Method for reducing temperature peak in fuel cell

Abstract

To provide a method for reducing temperature peaks in a fuel cell.SOLUTION: There are presented a method (100) and a system (10) for reducing temperature peaks during start-up of a fuel cell (12) with a two-phase cooling system. The method (100) includes: a step (102) of adjusting a saturation pressure of a coolant, via a pressure control module (14), to a first saturation pressure such that a maximum temperature of a coolant induced by boiling delay is below a maximum operating temperature of the fuel cell; a step (104) of starting the fuel cell; and a step (106) of, in response to the maximum temperature of the coolant induced by boiling delay being exceeded, adjusting the saturation pressure of the coolant, via the pressure control module (14), to a second saturation pressure that is higher than the first saturation pressure.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates generally to the aviation technical field, and in particular to a method for reducing temperature peaks in a fuel cell, as well as to an associated system and an aircraft equipped with such a system. [Background technology]

[0002] Fuel cells play a possible solution for emission-free propulsion or emission-free on-board power supply (APU = Auxiliary Power Unit), for example of aircraft. Polymer electrolyte fuel cells (PEMFC) generate current and power by producing water through an electrochemical reaction of hydrogen and oxygen. During this reaction, heat is generated that needs to be dissipated. In commercial fuel cell stacks, the heat dissipation is usually achieved by liquid cooling. One alternative that allows significant weight savings at the drive system level or on-board power system level is to replace the liquid cooling with a two-phase cooling circuit. In this case, the latent heat of vaporization is used to dissipate the large amount of heat from the fuel cell. Furthermore, the high heat transfer coefficient improves the performance of the cooling system compared to single-phase cooling. The two-phase cooling circuit is then based on a phase transition in the fuel cell (evaporator) and in a heat exchanger to the environment (condenser).

[0003] During two-phase cooling, and especially during the formation of boiling nuclei necessary for this, a temperature peak occurs, called "liquid superheat" or boiling delay. This effect leads to a higher temperature at the interface, since the boiling process has not yet fully started. As soon as a certain superheat is reached above the saturation point, boiling begins and the temperature drops to the saturation temperature. This is a temporary effect that starts the boiling process.

[0004] This boiling delay effect can increase the rate of degradation of the fuel cell as temperature peaks are reached. Summary of the Invention [Problem to be solved by the invention]

[0005] The objective of the present invention can be seen as providing a method for optimizing the operation and improving the durability of a fuel cell. [Means for solving the problem]

[0006] This problem is solved by the subject matter of the independent claims. Further embodiments are given in the dependent claims and in the following description.

[0007] According to one aspect, a method for reducing temperature peaks during start-up of a fuel cell using a two-phase cooling system includes: adjusting the saturation pressure of the coolant via a pressure control module to a first saturation pressure such that a maximum temperature of the coolant caused by boiling delay is less than a maximum operating temperature of the fuel cell; starting up the fuel cell; and adjusting, via the pressure control module, the saturation pressure of the coolant to a second saturation pressure higher than the first saturation pressure in response to an exceedance of the maximum temperature of the coolant caused by the boiling delay.

[0008] During two-phase flow, the saturation temperature is pressure dependent. Therefore, the proposed operating strategy is to establish the maximum temperature due to boiling delay below the temperature limit of the cell components during the start-up phase by lowering the saturation pressure of the cooling system. Once the peak value is exceeded and the boiling process is initiated, the target value of the pressure regulator can be increased to the nominal operating pressure / temperature.

[0009] One of the advantages of this method of reducing temperature peaks during start-up of a fuel cell using a two-phase cooling system is that the saturation pressure and therefore the temperature of the coolant can be effectively controlled and regulated.

[0010] By adjusting the saturation pressure of the coolant to a first saturation pressure below the maximum operating temperature of the fuel cell, the undesirable effects of boiling delay at excessively high temperatures and thus overheating above the adjusted boiling temperature are reliably avoided, which can reduce the risk of temperature peaks that may occur during start-up.

