High-temperature fuel cell aircraft generator unit

Abstract

The invention relates to a generator unit for an aircraft, comprising an electric machine (1) and a fuel cell (3), and further comprising a rotary compressor (5), a combustion chamber (7) and a turbine (9), the turbine (9) being adapted to be coupled via a shaft to the electric machine (1) by torque transmission, and comprising a return line (11) for returning the exhaust air from the fuel cell (3) into the gas flow upstream of the fuel cell (3) further comprising a supply line for supplying at least part of the exhaust air from the combustion chamber (7) to the fuel cell (3), further comprising a first bypass line which, starting from the supply line, passes around the fuel cell (3). Abstract figure: Figure 1

Description

Title of the invention: Generator unit for aircraft, with high-temperature fuel cell Technical field of the invention

[0001] The invention relates to a generator unit for producing electric current for an aircraft. State of the prior art

[0002] A large number of conventional aircraft engines use fuel that is oxidized in a combustion chamber. This oxidation with an oxidant such as atmospheric oxygen is an exothermic reaction; the released and usable energy is used to generate the thrust of the aircraft. For this purpose, there are several degrees of freedom in the configuration of a combustion chamber. Different types of concepts are known from the prior art, also based in part on different fuels. While liquid hydrocarbon fuels are typically converted into carbon dioxide and water in a high-temperature combustion chamber, the use of hydrogen as an energy carrier offers the possibility of being used in a fuel cell which, also with the aid of an oxidant, typically atmospheric oxygen, can be used as a source of electrical energy to drive an electric machine.Furthermore, such a reducing agent used for a fuel cell, such as for example the mentioned hydrogen, can be used for combustion in a conventional engine configuration with a thermal combustion chamber. Fuel cells and thermal combustion chambers can furthermore be used together, in particular for using hydrogen both in a combustion chamber engine and in a fuel cell as a reducing agent for electricity generation.

[0003] In this context, document US 20220297844 A1 relates to a hybrid jet engine whose functions are intended to meet the requirements of aircraft thrust, passenger airflow and fuel cells. An engine has a combustion chamber that burns the same fuel as the fuel cell. The engine has more electric motors to utilize the power of the fuel cell. The jet engine shafts are equipped with clamping parts so that the motors can drive the compressors and operate the turbines. The engine has a variable flow path geometry to bypass the combustion chamber.

[0004] Document US 10644331 B2 further relates to a quick start group and a method of operating a quick start group. A fuel cell converts combustible fuel into electrical energy during a normal operating phase, after initially producing little or no electrical energy. A combustor receives unburned fuel emitted by the fuel cell and burns the unexpended fuel to produce a first heated gas stream. Another combustor receives combustible fuel and burns the combustible fuel to produce a second heated gas stream during the first start-up phase. A turbine receives and is driven by the first and second heated gas streams to drive a drive shaft. A generator coupled to the drive shaft generates electrical energy during the first start-up phase and additional energy during the normal operating period.In another embodiment, a two-stage combustion chamber is used instead of two separate combustion chambers arranged in series.

[0005] Document US 20230039759 A1 further relates to an integrated fuel cell and combustion chamber assembly with a combustion chamber that is fluidly coupled to at least one upstream-connected compressor, which generates compressed air. A fuel cell stack having a cathode and an anode is fluidly coupled to the combustion chamber. The fuel cell stack is configured to receive intake fuel and a portion of the compressed air as intake air, to generate fuel cell power using the intake fuel and the intake air, and to conduct an exhaust of fuel and air outward from the fuel cell into the combustion chamber.A self-contained air supply system is fluidly coupled to the at least one upstream compressor and the fuel cell stack, and configured to supply intake air to the fuel cell stack. A fault-tolerant controller is configured to recognize a transient event within the combustor and control the self-contained air supply system during the transient event.

