Aircraft propulsion system and method

Abstract

The invention relates to an aircraft propulsion system (100) comprising: a fuel cell arrangement comprising at least one fuel cell (110); an air source (130) for providing air to the fuel cell device; a compressor arrangement comprising a first compressor (120) in fluid communication with the air source and a fuel cell of the fuel cell arrangement; and a turbine arrangement comprising a first turbine (124) mechanically coupled to the first compressor, where the first turbine is in fluid communication with the at least one fuel cell (110), the system is arranged such that, in use, air from the air source (130) flows sequentially to the first compressor (120), the fuel cell device and the first turbine (124).

Description

Technical Field

[0001] The present invention relates to aircraft propulsion systems and power systems. In particular, it relates to aircraft propulsion devices capable of providing controllably variable levels of power and therefore providing thrust at different pressure levels. Different levels of thrust can be delivered to an aircraft based on a particular flight phase when the flight phase involves pressures experienced by the thrust generating portion of the aircraft. The present invention also relates to auxiliary power units (APUs) and secondary power units (SPUs) for aircraft. Pressure differences may complicate the delivery of power or thrust within an aircraft. Background Art

[0002] An aircraft gas turbine system typically provides in the region of 50% of its ground static propulsion power (the power required to provide thrust) at the top of a climb, but approximately 100% during takeoff. Therefore, there is a difference between the power that will be delivered by the aircraft propulsion system during different flight phases of the aircraft.

[0003] Generally, gas turbines operate well in this regard because the thrust derate of the gas turbine engine and therefore the thrust to power ratio at takeoff and top of climb is generally well suited to the inherent characteristics of the gas turbine. In addition, the high specific power provided by larger and fewer gas turbines results in little competition from other propulsion architectures due to economic considerations. Therefore, modern systems favor gas turbines for aircraft propulsion.

[0004] Disadvantages of gas turbine engines include environmental requirements, however, to date there is no serious alternative to gas turbine engines that can provide varying thrust in the same manner, with similar economic considerations. Gas turbines are therefore the preferred and practical choice for aircraft.

[0005] Although hydrogen fuel and hydrogen synthetic fuels (synfuels) are occasionally used in aircraft, this is not routine in larger aircraft and not routine at all in passenger aircraft. This is due to the specific power that can be provided by a gas turbine compared to the specific power provided by a hydrogen system. For a typical system, a gas turbine can achieve approximately 5 to 8 kW / kg, while a hydrogen fuel cell system can achieve approximately 1 kW / kg. Therefore, hydrogen is a reasonable and environmentally conscious choice for smaller aircraft, but it is completely prevented from use in commercial larger systems.

[0006] Fuel cells using hydrogen are being investigated, for example polymer exchange membranes (PEMs), and recent work has shown that specific power values ​​for such systems could optimistically reach 2 kW / kg over the next 5 to 10 years. Some other work has indicated that there may be an absolute maximum of about 1.8 kW / kg. It would therefore appear that these systems cannot be used in commercial airliners without significant economic drawbacks.

[0007] The fuel cell can be operated in an overrated function to provide approximately 25% higher output for a small amount of time. This figure is higher at the beginning of the life of the fuel cell, but decreases towards the end of life. Due to the mechanism of overrating, if the overrating is prolonged, damage may occur to the fuel cell and in any case the life of the fuel cell will be degraded. However, it is clear that even using this method, the significant difference between takeoff thrust and top of climb thrust cannot be taken into account in a fuel cell propulsion system.

[0008] Therefore, the aircraft generally requires about twice the power during takeoff and climb compared to cruising. Compared to the flight time of more than 1 hour (and up to more than 12 hours), this takeoff and climb phase can last about 5-20 minutes. The total duration of maximum power in flight is about 5 to 30 minutes. The duration of the transition from takeoff to cruising altitude is about the order of <300s for peak power. The remaining peak power is for risk contingencies for go-arounds (during the pre-landing phase) and deviations to another airport. The current state of the art arrangement contains such a remaining peak power for about three go-arounds and one deviation to another airport.

[0009] To maintain hydrogen fuel, fuel cell systems are typically designed to consume hydrogen and result in a waste of up to 50% of the air (and therefore oxygen). While this can benefit from low mass heat dissipation due to reaction into air, it requires greater compression power (almost twice) and therefore increases compression parasitic losses between 15%-45% of the fuel cell power with the most significant parasitic power losses. Considerations regarding the cathode size of the stack take into account the required oxygen reaction rate, whereby O2 is approximately 20% of atmospheric air.

[0010] Oxygen can be used in fuel cells, however, oxygen has 8 times the mass of hydrogen and requires a ratio of 4:1 (for H20). Therefore, carrying oxygen on board aircraft is not considered efficient for flight.

[0011] Two-stage compression has been used to achieve the high pressure ratios required to operate a fuel cell at a certain altitude, however, when operating a fuel cell at low and high altitudes (where low and high pressure ratios are required, respectively), operating in a fixed configuration may not be efficient. Therefore, it is necessary to consider the use of fuel cells over a range of altitude conditions and deliver the necessary airflow to achieve appropriate power for different flight phases.

[0012] There are therefore developments that may be made in this field and advantages that may be obtained from such developments. However, the inventors of the invention described herein have created an alternative propulsion device having a wide range of previously unavailable advantages as described herein. Summary of the invention

[0013] Various aspects of the invention are set out in the accompanying claims.

[0014] From a first aspect, there is provided an aircraft propulsion system comprising: a fuel cell device comprising at least one fuel cell; an air source for providing air to the fuel cell device; a compressor device comprising a first compressor connected to the air source and the fuel cell fluid of the fuel cell device; and a turbine device comprising a first turbine mechanically coupled to the first compressor, wherein the first turbine is connected to the at least one fuel cell fluid, the system being arranged so that in use, air from the air source flows sequentially to the first compressor, the fuel cell device and the first turbine.

[0015] The invention described herein allows the user to have great control over the propulsion output of the system so that the user can tailor the system to the conditions in which the system is used. This in turn provides efficiency benefits and therefore more economical flying.

[0016] The compressor can be used to provide a higher concentration of a particular fuel, such as oxygen, to the fuel cell. In this way, the system can take into account low oxygen environments and still provide efficient energy generation to the propulsion system.

[0017] From another aspect, a method for generating propulsion for an aircraft is provided, comprising: delivering air from an air source to a first compressor; compressing the air; delivering the compressed air to a fuel cell device including at least one fuel cell for generating energy; delivering the fuel cell output air to a first turbine for operating the turbine; and operating the compressor and the turbine, wherein the compressor and the turbine are mechanically coupled.

[0018] From another aspect, an auxiliary power unit (APU) for use in an aircraft is provided, comprising: a fuel cell device including at least one fuel cell; an air source for providing air to the fuel cell device; a compressor device including a first compressor connected to the air source and the fuel cell fluid of the fuel cell device; and a turbine device including a first turbine mechanically connected to the first compressor, wherein the first turbine is connected to the at least one fuel cell fluid, the system being arranged so that in use air from the air source flows sequentially to the first compressor, the fuel cell device and the first turbine, and wherein the air source can be selected from a combination of ambient air, environmental control system exhaust or oxygen. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] One or more embodiments of the present invention will now be described, by way of example only, and with reference to the following drawings, in which:

[0020] Figure 1 shows a schematic diagram of a fuel cell propulsion system including multiple stacks and a turbo compressor;

[0021] Figures 2a to 9 A schematic diagram of a fuel cell propulsion system having a switched multi-stage compressor and turbine arrangement is shown;

[0022] Fig.10 shows a schematic diagram of a fuel cell propulsion system including a bypass valve connected to the fuel cell system; and

[0023] Fig.11 A schematic diagram of a fuel cell propulsion system with a switched 2-stage compressor and turbine arrangement is shown.

