AIRCRAFT ENGINE

Description

Technical area

[0001] The invention relates to an aircraft engine for commercial aircraft. State of the art

[0002] In civil aviation, there is a need for engines that are free of climate-damaging emissions, particularly for CO2-free engines. In this respect, fuel cell-based engines are known in the state of the art, in which the required thrust is generated by an electrically driven axial fan. For use in commercial aircraft, this poses the practical problem that operation is not economical. The capacity required to provide the maximum power required during the takeoff phase leads to a total mass that is too high for economical operation due to the high power-to-weight ratio or mass-to-power ratio of currently available fuel cells. The commercial aircraft would fly but would not be able to carry a sufficient load.

[0003] WO 2018 / 158767 A1 discloses an aircraft with a hydrogen afterburner and at least one propeller arranged along the longitudinal axis of the aircraft. WO 2018 / 158767 A1 does not disclose a technical solution for the detailed technical design or operation of the propellers. For housing the afterburner, WO 2018 / 158767 A1 discloses the arrangement in a convergently shaped housing, i.e., one that narrows in the direction of flow.

[0004] EP 2 878 795 A1 discloses an engine for propelling an aircraft, comprising a housing with an inlet and an outlet, a fan arranged therein, and driven by an electric motor that can be coupled to a fuel cell assembly. The engine may have an additional combustion engine. EP 2 878 795 A1 does not disclose any technical solutions for the physical design of the housing or the detailed technical configuration and arrangement of the combustion engine. Disclosure of the invention

[0005] The invention is based on the object of providing an aircraft engine with a fuel cell-based, electrically operated axial fan, which, due to its type and design, enables an optimization of the power-to-weight ratio and can be used as a climate-friendly drive for a civil airliner.

[0006] The object is achieved according to the invention by an aircraft engine according to claim 1. Advantageous developments of the invention are specified in the subclaims.

[0007] The core of the invention is an aircraft engine, comprising a housing with an inlet and an outlet, an axial fan arranged adjacent to the inlet in a first housing section with at least one impeller, at least one electric motor designed to drive the impeller, at least one fuel cell unit designed to supply power to the electric motor, and at least one combustion drive arranged downstream of the axial fan within the housing, wherein the housing is designed with a convergent section adjacent to the first housing section and with a divergent section adjacent to the convergent section, and wherein the combustion drive comprises a combustion chamber with a hydrogen injection system, which are arranged or formed within the divergent section. Downstream in the sense of the invention means arranged downstream in the flow direction from the inlet to the outlet.In the context of the invention, convergent means narrowing in the direction of flow, divergent means widening in the direction of flow. The aircraft engine according to the invention has the advantage that the overall mass and thus also the power-to-weight ratio can be easily optimized due to the combination of an electrically operated axial fan supplied by at least one fuel cell unit with a combustion engine that can be used as a hydrogen afterburner. The power design of the at least one fuel cell unit and the axial fan is optimized in terms of mass for normal flight operation, while the maximum power required during the takeoff phase is achieved by activating the hydrogen afterburner. The arrangement of the two engines is also spatially highly integrated due to their physical design in a common housing and is optimized with regard to flow guidance and thrust generation.The integration of a hydrogen-based combustion engine is also system-efficient due to the presence of hydrogen, which is already required due to the fuel cell-based drive system. The storage, provision, and supply of a separate combustion fuel are unnecessary.

[0008] The electric drive is integrated efficiently and with high efficiency by comprising coil means arranged circumferentially on or in the housing of the impeller and permanent magnet means formed by the impeller blades, formed or arranged in a circumferential end section of the impeller blades, or formed or arranged in an outer ring surrounding the drive blades. In this embodiment, the impeller functions as an internal rotor. The electric drive is implemented as a low-friction brushless electric motor, since there is no conductive electrical contact between the rotor and stator, but rather a magnetic bearing.

[0009] To optimize the efficiency of the axial fan, a second, counter-rotating impeller is arranged downstream of at least one impeller. The counter-rotating principle allows for high power density in a compact design.

[0010] To optimize airflow and thrust, a diffuser is arranged downstream of at least one impeller or counter-rotating impeller pair. The swirling air flow emerging from one impeller due to the rotation of the impeller is deflected by the guide vanes of the downstream, stationary diffuser into a laminar, particularly thrust-effective airflow.

[0011] If the axial fan is designed with several impellers to increase the thrust, these are designed as several impeller / stator combinations arranged one behind the other within the first housing section or combinations of counter-rotating impellers with or without a downstream diffuser to optimize the flow path and the thrust effect and / or to optimize the efficiency.

