SOLID OXIDE FUEL CELL STACK FOR AN AIRCRAFT ENGINE

Abstract

A solid oxide fuel cell stack for an aircraft engine includes ring-shaped fuel cell assemblies of parallel tubular oxide fuel cells circumferentially around a central axis. A first stacking manifold for each fuel cell assembly is in contact with a first side of the individual fuel cell assembly, a second stacking manifold is in contact with a second side of the individual fuel cell assembly, and a central recess for leading an engine shaft through. Each fuel cell includes a tubular anode and tubular cathode, the fuel cell assemblies stacked in an axial direction through pairs of first and second stacking manifolds contacting each other. Each first stacking manifold includes a hydrogen inlet and is connected to first ends of the anodes of the fuel cells. Each second stacking manifold includes a hydrogen and steam outlet and is connected to second ends of the anodes of the fuel cells.

Claims

1. A solid oxide fuel cell stack for an aircraft engine, comprising: a plurality of ring-shaped fuel cell assemblies of a plurality of tubular solid oxide fuel cells each, the fuel cells being parallel to each other and distributed circumferentially around a central axis; at least one first stacking manifold for each fuel cell assembly in contact with a first side of the individual fuel cell assembly; at least one second stacking manifold for each fuel cell assembly in contact with a second side of the individual fuel cell assembly; and a central recess for leading an engine shaft through; wherein the fuel cells each comprise an anode and a cathode; wherein the fuel cell assemblies are stacked in an axial direction through pairs of first stacking manifolds and second stacking manifolds contacting each other; wherein each first stacking manifold comprises a hydrogen inlet and is connected to first ends of the anodes of the respective fuel cells; and wherein each second stacking manifold comprises a hydrogen and steam outlet and is connected to second ends of the anodes of the respective fuel cells.

2. The solid oxide fuel cell stack of claim 1, wherein the plurality of tubular solid oxide fuel cells of each ring-shaped assembly are staggered radially to form at least two rings of fuel cells.

3. The solid oxide fuel cell stack of claim 2, wherein at least one of the fuel cell assemblies comprises at least two groups of fuel cells separated in a radial direction, and wherein the at least two groups comprise different types of solid oxide fuel cells with different operating temperature ranges.

4. The solid oxide fuel cell stack of claim 3, wherein the operating temperature range of a radially outer group is higher than the operating temperature range of a radial further inward group.

5. The solid oxide fuel cell stack of claim 3, wherein at least one of the fuel cell assemblies comprises three groups of fuel cells separated in the radial direction with different operating temperature ranges.

6. The solid oxide fuel cell stack of claim 5, wherein a radially outermost group comprises electrolyte supported solid oxide fuel cells, wherein a radially central group comprises anode supported solid oxide fuel cells, and wherein a radially innermost group comprises metal supported solid oxide fuel cells.

7. The solid oxide fuel cell stack of claim 6, wherein the radially outermost group comprises an operating temperature range of 750? C. to 850? C., wherein the radially central group comprises an operating temperature range of 650? C. to 750? C., and wherein the radially innermost group comprises an operating temperature range of 550? C. to 650? C.

8. A solid oxide fuel cell stack of claim 1, wherein the first stacking manifold and the second stacking manifold are configured to alternately flow hydrogen from the hydrogen inlet of the first stacking manifold through circumferentially successive fuel cells in an alternating axial flow direction in a zigzag manner.

9. The solid oxide fuel cell stack of claim 1, wherein the first stacking manifold is configured to flow hydrogen from the hydrogen inlet of the first stacking manifold through circumferentially successive fuel cells in a same axial flow direction towards the second stacking manifold.

10. The solid oxide fuel cell stack of claim 1, wherein the fuel cells are spaced apart from each other in a radial direction, wherein the fuel cell stack comprises a housing enclosing the fuel cells, and wherein an air inlet and an air outlet are arranged at the housing to let air flow through the housing to flush the fuel cells with air.

