Aircraft fuel cell propulsion unit

Abstract

The invention relates to an aircraft fuel cell propulsion unit (10) comprising a fuel cell system (12) that includes at least one anode (14), at least one cathode (15) and a process gas device (17) for supplying fuel and ambient air to the anode (14) and the cathode (15) and evacuating spent process gases, further comprising a ram air duct (21) through which compressed ram air (22) flows, and a heat exchanger (20) which is located in the ram air duct (21) and is designed to give off heat generated by the fuel cell system (12) to the environment.

Description

[0001] Aircraft fuel cell propulsion

[0002] The invention relates to an aircraft fuel cell drive with a fuel cell system comprising at least one anode and at least one cathode, as well as a process gas device for supplying the anode and the cathode with fuel and ambient air and for removing spent process gases. Furthermore, the invention relates to a method for operating such an aircraft fuel cell drive.

[0003] To make aircraft more environmentally friendly, efforts are being made to use fuel cells as energy converters for aircraft propulsion. Fuel cell propulsion systems typically generate large amounts of waste heat at low temperatures during operation, requiring a liquid cooling system for the fuel cells that can dissipate this waste heat to the environment to enable safe, stable operation of the fuel cells. A key component for dissipating heat from this liquid cooling system to the environment is a large (main) heat exchanger. This is typically located in or on a ram air duct of an engine in the free flow or behind a propeller.In order to achieve a sufficient cooling effect, such a main heat exchanger must have large dimensions, which makes it difficult to integrate it into the aircraft and can create large additional aerodynamic drag on the aircraft.

[0004] Based on this, it is an object of the present invention to propose an improved aircraft fuel cell drive, with which, in particular, the aerodynamic properties of the drive can be improved and / or maintenance costs can be reduced. Furthermore, a method for operating such an aircraft fuel cell drive is to be 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 fuel cell drive with a fuel cell system is proposed, wherein the fuel cell system has at least one anode and at least one cathode, as well as a process gas device for supplying the anode and the cathode with fuel and ambient air, and for removing spent process gases. Furthermore, the aircraft fuel cell drive has a ram air duct through which ram air flows, and a heat exchanger arranged in the ram air duct, which is configured to dissipate heat generated by the at least one fuel cell to the environment. A supply device configured to introduce water into the ram air flow is arranged upstream of the heat exchanger. The water is provided at least partially from the process gas of the fuel cell system by means of a recovery device.

[0006] The chemical reaction of hydrogen and oxygen in the fuel cell system during operation produces ultrapure, deionized water. Using the recovery device, a particularly liquid water component can be separated from the process gas and fed into a water reservoir in the recovery device and / or into the ram air flow. Thus, the operation of the fuel cell system can be used to provide ultrapure water that meets specific operating requirements. Using the deionized water generated or recovered in this way can reduce or even prevent contamination and / or deposit formation on or in the heat exchanger. This can reduce the risk of damage and / or maintenance effort for the heat exchanger.The integration of a water supply for improved heat transfer in or at the heat exchanger, made possible by the proposed aircraft fuel cell propulsion system, eliminates the need for external water supply, which can result in cost savings.

[0007] By supplying or injecting liquid, deionized water into the ram air duct at the heat exchanger inlet, heat transfer at or within the main heat exchanger can be increased. Experimental studies show a potential performance increase of up to 50% in terms of the amount of waste heat transferred per area. Since the total amount of heat to be dissipated by the aircraft or aircraft fuel cell engine remains unchanged, this creates the potential to reduce the size of the main heat exchanger, which can, for example, result in a reduction in the inflow area, volume, and weight of the (main) heat exchanger. This allows for improved integration into the aircraft fuel cell engine, thereby reducing drag and flow losses on the aircraft. Overall, this can result in an improvement in the overall efficiency of the aircraft fuel cell engine or the aircraft.

[0008] A fuel cell system comprises at least one fuel cell, in particular a plurality of fuel cells, which are arranged, for example, in the form of fuel cell stacks. Such a fuel cell arrangement, which accordingly comprises at least one fuel cell, is also referred to simply as "a fuel cell" in the context of the description of the invention. Accordingly, the plurality of fuel cells usually also comprises a plurality of anodes, which are supplied with a fuel, such as in particular hydrogen, to generate electrical energy, and a plurality of cathodes, which, in cooperation with the anodes, are supplied with ambient air to generate electrical energy in order to supply the atmospheric oxygen contained therein to the fuel cell as an oxidizing agent.