[0012] To ensure operation at higher altitudes, at least one compressor is provided, which is integrated into the housing or designed as an external component and interacts with the aircraft engine. This compressor supplies the at least one fuel cell unit with air at a pressure higher than the ambient pressure. This ensures proper operation of the fuel cells even at higher altitudes above approximately 3,000 meters, where the ambient pressure is considerably lower. This design also enables a general improvement in the efficiency of the at least one fuel cell unit, regardless of the altitude, by supplying the fuel cells with air at a defined pressure higher than the ambient pressure. As an externally designed compressor, it can be arranged, for example, in a wing or the tail unit to save space.

[0013] In a structurally integrated and compact design of the aircraft engine, the compressor is formed as an axial end section of an existing impeller or by a separate impeller arranged in the first casing section. The pressure increase is achieved by redirecting the compressed air flow generated by the impeller blades of the compressor through a corresponding duct to the fuel cells.

[0014] To improve efficiency, a diffuser, designed as a component through which liquid hydrogen flows, is arranged downstream of the compressor, which is designed as an impeller. Hydrogen has a much lower boiling point of -252.9 °C. The component through which liquid hydrogen flows provides a heat sink for the compressed air, dissipating the heat energy generated during compression and achieving isothermal compression.

[0015] To further improve the efficiency of the at least one fuel cell unit, at least one valve device is provided, with which hydrogen is also supplied to the at least one fuel cell unit at a pressure higher than the ambient pressure. Preferably, the hydrogen is stored at a pressure level sufficiently increased compared to the ambient pressure, for example, 6 bar, whereby a sufficient pressure level is present in the overall system. With other forms of storage, compression by a compressor can take place before being supplied to the at least one fuel cell unit, before the hydrogen is supplied valve-controlled at a defined overpressure.

[0016] Tests have shown that optimal efficiency for modern, commercially available fuel cells with closed cathodes is achieved with a charging pressure of 2 bar, at which the fuel cells develop a current density of up to 2 A / cm2 or more. To optimize efficiency, the compressor and the valve device are therefore preferably configured such that the at least one fuel cell unit is pressurized with air and hydrogen at a pressure of 2 bar each.

[0017] To further improve the efficiency of the fuel cell device, at least one heat exchanger device is provided, either integrated into the housing or embodied as an external component and interacting with the aircraft engine. Outside air is passed over or through components through which liquid hydrogen flows, and the resulting condensate is mixed with the air supplied to the fuel cell device. Hydrogen has a lower boiling point of -252.9 °C than oxygen (-183 °C), so that the oxygen contained in the air stream at least partially condenses as it flows around the components through which liquid hydrogen flows, i.e., it changes from a gaseous to a liquid state.By adding the condensate, a higher oxygen saturation of the air supplied to the fuel cell device is achieved with an increased oxygen content of, for example, 40% instead of 21%, which is available for the oxidation reaction in the fuel cell device.

[0018] To increase the power density, the at least one fuel cell unit is formed from several flat fuel cell layers arranged one above the other and connected to each other as a stack (also referred to as a "stack").

[0019] In a structurally highly integrated and highly compact design of the aircraft engine, the at least one fuel cell unit has a ring-shaped or circular-segment-shaped cross-section, and one or more such fuel cell units is or are arranged circumferentially on the housing. This design also features improved thermal management due to its structural and physical design alone, because the heat generated in the fuel cell unit(s) during operation during normal flight (i.e., with the afterburner inactive) is at least partially dissipated into the atmosphere surrounding the aircraft engine by convection via the housing and the air flow within the housing.

[0020] A further improvement in the mass balance of the aircraft engine is achieved by arranging a device for injecting the water produced during operation of the at least one fuel cell unit in the transition region from the convergent to the divergent section. Each fuel cell is a galvanic cell that converts the chemical reaction energy of the hydrogen continuously supplied as fuel and the oxygen supplied as an oxidant into electrical energy, which is used in the aircraft engine according to the invention to operate the electric motor. During the chemical reaction according to reaction equation 2 H 2 + O 2 → 2 H 2 OWater is produced during operation. As the combustion product, water, is continuously released into the atmosphere surrounding the aircraft engine during operation, the aircraft becomes increasingly lighter during flight. This is achieved particularly effectively by injecting the fuel in the area of ​​the transition from the convergent to the divergent section of the casing, as this results in an immediate expansion of the fluid flow.

[0021] Further advantages of the invention are described in more detail below, together with a description of a preferred embodiment of the invention, with reference to the figures. They show: Fig. 1 a schematic perspective view of an aircraft engine. Fig. 2 a schematic perspective sectional view of the aircraft engine according to Fig. 1 . Fig. 3 a frontal view of the aircraft engine according to Fig. 1. Fig. 4 a schematic longitudinal section of the aircraft engine along the line II according to Fig. 3 .