[0006] Fuel cells, as used in the aforementioned prior art, typically require a certain minimum temperature to operate either in absolute terms or at high efficiency. In the case of a high-temperature fuel cell such as a solid oxide fuel cell (also called a "solid oxide fuel cell", abbreviated "SOFC"), inlet temperatures of the reducing agent (typically molecular hydrogen) and the oxidizing agent (typically atmospheric oxygen) of about 800°C may be desired or required. Therefore, preheating of the material streams feeding the fuel cell is necessary. While heat release occurs when using the fuel cell in its own operation, and can in principle be used for preheating, the heat release is not available when a drive unit equipped with such a fuel cell is started from standstill. Presentation of the invention

[0007] The objective of the invention is to improve an electric generator unit provided with a fuel cell for generating an electric power flow for an aircraft. Summary of the invention

[0008] A first aspect of the invention relates to a generator unit for an aircraft, comprising an electrical machine and a fuel cell, and further comprising a rotary compressor with compressor blades, a first combustion chamber and a turbine, the compressor, the first combustion chamber and the turbine being arranged in series such that a gas flow from a surrounding air is compressed by the compressor during operation of the generator unit, is further used in its flow direction for the combustion of a fuel in the first combustion chamber by subsequent flow in the turbine to drive the turbine, the turbine being able to be coupled to the electrical machine via a shaft with torque transmission, in particular by a controllable coupling, or be permanently coupled with torque transmission,and having a return line for returning exhaust air from the fuel cell into the gas flow upstream of the fuel cell, preferably upstream of the first combustion chamber, also having a supply line for supplying at least part of the exhaust air from the first combustion chamber to the fuel cell, also having a first bypass line which, starting from the supply line and / or starting from a bypass around the combustion chamber or starting from a line after mixing of the supply line with a second bypass line around the combustion chamber, leads around the fuel cell.

[0009] The fuel cell is preferably a high-temperature fuel cell, for example a solid oxide fuel cell (acronym "SOFC"). The compressor is made to rotate, like the turbine, and therefore, unlike piston compressors, it falls into the category of turbomachinery components - hence the term rotary compressor.

[0010] The fuel for the combustion chamber is drawn from a fuel tank, alternatively or additionally, exhaust gases from the fuel cell, which are introduced into the gas flow before the combustion chamber via the return line, may still contain a portion of fuel and may be used as fuel for the combustion chamber. In particular, when When starting the generator unit, preferably only fuel from the fuel tank will be used for combustion in the combustion chamber, since in this case no fuel cell exhaust gas is yet available and therefore no fuel portion in the fuel cell exhaust gas can be used. However, during normal operation of the generator unit, the fuel present in the fuel cell exhaust gas can be transferred for combustion in the combustion chamber via the return line.

[0011] Instead of one combustion chamber, several combustion chambers can also be provided, which can be connected in series or in parallel.

[0012] By using the first bypass line, it is possible to implement an architecture with a return line and a supply line, both of which are used for thermal optimization of the gas flows in the generator unit. Via the return line, the exhaust air from the fuel cell, heated by the fuel cell, can be guided into the gas flow upstream of the combustion chamber, whereby the gas flow heated by the combustion in the combustion chamber can in turn be led at least partially to the fuel cell by means of the supply line.The supply of fresh air containing oxygen to both the fuel cell and the combustion chamber, which are integrated in this partially closed circuit, is achieved on the one hand through the first bypass line so as not to pass the entire gas flow through the fuel cell but a part around it, as well as preferably through a second bypass line which leads around the combustion chamber so that the combustion chamber cannot extract too high a degree of oxygen from the gas flow and cause an oxygen deficiency at the fuel cell.

[0013] There is thus on the one hand a circuit passing through the combustion chamber to the fuel cell and returning to the inlet of the combustion chamber, and on the other hand a path from the ambient air, which is admitted by the generator unit, through the second bypass line, and then via the first bypass line through the turbine to the environment. The two paths (in the circuit through the combustion chamber and through the fuel cell as well as along the combustion chamber and the fuel cell) intersect, however, which causes a constant mixing of the gas flows at the nodes. It is thus ensured, on the one hand, that a sufficient quantity of oxygen is available for oxidation both in the combustion chamber and in the fuel cell, and on the other hand, at least in stationary operation of the generator unit, a gas flow supplying the combustion chamber and a gas stream feeding the fuel cell are preheated.

