FUEL CELL ASSEMBLY FOR AN AIRCRAFT PROPULSION SYSTEM

Description

TECHNICAL FIELD

[0001] The present invention relates to an assembly for an aircraft propulsion system comprising several fuel cells arranged one behind the other in an airflow, an aircraft propulsion system comprising such an assembly and an aircraft comprising at least one such propulsion system. PREVIOUS STATE OF THE ART

[0002] Propulsion for transport or passenger aircraft is generally provided by propulsion systems. Such a propulsion system includes a combustion engine using hydrocarbon-based fuel, resulting in a certain carbon footprint. The propulsion system also includes a nacelle with a forward air intake containing a fan. Air is drawn through the fan into the air intake to power the engine housed within the nacelle.

[0003] Air is compressed in a compressor located just behind the air intake and injected into the engine's combustion chamber along with hydrocarbon-based fuel. The combustion gases are expelled through an exhaust nozzle via a turbine. The passage of these gases through the turbine causes it to rotate.

[0004] The compressor and the turbine each have an upstream stage and a downstream stage.

[0005] The compressor's downstream stage and the turbine's upstream stage are mounted on a first shaft so that the rotation of the turbine's upstream stage drives the compressor's downstream stage. Similarly, the compressor's upstream stage, the turbine's downstream stage, and the blower are mounted on a second shaft, and the turbine's downstream stage rotates the compressor's upstream stage and the blower.

[0006] To reduce hydrocarbon-based fuel consumption, it is known to use hydrogen as a fuel and it is also known to use solid oxide fuel cells to generate an electric current.

[0007] In such an embodiment, the fuel cell replaces the combustion chamber in order to generate an electric current to turn an electric motor and heat which is recovered to turn a turbine which drives a blower.

[0008] Such a propulsion system uses the Brayton cycle and even if it works correctly, its efficiency can be improved.

[0009] The documents US2023 / 211889A1, US2012 / 153076A1 and PIRKANDI JAMASB ET AL: "Thermodynamic performance analysis of three solid oxide fuel cell and gas microturbine hybrid systems for application in auxiliary power units" (XP036525377) each describe an assembly for an aircraft propulsion system. DESCRIPTION OF THE INVENTION

[0010] An object of the present invention is to provide a set of fuel cells for an aircraft propulsion system which comprises several fuel cells arranged one behind the other in an airflow.

[0011] To this end, an assembly is proposed for an aircraft propulsion system, said propulsion system defining a channel in which an airflow circulates, said assembly being intended to be placed in the airflow and comprising: a compressor, a turbine downstream of the compressor, a secondary shaft having a secondary longitudinal axis and fixed between the compressor and the turbine, and at least two fuel cells arranged between the compressor and the turbine, one behind the other along the secondary longitudinal axis in the airflow exiting the compressor where the airflow exiting the last fuel cell feeds the turbine and where each fuel cell is supplied with dihydrogen.

[0012] With such an arrangement, the oxygen heats up as it passes through the fuel cells before reaching the turbine.

[0013] Advantageously, the operating temperatures of fuel cells increase from upstream to downstream.

[0014] Each fuel cell includes: an inlet manifold having a dihydrogen inlet, an outlet manifold having a dihydrogen outlet, a plurality of tubular fuel cells arranged side by side parallel to the secondary longitudinal axis between the inlet manifold and the outlet manifold, wherein each tubular fuel cell has an anode in the form of an inner tube, the upstream end of which is fluidically connected to the inlet manifold and the downstream end of which is fluidically connected to the outlet manifold, a cathode in the form of an outer porous tube around the anode and between the anode and the cathode, an electrolyte.

[0015] Advantageously, each collector comprises a hollow outer torus fluidly connected to the dihydrogen inlet, respectively to the dihydrogen outlet, and a plurality of hollow crossbars arranged inside the outer torus and where each end of each crossbar is fluidly connected to said outer torus and where the upstream end and the downstream end of each tubular fuel cell are fluidically connected to a crossbar of the collector considered.

