Fuel cell system

Abstract

The present invention relates to a fuel cell system for an aircraft engine, having a first fuel cell stack, a second fuel cell stack and a reinforcement element, wherein the first fuel cell stack and the second fuel cell stack each have a plurality of fuel cells stacked on one another in a stacking direction, and wherein the reinforcement element stabilises both the first and the second fuel cell stack in directions transverse to the stacking direction.

Description

[0001] FUEL CELL SYSTEM

[0002] DESCRIPTION

[0003] Technical area

[0004] The present invention relates to a fuel cell system for aircraft propulsion.

[0005] State of the art

[0006] The fuel cell system comprises a fuel cell stack, also referred to as a stack. In such a fuel cell stack, several fuel cells are arranged one after the other in a stacking direction. The number of fuel cells connected in series in this way allows, for example, the power or voltage of the stack to be adapted to the application. As discussed in detail below, a cover element, also referred to as an end plate, can be provided at the ends to mechanically secure the fuel cells in the stack. This cover element can be pressed or clamped against the fuel cells counter to the stacking direction, thus holding the adjacent cells together in the stacking direction.

[0007] Description of the invention

[0008] The present invention is based on the technical problem of providing an advantageous fuel cell system.

[0009] This is achieved according to the invention with the fuel cell system according to claim 1. This has at least two fuel cell stacks, namely, in the terminology of the claims, a "first" and a "second" fuel cell stack. In addition, a stiffening element is provided, which creates stabilization in directions transverse to the stacking direction. The stiffening element stabilizes both the first and the second fuel cell stack in the transverse direction; in other words, several fuel cell stacks are stabilized against thrust forces using the same stiffening element. Such thrust forces can occur during operation, for example, due to vibrations or inclined positions during flight, e.g., during cornering. As a result, the fuel cells within a respective stack can be deflected or slip slightly transversely to the stacking direction, even if they are compressed in the stacking direction (see above).This can represent a mechanical load, for example, for the seals arranged between individual cell plates. Conversely, stabilization can prevent degradation or fatigue processes, for example. By using the same stiffening element for multiple fuel cell stacks, the additional weight associated with stabilization can at least be reduced, which can be advantageous for flight applications. In summary, special loads can occur during flight operations, which can be prevented with this approach, also taking weight requirements into account.

[0010] Preferred embodiments can be found in the dependent claims and the entire disclosure, whereby the presentation of the features does not always distinguish in detail between device and method or use aspects; in any case, the disclosure is implicitly to be read with regard to all claim categories. For example, if a specific fuel cell system is described, this is also to be read as a disclosure of an aircraft propulsion system with such a fuel cell system or its application in an aircraft.

[0011] In the "stacking direction," the fuel cells of the respective fuel cell stack are arranged one after the other; perpendicular to the stacking direction, for example, the fuel cells each have their planar extent (and their area is taken accordingly). For example, a two- or even three-digit number of fuel cells can be placed next to one another, meaning that a respective stack can, for example, comprise several hundred fuel cells. In detail, a respective fuel cell can also be constructed in multiple layers, for example, comprising a catalyst-coated membrane layer or "catalyst membrane layer" and a plate or "bipolar plate" that forms a channel structure (flow field) through which the catalyst membrane layer can be supplied with reaction gas, for example. Regardless of the specific structure, the tightness discussed above can also be relevant, for example, with regard to the reaction gas supply.As mentioned above, a respective fuel cell stack can have a cover element at its end, which holds the fuel cells of the stack together. For this purpose, the cover element arranged at the end is pressed against the fuel cells; in particular, it can be clamped toward the end of the stack opposite the stacking direction. A clamping system can be provided for this purpose, which can, for example, comprise one or more tie rods.

[0012] Regardless of these details, for conceptual differentiation, reference is made to a "first cover element" in the case of the first fuel cell stack and to a "second cover element" in the case of the second fuel cell stack. In this case, each stack can also have a further cover element at the opposite end in the stacking direction, i.e., the first fuel cell stack can have a further cover element opposite the first cover element, and the second fuel cell stack can have a further cover element opposite the second cover element. The opposing cover elements can be clamped to one another with the clamping system for each stack, for example, with one or more tie rods.

[0013] In a preferred embodiment, the stiffening element stabilizes the first cover element, thus preventing, for example, deflection of the first cover element transverse to the stacking direction. The stiffening element is preferably connected to the first cover element, see below for details. Relative to the second fuel cell stack, the stiffening element can generally also be connected to its bracing system, for example, by being connected to a tie rod.