[0014] An advantage of the generator unit is that the number and / or size of conventional heat exchangers can be reduced, and thus the mass and installation volume can also be reduced. Instead of a configuration with heat exchangers in the air supply, preheating of the air supply using the return air flow is provided. In addition, the heating of the air supplied to the fuel cell is supported by the combustion chamber taking into account the air flow direction upstream of the fuel cell. In addition, the reducing agent, such as for example hydrogen, can be preconditioned, in particular with heat exchangers that absorb heat from the gas flow.

[0015] The features described in the following paragraphs may be optionally implemented. They may be implemented independently or in combination with each other:

[0016] Even more advantageously, the solid oxide fuel cell may be structurally integrated instead of being provided as an independent component.

[0017] According to another advantageous embodiment, the generator unit further comprises a control unit, designed to operate the electrical machine in a generator mode or possibly in a motor mode, and to start the motor mode at least when starting or starting up the generator unit, and comprising valves controllable by the control unit to adapt the fluid flow rates in the generator unit.

[0018] The fluid flows include at least the gas flow, but may also include fuel flows: While some valves specifically regulate the ratios of the gas flow shares through the combustion chamber, the fuel cell and a respective bypass, other valves can be used to regulate the mass flow of the reducing agent, for example hydrogen. A control unit advantageously optimizes the operation of the generator unit by means of coordinated control of the valves and can thus ensure that the required useful power of the generator unit is available in each operating range (start-up, stationary continuous operation, aircraft take-off, etc.), and this in a range of the highest possible efficiency. In the event of a failure, the valves can also be controlled in such a way that a drive without a fuel cell is possible.

[0019] The fuel cell is advantageously dimensioned relative to the other components such that at least during stationary operation of the generator unit, for example during cruising flight of the aircraft, at least half of the total heat generation in the generator unit comes from the fuel cell. Furthermore, it is advantageously provided that during this operation of the generating unit, at least half of the gas mass flow is guided through the fuel cell itself, rather than diverted around a bypass surrounding it.

[0020] According to another advantageous embodiment, the generator unit further comprises a propeller or fan, which can be coupled to the shaft and / or to the electric machine for the transmission of torque, and which serves to generate aerodynamic thrust for the aircraft.

[0021] According to another advantageous embodiment, the electric machine and the shaft are connected to each other via a transmission.

[0022] By using a summing gear, for example a planetary gear, the generator unit can be started without a rotating propeller, if applicable, and can also supply electricity. In addition to the summing gear, one or more couplings can also be provided so that the turbine, the electrical machine and the propeller can be switched (preferably independently of each other), i.e. can be connected to the torque chain at the at least one shaft between the turbine and the compressor or can be decoupled therefrom. This construction makes it possible on the one hand to ensure the controllability of the system; on the other hand, a start-up without propeller movement is possible. Optionally, a braking unit is provided, which is connected in particular to the propeller to stop it and to operate the electrical machine without rotating the propeller by decoupling the coupling.

[0023] According to another advantageous embodiment, the first branch and / or the second branch of the return pipe comprises a compressor.

[0024] According to another advantageous embodiment, the return pipe comprises a first branch and a second branch which lead to different pressure stages in and / or behind the compressor.

[0025] If several compressor stages are provided, a first branch can lead between the compressor stages. If another branch is led behind the last compressor stage in the flow direction, a separate return line compressor must be provided for this return line branch.

[0026] According to another advantageous embodiment, the compressor comprises a low pressure stage and a high pressure stage, a return line compressor being arranged in the second branch.

[0027] According to another advantageous embodiment, the generator unit further comprises a second bypass pipe around the first combustion chamber, the second bypass pipe opening into the supply pipe.

[0028] According to another advantageous embodiment, the return pipe leads into the gas flow of the second bypass pipe.

[0029] According to another advantageous embodiment, the generator unit further comprises a second combustion chamber which is arranged in the direction of flow of the gas flow between the fuel cell and the turbine.

[0030] In certain operating modes of the generator unit, the first combustion chamber can, in another embodiment, be disconnected, so that a complete gas flow is guided around the first combustion chamber by means of a bypass. Preferably, a central control unit, which serves to control valves for setting a mass flow ratio of the bypass and the combustion chamber or the fuel cell as well as to control the flow of the fuel supply, is also designed for the disconnection of the first combustion chamber.

