High efficiency hydrogen fueled high altitude thermal fuel cell system and vehicle using same

Abstract

An efficient hydrogen fuel system for high altitude aircraft utilizes a compressor to compress air to a high enough pressure for a fuel cell. Liquid hydrogen is compressed and then used in a heat exchanger to cool the compressed air, keeping the air at a low enough temperature for the fuel cell. The hydrogen is also used to cool the fuel cell as it is also depressurized before entering the fuel cell cycle. A water condensation system allows water to be removed from the air stream to reduce the impact on the atmosphere. The hydrogen fuel system can be used with VTOL aircraft, which can enable them to fly at higher altitudes. The hydrogen fuel system can be used with other subsonic and supersonic aircraft, such as asymmetric wing aircraft.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 039,407, filed June 15, 2020, the entire contents of which are incorporated herein by reference. This application also claims priority to U.S. Provisional Patent Application No. 63 / 187,915, filed May 12, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to aircraft, specifically aircraft that use hydrogen fuel at high altitudes. Background Technology

[0004] The world is moving away from fossil fuels and needs high-energy-density energy storage to support the transition of long-range aviation to renewable energy. High-altitude air travel allows for higher speeds and shorter flight times compared to the lower atmosphere, while keeping landing and takeoff speeds at moderate levels to allow for operations at a wider range of airports.

[0005] Liquid hydrogen could provide a suitable way to store and transport energy for aviation. It can be efficiently produced from decentralized renewable energy sources and has the highest energy density of all potential aviation fuels, making it potentially the best solution for long-range flights. Attached Figure Description

[0006] Figure 1 The illustration shows a high-efficiency hydrogen fuel cell system according to some embodiments of the present invention.

[0007] Figure 2 The illustration shows the airflow of a high-efficiency hydrogen fuel cell system according to some embodiments of the present invention.

[0008] Figure 3 The illustration shows the hydrogen flow through a high-efficiency hydrogen fuel cell system according to some embodiments of the present invention.

[0009] Figure 4A The illustration shows the exhaust gas flow of a high-efficiency hydrogen fuel cell system according to some embodiments of the present invention.

[0010] Figure 4B The illustration shows water flow in a high-efficiency hydrogen fuel cell system according to some embodiments of the present invention.

[0011] Figure 5 This is a forward-angled view of a vertical take-off and landing aircraft in a forward-flying configuration according to some embodiments of the present invention.

[0012] Figure 6is a rear perspective view of a vertical take-off and landing aircraft in a forward flight configuration according to some embodiments of the invention.

[0013] Figure 7 is a front perspective view of a vertical take-off and landing aircraft in a vertical flight configuration according to some embodiments of the invention.

[0014] Figure 8 is a rear perspective view of a vertical take-off and landing aircraft in a vertical flight configuration according to some embodiments of the invention.

[0015] Figure 9 is a front perspective view of a vertical take-off and landing aircraft according to some embodiments of the invention.

[0016] Figure 10 is a front perspective view of an asymmetric wing aircraft according to some embodiments of the invention.

[0017] Figure 11 is a view of an asymmetric wing aircraft according to some embodiments of the invention.

[0018] Figure 12 illustrates a cabin with a high efficiency hydrogen fuel cell system with a front fan according to some embodiments of the invention.

[0019] Figure 13 illustrates a cabin with a high efficiency hydrogen fuel cell system with a front fan according to some embodiments of the invention.

[0020] Figure 14 illustrates a cabin with a high efficiency hydrogen fuel cell system with a rear fan according to some embodiments of the invention.

[0021] Figure 15 illustrates a method of using a high efficiency hydrogen fuel cell system according to some embodiments of the invention. SUMMARY

[0022] A high efficiency hydrogen fuel system for high altitude aircraft utilizes a compressor to compress air to a high enough pressure for a fuel cell. Liquid hydrogen is pumped to a higher pressure and then used in a heat exchanger to cool the air during the compression process, keeping the air at a low enough temperature for the fuel cell. The hydrogen is also used to cool the fuel cell as it is also expanded and cooled before entering the fuel cell cycle. A water condensation system allows water to be removed from the air stream to reduce the impact of water vapor on the atmosphere. The hydrogen fuel system can be used with VTOL aircraft, which can enable them to fly at higher altitudes. The hydrogen fuel system can be used for other subsonic and supersonic aircraft, such as asymmetric wing aircraft. DETAILED DESCRIPTION

[0023] It is an object of the present invention to provide a hydrogen fuel high energy and power density propulsion system suitable for long range, high altitude aircraft propulsion. Without a particular improvement in battery performance, high altitude aviation will require the use of high density hydrogen or hydrogen containing fuels that react with atmospheric oxygen to produce water vapor, which if this water is emitted into the upper atmosphere, can have an extended average residence time of years depending on altitude, meaning that extensive operation of aviation in the upper atmosphere can result in unacceptable accumulation of water vapor in the upper atmosphere. Water vapor is a potent greenhouse gas and can have an impact both as a gas and as ice crystals in the upper atmosphere, so if there are large numbers of flights operating in the upper atmosphere, there can be a significant impact on the climate.

[0024] The condensation of water vapor into liquid water and ice releases energy that can be used to heat the air, which can be used effectively to increase overall propulsion thrust through the Meridith effect or ram-jet effect, where inlet air in a fast moving aircraft experiences compression in the inlet, then is heated and experiences greater expansion at the exit to produce an exit velocity higher than the aircraft flight velocity, resulting in a net propulsion effect. The condensed water and ice formation can thus produce useful secondary propulsion boost and higher overall propulsion efficiency.

[0025] It is therefore another object of the present invention to provide a method of reducing the amount of water vapor released into the upper atmosphere by long range, high altitude aviation. Large aircraft are currently the standard solution for long distance passenger flights due to the advantages of gas turbine propulsion systems, with increasing size comes increasing efficiency, durability and power to weight ratio of the gas turbine propulsion system. Aerodynamic efficiency also improves with size as the useful volume within the airframe increases with size compared to the surface area of the aircraft.