[0024] Any reference to prior art documents in this specification should not be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words "comprise", "include" and similar words should not be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including but not limited to". The present invention is further described with reference to the following examples. It should be understood that the claimed invention is not intended to be limited to these examples in any way. It will also be appreciated that the present invention not only covers individual embodiments, but also covers the combination of the embodiments described herein.

[0025] The various embodiments described herein are proposed only to help understand and teach the claimed features. These embodiments are provided only as representative samples of embodiments, and are not exhaustive and / or exclusive. It should be understood that the advantages, embodiments, examples, functions, features, structures and / or other aspects described herein are not considered to be limitations on the scope of the present invention defined by the claims or the limitations of the equivalents of the claims, and other embodiments can be utilized and can be modified without departing from the spirit and scope of the claimed invention. In addition to those specifically described herein, various embodiments of the present invention may appropriately include, consist of or substantially consist of the appropriate combination of disclosed elements, parts, features, parts, steps, parts, etc. In addition, the present disclosure may include other inventions that are not currently claimed but may be claimed in the future. DETAILED DESCRIPTION

[0026] The invention described herein relates to generating propulsion and power systems for aircraft. A particular engine system for an aircraft may involve a fuel cell, at least one compressor, and at least one turbine. The generation of propulsion depends on factors that may be affected by altitude. Therefore, the aircraft propulsion system herein is arranged to take into account different power requirements during different flight phases due to different pressures at different altitudes. Additional power may be provided during takeoff / climb, and then not provided during cruise. Therefore, additional power for takeoff and climb is required at a higher pressure when on the ground and at a lower pressure near the top of the climb phase.

[0027] Advantageously, the fuel cell stack can tolerate some variation in operating pressure (approximately 1 to 3 bar). To utilize ambient air at certain altitudes, the air delivery system can have a higher pressure ratio. The air consumption of the fuel cell stack is proportional to the power produced based on the stoichiometry of the stack. Therefore, the air delivery system can vary the mass flow of air to the fuel cell stack according to the power requirements.

[0028] The invention described herein relates to power generation by an auxiliary power unit (APU) which may be designed to provide a number of necessary functions to an aircraft. The APU may be small and provide only aircraft electrical power (usually secondary or emergency), or may be larger in size to provide propulsion alternatively or additionally. The APU may be connected to or contain an accessory shaft arranged to connect the APU to a generator.

[0029] The present invention provides a number of inventive strategies that enable compression and more efficient use of compressed fuel in a fuel cell propulsion system.

[0030] Oxygen sources that can provide oxygen for use in fuel cell propulsion systems (e.g., in aircraft installations) include an environmental control system (ECS) that obtains oxygen (O2) via enrichment of ambient air or use of a dedicated (or other) oxygen source. The oxygen source can be a liquid oxygen source (LOx). Advantageously, liquid oxygen is less spatially dense than oxygen in the gas phase, so there are capacity advantages associated with using LOx in any system described herein. Specifically, the volume density of LOx is superior to oxygen in gaseous form.

[0031] Aircraft often carry oxygen on board, and this is a byproduct of the electrolysis process when hydrogen (H2) is produced from water. Many current aircraft carry oxygen on board in bottles, which can be used in the event of cabin depressurization, such as might occur due to a blown window, etc. The amount stored is suitable to cover the period until a descent to a safe altitude can be achieved. While passengers use drop-down oxygen masks, crew members can, for example, use portable oxygen bottles. Therefore, current aircraft often have onboard oxygen generators or, more commonly, gaseous oxygen tanks.

[0032] By supplying compressed fuel into a fuel cell, additional power can be provided from a fuel cell device. In particular, compressed oxygen and hydrogen are then provided to a fuel cell, a fuel cell stack or a fuel cell array.

[0033] Reference now Figure 1 , a propulsion system 100 is shown including a fuel cell stack 110. The fuel cell stack 110 is connected to an H2 supply 112 via an H2 supply line. The hydrogen portion is marked by portion 102.

[0034] Although a hydrogen supply will be used in the examples shown herein, alternative suitable fuels such as hydrocarbons, ethanol, methanol, ammonia, etc. may be used with the proposed propulsion system. The hydrogen supply may contain 100% hydrogen or a lower percentage of carbon monoxide (CO), carbon dioxide (CO2), nitrogen dioxide (NO2) and / or hydrogen sulfide (H2S) in the supply. The hydrogen supply (or hydrogen source) may provide liquid or gaseous hydrogen. Liquid hydrogen may be used for cooling functions before being used in a fuel cell in gaseous form.

[0035] The propulsion system 100 has a compressor 120, an electric motor / generator 122, and a turbine 124. The compressor 120 is connected to a heat exchanger 126, and the turbine 124 is connected to another heat exchanger / condenser 128. The compressor 120 is connected to an ECS exhaust supply, an oxygen supply, or an ambient air supply 130. The compressor 120 can be a single-stage centrifugal turbo compressor, and needs to provide a full range of pressure ratios from about 3 to about 9 pressure ratios for all operating conditions. The system can be an electric drive compressor 120, and the turbine 124 can be used to collect energy from the cathode (hot exhaust) 132. The compressor 120 can be part of a compressor device, which can include multiple compressors located within the system 100. The compressors of the compressor device do not need to be directly connected, but can be directly connected. The turbine 124 can be part of a turbine device, which can include multiple turbines located within the system 100. The turbines of the turbine device do not need to be directly connected, but can be directly connected.

[0036] The compressor and turbine shown herein may be a single-inlet, single-stage centrifugal type, which may also be referred to as a radial compressor and turbine. Alternatively, the compressor and turbine shown herein may be a dual-inlet centrifugal compressor or an axial compressor and turbine.

[0037] An ECS exhaust supply, an oxygen supply, or an ambient air supply 130 is shown as providing air to the compressor 120. The compressor 120 may use any one of these supplies or a combination of these supplies. In this way, the air supplied to the compressor 120 may be enriched by an oxygen concentrator or by providing a greater percentage of oxygen from the oxygen supply. In addition, oxygen enrichment of any of these supplies may occur before or after the oxygen reaches the air supply 130 in the process. The turbine 124 is connected to the cathode exhaust port 132. The air / exhaust portion is marked by portion 104. Element 130 is referred to as an ECS exhaust supply, but may also be an external (ambient) air supply, etc. The primary function of element 130 is to provide air (whether oxygen is enriched in some way) for use in the fuel cell stack 110 via a single compressor 120 of the system 100.

[0038] Two heat exchangers 126, 128 are connected to the fuel cell stack 110. The heat exchanger 126 is connected to the compressor 120 and the fuel cell stack 110 and cools the air exhausted from the compressor 120. The heat exchanger 120 may be optional depending on the temperature limit of the fuel cell stack 110 and the temperature limit of the air temperature after compression by the compressor 120. The fuel cell stack 110 is connected to the water tank 140 via a water pump 142 and a heat exchanger 144. The water tank 140 is connected to the heat exchanger / condenser 128. The water portion is marked by portion 106.