[0031] According to another advantageous embodiment a nozzle is arranged behind the turbine in the flow direction in order to generate thrust for the aircraft by the flow of gas emerging through the nozzle into the environment.

[0032] The nozzle preferably has a cross-sectional layout with local narrowing in order to feed the gas flow through the generator unit at higher speeds before its discharge into the environment. An increased pressure and / or an increased temperature of the gas flow are therefore at least partially energetically converted into kinetic energy. The resulting impulse on the aircraft generates thrust.

[0033] According to another advantageous embodiment the generator unit further comprises at least one heat exchanger designed to extract heat from the gas stream and transfer it to the fuel in a fuel supply line.

[0034] Another aspect of the invention relates to an aircraft provided with a generator unit as described above and below.

[0035] According to another advantageous embodiment the generator unit further comprises at least one heat exchanger designed to extract heat from the gas stream and transfer it to the fuel in a fuel supply line.

[0036] Further advantages, features and particularities will emerge from the following description, in which at least one exemplary embodiment is described in detail - where appropriate with reference to the drawing. Identical, similar and / or functionally identical parts bear the same reference numbers. Brief description of the figures

[0037] They show: Fig.l

[0038] [Fig.l] is a generator unit according to an exemplary embodiment of the invention in section. Fig. 2

[0039] [Fig.2] is a schematic operating principle of a generator unit according to another exemplary embodiment of the invention. Fig. 3

[0040] [Fig.3] is a schematic operating principle of a generator unit according to another exemplary embodiment of the invention. Detailed description of the invention

[0041] The representations in the figures are schematic and not to scale.

[0042] [Fig.l] shows a generator unit for an aircraft. The generator unit primarily serves as a power source for electric motors, which are distributed along a wing of the aircraft and are connected to respective small propulsion propellers. For the purpose of generating electricity, the generator unit has on the one hand an electric machine 1 as well as an annular fuel cell 3. The electric machine 1 is an electric motor which is preferably used as an electric generator during a cruising flight. The fuel cell 3 uses hydrogen as fuel T and oxygen from the supplied ambient air.Since the fuel cell 3 requires a certain temperature to carry out the oxidation of the fuel T and furthermore to carry it out at a high efficiency, two mechanisms are employed to preheat the mass flow rates of ambient air and fuel T supplied to the fuel cell 3: On the one hand, a return line 11 is provided which again conducts the exhaust gases from the fuel cell 3 to a combustion chamber 7. In this way, the gas flow introduced from the environment into the generator unit is heated from the ambient air. Furthermore, when ambient air is supplied through a supply line 13 (see [Fig. 2]), exhaust gases from the combustion chamber 7 are led to the fuel cell 3, which in turn are heated by combustion in the combustion chamber 7.This results on the one hand in a possibility of generating electrical energy by means of the fuel cell 3, and on the other hand in another possibility of generating electricity using the electric machine 1. After the ambient air is introduced into the generator unit at the left end of the drawing shown in [Fig.l], it is compressed by a compressor 5 with compressor blades. The compressor 5 has a first stage 27 and a second stage 29. In this exemplary embodiment, the return line 11 leads between the two stages of the compressor 5, however there are degrees of design freedom in order to find an optimal configuration of each respective individual generator unit. The gas flow compressed by the compressor 5 is heated by the exhaust gases of the fuel cell 3 guided through the return line 11 and led to the combustion chamber 7; the fuel T is burned there and the gas mixture . energetically charged, after additional heating, is led into the fuel cell 3, in which the fuel T is used, and then expanded in a turbine 9. Possible particular lines of the gas flow and the fuel flows are shown in Figures 2 and 3. In the implementation of [Fig.l], the turbine 9 also has a high-pressure stage and a low-pressure stage, the low-pressure stage 35 of the turbine 9 (see [Fig.2]) being connected to the low-pressure stage 27 of the compressor 5 with a first shaft, while the high-pressure stage 33 of the turbine 9 is connected to the high-pressure stage 29 of the compressor 5 with a second shaft. At least one of the two shafts is further connected to a transmission 21, which is itself coupled to the electric machine 1.Furthermore, a propeller 15 is provided so that the generator unit, in addition to generating electrical energy, can itself directly generate thrust in two ways: On the one hand by discharging the gas flow behind the turbine 9 through a nozzle, on the other hand by the rotation of the propeller 15 when the latter is coupled with torque transmission with a coupling to be provided on at least one of the shafts. As an example, but not necessarily in all embodiments, in the embodiment of [Fig.l], the propeller 15 is shown, and can be provided, without being mandatory. When starting the aircraft, in particular, the propeller 15 can provide additional thrust, while the electric machine 1 can additionally operate as an electric motor to support the rotation of the propeller 15. An additional battery can optionally be provided to drive the electric machine 1.When starting the generator unit from standstill, the electrical machine 1 can also be used via supplied electric current, in order to start the system, in particular from the compressor 5 and the turbine 9, i.e. to set the gas flow in motion. Alternatively, the start can be carried out using compressed air. In both cases, the fuel cell 3 is slowly heated, while preferably a bypass 12 (see [Fig. 2]) remains closed around the fuel cell 3. When starting the combustion chamber 7, the bypass 12 around the fuel cell 3 is regulated in such a way that a continuous slow rise in temperature occurs in the fuel cell 3 and the heat exchanger 25 possibly provided for preheating the fuel T is efficiently put into operation (see [Fig. 2]). After fuel cell 3 has been successfully preheated, it is put into operation.However, after starting the aircraft, the propeller 15 can optionally be disconnected and the electric machine 1 can be used in generator mode by receiving torque via a corresponding coupling, to at least one of the two shafts, and outputting electrical power. In cruising flight or after reaching a stationary state, the combustion chamber 7 can also be switched to operation with only residual fuel from . of the fuel cell 3. Alternatively, the combustion chamber 7 can be disconnected and the remaining fuel from the fuel cell 3 is then burned in another combustion chamber 23 (see [Fig. 3]). Alternatively, excess mechanical energy from a shaft connection of the compressor 5 and the turbine 9 can be distributed to the electric machine 1 and the propeller 15. In the event of excess electrical energy, this can be directed to another thrust propeller of the aircraft or to a battery. Advantageously, in the event of a failure in the fuel cell 3, the bypass 12 around the fuel cell 3 can be completely opened, and the generator unit can be used as a gas turbine coupled to an electric machine 1.Depending on the specific architecture, the generator unit allows further optimizations of the control by using the degrees of freedom of the couplings, gears 21, valves 25, possibly connected batteries, etc.; .

