Air supply system for a fuel cell stack

Abstract

The invention relates to an air supply system (10) for a fuel cell stack (2), in particular for a fuel cell stack (2) of an aircraft fuel cell drive (1), comprising an air provision device (20) for providing an air flow for the fuel cell stack (2) and an air feed device (30) which is arranged downstream of the air provision device (20), can be connected to the fuel cell stack (2), in particular to the cathode side thereof, and can conduct air to the fuel cell stack (2), wherein a humidifying apparatus (31) for humidifying the air for the fuel cell stack (2) is arranged in the air feed device (30). One problem addressed by the invention is that of specifying an air supply system for a fuel cell stack which offers greater robustness against the fuel cell stack drying out. According to the invention, an air supply system (10) which solves this problem is provided in that a water injection apparatus (40) for injecting water into the air flow is arranged between the air provision device (20) and the air feed device (30).

Description

[0001] Air supply system for a fuel cell stack

[0002] The invention relates to an air supply system for a fuel cell stack according to the preamble of claim 1.

[0003] Fuel cells in fuel cell stacks of an aircraft fuel cell propulsion system provide electrical energy for the propulsion and systems of the aircraft by means of an electrochemical reaction using air as an oxidant and hydrogen as fuel.

[0004] DE 10 2021 200 088 A1 relates to an air supply system and a method for supplying compressed air to a fuel cell stack of an aircraft fuel cell propulsion system, wherein the aircraft fuel cell propulsion system has an air supply unit with a compressor arrangement, and wherein ambient air is compressed by means of the compressor arrangement and at least a portion of the compressed air is supplied to the fuel cell stack. A humidification unit serves to humidify the compressed air supplied to the fuel cell. Furthermore, an air cooler is arranged between the humidification unit and the fuel cell stack, which can cool the supplied compressed air to a temperature favorable for the fuel cells of the fuel cell stack. The humidification unit is supplied by the water contained in the cathode exhaust air or by the water precipitated at the cathode.

[0005] A disadvantage of the invention is that, in dry air conditions, the fuel cell or fuel cell stack may dry out, and the amount of water removed may no longer be sufficient to operate the humidification system efficiently. This, in turn, leads to further drying of the fuel cell stack, potentially resulting in a loss of efficiency in the fuel cell reactions and possibly damage to the membranes of the fuel cells within the fuel cell stack. Therefore, the object of the invention is to provide an air supply system for a fuel cell stack that offers greater robustness against drying out of the fuel cell stack.

[0006] This problem is solved according to the invention by an air supply system according to claim 1.

[0007] A generic air supply system for a fuel cell stack, in particular for a fuel cell stack of an aircraft fuel cell propulsion system, comprises an air supply device for providing an airflow to the fuel cell stack, and an air supply device arranged downstream of the air supply device, which can be connected to the fuel cell stack, in particular its cathode side, and can direct the airflow to the fuel cell stack. A humidification device for humidifying the air for the fuel cell stack is arranged in the air supply device.

[0008] The problem is solved by the air supply system according to claim 1 in that a water injection device, in particular with a water injector, for injecting water is arranged between the air supply device and the air supply device.

[0009] A water injection device integrates an additional water supply into the air supply, allowing for greater flexibility in humidification. Furthermore, compared to prior art humidification systems, this humidification unit can be designed to be significantly smaller, resulting in cost and weight reduction.

[0010] Furthermore, this saves space, allowing the overall system to be designed in a more compact way.

[0011] The air supply system can be part of a fuel cell system. The air supply unit can primarily serve to provide an airflow at a specific pressure and / or velocity. The air supply unit can primarily serve to regulate the airflow to the correct temperature and humidity. The air can serve as an oxidizer for the fuel cell stack. A filter can be arranged in the air supply unit to purify the airflow. Furthermore, a compressor assembly can be provided in the air supply unit to supply the fuel cell stack with compressed air. In particular, an aircraft fuel cell propulsion system relies on a supply of compressed air under flight conditions. The compressor assembly can comprise one or more compressors. A compressor can preferably be driven by an electric motor.The air supply system may include components other than the humidifier. The humidifier may be positioned upstream of a cooling unit. The fuel cell stack typically consists of several fuel cells connected in series, with the reaction for generating electrical energy taking place within the fuel cells. The fuel cells may contain a membrane. Preferably, the fuel cells in the fuel cell stack are proton exchange membrane (PEM) fuel cells. The water in the airflow can be used to humidify the membranes, thereby increasing their lifespan and efficiency.

