Aircraft propulsion system, apparatus and method

Abstract

The invention relates to a power unit for an aircraft, comprising: at least one fuel cell; at least two fuel sources for providing fuel to the at least one fuel cell; wherein the first fuel source is a hydrogen supply arranged for providing hydrogen to a first of the at least one fuel cell, and wherein the second fuel source is an air gas supply arranged for providing hydrogen to a second of the at least one fuel cell, the air gas supply is arranged for providing air gas to a first fuel cell of the at least one fuel cell.

Description

Technical Field

[0001] The present invention relates to aircraft propulsion systems and power systems. In particular, it relates to aircraft propulsion arrangements capable of providing controllably variable power levels and thus thrust. Depending on the particular flight phase of the aircraft, different levels of thrust can be delivered to the aircraft. The present invention also relates to auxiliary power units (APUs) and slave power units (SPUs) for aircraft. Background Art

[0002] The gas turbine system of an aircraft 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 about 100% during takeoff. Therefore, there are differences in the power to be delivered by the aircraft propulsion system during different phases of the aircraft's flight.

[0003] Gas turbines generally operate well in this regard because the thrust of the gas turbine engine drops 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. Furthermore, 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 prefer gas turbines for aircraft propulsion arrangements.

[0004] Disadvantages of gas turbine engines include environmental requirements, but, 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 de facto choice for use on aircraft.

[0005] While hydrogen fuel and hydrogen synthetic fuels (synfuels) are occasionally used on aircraft, they are not often used on larger aircraft and are not used at all on passenger aircraft. This is due to the specific power that gas turbines are able to provide compared to the specific power provided by hydrogen systems. For a typical system, a gas turbine can achieve about 5 to 8 kW / kg, while a hydrogen fuel cell system can achieve about 1 kW / kg. Therefore, hydrogen is a reasonable and environmentally friendly option for small aircraft, but is almost completely unavailable for commercial large systems.

[0006] Fuel cells using hydrogen are being investigated, such as proton exchange membranes (PEMs), and recent work has shown that specific power values ​​for such systems could optimistically reach 2 kW / kg within the next 5 to 10 years. Other work suggests that the absolute maximum could be around 1.8 kW / kg. These systems therefore seem unlikely to be used on commercial airliners without significant economic disadvantages.

[0007] The fuel cell can be operated at an over-rated function to provide about 25% greater output for a short period of time. This figure is higher at the beginning of the fuel cell's useful life, but decreases towards the end of the useful life. Due to the mechanism of over-rating, damage to the fuel cell may occur if it is over-rated for a long period of time, and will in any case result in a decrease in the useful life of the fuel cell. However, even with this approach, it is obvious that the significant difference between take-off thrust and top-of-climb thrust cannot be taken into account in a fuel cell propulsion system.

[0008] Therefore, compared with cruising, the aircraft usually needs about twice the power during takeoff and climb. This takeoff and climb phase can last about 5-20 minutes, while the flight time is more than 1 hour (and up to more than 12 hours). In one flight, the total duration of maximum power is about 5 to 30 minutes. The duration of peak power conversion from takeoff to cruising altitude is about <300 seconds (s). The remaining peak power is a risk emergency measure for go-around (in the pre-landing stage) and detour to another airport. The current state of the arrangement structure of the prior art contains such a remaining peak power for about 3 go-arounds and 1 detour to another airport. For vertical take-off aircraft, the peak power used for vertical flight is about three to four times the power required for cruising. The duration of the peak power required for takeoff / landing and conversion between flight modes can be about 15 to 60 seconds, with a total time of less than 120 seconds, but this may depend on the specific requirements of the operation.

[0009] In order to conserve hydrogen fuel, fuel cell systems are typically designed to consume hydrogen, resulting in up to 50% air (and therefore oxygen) waste. While this may have the benefit of low mass heat dissipation due to reaction into air, it requires greater compression power (almost twice) and thus increases parasitic losses, with compression accounting for between 15-45% of fuel cell power and being the most significant parasitic power loss. Considerations regarding the cathode size of the stack take into account the required oxygen reaction rate, with O2 accounting for approximately 20% of atmospheric air.

[0010] Oxygen can be used in fuel cells, however, oxygen has 16 times the mass of hydrogen and requires an 8:1 ratio (for H20). Therefore, carrying oxygen on board aircraft is not considered economically efficient for flying.

[0011] Therefore, developments can be made in this area and advantages can be gained from such developments. However, the inventors of the invention described herein have created an alternative propulsion arrangement having a wide range of previously unavailable advantages, as described herein. Summary of the invention

[0012] Various aspects of the invention are set out in the accompanying claims.

[0013] From a first aspect, there is provided a power unit suitable for an aircraft, comprising: at least one fuel cell; at least two fuel sources, the at least two fuel sources being used to provide fuel to the at least one fuel cell; wherein the first fuel source is a hydrogen supply source, the hydrogen supply source being arranged to provide hydrogen to a first fuel cell among the at least one fuel cell, and wherein the second fuel source is an air gas supply source, the air gas supply source being arranged to provide air gas to a first fuel cell among the at least one fuel cell.

[0014] Providing hydrogen and an air source to the fuel cell enables the fuel cell to be operated to output efficient electrical power. The fuel cell does not produce emissions in the way that an internal combustion engine might. In this way, the use of such a power unit provides cleaner energy production for the generation of thrust, for example, for flight. The thrust may be provided by the power output of the power unit of the first aspect.

[0015] In one example, a power unit is provided, wherein the at least one fuel cell comprises a first fuel cell and a second fuel cell, and wherein the third fuel source is an oxygen supply source arranged to provide oxygen to the second fuel cell. In one example, a power unit is provided, wherein the hydrogen supply source is further arranged to provide hydrogen to the second fuel cell.

[0016] The arrangement provides a second fuel cell operating on a higher percentage oxygen supply. Oxygen as an oxidant acting as a fuel and hydrogen as a reactant acting as a fuel are combined in the second fuel cell to provide a high energy output fuel cell. The high energy output is aided by the use of high purity oxygen and high purity hydrogen.

[0017] Thus, the arrangement has a medium energy output fuel cell operating on high purity hydrogen and air, and a high energy output fuel cell operating on high purity hydrogen and high purity oxygen, which when operated together with the medium energy output fuel cell can provide a boost in power output, etc. The arrangement is particularly useful in systems with power requirements that vary significantly over time. This is the case in systems or vehicles that require thrust changes over various phases of travel, such as an aircraft during takeoff and climb, or a race car on the straight section of a racetrack. The two fuel cells also have emissions-based advantages over conventional combustion engines.

[0018] In one example, a power unit is provided, wherein the air gas supply source is further arranged to provide fluid communication of air gas between the air gas supply source and a second fuel cell. In one example, a power unit is provided, wherein the oxygen supply source is further arranged to provide oxygen to the first fuel cell.

[0019] This arrangement provides a selective powering function for the first fuel cell. By controlling the ratio of high purity oxygen and air used for the fuel in the first fuel cell, the operator can have more control over the power provided from the power unit. In this way, the user has a more flexible arrangement for the power provided from the power unit, and can therefore customize it to suit the situation it finds itself in. For example, maximum power output can be provided by providing high purity oxygen to both fuel cells, while standard power output can be provided by providing air and oxygen to the first fuel cell. In this way, the user has additional control over the "boost" function of the fuel cell within the power unit.

[0020] In one example, a power unit is provided, wherein the system further includes: at least one compressor for compressing a fuel source among the at least two fuel sources, wherein a first compressor among the at least one compressor and a fuel source among the at least two fuel sources are arranged such that fuel from the fuel source is delivered to the compressor before being provided to a fuel cell among the at least one fuel cell.