[0043] [Fig. 2] shows a topology of a possible embodiment of the generator unit. The fuel T is taken from a tank and preconditioned in a fuel preconditioning unit. When, in particular, the generator unit is started, this fuel preconditioning unit itself ensures that the fuel T is at the correct temperature. Furthermore, at the left end of the diagram, ambient air is admitted, compressed by a low-pressure stage 27 of the compressor 5, further compressed by a high-pressure stage 29 of the compressor 5, and distributed in a second bypass 17 around a combustion chamber 7 as well as in the supply to the combustion chamber 7. The exhaust gases from the combustion chamber 7 and the second bypass are then combined to be distributed in a first bypass line 12 around the fuel cell 3 and in a supply to the fuel cell 3.After mixing with the first bypass line 12, the exhaust gases from the fuel cell 3 are partially returned to the gas flow between the compressor stages 27 and 29 and behind the compressor 5 through a return line 11, a return line compressor 31 being provided in the return line directly behind the compressor 5 in this branch. Alternative arrangements and numbers of branches of the return line 11 are possible. Furthermore, a large number of heat exchangers 25 are provided, which absorb heat along the gas flow preferably from the fuel cell 3 and return it to the fuel T. A guidance of the heat flows can then be provided as in the paths shown in dotted lines.Depending on the condition of the generating unit and the exact design, these heat exchangers 25 can be connected in series, or alternatively, only a part of these heat exchangers 25 can be used. A control unit can regulate this by means of appropriate valve controls.

