AIRCRAFT WITH A FUEL CELL AND METHOD FOR OPERATION OF A FUEL CELL OF AN AIRCRAFT

Description

[0001] The invention relates to an aircraft with a fuel cell and a method for operating a fuel cell of an aircraft with an air supply device for operating the fuel cell and for cooling a heat exchanger connected to the fuel cell.

[0002] Fuel cells installed in aircraft generate large amounts of heat, which is dissipated via heat exchangers. Accordingly, the heat exchangers of fuel cells operated in aircraft, particularly when they are used to generate the aircraft's propulsion energy, are often arranged within an air-flow area such as the engine nacelle or within an air duct so that ram air and / or propeller downwash air can be used to cool at least one heat exchanger of the fuel cell(s). In this case, an air flow is usually directed onto at least one cooling surface of the heat exchanger in order to absorb thermal energy from the heat exchanger. In addition to a fuel, fuel cells also require an oxidant to operate, which in the case of fuel cells used in aircraft is usually air orThe oxygen contained therein is formed, whereby the air is compressed to achieve high fuel cell efficiency. Disadvantages of known air supply systems include the deterioration of the aircraft's aerodynamics caused by devices for collecting and directing ram air and / or propeller downwash, as well as the energy required to compress the air before feeding it to the fuel cell.

[0003] An aircraft with an air supply device for fuel cells is known from EP 3 043 408 A. Further exemplary air supply devices for fuel cells are known from the documents US2020075971A1 and US2007298308A1.

[0004] Based on this, it is an object of the present invention to propose an improved aircraft with a fuel cell and an air supply system. Furthermore, an improved method for operating a fuel cell of an aircraft with an air supply system is provided. This is achieved according to the invention by the teaching of the independent claims. Advantageous embodiments of the invention are the subject of the dependent claims.

[0005] To achieve this objective, an aircraft with a fuel cell and an air supply device for supplying air for operating the fuel cell and for cooling a heat exchanger connected to the fuel cell is proposed. The aircraft has at least one air duct whose cross-section widens in the direction of air flow after an air inlet opening in at least one region of the circumferential surface. The air duct has at least one flow opening in the at least one widening region of the circumferential surface, through which air can be discharged for operating the fuel cell.

[0006] The invention relates to aircraft, such as in particular airplanes, helicopters, or unmanned aerial vehicles, which have at least one fuel cell with a heat exchanger connected to cool the fuel cell. The heat exchanger is designed to release thermal energy, for example, via cooling surfaces, particularly to the environment. An air stream passing over the cooling surfaces can absorb thermal energy from the heat exchanger. A fuel cell is an electrochemical device that generates heat and electrical energy from a fuel and an oxidizing agent. Known fuel cells use, for example, hydrogen as the fuel and, in particular, oxygen contained in the ambient air as the oxidizing agent.Fuel cells are usually designed in the form of fuel cell stacks, which in the context of the description of the invention are referred to simply as "fuel cells" in accordance with common usage.

[0007] The aircraft has at least one air duct with at least one air inlet opening, which is arranged at least predominantly in the direction of flight of the aircraft to supply air from the aircraft's surroundings to the air duct, particularly during flight. The at least one air inlet opening is arranged at a suitable position on the outer skin of the aircraft, such as in particular on a fuselage or a wing. In particular, the air inlet opening is positioned such that ram air or propeller downwash is supplied to the air duct through it.

[0008] The air duct is designed such that its cross-section widens in the direction of air flow downstream of the air inlet opening in at least one region of the circumferential surface. Accordingly, the air duct is designed in the manner of a diffuser, whereby the flow velocity of the air flowing through this section is reduced, with the air pressure simultaneously increasing. The cross-section of the air duct widens in at least one region of the wall, so that the wall is designed to widen in at least one region, for example with an opening angle arranged at an angle to the longitudinal direction of the air duct. At the same time, the wall can have a larger or smaller opening angle in at least one other region of the air duct cross-section, for example, or be aligned parallel to the longitudinal direction of the air duct.In principle, the wall can also be designed to expand uniformly and / or at least in sections in a rotationally symmetrical manner over the circumference.

[0009] In the proposed design, the air duct has at least one flow opening in the at least one widening region of the circumferential surface, through which air can be discharged from the air duct for operating the fuel cell. In particular, the at least one flow opening is designed and arranged such that air flowing directly past or along the wall of the widening region of the circumferential surface is discharged through it. This is particularly advantageous in regions that widen with larger opening angles, in which there is a risk of the boundary layer of the air flow separating. By discharging the air flowing past the wall, a stabilization of the ideally laminar boundary layer and a reduction in the risk of the air flow separating can be achieved.In particular, taking into account the flow conditions on the circumferential surface, one or more flow openings of the same or different size, distributed uniformly or in another way, can be arranged in an expanding region of the circumferential surface.