[0021] Compression of the fuel supplied to the fuel cell can increase the power output of the fuel cell. Again, by compressing the fuel source, a greater amount of, for example, hydrogen or oxygen can be supplied to the fuel cell, thereby providing the user with a greater level of control over the electrical output of the fuel cell. Combined with the above advantages, this arrangement significantly increases the level of control the user has over the power output of the power unit.

[0022] In one example, a power unit is provided, wherein the oxygen supply source is arranged to be in fluid communication with a second compressor of the at least one compressor, and the oxygen supply source is arranged to: provide oxygen to a second fuel cell; provide oxygen to a second compressor; and provide oxygen to a first fuel cell. In one example, a power unit is provided, wherein the oxygen supply source is arranged to provide uncompressed oxygen to the second fuel cell and compressed oxygen to the first fuel cell.

[0023] This arrangement provides a wide range of combinations of compressing oxygen and providing oxygen to the fuel cell for the user to use as required. Again, each of these steps increases the user's overall control over the output of the power unit. In this way, the power unit can be used to provide the power best suited to the requirements at the time. As mentioned above, this is particularly effective in transportation and vehicle settings.

[0024] This controllable power output makes the use of fuel cells very attractive in areas of technology dominated by combustion engines. In this way, previous disadvantages of using fuel cells are overcome, and this, in turn, reduces the environmental impact of providing power in vehicles, since conventional fuels can be replaced by environmentally friendly fuels without compromising performance.

[0025] In one example, a power unit is provided, comprising a control unit for supplying fuel from the at least two fuel sources to the at least one fuel cell, wherein the second fuel cell can be selectively activated by selectively supplying fuel to the second fuel cell.

[0026] This arrangement provides the user with greater control when operating the power unit.

[0027] In one example, a power unit is provided wherein a first fuel cell and a second fuel cell are arranged to use a common auxiliary device.

[0028] This arrangement provides a power unit that uses the same auxiliary equipment for both fuel cells. Auxiliary equipment refers to the supporting components and auxiliary systems of the power unit that are required to deliver energy from the power unit. Therefore, in a power unit with one fuel cell, the unit requires a certain number of components to function properly. When the same infrastructure can be used for the second fuel cell, it is most efficient from a weight and electrical perspective to include a second fuel cell. In examples, the second fuel cell may require some minor additional components, so the same auxiliary equipment can be used, or only a small amount of additional auxiliary equipment is required for the second fuel cell. This makes this power unit particularly effective in providing a "boosted" fuel cell to a system at a very low weight cost.

[0029] In one example, a power unit is provided, comprising: a liquid heat exchanger arrangement structure for exchanging heat with at least one fuel cell, the liquid heat exchanger comprising a fluid arranged to be thermally connected to the at least one fuel cell at at least one point in the liquid heat exchanger arrangement structure; and a low-temperature heat exchanger arrangement structure, the low-temperature heat exchanger arrangement structure being arranged to be thermally connected to the fluid at at least one point.

[0030] This arrangement provides a very efficient heat exchange function for the various components in the system. Due to the presence of the cryogenic heat exchanger, the liquid in the heat exchanger can be kept at a very low temperature, thereby improving the electrical efficiency of the fuel cell through the cold fluid in the liquid heat exchanger.

[0031] In an example, a power unit is provided, wherein the third fuel source is a liquid oxygen supply, and the third fuel source is arranged to provide oxygen to the cryogenic heat exchanger arrangement.

[0032] This arrangement provides highly efficient heat exchange functions for the various components of the system. In particular, in systems where cryogenic oxygen is present, the use of cryogenic oxygen in the exchange of thermal energy provides high electrical efficiency through highly improved component cooling.

[0033] In one example, a power unit is provided wherein the third fuel source is arranged to: provide liquid oxygen to the low temperature heat exchanger arrangement to cool the fluid; and provide gaseous oxygen from the low temperature heat exchanger arrangement to the at least one fuel cell.

[0034] This arrangement provides a highly efficient heat exchange function for various components in the system. In particular, where cryogenic oxygen is present and used in an electrical power generation system, the use of cryogenic oxygen in heat exchange prior to introduction into the fuel cell provides a synergistic effect with high electrical efficiency, both from cooling the components and from improved performance of the fuel cell.

[0035] In one example, a power unit is provided, wherein the liquid heat exchanger arrangement includes a fluid conduit and a liquid heat exchanger, through which a fluid can flow, and wherein the low-temperature heat exchanger arrangement includes a refrigerant conduit and a low-temperature heat exchanger, through which a refrigerant can flow.

[0036] This arrangement provides for careful and controlled delivery of the fluid for cooling and the refrigerant for cooling and which is subsequently delivered to the fuel cell.

[0037] In one example, a power unit is provided, wherein the air gas supply source is an environmental control system exhaust, or ambient air.

[0038] By using the described environmental control system exhaust, a higher percentage of oxygen can be provided to the fuel cell than using air. The ambient air can be compressed to provide a similarly higher percentage of oxygen fuel to the fuel cell. This provision is controllable to allow a temporary increase in the electrical output of the fuel cell during a desired period. This temporary increase in electrical output can be referred to as a boost period.

[0039] In one example, a power unit is provided, wherein the hydrogen supply source is a hydrogen supply source for providing hydrogen, the hydrogen supply source being arranged to provide hydrogen to a first fuel cell of the at least one fuel cell. The hydrogen may be provided as a compressed gas, may be retained in a storage as a liquid, and then used for evaporation in a heat exchange process, and then provided to the fuel cell as gaseous hydrogen. When provided to the fuel cell, this gaseous hydrogen may still have a relatively low temperature, or have a temperature that is most suitable for the usage scenario and the efficiency of the fuel cell.

[0040] From another aspect, a power unit is provided, which includes: at least two fuel cell stacks; at least two fuel sources for providing fuel to the two fuel cells; wherein the first fuel source is a hydrogen supply source, which is arranged to provide hydrogen to each of the two fuel cells; and wherein the second fuel source is an air gas supply source, which is arranged to provide air gas to each of the two fuel cells.

[0041] Viewed from another aspect, there is provided an aircraft propulsion system comprising the power unit of any earlier aspect or example.

[0042] The use of such power units in aircraft propulsion systems is particularly beneficial, as the controllable power output takes very good account of the differences in power required between the take-off, climb and cruise phases of flight. In addition, the environmental advantages of using clean fuels over burning fuels reduces the environmental cost of a popular and increasingly used method of transportation.

[0043] From another aspect, a method for providing variable power for use in an aircraft is provided, comprising: providing a first fuel from a first fuel source to a first fuel cell, wherein the first fuel source is a hydrogen supply source for providing hydrogen to the first fuel cell; providing a second fuel from a second fuel source to the first fuel cell, wherein the second fuel source is an air gas supply source, and the air gas supply source is used to provide air gas to the first fuel cell; activating the first fuel cell to use the hydrogen and the air gas to provide power; providing hydrogen from the hydrogen supply source to a second fuel cell; providing a third fuel from a third fuel source to the second fuel cell, wherein the third fuel source is an oxygen supply source, and the oxygen supply source is used to provide oxygen to the second fuel cell; and selectively activating the second fuel cell to provide additional power.

[0044] As mentioned above, providing variable power for an aircraft is particularly beneficial because the controllable (variable) power output takes very good account of the power differences required between the take-off, climb and cruise phases of flight. In addition, there are environmental benefits as mentioned above.

[0045] In one example, a method is provided in which a second fuel cell is selectively activated during a takeoff phase and a climb phase of aircraft flight. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 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:

[0047] Figure 1 A schematic diagram of a fuel cell propulsion system according to an example of the present invention is shown;

[0048] Figure 2 A schematic diagram of a fuel cell propulsion system according to an example of the present invention is shown;

[0049] Figure 3 A schematic diagram of a fuel cell propulsion system according to an example of the present invention is shown;

[0050] Figure 4 A schematic diagram of a fuel cell propulsion system according to an example of the present invention is shown;

[0051] Figure 5 A schematic diagram showing a fuel cell propulsion system according to one example of the present invention; and

[0052] Figure 6 A schematic diagram showing a fuel cell propulsion system according to one example of the present invention; and

[0053] Figure 7 A schematic diagram of a fuel cell propulsion system according to one example of the present invention is shown.