11. The solid oxide fuel cell stack of claim 10, comprising baffle plates inside the housing, wherein the baffle plates are spaced apart from each other in an axial direction and extend in a radial direction, wherein axially consecutive baffle plates have different radial dimensions, and wherein the baffle plates have openings to let the fuel cells pass through.

12. The solid oxide fuel cell stack of claim 1, wherein the stacking manifolds comprise stainless steel and an aluminum oxide coating.

13. The solid oxide fuel cell stack of claim 1, wherein the stacking manifolds comprise a hole for each of the fuel cells.

14. An aircraft engine, comprising: a solid oxide fuel cell stack of claim 1; a combustion chamber downstream of the fuel cell stack; a turbine unit downstream of the combustion chamber; and a compressor unit upstream of the fuel cell stack and connected to the turbine unit through an engine shaft extending through the central recess.

15. The aircraft engine of claim 14, wherein the combustion chamber is in fluid communication with the hydrogen and steam outlets of the fuel cell assemblies and comprises an air inlet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In the following, the attached drawings are used to illustrate example embodiments in more detail. The illustrations are schematic and not to scale. Identical reference numerals refer to identical or similar elements.

[0036] FIG. 1 shows a schematic sectional illustration of an aircraft engine having a fuel cell stack according to an exemplary embodiment.

[0037] FIG. 2 shows a schematic illustration of the fuel cell stack and a combustion chamber.

[0038] FIGS. 3a and 3b show a schematic illustration of segments of a stacking manifold as well as a schematic sectional view of a stacking manifold.

[0039] FIG. 4 shows a schematic illustration of a plurality of interconnected segments of a stacking manifold.

[0040] FIG. 5 shows a schematic illustration of a front face of a fuel cell assembly.

[0041] FIG. 6 shows a schematic illustration of a hydrogen supply into a fuel cell assembly.

[0042] FIG. 7 shows a schematic illustration of a ring of fuel cells of FIG. 6 and their hydrogen supply.

[0043] FIG. 8 shows a modified hydrogen distribution into a ring of fuel cells.

[0044] FIG. 9 shows an interior space of a fuel cell assembly and an air flow created therein.

[0045] FIG. 10 shows a modified interior space of a fuel cell assembly and an air flow created therein around baffle plates.

DETAILED DESCRIPTION

[0046] FIG. 1 shows an aircraft engine 2 in a schematic sectional drawing. A front side 4 is arranged on the left-hand side of FIG. 1, while a rear side 6 is arranged on the right-hand side of FIG. 1. At the front side 4, a compressor unit 8 is present, which comprises exemplarily three compressor wheels 10 arranged one behind each other on an engine shaft 12. They receive air 14 from the surrounding of the engine 2 and compress it. A part of the compressor wheels 10 may be realized in the form of a fan.

[0047] Downstream of the compressor unit 8, a solid oxide fuel cell stack 16 is provided, which will be explained in further detail below. It comprises air inlets 18, which are in fluid communication with the compressor unit 8. Air that enters the fuel cell stack 16 flows out through air outlets 20. Furthermore, hydrogen inlets 22 are provided, which are coupled with a hydrogen source 24 for flowing hydrogen into the fuel cell stack 16. Hydrogen and steam outlets 26 are provided to let residual hydrogen as well as steam exit the fuel cell stack 16. The fuel cell stack 16 is provided for conducting a fuel-cell process by consuming hydrogen from the hydrogen source 24 and oxygen from air 14 to produce electricity.

[0048] Downstream the fuel cell stack 16, a combustion chamber 28 is provided, which receives air from the fuel cell stack 16 through the air outlet 20 as well as residual hydrogen and steam from the hydrogen and steam outlet 26. In addition, a separate hydrogen inlet 30 and an additional air inlet 32 are provided, through which additional hydrogen from the hydrogen source 24 and air from the compressor unit 8 is fed into the combustion chamber 28. Resultantly, oxygen depleted air and steam exit the combustion chamber 28 and are fed into a turbine unit 34 downstream the combustion chamber 28.