[0014] In a preferred embodiment, however, the stiffening element stabilizes the first and the first cover element relative to one another, for which purpose it can, for example, be connected to both the first and the second cover element. The stiffening element can hold the first and second cover elements in a defined relative position, for example perpendicular to the stacking direction, for example preventing the cover elements from moving away from one another and / or towards one another. With respect to an orientation of the assembled fuel cell system, for example with respect to its arrangement in an aircraft engine or aircraft, the first and second cover elements are preferably each located on top of the respective fuel cell stack. In detail, the orientation here refers to the stationary aircraft (when it is parked horizontally on the ground); in other words, the stacking direction is then, for example, vertical.In any case, the fuel cell stacks are also stabilized relative to each other at their upper ends by the stiffening element; in the case of a three-dimensional stiffening body (see below in detail), this can provide additional stiffening below.

[0015] According to a preferred embodiment, the first and second cover elements lie in a common plane. This plane can, for example, be perpendicular to the respective stacking direction and intersect the respective cover element. The stiffening element then preferably also lies in the common plane, i.e., at least a portion or section of the stiffening element (compare the three-dimensional stiffening body below). A stabilizing force imparted by the stiffening element between the cover elements can also lie in the plane, for example, when viewed vectorially, or have at least a portion lying in the plane.

[0016] In general, the stiffening element can also be formed monolithically with a cover element, i.e., it can be formed continuously from the same material without interruption. The reinforcing element can, for example, be formed as a web or pin, etc., protruding laterally from the cover element, e.g., perpendicular to the stacking direction, which can then be attached to the other cover element, for example.

[0017] In a preferred embodiment, however, the stiffening element is attached to both the first and second cover elements, whereby this attachment can be materially, positively, and / or frictionally connected. The stiffening element can therefore be screwed and / or hooked to the cover element(s), for example, but generally can also be welded to it, for example. A frictionally and / or positively connected connection can, however, offer advantages, for example, with regard to assembly or disassembly, for example for maintenance purposes.

[0018] According to a preferred embodiment, the stiffening element comprises at least one strut; in general, the stiffening element can also be provided in the form of a single strut. However, it preferably comprises a plurality of struts, each of which has a stabilizing function along its longitudinal direction, for example. Preferably, the at least one strut(s) is / are stiff in the longitudinal direction, thus stabilizing it against tension and compression.

[0019] According to a preferred embodiment, which relates to the cover elements arranged in a plane, the at least one strut also extends in the common plane. Preferably, the at least one strut runs diagonally between the cover elements. A quadrilateral, in particular a rectangle, which lies in the plane between the first and second cover elements, is crossed, for example, diagonally by the "diagonal" strut. Particularly preferably, at least two struts cross said quadrilateral, whereby there may also be one or more struts along the side edges.

[0020] If more than two fuel cell stacks are provided, for example, a third fuel cell stack, and possibly a fourth fuel cell stack, one or more struts can also be provided between their cover elements. In general terms, for example, at least two struts can be provided between each two cover elements of adjacent fuel cell stacks. These at least two struts preferably cross diagonally a square or rectangle located between the respective cover elements (see above).

[0021] According to a preferred embodiment, the stiffening element has at least one plate. This is preferably arranged such that its surface extension is angled, in particular perpendicular to the stacking direction. This means that the transverse or shear loads lie in the plate surface or plane, whereby good stabilization can be achieved even with comparatively small thicknesses. In a preferred embodiment, the at least one plate lies in the common plane with the first and second cover elements. The plate can in particular fill the rectangle mentioned above in the context of the struts. If more than two cover elements are stabilized relative to one another by means of the plate, for example if a third and possibly fourth fuel cell stack is provided, the plate can fill the space between them accordingly, for example having an L-shape or, in particular, a cross-shape.

[0022] According to a preferred embodiment, the plate is part of a three-dimensional body, e.g., a cuboid-shaped box. In other words, the stiffening element is a stiffening body that stabilizes the fuel cell stacks relative to one another, for example, not only between the upper cover elements, but also at other locations underneath. In the case of the box, the coplanar plate arranged between the cover elements can, for example, be an upper side wall of the box; the latter can, for example, additionally have lateral plates as side walls, and optionally a lower side wall as the base. However, the box does not necessarily have to be completely closed; for example, its side surfaces facing the fuel cells can also be open.

[0023] As mentioned several times, the fuel cell system can also have more than two fuel cell stacks, i.e., at least a third fuel cell stack (although more than three fuel cell stacks are also possible). Preferably, the stiffening element then also stabilizes the third fuel cell stack, as well as a fourth fuel cell stack, if present. Reference is made to the initial note; multiple use can, for example, offer weight advantages. Furthermore, rigidity can be further increased by connecting additional fuel cell stacks.