[0054] Any reference to prior art documents in this specification should not be regarded as an admission that such prior art is widely known or forms part of the common general knowledge in the field. "Comprise", "comprising" and similar words used in this specification 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 in conjunction with the following examples. It will be understood that the claimed invention is not intended to be limited in any way by these examples. It will also be recognized that the present invention includes not only a single embodiment, but also a combination of these embodiments described herein.

[0055] The various embodiments described herein are presented only to aid in understanding and teaching 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 should not be regarded as limitations on the scope of the invention as defined by the claims or limitations on the equivalents of the claims, and other embodiments and modifications may be used without departing from the spirit and scope of the claimed invention. Various embodiments of the present invention may appropriately include, consist of, or consist essentially of appropriate combinations of elements, components, features, parts, steps, devices, etc. other than those specifically described herein. In addition, this disclosure may include other inventions that are not currently claimed but may be claimed in the future. DETAILED DESCRIPTION

[0056] The invention described herein relates to the generation of propulsion for an aircraft and power system. A particular engine system of an aircraft includes a plurality of fuel cells. The generation of propulsion is controllably variable so as to provide additional power during phases of flight where additional power is required. Additional power may be provided during takeoff / climb, but not during cruise. The invention described herein relates to the generation of power by an auxiliary power unit (APU), which may be designed to provide a plurality of necessary functions for an aircraft. The APU may be small and provide only electrical power for the aircraft (typically slave or emergency power), or may be larger in size so as to provide propulsion as an alternative or in addition.

[0057] The present invention provides many creative strategies that enable oxygen to be used more efficiently in a fuel cell propulsion system, or that enable oxygen enrichment to be used in a fuel cell propulsion system. The fuel cell operates by providing a portion of hydrogen and a portion of oxygen (e.g. from the air) as reactants and oxidants, respectively, to the fuel cell. The fuel cell uses these to provide electrical energy. Here, these are generally referred to as "fuels" provided to the fuel cell, that is, hydrogen and oxygen are referred to as "fuels". The term "fuel" as used in the first sense is as a reactant, and the term "fuel" as used in the second sense is as an oxidant. The term is generally used to refer to a substance that changes in some way in a process that may produce usable energy, for example, converting hydrogen and oxygen into water when releasing electrical energy.

[0058] Oxygen sources that can be used to provide oxygen in a fuel cell propulsion system (e.g., in an aircraft arrangement) include an environmental control system (ECS), which obtains oxygen (O2) by enriching ambient air or via the use of a dedicated (or other) oxygen source. The oxygen source can be a liquid oxygen source (LOx). Advantageously, liquid oxygen has a low spatial density compared to oxygen in the gas phase, so the use of LOx in any of the systems described herein has an associated capacity advantage. Specifically, the volume density of LOx is superior to oxygen in gaseous form. Organic carrier oxygen is often carried on aircraft, and oxygen is a byproduct of the electrolysis process of producing hydrogen (H2) from water. Bottled onboard oxygen is carried on many current aircraft, and these bottles of onboard oxygen can be used in the case of cabin decompression (possibly due to window bursting, etc.). The amount stored is suitable for covering the period before being able to achieve a descent to a safe altitude. When passengers use drop-down oxygen masks, for example, crew members can use portable oxygen bottles. Therefore, current aircraft usually have oxygen generators, or more commonly have onboard gaseous oxygen tanks.

[0059] By using a control law, additional power can be provided from a fuel cell arrangement where, in the process, oxygen (O2) is utilized and H2 is consumed (which can be recycled back into the system and thus reused). This arrangement can achieve one advantage involving the benefit that the mass of H2 is lower, being 1 / 16 of the mass of O2 and a factor of 1 / 8 in the reaction with H2O. The volume and mass of H2 are such that a small increase in mass and volume is relatively minor in the design. Recirculation of H2 is also easier to achieve and beneficial because there is no need to handle oxygen-depleted air. Another advantage is that if air is released from the aircraft (overflowing overboard), energy is not wasted on compression. By using oxygen and hydrogen, the only waste from the fuel cell is water, rather than nitrogen etc. produced by using air.

[0060] Other methods for controllably providing additional power are shown in the following figures.

[0061] Reference now Figure 1 , shows a propulsion system 100 including a fuel cell stack 110. The fuel cell stack 110 is connected to a H2 supply source 112 via an H2 supply line. The hydrogen portion is labeled portion 102.

[0062] Although a hydrogen supply source will be used in all examples shown herein, the proposed propulsion system can use alternative suitable fuels, such as reformed hydrocarbons, etc. The hydrogen supply source can include 100% hydrogen or a lower percentage of hydrogen. Common hydrogen sources can have small amounts of impurities, such as carbon monoxide (CO), carbon dioxide (CO2), nitrogen dioxide (N2), hydrogen sulfide (H2S), but preferably hydrogen with a purity of about 99.99% or higher.

[0063] .The propulsion system 100 has a compressor 120, a 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 130. The ECS exhaust supply 130 may be enriched by an oxygen concentrator. This enrichment may occur before or after the oxygen reaches the air supply 130 in the process. The turbine 124 is connected to a cathode exhaust port 132. This air / exhaust portion is labeled as 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 enriched with oxygen in some way) for the fuel cell stack 110.

[0064] 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 126 may be optional depending on the temperature limit of the fuel cell stack 110 and the temperature of the air after being compressed by the compressor 120. The fuel cell stack 110 is connected to a 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 labeled as portion 106.

[0065] The examples shown herein are water-cooled fuel cell stack systems. 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 for the cathode air supply source. Therefore, although not explicitly shown, these features can be included in the present arrangement. In addition, the present arrangement can be used for evaporatively cooled fuel cell stacks.

[0066] In fact, the condensing heat exchanger 128 may be optional for high power stages where no condensed water is extracted. Instead, the humid air may be sent off-board ("overflow") or stored in an intermediate container until it can be sent off-board. In this way, in this arrangement, the pressure losses inherent in the use of the condensing heat exchanger 128 will not be included, which results in a higher performance system (in the form of more power). To compensate for this off-board overflow of the humid air, a slightly larger water storage tank may be used.

[0067] exist Figure 1 In the arrangement shown, the propulsion system 100 uses ECS air through an oxygen concentrator. There are many advantages that derive from this arrangement.

[0068] 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 ambient air outside. Using a higher percentage of O2 during a period 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. As a result, many current fuel cell systems waste air and consume H2 to the maximum. This is inevitable when using ambient air, because about 21% of the O2 (such as O2 in the air) will become depleted and may starve the fuel cell of oxygen. This is not the case when using an oxygen supply system. In the reactant ratio, O2 is 4 times heavier than H2, and therefore, if waste is to occur, it makes more sense to waste H2. This is further demonstrated because much more H2 is stored than O2, and therefore, the change in mass at the system level (particularly the tank mass) is lower. In addition, and advantageously, in the case of high power of the cryogenic cooling system, this arrangement allows more available heat dissipation in the liquid hydrogen.

[0069] The source air requires less compression than the outside ambient air (which may be lower at altitude). Our estimates suggest that the compression is about 3 times, rather than 9 times, the compression that would be required for ambient air. This is because the source air may come from cabin air that has been pressurized, and because the air may be enriched with oxygen. Enrichment with oxygen results in less air being required, and therefore, less compression being required.

