplary embodiment. The fuel cell stack startup system 2997 in the thermal management system 2996 is Fig.19 2997 depicts components that may be implemented in a single wing having three nacelles. For example, the wing may be Fig.26 2632 of first wing 2632 of aircraft 2600. In this example, components of nacelle 2950, ​​nacelle 2952, and nacelle 2954 are shown. Each nacelle may include, for example, Fig.28 Components shown in the fuel cell stack startup system 2800.

[0258] In this illustrative example, piping system 2990 is used to facilitate the flow of fluids between components in these nacelles. Piping system 2990 includes pipes, such as tubes and conduits. The flow through these pipes can be controlled by valves to produce different flows through the piping system to heat load 2933. In addition, the piping system can include pumps for moving fluids. Piping system 2990 is connected to different components. These connections can be thermal connections where the fluids are 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 a 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-LTHX) 2914, and a ram air radiator 2927. In this example, a liquid hydrogen heat exchanger (LH2 LX) 2913 is located near the LH2 tank 2971, such as in the wing. In some examples, this component may be present in each of the three nacelles or in only one nacelle. The nacelle also includes heat loads 2933. These heat loads may include controllers, tanks, motors, and other components that generate heat. A pump 2925 is used to move coolant to these heat loads.

[0260] In this depicted example, the HTPEM fuel cell stack 2921 is located in a nacelle 2952. Other components in the nacelle include a startup heater 2930, a pump 2931, a boost 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 a nacelle 2954. Other components within the nacelle include a start-up heater 2960, a pump 2961, a charge air heat exchanger (HX) 2966, and a ram air radiator 2967. The nacelle 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 nacelle 2950.

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

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

[0266] 2. Open bypass valve 2973 to allow coolant to bypass ram air radiator 2927, ensuring that ram air radiator 2927 is not heated. At this point, the coolant is heated to bring the fuel cell stack up to operating temperature. Therefore, no heat rejection is required.

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

[0268] In this example, the heated coolant flows through a subset of the fuel cell stacks, which is HTPEM FC stack 2920. Furthermore, in this example, the flow is 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. Once the HTPEM FC stack 2920 reaches the minimum operating temperature for electrochemical activity, air (by powering the air management system) and fuel can be supplied to the stack so that the HTPEM FC stack 2920 can begin to generate electricity independently. In addition, due to the low efficiency of operation at this initial operating temperature, applying electrical traction on the HTPEM FC stack 2920 at this time will help the HTPEM FC stack 2920 to heat itself.

[0270] At this point, the electricity generated by the HTPEM FC stack 2920 can be used to power the startup heaters of adjacent nacelles to begin heating those HTPEM fuel cell stacks. Once these HTPEM fuel cell stacks reach operating temperature, air (via the single startup stack that powers its air management system) and fuel can be supplied to the remaining fuel cell stacks so that they can also independently begin generating electricity.

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

[0272] Thus, the heated coolant from the HTPEM FC stack 2920 can be exchanged with coolant in other HT coolant loops for other nacelles to begin 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 begin operation of those fuel cell stacks. In addition, this type of heating can also make it possible to illuminate the start-up heaters used in other nacelles. Thus, the number of heaters can be reduced, thereby reducing the weight of the aircraft.

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

[0274] Next turn Fig.30 , a diagram depicting a schematic diagram of a fuel cell stack startup system in a thermal management system according to an exemplary embodiment. Fig.30 A configuration of a fuel cell stack startup system 2997 is depicted in which the high temperature cooling circuits are isolated from each other by a configuration of piping 2990. There are no piping that enables exchange of high temperature coolant between fuel cell stacks in different nacelles.

[0275] In this example, the startup of the HTPEM fuel cell (FC) stack 2921 and the HTPEM fuel cell (FC) stack 2922 is initiated by power sent from the HTPEM fuel cell (FC) stack 2920 to the startup heaters 2930 and 2960 in response to the startup heater 2910 generating heat so that the HTPEM fuel cell (FC) stack 2920 reaches an operating temperature. In this example, coolant is not exchanged between different nacelles 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.19 1900. 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 startup heater may be used in other fuel cell stack startup systems. In another exemplary example, the battery may be included in the nacelle.