[0024] The invention also relates to an aircraft propulsion system that, in addition to a fuel cell system disclosed herein, comprises a mechanical power generator and a propulsor. The latter serves to generate thrust and can, for example, be provided in the form of a propeller. The mechanical power generator can, in particular, be an electric motor that drives the propulsor or propeller in rotation. The mechanical power generator converts electrical power, which is provided by the fuel cell system.

[0025] The invention further relates to the use of a fuel cell system or aircraft propulsion system disclosed herein in an aircraft, in particular in an airplane. The stiffening element stabilizes the fuel cell stack against thrust forces occurring during operation, which may also arise, for example, from acceleration / deceleration or be due to vibrations (see the initial remarks).

[0026] Short description of the drawings

[0027] In the following, the invention is explained in more detail using exemplary embodiments, whereby the individual features may also be of interest independently of one another within the scope of the independent claims and no distinction is made in detail between the different claim categories.

[0028] In detail,

[0029] Figure 1 shows a schematic representation of an aircraft with a fuel cell system for flight propulsion;

[0030] Figure 2 shows a single fuel cell stack of a fuel cell system to illustrate some details;

[0031] Figure 3 shows a fuel cell system with four fuel cell stacks and a stiffening element;

[0032] Figure 4 shows a fuel cell system with four fuel cell stacks, with an alternative stiffening element to Figure 3;

[0033] Figure 5 shows a fuel cell system with four fuel cell stacks, with an alternative stiffening element to Figure 3 / 4. Preferred embodiment of the invention

[0034] To illustrate the application environment, Fig. 1 shows a schematic top view of an aircraft 1, in this example an airplane. This aircraft is equipped with a propulsion system 5, which has a propulsor 6, in this case a propeller 7, to generate thrust. This is driven by a mechanical power generator 8, in this case an electric motor 9. A fuel cell system 10 is provided to supply electrical power, which in this example is mounted on the wing together with the other components. This can particularly promote the introduction of vibrations or shear forces; see the initial comments.

[0035] Fig. 2 shows a schematic view of a fuel cell stack 20, of which the fuel cell system 10 then comprises a plurality (see Figures 3-5). In the fuel cell stack 20, fuel cells 22 are arranged one after the other in a stacking direction 21, for example around four hundred individual fuel cells 22. These are held together by a cover element 30, which is shown here as a simple plate, but can also be formed, for example, with stiffening ribs etc. for mechanical stabilization. At the end opposite to the stacking direction 21, a further cover element 35 is provided, and the cover elements 30, 35 are braced to one another with a bracing system 25, in this example with several tie rods 26. The cover elements 30, 35 are thus pressed towards one another with respect to the stacking direction 21 and thus against the fuel cells 22, holding them together in the stacking direction 21.

[0036] Figure 3 shows an oblique view of a fuel cell system 10 with a total of four fuel cell stacks, namely a first 20.1, second 20.2, third 20.3, and fourth fuel cell stack 20.4. Also shown are their respective cover elements 30.1-30.4, as well as the respective additional cover elements 35.1-35.4 at the opposite lower end (not visible in the third fuel cell stack 20.3). For the sake of clarity, the individual fuel cells and the respective bracing systems are not shown. The stacking direction 21 coincides with a vertical direction 41, and the cover elements 30.1-30.4 are each located at the upper end of the respective fuel cell stack 20.1-20.4.

[0037] A stiffening element 50 is provided between the fuel cell stacks 20.1-20.4. This stiffening element stabilizes the cover elements 30.1-30.4 transversely to the stacking direction 21, i.e., relative to directions 61, 62. The stiffening element 50 stabilizes not only a single stack, but several fuel cell stacks 20.1-20.4 relative to one another. For this purpose, the stiffening element 50 is attached, e.g., hooked or screwed, to the respective cover elements 30.1-30.4. The stiffening element 50 has several struts 51, 52, with the struts 51 crossing diagonally between the cover elements 30.1-30.4, and the struts 52 connecting the side edges provide additional stability.

[0038] The fuel cell system 10 according to Figure 4 also has four fuel cell stacks 20.1-20.4, for the design of which reference is made to the comments on Figures 2 and 3. The same reference numerals denote the same parts or parts with a comparable function. In Figure 4, the stiffening element 50 is provided in the form of a plate 55, which in this example extends crosswise between the cover elements 30.1-30.4. The plate 55 is connected to the cover elements 30.1-

[0039] 30.4, e.g., screwed to it via eyelets not shown here. The cover elements 30.1-30.4 lie in a common plane 65 (which also applies to Figure 3); plate 55 also lies in this plane 65.

