Fuel cell for an aircraft

Abstract

A fuel cell for an aircraft, comprising: a cell stack (2) comprising an anode (27), a cathode (29) and a proton exchange membrane (28); a front end plate (1) placed at one end of the battery stack (2); a rear end plate (3) placed at the other end of the battery stack (2); and an insulating panel (5, 8, 9) made of a polymeric material, placed between the battery stack (2) and one or both of the front end plate (1) and the rear end plate (3). The invention allows the provision of a fuel cell which solves the problem of electrical insulation of aviation fuel cells and allows the connection of a floating bonding network in an aircraft.

Description

Technical Field

[0001] This invention relates to fuel cells for aircraft that solve the electrical insulation problem of fuel cells used in aviation and allow for the connection of floating bonding networks in aircraft. Background Technology

[0002] A fuel cell is an electrochemical device that generates heat and electricity by causing an electrochemical reaction between fuel (hydrogen, methanol, natural gas, etc.) and oxygen at the anode. The heat and electricity can be used to power vehicles or provide power for stationary applications.

[0003] Fuel cells offer numerous advantages over traditional heat engines, such as performance, size, and dynamic response to transient or demand-driven conditions—qualities highly valued in the aerospace industry. However, there is still a long way to go in terms of power-to-weight ratio, as weight is critical for aircraft payload.

[0004] Fuel cells can be manufactured in different forms and types depending on their technology. These include low-temperature alkaline fuel cells (AFC), polymer fuel cells (PEMFC), direct methanol fuel cells (DMFC), high-temperature solid oxide fuel cells (SOFC), molten carbonate fuel cells (MCFC), and high-temperature polymer (HT-PEM) fuel cells.

[0005] A fuel cell comprises one or more cells connected in series to form a stack. These cells include an anode and a cathode, where fuel oxidation occurs at the anode and oxygen is reduced to produce water at the cathode. The anode and cathode are separated by a generally conductive membrane or ceramic, allowing ions to diffuse freely from the anode to the cathode.

[0006] On this membrane, catalyst particles are deposited on both sides. To improve gas diffusion across the membrane, carbon cloth or mesh is added to make the membrane conductive, thereby improving the contact between the phases and providing a larger possible diffusion area. This part is called the gas diffusion layer or GDL.

[0007] Several polymer gaskets are placed between the assembled membrane, catalyst membrane, and GDL on both sides to seal the membrane on both sides using bipolar or monopolar plates placed at the ends of the stack.

[0008] A bipolar plate is a plate with channels of a certain shape made of any conductive material. Hydrogen or fuel passes through the channel to the anode, or oxygen or air passes through the channel to the cathode, thereby uniformly distributing the reagents on both sides of the membrane and effectively removing reaction products, such as water, and avoiding the formation of hot spots on the membrane.

[0009] A bipolar plate is called a bipolar plate because it serves as both the cathode and anode; one side is the cathode of one cell, and the other side is the anode of an adjacent cell. Inside the bipolar plate, which typically consists of two sections separated by a seal, a coolant is circulated as needed and, depending on the type of fuel cell, to cool the fuel cell; this coolant acts like the outer shell.

[0010] The monopole plate is located at the end of the stack. The monopole plate is simple because it only has one side through which air or fuel circulates, and depending on the cell arrangement of the stack, it is either the cathode or the final anode. Near the monopole plate are current collector plates made of copper or other conductive materials; these current collector plates are the fuel cell terminals for external electrical connections. To enclose the stack, end plates or sealing plates are placed along with the external interfaces. These plates are external to the stack and their function is to provide sufficient mechanical integrity to prevent “sandwich” disassembly. These plates can be made of different insulating materials, such as thermoplastics (e.g., polyphenylene sulfide) or metals (e.g., anodized aluminum, stainless steel, etc.).

[0011] These plates have a nominal current leakage, which can be higher or lower depending on the quality of the internal stacked insulation. Mechanical interfaces are located on these plates, and these interfaces can also be made of the same material as the end plates. These interfaces are responsible for connecting the different ports of the stack—oxygen or air, hydrogen or fuel, and coolant—to auxiliary equipment, allowing the stack to operate.