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

[0278] Low temperature proton exchange membrane (LTPEM) fuel cells provide a zero-emission, 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 a compressor to maintain an adequate reactant supply and increase performance through 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 exemplary embodiment, cooling load and efficiency are factors in the cooling design system. It is desirable to reduce the overall cooling load of the cooling system and increase the efficiency.

[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 to the fuel cell stack, usually oxygen from the air. In the compressed air, heat is also added. Depending on the degree of compression, the air is cooled before entering the fuel cell stack to avoid overheating and drying out the fuel cell stack membrane.

[0282] This cooling can be done using an air-to-liquid intercooler. However, this type of cooling places a burden on the stack cooling system to cool the air. In addition, current systems cannot take advantage of energy recovery opportunities.

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

[0284] In one exemplary embodiment, a charge air heat exchanger is used. This component utilizes the cooled output stack air 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 air 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 injected into 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 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 exemplary 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 is increased. The exemplary examples use a heat exchanger in addition to the intercooler to reduce the cooling load and increase energy recovery of the expander. In some exemplary examples, a charge air heat exchanger can replace the charge air intercooler, rather than simply reducing the size of the charge air intercooler.

[0289] Next reference Fig.31 , depicts a diagram of a block diagram of an aircraft management system according to an exemplary embodiment. In this exemplary 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 sent to the fuel cell stack 3105 for use with the 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 , ducting 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 also includes a compressor 3107 . The compressor 3107 is connected to the duct system 3104 and produces heated air 3120 that flows through the air heat exchanger 3102 .

[0294] In this example, heated air 3120 , cooled 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 uses the oxygen in the cooled air 3124 and the gaseous hydrogen 3140 to generate electricity. In this example, the air is cooled to an operating temperature 3125.

[0297] Fig.31 The block diagram of aircraft air management system 3100 in the figure is not meant to imply physical or architectural limitations to the manner in which the exemplary embodiments may be implemented. Other components in addition to or in place of the components illustrated may be used. Some components may not be necessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the exemplary 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, a 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, depending on 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 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 power generation level to be generated. This type of management is performed on the compressed air 3126 reaching the fuel cell stack 3105 to avoid increasing the temperature gradient that reduces the power generation efficiency. Therefore, the compressed air 3126 can be heated or cooled to have a temperature relative to the operating temperature of the fuel cell stack 3105, which provides the desired power generation level.

[0300] Next go to Fig.32 , an illustration of a flow diagram of a process for air management, according to 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.

[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 sends the cooled air to the fuel cell stack (operation 3206). The process terminates thereafter.

[0303] exist Fig.32 In the invention, the air heat exchanger, intercooler and fuel cell stack are located in a nacelle of an engine for an aircraft. Ambient air is led via the nacelle inlet to the 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 the fuel cell stack temperature by heat exchange with the fuel cell stack cathode outlet.

[0304] The air is then further conditioned to the fuel cell stack temperature by 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 and air react with hydrogen as the oxygen moves through the individual fuel cells. When leaving the stack, the destroyed air also removes some amount of water products to prevent flooding of the fuel cell stack.

[0305] Once exhausted from the stack, the air passes through a charge air heat exchanger, then passes through a turbine where it expands to recover energy utilized towards the compression process, and finally, leaves the nacelle as exhaust gas.

[0306] See now Fig.33 , depicts a diagram of a schematic diagram of an aircraft air management system according to an exemplary embodiment. Air management system 3301 operates to cool fuel cell stack 3304. In this example, air management system 3301 includes a charge heat exchanger (HX) 3300 and a charge intercooler 3302 and ductwork 3303. Air management system 3301 also includes a compressor (C) 3305, a turbine (T) 3311, an electric motor 3341, and a controller 3342.

[0307] In this example, compressor (C) 3305 receives inlet air 3317 entering the nacelle and produces compressed air 3318 having a higher pressure than inlet air 3317. In this example, compressor 3305 is operated by engine 3341 under the control of controller 3342. In addition, compressed air 3318 has a temperature that may be higher than the desired temperature in fuel cell stack 3304. The compressed air can be cooled using charge air heat exchanger (HX) 3300 and charge air intercooler 3302 to form cooled compressed air 3319. Charge air heat exchanger (HX) 3300 initially cools compressed air 3318 to form cooled air 3321. The cooled compressed air can be further cooled by charge air intercooler 3302 providing further cooling to form cooled compressed air 3319. Therefore, cooled compressed air 3319 is compressed air that can have a desired temperature for use with 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 for powering components such as the motor 3341 and the controller 3331. The motor 3341 in turn provides mechanical energy for rotating the propeller 3362. The hydrogen fuel system 3320 may 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. This 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 air 3313.