[0016] Advantageously, each collector has a hollow inner torus and is disposed inside the outer torus, the two inner tori are coaxial, the secondary shaft passes through the two inner tori, and crossbars disposed between the outer torus and the inner torus have one end fluidly connected to said outer torus and one end fluidly connected to said inner torus.

[0017] Advantageously, there are three fuel cells, and the operating temperatures of the three fuel cells from upstream to downstream are respectively around 700°C, 800°C and 900°C.

[0018] The invention also proposes an aircraft propulsion system, said propulsion system comprising: a nacelle delimiting a channel in which an airflow circulates, a propeller mounted movably in or ahead of the airflow around a main longitudinal axis parallel to the secondary longitudinal axis, a main turbine mounted movably in the airflow around the main longitudinal axis, a main shaft extending along the main longitudinal axis and fixed between the propeller and the main turbine, an assembly according to one of the preceding variants, where the compressor is downstream of the propeller, where the turbine is upstream of the main turbine, and an electric motor whose drive shaft is the main shaft electrically powered by the fuel cells.

[0019] Advantageously, the secondary longitudinal axis and the main longitudinal axis are coaxial and the secondary shaft is mounted movable around the main shaft.

[0020] The invention also proposes an aircraft comprising at least one propulsion system according to one of the preceding variants. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which: There figure 1 is a side view of an aircraft comprising a propulsion system according to the invention, The figure 2 is a schematic representation of a propulsion system according to a first embodiment of the invention, The figure 3 is a schematic representation of a propulsion system according to a second embodiment of the invention, The figure 4 is a perspective view of a fuel cell stack implemented in the first embodiment of the invention, The figure 5 is a perspective view of a fuel cell stack implemented in the second embodiment of the invention, and The figure 6 is a perspective view of a tubular solid oxide fuel cell used in stacks. DETAILED EXPLANATION OF IMPLEMENTATION METHODS

[0022] There figure 1 Figure 1 shows an aircraft 1 which has a propulsion system 50, which here takes the form of a turbojet but could be a turboprop. Aircraft 1 has a fuselage 3, on each side of which a wing 2 is attached. Under each wing 2, a propulsion system 50 is attached by means of a reactor pylon 4.

[0023] In the following description, terms relating to a position are taken with reference to an aircraft in its normal flight position, that is, as it is represented on the figure 1 and the "forward" and "rear" positions are taken with respect to the front and rear of the turbojet and with respect to the direction of forward movement of aircraft 1 when the propulsion system 50 is operating.

[0024] As described below, the terms "upstream" and "downstream" refer to the airflow within the propulsion system 50, moving from front to back. Upstream is therefore forward and downstream is backward.

[0025] In the following description, and by convention, X is called the main longitudinal axis of the propulsion system 50 which is parallel to the longitudinal axis of aircraft 1, Y is called the transverse axis which is horizontal when aircraft 1 is on the ground, and Z is called the vertical axis which is vertical when aircraft 1 is on the ground, these three directions X, Y and Z being orthogonal to each other.

[0026] THE figures 2 And 3They show propulsion systems 50 according to two embodiments of the invention. The propulsion system 50 comprises a nacelle 51 which surrounds an engine. The nacelle 51 defines a channel 52 in which an airflow 10 flows from the front to the rear of the nacelle 51. The nacelle 51 has an air inlet 53 at the front and an ejection nozzle at the rear.

[0027] The propulsion system 50 comprises a propeller 54 which is mounted to rotate freely around the main longitudinal axis X, which is generally parallel to the airflow 10. In the embodiment of the invention presented in the figures 2 And 3In this embodiment, the propeller 54 is located in the nacelle 51 and therefore in the airflow 10, acting as a fan, and the propulsion system 50 takes the form of a turbojet. In another embodiment not shown, the propeller 54 may be an external propeller, which is therefore located ahead of the air inlet 53 and thus ahead of the airflow 10, and the propulsion system 50 takes the form of a turboprop.

[0028] The propulsion system 50 also includes a main turbine 56 which is mounted movable in rotation in the airflow 10 around the main longitudinal axis X and which is disposed towards the rear of the nacelle 51.