[0026] Hydrogen is very low in density, and storing enough hydrogen for long range flight requires storing large amounts of fuel, with corresponding large heavy cryogenic storage tanks with significant insulation requirements. These tanks take up a large portion of the overall vehicle volume, with increasing vehicle volume to accommodate passengers and payload, tanks and other systems resulting in increased vehicle drag. This is especially true in small vehicles, where the increase in internal volume comes at a greater drag penalty compared to large aircraft. To minimize the volume and mass of hydrogen required and to reduce fuel costs, it is desirable to have a high efficiency conversion scheme for converting the hydrogen to propulsion power. The system also needs to operate adequately over a wide range of atmospheric pressures and temperatures encountered from the ground to high altitude.

[0027] It is therefore an object of the present invention to create a liquid hydrogen gas powered propulsion system suitable for small high speed aircraft operating at high altitudes at high power levels with high efficiency and reliability. The liquefaction of hydrogen gas requires a large amount of energy, but this energy can be partially recovered by using an appropriate thermodynamic process which can further increase the energy density of the hydrogen fuel and effectively reduce the necessary tank volume and mass. The process can have the secondary useful effect of providing additional cooling as the energy extracted from the hydrogen gas expanding in a turbine or similar device is used to further cool it and means that it can provide additional heat dissipation for other components of the propulsion system.

[0028] It is a further object of the present invention to optionally integrate a device for producing propulsion power from pressurisation of liquid hydrogen gas fuel followed by heating of the liquid to convert it to a hot gas so that it can be expanded through one or more stages of a turbine, being one or more of the list comprising a rotary screw expander, a rotary scroll expander, a reciprocating piston expander or a turbomachinery turbine, optionally reheated after each expansion stage to further heat the gas, thereby providing additional mechanical work to the propulsion system before the hydrogen gas is used as fuel and oxidised to release energy in the propulsion system. The heating of the hydrogen gas can preferably provide useful cooling for elements of the propulsion system or other elements of the aircraft.

[0029] Proton exchange membrane fuel cells (PEMFC) have many advantages for aerospace applications. They have high efficiency and high power to weight ratio but the disadvantage is that they need to be kept cool, typically in the range 70-80°C, and require a large amount of cooling to dissipate the heat typically from 40-60% of the hydrogen oxidation energy that is not converted to electricity. Furthermore, they require reactants to be supplied at high pressure. There are many challenges in achieving this in a way that maintains the high power to weight ratio and high efficiency advantages even when operating at high altitude and in particular low ambient pressure for small size. It is a further object of the present invention to provide a fuel cell system that can keep the fuel cells in their optimum operating temperature range and perform near optimum pressurisation of the air and hydrogen supplied to the fuel cells throughout the range of operating altitude, ambient air pressure and temperature while minimising the drag produced by the fuel cell propulsion system.

[0030] Preferably, the air taken in for running and cooling the fuel cell is expelled from the aircraft at approximately the same rearward velocity as other propulsion actuators, such as propeller fans and the like, so as to make the best contribution to the overall driving thrust of the aircraft without wasting energy. Preferably, the air provided to the fuel cell for cooling and to provide oxygen to react in the fuel cell will be accelerated by the action of a mechanically driven fan or the like, so that it will exit the vehicle at a similar velocity to the air exiting other propulsion elements of the aircraft. In some aspects, the taken in air can be driven with a propeller or fan in order to accelerate / increase the pressure of the air introduced into the system. In some aspects, the taken in air can be driven at such a high velocity (or high pressure) that the exiting air from the air passage system is used as a source of propulsion for the aircraft.

[0031] Figure 1 A high efficiency hydrogen fuel high altitude thermal fuel cell system 300 is illustrated in accordance with some embodiments of the present application. In some aspects, the system 300 is adapted to deliver electrical power to power an electrically powered aircraft, which can then use the electrical power to power electric motors. In some aspects, the electrically powered aircraft can be a vertical takeoff and landing aircraft. In some aspects, the aircraft can be an asymmetric wing aircraft. In other aspects, other aircraft configurations can utilize the high efficiency hydrogen fuel thermal fuel cell system 300. In some aspects, the system 300 also provides thrust as part of the air expelled from the system.

[0032] The hydrogen fuel thermal fuel cell system can include a series of interwoven passages, such as one or more passages for intake air, passages for hydrogen gas, passages for byproducts from the fuel cell, and passages for water condensed from the byproducts from the fuel cell.

[0033] An air inlet 301 allows air to enter the hydrogen fuel thermal fuel cell system. In some aspects, the fuel cell system provides power for electrically powered propeller fans, which can be part of a VTOL aircraft. In some such systems, the intake air can be delivered through intake passages at different locations on the aircraft. For example, in the case of a VTOL aircraft, the intake passages can deliver intake air through an intake fan 302 as part of the intake air route. In some aspects, such as with a fan duct as described below, the intake air can be the air entering the fan duct, and the intake fan 302 can also be a thrust fan. In some aspects, the fuel cell system provides power for an electrically powered fan system, and in some such systems, the intake air can be input from within the fan duct. In some aspects, the intake fan 302 is used to accelerate the air into the air inlet 301. The air passages are described in more detail below. Figure 2The air passing through the system can be compressed by a series of compressors 303, 304, 305, for example, which can compress the air 30 times higher than the inlet pressure, since the system can be used at very high altitudes where the pressure is low. After compression in the first compressor 303, the compressed air can first be cooled in an air-to-air first intercooler 323, where it is cooled by incoming air that is not fed to the first compressor 303. The compressed air is then further cooled at the second intercooler 308 by a stream of liquid hydrogen. The cooled air is then fed to the second compressor 304 and thereafter again passed through a third intercooler 324 and a fourth hydrogen intercooler 309, which is again cooled by incoming air in the third intercooler 324 and further cooled by a stream of hydrogen in the fourth hydrogen intercooler 309. The cooled air is then fed to the third compressor 305, after which it is fed to the fuel cell section 322. A portion of this compressed inlet air can be fed to the combustor 315. Using the above cooling methods, the air stream can be compressed to a sufficiently high pressure required by the fuel cell, while also being able to be delivered at a sufficiently low temperature required by the fuel cell. In some aspects, there can be a bypass system that allows one or more of the compressors 303, 304, 305 to be bypassed, for example, when the ambient pressure is higher at lower altitudes, to enable efficient operation over a range of flight altitudes.