[0310] The thermal management system operates to remove heat from the fuel cell stack 3304, the motor 3341, and the controller 3331, while the ram air radiator 3350 rejects this heat to the ambient air. The thermal management system uses a liquid hydrogen heat exchanger (LH2 HX) 3335 for 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 may also provide a highly efficient way to generate at least one of propulsion or electricity for aircraft systems.

[0313] The lower operating temperatures compared to conventional turbomachinery result in large and heavy thermal management system (TMS) designs.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 driving potential, which enables significant miniaturization of the thermal management system. In this example, the thermal driving potential is the temperature difference between the ambient air and the coolant leaving the fuel cell. However, other electric propulsion components such as electric motors, their controllers and other power electronics typically operate at temperatures closer to that of the LTPEM fuel cell. Therefore, HTPEM fuel cell powered aircraft can use a different approach to thermal management other than having a single shared system for all electric propulsion components.

[0315] In this exemplary embodiment, 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 nacelle for the fuel cell air management system, cooling fans, and propulsion. In other words, one circuit can be used for the HTPEM fuel cell stack and the other circuit can be used for the generator components other than the fuel cell stack. These heat generating components can be the motors, controllers, and power electronics in the nacelle.

[0316] In one example, a low temperature (LT) cooling loop includes coolant that cools 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 nacelle heat exchanger for the lower temperature, liquid cooled components within the nacelle.

[0317] The high temperature (HT) loop includes a coolant for managing the temperature of the fuel cell stack. This managing temperature may include at least one of heating or 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 a nacelle heat exchanger. This heat exchanger is a different heat exchanger used in the low temperature loop in the nacelle of the engine. Separate low temperature (LT) and high temperature (HT) cooling loops are used to cool the fuel cell stack and lower temperature heat loads. A low temperature heat load is a heat load that has a lower temperature than the fuel cell stack. These separate cooling loops remove 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 a block diagram of an aircraft thermal management system according to an exemplary embodiment. In this exemplary embodiment, aircraft thermal management system 3400 may be Figure 4 In the aircraft 400, the Figure 4 406. The aircraft thermal management system 3400 provides thermal management during operation of a fuel cell stack and other components that generate heat in an engine 406. In this example, the aircraft thermal management system 3400 provides cooling for a 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 electronics device, or some other component that generates heat.

[0320] In this illustrative example, aircraft thermal management system 3400 includes high temperature loop 3401 and low temperature loop 3402. High temperature loop 3401 and low temperature loop 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 nacelle 3406 using the nacelle heat exchanger 3421. In 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 may use a coolant 3430 to remove heat from the fuel cell stack 3405 in the high temperature loop 3401. The coolant 3430 may be cooled using a nacelle heat exchanger 3421 to a temperature sufficient to cool or heat the fuel cell stack 3405 such that a temperature 3410 of the fuel cell stack 3405 has an operating temperature 3411 within an 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 sent into the ambient air as part of the exhaust gas exiting the nacelle 3406. In response to the operating temperature 3411 being lower than the operating temperature limit 3419, heat may be added to the fuel cell stack 3405. In other words, the coolant 3430 may be hotter than the operating temperature limit 3419. For example, during startup of the fuel cell stack, the coolant 3430 may be hotter than the operating temperature limit 3419.

[0324] Cryogenic circuit 3402 is configured to use thermal capacity 3407 of liquid hydrogen 3408 to cool multiple heat loads 3416 in nacelle 3406. In this example, thermal capacity 3407 of liquid hydrogen 3408 may be used to cool coolant 3430 in cryogenic circuit 3402 for cooling multiple heat loads 3416.