[0022] The Fig. 1 to 4 show the aircraft engine 1 in different views. Fig. 1 shows the aircraft engine 1 in a schematic perspective view. Fig. 2 shows the aircraft engine 1 in the same perspective as a schematic sectional view. Fig. 3 shows the 1 shows the aircraft engine 1 in a schematic front view. Fig. 4 shows the 1 shows the aircraft engine 1 in a schematic longitudinal sectional view along the line II according to Fig. 3 .

[0023] The aircraft engine 1 comprises a housing 2 with an inlet 3 and an outlet 4, the axial housing sections A to C of which are shown in the longitudinal section according to Fig. 4are shown. In the first housing section A on the inlet side, an impeller 5 forming an axial fan is arranged. The impeller 5 forms a hub in its center, which is guided for rotatable mounting on a concentrically arranged, static component or component assembly, for example an axle or a pin. Such components are shown in the illustrations of Fig. 1 to 4 not shown for the sake of clarity. Such bearing parts can be mounted in the casing 2, for example, by means of struts extending in the circumferential direction to the inner surface of the casing 2 and connected thereto. An alternative bearing can be provided, for example, via an axle or a journal extending from a static guide wheel arranged downstream of the impeller 5 (such an embodiment is shown in the illustrations of the Fig. 1 to 4not shown). The blade ends of the impeller 5 are surrounded by and connected to a tubular outer ring 6. On the outside of the outer ring 6, a plurality of permanent magnets 7 are arranged circumferentially, of which in the illustrations of the Fig. 2 to 4 For reasons of illustration, only some of the visible permanent magnets 7 are numbered as examples. The permanent magnets are preferably designed as neodymium magnets, which have a high energy density and thus a favorable mass-energy ratio. Also in the first housing section A, several coil means 8 are arranged circumferentially on the housing 2, of which only a few are shown in the illustrations of the Fig. 1 to 4For reasons of illustration, only a few of the visible coil means are numbered as examples. The impeller 5, together with the outer ring 6, the permanent magnets 7, and the coil means 8, forms an electric motor designed as a contactless direct current motor (= brushless DC motor or BLDC). The impeller 5, together with the outer ring 6 and the permanent magnets 7, forms the rotor of the electric motor, which is designed as an internal rotor. The coil means 8 arranged circumferentially in the housing section A on the housing 2 together form the stator of the electric motor. The electric motor can be controlled either digitally using a programmable logic controller (PLC) or electromechanically, with the coil means 8 being controlled, for example, via inductive or optical sensors. Electromechanical control can enable greater robustness depending on the desired application.

[0024] To supply power to the electric motor, the aircraft engine 1 comprises several fuel cell units 9, which have a circular cross-section and are arranged circumferentially on the housing 2. In the illustrations of the Fig. 1 to 4 For illustrative reasons, only individual fuel cell units 9 are numbered as examples. Each of the fuel cell units 9 is formed as a stack consisting of a plurality of flat, superimposed and interconnected fuel cell layers (also referred to as a "stack").

[0025] The housing 2 further comprises a second, convergently shaped housing section B adjoining the first housing section A and a further third, divergently shaped housing section C adjoining the housing section B. In the third, divergently shaped housing section C, a combustion drive is arranged, which comprises a combustion chamber and a hydrogen injection. The combustion chamber is formed in the divergent housing section C by the housing shell. The hydrogen injection is formed by the injection openings 10 arranged in a ring shape in the divergently shaped housing section C for the injection of hydrogen, of which in the illustrations of the Fig. 2 and 4For technical reasons, only individual injection openings are numbered as examples. Depending on the density and pressure conditions in the specific application context, the combustion process is initiated either as a self-ignition process or by means of a separate ignition device (in the illustrations of the Fig. 1 to Fig. 4 not shown).

[0026] In the transition area from the convergently shaped housing section B to the divergently shaped housing section C, annularly arranged outlet openings 11 are also provided for the discharge of water, of which only individual outlet openings are numbered as examples for reasons of illustration. The outlet openings 11 serve to discharge water produced during operation of at least the fuel cell units 9 into the air flow of the aircraft engine 1. The water, the combustion product produced in the fuel cell units 9 during operation, is continuously released into the air flow during operation into the atmosphere surrounding the aircraft engine, whereby the aircraft constantly becomes lighter during flight. Hydrogen present in the aircraft's tanks is consumed as fuel, while the water produced as a reaction product in the fuel cell units 9 is disposed of.Disposal is particularly effective when discharge occurs in the area of ​​the transition from the convergent to the divergent section of the housing, as this results in immediate expansion of the fluid flow. A further improvement in the mass balance is achieved in this context by additionally using part of the water produced as a combustion product during operation of the fuel cell units 9 as process water during flight. For this purpose, the water produced in the fuel cell units 9 is pumped into the aircraft's process water tanks during operation (in the illustrations of the . Fig. 1 to Fig. 4 not shown).