[0012] Further advantages and features will become apparent from the following description of some preferred embodiments and the dependent claims.

[0013] According to an advantageous embodiment of the invention, the amount and / or type of water discharged by the water injection device can be variably adjusted. Advantageously, this allows the humidity of the airflow supplied to the fuel cell stack to be controlled, which can particularly counteract the drying out of the membranes. Preferably, the amount and / or type of water discharge can be specifically tailored to the current humidity requirement of the fuel cell stack. The type of water discharge can, for example, be the exit velocity of the droplets, the droplet size, and / or the spray pattern of the water injection device. According to a further advantageous embodiment of the invention, the water injection device can comprise a water injector and a variably adjustable water supply device that delivers water to the water injector.By using an injector (especially a passive one) and an actively operated water supply system, the water injection device can be advantageously robust and precise water injection into the airflow can be achieved. The water injector can be designed to spray a water mist into the airflow. For this purpose, the water injector can include a water atomizer.

[0014] According to a preferred embodiment of the invention, the water supply device can include a controllable water pump. The water supply device can be variably adjustable, particularly by means of the controllable water pump. A water pump can advantageously provide a high and / or constant pressure and thus a precisely controlled water delivery rate. The water pump can, in particular, be controllable by a control device. Through active control, the water delivery rate can advantageously be adjusted to the current conditions of the fuel cell stack.

[0015] According to a further preferred embodiment of the invention, the water injection device can be supplied with water from a water reservoir. Injecting water from a water reservoir advantageously makes the fuel cell system independent of the humidity of the supplied airflow.

[0016] According to a particularly preferred aspect of the invention, a heat exchanger can be arranged between the air supply device and the water injection device, wherein the heat exchanger can heat or cool the water-containing airflow directed from the water injection device. By means of a heat exchanger downstream of the water injection device, the temperature of the humidified air can advantageously be increased or decreased to an optimal range for the operation of the fuel cell stack. For example, a temperature between 100°C and 200°C can be provided downstream of the air supply device by means of air compression. However, an airflow with a temperature below 100°C is to be supplied to the fuel cell stack. To achieve this, the heat exchanger can cool the airflow.It can also happen that the outside temperature, especially at high altitudes, is so low that the supplied airflow needs to be heated. In this case, the heat exchanger can advantageously warm the airflow. Furthermore, additional cooling or heating elements can be made smaller or even omitted entirely. Particularly in combination with a variably adjustable water injection system, temperature peaks of the fuel cell stack and / or the incoming air can be compensated for even with a relatively small heat exchanger design.

[0017] In a further development, the heat exchanger can be designed to evaporate the water from the water injection device. This allows the humidity of the airflow to be advantageously and precisely controlled.

[0018] Preferably, the heat exchanger can have at least one evaporation surface, wherein the water injection device, in particular the water injector, is designed to spray water onto the evaporation surface. This allows for uniform evaporation, which advantageously leads to a homogeneously humidified airflow.

[0019] Furthermore, the heat exchanger can be designed as an air-liquid heat exchanger. This means that on a primary side, the heat exchanger is permeated by the humidified airflow, and on a secondary side, it is permeated by a liquid, for example, water, a water-glycol mixture, or another coolant. The fact that the heat exchanger is permeated by a liquid on the secondary side advantageously promotes the transfer of heat from the primary to the secondary side. Moreover, by controlling the liquid flow through the secondary side, the heat transfer of the heat exchanger can be specifically influenced, thereby achieving particularly optimal temperature control of the airflow on the primary side of the heat exchanger. In another advantageous embodiment of the invention, the heat exchanger can be provided with a variably adjustable liquid supply.

[0020] The performance of the heat exchanger can be specifically influenced by a variably adjustable liquid supply in order to temper the primary-side airflow.

[0021] According to an advantageous embodiment of the invention, the liquid supply can be variably adjustable by means of a controllable liquid pump. A controllable liquid pump can advantageously adjust the flow rate of the secondary-side liquid with particular precision, thereby particularly advantageously controlling heat transfer in order to influence the primary-side temperature of the airflow. According to a further advantageous embodiment of the invention, the liquid pump can be designed to be controllable by a control device. In this way, the flow rate of the liquid pump can be adjusted particularly easily and precisely, thus influencing the temperature of the primary-side airflow as described above.

