Aircraft propulsion unit and method for operating an aircraft propulsion unit

Abstract

The invention relates to an aircraft propulsion unit (10) having a ram air duct (21), through which ram air (S) flows, and a heat exchanger (20) which is arranged in the ram air duct (21) and is designed to discharge heat to the environment (U), wherein a supply device (51) is arranged in the ram pressure duct (21) upstream of the heat exchanger (20) and is designed to feed water (W) into the ram air flow (S). The invention also relates to a method (100) for operating an aircraft propulsion unit (10).

Description

[0001] Aircraft propulsion and methods for operating an aircraft propulsion system

[0002] The invention relates to an aircraft engine comprising 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 to the environment, wherein a feed device is arranged upstream of the heat exchanger in the ram air duct, which is configured to introduce water into the ram air flow. The invention further relates to a method for operating such an aircraft engine.

[0003] To make aircraft more environmentally friendly, new propulsion systems are being investigated, for example, to utilize fuel cells as energy converters for aircraft engines. As with other propulsion systems, these new systems can also generate significant amounts of waste heat during operation. Therefore, a cooling system is needed to dissipate this heat to the environment, ensuring safe and stable operation of the aircraft engine. A key component for heat dissipation is a large (main) heat exchanger. This is typically located in a ram air duct of an aircraft engine, in the free airflow or behind a propeller. To achieve sufficient cooling, such a main heat exchanger must be large, which makes its integration into the aircraft unsatisfactory and sometimes results in significant additional aerodynamic drag.To increase the power density of the main heat exchanger, water injection systems are used to humidify the cooling air. Such systems distribute the water evenly across the heat exchanger and consume a large amount of water, resulting in the aircraft carrying significant quantities of water, which negatively impacts the weight and overall efficiency of the propulsion system.

[0004] Starting from this premise, it is an object of the present invention to propose an improved aircraft propulsion system with which, in particular, the aerodynamic properties of the propulsion system can be improved and / or the efficiency of the propulsion system can be increased. Furthermore, a method for operating such an aircraft propulsion system is to be provided. This is achieved according to the invention by the teachings of the independent claims. Advantageous embodiments of the invention are the subject of the dependent claims.

[0005] To solve the problem, an aircraft propulsion system is proposed, comprising 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 to the environment. Upstream of the heat exchanger in the ram air duct, a feed device is arranged for introducing water into the ram air flow. The feed device is configured to introduce the water into the ram air flow in such a way that at least one region of the heat exchanger with a higher operating temperature can receive more water than at least one region of the heat exchanger with a lower operating temperature.

[0006] By introducing liquid water, for example, by injection, into the stagnant air duct and thus into the stagnant air flow within the duct, the cooling effect of the stagnant air flow can be increased both by cooling the stagnant air flow and by wetting the surface of the heat exchanger, particularly by dissipating the associated evaporative energy. By introducing water to at least one, preferably predetermined, area of ​​the heat exchanger, especially one with high operating temperatures or material temperatures at its surface, heat dissipation can be improved, particularly with regard to the amount of water used, thereby increasing the heat exchanger's performance.In particular, those (surface) areas of the heat exchanger that heat up less during operation and therefore have lower temperatures require smaller amounts of water to be sufficiently cooled than areas that heat up more during operation of the heat exchanger and therefore have higher temperatures and a greater cooling requirement.

[0007] By configuring the water supply system to introduce water into the ram airflow in such a way that at least one area of ​​the heat exchanger with a higher operating temperature receives more water than at least one area with a lower operating temperature, an adaptable operating strategy for water supply is enabled, resulting in particularly more efficient use of the water. Specifically, compared to a uniform distribution of water across the heat exchanger or its cross-section in the ram airflow, the same cooling effect or performance increase can be achieved with smaller quantities of water. The resulting reduced water requirement allows the components of the supply system to be smaller, and therefore lighter and / or more space-saving. Furthermore, the amount of water carried in a water tank can be reduced.This can have a further beneficial effect on the system weight, thereby achieving weight and / or space savings for the aircraft engine or the aircraft itself.