[0325] The heat capacity of liquid hydrogen 3408 is the energy required to convert liquid hydrogen 3408 to gaseous hydrogen 3445. Liquid hydrogen 3408 is converted to gaseous hydrogen 3445 and cooled. Therefore, this cooled coolant can be used to cool the heat load 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 while using charge air heat exchanger 3420 to add or remove heat from exhaust air to fuel cell stack 3405. This compressed air is fed into 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 send 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 produce 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 far above operating temperature 3411 of fuel cell stack 3405, heated compressed air 3440 is cooled. If heated compressed air 3440 is too far below operating temperature 3411 of fuel cell stack 3405, heated 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 air flow through the nacelle 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 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 exemplary embodiment enables conditioning of air for use by 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 of aircraft thermal management system 3400 in the figure is not meant to imply physical or architectural limitations to the manner in which the exemplary embodiments may be implemented. Other components in addition to or in place of the components illustrated may be used. Some components may not be necessary. In addition, the blocks are presented to illustrate some functional components. When implemented in the exemplary 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, the nacelle 3406 may include one or more fuel cell stacks in addition to the fuel cell stack 3405. In another example, another heat exchanger (eg, an intercooler) may be used with the boost heat exchanger 3422 to further cool the heated compressed air 3440.

[0334] Next go to Fig.35 , depicts an illustration of a flow diagram of a process for thermal management according to an example implementation. Fig.35The 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 a nacelle using a nacelle heat exchanger in a high temperature loop (operation 3500 ).

[0336] The process cools a plurality of heat loads in a nacelle using a cryogenic loop to cool the plurality of heat loads using the heat capacity of liquid hydrogen (operation 3502 ). The process terminates thereafter.

[0337] See now Fig.36 , depicts a diagram of a flow chart of a process for managing the temperature of a fuel cell stack according to an exemplary 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 power 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.

[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 exemplary embodiment. The figure shows the layout of the hardware housed within a single nacelle 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 electricity. This electricity is used to power an electric motor via a controller for the electric motor, which in turn rotates a propeller.

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

[0341] Low temperature loop 3782 uses the heat capacity of liquid hydrogen in hydrogen fuel system 3711 to cool heat loads that have 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 produce 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 loop. In this example, the coolant is used to cool the fuel cell stack 3710. The result of this cooling is exhaust air 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 may be used to produce compressed air for fuel cell stack 3710. The air may be used with gaseous hydrogen from hydrogen (H2) fuel system 3711 to produce 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 at the nacelle inlet as ambient air and is directed to the compressor 3705 and the 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 sent to the charge air intercooler 3720, where the compressed air is conditioned to 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 can 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 sent to the fuel cell stack 3710. Within the fuel cell stack 3710, as the oxygen in the conditioned air moves through the various fuel cells in the fuel cell stack 3710, the oxygen reacts with the gaseous hydrogen.

[0347] The air exits the fuel cell stack 3710. The air is corroded and may include an amount of water product to prevent flooding of the fuel cell stack 3710. Once exhausted from the fuel cell stack 3710, the air passes through a turbine 3706. The air expands to recover the energy used in the compression process and is exhausted as exhaust air 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 exhausted in exhaust air 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 through the fuel line. 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 sent 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 sent 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 low temperature loop 3782 uses a liquid coolant to remove heat from low temperature heat loads. For example, these heat loads can be motors 3750, controllers 3751, and other power electronics such as DC to DC (DC / DC) converters 3752. The heat in the coolant can be transferred to the liquid hydrogen at the LH2 HX 3712 to vaporize the liquid hydrogen.

[0352] In this example, electric 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-LT HX 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 provide 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 feeding system for fuel cell powered aircraft

[0357] In this illustrative example, hydrogen for a fuel cell powered aircraft is stored as a liquid. Hydrogen may be stored as a liquid at about -218°C, i.e., about -424°F. The storage tank is a liquid hydrogen tank, such as a cryogenic tank that stores hydrogen under pressure. Different techniques may 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 venting gas away from the aircraft. This gas venting avoids undesirable tank over-pressurization.

[0358] Maintaining pressure in the fuel tanks is accomplished by venting liquid hydrogen from a common feed line, running it through a heat exchanger, then compressing it to 0.34 bar, or about 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 ambient heat leaks. Due to the highly flammable nature of hydrogen, the vent system may include a flame arrester at the end to prevent back flash of the vent line in the event of ignition of the vented hydrogen. The design of the flame arrester acts to trap water in the narrow passage. If a pulse of hot hydrogen is vented before the safety valve is opened, this action will push any water out of the flame arrester. This process is performed to avoid freezing of water in the flame arrester due to low temperatures, which would vent the hydrogen and block flow through the flame arrester.