[0039] The examples shown herein are examples of water-cooled fuel cell stack systems. The examples shown will also operate well in air-cooled or evaporative cooling devices, or when using another coolant medium. The examples shown have been simplified to emphasize the most creative elements of the present system. However, these are only examples. Such examples may omit in-depth details related to less common elements in the system, such as an optional recirculation system that can be used to recirculate hydrogen. Other omissions include a humidifier that can be used on the cathode air supply. Therefore, although not explicitly shown, such features may be included in the present device. In addition, the present device may be used with an evaporatively cooled fuel cell stack.

[0040] In fact, the condensing heat exchanger 128 may be optional for the high power stage, without extracting the condensed water. Instead, the humid air may be sent outside the aircraft ("overflow") or stored in an intermediate container until it can be sent outside the aircraft. In this way, the pressure losses inherent in the use of the condensing heat exchanger 128 will not be included in the device, which results in a higher performance system (in the form of more power). To compensate for this external overflow of the humid air, a slightly larger water tank will be required.

[0041] exist Figure 1In the arrangement shown, the propulsion system 100 uses ECS air with an oxygen concentrator. There are many advantages that derive from such an arrangement.

[0042] An oxygen concentrator (oxygen separator) can be used to produce a higher percentage of O2 in the air in section 104 than in the cabin or in the outside ambient air. Using a higher percentage of O2 for a certain period of time will enable the fuel cell to operate at a higher net power level during that period. In contrast, a system without an oxygen concentrator uses the oxygen contained in the ambient air. The result is that many current fuel cell systems waste air and consume H2 to their maximum extent. This is necessary for ambient air because the approximately 21% of O2 (as in air) will be depleted and may cause the fuel cell to fail. This is not the case with oxygen systems. O2 in the reactant ratio is 4 times heavier than H2, and therefore, it makes more sense that if waste is to occur, H2 is wasted. This is further reasonable because significantly more H2 is stored compared to O2, and therefore, the mass variation at the system level (specifically, tank mass) is lower. Additionally and advantageously, in the high power case of the cryogenic cooling system, such a device allows more available heat dissipation in the liquid hydrogen.

[0043] The source air requires less compression than the outside ambient air (which may be low in altitude). Our estimates show that the compression is about 3 times that required for ambient air, rather than 9 times. This is because the source air may come from cabin air that is already pressurized, and because the air may be enriched with oxygen. The enrichment with oxygen results in less air being required, and therefore less compression being required.

[0044] With reference to the three supplies 130 shown, there may be a benefit to using the exhaust gas from the ECS without supplying additional oxygen. The ECS exhaust gas has a lower oxygen concentration, so when used in the fuel cell stack 110, the stack 110 will produce less power. However, since the parasitic power requirements from the compressor may be lower than a conventional system using ambient air, the fuel cell system as a whole may still be more efficient. This benefit also increases with altitude, providing a particular benefit to the present system.

[0045] Additional advantages can be obtained from the lower temperature air in the air source when compared to compressed ambient air. In an arrangement in which the heat exchanger 126 is omitted, there is no pressure loss associated with including the heat exchanger 126. Therefore, the lower air temperature on the cathode side means that the fuel cell stack 110 can dissipate more heat into the air before reaching the equivalent stack temperature (equivalent to the temperature of the device including the heat exchanger 126). In this way, omitting the heat exchanger 126 can be beneficial due to the ability to operate the fuel cell stack 110 at a higher power.

[0046] The oxygen concentrator may be used to increase the O2 ratio within the air supplied in the portion 104, or the oxygen concentrator may be used to supply pure oxygen to the system 100. As previously described, using a higher ratio of O2 in the air supply 130 to the fuel cell stack 110 enables greater power output from the fuel cell stack 110 because less non-reactive air (nitrogen, etc.) passes through the fuel cell stack 110. Alternatively, a smaller fuel cell stack may be provided that provides the same output power (as a result of the greater power output per size of the present fuel cell stack 110 arrangement).

[0047] Where liquid oxygen is used from an oxygen supply (e.g., a tank, etc.), the specific heat of vaporization and the specific heat capacity of oxygen may be used to cool the elements of the propulsion system 100. The cooling of the electrical components may be more efficient due to the lack of eddy currents, etc. In addition, the use of pure oxygen in the system 100 may enable the use of a smaller fuel cell area and therefore a smaller and lighter stack 110. This results in efficiency benefits due to the mass of the stack that needs to be carried, for example, by an aircraft in use. The lower the mass of the stack, the less fuel is required to account for that mass compared to a heavier system.

[0048] Liquid oxygen enables an even lower inlet temperature of the oxidant, which in turn enables the fuel cell stack 110 to operate with potentially higher heat dissipation and therefore higher power. Additional potential advantages include that since the only gas component is oxygen, this oxygen may be completely consumed. With air systems, typically only 50% of the oxygen may be consumed, since the system must ensure that the fuel cell stack has sufficient O2, so an oversupply of O2 is preferred. The current system 100 has benefits in ensuring less oxygen waste and lowering pressure losses (including back pressure) at the outlet of the stack 110.

[0049] exist Figure 1 In the example shown, the fuel cell stack 110 needs to operate well in both of the above situations, so the more primary advantages relate to increased stack power (before considering parasitic losses, i.e., turbine compressor, pumps, etc.) and net power, rather than the slightly more secondary advantages of adjusting the size of the stack 110.

[0050] By reusing ECS ​​air via supply 130, system 100 does not require an external air intake to bring in air from the surrounding environment. Therefore, there is an aerodynamic drag benefit associated with omitting an external air intake element. This drag benefit translates into a benefit associated with the energy requirements on the entire system 100; it will be appreciated that system 100 will need to provide greater thrust to accommodate an element that may provide additional drag. By eliminating the need for this element, system 100 is more efficient.

[0051] As mentioned, the system has a fixed configuration which may not be efficient for providing power over a wide range of altitudes and therefore pressures.

[0052] Reference now Figure 2a , showing something like Figure 1 The propulsion system 200 of the propulsion system 100 is shown in FIG. 200 . Reference numerals for similar components of the propulsion system 200 will be Figure 1 Those used in , where the numbers are increased by 100. For convenience, a complete description of similar components may not be provided.

[0053] The propulsion system 200 includes a fuel cell system 201. The fuel cell system 201 may also be referred to as a fuel cell device 201. The fuel cell system 201 will include Figure 1 The H2 supply unit 112 of the water portion 106, the fuel cell stack 110, the water tank 140, the water pump 142 and the heat exchanger 144. These features are Figure 2a Not shown in detail.

[0054] The propulsion system 200 includes an air intake 230 (similar to the ECS 130) connected to a first compressor 220. The first compressor 220 is connected to the fuel cell system 201 and a first motor / generator 222. The motor / generator 222 is connected to a turbine 224. Figure 1 The arrangement of the elements shown is contained in the primary part 208 .

[0055] Propulsion system 200 also includes a secondary section 209. Secondary section 209 includes a second compressor 250, a second motor / generator 252, and a second turbine 254. Figure 2a The device shown in the figure shows the switching of the ( Figure 2a The propulsion system 200 is selectively controlled to provide additional pressure by using the optional second section 209 (which includes the compressor 250, the electric motor / generator 252 and the turbine 254) so ​​that the fuel cell system 201 experiences the same absolute pressure regardless of altitude. In this example, the compressor arrangement includes two compressors 220, 250, and the turbine arrangement includes two turbines 224, 254.