[0022] According to a preferred embodiment of the invention, a bypass line running parallel to the humidification device can be arranged in the air supply device and can be switched to open instead of or in addition to the humidification device. This allows the additional humidification by the humidification device to be reduced or completely bypassed if the airflow already contains too much water or the fuel cell stack is too wet. The opening cross-section of the bypass valve or bypass line can be designed to be gradually adjustable in order to direct the airflow precisely.

[0023] According to a further preferred embodiment of the invention, the bypass line can be configured to be switchable by means of at least one bypass valve. By blocking the bypass line by means of at least one bypass valve, the airflow through the humidification device can be advantageously controlled. In particular, the bypass valve can be configured to be controllable by a control device. Bypass valves can usually be switched relatively quickly, so that the humidity in the fuel cell stack can advantageously be regulated almost immediately.

[0024] According to a particularly preferred embodiment, the humidification device can be supplied with water from a cathode outlet of the fuel cell stack. This allows the water effluent from the cathode to be advantageously reused in the fuel cell system. The water supply can be passive or active, with active supply meaning that the water is pumped.

[0025] Another aspect of the invention relates to an aircraft fuel cell propulsion system comprising at least one fuel cell stack for generating electrical energy, at least one air supply system according to one of the preceding claims for the at least one fuel cell stack, wherein at least one of the at least one air supply system is connected to a cathode inlet of one of the at least one fuel cell.

[0026] The invention is explained in more detail with reference to the following drawing and a preferred embodiment of the invention.

[0027] Fig. 1 shows a schematic representation of an embodiment of an air supply system according to the invention.

[0028] Fig. 1 shows a schematic representation of an embodiment of an air supply system 10 according to the invention for a fuel cell stack 2, wherein the air supply system 10 is arranged in an aircraft engine 1, in particular an aircraft fuel cell engine 1, and, like the fuel cell stack 2, can be part of a fuel cell system. The fuel cell stack 2 can comprise a plurality of fuel cells connected in series. The air supply system 10 can have an air inlet 11 and an air outlet 12 to supply the air supply system 10 and the fuel cell 2 connected thereto with air or, in particular during cruise flight, with compressed air, and to discharge air released from the fuel cell 2. The air from the air inlet 11 can additionally be filtered, whereby a filter, not shown here, located downstream of the air inlet 11 can serve this purpose.The air inlet 11 can, for example, be located in a bypass duct of the aircraft engine 1. Additionally or alternatively, the airflow can be provided from a tank of compressed air connected to the air inlet 11.

[0029] In the air supply system, an air supply unit 20 is connected downstream of the air inlet 11. This unit may include a compressor assembly 21 to compress the air. The compressor assembly 21 may have at least one compressor 22. It is also possible for the compressor assembly 21 to have several compressors 21 connected in parallel and / or in series. The compressor 21 is preferably driven by an electric motor 23, but can also be driven mechanically, for example by an engine shaft (not shown). The electric motor 23 can be controlled by a control unit 70 connected to the electric motor 23 via signal lines 71. The air can be directed from the air inlet 11 to the compressor assembly 21 via an air inlet line 24.

[0030] Further downstream of the air supply unit 20, a water injection device 40 is arranged according to the invention to inject water into the airflow. The air can be directed from the air supply unit 20, and in particular from the compressor assembly 21, to the water injection device 40 via an air line 25.

[0031] The water injection device 40 is provided in addition to a humidification device 31, which will be described in more detail below, within an air supply device 30, which will also be described in more detail below. This gives the air supply system 10 significantly greater flexibility in humidification. At the same time, the humidification device 31 can advantageously be made considerably smaller, since humidification of the airflow no longer has to be carried out exclusively by the humidification device 31. This advantageously increases the reliability and service life of the fuel cells of the fuel cell stack 2. In a preferred embodiment, the water injection device 40 is variably adjustable. For this purpose, the water injection device 40 can have a water injector 41 and a variably adjustable water supply device 42, so that the water can be sprayed into the airflow by the water injector 41.For this purpose, the water supply device 42 can include a controllable water pump 43. The water pump 43 can variably deliver a quantity and / or type of water to the water injector 41 in order to optimally adjust the water injection into the airflow for the fuel cell stack 2. The water pump 43 can be controlled by a control unit 70 connected to the water pump 43 via signal lines 71.