[0070] Additional advantages can be obtained from the lower temperature air from the air source compared to compressed ambient air. In an arrangement in which the heat exchanger 126 is omitted, there is no pressure loss associated with the inclusion of 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 an equivalent stack temperature (relative to the equivalent temperature of an arrangement including the heat exchanger 126). Thus, omitting the heat exchanger 126 may be beneficial because it can enable the fuel cell stack 110 to operate at a higher power.

[0071] An oxygen concentrator may be used to increase the O2 ratio in the air supplied in portion 104, or an oxygen concentrator may be used to supply pure oxygen to the system 100. As previously described, the use of a higher ratio of O2 in the air supply 130 of the fuel cell stack 100 enables greater power output from the fuel cell stack 10 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 (due to the greater power output per unit size of the present fuel cell stack 110 arrangement).

[0072] In the case of using liquid oxygen from an oxygen supply source (such as a tank), the specific heat of vaporization and specific heat capacity of oxygen can be used to cool the components of the propulsion system 100. Due to the lack of eddy currents, for example, the cooling of electrical components will increase the gain. In addition, the use of pure oxygen in the system 100 can enable the use of a smaller fuel cell area, and therefore a smaller and lighter battery stack 110. This brings efficiency benefits because, for example, an aircraft needs to carry a large number of battery stacks in use. Compared with a heavier system, the lower the mass of the battery stack, the less fuel is required to take into account the mass.

[0073] Liquid oxygen enables lower inlet temperatures for the oxidant, which in turn enables the fuel cell stack 110 to operate at potentially higher heat dissipation and therefore higher power. Further advantages include that since the only gas content is oxygen, this oxygen can be completely consumed. For air systems, typically only 50% of the oxygen is consumed because the system must ensure that there is enough O2 for the fuel cell stack, so an oversupply of oxygen is preferred.

[0074] exist Figure 1 In the example shown, the fuel cell stack 110 needs to operate well in both cases as the more significant advantage relates to increased stack power (before considering parasitic losses, i.e. turbine compressor, pumps, etc.) and net power, rather than the slightly less significant advantage associated with sizing the stack 110 .

[0075] 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 the external air intake element. This drag benefit translates into a benefit associated with the energy requirements of system 100 as a whole; it will be appreciated that system 100 will need to provide more thrust to accommodate an element that may provide additional drag. By eliminating the need for this element, system 100 is more efficient.

[0076] Alternatively, an air inlet may be included and have a fixed geometry in size and shape. The air inlet may be larger during takeoff and climb, and smaller during cruise. This may have the effect that the air inlet overflows during cruise, or the excess is consumed by the system and discharged overboard. This may use more energy during cruise, and is a heavier (i.e., more massive) solution than without an air inlet. Another alternative is that the air inlet has a variable geometry, with its size varying between different flight phases. However, this solution is technically more complex and is generally heavier than a fixed area air inlet.

[0077] In the present system, the use of fixed thresholds is beneficial because there is no undesirable performance loss between takeoff and cruise as in other systems.

[0078] Reference Figure 2 , a propulsion system 200 is shown. Figure 2 The system 200 shown in FIG. Figure 1 The systems 100 in FIG. 1 share many components. Figure 2 The same or similar components are shown in Figure 1 , and increase the number by 100. So, for example, Figure 1 The system 100 is similar to Figure 2 The system 200 in FIG. 1 is a system 200. For the sake of brevity, not all components will be discussed and identical components will be omitted from the discussion.

[0079] Figure 1 and Figure 2 The fuel cell stack layout structures are different. Figure 1 The fuel cell stack 110 in the system 100 is the central single stack of the system 100 (although in Figure 1 In the arrangement, it is not necessary to have only one fuel cell stack). Figure 2 In the system 200, there are two fuel cell stacks 210, 211. In the system 200, the fuel cell stack A 210 is arranged toward the compressor 220, the motor / generator 222 and the turbine 224 of the air / exhaust section 204. The fuel cell stack B is arranged toward the water tank 240, the water pump 242 and the heat exchanger 244 of the water section 206. Although not explicitly shown, the system may include a regulating element, such as a controller, etc., which regulates the supply of water and hydrogen from the supply source to the two fuel cell stacks 210, 211 shown. The regulation will be performed according to the power and cooling requirements of each fuel cell stack 210, 211. The regulation may include a feedback sensor or detector for reading the characteristics of the fuel cell stacks 210, 211.

[0080] Figure 1 The ECS exhaust supply source 130 has been changed to Figure 2 The air supply source 230 in the system 200. Figure 2 The system 200 does not necessarily utilize Figure 1The ECS exhaust of system 100 is not present, but it can utilize that ECS exhaust. The advantages of using ECS ​​air have been mentioned previously, including no compression required (because the ECS air is already compressed to some extent) and higher O2 content. Air supply source 230 is connected to compressor 220, which is connected to heat exchanger 226 and motor / generator 222. Heat exchanger 226 is connected to fuel cell stack A 210. Motor / generator 222 is connected to turbine 224, which is connected to cathode exhaust port 232 and heat exchanger / condenser 228. The heat exchanger / condenser 228 is connected to fuel cell stack A 210 and fuel cell stack B 211. These elements are part of the air / exhaust portion 204 of system 200. However, in Figure 2 In a variation of the example shown, the second exhaust line connecting the heat exchanger / condenser 228 to the fuel cell stack B 211 can be removed. In this arrangement, we have the advantages associated with the oxygen stack, which will be referred to below. Figure 5 For a more detailed explanation.

[0081] The water section 206 is connected to the fuel cell stacks 210, 211. The water section 206 has a water tank 240, a water pump 242, and a heat exchanger 244. The water section 206 can remove water generated during operation of the fuel cell and provide water back to the fuel cell for cooling. For systems where the water loop is used only for cooling, another cooling medium, such as oil or refrigerant, can be used.

[0082] Although the heat exchanger 244 is Figure 2 A single heat exchanger is shown in FIG, but two or more heat exchangers may be used in this arrangement. Figure 2 In a variation of , each fuel cell stack 210, 211 has a heat exchanger. A separate heat exchanger for each fuel cell can be advantageous because fuel cells can have different temperatures and amounts of steam. Thus, an exchanger designed for a particular fuel cell and the characteristics of that fuel cell can be more effective than an exchanger designed as a compromise between the idealized conditions of a variety of different fuel cells. Figure 2 In another variation, there is an additional heat exchanger for pre-cooling the steam from fuel cell stack A 210 before it enters the heat exchanger 244.

[0083] exist Figure 2In another variation, during the high power operating mode, rather than using a heat exchanger, water is collected or discharged from at least fuel cell stack A 210 (and possibly fuel cell stack B 211) to the outside of the aircraft. An advantage associated with collecting or discharging water is that no cooling is required, as such cooling would most likely use an air intake that would need to be included in any aircraft design in order to be used with such an arrangement, and would therefore increase the drag of the aircraft design. Discharging to the outside of the aircraft results in additional considerations, such as when to discharge, and therefore it may be useful for the water to be collected in a tank prior to discharge. Advantageously, this allows the user to control when and where the water is discharged to the outside of the aircraft. Using a tank allows the user to avoid water splashing onto areas such as runways, taxiways, or airport gates. Such control may allow for avoidance of water spraying onto populated areas that may be located below the flight path.

[0084] This is easier to achieve in system 200 because fuel cell stack B 211 does not need to be connected to heat exchanger 244. For systems 200, 300, 400, 500, and 600 (eg, Figures 2 to 6 For all arrangements (shown), the heat exchanger 244 can be sized for water flowing overboard in cruise-only conditions (i.e., where only one fuel cell stack - typically fuel cell stack A 210 - needs to be operated) and in dual power conditions (where both fuel cell stacks are operated, or to provide a special over-rated arrangement).