[0012] These interfaces are connected to all the batteries inside them, and the insulation of these interfaces is very important because, depending on the insulation, there will be more or less current leakage toward the air and fuel supply pipes and exhaust pipes, which should also be insulated and grounded.

[0013] On these current collector plates, insulating layers or components made of polymers or oxides are introduced in the form of components or coatings, such as those mentioned in patent US6773841B2, which proposes the use of electrolytic deposition coatings by PVD or CVD technology, which includes physical deposition (PVD) or chemical deposition (CVD) of insulating materials by means of plasma of its ions.

[0014] This electrical insulation layer allows the stacked components to be electrically connected as floating devices, meaning that the power terminals are completely insulated from the outside, which is a basic requirement in aircraft.

[0015] Insulation layers produced using PVD or CVD technology require a more laborious process during manufacturing, which can be eliminated by placing another type of insulation, such as that used in aerospace, in the stacked components, thus allowing the metal interfaces to be insulated and the weight to be negligible.

[0016] The integration and operation of fuel cells with aviation requirements—where the amount of flammable materials must be reduced and the interfaces must withstand the varying loads and g-forces of the aircraft—requires the use of reinforcing or metallic materials, with metallic materials being the preferred choice.

[0017] Therefore, this means a change in the materials used in the interfaces, especially in the cooling and air interfaces. Cooling and air interfaces, typically used in the automotive industry, are electrically insulated and were originally made of thermosetting plastics such as PPS, nylon, ABS, or even PC. In addition to the change in interface materials, the end plates of the stacked components also require non-flammable materials.

[0018] Due to these changes in non-flammable materials from plastic to metal, the insulation of the entire stack decreases as the ohmic resistance of these materials decreases, resulting in some current leakage through the tubes and stack endplates.

[0019] This lack of electrical insulation needs to be prevented when fuel cells are mounted on aircraft, because the system needs to be floating, meaning that the positive and negative stack power terminals are not completely isolated from the aircraft structure and pose an electrical risk to the operation of other equipment. Summary of the Invention

[0020] Therefore, the object of the present invention is to provide a fuel cell that solves the electrical insulation problem of fuel cells for aviation and allows for the connection of floating bonding networks in aircraft.

[0021] The fuel cell of the present invention overcomes the above-mentioned disadvantages and has other advantages that will be described below.

[0022] One aspect of the invention describes a fuel cell for an aircraft according to the invention, and other aspects of the invention include optional additional features.

[0023] Specifically, the fuel cells used in aircraft include:

[0024] - A battery stack comprising an anode, a cathode, and a proton exchange membrane;

[0025] - Front-end board, which is placed at one end of the battery stack;

[0026] - A back-end board, which is placed at the other end of the battery stack; and

[0027] An insulating panel, made of polymer material, is placed between one or both of the battery stack and the front and rear panels.

[0028] Preferably, the insulating panel includes:

[0029] - First insulating sheet;

[0030] - Second insulating sheet; and

[0031] - An insulating layer placed between a first insulating sheet and a second insulating sheet.

[0032] The insulating panel may also include an additional insulating sheet placed between the first insulating sheet and the front end plate in a manner that contacts the first insulating sheet.

[0033] In addition, the insulating panel may also include a seal that is placed in contact with the first insulating sheet.

[0034] According to a preferred embodiment, the first insulating sheet and the second insulating sheet are made of 4,4'-oxodiphenylene-pyromellitic tetracarboxylate.

[0035] In addition, the first insulating sheet and the second insulating sheet can be attached to the insulating layer.

[0036] According to a preferred embodiment, the insulating layer may be made of polyetheretheretherketone or polyphenylene sulfide.

[0037] The front end plate preferably includes an interface for fluid inlet and outlet, and an insulating reinforcement may be placed between the end interface and the front end plate.

[0038] In addition, each insulating reinforcement may include a groove in which an O-ring is accommodated.

[0039] The front-end board may also include insulating pads corresponding to the interfaces.

[0040] According to a preferred embodiment, the first insulating sheet and the second insulating sheet have a thickness of less than 0.5 mm, preferably 20 µm to 80 µm.

[0041] Furthermore, the proton exchange membrane preferably includes a catalyst, and seals are placed on both sides of the proton exchange membrane.