[0009] A process gas device is configured to conduct process gas and supplies the fuel cell or fuel cell system with the reactants necessary for generating electrical energy via the process gas, and removes used process gas or reaction gas from the fuel cell. For this purpose, the process gas device is configured to supply the anode with fuel and the cathode with oxidizing agent, as well as to remove or circulate, in particular, at least partially used process gases. The process gas device can thus form an open gas circuit.

[0010] During operation of a fuel cell, a reducing agent such as hydrogen is supplied to the anode, and an oxidizing agent such as ambient air is supplied to the cathode. At the anode, the hydrogen is catalytically oxidized to hydrogen ions, releasing electrons. These ions pass through the electrolyte, usually in the form of a membrane, into the cathode region, where they react with the oxygen supplied to the cathode and the electrons conducted to the cathode via an external circuit to form water. To ensure stable operation of the fuel cell system, it can be cooled using a cooling system or coolant circuit.This coolant circuit can be connected to the (main) heat exchanger, wherein the heat exchanger is designed to absorb heat generated by the at least one fuel cell and, in particular, transported to the heat exchanger by means of the coolant circuit, and / or to release it to the environment. For this purpose, the heat exchanger can have at least one cooling surface connected to the coolant circuit, over which a fan and / or ram air flow flows during operation. The cooling surface of the heat exchanger absorbs heat from the coolant circuit and dissipates it, in particular convectively, from the heat exchanger. Within the scope of the invention, the heat exchanger can also have a plurality of heat exchanger devices arranged spatially next to one another and / or in a distributed manner, which can, in particular, (each) have a plurality of cooling surfaces.In this context, a cooling surface is any surface arranged on the heat exchanger which is heated by the heat energy to be dissipated and from which heat can be dissipated by a ram air flow passing over it.

[0011] In order to improve the heat transfer in the heat exchanger or on the cooling surfaces, liquid water or water in a liquid state is introduced into the ram air flow by means of the supply device. The supply device is particularly designed to deliver the water into the ram air flow or the ram air duct, in particular to inject it, to nozzle it in and / or to atomize it, whereby the water can be introduced into the flow with an increased volume-to-surface ratio and / or with a uniform distribution across the cross-section of the ram air flow. By supplying water, a cooling of the ram air flow can be achieved and / or a heat transfer between the ram air flow and the cooling surfaces of the heat exchanger can be improved, in particular by a water-based change in the thermal conductivity of the ram air flow. As a result, a thermal efficiency orthe power density of the (main) heat exchanger can be increased and thus, in particular, the size of the heat exchanger can be reduced.

[0012] In one embodiment, the recovery device comprises at least one water separator. The recovery device is connected, in particular, to the process gas device on an outlet side of the fuel cell system, in particular in a fluid-conducting manner, in order to separate water present in the reaction gas. By means of the water separator, a particularly liquid water component can be separated from the process gas or reaction gas of the fuel cell system and can, for example, be fed into a water reservoir of the recovery device, collected there, and / or supplied to the ram air flow or the heat exchanger. The water recovered by means of the water separator can be made available to the supply device so that it can be introduced into the ram air flow in order to increase potential heat transfer between the ram air flow and the heat exchanger.Because the water recovered in this way is deionized, impurities and the associated susceptibility to defects in the heat exchanger can be reduced.

[0013] In one embodiment, the process gas is an anode-side reaction gas and / or a cathode-side reaction gas. For example, the water separator can be fluidly connected to an exhaust line and / or a gas recirculation system of the process gas device, or a gas connection of the water separator can be fluidly connected to a cathode outlet or an anode outlet of the fuel cell system in order to separate liquid water from the respective reaction gas.

[0014] Since water can be present in both the anode-side reaction gas and the cathode-side reaction gas, particularly in the gaseous state, some embodiments provide a condenser upstream or downstream of a respective water separator to improve the separation of water from the reaction gas. This allows a smaller water reservoir for the recovered water than in a system without a condenser, thereby reducing the system weight in the aircraft.

[0015] In some embodiments, the recovery device can be provided only on the anode side; in other embodiments, the recovery device can be provided only on the cathode side; and in yet other embodiments, the recovery device can be provided on both the anode and cathode sides to enable water recovery. The water recovery enabled in this way enables continuous operation of the water supply to the ram air flow, thereby increasing the performance of the heat exchanger even during cruise flight.