[0085] Preferably, the water level in the system remains substantially constant throughout use. Thus, if water is removed from the system, as is the case in one of the examples above, water produced using the fuel cell stacks 210, 211 may be introduced into the system so that the water level remains substantially constant throughout. The amount of water required in the system may be calculated so that the quality of that water is optimized by minimizing the amount of water required to allow full operation of the system, thereby improving efficiency by avoiding carrying unnecessary mass.

[0086] There is a hydrogen supply source 212 connected to the two fuel cell stacks 210, 211. The hydrogen supply source 212 is a part of the hydrogen section 202. Hydrogen is supplied to the two fuel cell stacks 210, 211 for fuel cell reactions.

[0087] Additionally, in the system 200, an oxygen supply source 214 is provided that is connected to the fuel cell stack B 211. Advantageously, the oxygen in the oxygen supply source 214 may be liquid oxygen. As previously described, the use of liquid oxygen has advantages in terms of volume density. An additional benefit of using this arrangement may be that the fuel cell stack B 211 may be used as an evaporator to help increase the temperature of the oxygen for input into the fuel cell stack B 211. Additionally, the oxygen may be used to cool the coolant (in the Figure 2In this way, the coolant is more effective in its function of dissipating heat.

[0088] In one example, the liquid oxygen may be warmed prior to input into fuel cell stack B 211. The heat energy used to warm the liquid oxygen in oxygen supply 214 may be obtained from a fluid that dissipates heat from either fuel cell stack A 210 or fuel cell stack B 211 (or from both fuel cell stacks). Figure 2 In the example of FIG. 1 , the fluid that dissipates heat from the fuel cell stack is water flowing in the water portion 206 including the water tank 240, the pump 242, and the heat exchanger 244. The path of the water portion 206 and the path of the oxygen portion 208 overlap, and thus heat exchange can occur. These paths can be arranged as Figure 2 The overlap shown in the example of is greater to provide more efficient heat exchange. In one specific example, the liquid oxygen can be warmed to 325 Kelvin before being injected into the stack. This can provide a significant improvement over a typical heat exchanger alone and can be used in series with, or in place of, a typical heat exchanger. This improved heat transfer has been shown to be around 12% compared to a conventional heat exchanger.

[0089] A dedicated heat exchanger may be introduced into the arrangement disclosed herein that uses liquid oxygen as a source for removing thermal energy. Such a heat exchanger may be referred to as a "cryogenic heat exchanger" where, in one example, the incoming warmed liquid coolant is pre-cooled by the outgoing cryogenic liquid oxygen (LOx).

[0090] LOx can be stored at a temperature of about 90 Kelvin, etc., and can be arranged to absorb sufficient thermal energy to bring the temperature to about 325 Kelvin. LOx flowing into the low temperature heat exchanger removes more heat from the fuel cell stack and can also change the stoichiometric ratio of oxygen (O2) in the air inlet, further improving the performance of the stack.

[0091] The arrangement disclosed herein can be used in aerospace applications, such as aircraft, and can therefore be used at high altitudes. Continuous power loss due to a reduction in air density (particularly O2) can be a problem in the use of efficient fuel cells. Injecting a higher concentration of O2 air into the cathode can alleviate these problems. In a specific example, enrichment of the O2 concentration in the inlet air is an effective method for improving the overall efficiency of the fuel cell stack. The current arrangement of the low-temperature heat exchanger provides a huge overall improvement in fuel cell performance by providing efficient heat dissipation and synergistically improved fuel cell O2 concentration. Both of these contribute to greatly improving the electrical efficiency provided by the present low-temperature heat exchanger. This arrangement can also be used for high-temperature fuel cells.

[0092] Oxygen is delivered via the oxygen portion 208 of the system 200. Delivering oxygen to the fuel cell stack B 211 enables the fuel cell stack B 211 to operate at a higher power output than when only ambient air with a lower percentage of oxygen is used. Therefore, the oxygen supply source 214 provides additional oxidant to the fuel cell stack B 211 to provide additional power. The oxygen supplied to the fuel cell stack B 211 can be supplied at a lower temperature than air. This results in the fuel cell stack B 211 requiring less cooling to achieve the same power. In turn, this leads to mass savings because less auxiliary equipment (BoP) is required to achieve power equivalent to the fuel cell stack A 210. Therefore, in this arrangement, the system 200 has a standard operating fuel cell stack A 210 and a higher power output operating fuel cell stack B 211.

[0093] Thus, the system 200 can advantageously be used in two main modes. In the first mode, both fuel cell stacks 210, 211 are operating and the system 200 is providing a large amount of power. In the second mode, fuel cell stack A 210 is operating and fuel cell stack B 211 is not operating. This second mode provides a lower amount of power than the first operating mode. Thus, the system 200 provides an arrangement for a fuel cell propulsion system that can controllably provide different levels of power, which can be selected by an operator or by a controller based on environmental conditions. Thus, the system 200 is well suited for use in transportation modes that may require additional power in different parts of the trip, such as aircraft, which require additional power when taking off and do not require such power when cruising.

[0094] When Figure 1 When providing a second fuel cell stack for the system 100, weight needs to be considered. If the weight of the second fuel cell stack is too large, this will result in an inefficient system 200, because during transportation, the first fuel cell stack 210 needs to provide more power to take into account the weight of the second fuel cell stack 211. Therefore, the system 200 can be arranged to carry just enough liquid oxygen during takeoff and climb to provide about 6 minutes of additional power (provided by fuel cell stack B 211). In this way, once cruising, the first fuel cell stack A 210 carries the minimum amount of additional weight, that is, only the required weight, thereby ensuring that the system 200 is as light as possible. This arrangement, that is, fuel cell stack A 210 only has the required fuel and fuel cell stack B 211 does not have any fuel, is still lighter than two conventional fuel cell systems. Therefore, the system 200 is particularly efficient in this arrangement.

[0095] The fuel cell stacks 210, 211 may not be the same size. The stacks may be load balanced to provide optimal power for a particular use of the system 200. For example, if the system 200 is used in an aircraft, the higher operating power fuel cell stack B 211 may be 50-60% smaller than the fuel cell stack A 210. In this way, the system 200 may be arranged to have minimal impact on the space required to accommodate the system 200.

[0096] Thus, the additional fuel cell stack 211 will not require additional auxiliary equipment, or at least limited additional auxiliary equipment, which in turn increases the specific power output. Since the mass of the stack 110 is about 50-60% of the mass of the system 100, this may result in an increase in the overall specific power of the system 200 of about >100% (e.g., about 3.1-4.1 kW / kg for a 1.5 kW / kg base system).

[0097] The benefit of having the second fuel cell stack 211 associated exclusively with an oxygen source (i.e., using pure oxygen or air with a very high oxygen percentage) is that auxiliary equipment can be kept to a minimum for such stack integration. The fuel cell stack 211 will have a sufficiently high power density compared to the baseline case (about 20% of the ratio of the oxidant volume to the cathode volume of air can become 100%).

[0098] Reference Figure 3 , a propulsion system 300 is shown. Figure 3 The system 300 shown in FIG. Figure 2 The systems 200 in FIG. 2 share many components. Figure 3 The same or similar components are shown in Figure 2 , and increase the number by 100. So, for example, Figure 2 The system 200 is similar to Figure 3 300 in the system. For the sake of brevity, not all elements will be discussed and the same elements will be omitted in the discussion.

[0099] and Figure 2 Compared to the system 200 shown, Figure 3 The system 300 has an additional oxygen line from the oxygen source 314 to the first fuel cell stack A 310. Thus, the oxygen source 314 can provide oxygen to both fuel cell stacks 310, 311. The oxygen source can provide cooled oxygen, such as from a liquid oxygen source, which is expanded into both stacks 310, 311. Thus, as described above, the benefits of cooling can be provided to both stacks, thereby enabling the stacks 310, 311 to operate more efficiently.