[0008] The aircraft engine can be cooled, for example, by means of a cooling system, which in particular includes a coolant circuit. Such a coolant circuit can be connected to the (main) heat exchanger, the heat exchanger being configured to transfer heat, in particular via the coolant circuit, to a cooling medium and / or the environment. For this purpose, the heat exchanger can have at least one cooling surface connected to the coolant circuit, which is subjected to a fan and / or ram air flow during operation. The ram air flow absorbs heat from the coolant circuit onto the cooling surface of the heat exchanger and carries it away from the heat exchanger, in particular convectively.According to the invention, the heat exchanger can also have several heat exchange devices arranged spatially adjacent to each other and / or distributed in the direction of flow of the ram air, which in particular can each have several cooling surfaces. In this context, a cooling surface is defined as any (upper) surface arranged on the heat exchanger that is heated by the heat energy to be dissipated and from which heat can be carried away by a ram air flow passing over it.

[0009] To improve heat transfer from the heat exchanger, or from its surface, which primarily acts as a cooling surface, liquid water is introduced into the stagnant air stream by means of a feed device. This feed device can be positioned relatively close to the heat exchanger within the stagnant air duct, so that the stagnant air stream is already slightly warmer than when it enters the duct, thus improving its water absorption capacity. The feed device is specifically designed to deliver the water into the stagnant air stream or duct, particularly by injecting, nozzles, and / or atomizing it. This allows the water to be introduced into the stream with an increased volume-to-surface-area ratio and / or across the entire cross-section of the stagnant air stream.The introduction of water can cool the stagnant airflow and / or improve heat transfer between the stagnant airflow and the cooling surfaces of the heat exchanger, particularly through a water-induced change in the thermal conductivity of the stagnant airflow, and / or a greater temperature difference. This can increase the thermal efficiency or power density of the heat exchanger and thus, in particular, reduce its size.

[0010] By selectively introducing water into the stagnant airflow or into at least one area of ​​the heat exchanger that heats up during operation, the efficiency of the heat exchange can be increased in terms of the amount of waste heat transferred per unit area. An area with a higher operating temperature can, for example, be located on the coolant inlet side of the heat exchanger, since a heated coolant can enter the heat exchanger here, while on the coolant outlet side, heat has already been dissipated from the coolant by the heat exchanger, or the coolant has already been cooled. Accordingly, more water can be introduced at such an inlet side to improve the cooling effect in this area.

[0011] If the total amount of heat to be dissipated from the aircraft or aircraft engine remains unchanged, the proposed design offers the potential to reduce the size of the heat exchanger, thereby enabling, for example, a reduction in the heat exchanger's frontal area, volume, and / or weight. This allows for improved integration of the heat exchanger into the aircraft engine, which can also reduce drag and flow losses on the aircraft. Overall, this can lead to an improvement in the overall efficiency of the aircraft engine and / or the aircraft itself.

[0012] In one embodiment, the aircraft propulsion system incorporates a fuel cell system, and the water is at least partially supplied by means of a recovery device from a process gas of the fuel cell system. The fuel cell system can include at least one anode and at least one cathode, as well as a process gas system for supplying the anode and cathode with fuel and ambient air and for removing spent process gases.

[0013] A fuel cell system comprises at least one fuel cell, and 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, for the purposes of this description of the invention, simply as "a fuel cell". Accordingly, the plurality of fuel cells typically also comprises a plurality of anodes, which are supplied with a fuel, such as hydrogen, for generating electrical energy, and a plurality of cathodes, which, in conjunction with the anodes, are supplied with ambient air to generate electrical energy, thereby supplying the oxygen contained therein to the fuel cell as an oxidizing agent.

[0014] A process gas system is designed to supply process gas to the fuel cell or fuel cell system with the reactants necessary for generating electrical energy via the process gas, and to remove used process gas or reaction gas from the fuel cell. For this purpose, the process gas system is configured to supply the anode with fuel and the cathode with oxidizer, as well as to remove or recirculate, in particular, at least partially consumed process gases. The process gas system can thus form an open gas circuit.

[0015] In 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, which is 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.