[0010] The proposed design of the air duct, with its widening cross-section downstream of the air inlet opening in at least one widening area, creates a diffuser effect on the air flowing through the air duct, resulting in a reduction in flow velocity while simultaneously increasing pressure. Because the air pressure increases in the air duct downstream of an inlet opening, the air discharged through the at least one flow opening also has a higher pressure, so that the energy required to compress the air supplied to the fuel cell for its operation can be reduced accordingly.In this way, the proposed solution enables functional integration based on increasing the air pressure while simultaneously reducing the air flow velocity in order to improve the cooling effect for the heat exchanger and the supply of compressed air to the fuel cell, and furthermore to reduce the risk of air detachment from the wall in the expanding area of ​​the air duct.

[0011] In one embodiment of the aircraft, the heat exchanger is arranged in the expanded cross-section of the air duct. As already explained, the diffuser effect of the expanding air duct in the flow direction upstream of the expanded cross-section of the air duct leads to a reduction in the flow velocity of the inlet air while simultaneously increasing the pressure. This allows favorable air flow conditions to be achieved for the dissipation of thermal energy from the cooling surfaces of a heat exchanger arranged in the expanded cross-section of the air duct.

[0012] In one embodiment of the aircraft, the cross-section of the air duct decreases in the flow direction upstream of an air outlet opening. The cross-section of the air duct decreases in at least one region of the circumferential surface. This tapered region of the air duct is arranged in particular behind the at least one heat exchanger. The cross-section of the air duct decreases in at least one region of the wall, so that the wall is tapered in at least one region, for example with a taper angle arranged at an angle to the longitudinal direction of the air duct. At the same time, the wall can have a larger or smaller taper angle in at least one other region of the air duct cross-section, for example, or be aligned parallel to the longitudinal direction of the air duct.In principle, the wall can also be tapered evenly and / or at least in sections, rotationally symmetrically distributed around the circumference. Accordingly, the air duct is designed like a nozzle, increasing the flow velocity of the air flowing through this section while decreasing the air pressure. The nozzle-like design of the air duct in front of an air outlet leads to an acceleration of the air flow and thus to an increased flow velocity of the outgoing air, resulting in additional thrust for the aircraft.

[0013] In one embodiment of the aircraft, the air duct has at least one air supply opening for supplying exhaust air from the fuel cell upstream of an air outlet opening. Thus, the exhaust air from the fuel cell is returned to the air duct from which it was taken. Furthermore, additional thermal enthalpy is supplied to the air duct, which further increases the total enthalpy of the outflowing air upstream of the air outlet opening and thus further enhances the protective effect.

[0014] In one embodiment of the aircraft, the at least one flow opening is connected to an air supply duct for supplying air to the fuel cell, in particular as an oxidizing agent for the operation and / or cooling of the fuel cell. The air supply duct has a compressor device for compressing the air before the air is supplied to the fuel cell. Simultaneously or alternatively, the compressor device can be provided for extracting the air from the air duct through the flow opening. In particular, due to the diffuser effect in the region in which the at least one flow opening is arranged, the air that can be discharged from the air duct through the flow opening regularly has a higher pressure than the ambient pressure.Depending on the boundary conditions (in particular ambient pressure, ambient temperature, flight speed, design of the air duct), the pressure gradient between the air duct and the air supply duct to the fuel cell may already be sufficient to discharge air from the air duct through the at least one flow opening. In particular, if there is insufficient pressure gradient, a suitable pressure gradient can be generated by means of the compressor device in order to supply a sufficient amount of air from the air duct to the fuel cell. Additionally or alternatively, the air can be further compressed by means of the compressor device before being supplied to the fuel cell in order to set a suitable air pressure for operating the fuel cell, in particular with a suitable efficiency.

[0015] In one embodiment of the aircraft, the fuel cell is part of the aircraft's propulsion system. The energy generated by the fuel cell can be the primary propulsion source for the aircraft's propulsion system or supplement it. In another embodiment of the aircraft, the energy generated by the fuel cell is at least partially made available for non-propulsion systems of the aircraft, such as for powering auxiliary units or for the on-board power supply.

[0016] In a further aspect of the invention, a method for operating a fuel cell of an aircraft with an air supply device for operating the fuel cell and for cooling a heat exchanger connected to the fuel cell is proposed. The aircraft has at least one air duct whose cross-section widens in the direction of air flow after an air inlet opening in at least one region of the circumferential surface, in which at least one flow opening is arranged for discharging air for operating the fuel cell.