[0034] In addition to the separate line to the above compressors, the very cold incoming air is also delivered to intercoolers. The inlet air can be delivered to a heat exchanger 347 in an ice maker 345 to help freeze water condensed from the fuel cell exhaust. This air path can then continue to a seventh intercooler 317, where it cools the fuel cell exhaust, after which it can lead to the system air outlet stream 370. The incoming air can also lead to the third intercooler 324 to cool the compressed air from the second compressor 304.

[0035] Liquid hydrogen can be stored in a liquid hydrogen tank 306 and delivered to a liquid hydrogen pump 307, where it is raised in pressure. The hydrogen path continues to the second intercooler 308, where it cools the compressed air from the first compressor 303. The hydrogen path then continues to the fourth intercooler 309, where it cools the compressed air from the second compressor 304. The hydrogen path then continues to the sixth intercooler 313, where it cools the compressed air from the third compressor 305. The hydrogen path then continues to the combustor 315, where it is used to cool the combustor. Figure 3Liquid hydrogen can be delivered through a second intercooler 308 where it helps cool the compressed air as it evaporates. The hydrogen is then delivered through a fourth intercooler 309 where it again helps cool the compressed air downstream of the air passage. The hydrogen can then be expanded at a first expander to extract useful mechanical power and effectively cool the hydrogen before being delivered to the fuel cell. In some aspects, the hydrogen can be expanded at a first expander 313 before being delivered to the fuel cell 314. In some aspects, the hydrogen can be expanded at a first expander, re-delivered through the fuel cell as a cooling stream, further expanded at a second expander, and then delivered to the fuel cell.

[0036] A portion of the hydrogen stream can be delivered to a combustor 315, which can provide heat in an exchanger that can flow to a series of turbochargers 318, 319, 320, which can be used to help power the compressors 303, 304, 305, which can be powered primarily by electric motors 330, 331, 332.

[0037] Exhaust gas 340 from the fuel cell 314 follows Figure 4A The exhaust gas flow path is highlighted more clearly in the middle. In some aspects, the exhaust gas from the fuel cell is primarily composed of partially oxygen-depleted air and water vapor. The exhaust gas 340 passes to a sixth intercooler 316 and then to a seventh intercooler 317. Water in the exhaust gas condenses out during this cooling process and is separated out in a trap 341. Some of the water stream 342 can be delivered to a water reservoir 343, while some water can be alternatively sent to an ice-making unit 345. The water stream as Figure 4BThe ice making unit 345 can be cooled by very cold air introduced at high altitude, and the ice produced is then expelled from the aircraft. After exiting the trap 341, the air stream can enter an eighth intercooler 334 where it is heated by exhaust air from the combustor 315. As mentioned above, expelling water in the form of ice allows the ice to descend to lower altitudes before it melts and adds water vapor to the atmosphere. In some aspects, water in the water reservoir 343 can also be delivered to a water pump 344, which then feeds a water spray unit 350 that expels water 351 into the air flow path prior to an eighth intercooler 360 suitable for cooling the fuel cell. The water spray 351 enhances the cooling rate of the eighth intercooler 360, which can be thermally coupled to a closed loop cooling system 361 suitable for cooling the fuel cell by heat exchange section 363. The closed loop cooling system 361 can include a pump 362 and suitable coolant. As mentioned above, water can be condensed from the stream from the fuel cell system at the exhaust water condenser 341, which can then allow the condensed water to be frozen and expelled from the aircraft as solid ice. This can allow the ice to descend to lower altitudes before it melts, so as not to add water vapor to the uppermost flight regions of the aircraft. If liquid water were expelled into the upper atmosphere, the average residence time of the liquid water can extend to years depending on the altitude, meaning that a significant number of flights operating at high altitudes can result in unacceptable build-up of water vapor in the upper atmosphere. Water vapor is a potent greenhouse gas and can have an impact both as a gas and as ice crystals in the upper atmosphere, so if there are a significant number of flights operating at high altitudes, there can be a significant impact on the climate. Implementation of such an ice ejection system can significantly reduce or eliminate this impact.

[0038] The use of a Rankine cycle, pumping liquid hydrogen to high pressure before heating, and using available heat sources and expanding through a mechanical turbine to recover additional energy from the liquid hydrogen before it is consumed by the fuel cell, provides an improvement over any previous system. The condensation of water from the exhaust of the propulsion system provides another advantage, as the heat transferred to the cooling air can produce useful propulsion thrust benefits through the Meredi th effect or ram-jet effect, thereby converting a large amount of wasted heat energy into useful thrust. Furthermore, the fuel cell operates at elevated pressure, preferably above 2 bar absolute, and at the operating temperature of the fuel cell, most of the output water will be present as water. Another improvement is to utilize a recuperated counterflow heat exchange system, where most of the heat dissipation required to cool the fuel cell exhaust and condense water vapor is provided by the exhaust, where the water is removed, heated back to near the fuel cell operating temperature, and condenses water vapor from some combination of additional incoming cooling air that is not used for hydrogen reactions in the fuel cell or subsequently used to power the propulsion system through supplemental cooling.

[0039] In an exemplary embodiment, the aircraft is flying at 75 m / s at an altitude of 15 km, with air temperature of 217 K and pressure of 7.6 kPa. The inlet air is passed through the inlet fan and is at a pressure of 9.2 kPa and temperature of 232 K. In this case, some of these air can be bypassed to the first and third intercoolers, but the inlet air continues into the first compressor, where it exits at a pressure of 32.3 kPa and temperature of 354 K. That air then enters the first intercooler, where it is cooled by the inlet air that was bypassed to the first intercooler. That inlet air exits the first intercooler at a pressure of 32.3 kPa and temperature of 252 K. These air then enters the second intercooler, where it heats liquid hydrogen, and these air exit the second intercooler at a temperature of 231 K and pressure of 32.3 kPa, where it enters the second compressor. The air exits the second compressor at a temperature of 352 K and pressure of 107 kPa, where it enters the third intercooler, where it exchanges heat with the original inlet air. It exits the third intercooler at a temperature of 252 K and pressure of 107 kPa and continues into the fourth intercooler, where it exchanges heat with hydrogen. The air exits the fourth intercooler at a temperature of 231 K and pressure of 107 kPa, then enters the third compressor. It exits the third compressor at a temperature of 290 K and pressure of 0.2 MPa, now in condition to enter the fuel cell, where a portion can be delivered to the combustor. On the way to the fuel cell, it heats hydrogen twice, and is cooled twice by the bypassed original cold inlet air.