[0016] The chemical reaction of hydrogen and oxygen in the fuel cell system during operation produces highly purified, deionized water. Using the recovery unit, a portion of this water, particularly the liquid portion, can be separated from the process gas and fed into a water storage tank within the recovery unit and / or added to the compressed air stream. Thus, the operation of the fuel cell system can be used to provide highly purified water that meets specific operational requirements. Using this generated or recovered deionized water reduces or even prevents fouling and / or deposit formation on the heat exchanger. This, in turn, reduces the risk of damage and / or maintenance requirements for the heat exchanger.

[0017] To ensure stable operation of the fuel cell system, it can be cooled by means of the cooling system or a coolant circuit. This coolant circuit can be connected to the heat exchanger, which is designed to absorb the heat generated by the at least one fuel cell and transfer it to the environment. The integration of a water supply for improved heat transfer at the heat exchanger, thus enabling improved heat transfer, may eliminate the need for an external water supply, potentially resulting in cost savings.

[0018] In one embodiment of the aircraft propulsion system, the feed device is arranged in a duct wall that, in particular, radially surrounds the ram air duct. Here, the ram air duct can be completely enclosed by the duct wall, and thus also by the feed device, in one direction of the ram air flow, in order to delimit the ram air duct. By integrating the feed device into the duct wall, an inflow cross-section of the ram air flow to the heat exchanger can remain unobstructed, thereby preventing any, particularly negative, influence of the feed device on the ram air flow. In this context, at least one feed line and / or device required for water supply or injection can be arranged in the duct wall or lining of the ram air duct and / or integrated therein.In this way, the feed system can present no or only reduced flow resistance to the airflow in the ram air duct, especially when no water is supplied. In dry operation and / or in operation with water supply, this can result in higher overall efficiency for heat dissipation and thus for the aircraft propulsion system.

[0019] In one embodiment of the aircraft propulsion system, the feed device is configured to introduce the water at a predetermined angle to the flow direction of the ram air. The flow direction of the ram air can be the same as a main flow direction through the ram air duct and / or a longitudinal axis of the ram air duct, whereby the water can be introduced into the ram air duct or the ram air flow at an angle of 90° or less (acute angle to the flow direction), particularly to achieve the introduction of the water into specific areas of the duct cross-section or at a distance from the duct wall. The flow velocity of the ram air flow can be used to distribute the water within the ram air flow. For example, a directed water feed can create a predetermined distribution profile for the water in the ram air duct.the stagnant airflow is generated and / or a direct or indirect supply of water to the heat exchanger or its surface and thus to at least one area of ​​the heat exchanger is achieved, which can improve the effectiveness of the water injection, especially when cooling the heat exchanger.

[0020] In one embodiment of the aircraft propulsion system, the feed device comprises a number of nozzle assemblies, which are arranged in different spatial configurations. Their distribution around the circumference of the flow channel depends, in particular, on the arrangement of the heat exchanger sections with higher or lower operating temperatures. The nozzle assemblies can be configured to inject, nozzle, and / or atomize the water into the ram air channel. The water can be introduced using multiple nozzle assemblies with larger opening cross-sections and / or a multitude of nozzle assemblies with smaller opening cross-sections. In this way, the droplet size or degree of atomization of the water supplied can be adjusted by means of the feed device. A small droplet size or a high degree of atomization of the water can reduce heat transfer between the ram air flow and the heat exchanger surface.whose areas are enhanced because the number of water droplets, and thus their surface area available for heat exchange, can be increased. Furthermore, the water droplets or droplets can distribute themselves in a predetermined distribution profile within the stagnant air flow to ensure effective operation in the areas of the heat exchanger with lower and / or higher operating temperatures, and thus, in particular, across the entire cross-section of the stagnant air flow. This enables efficient use of the available water volume. The nozzle assemblies can be designed as individual nozzles or nozzle arrangements with a multitude of nozzle openings and can be mounted on or integrated into the duct wall of the stagnant air channel. The number and / or arrangement of these nozzle assemblies can vary along the length of the duct wall, particularly in the direction of flow or perpendicular to it.For example, a first set of nozzles can be arranged radially around a first position in the stagnant air duct, and a second set of nozzles can be arranged radially spaced from this first position to create a spatially optimized injection profile for the water supply. Furthermore, a larger number of nozzles can reduce the reduction in effectiveness in the event of a failure of individual nozzles.