[0056] An advantageous arrangement is for compressor 250 to have a high capacity so that compressor 250 can be used upstream of compressor 220 (which would have a lower capacity). Turbines 224, 254 have a similar arrangement, with turbine 224 having a lower capacity and turbine 254 having a higher capacity.

[0057] In this arrangement, while the absolute mass flow through compressors 220, 250 may be the same when connected in series, the corrected mass flow (to allow for density variations when the gases are at different temperatures and pressures) will be higher for compressor 250 and lower for compressor 220.

[0058] In the example, the primary part 208 is operated without the secondary part 209. Figure 2a 201. The operation is shown by the dotted line (low pressure ratio, lower mass flow). This operation is particularly beneficial when a low pressure ratio is required, such as during takeoff, where the ambient air pressure is high, or where ECS air 230 is used and is already pressurized. This operation may also be particularly beneficial in situations where a lower mass flow of reactants is required, either because of a high concentration of oxygen or because the fuel cell system 201 requires lower power.

[0059] In another example, both the primary section 208 and the secondary section 209 are operated. This operation is particularly beneficial at high altitudes, where an additional compression stage is utilized to achieve a compression level for the fuel provided to the fuel cell stack so that the fuel cell stack experiences the same pressure as at lower altitudes. Similarly, the additional turbine 254 can be activated to recover energy from the exhaust at high altitudes.

[0060] In yet another example, the secondary part 209 operates without the primary part 208. Figure 2a This operation may be advantageous where the secondary section 209 has a higher flow rate than the primary section and requires the system 200 to operate at high power where the fuel cell stack requires a large mass flow of air but at a low pressure ratio.

[0061] Figure 2a A solid line is included to indicate operation of system 200 when a high pressure ratio exists. Figure 2a Dashed lines are included to indicate operation of system 200 when low pressure ratios, higher mass flows exist. Figure 2a Dotted lines are included to indicate the operation of system 200 when low pressure ratios, lower mass flows, exist. Dashed-dotted lines are used to indicate mechanical shafts between turbines of system 200. This style will be used in subsequent figures and will be labeled as such in the figures.

[0062] An advantage of selectively using the secondary compressor arrangement is that when additional compression is required this can be provided, but when additional compression is not required there are no associated losses from using the secondary section 209. Thus, the arrangement provides a controllable balance to the output of the propulsion system 200 that takes into account losses when in use and provides the additional benefit from compression while avoiding said losses when not in use. Thus, at low altitudes there are no parasitic losses, but switching the secondary section 209 at higher altitudes enables a high pressure ratio of, for example, between 6 and 9 to be provided to the fuel cell at high altitudes.

[0063] Figure 2aThe device shown is a dual shaft system, one shaft 221 is present in the primary part 208, and one shaft 251 is present in the secondary part 209. Each shaft has a compressor, a motor / generator, and a turbine. As described above, the two shafts 221, 251 can be operated simultaneously or alternatively to suit the requirements for the propulsion system 200 and the environment in which the propulsion system 200 is located.

[0064] The shaft 251 on which the compressor 252, the motor / generator 254, and the turbine 256 are arranged can be referred to as a "low-pressure" shaft because the shaft 251 can be used to provide additional compression when in a low-pressure environment, which can be beneficial in increasing the power output from the fuel cell system 201 and the propulsion system 200 as a whole.

[0065] System 200, both shafts 221, 251 have a motor (each) to drive the shafts 221, 251. This enables the user to vary the amount of energy recovery to eliminate the requirement for the second motor 252. In the following Figure 3 This possibility was explored in . Figure 2b A three-axis system 2000 is shown.

[0066] Reference now Figure 2b , showing something like Figure 2a The propulsion system 2000 of the propulsion system 200 is shown in FIG. 20. Reference numerals for similar components of the propulsion system 2000 will be Figure 2a , where the numbers have "0" appended to them, so Figure 2b The System 2000 is similar to Figure 2a system 200. Although Figure 2a The example shows a 2-axis system, and Figure 2b A 3-axis system is shown, but these are examples and additional axes may be included in the systems taught by the present disclosure.

[0067] exist Figure 2b In a similar Figure 2a Next to the features of the primary section 2080, there is a primary section 2080, a secondary section 2090 and a third section 2085, the third section 2085 being located between the primary section 2080 and the secondary section 2090. The third section 2085 includes a compressor 2205, which is connected to both the compressor 2200 of the primary section 2080 and the compressor 2500 of the secondary section 2090. The compressor 2205 of the third section 2085 is arranged on a third shaft 2215 and is connected to a motor / generator 2225. The motor / generator 2225 is in turn connected to a turbine 2245. The turbine 2245 of the third section 2085 is connected to the turbine 2240 of the primary section 2080 and the turbine 2540 of the secondary section 2090.

[0068] In use, the third shaft can be used in applications above 7500m altitude. This may be particularly useful when the air inlet 2300 provides ambient air. By enabling the use of ambient air in a low pressure environment, such an arrangement reduces the need for an oxygen air source or the use of ECS air. In this example, the compressor arrangement includes three compressors 2200, 2205, 2500, and the turbine arrangement includes three turbines 2240, 2245, 2540. In a similar arrangement not shown, the system may have more than three compressors and / or more than three turbines.

[0069] The arrangements herein may be used to provide further systems that utilize more axes than the specific examples shown herein. Figure 2b The third axis 2215 can be used at higher altitudes. Additional axes can be used and at correspondingly higher altitudes. Additional axes can be used for increased altitudes. For example, additional axes can be included to enable the system to be used up to 15,000 m altitude and above 15,000 m altitude.

[0070] Reference now Figure 3 , shows a propulsion system 300 similar to the propulsion system 200 of Figure 2. Reference numerals for similar components of the propulsion system 300 will be the reference numerals used in Figure 2, with the numerals increased by 100. For convenience, a complete description of similar components may not be provided.

[0071] The propulsion system 300 includes a fuel cell system 301. The fuel cell system 301 will contain Figure 1 The H2 supply unit 112 of the water portion 106, the fuel cell stack 110, the water tank 140, the water pump 142 and the heat exchanger 144. These features are Figure 3 Not shown in FIG.

[0072] The propulsion system 300 includes an air intake 330 (similar to Figure 1 The first compressor is connected to the fuel cell system 301 and the first motor / generator 322. The motor / generator 322 is connected to the turbine 324. Figure 1 The arrangement of the elements shown is contained in the primary part 308 .

[0073] and Figure 2a Like the subsection 209, Figure 3 The device 300 has a compressor 350 and a turbine 354 arranged on a secondary shaft 351. In this device, the motor / generator shown in the device of Figure 2 is not included. The lack of a motor / generator reduces the losses associated with the weight of the motor / generator.

[0074] The device 300 can be operated by balancing the turbine work split on the two shafts 321, 351. Another advantage of such a device is that the compressor 350 can be driven by the turbine 354, whereby the turbine 354 is driven due to the pressure difference between the pressure from the outlet of the turbine 324 (in the case of a solid line) or the outlet pressure of the fuel cell stack in the fuel cell system 301 (in the case of a dashed line) and the exhaust pressure 322. The exhaust pressure 322 may be connected to the ambient pressure.