[0100] Since the percentage of oxygen supplied to the first fuel cell stack A 310 is increased by providing additional oxygen, the first fuel cell stack A 310 operates at a high power. Therefore, this is a solution to obtain a higher net power output from the first fuel cell stack A 310 without using a turbo compressor to provide additional oxygen. By omitting the turbo compressor, the mass of the aircraft propulsion system 300 can be reduced, thereby reducing the amount of fuel required for the system 300 to operate and fly. Therefore, by using Figure 3 The arrangement shown can improve efficiency. Thus, fuel cell stack A 310 can be arranged to operate using air from air source 330 and / or oxygen from oxygen source 314. In this case, it is expected that the specific energy will increase by >100%, for example, for a base system of 1.5 kW / kg, the specific power will be between 3.5-4.7 kW / kg.

[0101] Reference Figure 4 , a propulsion system 400 is shown. Figure 4 The system 400 shown in FIG. Figure 3 The systems 300 in FIG. 3 share many components. Figure 4 The same or similar components are shown in Figure 3 , and increase the number by 100. So, for example, Figure 3 The system 300 is similar to Figure 4 4. For the sake of brevity, not all components will be discussed and identical components will be omitted from the discussion.

[0102] The heat exchanger 426 of the air section 404 is connected to both fuel cell stacks 410, 411. Furthermore, the oxygen supply source 414 of the oxygen section 408 is connected to both fuel cell stacks 410, 411.

[0103] It is a preferred embodiment that at least fuel cell stack A 410 is designed to operate using air from air supply 430 and / or oxygen from oxygen supply 414. In this way, a turbo compressor (as described above) is not necessarily required during such high power operation, thus saving about 15-25% of parasitic losses. In this case, it is expected that the specific energy will increase by >100%, for example, for a base system of 1.5 kW / kg, the specific power will be between 3.0-4.3 kW / kg. From the perspective of availability and service life, this is a preferred embodiment of the system 400, because redundancy between the fuel cell stacks can be provided in this arrangement.

[0104] exist Figure 4In an alternative arrangement, one turbocompressor of increased capacity or two turbocompressors are provided to assist the aircraft, the aircraft is operated at twice the power during takeoff and climb, and correspondingly, at 1 times the power during high altitude cruising. In the case of the use of oxygen, there may be two benefits:

[0105] (1) less waste of O2 (as part of air) or associated pressure losses, and

[0106] (2) When using O2, compression is not required.

[0107] Thus, the turbo compressor may be a single turbo compressor system optimized for altitude only, or may be two turbo compressors.

[0108] Either of the first fuel cell stack 410 and the second fuel cell stack 411 may be arranged for operation with air from the air supply 430 or with oxygen from the oxygen supply 414. There are different advantages associated with each of these approaches.

[0109] The benefit of having two fuel cells built to almost identical specifications and both capable of operating on air is that the overall development costs, including lifecycle costs (due to maintenance repairs and overhauls), will be reduced. The life of a fuel cell stack is about 3,000 to 20,000 hours. If used in an aircraft, the aircraft life may be around 90,000-180,000 hours. Therefore, a large number of stack replacements (refurbished or new parts) are required. If two identical stacks are used, then the two stacks can be used in turn and provide further redundancy in the event of failure of one stack's operation, etc. Due to the shorter operation of the second stack, the time between overhauls can be almost doubled if these stacks are used alternately. This scheme requires doubling the water and air pipe connections (including valve control) to select the configuration. Further predictive performance will enable the stacks to be used preferentially until both are aged and need to be replaced. This activation of the fuel cell stack can be selectively accomplished by a valve system and / or an electronic controller system that can control valves, etc. One advantage of this configuration relates to the ability to selectively use the life of the two fuel cell stacks thereby. In this way, the fuel cell life, and therefore the time between maintenance, can be doubled if each fuel cell is used alternately to maintain the life of the other fuel cell. Figure 2 These advantages can also be obtained from this example arrangement with slight modifications to the construction of .

[0110] This arrangement enables a reduction in the reaction area of ​​the fuel cell and / or a reduction in the cell width of the second cell stack 411. The reduction in cell area enables preferential integration, a reduction in the mass of the system 400 as a whole, and a reduction in leakage of reactants (especially H2). The reduction in cell area results in a reduction in circumference, which in turn reduces the length of the required seal, so leaks are less likely to occur, thereby reducing leakage. In addition, over a smaller area, this allows better control of the tolerances of the plate at the seal. In the case where the second fuel cell stack 411 uses pure oxygen, it is also not necessary to exhaust air from the cathode to ensure a constant supply of O2, but only water needs to be removed. Therefore, no air outlet is required for normal operation, but an air outlet can optionally be used or included to purge the system 400. Another advantage is that the use of LOx means that oxygen (GO2) in gaseous form can be supplied at a lower temperature, thereby reducing the cooling requirements of the fuel cell stack.

[0111] Through the above Figure 2 The arrangement and the following Figure 4 and Figure 5 The arrangement can also provide these advantages.

[0112] Reference Figure 5 , a propulsion system 500 is shown. Figure 5 The system 500 shown in FIG. Figure 4 The systems 400 in FIG. 4 share many components. Figure 5 The same or similar components are shown in Figure 4 , and increase the number by 100. So, for example, Figure 4 The system 400 is similar to Figure 5 5. For the sake of brevity, not all components will be discussed and identical components will be omitted from the discussion.

[0113] like Figure 4 As shown, Figure 5 The system 500 has two fuel cell stacks 510, 511. There is a hydrogen section 502 that provides hydrogen to the two fuel cell stacks 510, 511 from a hydrogen source 512. There is a water section 506 that provides fluid communication for water between the fuel cell stacks 510, 511, a water pump 542, a water tank 540, a heat exchanger 544, and a heat exchanger / condenser 528.

[0114] Air portion 504 and oxygen portion 508 of system 500 are different from air portion 404 and oxygen portion 408 of system 400. Figure 4 Compared with the system 400, Figure 5The system 500 has an additional compressor 521. Compressor B 521 is connected to the oxygen source 514 via the fuel cell stack B 511 and directly connected to the fuel cell stack A 510. Therefore, the compressor B 521 is part of both the air section 504 and the oxygen section 508. The air section 504 of the system 500 provides air to the fuel cell stack A 510 from the air supply source 530, but in this arrangement, air is not provided to the fuel cell stack B in particular. The oxygen line leading from the fuel cell stack B 511 can be directly fed into one of the existing air lines that feeds the fuel cell stack A 510. This reuse of the air path line reduces the total air path line required, and thus reduces the mass of the system 500, providing the associated benefits of a lighter system as described above. A shutoff valve can be used to control the passage of air along the air path line, particularly when oxygen is introduced from the fuel cell stack B 511 into the air path line entering the fuel cell stack A 510.

[0115] Thus, the system 500 allows for particularly efficient use of the oxygen supplied by the oxygen source 514. When the system 500 is operated at high power, oxygen is supplied directly to the fuel cell stack B 511, which produces a high power output due to the use of oxygen in the fuel cell stack, and additionally, the unused oxygen is subsequently delivered to the fuel cell stack A 510 to increase the oxygen concentration in the air supplied to the fuel cell stack A 510. In this way, the fuel cell stack B 511 provides a high power output, and the percentage of oxygen supplied to the fuel cell stack A 510 is increased, thereby also increasing its power output. Therefore, this is a particularly efficient arrangement, because the oxygen provided by the oxygen source 514 is (almost) completely used. However, the system 500 only supplies air to the fuel cell stack A 510 from the air supply source 530. Therefore, Figure 5 The arrangement shown provides the benefits associated with providing a proprietary high power fuel cell operating on pure (or higher percentage) oxygen.