[0011] After the fuel cell starts up, the method continuously monitors the temperature of the coolant. If the maximum temperature caused by boiling delay is exceeded, the pressure control module is used to adjust the saturation pressure of the coolant. The saturation pressure is adjusted to a second, higher saturation pressure. This increases the heat dissipation by the coolant, improves the cooling performance, and effectively controls the temperature of the fuel cell.

[0012] The advantage of this method is that it can prevent or reduce temperature peaks during start-up. By adjusting the saturation pressure in time, it can ensure optimal cooling performance without overheating above the target operating temperature due to boiling delay. This contributes to the stability and lifespan of the fuel cell and allows the system to operate smoothly.

[0013] In summary, the method described above allows for precise control of the coolant saturation pressure to minimize temperature peaks during the fuel cell start-up process, improving fuel cell reliability, performance and lifetime, and optimizing the overall operating efficiency of the fuel cell system.

[0014] According to one embodiment, the pressure control module is a pressure accumulator.

[0015] The use of a pressure accumulator as a pressure control module offers several advantages: the saturation pressure can be quickly and accurately adjusted to accommodate changing operating conditions and demands, thereby ensuring efficient cooling and optimal performance of the fuel cell.

[0016] Additionally, the accumulator helps stabilize the pressure in a two-phase cooling system. By buffering pressure fluctuations and maintaining a constant pressure level, a uniform coolant supply is ensured, which improves heat transfer and cooling.

[0017] The accumulator also provides a degree of redundancy and safety: it acts as an additional coolant reservoir and can compensate for unexpected fluctuations in system pressure, thereby minimizing potential damage to the fuel cells due to pressure peaks or drops.

[0018] According to one embodiment, the accumulator is connected to the outlet of the fuel cell and is configured to separate the vapor and liquid phases of the coolant from each other, which is essential in two-phase cooling.

[0019] According to one embodiment, the accumulator is configured to regulate the temperature of the coolant.

[0020] The use of the accumulator as a temperature adjustable pressure control module offers several advantages: by being able to adjust the temperature of the accumulator, the saturation pressure of the coolant can be precisely controlled. This allows for an effective cooling of the fuel cell and also prevents temperature peaks during operation.

[0021] According to one embodiment, the accumulator is configured to regulate the pressure of the coolant.

[0022] The use of the accumulator as a pressure-controlled module with adjustable pressure also offers various advantages. By being able to adjust the pressure in the accumulator, the saturation pressure and therefore the temperature of the coolant can be precisely controlled to match the requirements of the fuel cell. This allows for efficient cooling. A further advantage of a pressure-controlled accumulator is that the evaporation pressure can be instantly adjusted.

[0023] The adjustable pressure or temperature feature of the accumulator also offers the flexibility to adapt the cooling system to different operating conditions and demands. Depending on the specific requirements, the pressure can be appropriately adjusted to ensure optimal cooling and performance of the fuel cell.

[0024] Overall, the use of the accumulator as a temperature or pressure adjustable pressure control module allows for precise control of the saturation pressure of the two-phase cooling system, which contributes to improved performance, efficiency and reliability of the fuel cell system and supports stable and safe operation.

[0025] According to one embodiment, the pressure control module is a combination pump and throttle valve.

[0026] The use of a pump and throttle valve combination as a pressure control module provides several advantages: The pump allows for active control of the coolant pressure by pumping the coolant through the system at a specific speed and pressure, allowing the coolant saturation pressure to be precisely controlled to maintain the optimum operating temperature of the fuel cell.

[0027] At the same time, the pump and throttle valve combination offers the potential to save weight and installation space requirements of the cooling system by reducing the size of the accumulator required or eliminating the accumulator altogether.