[0017] The procedure includes the following steps: a) guiding air through the air inlet opening into the air duct; b) compressing the air in the air duct downstream of the air inlet opening; c) discharging compressed air from the air duct through the at least one flow opening; d) guiding the air from the flow opening to the fuel cell; e) directing the compressed air onto at least one cooling surface of the heat exchanger; and f) discharging the air from the air duct.

[0018] In a first method step, air is guided through the air inlet opening into the air duct. The air inlet opening can, of course, also be designed in multiple parts. Typically, the air inlet opening is arranged in the direction of flight at a position of the aircraft that is particularly favorable for absorbing ram air and / or propeller downwash, thereby ensuring sufficient air is guided into the air duct during a flight phase. Of course, it is also possible to provide additional devices such as at least one fan impeller or the like for guiding air through the air inlet opening into the air duct.

[0019] In a further step, the air in the air duct is compressed downstream of the air inlet opening. The cross-section of the air duct proposed for implementing the method expands in the direction of air flow downstream of the air inlet opening in at least one region of the circumferential surface. Accordingly, the air duct is designed like a diffuser, which reduces the flow velocity of the air flowing through this section and simultaneously increases the air pressure. Of course, it is also possible to provide further devices in the air duct, particularly for additional air compression.

[0020] In further process steps, compressed air is discharged from the air duct through the at least one flow opening and guided to the fuel cell. The at least one flow opening is designed and arranged in such a way that air flowing directly past or along the wall of the expanding region of the circumferential surface can be discharged through it. This stabilizes the ideally laminar boundary layer on the wall of the air duct and reduces the risk of air flow separation in expanding regions of the air duct.

[0021] In a further step, the air discharged from the air duct through the at least one flow opening, in particular compressed by the diffuser effect in the air duct, is directed onto at least one cooling surface of the heat exchanger. Due to the diffuser effect of the expanding cross-section of the air duct, the air pressure increases, but simultaneously the flow velocity also decreases, so that the proposed method additionally creates favorable flow conditions for the heat absorption of the air as it passes over the cooling surfaces of the at least one heat exchanger. Finally, the air is discharged from the air duct again, in particular into the environment, wherein the air has absorbed energy during the process to generate additional thrust.

[0022] The proposed method thus enables an energy-efficient supply of air to at least one fuel cell for its operation and to cool the associated heat exchanger. Depending on the design of the air duct, the method can also provide additional thrust for the aircraft.

[0023] In one embodiment of the method, the air is discharged through the at least one flow opening by means of suction, so that the air is sucked out through the at least one flow opening. This may be necessary in particular if the pressure gradient at the at least one flow opening is insufficient to discharge a sufficient amount of air from the air duct. The suction can be generated in particular by a compressor device arranged in the air supply duct from the flow opening to the fuel cell.

[0024] One embodiment of the method comprises, as a further step, compressing the air guided from the flow opening to the fuel cell. This step may also be necessary in particular if the pressure of the air extracted from the air duct via the at least one flow opening is lower than that required for supplying the fuel cell for its operation. The suction can be generated in particular using a compressor arranged in the air supply duct from the flow opening to the fuel cell. In particular, it is possible to use a common compressor device, in particular arranged in the air supply line, for a combination of discharging the air through the at least one flow opening by means of suction and compressing the air guided to the fuel cell.

[0025] One embodiment of the method comprises, as a further step, accelerating the air in the air duct downstream of the at least one heat exchanger. This allows the air to provide additional thrust for the aircraft when it is subsequently discharged to the environment. Since a lower air flow velocity is advantageous for absorbing thermal energy from the heat exchanger, acceleration of the air advantageously only occurs after the absorption of thermal energy from the heat exchanger. In particular, this acceleration can be achieved by tapering the cross-section of the air duct downstream of the heat exchanger. The energetic enrichment of the air at the heat exchanger enables higher acceleration and flow velocity at the air outlet opening and thus the achievement of additional thrust when the air is discharged to the environment.

[0026] An embodiment of the method comprises, as a further step, feeding the exhaust air from the fuel cell into the air duct downstream of the heat exchanger. The exhaust air from the fuel cell has a higher thermal enthalpy than the ambient air, so that feeding the exhaust air into the air duct downstream of the heat exchanger, particularly in conjunction with an acceleration of the air in this section of the air duct, enables additional thrust when discharging the air from the air outlet opening to the environment.