[0021] In one embodiment of the aircraft propulsion system, at least two nozzle assemblies have different nozzle opening sizes. This allows, for example, the adjustable amount of water supplied in specific feed areas to enable variable water delivery to different sections of the heat exchanger. For this purpose, nozzle assemblies with larger nozzle opening sizes or diameters can be used in areas requiring a larger water supply than in areas with lower water demand. Furthermore, the spatial concentration of nozzle assemblies can be increased in at least one area with higher water demand. CFD simulation, for example, can be used to position and / or dimension the nozzle assemblies.Similarly, it is possible to use nozzle devices with different opening geometries to enable suitable introduction of water into the stagnant airflow.

[0022] In one embodiment, the aircraft propulsion system can include a heat recovery unit and a control unit, the control unit being configured to control the supply unit, the heat recovery unit, the at least one nozzle unit, and / or the heat exchanger. In particular, the heat dissipation rate or heat transfer at or by means of the heat exchanger can be adjusted by regulating the coolant flow rate of the heat exchanger and / or the water supply to the ram air flow or the supply to at least one area of ​​the heat exchanger. Thus, the heat exchange capacity of the heat exchanger can be varied by means of the control unit. The control unit can thereby select a specific operating state or...a heat exchange capacity for the heat exchanger, for example, depending on an ambient temperature, a humidity level, a flow rate of the air inside the heat exchanger and / or taking into account other operating parameters, such as operating parameters of the fuel cell system.

[0023] According to a further aspect, a method for operating an aircraft engine is proposed, comprising a ram air duct and a heat exchanger arranged in the ram air duct, which is configured to dissipate heat to the environment, wherein a feed device is arranged in the ram air duct upstream of the heat exchanger, which is configured to introduce water into the ram air duct. The proposed method comprises the steps of flowing ram air through the ram air duct with ram air and introducing water into the ram air flow by means of the feed device such that more water is supplied to at least one region of the heat exchanger with a higher operating temperature than to at least one region of the heat exchanger with a lower operating temperature.

[0024] In this process, water is introduced into the stagnant air flow passing through the stagnant air duct, particularly before it reaches the heat exchanger, by means of a supply device, in order to improve the cooling effect of the stagnant air flow on the heat exchanger surface. The water can be supplied to the stagnant air flow, for example, in a predetermined distribution, quantity, angle of introduction, and / or at a predetermined pressure, in order to influence the distribution of the water within the stagnant air flow and to direct it to specific areas of the heat exchanger. Furthermore, the supply device can be configured to set or vary a temperature (heating and / or cooling) of the water and / or a predetermined operating pressure for the water, in order, for example, to adapt the properties of the supplied water to the operating parameters of the stagnant air flow or the heat exchanger.

[0025] In one embodiment of the method, the water is introduced into the ram air flow in a predetermined spatial distribution profile, whereby the distribution profile of the water to be supplied can be predefined depending on parameters of the heat exchanger and / or the aircraft engine. Such parameters can include, for example, the current temperature, velocity, pressure, composition, and / or specific gravity of the ram air flow. Furthermore, operating parameters of the aircraft engine, a flight phase, or an environment can also be taken into account when determining the distribution profile and / or the volume flow rate of the water to be supplied. This can, in particular, improve the heat dissipation performance of the heat exchanger.The term “spatial” distribution profile should also include designs in which the water is introduced starting from a 2-dimensional cross-section of the flow channel and is subsequently distributed in a third dimension and thus spatially with the flow of the ram air.

[0026] In one embodiment of the method, the water introduction is time-varying. Time-varying introduction, for example in the form of water injection, can be controlled by a control unit of the aircraft engine and / or the heat exchanger, taking into account influencing parameters such as ambient air temperature, power requirements of the aircraft engine, and / or sufficient water availability, particularly in connection with a flight phase of the aircraft.