[0016] In one embodiment, the supply device is configured to introduce the water in atomized form into the ram air flow. The supply device can be configured to inject, nozzle, and / or atomize the water into the exhaust gas flow and, for this purpose, can comprise, in particular, an injection, nozzle, and / or atomization device arranged at a point at which the water is supplied to the ram air flow. The degree of atomization or the droplet size of the water to be supplied can be adjustable by means of the supply device. A high degree of atomization of the water or a small droplet size of the water can promote heat transfer between the ram air flow and the heat exchanger, since the number of water droplets and thus the surface area available for heat exchange can be increased.Furthermore, the atomized water can be distributed evenly in the ram air flow to enable an improvement in effectiveness across the entire cross-section of the ram air flow.

[0017] In one embodiment, the supply device comprises a pulse valve. The pulse valve can be arranged between a pump of the supply device and a water supply point in the ram air flow. The supply device is, in particular, fluidically connected to the water reservoir of the recovery device and configured to transport water to an injection, nozzle, and / or atomization device at the supply point.

[0018] The pulse valve can be used to control the water flow rate at an injection, nozzle, and / or atomization device arranged at the supply point, or the water can be introduced into the ram air flow using the pulse valve. For this purpose, the pulse valve is designed, for example, as a pilot-controlled 2 / 2-way valve and / or is configured to enable water to be transported at predetermined intervals and / or in predetermined quantities, thereby enabling improved atomization of the water over a wide operating range. The pulse valve can be configured to pulse the water or generate a pulsating water flow and / or adjust an amplitude and / or frequency of the pulsating water flow. This allows the water to be supplied to the ram air flow, for example, in batches and / or at a predetermined pressure, in order to influence the distribution of the water in the ram air flow.In addition, the pulse valve can be configured to set or vary a pulse duration, a temperature (heating and / or cooling) of the water and / or a predetermined operating pressure for the water in order, for example, to be able to adapt the properties of the water to be supplied to the operating parameters of the ram air flow or the aircraft fuel cell drive.

[0019] According to a further aspect, a method for operating an aircraft fuel cell drive with at least one fuel cell system is proposed. The aircraft fuel cell drive is designed, in particular, according to the preceding description. In the proposed method, ram air is flowed through the ram air duct, the fuel cell system is operated, and water is supplied to the ram air flow by means of the supply device, in particular before or upon entry into the heat exchanger.

[0020] The aircraft fuel cell drive can have a control device configured to control the supply device, the recovery device, the pulse valve, and / or the heat exchanger. In particular, a degree of heat dissipation or heat transfer at or by means of the (main) heat exchanger(s) can be adjusted by regulating a coolant flow rate of the heat exchanger and / or a water supply to the ram air flow. Thus, a heat exchange performance of the heat exchanger can be varied by means of the control device. The control device can specify a respective operating state or heat exchange performance for the heat exchanger, for example, depending on an ambient temperature, a ram air humidity, a ram air flow velocity, and / or taking into account other operating parameters, such as those of the fuel cell system.

[0021] In one embodiment, the water is at least partially obtained from a process gas of the fuel cell system. The process gas is an anode-side reaction gas and / or a cathode-side reaction gas. Since the reaction of hydrogen and oxygen in the fuel cell system produces reaction gases containing highly pure, deionized water, which are removed from the fuel cell and / or at least partially recirculated to the anode and / or cathode, this water can be separated from the anode-side and / or cathode-side reaction gas, in particular by means of the recovery device, and fed to the ram air flow. Due to the purity of the water thus obtained, contamination and / or deposit formation on or in the heat exchanger can be reduced or even avoided, in order to reduce the likelihood of damage and / or a reduction in efficiency.

[0022] In one embodiment, a volume flow of the water to be supplied can be specified depending on parameters of the aircraft fuel cell drive, in particular by controlling the pulse valve. An injection, nozzle, and / or atomization device arranged at a water supply point into the ram air flow can be configured to adjust the volume flow. Parameters of the aircraft fuel cell drive can include, for example, a current temperature, a speed, a pressure, a composition, and / or a specific gravity of the ram air flow. Furthermore, operating parameters of the aircraft engine or an environment can also be taken into account when determining the volume flow to be supplied. This allows the heat transfer performance of the heat exchanger, and in particular water recovery from the process gas of the fuel cell system, to be operated efficiently under varying conditions.

[0023] In one embodiment, the degree of atomization of the water to be introduced can be varied, in particular by controlling the pulse valve, depending on parameters of the aircraft fuel cell drive and in particular on operating parameters of the aircraft engine and / or an environment. When water is supplied with a high degree of atomization, the smallest possible water droplets are supplied to the ram air flow, whereby, with the same supply quantity, the number of water droplets can influence the evaporation in the heat exchanger. This can, for example, increase the heat transfer performance of the heat exchanger or keep it constant if necessary. Further features, advantages, and possible applications of the invention will become apparent from the following description in conjunction with the figures.In general, features of the various exemplary aspects and / or embodiments described herein may be combined with one another unless clearly excluded in the context of the disclosure.