[0049] The turbine unit 34 is coupled with the compressor unit 8 through the engine shaft 12. It is impinged by oxygen depleted air and steam and will thus be driven to rotate. The rotation is transferred to the compressor unit 8 through the engine shaft 12 and leads to providing mechanical power for the compressor unit 8. The engine 2 thus produces thrust and electrical power.

[0050] FIG. 2 shows the fuel cell stack 16 in a more detailed illustration. Here, a plurality of ring-shaped fuel cell assemblies 36a, 36b, 36c, 36d, 36e, and 36f are shown. They are arranged one after another in an axial direction along the engine shaft 12 and form the fuel cell stack 16. To route the engine shaft 12 through the fuel cell stack 16, a central recess 38 is provided that extends through all ring-shaped fuel cell assemblies 36a to 36f.

[0051] Each of the fuel cell assemblies 36a to 36f comprise a first stacking manifold 40 and a second stacking manifold 42. The first stacking manifolds 40 each comprise a plurality of air inlets 18, which are distributed in a circumferential direction. In this exemplary embodiment, air inlets 18 are provided at radial outer regions and radial inner regions at the same time. Exemplarily, an air manifold 44 is provided, which delivers air to several circular pipes 46, which each surround one of the first stacking manifolds 40 leading to the radial outer air inlets 18. An inner circular pipe 47, which receives air as well, surrounds the engine shaft 12 and is connected to the radial inner air inlets 18. Each of the second stacking manifolds 42 comprises air outlets 20, e.g. in a radial inner region of the second stacking manifolds 42, which outlets 20 are directly connected to the combustion chamber 28.

[0052] Still further, each of the first stacking manifolds 40 comprises the hydrogen inlet 22, which is connected to a hydrogen supply pipe 48. In analogy to this, each of the second stacking manifolds 42 comprises the hydrogen and steam outlet 26 connected to a hydrogen and steam pipe 50. Exemplarily, the fuel cell assemblies 36a to 36f may constitute an electrical serial connection by directly contacting them through their opposed stacking manifolds. By providing such a serial arrangement, the delivered voltages of each fuel-cell assembly 36a to 36f are added to a total voltage. Still further, each of the fuel cell assemblies 36a to 36f comprises a plurality of fuel cells, which are electrically interconnected depending on desired electrical parameters and will be explained in the following. However, it may also be possible to provide gaps 37 between the individual fuel cell assemblies 36a to 36f and choose a different connection scheme through a suitable wiring.

[0053] As apparent from both FIG. 1 and FIG. 2, the combustion chamber 28 may comprise a hollow-cylindrical shape having an outer diameter that at least substantially corresponds to the outer diameter of the fuel cell assemblies 36. The detail design of the combustion chamber 28 is not crucial for the gist of the disclosure herein and is thus not explained in detail herein. A skilled person will be able to consider a suitable design for the combustion chamber 28.

[0054] FIG. 3a shows a part of a first stacking manifold 40, which comprises a plurality of holes 52 for receiving a tubular fuel cell 54 each. Inside each of the holes 52, an interface connector 56 is provided in the form of uncoated stainless steel. The first stacking manifold 40 is as an example made from stainless steel and comprises a thin aluminum oxide coating 58 except in places, where an electrical contact is required, e.g. at the interface connectors 56. This allows to provide a design solution for compiling the stacking manifolds 40 and 42 and the interface connectors 56 as a single component, which minimizes the stack weight, improves the electron transport, and also minimizes chromium release from the stacking manifolds 40 and 42.

[0055] The fuel cell 54 comprises a cathode 60 as an outer layer, an anode 62 as an inner layer and an electrolyte 64 between both. For their operation, hydrogen is routed into the anodes 62 and flows through the tubular fuel cells 54, while air enters the fuel cells 54 through pores inside the cathode 60. Hence, the first stacking manifold 40 is designed to let the hydrogen flow through holes 52 into the anodes 62. The holes 52 are distributed on the stacking manifolds 40 and 42 to space apart the fuel cells 54 from each other, such that the cathodes 60 can be flushed by air.