[0029] The propulsion system 50 also includes a main shaft 58 which extends along the main longitudinal axis X and is fixed between the propeller 54 and the main turbine 56. Thus, the rotation of the main turbine 56 causes the rotation of the propeller 54.

[0030] The propulsion system 50 also includes an electric motor 60 whose drive shaft is the main shaft 58 and which is electrically powered by fuel cells 108a-b of an assembly 100 according to the invention.

[0031] The assembly 100 is arranged in the airflow 10 and it includes a compressor 102, a turbine 104 and a secondary shaft 106 which extends along a secondary longitudinal axis x parallel to the main longitudinal axis X.

[0032] The compressor 102 and the turbine 104 are fixed on the secondary shaft 106 and these elements are mounted to rotate freely around the secondary longitudinal axis x. The compressor 102 is forward and the turbine 104 is rearward, i.e. downstream of the compressor 102 with respect to the airflow 10 and the secondary shaft 106 is between them.

[0033] The compressor 102, the turbine 104 and the secondary shaft 106 are arranged in the airflow 10. The rotation of the turbine 104 causes the rotation of the compressor 102.

[0034] The assembly 100 also includes at least two fuel cells 108a-b arranged in series in the airflow 10, i.e. one behind the other along the secondary longitudinal axis x between the compressor 102 and the turbine 104.

[0035] Thus, the air flow 10 exiting the compressor 102 supplies dioxygen to the fuel cells 108a-b, starting with the one furthest upstream, and the air flow 10 exiting the last fuel cell 108b, that is to say the one furthest downstream, supplies the turbine 104.

[0036] Each fuel cell 108a-b is further supplied with dihydrogen by a network of pipes which brings the dihydrogen from a dihydrogen tank which the aircraft 1 presents.

[0037] Thus, the airflow 10 passes successively through the compressor 102 where it is compressed, the fuel cells 108a-b where it is heated, then it passes through the turbine 104 which it rotates, driving the compressor 102 at the same time.

[0038] The compressor 102 is downstream of the propeller 54 and the turbine 104 is upstream of the main turbine 56, so the airflow 10 after the propeller 54 enters the compressor 102 and the airflow 10 exiting the turbine 104 enters the main turbine 56 which it rotates, driving at the same time the propeller 54 through the main shaft 58.

[0039] The installation of several fuel cells 108a-b in series allows for greater heating of the air in the air stream 10 before it enters the turbines 104 and 56, resulting in improved efficiency. Indeed, by increasing the enthalpy between the compressor 102 and the turbine 104, the efficiency of the Brayton cycle is enhanced.

[0040] Such an arrangement is particularly efficient when the operating temperatures of the 108a-b fuel cells increase from upstream to downstream, i.e. the temperature of the upstream 108a fuel cell is lower than the temperature of the downstream 108b fuel cell.

[0041] The operating temperature of a fuel cell refers to the temperature range at which it operates during normal use. When a fuel cell is running, it produces electricity by catalyzing the chemical reaction between a fuel (such as hydrogen) and an oxidant (such as oxygen from the air). This reaction occurs at a specific temperature that depends on the type of fuel cell.

[0042] According to a particular embodiment of the invention, there are three fuel cells 108a-b (only two are shown in the figures 2 And 3), and the operating temperatures of the three fuel cells 108a-b from upstream to downstream are respectively on the order of 700 °C, 800 °C and 900 °C, preferably with a tolerance of + / - 50 °C. Thus, the temperature of the air stream 10 increases as it passes through the fuel cells 108a-b.

[0043] According to a particular embodiment, the most upstream fuel cell operating between 650°C and 750°C is a metal-supported solid oxide fuel cell (MSC), the intermediate fuel cell operating between 750°C and 850°C is a supported anode solid oxide fuel cell (ASC), and the most downstream fuel cell operating between 850°C and 950°C is a supported electrolyte solid oxide fuel cell (ESC).

[0044] THE figures 2 And 3 show two examples of 108a fuel cells implemented in assembly 100.