[0116] Figure 5 The system 500 shown has two compressors 521, 522. However, in an alternative arrangement of the system 500, the second compressor 522 may not be required. If the compressed O2 is initially used in gaseous form or is used from a liquid form, such a compressor is not required. Instead:

[0117] (1) The entire system 500 will be pressurized at the same or different pressures as required, or

[0118] (2) Liquid oxygen will be used and evaporated to the appropriate pressure - this function can be provided by a heat exchanger system.

[0119] In this case, the second fuel cell stack B 511 can be operated at a lower O2 pressure than the first fuel cell stack A 510 (because fuel cell stack A 510 is designed for air), or the first fuel cell stack A 510 can be operated at a higher pressure to compensate.

[0120] Figure 5 The system 500 advantageously and efficiently utilizes the unconsumed oxidant from the fuel cell stack B 511 in the fuel cell stack A 510. Providing a high percentage of oxygen (or pure oxygen) increases the oxygen concentration in the air supplied to the fuel cell stack A 510. Therefore, this increases the specific power of the fuel cell stack A 510. A small additional compressor may be required to re-pressurize the unconsumed oxygen, which is shown as compressor B 521 in the system 500. Figure 1 This arrangement can increase the power provided by system 500 compared to the power provided by system 100. Thus, even with the inclusion of additional components, Figure 5 The performance provided by system 500 is still significantly improved (e.g., about 2.9-3.9 kW / kg for a 1.5 kW / kg base system).

[0121] Reference Figure 6 , a propulsion system 600 is shown. Figure 6 The system 600 shown in FIG. Figure 1 The systems 100 in FIG. 1 share many components. Figure 6 The same or similar components are shown in Figure 1 , and increase the number by 500. So, for example, Figure 1 The system 100 is similar to Figure 6 600 in the system. For the sake of brevity, not all components will be discussed, and the same components may be omitted from the discussion.

[0122] like Figure 1 As shown, Figure 6 The system 600 has a fuel cell stack A 610. There is a hydrogen section 602 that provides hydrogen to the fuel cell stack A 610 from a hydrogen source 612. There is a water section 606 that provides fluid communication for water between the fuel cell stack A 610, a water pump 642, a water tank 640, a heat exchanger 644, and a heat exchanger / condenser 628.

[0123] and Figure 1 The system 100 shown is different. Figure 6The system 600 also has a second fuel cell stack B 611. The hydrogen portion 602 also provides hydrogen to the second fuel cell stack 611, and the water portion 606 also provides fluid communication for water between the first fuel cell stack 610, the second fuel cell stack 611, the water pump 642, the water tank 640, the heat exchanger 644 and the heat exchanger / condenser 628.

[0124] Figure 6 The system 600 also has an air / exhaust portion 604 that allows air or oxygen to be delivered from an air / oxidant supply 630 to the two fuel cell stacks 610, 611. The system 600 is not as Figure 5 The system 500 is shown with an additional compressor.

[0125] The system 600 uses additional fuel cell stacks 611 to provide additional power when needed (with Figure 1 In one example, this may be during takeoff and climb of an aircraft, when additional power is needed. During the short duration required for takeoff and climb, oxidant can be supplied to fuel cell stack B 611 by operating auxiliary equipment at overrated conditions (10% to 25%, although a larger proportion is desired, but this may not be feasible in terms of the life of the fuel cell). When the fuel cell is operated at overrated, the pressure of the air entering the fuel cell increases. Advantageously, this increases the amount of oxygen entering the fuel cell. Therefore, this increases the power output of the fuel cell, but this process also degrades the membrane on the bipolar plates (at a greater rate than under normal use conditions), which may shorten the service life of the fuel cell. In one example, the overrated condition may be the use of an overrated value of about 10% to 25%.

[0126] When used in this manner, the system 600 can provide an increase in power output, with a maximum achievable specific power of about 2 to 2.46 kW / kg for a 1.5 kW / kg base system. In particular, with this arrangement 600, losses due to pumps and heat exchangers can be reduced because the number of fuel cell stacks has been doubled (compared to Figure 1 ), but the number of pumps and heat exchangers is not exactly doubled (compared to Figure 1 ). Therefore, Figure 1 Compared with the arrangement of Figure 6 The available power per unit weight in the arrangement is greater.

[0127] Reference Figure 7, a propulsion system 700 is shown. The propulsion system 700 has a fuel cell system 725 that includes features as shown in previous figures, such as a fuel cell stack. An air supply source 730 feeds the fuel cell system 725. A liquid hydrogen supply source 712 provides liquid hydrogen to a heat exchanger 715. At the heat exchanger 715, the liquid hydrogen interacts with a helium supply source 750. The liquid hydrogen leaves the heat exchanger 715 as gaseous hydrogen and enters the fuel cell system 725.

[0128] The fuel cell system 725 provides electrical energy in the form of direct current. The fuel cell system 725 also provides air and water and provides thermal energy in the form of heat. The electrical energy from the fuel cell system 725 is provided to the network controller 760. The current is then provided to the motor and generator arrangement 770 to provide kinetic energy to the propeller with the electrical energy for providing motion.

[0129] The helium in the helium loop is cooled by liquid hydrogen in the heat exchanger 715. The cooled helium can then provide cooling for direct components, such as the electrical connections that provide electrical energy from the network controller to the motor and generator arrangement 770, and the motor and generator arrangement 770 itself. Helium is advantageous in such a system because it has a lower melting point than hydrogen, and can therefore be cooled with hydrogen without the risk of freezing in the conduits holding the helium. Other cryogenic coolants can be used, but helium is particularly advantageous.

[0130] There are a number of advantages provided by the fuel cell propulsion system disclosed herein. In an arrangement utilizing liquid oxygen (e.g., at least Figure 2 , Figure 3 and Figure 4 In the example of the system shown), the heat capacity and specific heat of vaporization of oxygen can be used to dissipate thermal loads during high power operation (of both fuel cell stacks or particularly of a high power fuel cell stack).

[0131] In all of the systems disclosed herein, the air intake required for the system as a whole is reduced compared to modern systems. This in turn reduces the drag penalties associated with larger air intake requirements (which is reflected in the propulsion power and energy required for the system with the intake). In the case where the system uses pure oxygen, such as Figures 2 to 4 As shown, the size of the air inlet is minimized for use with only fuel cell stack A in cruise. Alternatively, the air inlet may be designed to support all flight conditions. One consequence may be that the air inlet is stowed / closed unless stack A is operating on air in cruise. In this way, the drag improvements over modern systems may also be achieved for the system disclosed herein.

[0132] The advantage of these schemes is that the advantages provided by these systems are achieved by means of the arrangement and components of the system itself. These arrangements and components are independent, and therefore these advantages do not negatively affect other areas of the wider system in which the fuel cell propulsion system is used. In particular, these arrangements are independent of performance improvements in the prior art. The performance of the system disclosed herein provides a certain factor improvement in the capacity of the fuel cell stack and conventional auxiliary equipment components. If the performance of the prior art fuel cell is improved in the future, the improvements disclosed herein will still follow at a similar rate.

[0133] The systems disclosed herein have significant advantages associated with them in providing propulsion. These systems also overcome the prejudices that exist in the current prior art. In particular, the systems disclosed herein reverse the common scheme of consuming oxygen rather than hydrogen to obtain range rather than power. This scheme is logically applicable to using fuel cells as range extenders, but it is worth noting that it cannot be used as a primary power source. In this case, due to the energy used and the mass / volume of hydrogen, the opposite scheme is more appropriate.

[0134] The system disclosed herein can advantageously utilize already pressurized ECS effluent air to reduce the compression requirements of the fuel cell turbine compressor (or compressors). This air can be enriched with oxygen (due to the use of an oxygen filter, as described above) and / or the air can be further oxygen separated before compression to reduce energy consumption. In addition, in modern aircraft, there is a trend to increase the oxygen content of cabin air, and there is also a trend to increase the number of air changes (the number of times the cabin air is theoretically completely refreshed), and these factors all provide benefits that are utilized in the currently disclosed system. In particular, the number of air changes has been increasing over time and now averages about 15 times; older aircraft may have 8 air changes, while modern aircraft may have 20 or more air changes.