[0044] [Fig. 3] shows a variant of the generator unit of [Fig. 2], in which a second combustion chamber 23 is provided behind the fuel cell 3 taking into account the flow direction of the gas flow. This does not make the first combustion chamber 7 completely unnecessary; on the contrary, depending on the operating state, both combustion chambers 7, 23 can be used, or the first combustion chamber 7 can be disconnected, in particular when the aircraft is in cruising flight, when the fuel cell 3 itself already produces, after a certain operating time of the generator unit, sufficient heat to be able to supply electrical energy effectively and efficiently. The operation of the electrical machine 1 is then, depending on the circumstances, no longer necessary or is only necessary to a significantly lesser extent, and the first combustion chamber 7 can be disconnected.

[0045] Although the invention has been illustrated and explained in detail by examples of preferred embodiments, it is not limited by the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a large number of possible variations exist. It is also clear that the examples of embodiments cited represent only examples which should in no way be interpreted as constituting a limitation of the scope of protection, the possibilities of implementation or the configuration of the invention.On the contrary, the above description and the description of the figures enable the skilled person to concretely implement the exemplary embodiments, the skilled person, having knowledge of the disclosed inventive concept, being able to make various modifications, for example with regard to the function or arrangement of individual elements cited in an exemplary embodiment, without departing from the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description. List of reference signs

[0046] 1 electric machine

[0047] 3 fuel cells

[0048] 5 compressor

[0049] 7 first combustion chamber

[0050] 9 turbine

[0051] 11 return line

[0052] 12 first bypass line

[0053] 13 supply line

[0054] 15 propeller

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064] 17 second bypass line 19 valve 21 transmission 23 second combustion chamber 25 heat exchanger 27 compressor low pressure stage 29 compressor high pressure stage 31 return line compressor 33 turbine high pressure stage 35 turbine low pressure stage

Claims

Claims

1. A generator unit for an aircraft, comprising an electrical machine (1) and a fuel cell (3), comprising a rotary compressor (5) with compressor blades, a first combustion chamber (7) and a turbine (9); the compressor (5), the first combustion chamber (7) and the turbine (9) being arranged in series such that a gas flow from a surrounding air is compressed by the compressor (5) during operation of the generator unit, the gas flow being further used in its flow direction for the combustion of a fuel (T) in the first combustion chamber (7) by subsequent flow into the turbine (9) to drive the turbine (9), the turbine (9) being adapted to be coupled by torque transmission and via a shaft, to the electrical machine (1),the generator unit comprising a return line (11) for returning the exhaust air from the fuel cell (3) to the gas flow upstream of the fuel cell (3), the generator unit further comprising a supply line (13) for supplying at least part of the exhaust air from the combustion chamber (7) to the fuel cell (3), the generator unit further comprising a first bypass line (12) which passes around the fuel cell (3).,

2. A generator unit according to claim 1, comprising a control unit, designed to operate the electrical machine (1) in a generator mode or optionally in a motor mode, and to start the motor mode at least when starting the generator unit, the generator unit comprising valves (19) controllable by the control unit to adapt the fluid flow rates in the generator unit.

3. A generator unit according to any preceding claim, further comprising a propeller (15) or fan, which can be coupled to the shaft and / or the electric machine (1) for torque transmission, and which serves to generate aerodynamic thrust for the aircraft.

4. A generator unit according to any preceding claim, wherein the electrical machine (1) and the shaft are connected to each other via a transmission (21).

5. Generator unit according to one of the preceding claims, wherein the return line (11) has a first branch and a second branch which lead to different pressure stages in and / or behind the compressor (5).

6. Generator unit according to one of the preceding claims, further comprising a second bypass pipe (17) around the first combustion chamber (7), the second bypass pipe (17) opening into the supply pipe (13).

7. Generator unit according to one of claims 5 and 6, wherein the first branch and / or the second branch of the return line (11) comprises a compressor (31).

8. Generator unit according to one of the preceding claims, further comprising a second combustion chamber (23) which is arranged in the flow direction of the gas flow between the fuel cell (3) and the turbine (9).

9. A generator unit according to any preceding claim, which comprises a nozzle arranged behind the turbine (9) in the flow direction to generate thrust for the aircraft by the flow of gas emerging through the nozzle into the environment.

10. A generator unit according to any preceding claim, comprising at least one heat exchanger (25) designed to extract heat from the gas stream and transfer it to the fuel (T) in a fuel supply line.

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