[0040] In the embodiment according to Figure 5, a plate 55 is also provided for stabilizing the cover elements 30.1-30.4. This is part of a three-dimensional stiffening body 150, which is box-shaped and is arranged between the fuel cell stacks 20.1-

[0041] 20.4. The stiffening body 150 stabilizes the fuel cell stacks 20.1-20.4 at their (upper) cover elements 30.1-30.4 and also across their respective vertical extensions. Specifically, the box shape can be completely closed or partially open. LIST OF REFERENCE SYMBOLS

[0042] Aircraft 1

[0043] Flight propulsion 5

[0044] Propulsor 6

[0045] Propeller 7

[0046] Mechanical power generator 8

[0047] Electric motor 9

[0048] Fuel cell system 10

[0049] Fuel cell stack 20

[0050] First fuel cell stack 20.1

[0051] Second fuel cell stack 20.2

[0052] Third fuel cell stack 20.3

[0053] Fourth fuel cell stack 20.4

[0054] Stacking direction 21

[0055] Fuel cells 22

[0056] Bracing system 25

[0057] Tie rod 26

[0058] Cover element 30

[0059] First to fourth cover elements 30.1-30.4

[0060] Additional cover element 35

[0061] First to fourth additional cover element 35.1-35.4

[0062] Vertical direction 41

[0063] Stiffening element 50

[0064] Struts 51, 52

[0065] Plate 55

[0066] Directions 61, 62

[0067] Common Level 65

[0068] Three-dimensional body 150

Claims

CLAIMS 1. A fuel cell system (10) for an aircraft propulsion system (5), comprising a first fuel cell stack (20.1), a second fuel cell stack (20.2), and a stiffening element (50), wherein the first fuel cell stack (20.1) and the second fuel cell stack (20.2) each have a plurality of fuel cells (22) placed next to one another in a stacking direction (21), and wherein the stiffening element (50) stabilizes both the first and the second fuel cell stack (20.1, 20.2) in directions (61, 62) transverse to the stacking direction (21).

2. Fuel cell system (10) according to claim 1, wherein the first fuel cell stack (20.1) has a first cover element (30.1) which is braced against the fuel cells (22) of the first fuel cell stack (20.1) and holds them together, wherein the stiffening element (50) stabilizes the first cover element (30.1).

3. Fuel cell system (10) according to claim 2, wherein the second fuel cell stack (20.2) has a second cover element (30.2) which is braced against the fuel cells (22) of the second fuel cell stack (20.2) and holds them together, wherein the stiffening element (50) stabilizes the first and the second cover element (30.1, 30.2) relative to one another.

4. Fuel cell system (10) according to claim 3, wherein, with respect to an orientation of the assembled fuel cell system (10), the first and the second cover element (30.1, 30.2) are each arranged on the upper side of the respective fuel cell stack (20.1, 20.2).

5. Fuel cell system (10) according to claim 3 or 4, wherein the first and the second cover element (30.1, 30.2) lie in a common plane (65), wherein the stiffening element (50) also extends at least partially in the common plane (65).

6. Fuel cell system (10) according to one of claims 3 to 5, wherein the stiffening element (50) is attached to both the first and the second cover element (30.1, 30.2).

7. Fuel cell system (10) according to one of the preceding claims, wherein the stiffening element (50) has at least one strut (51, 52), preferably a plurality of struts (51, 52).

8. Fuel cell system (10) according to claims 5 and 7, wherein the at least one strut (51) extends diagonally in the common plane (65) between the first and the second cover element (30.1, 30.2).

9. Fuel cell system (10) according to one of the preceding claims, wherein the stiffening element (50) has at least one plate (55).

10. Fuel cell system (10) according to claims 5 and 9, wherein the at least one plate (55) lies in the common plane (65) and extends between the first and the second cover element (30.1, 30.2).

11. Fuel cell system (10) according to claim 9 or 10, wherein the at least one plate (55) is part of a three-dimensional body (150), in particular a box, wherein the three-dimensional body (150) is arranged between the first and the second fuel cell stack (20.1, 20.2).

12. Fuel cell system (10) according to one of the preceding claims, which additionally comprises a third fuel cell stack (20.3), in particular a total of at least four fuel cell stacks (20.1-20.4), wherein the stiffening element (50) also stabilizes the third fuel cell stack (20.3), and if present the fourth fuel cell stack (20.4), in directions transverse to the stacking direction (21).

13. Flight propulsion system (5) with a mechanical power generator (8), in particular an electric motor (9), a propulsor (6) coupled to the mechanical power generator (8) for generating thrust, and a fuel cell system (10) according to one of the preceding claims for supplying the mechanical power generator (8) with electrical power.

14. Use of a fuel cell system (10) according to one of claims 1 to 12 or of an aircraft propulsion system (5) according to claim 13 in an aircraft (1).

15. Use according to claim 14, wherein the stiffening element (50) stabilizes both the first and the second fuel cell stack (20.1, 20.2) against shear forces occurring during operation.

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