[0042] According to the present invention, insulation is achieved by forming several electrically insulating portions of an insulating panel made of a polymer, preferably 4,4'-oxophenylene-pyromellitictetramethylimide.

[0043] These parts can be bonded internally by external physical connections or by mixing with adhesives, such as silicone adhesives or acrylic adhesives. If the part is a single layer, it is glued to the inside of the interface and the inner surface of the collector.

[0044] This nominal current leakage through the endplates and interfaces also depends on the quality of the coolant in terms of conductivity, which is determined by the amount of ions dissolved in the coolant. Coolants with high conductivity allow current to flow to the endplates and interfaces of the stack, or even create short circuits between the anode and cathode.

[0045] Therefore, proper insulation is essential to minimize current leakage to the interface or stack fixtures located at the endplates, where the stack is supported within the aircraft structure, and to avoid safety issues.

[0046] On the other hand, insulation quality can be monitored in real time by an insulation meter located within the aircraft's own system. If the system's insulation deteriorates, the insulation meter can be used to disconnect or shut down the fuel cell system. Furthermore, to check for insulation losses due to coolant, a conductivity sensor can be added to the cooling circuit itself.

[0047] On the other hand, another requirement in aviation is maintainability, as maintenance involves various components of the aircraft. Fuel cells are a fundamental component for maintenance registration, and although they tend to have a shorter lifespan compared to fuel cells used in other applications, such as stationary fuel cells and batteries dedicated to heavy-duty applications, they require special attention.

[0048] Maintenance typically applied to fuel cell systems involves replacing filters, deionizers, and coolants to improve fuel cell insulation. Polymer materials, such as Kapton, offer the advantage of reusing components such as endplates, interfaces, or parts of their internal structures. These components can be embedded and glued to new sheets made of this material, as long as they are cleaned, thus maintaining the original insulation requirements.

[0049] This allows layers of minimal thickness to have the same electrical insulation effect as other existing insulating materials used in fuel cells, such as PPS and PEEK, thus saving cost and weight. Attached Figure Description

[0050] To better understand the above description, accompanying drawings are provided, which schematically and by way of non-limiting example illustrate the actual implementation of the embodiments.

[0051] Figure 1 This is a front view schematic diagram of a fuel cell according to the present invention;

[0052] Figure 2 This is a cross-sectional view of the battery stack of the fuel cell according to the present invention; and

[0053] Figure 3This is a cross-sectional view of the front end plate of the fuel cell according to the present invention. Detailed Implementation

[0054] Figure 1 A fuel cell according to the present invention is shown, which includes a front end plate 1, a plurality of cells forming a stacked cell 2, and a rear end plate 3.

[0055] In addition, the front-end board 1 includes an interface 4 for supplying oxygen or air, hydrogen or fuel and coolant to the battery stack 2 when needed.

[0056] One of the requirements for aviation fuel cell systems is that the aviation fuel cell system must be electroflotal, meaning that there is no current leakage to the outside and it must be completely isolated from electrical terminals, positive ground, and negative ground.

[0057] If the stack is of PEM type, the stack is formed by one or more repeating cells 2 including a polymer proton exchange membrane 28, such as Figure 2 As shown, Figure 2 This is a cross-sectional side view of the fuel cell stack.

[0058] exist Figure 2 The image shows an anode 27 through which hydrogen or fuel passes. The anode 27 includes one or more channels that uniformly distribute and discharge fuel and water that can be generated in the region across the entire membrane.

[0059] The cathode 29 also includes one or more channels in which air supplied from the outside by a compressor, blower or fan, or oxygen from an external system, such as a bottle or canister, reacts with fuel, such as hydrogen, to produce water vapor and electricity.

[0060] At cathode 29, almost all the water produced during the reaction is drained. If the fuel cell is a single cell, then anode 27 and cathode 29 are unipolar plates, or if the fuel cell includes more cells, then anode 27 and cathode 29 are bipolar plates with unipolar terminals.

[0061] These plates can be made from different materials depending on the technology used, most commonly graphite, graphite composite with titanium, or steel if stamped with a titanium-based coating or a chromium-based coating to improve its conductivity.