[0360] In addition to the push of water, heaters can be added to the flame arrestor to prevent ice accumulation when ambient temperatures may result in freezing.

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

[0362] In the illustrative example, by exhausting the hydrogen out the top of the vertical stabilizer, the exhaust gas will not impact any aircraft surfaces and will warm to a point where it is less dense than air and will therefore rise when on the ground.

[0363] Due to the temperature of liquid hydrogen, there are only two substances known 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 purify the vented hydrogen, the first step involves performing a pressure cycle of warm hydrogen to bring the system to approximately -160°C, or 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 recirculation system according to an exemplary embodiment. In this exemplary embodiment, the hydrogen recirculation system 3800 may be Figure 4 implemented in the aircraft 400 so that Figure 4 Hydrogen gas is recycled from 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 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 exemplary embodiment, controller 3802 may control piping system 3801 to remove gaseous hydrogen 3811 from the set of liquid hydrogen tanks 3810. In one exemplary embodiment, controller 3802 controls piping system 3801 to perform a number of different operations. For example, controller 3802 sends 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 may be, for example, Fig.37 The controller 3802 sends 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 heated gaseous hydrogen 3823 is an amount of heated gaseous hydrogen 3823 that maintains a pressure level in a set of liquid hydrogen tanks 3810 that enables liquid hydrogen 3807 to flow to the fuel cell stack 3822. The liquid hydrogen stream 3807 includes liquid hydrogen 3807 that flows from the set of liquid hydrogen tanks 3810 and is 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 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, if greater than a specified tolerance, the controller 3802 can send 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. In this example, the vent 3860 is considered to be part of the hydrogen recirculation 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 sent from the group of liquid hydrogen tanks 3810 to the vent 3860 in the aircraft 3855.

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

[0372] In another illustrative example, controller 3802 may perform similar operations with liquid hydrogen 3807 stored in a 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 operate in place of or in conjunction 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 group of liquid hydrogen tanks 3810 and sends the liquid hydrogen 3807 to the tank heat exchanger 3820 to form heated gaseous hydrogen 3823. The controller 3802 can send 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 group of liquid hydrogen tanks 3810.

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

[0375] Fig.38The block diagram illustration of the hydrogen recirculation system 3800 in the example is not meant to imply physical or structural limitations on the manner in which the exemplary 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 exemplary embodiments, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0376] refer to Fig.39 , an illustration of a flow diagram of a process for recycling hydrogen gas, according to an exemplary embodiment, is depicted. Fig.39 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.38 The process is implemented in the hydrogen recirculation system 3800. 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 sends the gaseous hydrogen extracted from the bank of liquid hydrogen tanks through a tank heat exchanger in a nacelle of an engine for the aircraft to form heated gaseous hydrogen (operation 3902).

[0378] The process sends a first portion of the heated gaseous hydrogen to a fuel cell stack in an engine for 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 , an illustration of a flow diagram of a process for recycling hydrogen gas, according to an exemplary embodiment, is depicted. Fig.40 The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.38 The process is implemented in the hydrogen recirculation system 3800. 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 routes the liquid hydrogen to a tank heat exchanger to form heated gaseous hydrogen (operation 4002).

[0381] The process sends 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 , an illustration of a flow diagram of a process for recycling hydrogen gas, according to an exemplary embodiment, is depicted. Fig.41The process in can be implemented in hardware, software, or both. For example, the process can be implemented in Fig.38 The process is implemented in the hydrogen recirculation system 3800. 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 the 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 liquid hydrogen recirculation system for tank pressure control according to an exemplary embodiment. As shown in this example, a recirculation system 4200 for recirculating gaseous hydrogen (GH2) can 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 sending 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 through 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) is boiled off in the liquid hydrogen tank and affects the tank pressure. In this example, more boil-off leads to a greater pressure increase.

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

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

[0389] 2. Gaseous hydrogen is sent through heat exchanger 4205 along with hot coolant from the fuel cell stack as a heating fluid. The hot coolant is heated by the heat load in the low temperature loop.

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

[0391] 4. The gaseous hydrogen is separated 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 sent to the fuel cell stack.