[0075] In such an arrangement, the work distribution can be changed so that the low-pressure turbine 354 provides enough power to drive the low-pressure compressor 350. Then only the electric motor / generator 322 on the other shaft 321 is needed, thus providing the above-mentioned weight savings. Shaft 321 can be operated separately from shaft 351, and thus, in one example, during takeoff (at higher ambient air pressure), shaft 321 with motor 322 can be used independently of shaft 351 without the motor. Once the propulsion system 300 is at a certain altitude (at lower ambient air pressure), the second shaft 351 can be used to increase the compression of the fuel provided to the fuel cell system 301.

[0076] Furthermore, the shaft 321 and associated compressor 320, motor / generator 322, turbine 324 may be optimized for use at sea level so that when the shaft 321 may function alone (i.e., without the second shaft 351), the system 300 benefits from the maximum output from the shaft 321. In this way, the system 300 is more reliable when operating without the benefit from the second shaft 351.

[0077] exist Figure 3 The arrangement 300 shown can be such that the turbine 324 does not have to do as much work, which will leave more energy in the exhaust flow. If enough energy is left in the exhaust flow (which can be controlled by the user controlling the behavior of the turbine 324), then this excess energy can drive the turbine 354 and subsequently operate the compressor 350. This is a particularly energy-efficient operating arrangement. This operating arrangement utilizes the pressure of the effluent leaving the first turbine 324 and the ambient pressure. Therefore, this operating arrangement is particularly advantageous when the system 300 is at a certain altitude. Figure 3 In the method of operation, the flow bypasses turbine 324, leaving enough energy in the exhaust flow to power turbine 354. Figure 3 In an alternative arrangement (not shown), turbine 324 may be omitted.

[0078] So, we Figure 3 A device 300 is provided which includes a motor / generator and can thus provide Figure 2a The advantages associated with the omission of one of the motor / generators. Figure 3 Omitted from Figure 2a The motor / generator 252 is shown in FIG. 1 , but in an alternative arrangement, the motor / generator 222 may be omitted and the motor / generator 252 may be included.

[0079] Figure 3 A further advantageous use of the device 300 is Figure 3 In this case, when the intake air is at a much higher pressure than the exhaust 332 (e.g., if ECS air, oxygen, and / or ambient air 330 from a tank is used and the system is exhausted to ambient (i.e., low) pressure at high altitude), the motor shaft 321 of the primary section 308 is not required, and only the shaft 351 of the secondary section 309 is required. Such use of the device 300 can be very energy efficient due to the reduction of parasitic losses to near zero.

[0080] Reference now Figure 4 , showing something like Figure 3 The propulsion system 400 of the propulsion system 300 is shown in FIG. 4 . Reference numerals for similar components of the propulsion system 400 will be Figure 3 Reference numerals are used in the drawings wherein the numerals are increased by 100. For the sake of convenience, a complete description of similar components may not be provided.

[0081] The propulsion system 400 includes a fuel cell system 401. The fuel cell system 401 will contain Figure 1 The H2 supply unit 112 of the water portion 106, the fuel cell stack 110, the water tank 140, the water pump 142 and the heat exchanger 144. These features are Figure 4 Not shown in FIG.

[0082] Due to the omission of the second shaft 251, 351, the system 400 is similar to FIG. Figure 3 In the system 400 shown, there is a shaft 421 on which two compressors 420, 450, a motor / generator 422 and two turbines 424, 454 are arranged.

[0083] Propulsion system 400 includes an air intake 430 (similar to ECS 130) connected to a compressor 450. The compressor 450 is connected to another compressor 420, which is connected to a fuel cell system 401 and a motor / generator 422. The motor / generator 422 is connected to a turbine 424. The turbine 424 is connected to another turbine 454. Figure 1 Sample, Figure 1 Elements of are present in the device, although not shown for clarity.

[0084] Figure 4The arrangement 400 of FIG. 400 (in which the compressor is arranged on said one shaft) advantageously provides weight savings due to the omission of the second shaft. In the same manner, the omission of the second motor / generator (such as Figure 3 ) provides weight savings. In the arrangement 400 , both compressors 420 , 450 and both turbine stages 424 , 454 are powered by a single motor / generator 422 .

[0085] The selection of the size of the compressors 420, 450 may enable weight savings relative to previous arrangements. Figure 2a Although the peak power of motor / generator 252 is at a different operating condition than motor / generator 222, both motor / generators 222 and 252 will be sized for their respective peak power conditions. Figure 2a In an arrangement where the motor / generator pair will not operate at peak power simultaneously. However, in Figure 4 The device 400 (and the Figure 5 and Figure 6 ), motor / generator 422 may be sized for an overall peak power that may be less than the sum of the peak powers of motor 252 and motor 222.

[0086] Reference now Figure 5 , showing something like Figure 4 The propulsion system 500 of the propulsion system 400 is shown in FIG. 5 . Reference numerals for similar components of the propulsion system 500 will be Figure 4 Reference numerals are used in the drawings wherein the numerals are increased by 100. For the sake of convenience, a complete description of similar components may not be provided.

[0087] The propulsion system 500 includes a fuel cell system 501. The fuel cell system 501 will contain Figure 1 The H2 supply unit 112 of the water portion 106, the fuel cell stack 110, the water tank 140, the water pump 142 and the heat exchanger 144. These features are Figure 5 Not shown in FIG.

[0088] and Figure 4 2 and 3. Figure 3 In the system 500 shown, there is one shaft 521 on which are arranged two compressors 520, 550, one motor / generator 522 and two turbines 524, 554.

[0089] Apart from Figure 4 In addition to the device 400 shown in FIG. Figure 5The device 500 shown in FIG. 5 also has a pair of clutches 562, 564. The first clutch 562 is arranged between the two compressors 520, 550. The second clutch 564 is arranged between the two turbines 524, 554. The clutches 562, 564 can be used to deactivate the compressor or the turbine so that the device 500 does not need to have both the compressors 520, 550 and the turbines 524, 554 operating at all points. When the system 500 is not experiencing low pressure, the clutches 562, 564 can be operated to deactivate the "low pressure" components (compressor 550, turbine 554).

[0090] Therefore, advantageously, using Figure 5 In the case of a device of this type, a user may deactivate either or both of the compressor 550 and turbine 554 in circumstances where deactivation is advantageous. This may be the case when the device 500 is at sea level (or similar) air pressure such that the fuel cell experiences higher pressure levels than, for example, during flight, as described above. At sea level, there is no need to activate the compressor 550 or turbine 554, and therefore it is advantageous to provide the user with the option to deactivate these components, and thus provide a more efficient system (by virtue of removing activation of unnecessary elements in the device 500).

[0091] Reference now Figure 6 , showing something like Figure 5 The propulsion system 500 is a propulsion system 600. Reference numerals for similar components of the propulsion system 600 will be Figure 5 Reference numerals are used in the drawings wherein the numerals are increased by 100. For the sake of convenience, a complete description of similar components may not be provided.

[0092] The propulsion system 600 includes a fuel cell system 601. The fuel cell system 601 will contain Figure 1 The H2 supply 112 of the water portion 106, the fuel cell stack 110, the water tank 140, the water pump 142 and the heat exchanger 144. These features are not included in Figure 6 Shown in.

[0093] Figure 6 The device 600 has a single shaft 621 on which two compressors 620 , 650 , a motor / generator 622 and two turbines 624 , 654 are arranged. Figure 6 The device 600 does not have Figure 5 The clutches 562, 564 of the device 500. Alternatively, the device 600 has a series of gearboxes 672, 674 arranged to allow the user to control each component of the device 600 to run at the optimal speed. In another device, there is an additional gearbox located between the motor / generator 622 and the turbine 624.