[0032] Further downstream, a heat exchanger assembly 50 can be arranged. The heat exchanger assembly 50 is supplied with humidified air from the water injection device 40 via a connecting line 45. The heat exchanger assembly 50 preferably comprises at least one heat exchanger 51. The humidified air flows through the primary side of the heat exchanger 51. The heat exchanger 51 can have an evaporation surface 52, which can be wetted with water, particularly by the water injection device 40, to evaporate the water. The supply line 45 can have a transition section that can be connected to and adapted to the water injector 41 at the inlet and allows for a uniform, particularly planar, distribution of water onto the evaporation surface 52 of the heat exchanger 51 at the outlet.On the secondary side, the heat exchanger 51 is preferably supplied with a liquid, for example water or a glycol-water mixture. It can be an air-liquid heat exchanger.

[0033] The heat exchanger 51 can be connected on the secondary side to a liquid circuit 54. The liquid circuit 54 has a liquid supply 55 to the heat exchanger 31 and a liquid discharge 56 from the heat exchanger 31. A controllable liquid pump 53 can be provided in the liquid circuit 54 for circulating the liquid. The liquid pump 53 can be controlled by a control unit 70 connected to the liquid pump 43 via signal lines 71.

[0034] The fluid circulating on the secondary side through the heat exchanger device 50 preferably has a temperature favorable for the operation of the fuel cell stack 2 in order to cool or heat the airflow accordingly to a temperature between 80° and 100°, preferably between 85° and 98°.

[0035] Downstream of the heat exchanger 50, the air supply unit 30 is arranged to supply the humidified and tempered air to the fuel cell stack 2 at its cathode inlet 36. The humidification unit 31 is arranged in the air supply unit 30, with a first air line 33 leading from the heat exchanger 50 to the humidification unit 31 and a further air line 35 leading from the humidification unit 31 to the cathode inlet 36. The humidification unit 31 is supplied with water from the fuel cell stack 2, as described in more detail below.

[0036] Parallel to the humidification device 31, a bypass line 34 can be arranged, through which the airflow can also be partially or completely directed. For this purpose, the bypass line 34 can be opened and closed by means of a bypass valve 32. The bypass line 34 preferably begins at the first air line 33 upstream of the humidification device 31 and opens into the further air line 35 downstream of the humidification device 31. This arrangement allows the humidity content of the airflow at the cathode inlet 36 to be further advantageously controlled.

[0037] An air outlet device 60 can be arranged on the outlet side of the fuel cell stack 2 to guide an outlet air from the fuel cell stack 2. A further air line 62 can lead from a cathode outlet 61 of the fuel cell stack 2 back to the humidification device 31. This air line, hereinafter also referred to as the return line 62, preferably opens into a flow line within the humidification device 31 that is as gas-tight as possible from the two air lines 33, 35 of the air supply device. The return line 62 simultaneously serves to return the byproduct water from the fuel cell reaction and, if applicable, any excess water from the previously humidified airflow to the humidification device 31, so that the water can be used to humidify the inlet air of the fuel cell stack 2.For this purpose, a water separator (not shown) can be provided in the humidification unit 31, which separates the water from the output air of the fuel cell stack 2. The output air can then be directed through a further air duct 63 leading from the humidification unit 31 to the air outlet 12 of the air supply system 10. In this way, any excess air not used for the fuel cell reaction can be expelled from the system.

[0038] The control units 70 mentioned herein can be formed by separate control units, each with its own computer unit, or by a control unit that is at least partially shared. The control units 70 can be connected via the signal lines 71 to sensors on the various components of the fuel cell system, that is, in particular to sensors of the compressor assembly 21, the water injection device 40, the heat exchanger assembly 50, and the air supply device 30, and collect information about the fuel cell system. This information can then be used by the control units 70 to control and / or regulate the controllable components, in particular the pumps 43, 53 and the electric motors 23 of the compressor assembly 21.