[0392] 5. This portion of gaseous hydrogen is directed 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 pressure in the cryogenic tank;

[0394] exist Fig.43 , a diagram of an exhaust system for gaseous hydrogen according to an exemplary embodiment is depicted. Exhaust system 4300 provides the ability to exhaust 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, this exhaust can occur through exhaust port 4304 in vertical tail 4306. In this example, exhaust port 4304 is connected to liquid hydrogen tank 4310 through piping system 4312.

[0395] Next reference Fig.44 , depicts a diagram of a system for recycling gaseous hydrogen for tank pressure control according to an exemplary embodiment. In the exemplary examples, the same reference numeral may be used in more than one drawing. Such reuse of reference numerals in different drawings represents the same element in the different drawings. This figure is Fig.43 A more detailed view of these 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 sent to the engine and some of the liquid hydrogen passes through the heat exchanger 4401 to warm and phase change 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 boiled off and affects the liquid hydrogen tank pressure.

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

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

[0399] 2. Hot coolant from a heat load such as an engine is fed as a heating fluid into liquid hydrogen through heat exchanger 4401;

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

[0401] 4. separating 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 refueling port for liquid hydrogen tank 4310, and another portion of the gaseous hydrogen is sent to the fuel cell stack via fuel cell stack line 4415;

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

[0403] 6. Return the portion of gaseous hydrogen for recycling to the liquid hydrogen tank 4310 and bubble through the liquid hydrogen to maintain the pressure in the liquid hydrogen tank 4310.

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

[0405] Additionally, pressure relief valve 4420 may provide pressure relief by opening to vent gaseous hydrogen. The valve may open when the pressure is greater than a selected threshold. The gaseous hydrogen may then flow to Fig.43 Exhaust port 4304 in vertical tail 4306.

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

[0407] Conventional single-phase cooling systems are not capable of thermally managing an electrified propulsion system within an acceptable size, weight, and power (SWaP) envelope for an aircraft, such as a liquid hydrogen powered aircraft.

[0408] The current solution is to pump liquid in the cooling circuit using ram air radiators. Ram air radiators for electric 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] These solutions currently used in aircraft are single phase liquid or gas 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 which typically operate at below 100 degrees Celsius.

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

[0411] In an 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 function as an evaporator and condenser, respectively.

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

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

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

[0415] Aircraft cooling system 4500 can take a variety of different forms. In one illustrative example, aircraft cooling system 4500 includes evaporator 4511, condenser 4512, accumulator 4513, pump system 4514, and piping system 4515. The flow of fluids such as liquid 4516 and steam 4519 between these various components is facilitated by 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 accumulator 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 steam 4519 to form liquid 4516. In one example, condenser 4512 can be a ram air condenser that uses air entering the inlet of the nacelle or a condenser that does not use ram air. Condenser 4512 receives steam 4519 and cools steam 4519, wherein cooling steam 4519 forms liquid 4516. Furthermore, in this example, condenser 4512 rejects heat from steam 4519 into the nacelle airflow. The nacelle airflow is the air flowing through the nacelle, which leaves the nacelle at the outlet of the nacelle.

[0419] In this example, the accumulator 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 accumulator 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 electricity. 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 steam 4519 from the evaporator 4511 and causes the generator 4530 to generate electricity, and wherein the condenser 4512 receives the steam 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, wherein the heated 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 exemplary 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 exemplary 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 flow chart depicting a process for cooling a thermal load 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 is implemented in an aircraft cooling system 4500. The process can 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 vapor in 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 an accumulator (operation 4606).

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

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

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

[0433] The process sends 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 diagram of a pumped two-phase (P2P) cooling loop according to an exemplary embodiment. As shown, the pumped two-phase cooling loop 4800 includes a pump 4802, an evaporator 4804, a condenser 4806, and an accumulator 4808. In this example, the accumulator 4808 is a reservoir for storing liquid. The pump 4802 can pump the liquid from the accumulator 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 the following: a fuel cell, a fuel cell stack, a motor, a computer system, an electronic housing, or a laser. The group of heat loads may include a fuel cell, a fuel cell stack, a motor, an electronic housing, a computer system, a laser, or other suitable types of components that generate heat.

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

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

[0437] In this example, pump 14902 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, which is cooled for use by pump 14902.