[0024] In the following part of the description, reference is made to the figures shown to illustrate specific aspects and embodiments of the present invention. It is understood that other aspects may be utilized and structural or logical changes to the illustrated embodiments are possible without departing from the scope of the present invention. The following description of the figures is therefore not to be understood as limiting. It shows

[0025] Fig. 1 is a schematic representation of an exemplary aircraft fuel cell drive according to the invention with a fuel cell system;

[0026] Fig. 2 is a schematic representation of a flow chart of a method according to the invention for operating an aircraft fuel cell drive with a fuel cell system.

[0027] Fig. 1 shows a schematic representation of an exemplary aircraft fuel cell drive 10 according to the invention, comprising a fuel cell system 12 and a heat exchanger 20. In order to operate the fuel cell system 12 reliably, it must be cooled. For this purpose, a fluid cooling device 40 is provided, which can transport heat generated by the fuel cell system 12 by means of a cooling fluid to the heat exchanger 20, where the heat is released to the environment by means of the heat exchanger 20. For this purpose, the cooling fluid can be fed to the fuel cell system 12 via a cooling fluid supply 41, absorb heat there, and be discharged from there via a cooling fluid discharge 42. In order to cool the cooling fluid, it is fed by the fluid cooling device 40 to a cooling fluid supply 43 of the heat exchanger 20, where heat is extracted from it. The cooling fluid can then be discharged from there via a cooling fluid discharge 44.The cooling fluid inlets 41, 43 and cooling fluid outlets 42, 44 can form a coolant circuit (not shown).

[0028] The fuel cell system 12 has a fuel cell 13 with an anode 14 and a cathode 15. The anode 14 is supplied with fuel, in the exemplary embodiment with hydrogen, from a fuel reservoir 16 via a process gas device 17, and the fuel is largely consumed in the fuel cell 13. The used process gas or the anode-side reaction gas is removed from the fuel cell 13. Fuel that has not been completely used up or excess hydrogen can be fed back to the fuel cell 13 via the process gas of the anode 14 with the help of a gas recirculation 27 or, in particular, released into the environment. The cathode 15 is supplied with ambient air taken from the environment 18 via the process gas device 17 and reacts as process gas in the fuel cell 13. The used ambient air orThe cathode-side reaction gas can be removed from the fuel cell 13 by means of the process gas device 17 and in particular released into the environment 19.

[0029] The heat exchanger 20 is arranged in or on a ram air duct 21 through which ram air pressure 22 flows and is configured to dissipate heat generated by the fuel cell system 12 to the environment 23. Upstream of the heat exchanger 20, a supply device 50 is arranged, which is configured to introduce water into the ram air flow 22. For this purpose, the supply device 50 has a nozzle device 51 arranged at or before the inlet of the ram air flow 22 into the heat exchanger 20, which nozzle device is configured to introduce the water in atomized form into the ram air flow 22. By means of the supplied water, a cooling effect of the heat exchanger 20 or a heat transfer at and / or in the heat exchanger 20 can be increased.

[0030] The water is at least partially provided from the process gas of the fuel cell system 12 by means of a recovery device 30. The recovery device 30 has a first water separator 31, which is fluidly connected to an anode-side section of the process gas device 17 downstream of the fuel cell system 12 and is configured to separate water from an anode-side reaction gas. To additionally recover water from the anode-side reaction gas, a first condenser 34 can be provided upstream of the first water separator 31. This first condenser 34 can have a cooling circuit with a coolant supply 341 and a coolant discharge 342.

[0031] In the illustrated embodiment, the recovery device 30 has a second water separator 32, which is fluidly connected to a cathode-side section of the process gas device 17 downstream of the fuel cell system 13 and is configured to separate water from a cathode-side reaction gas. To additionally recover water from the cathode-side reaction gas, a second condenser 35 can be provided upstream of the second water separator 32. This second condenser 35 can have a cooling circuit with a coolant supply 351 and a coolant discharge 352. The coolant circuits of the condensers 34, 35 can be connected to the fluid cooling device 40 of the fuel cell system 12 or its coolant circuit (not shown).