[0045] Thus, each fuel cell 108a-b comprises an inlet manifold 110 and an outlet manifold 112. The inlet manifold 110 has a hydrogen inlet 110a fluidly connected to the hydrogen reservoir, through which hydrogen enters the fuel cell 108a-b. Similarly, the outlet manifold 112 has a hydrogen outlet 112a through which unconsumed hydrogen exits the fuel cell 108a-b to return, for example, to the hydrogen reservoir.

[0046] The fuel cell 108a-b also includes a plurality of tubular fuel cells 208. Each tubular fuel cell 208 takes the form of a tube and the tubular fuel cells 208 are arranged next to each other parallel to the secondary longitudinal axis x between the inlet manifold 110 and the outlet manifold 112. Here the tube constituting the tubular fuel cell 208 has a circular cross-section, but the latter can take another shape such as elliptical, rectangular, polygonal, etc.

[0047] There figure 6 This shows an embodiment of a tubular fuel cell 208 comprising an anode 208a in the form of a hollow inner tube, the upstream end of which is fluidically connected to the inlet manifold 110 and the downstream end of which is fluidically connected to the outlet manifold 112, a cathode 208b in the form of an outer porous tube around the anode 208a and between the anode 208a and the cathode 208b, and an electrolyte 208c. The cathode 208b is porous for dioxygen.

[0048] Hydrogen enters and passes through anode 208a, while oxygen from the air enters fuel cell 208 through pores inside cathode 208b, which is surrounded by airflow 10. In fuel cell 208, the oxygen reduction reaction occurs in the porous cathode 208b by accepting electrons and producing oxide ions, which pass through the gas-tight electrolyte 208c to anode 208a. Hydrogen is oxidized at anode 208a by accepting oxide ions and producing electrons, which pass to cathode 208b via an external electrical circuit.

[0049] To this end, for each tubular fuel cell 208, there is provided an electrical contact connected electrically to the anode 208a and an electrical contact connected electrically to the cathode 208b. The various electrical contacts are connected in such a way as to supply an electric current capable of operating the electric motor 60.

[0050] Here, each collector 110, 112 has an external torus 114a formed of a hollow tube and fluidly connected to the inlet of dihydrogen 110a or to the outlet of dihydrogen 112a.

[0051] Each manifold 110, 112 also includes a plurality of hollow crossbars 114b arranged inside the outer torus 114a so that each end of each crossbar 114b is fluidly connected to the outer torus 114a so as to ensure fluidic continuity between the dihydrogen inlet 110a or the dihydrogen outlet 112a and the inside of each crossbar 114b through the inside of the hollow tube forming the outer torus 114a.

[0052] To ensure the passage of dihydrogen through each tubular fuel cell 208, the upstream end of each tubular fuel cell 208 is fluidically connected to a crossbar 114b of the inlet manifold 110 and the downstream end of each tubular fuel cell 208 is fluidically connected to a crossbar 114b of the outlet manifold 112.

[0053] In the implementation of the figure 5 , each collector 110, 112 has an inner torus 114c which is made of a hollow tube and which is arranged inside the outer torus 114a, here coaxially with respect to the outer torus 114a.

[0054] The two inner tori 114c are coaxial and the secondary shaft 106 passes through the two inner tori 114c so as to mount the fuel cell 108a-b around the secondary shaft 106 for space saving, unlike the embodiment of the figure 4 where the fuel cell 108a-b must be at a distance from the secondary shaft 106.

[0055] The cross bars 114b that could have been in the inner torus 114c are removed and the cross bars 114b that are arranged between the outer torus 114a and the inner torus 114c have one end fluidly connected to the outer torus 114a and one end fluidly connected to the inner torus 114c.

[0056] In the modes of embodiment of figures 2 And 3 , the main longitudinal axis X and the secondary longitudinal axis x can be coaxial and the secondary shaft 106 is then mounted to rotate freely around the main shaft 58 and the main shaft 58 is therefore inside the secondary shaft 106.

[0057] In the implementation of the figure 5 , the main shaft 58 also passes through the inner tori 114c.