[0027] In one embodiment of the method, water is introduced during at least one predetermined operating phase of the aircraft engine. Here, the water can be introduced into the ram air duct and thus into the ram air flow, for example, in a predetermined quantity and / or distribution, depending on the current flight phase. In particular, different amounts of waste heat are generated by an aircraft engine in different flight phases, requiring different cooling capacities.

[0028] In one embodiment of the method, the aircraft propulsion system can have a fuel cell system, wherein the water is at least partially recoverable from a process gas of the fuel cell system, wherein in a further step the fuel cell system is operated and the water is at least partially recovered from a process gas of the fuel cell system.

[0029] 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 can be combined with one another, unless this is explicitly excluded in the disclosure.

[0030] 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 used and structural or logical modifications of 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

[0031] Fig. 1 shows a schematic representation of an exemplary aircraft propulsion system according to the invention;

[0032] Fig. 2 shows a schematic representation of a longitudinal section through an exemplary flow channel of an aircraft propulsion system according to the invention;

[0033] Fig. 3 shows a schematic cross-section through an exemplary flow channel of an aircraft propulsion system according to the invention; and

[0034] Fig. 4 shows a schematic representation of a flowchart of a method according to the invention for operating an aircraft engine.

[0035] Fig. 1 shows a schematic representation of an exemplary aircraft propulsion system 10 according to the invention with a ram air duct 21 and a heat exchanger 20, wherein the aircraft propulsion system 10 of the present embodiment has a fuel cell system 12.

[0036] To operate the fuel cell system 12 reliably, it is necessary to cool it. For this purpose, a fluid cooling device 41, 42 is provided to transport the heat generated by the fuel cell system 12 to the heat exchanger 20 by means of a cooling fluid, where the heat is transferred to the environment U via the heat exchanger 20. The cooling fluid can be supplied to the fuel cell system 12 via a cooling fluid inlet 41, absorb heat there, and then discharged via a cooling fluid outlet 42. To cool the cooling fluid, it is supplied to the heat exchanger 20 via a cooling fluid inlet 43, where heat is extracted. The cooling fluid can then be discharged via a cooling fluid outlet 44. The cooling fluid inlets 41, 43 and cooling fluid outlets 42, 44 can form a coolant circuit (not shown).

[0037] The fuel cell system 12 comprises a fuel cell 13 with an anode 14 and a cathode 15. The anode 14 is supplied with fuel, in this exemplary embodiment with hydrogen, from a fuel storage device 16 via a process gas system 17, and the fuel is largely consumed in the fuel cell 13. The consumed process gas, or the anode-side reaction gas, is discharged from the fuel cell 13. Partially consumed fuel, or excess hydrogen, can be recirculated to the fuel cell 13 via the process gas of the anode 14 by means of a gas recirculation system 27, or, in particular, released to the environment. The cathode 15 is supplied with ambient air drawn from the surroundings U via the process gas system 17 and reacts as process gas in the fuel cell 13. The consumed ambient air, or hydrogen, can be discharged from the fuel cell 13.The cathode-side reaction gas can be removed from the fuel cell 13 by means of the process gas device 17 and in particular released to the environment U.

[0038] The heat exchanger 20 is arranged in a ram air duct 21 through which ram air S flows and is configured to transfer heat generated by the fuel cell system 12 to the environment U. Upstream of the heat exchanger 20, a feed device 51 is arranged, which is configured to introduce water W into the ram air flow S. For this purpose, the feed device 51, arranged in a duct wall 22 of the flow duct 21, has a number of nozzle devices 51 arranged at or before the inlet of the ram air flow S into the heat exchanger 20 or on its surface, which are configured to introduce the water W into the ram air flow S. The feed device 51 is configured to introduce the water W into the ram air flow S such that at least one region 20a (see Fig. 3) of the heat exchanger 20 with a higher operating temperature can be supplied with more water W than at least one region 20b (see Fig. 2).3) with a lower operating temperature. This is explained in more detail below with reference to Figures 2 and 3. By means of the supplied water W, the cooling effect of the heat exchanger 20 or the heat transfer at the heat exchanger 20, in particular at at least one area 20a of the heat exchanger 20 with a higher operating temperature, can be improved.