[0056] In the example embodiment, the first stacking manifold 40 and the second stacking manifold 42 comprise a plurality of individual segments 66, which provide a parallel connection to a small group of fuel cells 54. Several of these groups can be connected in a serial connection to each other through interface connectors 68, which are also realized in the form of uncoated surfaces of the first stacking manifold 40. The segments and 66 are spaced apart in the radial direction, such that a gap 70 is created, through which air can enter the respective fuel cell assembly 36 to flush the fuel cells 54 with air.

[0057] FIG. 3b shows a schematic sectional view of a first stacking manifold 40. Here, exemplarily one of the hydrogen inlets 22 is shown, through which hydrogen enters the first stacking manifold 40 and is distributed to all associated SOFCs 54. Furthermore, an air inlet 18 of the first stacking manifold 40 is shown, through which air enters the first stacking manifold 40 and is distributed to a plurality of air supply openings 19. These may be separate openings in the respective first stacking manifold 40 or may be realized through gaps between segments 66 in a radial and/or circumferential direction. In analogy, the second stacking manifold 42 may comprise several air exit openings, through which unused air from the air supply openings 19 can enter the second stacking manifold 42.

[0058] In FIG. 4, an example interconnection of several segments 66 is shown. For the sake of better understanding, positive terminals in the form of segments 66a are hatched differently than negative terminals 66b. Positive terminals 66a and negative terminals 66b follow on each other in an alternating manner in a circumferential direction to form a ring shape. They are connected through interface connectors 68 arranged at the sides of the segments 66a and 66b. A plurality of concentrically ring-shaped arrangements of segments 66a and 66b are created, which are only indicated partially in FIG. 4. A radial connection between one of the segments 66a or 66b of one ring is connected to one of the segments 66a or 66b of an adjacent ring through an additional connector 71. Here, a segment 66b constituting a negative terminal is connected to a radially further inwardly positioned segment 66a forming a positive terminal. The interconnections can be tailored to the individual needs.

[0059] FIG. 5 shows a schematic view of a fuel cell assembly 36. Here, a plurality of individual fuel cells 54 are shown in a dense packing. Here, several concentrical rings of fuel cells 54 are provided that enclose each other and form a hollow-cylindrical shape. Thus, the fuel cell assembly 36 a has a plurality of fuel cells 54 staggered radially and circumferentially. Exemplarily, three groups 72a, 72b and 72c of fuel cells 54 are created, which comprise different types of tubular SOFCs 54. For example, the radially innermost group 72a comprises electrolyte supported SOFC's, while the radially central group comprises anode supported SOFC's and while the radially outermost group 72c comprises metal supported SOFC's. These comprise different operating temperature ranges of substantially 550? C. to 650? C. for the first group 72a, 650? C. to 750? C. for the second group 72b and 750? C. to 850? C. for the third group 72c. Thus, a cumbersome and technically challenging harmonization of operating temperatures inside the fuel cell stack 16, i.e. inside each of the fuel-cell assemblies 36a to 36f, is not required.

[0060] FIG. 6 shows the hydrogen inlet 22 arranged in the first stacking manifold 40 and the distribution of hydrogen to the individual fuel cells 54. Here, the first stacking manifold 40 distributes the hydrogen to individual rings of fuel cells 54 one after another from the radial outermost position to a radial innermost position. Here, a flow path 74a directly follows on the hydrogen inlet 22 and runs in a circumferential direction about 360?. In doing so, all fuel cells 54 connected to this flow path 74a are supplied with hydrogen. Afterwards, hydrogen passes through an interconnection opening 76a and reaches into a second circumferential flow path 74b. Here, the hydrogen flows in a circumferential direction in an opposite direction about 360? and all connected fuel cells 54 are supplied with hydrogen as well. Afterwards, a further interconnection opening 76b is passed and hydrogen flows into a further flow path 74c, which again runs in a circumferential direction about 360? in an opposite direction and so on. Hence, all of the fuel cells 54 will be supplied with hydrogen flowing into the hydrogen inlet 22 one after another.