[0438] The flow of this liquid forms a liquid loop 4901 in a mixed two-phase (P2P) cooling loop 4900. In this case, the evaporator 4906 may be located separately from the heat load 4910. For example, the evaporator 4906 may be located closer to the condenser 4908.

[0439] For this example, the second liquid in the evaporator 4906 is heated to form vapor 4903 in a two-phase (P2P) loop 4915. The vapor is sent 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 the liquid used as a coolant or refrigerant.

[0440] The vapor 4903 is sent to the 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 , shows a diagram of a pumped two-phase (P2P) cooling loop with waste heat recovery according to an exemplary embodiment. As depicted, the pumped two-phase cooling loop 5000 includes a pump 5002 , an evaporator 5004 , a condenser 5006 , and an accumulator 5008 .

[0442] In this example, turbine 5010 is located between evaporator 5004 and condenser 5006. Liquid sent to the evaporator by pump 5002 cools heat load 5011. For this example, steam 5031 generated by evaporator 5004 that cools heat load 5011 can be used to turn turbine 5010. Turbine 5010 is connected to generator 5012, which uses steam 5031 to generate electricity in response to turbine 5010. Steam 5031 then flows to condenser 5006 to condense into liquid 5032 stored in accumulator 5008. As depicted, waste heat recovery system 5050 includes turbine 5010 and generator 5012.

[0443] Thus, one or more exemplary embodiments 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 steam 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 exemplary embodiments described herein are described in the appended clauses. These clauses are examples of features and are not intended to limit other exemplary embodiments.

[0446] Descriptions of different exemplary embodiments have been presented for purposes of illustration and description and are not intended to be exhaustive or limited to embodiments in the disclosed form. Different exemplary examples describe components that perform actions or operations. In exemplary embodiments, the components may be configured to perform the described actions or operations. For example, the components may have a configuration or design of a structure that provides the components with the ability to perform the actions or operations described as being performed by the components in the exemplary examples. In addition, to the extent the terms "includes," "comprising," "having," "containing," and variations thereof are used herein, 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 exemplary embodiments may provide different features than other desired embodiments. The selected one or more embodiments are selected and described to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure of various embodiments with various modifications suitable for the particular use contemplated.

Claims

1. An aircraft (199, 400, 3127, 3855, 4502), including: Body (102, 402, 2630, 3140, 3862); a wing (404) connected to the fuselage (102, 402, 2630, 3140, 3862); An engine (106, 406, 2601) connected to the wing (404), wherein each engine comprises: Nacelle (420); an electric motor (421) within the nacelle (420); a fuel cell stack (422) within the nacelle (420); and a nacelle heat exchanger (423) within the nacelle (420), the nacelle heat exchanger receiving air (430) flowing through an inlet (431) in the nacelle (420); and A liquid hydrogen tank (108, 408, 2602, 3810, 4310) configured to store liquid hydrogen (433), wherein the liquid hydrogen tank (108, 408, 2602, 3810, 4310) extends along the exterior of the fuselage (102, 402, 2630, 3140, 3862) and above the wing (404) and below a window (138, 427) in the fuselage (102, 402, 2630, 3140, 3862).

2. The aircraft (199, 400, 3127, 3855, 4502) according to claim 1, wherein: The liquid hydrogen tank (108, 408, 2602, 3810, 4310) is a cryogenic tank.

3. The aircraft (199, 400, 3127, 3855, 4502) according to claim 1, further comprising: A vent system (440) connected to the liquid hydrogen tank (108, 408, 2602, 3810, 4310), wherein the vent system (440) exhausts gaseous hydrogen (434) from the liquid hydrogen tank (108, 408, 2602, 3810, 4310).

4. The aircraft (199, 400, 3127, 3855, 4502) according to claim 3, further comprising: A vertical tail (110, 441, 3865, 4306) is connected to the fuselage (102, 402, 2630, 3140, 3862), wherein the ventilation system (440) exhausts the gaseous hydrogen (434) through the vertical tail (110, 441, 3865, 4306).

5. The aircraft (199, 400, 3127, 3855, 4502) of claim 1, wherein: The aircraft (199, 400, 3127, 3855, 4502) is selected from the group consisting of an unmanned aircraft, a manned aircraft, a remotely piloted aircraft, a passenger aircraft, a cargo aircraft, a commercial aircraft, and an autonomous aircraft.