[0040] In this same exemplary embodiment, the hydrogen is stored in liquid form in the fuel tank at a temperature of 20 K and pressure of 0.1 Mpa. The liquid hydrogen is first delivered to the compressor at a rate of 5 g / s, where it exits at a temperature of 21 K and pressure of 2 MPa. The hydrogen then enters the second intercooler, where it exits at a temperature of 125 K and pressure of 2 Mpa. The hydrogen then enters the fourth intercooler, where it exits at a temperature of 230 K and pressure of 2 Mpa. The hydrogen then enters one or more expanders to achieve a temperature of 142 K and pressure of 0.2 MPa. The fuel cell is a PEMFC with an efficiency of 54% and produces 300 kW of power.

[0041] In this exemplary embodiment, the exhaust from the fuel cell is delivered to the fifth, sixth, and seventh intercoolers. The fuel cell exhaust can exit the fuel cell at a temperature of 353 K, then pass through the sixth and seventh intercoolers, where it exits at a temperature of 274 K and a pressure of 0.2 Mpa. It then enters a water separator, where the water can then be delivered to an ice maker that is coupled to the inlet air stream at a temperature of 232 K. The dried exhaust then enters the sixth intercooler (recuperated condenser), then is heated in the fifth intercooler with heat from the combustor, where it exits at a temperature of 553 K and a pressure of 0.2 Mpa. These heated air can then be used to help power the air compressor, reaching a temperature of 487 K and a pressure of 118.2 kPa after passing through the first sequential turbine, a temperature of 350 K and a pressure of 35.1 kPa after passing through the second turbine, and a temperature of 211 K and a pressure of 10.4 kPa after passing through the last turbine, where it is then delivered to the exhaust.

[0042] A vertical takeoff and landing (VTOL) aircraft presents an unusual case when powered by a liquid hydrogen high-efficiency thermodynamic fuel system according to embodiments of the present application. VTOL aircraft can have the highest power load during hover, takeoff, and landing. The higher thrust required during these operations can place constraints on the design of the power system, including the thermal management system. While these operations typically occur at lower altitudes where the air is denser (e.g., thus not requiring as much inlet air compression), they do occur where the air temperature can be much higher than seen during high-altitude operations. To avoid designing and sizing the cooling system around the typically less than a minute operation mode, a water-assisted cooling mode can be added for use during hover, takeoff, and landing, and other times as needed.

[0043] By using the water reservoir 343, water 351 can be sprayed from the water spray unit 350 into the air stream upstream of the intercoolers suitable for cooling the fuel cell. The water spray unit can also be downstream of the air stream that leads from the intake air to the input of the fuel cell on its way to the compression system. In this way, the VTOL aircraft can provide this additional, assisted cooling for VTOL operations and avoid the need for an oversized thermal system for ordinary flight modes. While water can be condensed from the exhaust stream from the fuel cell as described herein, a water tank can be used to allow for the use of water cooling during initial flight operations such as takeoff before water is collected from the fuel cell exhaust during flight. An example of such a VTOL aircraft is discussed below.

[0044] As Figures 5-8As shown, the tiltrotor aircraft 100 includes a fuselage and a plurality of propulsion assemblies coupled to the fuselage. The aircraft 100 is operable between a hover mode, in which the plurality of propulsion assemblies 120 are arranged in a hover arrangement, and a forward mode, in which the plurality of propulsion assemblies are arranged in a forward arrangement. The hover arrangement defines the position of each propeller 122 in the plurality of propulsion assemblies relative to each other propeller in the plurality of propulsion assemblies and the fuselage during operation of the aircraft in the hover mode, and the forward arrangement likewise defines the relative position of each propeller relative to each other propeller and the fuselage during operation in the forward mode. The fuselage can include a left wing, a right wing, a body, and a tail, with the left and right wings coupled to the body 116 and positioned between the front of the tail 118. Each propulsion assembly includes a propeller, a tilt mechanism, and an electric motor. Each propulsion assembly is operable between a hover configuration and a forward configuration, preferably through the tilt mechanism 124 associated therewith, but can alternatively employ any other suitable manner, as described in further detail below. The tiltrotor aircraft can also include a power source, flight control surfaces and actuators, and any other suitable components.

[0045] The tiltrotor aircraft 100 is used to provide an aerial vehicle that can be operated between a hover mode (e.g., a rotary wing mode) and a forward mode (e.g., a fixed wing mode). The hover mode can include vertical takeoff, vertical landing, and / or substantially stationary hovering of the aircraft 100; however, the hover mode can additionally or alternatively include any suitable mode of operation in which vertical thrust is generated by one or more of the plurality of propulsion assemblies. The forward mode can include forward flight, horizontal takeoff, and / or horizontal landing (e.g., conventional takeoff and landing / CTOL) of the aircraft 100; however, the forward mode can additionally or alternatively include any suitable mode of operation in which horizontal thrust is generated by one or more of the plurality of propulsion assemblies. Thus, the hover mode and the forward mode are not mutually exclusive, and the tiltrotor aircraft 100 can be operated in a superposition of the hover mode and the forward mode (e.g., in which the plurality of propulsion assemblies 120 are arranged in a superposition of the hover arrangement and the forward arrangement, the superposition defined by a threshold configuration of each of the plurality of propulsion assemblies between the hover configuration and the forward configuration). The tiltrotor aircraft 100 can also be used to provide an aerial vehicle that is stable (e.g., maximally stable, stable within a defined stability window or envelope of flight conditions, stable to a stability threshold magnitude of various control inputs of the aircraft, etc.) in the hover mode and efficient (e.g., aerodynamically efficient, power efficient, thermally efficient, etc.) in the forward mode. The tiltrotor aircraft 100 can also be used to provide air transportation for passengers and / or cargo. However, the tiltrotor aircraft 100 can additionally or alternatively have any other suitable functionality.