[0061] The supply of one ring of tubular SOFCs 54 with hydrogen is shown in a spatial illustration in FIG. 7 for further clarification. Here, hydrogen enters the hydrogen inlet 22, is distributed in a circumferential direction of the first stacking manifold 40, to feed hydrogen into all individual fuel cells 54. After flowing through the fuel cells 54, hydrogen reaches the second stacking manifold 42 and exits through the hydrogen and steam outlet 26. It is clear that the hydrogen supply to the hydrogen inlet 22 is sufficient to feed further rings of tubular SOFCs by appropriately balancing all flow resistances in the first stacking manifold 40 and the tubular fuel cells 54 and choosing a suitable supply pressure at the hydrogen inlet 22.

[0062] FIG. 8 shows a modified approach for distributing hydrogen. Here, the first stacking manifold 40 and the second stacking manifold 42 are configured to alternately flow hydrogen from the hydrogen inlet 22 of the first stacking manifold 40 through circumferentially successive fuel cells 54 in an alternating axial flow direction in a zigzag manner.

[0063] In FIG. 9, a sectional view of a fuel cell assembly 36 is shown. Here, a central axis 78 is indicated, along which the central recess 38 extends. All tubular fuel cells 54 are arranged parallel to the central axis 78 and are packed between the first stacking manifold 40 and the second stacking manifold 42. As shown before, several air inlets 18 are provided, which let air flow in a radial direction into the first stacking manifold 40, from which it will be distributed into an interior space 80 of a housing 81 of the fuel cell assembly 36. The fuel cell assembly 36 exemplarily comprises a closed housing 81 having an outer housing skin 82 and an inner housing skin 84, which are provided extending between the first stacking manifold 40 and the second stacking manifold 42. The inner housing skin 84 has a hollow cylindrical shape with an inner diameter corresponding to the outer diameter of the central recess 38. The outer housing skin 82 has an outer diameter that corresponds to the outer diameter of the stacking manifolds 40 and 42. Air that enters the air inlets 18 are flowing through the interior space 80 and thereby all fuel cells 54 are flushed with air. After passing the fuel cells 54, the air exits the air outlets 20. In the exemplary embodiment of FIG. 9, the air flows in a substantially axial direction.

[0064] In FIG. 10 this arrangement is modified in that a plurality of baffle plates 86 having different sizes and extending in a radial direction is provided. The baffle plates have openings 88 for letting the fuel cells 54 pass through. By providing the baffle plates with different diameters, the air flow direction changes several times and thus, the flushing of the fuel cells 54 is improved. An additional perforation 90 allows air to pass through the baffle plates 86 in an axial direction.

REFERENCE NUMERALS

[0065] 2 aircraft engine [0066] 4 front side [0067] 6 rear side [0068] 8 compressor unit [0069] 10 compressor wheel [0070] 12 engine shaft [0071] 14 air [0072] 16 solid oxide fuel cell stack [0073] 18 air inlet [0074] 19 air supply opening [0075] 20 air outlet [0076] 22 hydrogen inlet [0077] 24 hydrogen source [0078] 26 hydrogen and steam outlet [0079] 28 combustion chamber [0080] 30 separate hydrogen inlet [0081] 32 additional air inlet [0082] 34 turbine unit [0083] 36 fuel cell assembly [0084] 37 gap [0085] 38 central recess [0086] 40 first stacking manifold [0087] 42 second stacking manifold [0088] 44 air manifold [0089] 46 circular pipe [0090] 48 hydrogen supply pipe [0091] 50 hydrogen and steam pipe [0092] 52 hole [0093] 54 tubular fuel cell [0094] 56 interface connector [0095] 58 aluminium oxide coating [0096] 60 cathode [0097] 62 anode [0098] 64 electrolyte [0099] 66 segment [0100] 68 interface connector [0101] 70 gap [0102] 71 connector [0103] 72 group of fuel cells [0104] 74 flow path [0105] 76 interconnection opening [0106] 78 central axis [0107] 80 interior space [0108] 81 housing [0109] 82 outer housing skin [0110] 84 inner housing skin [0111] 86 baffle plate [0112] 88 opening [0113] 90 perforation