Claims

1. Assembly (100) for a propulsion system (50) of an aircraft (1), said propulsion system (50) delimiting a channel (52) in which an airflow (10) circulates, said assembly (100) being intended to be arranged in the airflow (10) and comprising: - a compressor (102), - a turbine (104) downstream of the compressor (102), - a secondary shaft (106), which has a secondary longitudinal axis (x) and is fastened between the compressor (102) and the turbine (104), and - at least two fuel cells (108a-b) arranged between the compressor (102) and the turbine (104), one behind the other along the secondary longitudinal axis (x) in the airflow (10) leaving the compressor (102), wherein the airflow (10) leaving the last fuel cell (108a-b) supplies the turbine (104) and wherein each fuel cell (108a-b) is supplied with dihydrogen, characterized in that each fuel cell (108a-b) comprises: - an inlet manifold (110) comprising a dihydrogen inlet (110a), - an outlet manifold (112) comprising a dihydrogen outlet (112a), - a plurality of tubular fuel cells (208) arranged alongside one another parallel to the secondary longitudinal axis (x) between the inlet manifold (110) and the outlet manifold (112), wherein each tubular fuel cell (208) comprises an anode (208a) in the form of an inner tube, an upstream end of which is fluidically connected to the inlet manifold (110) and a downstream end of which is fluidically connected to the outlet manifold (112), a cathode (208b) in the form of a porous outer tube around the anode (208a), and between the anode (208a) and the cathode (208b), an electrolyte (208c).

2. Assembly (100) according to Claim 1, characterized in that the operating temperatures of the fuel cells (108a-b) increase from upstream to downstream.

3. Assembly (100) according to either of Claims 1 and 2, characterized in that each manifold (110, 112) comprises a hollow outer torus (114a) fluidically connected to the dihydrogen inlet (110a) and to the dihydrogen outlet (112a), respectively, and a plurality of hollow transverse bars (114b) arranged inside the outer torus (114a) and wherein each end of each transverse bar (114b) is fluidically connected to said outer torus (114a) and wherein the upstream end and the downstream end of each tubular fuel cell (208) are fluidically connected to a transverse bar (114b) of the manifold (110, 112) in question.

4. Assembly (100) according to Claim 3, characterized in that each manifold (110, 112) comprises a hollow inner torus (114c) arranged inside the outer torus (114a), in that the two inner tori (114c) are coaxial, in that the secondary shaft (106) passes through the two inner tori (114c), and in that transverse bars (114b) arranged between the outer torus (114a) and the inner torus (114c) have one end fluidically connected to said outer torus (114a) and one end fluidically connected to said inner torus (114c).

5. Assembly (100) according to one of Claims 1 to 4, characterized in that there are three fuel cells (108a-b), and in that the operating temperatures of the three fuel cells (108a-b) from upstream to downstream are of the order of 700°C, 800°C and 900°C, respectively.

6. Propulsion system (50) for an aircraft (1), said propulsion system (50) comprising: - a nacelle (51) delimiting a channel (52) in which an airflow (10) circulates, - a propeller (54) mounted so as to be able to move, in or upstream of the airflow (10), about a main longitudinal axis (X) parallel to the secondary longitudinal axis (x), - a main turbine (56) mounted so as to be able to move, in the airflow (10), about the main longitudinal axis (X), - a main shaft (58), which extends along the main longitudinal axis (X) and is fastened between the propeller (54) and the main turbine (56), - an assembly (100) according to one of Claims 1 to 5, wherein the compressor (102) is downstream of the propeller (54), wherein the turbine (104) is upstream of the main turbine (56), - an electric motor (60), the motor shaft of which is the main shaft (58) electrically powered by the fuel cells (108a-b).

7. Propulsion system (50) according to Claim 6, characterized in that the secondary longitudinal axis (x) and the main longitudinal axis (X) are coaxial and in that the secondary shaft (106) is mounted so as to be able to move about the main shaft (58).

8. Aircraft (1) comprising at least one propulsion system (50) according to either of Claims 6 and 7.