[0032] The separated water from both the water separators 31, 32 and the condensers 34, 35 can be collected in a water reservoir 33 of the recovery device 30. From there, the water can be fed to the ram air flow 22 by means of the feed device 50. For this purpose, the feed device 50 has a pump 52 to pump the water. A pulse valve 53 downstream of the pump 52 can be used to regulate or control the water flow at the nozzle device 51.

[0033] Fig. 2 shows a schematic representation of a flow diagram of an exemplary method 100 for operating an aircraft fuel cell drive 10 described herein with a fuel cell system 12. The steps of the method 100 can in particular be carried out or take place simultaneously or in a modified order and thus deviate from the sequence shown.

[0034] In a step a, ram air 22 flows through the ram air duct 21. In a step b, the fuel cell system 12 is operated to provide energy for an aircraft engine, and in a step c, water can be recovered from a reaction gas of the fuel cell system 12, in particular by means of the recovery device 30. In a step d, water is supplied to the ram air flow 22 before entering the heat exchanger 20 by means of the supply device 50. In this case, a volume flow and / or a degree of atomization of the water to be introduced can be controllable and / or regulated depending on parameters of the aircraft fuel cell drive 10 in order to increase the heat exchange performance of the

[0035] To be able to adapt the heat exchanger to operating conditions, for example of aircraft fuel cell propulsion.

[0036] LIST OF REFERENCE SYMBOLS

[0037] 10 aircraft fuel cell propulsion

[0038] 12 Fuel cell system

[0039] 13 Fuel cell

[0040] 14 Anode

[0041] 15 Cathode

[0042] 16 fuel storage

[0043] 17 Process gas system

[0044] 18 Surroundings

[0045] 19 Surroundings

[0046] 20 heat exchangers

[0047] 21 ram air duct

[0048] 22 Ram air pressure / ram air flow

[0049] 23 Surroundings

[0050] 27 Gas recirculation

[0051] 30 Recovery facility

[0052] 31, 32 Water separator

[0053] 33 water reservoirs

[0054] 34, 35 Capacitor

[0055] 40 Fluid cooling device

[0056] 41, 43 Cooling fluid supply

[0057] 42, 44 Cooling fluid discharge

[0058] 50 feeding device

[0059] 51 Nozzle device

[0060] 52 Pump

[0061] 53 Pulse valve

[0062] 341 Condenser coolant supply

[0063] 342 Condenser coolant discharge

[0064] 351 Condenser coolant supply

[0065] 352 Condenser coolant discharge

Claims

CLAIMS 1. An aircraft fuel cell drive (10) comprising a fuel cell system (12) having at least one anode (14) and at least one cathode (15), as well as a process gas device (17) for supplying the anode (14) and the cathode (15) with fuel and ambient air and for removing used process gases, a ram air duct (21) through which ram air pressure (22) flows, and a heat exchanger (20) arranged in the ram air duct (21) which is designed to dissipate heat generated by the fuel cell system (12) to the environment (23), wherein a supply device (50) is arranged upstream of the heat exchanger (20) and is designed to introduce water into the ram air flow (22), characterized in that the water is provided at least partially from the process gas of the fuel cell system (12) by means of a recovery device (30).

2. Aircraft fuel cell drive (10) according to claim 1, wherein the recovery device (30) has at least one water separator (31, 32).

3. Aircraft fuel cell drive (10) according to at least one of the preceding claims, wherein the process gas is an anode-side reaction gas and / or a cathode-side reaction gas.

4. Aircraft fuel cell drive (10) according to at least one of the preceding claims, wherein the supply device (50) is arranged to introduce the water in atomized form into the ram air flow (22).

5. Aircraft fuel cell drive (10) according to at least one of the preceding claims, wherein the supply device (50) has a pulse valve (53). Method (100) for operating an aircraft fuel cell drive (10) with a fuel cell system (12) according to at least one of claims 1 to 5, wherein a) ram air (22) flows through the ram air duct (21); b) the fuel cell system (12) is operated; c) water is obtained at least partially from a process gas of the fuel cell system (12); and d) water is supplied to the ram air flow (22) by means of the supply device (50). Method (100) according to claim 6, wherein the process gas is an anode-side reaction gas and / or a cathode-side reaction gas. Method (100) according to at least one of claims 6 or 7, wherein a volume flow of the water to be supplied can be predetermined depending on parameters of the aircraft fuel cell drive (10), in particular by controlling the pulse valve (53).Method (100) according to at least one of claims 6 to 8, wherein a degree of atomization of the water to be introduced can be varied depending on parameters of the aircraft fuel cell drive (10).

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