[0027] In one embodiment of the method for operating a fuel cell of an aircraft, the aircraft is configured according to at least one aspect of the aircraft described above. In particular, the aircraft may have one or more features and properties of the aircraft described above, particularly for implementing the proposed method.

[0028] Since the proposed aircraft and the proposed method are based on a common fundamental idea, the described features and properties of the proposed aircraft and the proposed method also represent features and properties for at least optional embodiments of the aircraft and the method and should therefore also be considered as disclosed for the respective reciprocal aspects.

[0029] Further features, advantages and possible applications of the invention will become apparent from the following description taken in conjunction with the figures. Fig. 1 shows a schematic representation of an air supply device of an exemplary aircraft according to the invention; Fig. 2 shows a schematic representation of a section of an exemplary aircraft according to the invention; and Fig. 3 shows a schematic representation of a flowchart of the method according to the invention.

[0030] Fig. 1shows a schematic representation of an air supply device 30 of an exemplary aircraft according to the invention. The air supply device 30 is connected to a fuel cell 20 in order to supply air to it for operation. The fuel cell 20 is cooled by a heat exchanger 21, which is arranged in an air duct 10. The cross-section of the air duct widens in the air flow direction 5 after an air inlet opening 11 in a region 35 of the circumferential surface. Furthermore, the air duct 10 has a flow-through opening 36 in the at least one widening region 35 of the circumferential surface, through which air can be supplied to the fuel cell 20 by means of an air supply duct 37 for its operation. The air supply duct 37 has a compressor device 33 for compressing the air before it is supplied to the fuel cell 20 and / or for sucking the air out of the air duct 10 through the flow-through opening 36.

[0031] In the schematic representation in Fig. 1 The heat exchanger 21 is arranged in the expanded cross-section of the air duct 10. The cross-section of the air duct 10 decreases in the flow direction 5 after the heat exchanger 21, before the air outlet opening 12, in at least one region 34. The air duct 10 has an air supply opening 38 in the tapered region 34 for supplying exhaust air from the fuel cell 20.

[0032] Fig. 2shows a schematic representation of a section of an exemplary aircraft 1 according to the invention with a section through an air duct 10. The aircraft 1 has a fuel cell 20 and an air supply device 30 for supplying air for operating the fuel cell 20 and for cooling a heat exchanger 21 connected to the fuel cell 20. The aircraft 1 or the air supply device 30 has at least one air duct 10, the cross-section of which widens in the air flow direction 5 after an air inlet opening 11 in at least one region 35 of the circumferential surface. The air duct 10 has at least one flow opening 36 in the at least one widening region 35 of the circumferential surface, through which air can be discharged for operating the fuel cell 20. The fuel cell 20 of the exemplary embodiment represents part of the flight propulsion system of the aircraft 1.

[0033] In the illustrated exemplary embodiment of the proposed aircraft 1, the heat exchanger 21 is arranged in the expanded cross-section of the air duct 10. The cross-section of the air duct 10 decreases in the flow direction 5 after the heat exchanger 21, upstream of the air outlet opening 12, in at least one region 34. In the decreasing region 34, the air duct 10 has at least one air supply opening 38 for supplying exhaust air from the fuel cell 20.

[0034] The at least one flow opening 36 is connected to an air supply channel 37 for supplying the air to the fuel cell 20, wherein a compressor device 33 is arranged in the air supply channel 37 for compressing the air before supplying it to the fuel cell 20 and / or for sucking the air out of the air channel 10 through the flow opening 36.

[0035] Fig. 3shows a schematic representation of a flow chart of the method according to the invention for operating a fuel cell 20 of an aircraft 1. An exemplary embodiment of such an aircraft is shown, for example, in Fig. 2 The aircraft 1 has an air supply device 30 for operating a fuel cell 20 and for cooling a heat exchanger 21 connected to the fuel cell 20. Furthermore, the aircraft 1 has at least one air duct 10, the cross-section of which widens in the air flow direction 5 after an air inlet opening 11 in at least one region 35 of the circumferential surface, in which a flow opening 36 is arranged for discharging air for operating the fuel cell 20.

[0036] In a first method step a), air is guided through the air inlet opening 11 into the air duct 10. In a second step b), the air in the air duct 10 is compressed downstream of the air inlet opening 11, for example, by means of a diffuser effect formed in the air duct. In a third method step c), compressed air is discharged from the air duct 10 through a flow opening 36 and, in a next step d), is guided to supply the fuel cell 20.

[0037] In an optional process step d1), the air supplied from the flow opening 36 to the fuel cell 20 is compressed. This step is carried out in particular when the pressure of the air extracted from the air duct via the at least one flow opening is lower than that required to supply the fuel cell for its operation.