[0028] The throttle valve acts as a control valve to limit the coolant flow rate and regulate the pressure. By adjusting the throttle valve, the pressure in the system can be controlled and regulated. This makes it possible to precisely control the saturation pressure of the cooling system to meet the requirements of the fuel cell and to avoid temperature peaks.

[0029] Additionally, the use of a pump and throttle valve combination allows for continuous monitoring and control of the coolant pressure, allowing the system to react to changing operating conditions and adjust pressure accordingly to ensure consistent cooling and safe operation of the fuel cell.

[0030] According to one embodiment, the first saturation pressure is in the range from 0 bar to 10 bar, preferably in the range from 0 bar to 5 bar, particularly preferably 1.25 bar.

[0031] According to one embodiment, the second saturation pressure is in the range from 0 bar to 10 bar, preferably in the range from 0 bar to 5 bar, particularly preferably it is 3 bar.

[0032] According to one embodiment, the maximum temperature of the coolant caused by the boiling delay is 50% to 100%, preferably 60% to 90%, particularly preferably 70% to 80% of the operating temperature.

[0033] According to one embodiment of the fuel cell system, methanol and / or ethanol are used as the coolant. This choice of coolant provides several advantages to the system.

[0034] Methanol and ethanol have high thermal conductivity and can efficiently dissipate heat from the fuel cell and bipolar plates.

[0035] This allows for effective cooling of the components and keeps the operating temperature of the fuel cell at an optimum level.

[0036] Furthermore, methanol and ethanol have low boiling points, which is advantageous since they can evaporate quickly when flowing through the coolant channels. By evaporation, heat is absorbed from the components, which results in effective cooling. In particular, the combination of boiling temperature and saturation pressure, which is suitable for the operation of fuel cells, proves advantageous here.

[0037] Furthermore, methanol and ethanol have a high enthalpy of vaporization, which allows for very low mass flows in the system, which reduces pressure losses and results in smaller piping and pumps than in liquid cooling, which translates into a lighter system.

[0038] According to one aspect, a system for operating a fuel cell with a two-phase cooling system is configured to perform a method for reducing temperature peaks during start-up and comprises at least one fuel cell, a pressure control module, a heat exchanger and a coolant circuit, the coolant circuit being configured to cool the fuel cell by a phase transition of the coolant, the pressure control module being configured to regulate a saturation pressure of the coolant contained in the coolant circuit.

[0039] The system comprises at least one fuel cell or a fuel cell stack, responsible for generating energy from a fuel supply. To effectively cool the fuel cell, a two-phase cooling system is used, which allows efficient heat dissipation and contributes to the stabilization of the operating temperature.

[0040] A key component of the system is the pressure control module, which is responsible for controlling the saturation pressure of the coolant supplied to the coolant circuit. The saturation pressure is regulated in such a way that the maximum temperature of the coolant during the start-up process is kept below the maximum operating temperature of the fuel cell. This avoids undesirable temperature peaks and ensures optimal cooling performance.

[0041] The coolant circuit is specially designed to allow efficient distribution and circulation of coolant, which is pumped through the fuel cells and a two-phase cooling system to dissipate generated heat and ensure uniform cooling.

[0042] The combination of these components and the precise adjustment of the coolant saturation pressure during the start-up process allows the system to effectively regulate the temperature of the fuel cell, thereby improving its lifespan and performance. The reduction of temperature peaks helps to minimize the thermal load and creates a reliable and stable operating environment for the fuel cell.

[0043] Overall, the system allows for efficient cooling of fuel cells using a two-phase cooling system, helping to optimize fuel cell performance and lifetime, which is crucial for reliable operation of fuel cell systems and their applications in various fields such as transportation, energy storage, and many other applications.

[0044] According to one aspect, an aircraft includes the above system, which can also be clearly used in other systems, such as automobiles, surface vessels, space travel, or other fuel cell powered units.