[0046] The tiltrotor aircraft 100 can operate between multiple modes, including a hover mode and a forward mode. In the hover mode, the plurality of propulsion assemblies can be arranged in a hover arrangement. In the hover arrangement, each of the plurality of propellers is preferably arranged in a hover configuration. In the forward mode, the plurality of propulsion assemblies can be arranged in a forward arrangement. In the forward arrangement, each of the plurality of propellers is preferably arranged in a forward configuration. However, each of the plurality of propellers can be independently arranged between any suitable state between the forward configuration and the hover configuration, and / or arranged in any suitable direction in the hover mode of operation of the aircraft 100; further, each of the plurality of propellers can be independently arranged between any suitable state between the forward configuration and the hover configuration, and / or in any other suitable direction in the forward mode of operation of the aircraft 100. Further, the tiltrotor aircraft 100 can operate in any suitable threshold mode between the hover mode and the forward mode, where a component of the thrust generated by one or more propulsion assemblies 120 is oriented along the vertical axis and the longitudinal axis (e.g., and / or the lateral axis).

[0047] Although the aircraft 100 is referred to herein as a tiltrotor aircraft 100, the terms "propeller" and "rotor" used herein can refer to any suitable rotary aerodynamic actuator, commonly referred to as a rotor, propeller, rotary airfoil, rotary wing, etc. While a rotor can refer to a rotary aerodynamic actuator using a hinged or semi-rigid hub (e.g., where the connection of the blades to the hub can be hinged, flexible, rigid, and / or otherwise connected), and a propeller 122 can refer to a rotary aerodynamic actuator using a rigid hub (e.g., where the connection of the blades to the hub can be hinged, flexible, rigid, and / or otherwise connected), when used herein there is no such distinction explicit or implicit, and the use of propeller can refer to either configuration of hinged or rigid blades and any other possible configuration, and / or any other possible configuration of the blade connection to the central member or hub. Thus, the tiltrotor aircraft 100 can be referred to as a tilt-propeller aircraft 100, a tilt-prop aircraft 100, and / or otherwise appropriately referred to or described. In the context of an electric motor, an electric motor can include a stator and a rotor in some variations, the rotor of the electric motor 126 can refer to the portion of the motor that rotates when electrical potential energy is converted to rotational kinetic energy in the operation of the electric motor.

[0048] The tiltrotor aircraft 100 includes a plurality of propulsion assemblies coupled to the airframe at a corresponding plurality of propulsion assembly attachment points. Each propulsion assembly preferably includes a propeller, a tilt mechanism, and an electric motor. The function of the propulsion assembly is to house and configure the propeller, the tilt mechanism, the electric motor, and any other suitable components related to the propeller and its electromechanical drive. The tiltrotor aircraft 100 preferably includes an even number of propulsion assemblies, and more preferably includes six propeller assemblies; however, the tiltrotor aircraft 100 can additionally or alternatively include an odd number of propulsion assemblies, eight propulsion assemblies, and any other suitable number of propulsion assemblies 120.

[0049] The function of the propeller 122 of the propulsion assembly 120 is to convert the rotational kinetic energy provided by the electric motor 126 into aerodynamic forces (e.g., for propelling the aircraft 100 in hover mode, forward mode, etc.). The propeller 122 can include a plurality of propeller 122 blades (e.g., blades, airfoils, etc.), a head (e.g., a hub and associated linkages), and any other suitable components. The propeller 122 is preferably a variable-pitch propeller 122 (e.g., where the pitch of each propeller 122 blade is coordinately variable, such as by collective control, where the pitch of each propeller 122 blade is independently variable, such as by cyclic control, etc.), but can additionally or alternatively be a fixed-pitch propeller. In some variations, the aircraft 100 can include variable-pitch and fixed-pitch propellers 122 associated with different propulsion assemblies 120 of the plurality of propulsion assemblies 120. In additional or alternative variations, the propeller 122 can be articulated into a negative angle of attack state, which can produce reverse thrust without changing the direction of rotation of the propeller. The propeller 122 preferably includes five blades per propeller, but can additionally or alternatively include any suitable number of blades per propeller 122 (e.g., two, three, four, six, etc.). The propeller 122 can define any suitable disc area (e.g., propeller disc, disc, etc.), and each blade can define any suitable cross-section and / or twist angle as a function of blade span.

[0050] In one specific example, each propeller of the plurality of propulsion assemblies 120 includes a set of propeller blades attached to a hub by a variable-pitch linkage that rotates each propeller blade about a long axis of the propeller blade and restricts motion of the propeller blade normal to the disc plane (e.g., the propeller blade does not substantially articulate forward or rearward from the disc plane).

[0051] The power source 130 is used to provide power to the propulsion assemblies and any other electrically powered components of the aircraft coupled thereto (e.g., motorized linkages, flight control surface actuators and any other electric actuators, sensors, transducers, displays, etc.). The power source can include one or more batteries, but can additionally or alternatively include a generator (e.g., a combustion driven generator, a fuel cell, a photovoltaic generator, etc.). In variations including a fuel cell, the air inlet 140 can be located at different locations around the aircraft, such as on the leading edge of a wing. The air inlet 140 provides inlet air for the thermodynamic fuel system described above. As shown in Figure 1 downstream of the inlet can be a fan 102 that increases the pressure of the air stream. As described above, a portion of these introduced air enters a multi-stage compressor system and is delivered to the fuel cell. Also as described above, a portion of these introduced air provides fuel cell cooling at the eighth intercooler 360. In the case of a VTOL aircraft, additional cooling can be required during VTOL operation. A water spray unit 350 can provide water 351 into the air stream upstream of the eighth intercooler 360. An exhaust outlet 141 for the fuel cell system and for the introduced cooling air can be located at an appropriate location along the wing or aircraft body. The tiltrotor aircraft 100 can include a power distribution system that couples the power source 130 to each electrically powered component (e.g., including each electric motor). The power distribution system can include a power transmission bus that distributes power from multiple power sources to the components of the aircraft 100 that require power. Each propulsion assembly 120 is preferably connected to at least one associated power source 130 that provides power to the electric motor assembly of the propulsion assembly. However, the power sources can additionally or alternatively be connected to each other and / or to one or more propulsion assemblies 120, such that any propulsion assembly 120 (or other powered component) can draw power from any suitable subset of power sources of the aircraft 100, and have any suitable relative power draw between the power sources.