[0039] Reference symbol list

[0040] 1 aircraft fuel cell propulsion

[0041] 2 fuel cell stacks

[0042] 10 Air supply system

[0043] 11 Air intake

[0044] 12 air outlets

[0045] 20 Air supply unit

[0046] 21 Compressor arrangement

[0047] 22 compressors

[0048] 23 Electric motor

[0049] 24 Air intake duct

[0050] 25 Air duct

[0051] 30 Air supply device

[0052] 31 Humidification device

[0053] 32 Bypass valve

[0054] 33 Air duct

[0055] 34 Bypass line

[0056] 35 Air duct

[0057] 36 Cathode inlet

[0058] 40 Water injection device

[0059] 41 Water injector

[0060] 42 Water supply system

[0061] 43 Water pump

[0062] 44 Water reservoir

[0063] 45 Connecting cable

[0064] 50 Heat exchanger unit 51 Heat exchanger

[0065] 52 Evaporation surface

[0066] 53 Liquid pump

[0067] 54 Fluid circulation 55 Fluid intake

[0068] 56 Fluid drainage

[0069] 60 Air outlet device

[0070] 61 Cathode outlet 62 Air duct

[0071] 63 Air duct

[0072] 70 Control unit

[0073] 71 Control line

Claims

Patent claims 1. Air supply system (10) for a fuel cell stack (2), in particular for a fuel cell stack (2) of an aircraft fuel cell propulsion system (1), comprising an air supply device (20) for providing an airflow for the fuel cell stack (2), an air supply device (30) arranged downstream of the air supply device (20), which can be connected to the fuel cell stack (2), in particular its cathode side, and which can direct the airflow to the fuel cell stack (2), wherein a humidification device (31) for humidifying the air for the fuel cell stack (2) is arranged in the air supply device (30), characterized in that a water injection device (40) for injecting water into the airflow is arranged between the air supply device (20) and the air supply device (30).

2. Air supply system according to claim 1, characterized in that a water delivery quantity and / or a water delivery method of the The water injection device (40) is variably adjustable.

3. Air supply system according to claim 1 or 2, characterized in that the water injection device (40) comprises a water injector (41) and a has a variably adjustable water supply device (42) that delivers water to the water injector (41).

4. Air supply system according to claim 3, characterized in that the water supply device (42) has a controllable water pump (43).

5. Air supply system according to one of the preceding claims, characterized in that the water injection device (40) is supplied with water from a water reservoir (44).

6. Air supply system according to one of the preceding claims, characterized in that a heat exchanger (51) is arranged between the air supply device (30) and the water injection device (40), wherein the air stream containing water, which is directed from the water injection device (40), can be heated or cooled by the heat exchanger (51).

7. Air supply system according to claim 6, characterized in that the heat exchanger (51) is used for evaporating the water from the Water injection device (40) is designed.

8. Air supply system according to claim 6 or 7, characterized in that the heat exchanger (51) has at least one evaporation surface (52), wherein the water injection device (40), in particular the water injector (41), is designed to spray water onto the evaporation surface (52).

9. Air supply system according to one of claims 6 to 8, characterized in that the heat exchanger (51 ) is designed as an air-liquid heat exchanger.

10. Air supply system according to one of claims 6 to 9, characterized in that the heat exchanger (51 ) has a variably adjustable liquid supply (55).

11. Air supply system according to claim 10, characterized in that, that the liquid supply (55) is variably adjustable by a controllable liquid pump (53), in particular that the liquid pump (53) is designed to be controllable by a control device (70).

12. Air supply system according to one of the preceding claims, characterized in that a bypass line (34) running parallel to the humidification device (31) is arranged in the air supply device (30) and can be switched to allow passage instead of or in addition to the humidification device (31).

13. Air supply system according to one of the preceding claims, characterized in that the bypass line (34) is designed to be switchable by means of at least one bypass valve (32), in particular wherein the bypass valve (32) is designed to be controllable by a control device (70).

14. Air supply system according to one of the preceding claims, characterized in that the humidification device (31 ) is supplied with water from a cathode outlet (61 ) of the fuel cell stack (2).

15. Aircraft fuel cell propulsion (1) comprising at least one fuel cell stack (2) for generating electrical energy, at least one air supply system (10) according to one of the preceding claims for the at least one fuel cell stack (2), wherein at least one of the at least one air supply system (10) is connected to a cathode inlet (36) of one of the at least one fuel cell (2).

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