[0045] The incorporation of this system into aircraft provides a sustainable and environmentally friendly energy source for propulsion or on-board power of aircraft. Fuel cells enable high energy efficiency while at the same time reducing emissions compared to conventional combustion engines. The two-phase cooling system ensures efficient cooling, contributing to the reliability and lifespan of the fuel cell system.

[0046] The use of this system in aircraft can achieve increased flight time and performance, while also reducing environmental impact and providing a sustainable alternative to traditional fuel sources, thereby contributing to cleaner and more environmentally friendly flight for aircraft incorporating this fuel cell system.

[0047] According to one embodiment, the method comprises the following method steps for starting a fuel cell at temperatures below 0 degrees Celsius: starting up the fuel cell; activating the pump after a predetermined time period, during which the coolant is essentially in a gas phase within the fuel cell; Since at these temperatures the avoidance of temperature peaks is particularly relevant for low-temperature materials.

[0048] Subzero temperatures lead to the formation of ice in the gas pipes. For this reason, the time to reach temperatures above 0 °C is considered to be the determining factor, and it is considered advantageous to reduce the thermal mass to be heated. In order to speed up this process compared to liquid cooling, technical solutions have been proposed that exploit the two-phase state of the coolant in the fuel cell and precisely control the coolant pump.

[0049] The above additional method steps for starting up a fuel cell at temperatures below 0° C. using a two-phase cooling system thereby provide an effective method for starting up and operating a fuel cell in a low temperature environment. A two-phase cooling system uses a special pump to supply a coolant, where the coolant is at least partially in the gas phase.

[0050] The start-up process begins with starting up the fuel cell according to normal procedures. After a specified time required for fuel cell start-up, the pump is started. During this specified time, the coolant is essentially in the gas phase within the fuel cell.

[0051] With this approach, several advantages are realized. First, the use of a two-phase cooling system allows efficient heat dissipation, ensuring optimal cooling of the fuel cell even at low temperatures. Second, the start-up of the pump after a defined time allows to reduce the start-up time of fuel cells with a small thermal mass, in order to reduce the start-up time or warm-up time before the coolant becomes subcooled. When the coolant is in the gas phase, it has a lower density than in the liquid phase. This lower density leads to a lower thermal mass, which leads to faster heating for the same heat input.

[0052] The use of this method therefore provides a reliable possibility for successful start-up and operation of the fuel cell even at low temperatures, which allows for efficient cooling and contributes to the long-term stability and performance of the fuel cell at low temperatures, and ensuring optimal operation of the fuel cell in low temperature environments increases the ease of use and reliability of the system.

[0053] Such a method for reducing temperature peaks during start-up and further starting up a fuel cell at temperatures below 0° C. can in particular be implemented using the above-described system for operating a fuel cell with a two-phase cooling system.

[0054] In the following, embodiments of the invention will be explained in more detail with reference to the accompanying drawings, in which the illustrations are schematic and not to scale, and in which the same reference signs refer to the same or similar elements. [Brief description of the drawings]

[0055] [Figure 1] 4 is a flow chart of a method for reducing temperature peaks during start-up of a fuel cell using a two-phase cooling system. [Figure 2A] FIG. 1 illustrates a system for operating a fuel cell using a two-phase cooling system according to a first embodiment. [Figure 2B] FIG. 2 illustrates a system for operating a fuel cell using a two-phase cooling system according to a second embodiment. [Diagram 3] FIG. 1 shows an aircraft equipped with a system for operating a fuel cell using a two-phase cooling system. [Figure 4] 2 shows two graphs showing temperature curves over time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] 1 shows a flow chart of a method 100 for reducing temperature peaks during start-up of a fuel cell using a two-phase cooling system. First, the saturation pressure of the coolant is adjusted 102 to a first saturation pressure (not shown) by the pressure control module 14. This first saturation pressure is selected such that the maximum temperature of the coolant caused by boiling delay is below the maximum operating temperature of the fuel cell.