[0052] In some embodiments of the invention, as shown in Figure 9 for example, another VTOL aircraft 160 is adapted for flight with a pilot and six passengers. The VTOL aircraft 160 is adapted for flight at a cruise speed of 340 knots at an altitude above 40,000 feet. The VTOL aircraft 160 uses a high efficiency hydrogen powered fuel cell system as described above.

[0053] In other embodiments of the invention, a high efficiency hydrogen fuel thermodynamic fuel cell system can be used with a fan duct propulsion system. A cross-sectional view of such a fan duct propulsion system is shown in Figures 12-14 and is discussed further below. In Figure 10An exemplary embodiment of the thrust units 114, 116, 118 in the fan tube propulsion system can be seen in the asymmetric winged aircraft 110, which is suitable for high speed and high altitude.

[0054] In some embodiments of the present application, as shown in FIG. 1, Figure 10 and 11 The multi-section canted wing aircraft 110 includes a center section 210, a left wing section 211, and a right wing section 212. The center section 110 is substantially thicker in the Zb direction (as defined below) and thick enough to allow passengers in the passenger area 119. The plurality of thrust units 114, 116, 118 can use pivoting pylons 113, 115, 117, which allow propulsion in different forward flight configurations. Rotation of the propeller units will change the sweep of the canted wing aircraft, both due to the change in thrust direction and due to the rudder effect of the pylons. There can be further trim and control surfaces and devices that assist in sweep change.

[0055] In some embodiments of the present application, as shown in FIG. 2, Figure 11 The multi-section canted wing aircraft 200 includes a center section 210, a left wing section 212, and a right wing section 211. The center section 210 has a leading edge 210a and a trailing edge 210b. The leading edge 210a and the trailing edge 210b of the center section 210 are substantially parallel, although there can be variations along their lengths. The center section 210 can be substantially thicker than the other sections and can be adapted to accommodate the pilot and passengers of the aircraft. Although the propulsion units are not shown, it should be understood that the multi-section canted wing aircraft 200 can be powered similarly to the aircraft 100 described above.

[0056] The left wing section 212 has a leading edge 212a and a trailing edge 212b. The left wing section 212 tapers as it extends outward from the center section 210, as the chord length decreases along the span of the wing section. The left wing section 212 can be substantially thinner than the center section 210 in the vertical direction Zb. The right wing section 211 has a leading edge 211a and a trailing edge 211b. The right wing section 211 tapers as it extends outward from the center section 210, as the chord length decreases along the span of the wing section. The right wing section 211 can be substantially thinner than the center section 210 in the vertical direction Zb.

[0057] Figure 11The coordinate systems for various aspects of the system are introduced. The wind coordinate system 230 includes the prevailing air flow over the wing as a composite of Xw and Yw, where Xw is the direction of air flow as seen in forward flight directly into the wind. The body coordinate system 231 is set to remain constant with the body of the wing, with the Yb axis set to be approximately parallel to the composite average direction of the leading edges 212a, 21 la of the wing. The Zb axis of the body coordinate system comes out of the view, toward the viewer. The quarter chord coordinate system 232 sets Yl to be parallel to the quarter chord tangent at that point, and sets Xl to be perpendicular to the quarter chord at that point. The body coordinate system 231 remains fixed relative to the aircraft. The wind coordinate system 230 is a product of the environment and is independent of the wing, and the quarter chord coordinate system 232 is a function of the wing design but changes relative to the point on the wing being referenced.

[0058] The multi-section wing can be considered to have a transition from the left wing section 212 to the center section 210 at reference line 220, and to have a transition from the right wing section 211 to the center section 210 at reference line 221. Within the reference lines 220, 221, the leading edge 210a and the trailing edge 210b of the center section 210 are substantially parallel.

[0059] The thrust units 116, 114, 118 can be electric fan units with internal fans. In some aspects, each electric fan unit can be powered by a plurality of fuel cells. As Figure 12 As shown in cross-section in FIG. 4, the exemplary fan duct 400 has an inlet 405 that allows for inlet air flow 406. Within the fan duct 400 is a fan 402. The fan 402 can have an electric motor and be electrically coupled to the aircraft electrical power system, which in turn is coupled to one or more fuel cells. Downstream of the fan 402 can be one or more air system inlets 407 that are adapted to deliver air to a series of compressors for compressing the air before delivery to the fuel cells, and that are also adapted to deliver air to the various cooling passages as described above. There can also be an exhaust duct 404 in the fan duct 400 that delivers fuel cell exhaust and incoming air that has passed through the cooling passages back into the air duct 400 before the nozzle area 410, which then merges with other pushed air from the fan 402 into the outlet flow 370.

[0060] In certain aspects, as shown in FIG. 5, a more complex air duct configuration can also include a heat exchanger 360 downstream of the fan 402. A water spray unit 350 can be provided upstream of the heat exchanger 360 to introduce water from a water reservoir into the air flow to enhance cooling. Although in Figure 13 Figure 13 ​The fan duct is described, but it is understood that in a thermal system of a VTOL aircraft, a similar configuration of inlet fan, water spray unit, and downstream heat exchanger will be used as described above, even when this portion of the system is not the primary thrust producing aspect of the aircraft, as discussed above. Figure 14 An embodiment is illustrated in which the heat exchanger 405 is upstream of the fan 402.