[0027] During operation of the aircraft engine 1, the combustion engine is switched on and used only during the takeoff phase of the aircraft, alongside the operation of the axial fan as an additional afterburner, in order to generate the total thrust required for takeoff. Once the desired cruising altitude is reached, the combustion engine is switched off, and the thrust required for cruising operation at a substantially constant altitude is generated solely by the operation of the axial fan. This mode of operation offers the advantage of being able to optimize the performance of the axial fan and the fuel cell units 9 in relation to mass for normal flight operations, since the maximum power required during the takeoff phase is generated by the activation of the hydrogen afterburner.The arrangement of the two engines in the shared housing 2 is also highly spatially integrated due to its physical design and optimized for flow control and thrust generation. The integration of a hydrogen-based combustion engine as an afterburner is also system-efficient due to the presence of hydrogen, which is required anyway for the fuel cell-based power supply of the electric axial fan. The storage, provision, and supply of a separate combustion fuel for the afterburner, which is only used during the start-up phase, is not required.

[0028] The hydrogen required to operate the fuel cell units 9 is stored in a suitable manner in appropriate tanks. Preferably, storage takes place in cryogenic liquid form at a pressure that is simultaneously higher than the external pressure, depending on the application environment, for example, a pressure of 6 bar. List of reference symbols

[0029] A, B, C Housing sections 1 Aircraft engine 2 Housing 3 Inlet 4 Outlet 5 Impeller 6 Outer ring 7 Permanent magnet 8 Coil center 9 Fuel cell unit 10 Injection port 11 Exhaust port

Claims

1. Aircraft engine (1), comprising a housing (2) having an inlet (3) and an outlet (4), an axial fan which is arranged adjacent to the inlet in a first housing section and has at least one impeller (5), at least one electric motor which is designed to drive the impeller, at least one fuel cell unit (9) which is designed to supply power to the electric motor, and at least one combustion drive arranged downstream of the axial fan within the housing, the housing being formed with a convergent section adjacent to the first housing section and with a divergent section adjacent to the convergent section, characterized in that the combustion drive comprises a combustion chamber with a hydrogen injection means (10), which are arranged or formed within the divergent section.

2. Aircraft engine according to claim 1, characterized in that the at least one electric motor comprises coil means (8) arranged circumferentially with respect to the impeller on or in the housing and permanent magnet means (7) formed by the impeller blades or formed or arranged in a circumferential end portion of the impeller blades or formed or arranged in an outer ring (6) surrounding the drive blades.

3. Aircraft engine according to claim 1 or 2, characterized in that a second, counter-rotating impeller is arranged downstream of the at least one impeller.

4. Aircraft engine according to any of claims 1 to 3, characterized in that a guide wheel is arranged downstream of the at least one impeller or the counter-rotating impeller pair.

5. Aircraft engine according to claim 3 or 4, characterized in that a plurality of impeller / guide wheel combinations or combinations of counter-rotating impellers with or without a downstream guide wheel are arranged one behind the other within the first housing section.

6. Aircraft engine according to any of claims 1 to 5, characterized in that at least one compressor is provided which is integrated into the housing or designed as an external component and interacts with the aircraft engine, and by means of which air is supplied to the at least one fuel cell unit at a pressure greater than the ambient pressure.

7. Aircraft engine according to claim 6, characterized in that the compressor is formed as an axial end portion of an existing impeller or by a separate impeller arranged in the first housing section.

8. Aircraft engine according to claim 7, characterized in that a guide wheel, which is designed as a component through which liquid hydrogen flows, is arranged downstream of the compressor, which is designed as an impeller.

9. Aircraft engine according to any of claims 6 to 8, characterized in that at least one valve device is provided, by means of which hydrogen is supplied to the at least one fuel cell unit at a pressure greater than the ambient pressure.

10. Aircraft engine according to claim 9, characterized in that the compressor and the valve device are designed such that the at least one fuel cell unit is supplied with air and hydrogen at a pressure of 2 bar in each case.

11. Aircraft engine according to any of claims 1 to 10, characterized in that at least one heat exchange device is provided which is integrated into the housing or designed as an external component and interacts with the aircraft engine, and in which outside air is passed over or through one or more components through which liquid hydrogen flows, and the condensate thus formed is mixed with the air supplied to the fuel cell device.

12. Aircraft engine according to any of claims 1 to 11, characterized in that the at least one fuel cell unit is formed from a plurality of flat fuel cell layers arranged one above the other and connected to one another as a stack.

13. Aircraft engine according to claim 12, characterized in that the at least one fuel cell unit is ring-shaped or circular-segment-shaped in cross-section and one or more such fuel cell units is or are arranged circumferentially on the housing.

14. Aircraft engine according to any of claims 1 to 13, characterized in that a device for injecting the water produced during operation of the at least one fuel cell unit is arranged in the region of the transition from the convergent to the divergent section.