[0062] To enable the reaction, a platinum catalyst, typically used in PEMFC batteries, is placed on membrane 28 via catalytic deposition methods such as spraying, stamping, or inkjet printing. Air and fuel must diffuse well to the catalyst. Therefore, diffusion layers made of mesh or carbon cloth are used on both sides 30 and 31 of the membrane, allowing substances to diffuse freely throughout membrane 28, thereby promoting the reaction between the substances and the catalyst.

[0063] This component, referred to as a "MEA" membrane electrode assembly, includes a gas diffusion layer or GDL for the cathode 29 and anode 27, and a membrane 28 containing a catalyst. All components must be sealed by seals 32 to prevent air or fuel from escaping from the cell to the outside or mixing with air or fuel. These seals 32 can be made from various polymers depending on the fuel cell technology. Seals 32 are typically made of nitrile rubber (NBR), ethylene propylene diene rubber (EPDM), or fluororubbers such as Viton (trade name) or FKM for higher temperature and chemical resistance.

[0064] The battery forms a complete battery stack 2. In order for the system to have buoyancy, the battery stack 2 must be electrically isolated from the external environment on both the refrigerant side and the cathode 27 side or anode 29 side that flow between the bipolar plates.

[0065] Figure 3 This is a cross-section of the front end plate 1. The interface 4 of the stack 2 is located at the front end plate 1. The coolant enters and exits through the interface 4, which is the main reason for the insulation loss of the fuel cell.

[0066] For back-end board 3, the interface will be removed and back-end board 3 will be completely concealed with different machining and form to reduce the weight of the stacked components.

[0067] It must be pointed out that the insulating components disclosed in front-end board 1 below also apply to rear-end board 3.

[0068] To provide insulation, the front panel 1 includes an insulating panel made of polymer material.

[0069] The insulating panel includes a first insulating sheet 5 and a second insulating sheet 8, with one of the first insulating sheet 5 and the second insulating sheet 8 placed on each side of the insulating layer 9, such as... Figure 3 As shown in the figure. Preferably, the first insulating sheet 5 and the second insulating sheet 8 are attached to the insulating layer 9.

[0070] Preferably, the first insulating sheet 5 and the second insulating sheet 8 are made of 4,4'-oxodiphenylene-pyromellitic tetracarboximide, also known as Kapton®, and have a thickness of less than 0.5 mm, preferably 20 µm to 80 µm, and the insulating layer 9 is preferably made of polyether ether ether ketone (PEEK), polyphenylene sulfide (PPS) or other electrically insulating polymers.

[0071] To prevent the first insulating sheet 5 from peeling off due to degradation of the adhesive—in this case, the adhesive could be a coolant-resistant acrylic or silicone type—an additional insulating sheet 10 can be optionally used, which also forms part of the insulating panel. This additional insulating sheet can be made, for example, of PEEK or PPS. Furthermore, the insulating panel may also include seals 19, 21 that contact the first insulating sheet 5. Depending on the application and operating temperature of the fuel cell, different elastomers, such as NBR, Viton, FKM, etc., can be used.

[0072] An insulating panel prevents coolant from leaking to the outside through the front panel 1, which can be made of stainless steel, aluminum, or even plastic, preferably aluminum that meets aerospace fire-resistant requirements, thereby reducing the use of flammable materials.

[0073] The front end plate 1 may accommodate interfaces 4 through which fluids 13, such as coolants or various reagents, enter and exit via separate, dedicated interfaces 4. These interfaces 4 may be flanged, threaded, or equipped with pin connectors. The materials of these interfaces 4 may be polymers such as PPS or metals to meet the requirements of non-flammability and higher mechanical strength. Preferably, the same metal is selected in the end plates to avoid the formation of galvanic couples that may cause corrosion problems over time.

[0074] The flanged interface can be connected to the front end plate 1 via bolts 22. These bolts 22 should be insulated or passivated to minimize any current leakage. In addition, if the interface 4 is metallic, an electrical insulation reinforcement 11 with a groove machined to receive an O-ring 18 can be fitted to the interface 4 to seal the interface 4 and prevent coolant leakage to the outside.

[0075] These interfaces 4 may internally include an insulating pad 6, such as an insulating pad 6 made of 4,4'-oxophenylene-pyromellitic tetracarboximide or Kaptun, which has the same shape as the orifice through which the coolant or fluid to be electrically insulated passes.