[0039] In the exemplary embodiment, the water W can be provided at least partially from the process gas of the fuel cell system 12 by means of a recovery device 30. The recovery device 30 can have a first water separator 31, which can be fluidically connected to an anode-side section of the process gas system 17 downstream of the fuel cell system 12 and 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, which can have a cooling circuit with a coolant supply 341 and a coolant discharge 342.

[0040] 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 system 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 condenser 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 41, 42 of the fuel cell system 12 or its (not shown) coolant circuit.

[0041] The separated water from both the water separators 31, 32 and the condensers 34, 35 can be collected in a water storage tank 33 of the recovery unit 30. From there, the water can be fed to the stagnant airflow S by means of the feed device 51. For this purpose, the feed device 51 has a pump 53 to pump the water, whereby the water flow rate can be regulated or controlled at the nozzle devices 52.

[0042] Fig. 2 shows a schematic representation of the ram air duct 21 of the exemplary aircraft propulsion system 10 according to the invention from Fig. 1 in a longitudinal section along the flow axis R. It can be seen that the feed device 51, or its nozzle assemblies 52, are arranged and configured in the duct wall 22 enclosing the ram air duct 21 to introduce the water W at a predetermined angle α to a flow direction R of the ram air S. This allows the water W to be introduced into the ram air duct 21, or the ram air S, in such a way that more water W can be supplied to areas of the heat exchanger 20 with higher operating temperatures than to areas of the heat exchanger 20 with a lower operating temperature. In some embodiments, the feed device 51, or its nozzle assemblies 52, can also be arranged or configured to apply water W directly to areas of the heat exchanger 20 to enable intensive cooling.

[0043] The nozzle devices 52 can have different nozzle opening sizes, particularly in different sections of the stagnation air duct 21, in order to achieve a predetermined distribution profile for the water W in the stagnation air duct 21, the stagnation air S or at the heat exchanger 20.

[0044] Fig. 3 shows a schematic representation of the ram air duct 21 of the exemplary aircraft propulsion system 10 from Fig. 1 in a cross-section perpendicular to the flow axis R.

[0045] This illustration shows that the nozzle devices 52 of the feed device 51 can be arranged such that more nozzle devices 52 are assigned to a region 20a of the heat exchanger 20 with a higher operating temperature than to a region 20b with a lower operating temperature. In the present embodiment, the higher operating temperature can result from the fact that, in a first region 20a of the heat exchanger 20, heated cooling fluid is fed to the heat exchanger 20 via the cooling fluid feed 43 in order to extract heat from the cooling fluid. In a second region 20b of the heat exchanger 20, the cooling fluid, which is cooler after flowing through the heat exchanger 20, can leave the heat exchanger 20 via a cooling fluid outlet 44, which can result in a lower operating temperature of the heat exchanger 20 in this region 20b.

[0046] Fig. 4 shows a schematic representation of a flowchart of an exemplary

[0047] Method 100 for operating an aircraft propulsion system 10 described herein with a fuel cell system 12. The steps of method 100 can in particular be carried out simultaneously or in a modified sequence and thus deviate from the sequence shown.

[0048] In step a, the ram air duct 21 is supplied with ram air S. In an optional step al, the fuel cell system 12 can be operated to provide energy for an aircraft engine, and in a further optional step a2, water can be obtained from a reaction gas of the fuel cell system 12, in particular by means of the recovery device 30.

[0049] In step b, water W is supplied to the ram air flow S before it enters the heat exchanger 20 by means of the supply device 51 such that at least one area 20a of the heat exchanger 20 with a higher operating temperature receives more water W than at least one area 20b with a lower operating temperature. A predetermined distribution profile for the water W can be specified by means of the supply device 51 or the nozzle devices 52, whereby, for example, a volume flow rate and / or a degree of atomization of the water W to be introduced can be controlled and / or regulated, particularly depending on parameters of the aircraft engine 10, in order to be able to adjust the heat exchange capacity of the heat exchanger 20 in a time-varying manner and / or depending on a predetermined operating phase of the aircraft engine 10.