[0061] In some aspects of the method according to the present invention, as Figure 15 A method of providing a high efficiency hydrogen fuel high altitude thermal fuel cell system powered aircraft, as shown in FIG. 1, includes the steps of: introducing air 501, delivering the introduced air through an inlet air fan 502, further delivering the introduced air to a series of one or more compressors and also delivering some of the introduced air to a plurality of thermal system passageways 504, 524, compressing the introduced air in the one or more compressors 503, delivering the compressed air to a fuel cell 514, delivering liquid hydrogen gas from a liquid hydrogen gas tank to a liquid hydrogen gas compressor 505, heating the hydrogen gas with the compressed air at an intercooler 504, expanding the hydrogen gas 515, delivering the expanded hydrogen gas to the fuel cell, generating electricity 506 at the fuel cell, powering electric thrust elements 507 with the generated electricity, delivering exhaust gas 514 through one or more intercoolers to condense water in the fuel cell exhaust gas 508, delivering some or all of the condensed water to an ice maker 509, and expelling ice 510 from the aircraft.

[0062] In some aspects, a method of providing a high efficiency hydrogen fuel high altitude thermal fuel cell system powered VTOL aircraft includes the steps of: introducing air, delivering the introduced air through an inlet air fan, further delivering the introduced air to a series of one or more compressors and also delivering some of the introduced air to a plurality of thermal system passageways, compressing the introduced air in the one or more compressors, delivering the compressed air to a fuel cell, delivering liquid hydrogen gas from a liquid hydrogen gas tank to a liquid hydrogen gas compressor, heating the hydrogen gas with the compressed air at an intercooler, expanding the hydrogen gas, delivering the expanded hydrogen gas to the fuel cell, providing power to a plurality of electric VTOL rotor assemblies, and spraying water 511 into the introduced air upstream of an intercooler of a cooled closed loop fuel cell thermal system.

[0063] In some aspects, a method of providing a high efficiency hydrogen fueled high altitude thermal fuel cell system powered aircraft having a fan duct includes the steps of: introducing air into the fan duct, delivering the introduced air through an air fan, further delivering a portion of the introduced air to a series of one or more compressors and also delivering some of the introduced air to a plurality of thermal system passages, compressing the introduced air in the one or more compressors, delivering the compressed air to a fuel cell, delivering liquid hydrogen gas from a liquid hydrogen gas tank to a liquid hydrogen gas compressor, heating the hydrogen gas with the compressed air at an intercooler, expanding the hydrogen gas, delivering the expanded hydrogen gas to the fuel cell, delivering exhaust air through one or more intercoolers to condense water in the fuel cell exhaust air, condensing the water into a water reservoir, discharging the exhaust air into the fan duct downstream of the air fan, and providing thrust to the aircraft from the fan duct. In certain aspects, the method further includes delivering an air stream in the fan duct through a heat exchanger that is part of the thermal system present within the fan duct.

[0064] From the foregoing description, it will be apparent that various modifications can be made to the embodiments described herein, and that the foregoing description is illustrative only. Accordingly, the application is not to be limited to the specific details and illustrative examples described. Thus, various modifications and applications might be made by those skilled in the art, without departing from the spirit or scope of the application.

Claims

1. A high efficiency hydrogen fueled thermofuel cell system for high altitude vehicles, the system comprising: an air inlet; a fan downstream of the air inlet; a first air compressor fluidly coupled to the air inlet downstream of the fan, the first air compressor adapted to compress incoming air into a fuel cell air pathway; a second air compressor fluidly coupled to the first air compressor downstream of the first air compressor; a third air compressor fluidly coupled to the second air compressor downstream of the second air compressor; a liquid hydrogen reservoir; a liquid hydrogen pump coupled to the liquid hydrogen reservoir, the liquid hydrogen pump adapted to pressurize liquid hydrogen through a hydrogen pathway; a first heat exchanger adapted to cool air downstream of the first air compressor with incoming air downstream of the fan; a second heat exchanger adapted to cool air downstream of the first air compressor with hydrogen from the liquid hydrogen pump; a third heat exchanger adapted to cool air downstream of the second air compressor with incoming air downstream of the fan; a fourth heat exchanger adapted to cool air downstream of the second air compressor with hydrogen from the second heat exchanger along the hydrogen pathway downstream of the liquid hydrogen pump; a hydrogen expander along the hydrogen pathway downstream of the fourth heat exchanger, and a fuel cell fluidly coupled to the hydrogen pathway downstream of the hydrogen expander, the fuel cell fluidly coupled to the fuel cell air pathway downstream of the third air compressor.

2. The high efficiency hydrogen fueled thermofuel cell system for high altitude vehicles of claim 1, further comprising: a closed loop cooling system adapted to cool the fuel cell, the closed loop cooling system comprising a cooling fluid and a pump; and an eighth heat exchanger thermally coupled to the cooling fluid and having incoming air downstream of the fan.

3. The high efficiency hydrogen fueled thermofuel cell system for high altitude vehicles of claim 2, further comprising: a sixth heat exchanger thermally coupled to an exhaust conduit conveying exhaust gas from the fuel cell; a seventh heat exchanger thermally coupled to the exhaust conduit downstream of the sixth heat exchanger; and a water separator coupled to the exhaust conduit downstream of the seventh heat exchanger.

4. The high efficiency hydrogen fueled thermofuel cell system for high altitude vehicles of claim 3, further comprising: a water reservoir fluidly coupled to the water separator through a water pathway; a water pump fluidly coupled to the water reservoir; and a water sprayer adapted to spray water into incoming air downstream of the fan and upstream of the eighth heat exchanger.

5. The high efficiency hydrogen fueled thermofuel cell system for high altitude vehicles of claim 4, further comprising: a combustor fluidly coupled to the hydrogen pathway downstream of the hydrogen expander, the combustor fluidly coupled to the fuel cell air pathway downstream of the third air compressor.

6. The high efficiency hydrogen fueled thermo-fuel cell system for high altitude aircraft of claim 5, wherein the heating output of the combustor is delivered to a fifth heat exchanger that heats dry fuel cell exhaust gas from a water separator.