[0038] In a next process step e), the air compressed after the air inlet opening 11 in the air duct 10 is directed to at least one cooling surface of the heat exchanger 21 in order to absorb heat energy from the heat exchanger 21 and to dissipate it from there.

[0039] In a further optional method step e1), the air in the air duct 10 is accelerated after flowing over the heat exchanger 21 so that the air can provide additional thrust for the aircraft 1 during subsequent discharge to the environment. In a still further optional method step e1), the exhaust air from the fuel cell 20 is fed into the air duct 10 after flowing over the heat exchanger 21, thereby adding additional mass and enthalpy to the air flow, which also enables additional thrust when the air is discharged from the air outlet opening 12 to the environment.

[0040] Finally, in a further method step f) of the proposed method, the air is discharged from the air duct 10, in particular through the air outlet opening 12. In particular, during the method, the air has absorbed energy to generate additional thrust, which is available for propulsion of the aircraft 1 depending on the positioning and design of the air outlet opening 12. LIST OF REFERENCE SYMBOLS

[0041] 1Aircraft 5Flow direction 10Air duct 11Air inlet opening 12Air outlet opening 20Fuel cell 21Heat exchanger 30Air supply device 33Compressor device 34Decreasing area of ​​the circumferential surface of the air duct 35Expanding area of ​​the circumferential surface of the air duct 36Flow opening 37Air supply duct 38Air supply opening

Claims

1. Aircraft comprising a fuel cell (20) and an air supply device (30) for supplying air for operating the fuel cell (20) and for cooling a heat exchanger (21) connected to the fuel cell (20), the aircraft (1) having at least one air duct (10),the cross section of which widens in the flow direction (5) of the air downstream of an air inlet opening (11) in at least one region (35) of the circumferential surface, characterized in that the air duct (10) has at least one through-flow opening (36) in the at least one widening region (35) of the circumferential surface, through which air can be discharged for operating the fuel cell (20).

2. Aircraft according to claim 1, characterized in that the heat exchanger (21) is arranged in the widened cross section of the air duct (10).

3. Aircraft according to at least one of the preceding claims, characterized in that that the cross section of the air duct (10) decreases in the flow direction (5) upstream of an air outlet opening (12).

4. Aircraft according to at least one of the preceding claims, characterized in that that the air duct (10) has at least one air supply opening (38) for supplying exhaust air from the fuel cell (20) upstream of an air outlet opening (12).

5. Aircraft according to at least one of the preceding claims, characterized in that that the at least one through-flow opening (36) is connected to an air supply duct (37) for supplying the air to the fuel cell (20), the air supply duct (37) being connected to a compressor device (33) for compressing the air before it is supplied to the fuel cell (20) and / or for drawing the air out of the air duct (10) through the through-flow opening (36).

6. Aircraft according to at least one of the preceding claims, characterized in that the fuel cell (20) is part of the flight propulsion system.

7. Method for operating a fuel cell (20) of an aircraft (1) comprising an air supply device (30) for operating the fuel cell (20) and for cooling a heat exchanger (21) connected to the fuel cell (20), wherein the aircraft (1) has at least one air duct (10), the cross section of which widens in the flow direction (5) of the air downstream of an air inlet opening (11) in at least one region (35) of the circumferential surface, in which a through-flow opening (36) for discharging air for operating the fuel cell (20) is arranged, wherein the method comprises the following steps: a) guiding air through the air inlet opening (11) into the air duct; b) compressing the air in the air duct (10) downstream of the air inlet opening (11); c) discharging compressed air from the air duct (10) through the at least one through-flow opening (36); d) guiding the air from the through-flow opening (36) to the fuel cell (20); e) conducting the compressed air onto at least one cooling surface of the heat exchanger (21); and f) discharging the air from the air duct (10).

8. Method for operating a fuel cell of an aircraft according to claim 7, characterized in that the air is discharged through the at least one through-flow opening (36) by means of suction.

9. Method for operating a fuel cell of an aircraft according to either claim 7 or claim 8, characterized by the additional step of: d1) compressing the air guided from the through-flow opening (36) to the fuel cell (20).

10. Method for operating a fuel cell of an aircraft according to any of claims 7 to 9, characterized by the additional step of: e1) accelerating the air before it is discharged from the air duct (10).

11. Method for operating a fuel cell of an aircraft according to any of claims 7 to 10, characterized by the additional step of: e2) supplying the exhaust air from the fuel cell (20) before the air is discharged from the air duct (10).

12. Method for operating a fuel cell of an aircraft according to any of claims 7 to 11 characterized in that the aircraft (1) is designed according to at least one of claims 1 to 6.