[0076] The interface gasket 6 can be secured by an insulating reinforcement 11, the end of which can be lip-shaped and the insulating layer 9 can also include a lip-shaped end, so that it can be fitted into an orifice through which the fluid 13 flows. Using this orifice, another additional reinforcement, not shown in the figure, also made of PPS, PEEK, etc., can be fitted to allow coolant to pass through.

[0077] In this way, the current collector 24, fuel cell terminal 26, battery stack 2, monopole plate 25 and plates 1 and 3 are protected, thereby keeping the structure containing the fuel cell capture component of the aircraft floating.

[0078] The solution is designed to allow the fuel cell to operate optimally with deionized water or ethylene glycol-based coolants, preferably with ethylene glycol (EGW) 60 / 40 (60% ethylene glycol and 40% deionized water) or ethylene glycol 50 / 50 (50% ethylene glycol and 50% deionized water) with low conductivity, so as to minimize the resistance of the fuel cell across the interface and impede the electrical conduction from the fuel cell to the cooling system.

[0079] During the lifespan of the battery stack 2, several inspections must be scheduled in conjunction with aircraft inspections to check and replace the coolant and particulate filter as necessary, and to perform both dry and wet measurements of electrical insulation. In dry measurements, the fuel cell is completely shut down and disconnected. In wet measurements, the electrical insulation of the battery stack is continuously measured during operation, with the coolant circulating through the interface to improve conductivity, allowing the effects of coolant and moisture on the electrical insulation itself to be studied.

Claims

1. A fuel cell for an aircraft, comprising: Battery stack (2), the battery stack (2) includes an anode (27), a cathode (29) and a proton exchange membrane (28). Front end plate (1), said front end plate (1) being placed at one end of the battery stack (2); and The rear end plate (3) is placed at the other end of the battery stack (2). The fuel cell is characterized in that it further includes an insulating panel (5, 8, 9) made of polymer material and placed between the battery stack (2) and one or both of the front end plate (1) and the rear end plate (3).

2. The fuel cell for an aircraft according to claim 1, wherein, The insulating panel includes: First insulating sheet (5); Second insulating sheet (8); and An insulating layer (9) is placed between the first insulating sheet (5) and the second insulating sheet (8).

3. The fuel cell for an aircraft according to claim 1 or 2, wherein, The insulating panel also includes an additional insulating sheet (10) placed between the first insulating sheet (5) and the front end plate (1) in a manner that contacts the first insulating sheet (5).

4. A fuel cell for an aircraft according to any one of the preceding claims, wherein, The insulating panel also includes seals (19, 21) placed in contact with the first insulating sheet (5).

5. The fuel cell for an aircraft according to claim 2, wherein, The first insulating sheet (5) and the second insulating sheet (8) are made of 4,4'-oxodiphenylene-pyromellitic tetracarboximide.

6. The fuel cell for an aircraft according to claim 2, wherein, The first insulating sheet (5) and the second insulating sheet (8) are attached to the insulating layer (9).

7. The fuel cell for an aircraft according to claim 2, wherein, The insulating layer (9) is made of polyether ether ether ketone or polyphenylene sulfide.

8. A fuel cell for an aircraft according to any one of the preceding claims, wherein, The front end plate (1) includes an interface (4) for fluid to enter and exit, and an insulating reinforcement (11) is placed between the end interface (4) and the front end plate (1).

9. The fuel cell for an aircraft according to claim 8, wherein, Each insulating reinforcement (11) includes a groove in which an O-ring (18) is received.

10. The fuel cell for an aircraft according to claim 8, wherein, The front-end board (1) includes an insulating pad (6) corresponding to the interface (4).

11. The fuel cell for an aircraft according to claim 2 or 5, wherein, The first insulating sheet (5) and the second insulating sheet (8) have a thickness of less than 0.5 mm, preferably 20 µm to 80 µm.

12. The fuel cell for an aircraft according to claim 1, wherein, The proton exchange membrane (28) includes a catalyst.

13. The fuel cell for an aircraft according to claim 1, wherein, Seals (32) are placed on both sides of the proton exchange membrane (28).

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