[0094] A user may controllably operate components of the device 600 using the gearbox to control the performance of the components of the device 600. Figure 5 The device 500 has two clutches 562, 564, but Figure 6 The device 600 has three gearboxes 672, 674, 676. Although this number is merely an example, any number of clutches or gearboxes (or a combination of both) may be present in the device. This decision is consistent with the desired outcome, i.e., what operating parameters the user wishes to control and how to control them.

[0095] Thus, arrangements are provided in which performance control elements such as clutches or gearboxes may be included to provide a user with greater control over components of the arrangement. Performance control elements may be mechanical or electrical elements that may affect the operation of some of the components within the various arrangements shown in the examples in the drawings herein. Controlling the operation of such components may allow a user to optimize the operation of the arrangement as a whole to provide efficiency benefits (e.g., at low altitudes where fewer components need to be operated) or to provide additional thrust (e.g., at high altitudes where additional components may be activated). Controlling the operation of a component may include controlling whether the component is activated or not, or the operating condition of the component (e.g., operating speed, etc.).

[0096] Reference now Figure 7a , showing something like Figure 2a The propulsion system 700 of the propulsion system 200 is shown in FIG. 2. Reference numerals for similar components of the propulsion system 700 will be the reference numerals used in FIG. 2 with the numerals increased by 500. For convenience, a complete description of similar components may not be provided.

[0097] The propulsion system 700 includes a fuel cell system 701. The system 700 has two shafts 721 and 751, each with a compressor 720, 750, a motor / generator 722, 752, and a turbine 724, 754. Figure 2a As with the illustrated apparatus 200 , the compressor 720 is coupled to the motor / generator 722 and the fuel cell system 701 .

[0098] Figure 7aThe device 700 shown has an air filter 780 arranged between the air inlet 730 and the compressor 720. In the device 700, in use, the air filter 780 can be cut in and out of activation together with the second compression stage. When needed, the user can controllably or selectively pass air through the air filter 780. This advantageously can reduce the amount of pollutants that can reach the fuel cell system 701. However, on the air filter 780, there will be a pressure loss. Therefore, a balance is made between filtering air to reduce the amount of pollutants that reach the fuel cell system 701 and increasing the pressure loss through the air filter.

[0099] Thus, in this device 700, a user may implement switching gas flow paths at sea level compared to at an altitude. In particular, because at an altitude, the air is generally cleaner than at sea level. Therefore, there is a reduced need for filtering at an altitude. In this way, such a device 700 provides the user with greater control in enabling filtering, but bypasses the air filter 780 when operating at an altitude. Thus, there is an efficiency benefit (not permanently using the air flow path with the air filter 780), while also providing an improved life benefit due to the reduced level of contaminants reaching the fuel cell system 701.

[0100] Reference now Figure 7b , showing something like Figure 7a The propulsion system 7000 of the propulsion system 7000. Reference numerals for similar components of the propulsion system 7000 will be Figure 7a The reference numbers used in the examples have an additional "0" so that Figure 7b The System 7000 is similar to Figure 7a System 700.

[0101] The air filter 7800 of the device 7000 is connected to the compressor 7500 and the fuel cell system 7010, instead of Figure 7a Compressor 720 and air intake 730 are shown. Figure 7b The fuel cell system 7010 is connected to the compressor 7200, the air filter 7800, the turbine 7240 and the turbine 7540. The high pressure ratio, filter inactive path and the low pressure ratio, filter active path are shown in solid lines and dashed lines, respectively. In this way, the user can operate as needed Figure 7b The device 7000 can be used with or without the air filter 7800. This provides a more efficient system, as explained in the related advantages above, which can improve the overall life of the air filter 7800 due to not being permanently used.

[0102] Reference now Figure 8 , showing something like Figure 7aThe propulsion system 800 of the propulsion system 700 is shown in FIG. 8. Reference numerals for similar components of the propulsion system 800 will be Figure 7a Reference numerals are used in the drawings wherein the numerals are increased by 100. For the sake of convenience, a complete description of similar components may not be provided.

[0103] Propulsion system 800 includes fuel cell system 801. System 800 has two shafts 821 and 851, each with a compressor 820, 850, a motor / generator 822, 852, and a turbine 824, 854. As with device 700 shown in FIG. 7 , compressor 820 is connected to motor / generator 822 and fuel cell system 801.

[0104] Figure 8 The illustrated apparatus 800 has an air inlet 830 and an environmental control system (ECS) exhaust source 831. The ECS exhaust source may have higher oxygen levels than exhaust gas and therefore may be particularly advantageous for obtaining power output from the fuel cell system 801.

[0105] These sources can be used controllably (in series or individually) to ensure the performance the user expects at that moment. As mentioned, the increased oxygen in the ECS exhaust can be used during takeoff to obtain a greater power output from the fuel cell than when the intake source is used alone. Alternatively, both can be used. Alternatively again, the ECS can be used at a certain altitude to provide a larger amount of pressurized air to the fuel cell system 801 because the air is less dense at a certain altitude than when the pressurized air is provided by the ECS exhaust source. In each of these situations, efficiency benefits can be obtained by controlling the use of the two air sources 830, 831.

[0106] In particular, such an arrangement 800 may be particularly advantageous for APU applications. APU power requirements may be low for typical operation at cruising altitudes, and thus ECS exhaust from ECS exhaust source 831 may be sufficient, however, occasional short duration events requiring additional power may require switching to ambient air (or enriching the ECS exhaust or ambient air with oxygen). Such short events may include in-flight relighting of conventional gas turbine engines, or anti-icing power when flying through ice forming conditions. This is an example where enabling a user to control the air source for the fuel cell system 801 may be very beneficial.

[0107] Additionally, when operating in a polluted environment, it may be beneficial to switch from ambient air to ECS air (enriched with oxygen or otherwise). Fuel cell membranes are very sensitive to particulate and chemical contamination. Filters are typically used as protection for the fuel cell membranes. However, if operation is required in an atmosphere of very high contamination (such as volcanic ash clouds, etc.) that could overwhelm the filters, it would be advantageous to allow a controlled switch from ambient air to an air source that does not come from the surrounding polluted environment. In such an example, ECS air with enrichment with oxygen or otherwise may be used.

[0108] Reference now Fig. 9 , showing something like Figure 8 The propulsion system 900 of the propulsion system 800 is shown in FIG. 9A. Reference numerals for similar components of the propulsion system 900 will be Figure 8 Reference numerals are used in the drawings wherein the numerals are increased by 100. For the sake of convenience, a complete description of similar components may not be provided.

[0109] The propulsion system 900 includes a fuel cell system 901. The system 900 has two shafts 921 and 951, each shaft having a compressor 920, 950, a motor / generator 922, 952, and a turbine 924, 954. Figure 8 As with the illustrated device 800 , compressor 920 is coupled to motor / generator 922 and fuel cell system 901 .

[0110] The compressor 950 of the low pressure shaft 951 is connected to the electric motor / generator 952 and the boost fuel cell system 902. In the device 900, there are two fuel cell systems 901, 902. Therefore, in use, at takeoff, when more power is required from the device 900, both fuel cell systems 901, 902 can be operated.

[0111] Although both fuel cell systems 901, 902 are fed from the air intake 930, one may be fed from the ECS source and the other from the air exhaust source. As described above for other examples, each may be enriched by an oxygen source. The fuel cell systems 901, 902 may be controllably operated so that additional power may be provided when needed (e.g., during takeoff). When such additional power is not needed, the additional fuel cell may be deactivated.