7. The high efficiency hydrogen fueled thermo-fuel cell system for high altitude aircraft of claim 6, wherein the heated dry fuel cell exhaust gas from the fifth heat exchanger is delivered to a third turbocharger adapted to power the third air compressor.

8. The high efficiency hydrogen fueled thermo-fuel cell system for high altitude aircraft of claim 7, wherein the heated dry fuel cell exhaust gas from the third turbocharger is delivered to a second turbocharger adapted to power the second air compressor.

9. The high efficiency hydrogen fueled thermo-fuel cell system for high altitude aircraft of claim 8, wherein the heated dry fuel cell exhaust gas from the second turbocharger is delivered to a first turbocharger adapted to power the first air compressor.

10. The high efficiency hydrogen fueled thermo-fuel cell system for high altitude aircraft of claim 9, further comprising: a first electric motor mechanically coupled to the first air compressor; a second electric motor mechanically coupled to the second air compressor; and a third electric motor mechanically coupled to the third air compressor.

11. A vertical takeoff and landing aircraft, comprising: a main vehicle body; a right side wing coupled to a right side of the main vehicle body; one or more right side rotor assemblies comprising a propeller and a motor, wherein the one or more right side wing rotors are attached to the right side wing; a right side tip rotor assembly comprising a propeller and a motor, wherein the right side tip rotor assembly is attached to an outboard tip of the right side wing; a left side wing coupled to a left side of the main vehicle body; one or more left side rotor assemblies comprising a propeller and a motor, wherein the one or more left side wing rotors are attached to the left side wing; a left side tip rotor assembly comprising a propeller and a motor, wherein the left side tip rotor assembly is attached to an outboard tip of the left side wing, wherein the right side rotor assemblies, the right side tip rotor assembly, the left side rotor assemblies, and the left side tip rotor assembly are attached by a deployment mechanism adapted to deploy the assemblies from a forward facing horizontal flight configuration to a vertical takeoff configuration; and a high efficiency hydrogen fueled thermo-fuel cell system, the thermo-fuel cell system comprising: an air inlet; a fan downstream of the air inlet; a first air compressor fluidly coupled to the air inlet downstream of the fan, the first air compressor adapted to compress incoming air into a fuel cell air passageway; a second air compressor fluidly coupled to the first air compressor downstream of the first air compressor; ​ ​ a third air compressor fluidly coupled to the second air compressor downstream of the second air compressor; a liquid hydrogen reservoir; a liquid hydrogen pump coupled to the liquid hydrogen reservoir, the liquid hydrogen pump adapted to pressurize liquid hydrogen through a hydrogen pathway; a first heat exchanger adapted to cool air downstream of the first air compressor with intake air downstream of the fan; a second heat exchanger adapted to cool air downstream of the first air compressor with hydrogen from the liquid hydrogen pump; a third heat exchanger adapted to cool air downstream of the second air compressor with intake air downstream of the fan; a fourth heat exchanger adapted to cool air downstream of the second air compressor with hydrogen from the second heat exchanger along the hydrogen pathway downstream of the liquid hydrogen pump; a hydrogen expander along the hydrogen pathway downstream of the fourth heat exchanger, and a fuel cell fluidly coupled to the hydrogen pathway downstream of the hydrogen expander, the fuel cell fluidly coupled to a fuel cell air pathway downstream of the third air compressor.

12. The VTOL aircraft of claim 11, wherein the high efficiency hydrogen fuel thermodynamic fuel cell system further comprises: a closed loop cooling system adapted to cool the fuel cell, the closed loop cooling system comprising a cooling fluid and a pump; and an eighth heat exchanger thermally coupled to the cooling fluid and having intake air downstream of the fan.

13. The VTOL aircraft of claim 12, wherein the high efficiency hydrogen fuel thermodynamic fuel cell system further comprises: a sixth heat exchanger thermally coupled to an exhaust conduit conveying exhaust gas from the fuel cell; a seventh heat exchanger thermally coupled to the exhaust conduit downstream of the sixth heat exchanger; and a water separator coupled to the exhaust conduit downstream of the seventh heat exchanger.

14. The VTOL aircraft of claim 13, wherein the high efficiency hydrogen fuel thermodynamic fuel cell system further comprises: a water reservoir fluidly coupled to the water separator through a water pathway; a water pump fluidly coupled to the water reservoir; and a water sprayer adapted to spray water into intake air downstream of the fan and upstream of the eighth heat exchanger.

15. A method of powering a VTOL aircraft powered by a high efficiency hydrogen fuel high altitude thermodynamic fuel cell system, the method comprising the steps of: intake air; conveying the intake air through an inlet air fan; conveying intake air downstream of the inlet air fan to a series of one or more compressors; conveying some of the intake air downstream of the inlet fan to a plurality of thermal system pathways; compressing the intake air in the one or more compressors; conveying the compressed air to a fuel cell; conveying liquid hydrogen from a liquid hydrogen tank to a liquid hydrogen compressor; heating the hydrogen with compressed air at an intercooler; expanding the hydrogen; conveying the expanded hydrogen to the fuel cell; and providing power to a plurality of electric VTOL rotor assemblies.

16. The method of claim 15, further comprising the step of spraying water into the incoming air downstream of the inlet fan and upstream of an intercooler of a closed loop cooling system adapted to cool the fuel cell.

17. The method of claim 15, further comprising the steps of: condensing water from the fuel cell exhaust; freezing the water condensed from the fuel cell exhaust; and expelling the frozen water from the aircraft.

18. The method of claim 16, further comprising the steps of: condensing water from the fuel cell exhaust; freezing the water condensed from the fuel cell exhaust; and expelling the frozen water from the aircraft.

19. The method of claim 15, further comprising the steps of: condensing water from the fuel cell exhaust; and storing the condensed water in a water tank.

20. The method of claim 15, further comprising the step of spraying water from the water tank into the incoming air downstream of the inlet fan and upstream of an intercooler of a closed loop cooling system adapted to cool the fuel cell. ​ ​ ​ ​ ​ ​ ​ ​

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