[0135] The use of oxygen enrichment can reduce the overall power requirements of the system. In one possible arrangement, LOx can supply pressurized GO2 to the fuel cell stack with minimal auxiliary equipment requirements. Oxygen is consumed, and therefore, the integrated mass of the system is not significantly increased. This approach reduces the dependence on the performance of the cell stack and prior art auxiliary equipment.

[0136] Although the disclosed fuel cell propulsion system is primarily described for aircraft, other vehicles, such as spacecraft and submarines, may also carry oxygen or liquid oxygen. Although such oxygen or liquid oxygen may be carried primarily for other reasons, the integration of additional oxygen for the fuel cells of the disclosed system will not be mechanically intensive. Alternatively or in addition, these vehicles may be advantageously arranged to provide excess oxygen or liquid oxygen to the fuel cell propulsion system described herein. Therefore, the disclosed system will advantageously be disposed in such a vehicle. Any vehicle that may be propelled by the fuel cell propulsion system described herein will benefit from the use of the system disclosed herein.

[0137] The systems disclosed herein may be advantageously used to provide propulsion in a vehicle or system that could benefit from a system capable of providing a controllable, variable amount of propulsion over a wide range of propulsion values.

[0138] Generating power from a fuel cell rather than through a combustion engine provides many advantages. Producing water in place of harmful gas emissions (NOx, CO2, etc.) has obvious associated advantages. In addition, the operation of the vehicle can have significantly reduced noise levels. In one specific example, the takeoff and landing phases of an aircraft can have significantly reduced noise levels due to the absence of high-speed exhaust.

[0139] The vehicle operator may also use the additional selectable thrust provided (by converting the fuel cell electrical power provided by the systems described herein into thrust via an electric motor or the like) whenever needed. This flexibility would allow the pilot to optimize thrust selection for a phase of flight or motion (e.g., a race car traveling in a straight line). These systems may also not limit the operator to a specific fuel cell stack if, for example, it is desired to change thrust during any phase of flight to overcome or adapt to changes in flight conditions.

[0140] Therefore, applications for such systems may include automotive, aerospace, domestic or commercial, etc.

[0141] As disclosed herein, a further benefit of using fuel cells compared to combustion engines is that microbial colonization that occurs in kerosene fuel tanks of existing aircraft is avoided. Currently, cleaning such tanks requires the use of detergents, pesticides, and cleaning agents that are somewhat damaging to the environment. In some cases, such cleaning may be performed after each long-distance flight. Therefore, reducing cleaning has further environmental benefits.

Claims

1. A power unit suitable for an aircraft, comprising: at least one fuel cell; at least two fuel sources for providing fuel to the at least one fuel cell; wherein the first fuel source is a hydrogen supply source, the hydrogen supply source being arranged to provide hydrogen to a first fuel cell of the at least one fuel cell, and The second fuel source is an air gas supply source, and the air gas supply source is arranged to provide air gas to a first fuel cell in the at least one fuel cell.

2. The power unit according to claim 1, wherein: The at least one fuel cell comprises a first fuel cell and a second fuel cell, Wherein, the third fuel source is an oxygen supply source, and the oxygen supply source is arranged to provide oxygen to the second fuel cell.

3. The power unit according to claim 2, wherein: The hydrogen supply is further arranged to provide hydrogen to the second fuel cell.

4. The power unit according to claim 2 or 3, wherein: The air gas supply is further arranged to provide fluid communication of air gas between the air gas supply and the second fuel cell.

5. The power unit according to any one of claims 2 to 4, wherein: The oxygen supply is further arranged to provide oxygen to the first fuel cell.

6. The power unit according to any one of claims 2 to 5, wherein: The system further comprises: at least one compressor for compressing a fuel source of the at least two fuel sources, Wherein a first compressor of the at least one compressor and a fuel source of the at least two fuel sources are arranged such that fuel from the fuel source is delivered to the compressor before being provided to a fuel cell of the at least one fuel cell.

7. The power unit according to claim 6, wherein: The oxygen supply source is arranged in fluid communication with a second compressor of the at least one compressor, the oxygen supply source being arranged for: providing oxygen to the second fuel cell; providing oxygen to the second compressor; and Oxygen is provided to the first fuel cell.

8. The power unit according to claim 7, wherein: The oxygen supply is arranged to provide uncompressed oxygen to the second fuel cell and compressed oxygen to the first fuel cell.

9. The power unit according to any one of claims 2 to 8, comprising a control unit for controlling the supply of fuel from the at least two fuel sources to the at least one fuel cell, in, By selectively providing fuel to the second fuel cell, the second fuel cell can be selectively activated.

10. The power unit according to any one of claims 2 to 9, wherein: The first fuel cell and the second fuel cell are arranged to use a common auxiliary device.

11. The power unit according to any one of claims 2 to 10, further comprising a liquid heat exchanger arrangement for exchanging heat with the at least one fuel cell, The liquid heat exchanger includes a fluid arranged to be in thermal communication with the at least one fuel cell at at least one point in the liquid heat exchanger arrangement, and A low temperature heat exchanger arrangement is arranged in thermal communication with the fluid at least at one point.

12. The power unit according to claim 11, wherein: The third fuel source is a liquid oxygen supply and is arranged to provide oxygen to the cryogenic heat exchanger arrangement.

13. The power unit according to claim 12, wherein: The third fuel source is arranged to: providing liquid oxygen to the cryogenic heat exchanger arrangement to cool the fluid, and Gaseous oxygen from the low temperature heat exchanger arrangement is provided to the at least one fuel cell.

14. The power unit according to claim 13, wherein: The liquid heat exchanger arrangement comprises a fluid conduit and a liquid heat exchanger, wherein a fluid can flow through the fluid conduit, and wherein the cryogenic heat exchanger arrangement comprises a refrigerant conduit and a cryogenic heat exchanger, wherein a refrigerant can flow through the refrigerant conduit.

15. The power unit according to any one of claims 1 to 14, wherein: The air gas supply source is exhaust from an environmental control system or ambient air.

16. A power unit according to any one of claims 1 to 15, wherein: The hydrogen supply source is a hydrogen supply source for providing hydrogen gas, and the hydrogen supply source is arranged to provide hydrogen gas to a first fuel cell of the at least one fuel cell.

17. A power unit, comprising: at least two fuel cell stacks; at least two fuel sources, the at least two fuel sources being used to provide fuel to the two fuel cells; wherein the first fuel source is a hydrogen supply source, the hydrogen supply source being arranged to provide hydrogen to each of the two fuel cells; and The second fuel source is an air gas supply source, and the air gas supply source is arranged to provide air gas to each of the two fuel cells.

18. An aircraft propulsion system comprising a power unit according to any one of claims 1 to 17.

19. A method of providing variable power for use in an aircraft, comprising: providing a first fuel from a first fuel source to a first fuel cell, wherein the first fuel source is a hydrogen supply source, and the hydrogen supply source is used to provide hydrogen to the first fuel cell; supplying a second fuel from a second fuel source to the first fuel cell, wherein the second fuel source is an air gas supply source, and the air gas supply source is used to provide air gas to the first fuel cell; activating the first fuel cell to provide power using the hydrogen gas and the air gas; providing hydrogen from the hydrogen supply source to a second fuel cell; supplying a third fuel from a third fuel source to the second fuel cell, wherein the third fuel source is an oxygen supply source, and the oxygen supply source is used to provide oxygen to the second fuel cell; The second fuel cell is selectively activated to provide additional power.

20. The method according to claim 19, wherein: The second fuel cell is selectively activated during takeoff and climb phases of aircraft flight.

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