[0112] Similarly, in an arrangement where the shaft 951 that would normally be "used for low pressure flow of the fuel cell system 2" is not activated, such as at sea level where the air pressure is such that the "low pressure" shaft 951 is not needed, the "low pressure" shaft 951 can be operated to provide additional power for thrust, such as during takeoff. Advantageously, this utilizes the shaft 951 that would "normally" be used for low pressure at a higher pressure. This improves the overall efficiency of the device 900, as the "low pressure" shaft 951 is not a dead weight during takeoff.

[0113] In the arrangement 900, the second fuel cell system 902 may not be operated during cruise, and the user may run the two compressors 920, 950 in series for cruise power. Such an arrangement effectively uses the balance of the power generation equipment to produce cruise power and uses the same balance of the power generation equipment to produce twice the power at sea level, as required during takeoff and climb conditions. Thus, such an arrangement 900 is particularly suitable for providing thrust according to the inherent mechanical requirements in flight.

[0114] The fuel cell stacks in the fuel cell systems 901, 902 may not be the same size. The stacks may be load balanced to best provide power for a particular use of the system 900. For example, if the system 900 is used in an aircraft, one fuel cell system 901 may be smaller than the other fuel cell system 902 (or vice versa). In this way, the system 900 may be arranged to have minimal impact on the space required to accommodate the system 900.

[0115] The size of the fuel cell stacks in the fuel cell systems 901, 902 may alternatively be very similar. The benefit of having two fuel cells built to almost the same specifications and both operable with air is that the overall development cost, including life costs (due to maintenance repairs and overhauls), will be reduced. The fuel cell stack life is approximately 3000 to 20000 hours. If used in an aircraft, the aircraft life can be in the region of 90000-180000 hours. Therefore, a large number of stack changes (refurbishment or new parts) are required. If two identical stacks are used, these stacks can be used alternately and provide further redundancy in the event of an operational failure, etc. Due to the short operation of the second stack, if these stacks are used alternatively, the time between overhauls can be almost doubled. This approach requires doubling the water and air pipes, including valves, to select this configuration. Further prognostic performance will enable these stacks to be used preferentially until both are aged and need to be replaced.

[0116] The additional fuel cell system 902 may not require additional power plant balancing, or at least limited additional power plant balancing, which in turn increases the specific power output. The fuel cell system 902 may be about 50% of the mass of the system 900, which may result in an increase of about >30% in the overall specific power of the system 900 (e.g., about 2 kW / kg for a 1.5 kW / kg base system).

[0117] In some figures, an air inlet is shown, while in other figures, an ECS exhaust is shown. It is not required that the type of air supply components shown in the examples be strictly followed. Where an air inlet is shown in the figures, this can be substituted with an ECS supply and vice versa. The advantages of using ECS ​​air have been mentioned previously and are no need for compression (as ECS air is already slightly compressed) and a higher O2 content. Furthermore, as mentioned above, any source can be enriched with oxygen.

[0118] Reference now Fig.10 , showing something like Fig. 9 The propulsion system 1000 of the propulsion system 900 is shown in FIG. 1 . Reference numerals for similar components of the propulsion system 1000 will be as in FIG. Fig. 9 Reference numerals are used in the drawings wherein the numerals are increased by 100. For the sake of convenience, a complete description of similar components may not be provided.

[0119] Propulsion system 1000 includes a fuel cell system 1001. System 1000 has a shaft 1021 with a compressor 1020, a motor / generator 1022, and a turbine 1024. Fig. 9 As with the illustrated device 900 , the compressor 1020 is connected to both the motor / generator 1022 and the fuel cell system 1001 .

[0120] The device 1000 also includes a bypass valve 1003 connected to the fuel cell system 1001 and the exhaust 1032. The bypass valve 1003 allows the system 1000 to operate while bypassing the turbine 1024. This is particularly useful in single-shaft systems (such as Fig.10 ), whereby in some operating modes, compressor 1020 delivers a higher flow than turbine 1024 is capable of delivering. In this case, bypass valve 1003 can be used to protect turbine 1034 and operate at a higher flow (and higher fuel cell power) than the turbine is capable of delivering.

[0121] Reference now Fig.11 , showing something like Figure 2a The propulsion system 1100 of the propulsion system 200 is shown in FIG. 1 . Reference numerals for similar components of the propulsion system 1100 will be Figure 2a Reference numerals are used in the drawings wherein the numerals are increased by 900. For the sake of convenience, a complete description of similar components may not be provided.

[0122] The propulsion system 1100 includes a fuel cell system 1101. Fig.11In the example shown, the fuel cell system 1101 shows the various elements of the fuel cell stack, heat exchanger, water pump and water tank. The system 1100 has two shafts 1121, 1151, each with a compressor 1120, 1150 and a turbine 1124, 1154. Figure 2a Like the device 200 shown in , the fuel cell system 1101 is connected to both compressors 1120 , 1150 and both turbines 1124 , 1154 .

[0123] The propulsion system 1100 does not have a motor disposed on either of the shafts 1121, 1151. Such an arrangement may be beneficial in the following scenarios. The fuel cell system 1101 may include a medium or high temperature proton exchange membrane (PEM) fuel cell, whereby the cathode outlet flow is sufficiently high energy (e.g., a temperature above about 120 degrees Celsius) that the turbine 1124, 1154 can recover sufficient energy from the outlet flow to power the compressor 1120, 1150 without the use of a motor.

[0124] The same usage can be applied to Figure 3 The device 300 wherein the shaft 351 does not have a motor. It is provided that the fuel cell cathode outlet flow is sufficient to operate the turbine 354 and power the compressor 350 without a motor. However, in Figure 3 In the exhaust flow, Fig.11 In the case of such high energy devices, there is a motor 322 to help operate the compressor 320.

[0125] These arrangements and arrangements similar to those shown above can be expanded to reintroduce the electric machine operating as a generator, as long as the power from the turbine is greater than the power required by the compressor.

[0126] Although the disclosed fuel cell propulsion system is primarily described in terms of aircraft, other vehicles such as spacecraft and submarines may carry oxygen or liquid oxygen for use in the proposed system (in lieu of an air intake or ECS supply). Although this oxygen or liquid oxygen may be carried primarily for other reasons, the integration of the additional oxygen used in the fuel cells of the presently disclosed system will not be mechanically intensive. Alternatively or additionally, these vehicles may advantageously be arranged to provide excess oxygen or liquid oxygen to the fuel cell propulsion system as described herein. Therefore, the disclosed system will advantageously be provided in such a vehicle. Any vehicle that can be propelled by a fuel cell propulsion system such as described herein will benefit from the use of the system disclosed herein.

[0127] The systems disclosed herein may be advantageously used to provide propulsion in a vehicle or system that may benefit from a system that can provide a controllably variable amount of propulsion over a wide range of propulsion values.

[0128] Many advantages are provided by generating power from a fuel cell rather than via a combustion engine. The generation of water instead of harmful gaseous emissions (NOx, CO2, etc.) has obvious related advantages. In addition, the operation of the vehicle can occur at a significantly reduced noise level. In a specific example, due to the lack of high-speed exhaust, the takeoff and landing phases of the aircraft can occur at a significantly reduced noise level. This may occur due to the lower exhaust velocity of the system described herein.