[0050] REFERENCE MARK LIST

[0051] 10 aircraft engines

[0052] 12 Fuel cell systems

[0053] 13 Fuel cell

[0054] 14 Anode

[0055] 15 Cathode

[0056] 16 fuel storage

[0057] 17 Process gas system

[0058] 20 heat exchangers

[0059] 21 Stale air duct

[0060] 22 Canal wall

[0061] 27 Gas recirculation

[0062] 30 Recovery unit

[0063] 31, 32 Water separator

[0064] 33 water reservoirs

[0065] 34, 35 Capacitor

[0066] 41, 43 Cooling fluid supply

[0067] 42, 44 Cooling fluid discharge

[0068] 51 Feeding device

[0069] 52 nozzle assembly

[0070] 53 Pump

[0071] 341 Condenser coolant supply

[0072] 342 Condenser coolant drain

[0073] 351 Condenser coolant supply

[0074] 352 Condenser coolant drain

[0075] S Ram air / Ram air flow

[0076] U surroundings

[0077] W water

Claims

REQUIREMENTS 1. Aircraft propulsion (10) comprising a ram air duct (21) through which ram air (S) flows and a heat exchanger (20) arranged in the ram air duct (21) which is configured to dissipate heat to the environment (U), wherein a feed device (51) is arranged in the ram air duct (21) upstream of the heat exchanger (20) which is configured to introduce water (W) into the ram air flow (S) such that at least one area (20a) of the heat exchanger with a higher operating temperature can be supplied with more water (W) than at least one area (20b) of the heat exchanger (20) with a lower operating temperature.

2. Aircraft propulsion (10) according to claim 1, wherein the aircraft propulsion comprises a fuel cell system (12) and the water (W) is provided at least partially by means of a recovery device (30) from a process gas of the fuel cell system (12).

3. Aircraft propulsion (10) according to at least one of the preceding claims, wherein the feed device (51) is arranged in a channel wall (22) enclosing the ram air channel (21).

4. Aircraft propulsion (10) according to at least one of the preceding claims, wherein the feed device (51) is configured to introduce the water (W) at a predetermined angle (a) to a flow direction (R) of the ram air (S).

5. Aircraft propulsion (10) according to at least one of the preceding claims, wherein the feed device (51) has a number of nozzle devices (52) which are in particular arranged differently in space.

6. Aircraft propulsion (10) according to claim 5, wherein at least two of the nozzle assemblies (52) have different nozzle opening sizes.

7. Aircraft propulsion (10) according to at least one of the preceding claims comprising a recovery device (30) and a control device, wherein the control device is configured to control the feed device (51), the recovery device (30), the at least one nozzle device (52) and / or the heat exchanger (20).

8. Method (100) for operating an aircraft engine (10), comprising a ram air duct (21) and a heat exchanger (20) arranged in the ram air duct (21) which is configured to dissipate heat (W) to the environment (U), wherein a feed device (51) is arranged in the ram air duct (21) upstream of the heat exchanger (20) which is configured to introduce water (W) into the ram air duct (21), comprising the steps: Flowing ram air (S) through the ram air channel (21); and introducing water (W) into the ram air flow (S) by means of the supply device (51) such that more water (W) is supplied to at least one area (20a) of the heat exchanger (20) with a higher operating temperature than to at least one area (20b) of the heat exchanger (20) with a lower operating temperature.

9. Method (100) according to claim 8, wherein the water (W) is introduced into the stagnant airflow in a predetermined spatial distribution profile.

10. Method (100) according to one of claims 8 or 9, wherein the introduction of the water (W) is variable in time.

11. Method (100) according to at least one of claims 8 to 10, wherein the water (W) is introduced depending on the operating phase of the aircraft propulsion (10).

12. Method (100) according to at least one of claims 8 to 11, wherein the aircraft propulsion system comprises a fuel cell system, wherein the water is obtained at least partially from a process gas of the fuel cell system.

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