6. The aircraft (199, 400, 3127, 3855, 4502) of claim 1, wherein: The engine (106, 406, 2601) includes 6 engines (106, 406, 2601).

7. The aircraft (199, 400, 3127, 3855, 4502) of claim 1, wherein: The aircraft (199, 400, 3127, 3855, 4502) are 50 passenger aircraft.

8. An aircraft (199, 400, 3127, 3855, 4502), including: Body (102, 402, 2630, 3140, 3862); a wing (404) connected to the fuselage (102, 402, 2630, 3140, 3862); as well as An engine (106, 406, 2601) connected to the wing (404), wherein each of the engines comprises: Nacelle (420); an electric motor (421) within the nacelle (420); a fuel cell stack (422) within the nacelle (420); and A nacelle heat exchanger (423) within the nacelle (420) receives air (430) flowing through an inlet (431) in the nacelle (420).

9. The aircraft (199, 400, 3127, 3855, 4502) according to claim 8, wherein: Each engine also includes: A piping system (424) is thermally connected to the nacelle heat exchanger (423), wherein the piping system (424) and the nacelle heat exchanger (423) form a thermal management system for cooling the fuel cell stack (422) in each engine.

10. The aircraft (199, 400, 3127, 3855, 4502) according to claim 8, further comprising: A plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310) are configured to store liquid hydrogen (433), wherein the plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310) are located outside the fuselage (102, 402, 2630, 3140, 3862).

11. The aircraft (199, 400, 3127, 3855, 4502) according to claim 10, wherein: The plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310) are located above the wing (404) along a plurality of sides of the fuselage (102, 402, 2630, 3140, 3862).

12. The aircraft (199, 400, 3127, 3855, 4502) of claim 10, wherein: The plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310) are below a window (138, 427) in the fuselage (102, 402, 2630, 3140, 3862).

13. The aircraft (199, 400, 3127, 3855, 4502) of claim 10, wherein: The plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310) are cryogenic tanks.

14. The aircraft (199, 400, 3127, 3855, 4502) of claim 10, further comprising: A vent system (440) connected to the plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310), wherein the vent system (440) exhausts gaseous hydrogen (434) from the liquid hydrogen tanks (108, 408, 2602, 3810, 4310).

15. The aircraft (199, 400, 3127, 3855, 4502) of claim 14, further comprising: A vertical tail (110, 441, 3865, 4306) is connected to the fuselage (102, 402, 2630, 3140, 3862), wherein the ventilation system (440) exhausts the gaseous hydrogen (434) through the vertical tail (110, 441, 3865, 4306).

16. An aircraft (199, 400, 3127, 3855, 4502), comprising: Body (102, 402, 2630, 3140, 3862); a wing (404) connected to the fuselage (102, 402, 2630, 3140, 3862); an engine (106, 406, 2601) connected to the wing (404); and A plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310) are configured to store liquid hydrogen (433), wherein the plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310) are located outside the fuselage (102, 402, 2630, 3140, 3862) and above the wing (404).

17. The aircraft (199, 400, 3127, 3855, 4502) according to claim 16, wherein: Each engine includes: Nacelle (420); an electric motor (421) within the nacelle (420); a fuel cell stack (422) within the nacelle (420); and A nacelle heat exchanger (423) within the nacelle (420) receives air (430) flowing through an inlet (431) in the nacelle (420).

18. The aircraft (199, 400, 3127, 3855, 4502) of claim 16, wherein: The plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310) are cryogenic tanks.

19. The aircraft (199, 400, 3127, 3855, 4502) of claim 16, further comprising: A vent system (440) connected to the plurality of liquid hydrogen tanks (108, 408, 2602, 3810, 4310), wherein the vent system (440) exhausts gaseous hydrogen (434) from the liquid hydrogen tanks (108, 408, 2602, 3810, 4310).

20. The aircraft (199, 400, 3127, 3855, 4502) of claim 19, further comprising: A vertical tail (110, 441, 3865, 4306) is connected to the fuselage (102, 402, 2630, 3140, 3862), wherein the ventilation system (440) exhausts the gaseous hydrogen (434) through the vertical tail (110, 441, 3865, 4306).

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