[0129] The operator of the vehicle may also use the provision of additional selectable thrust whenever necessary (by converting the fuel cell power provided by the systems described herein into thrust via electric motors, etc.). This flexibility will enable the pilot to optimize the thrust selection for a phase of flight or sport (e.g., racing along a straight line). These systems may also not limit the operator to a specific fuel cell stack if, for example, a change in thrust is desired at any phase in flight to overcome or accommodate changes in flight conditions.

[0130] Thus, applications for the system may include automotive, space, domestic or commercial, among others.

[0131] Another benefit of using a fuel cell over a combustion engine as disclosed herein is that the formation of microbial colonies that occurs in existing aircraft kerosene fuel tanks is avoided. Cleaning of such tanks currently requires washing with insecticide cleaners, which are somewhat environmentally damaging. In some cases, such cleaning may be after each long-haul flight. Therefore, the reduction in cleaning has further environmental benefits.

[0132] Each example shown and described herein may have a controller or control unit in the system for enabling a user to controllably activate or deactivate elements within the system. Such a control unit can help provide the advantages described in detail above. In an example, the control unit can control the activation or deactivation of a compressor, a turbine, an electric / generator, an air supply source (whether air, ECS, or oxygen or a mixture), or any other component. The selective activation of individual components allows the user to have great control over the overall output of the system.

[0133] A propulsion system is disclosed herein. The propulsion system has a fuel cell system including features as shown in the previous figures, such as a fuel cell stack. An air supply supplies the fuel cell system. A liquid hydrogen supply can be used to provide liquid hydrogen to the fuel cell system including the fuel cell stack. In an example not shown, the system may also include a helium circuit. The helium circuit may include a helium supply for supplying helium and a conduit for holding helium. The helium circuit may be arranged to provide additional cooling for specific parts of the propulsion system. Such parts may include electrical energy conducting parts and any electric / generators.

[0134] In one example, liquid hydrogen interacts with helium from a helium supply. The liquid hydrogen can cool the helium and become gaseous hydrogen. The gaseous hydrogen can then be provided to a fuel cell stack or the like for use in generating electrical energy.

[0135] The fuel cell system provides electrical energy in the form of direct current. The fuel cell system also provides thermal energy in the form of air and water and heat. The electrical energy from the fuel cell system can be provided into the network controller. The current can then be provided to any motor generator devices to provide kinetic energy from the electrical energy to thrusters, etc. to provide motion.

[0136] The helium in the helium loop is cooled by liquid hydrogen. The cooled helium can then provide cooling for direct items, such as cooling of the electrical connections that provide electrical energy from the network controller to any motor-generator devices. The cooled helium can also provide cooling to any motor-generator devices themselves. Helium is advantageous in such a system because it has a lower melting point than hydrogen and can therefore be cooled by hydrogen without the risk of freezing in the conduits holding the helium. Other cryogenic coolants may be used, however, helium is particularly advantageous.

Claims

1. An aircraft propulsion system comprising: A fuel cell device, the fuel cell device comprising at least one fuel cell; an air source, the air source being used to provide air to the fuel cell device; a compressor assembly comprising a first compressor in fluid communication with the air source and a fuel cell of the fuel cell assembly; as well as a turbine arrangement comprising a first turbine mechanically coupled to the first compressor, wherein the first turbine is in fluid communication with the at least one fuel cell, The system is arranged such that, in use, air from the air source flows sequentially to the first compressor, the fuel cell arrangement and the first turbine.

2. The aircraft propulsion system of claim 1, further comprising: an exhaust port for releasing exhaust gas from a propulsion system of the aircraft, Wherein, the exhaust port is in fluid communication with the first turbine. 3 . The aircraft propulsion system of claim 1 , further comprising a first motor or a first generator mechanically coupled to the first compressor and the first turbine.

4. An aircraft propulsion system according to any one of claims 1 to 3, wherein: The compressor arrangement further comprises a second compressor, and The turbine device further comprises a second turbine, wherein the second compressor is mechanically coupled to the second turbine, and The second compressor is in fluid communication with the first compressor, and the second turbine is in fluid communication with the first turbine. 5 . The aircraft propulsion system of claim 4 , further comprising a second motor or a second generator mechanically coupled to the second compressor and the second turbine.

6. The aircraft propulsion system according to claim 4 or 5, further comprising a second fuel cell arrangement, the second fuel cell arrangement comprising at least one fuel cell, At least one fuel cell of the second fuel assembly is in fluid communication with the second compressor and the second turbine.

7. The aircraft propulsion system of claim 6, wherein: The first fuel cell arrangement and the second fuel cell arrangement are optimized for operation at different ambient pressures.

8. An aircraft propulsion system according to any one of claims 4 to 7, wherein: The compressor arrangement further comprises a third compressor, and The turbine device further comprises a third turbine, wherein the third compressor is mechanically coupled to the third turbine, and wherein the third compressor is in fluid communication with the first compressor and the second compressor, and Wherein, the third turbine is in fluid communication with the first turbine and the second turbine.

9. An aircraft propulsion system according to any one of claims 1 to 8, wherein: The air source is a source of at least one of ambient air, environmental control system exhaust, and oxygen.

10. An aircraft propulsion system according to any one of claims 1 to 9, wherein: The mechanical coupling is provided by at least one shaft.

11. The aircraft propulsion system of any one of claims 1 to 10, further comprising at least one of a clutch, a gearbox, an air filter, or a bypass valve.

12. An aircraft propulsion system according to any one of claims 1 to 11, further comprising a control system for controlling selective activation of components within the aircraft propulsion system.

13. A method of generating propulsion for an aircraft, comprising: delivering air from an air source to a first compressor; compressing the air; delivering compressed air to a fuel cell device including at least one fuel cell for generating energy; routing fuel cell output air to a first turbine for operating the turbine; as well as The compressor and the turbine are operated, wherein the compressor and the turbine are mechanically coupled.

14. The method of generating propulsion for an aircraft according to claim 13, further comprising: A motor or generator is operatively coupled mechanically to the first compressor and the first turbine.

15. The method according to claim 13 or 14, further comprising: providing a second compressor and a second turbine, wherein the second compressor and the second turbine are mechanically coupled; and Air is selectively provided to the second compressor and the second turbine.

16. The method according to any one of claims 13 to 15, further comprising: At least one of a clutch or a bypass valve is provided for selectively activating the first compressor and the first turbine or the second compressor and the second turbine.

17. The method according to any one of claims 13 to 16, further comprising: Air is controllably delivered from the air source to an air filter for filtering the air before delivering the air to the fuel cell device.

18. The method according to any one of claims 14 to 17, further comprising: providing a plurality of fuel cell devices, selectively providing air to the fuel cell device, Therein, the fuel cell device is optimized for operation under different ambient pressures.

19. An auxiliary power unit (APU) for use in an aircraft, comprising: A fuel cell device, the fuel cell device comprising at least one fuel cell; an air source, the air source being used to provide air to the fuel cell device; a compressor assembly comprising a first compressor in fluid communication with the air source and a fuel cell of the fuel cell assembly; as well as a turbine arrangement comprising a first turbine mechanically coupled to the first compressor, wherein the first turbine is in fluid communication with the at least one fuel cell, The system is arranged so that, in use, air from the air source flows sequentially to the first compressor, the fuel cell device and the first turbine, and The air source can be selected from a combination of ambient environment, environmental control system exhaust, or oxygen.

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