[0057] After adjusting the saturation pressure, the fuel cell is started up (104). During the start-up process, boiling delays may occur that can increase the temperature of the coolant. After exceeding the temperature peak at the first saturation pressure 102, the saturation pressure of the coolant is adjusted by the pressure control module 14 to a second saturation pressure 106, which is higher than the first saturation pressure and allows for effective cooling near the maximum operating temperature of the fuel cell.

[0058] By proper adjustment of the saturation pressure of the coolant, the method can ensure accurate control of the temperature during the start-up process, and thus improve the operational reliability and service life of the fuel cell.

[0059] 2A and 2B each show a system 10 for operating a fuel cell 12 with a two-phase cooling system designed to ensure efficient cooling of the fuel cell and reduce temperature peaks during start-up. The system includes several components operating in an integrated coolant circuit 16 with a pump 20.

[0060] The central component of the system is the fuel cell 12, which converts chemical energy into electrical energy. A two-phase cooling system is used to ensure an optimal operating temperature of the fuel cell 12. This system uses a coolant that can exist in both liquid and gas phases to efficiently dissipate heat.

[0061] To control the coolant circuit, a pressure control module 14 is incorporated. This module allows precise regulation of the coolant in the coolant circuit 16. Control of the saturation pressure makes it possible to optimize the cooling capacity and to reduce temperature peaks in the conditions of boiling delay during the start-up process.

[0062] The system 10 operates in a continuous cycle where coolant flows through the fuel cells 12 and absorbs the heat generated. The coolant is then cooled via heat exchanger 18 and fed back into the coolant circuit 16. This ensures that the fuel cells 12 are constantly cooled and prevents overheating.

[0063] The basic difference between the embodiment of Figure 2A and Figure 2B is seen in the fact that the accumulator / collector is connected to the return line, allowing the gas phase to mix with the liquid phase. In this embodiment, a condenser bypass is used to minimize the heat mass due to the mass flow circulating through the fuel cell. A condenser bypass is a device or arrangement that allows a portion of the mass flow or coolant to bypass the condenser instead of passing through it. The condenser bypass forces the coolant to bypass the condenser. This reduces the thermal mass of the circulating coolant in the circuit and eliminates unnecessary heat dissipation to the environment during the start-up process.

[0064] The system 10 for operating a fuel cell using a two-phase cooling system provides efficient cooling, improved performance, and extended life for the fuel cell 12. It enables reliable operation even in extreme temperatures, resulting in consistent and efficient energy production.

[0065] 3 shows an aircraft 200 equipped with a system 10 for operating a fuel cell using a two-phase cooling system, which operates according to the principles described above to reduce temperature peaks during start-up and to efficiently cool the fuel cell.

[0066] The aircraft 200 incorporates the system 10 into its overall structure. The fuel cells 12, the pressure control module 14, and the coolant circuits 16 are specially adapted to the requirements of the aircraft.

[0067] The system 10 enables the aircraft 200 to generate energy in an environmentally friendly and efficient manner, whereby fuel cells generate electrical energy from a supply of fuel and atmospheric oxygen, and a two-phase cooling system provides optimal operating temperatures, whereby boiling delay is achieved below the operating temperature range.

[0068] 4 shows two graphs plotting the temperature of the fuel cell 12 over time. In the upper graph, the maximum temperature T caused by boiling delay is S is the operating temperature T BIt can be seen that the above-mentioned undesirable effects can occur.

[0069] The lower graph shows a temperature curve in which, in response to exceeding a maximum coolant temperature caused by boiling delay, the coolant saturation pressure is adjusted, via the pressure control module, to a second saturation pressure, the second saturation pressure being higher than the first saturation pressure.

[0070] Thereby, the maximum temperature T caused by the boiling delay S is lower, and the operating temperature T B below, thereby improving the operating behavior of the fuel cell.

[0071] It should further be noted that "comprises" or "comprises" does not exclude other elements or steps, and "a" does not exclude a plurality. It should further be noted that features or steps described with reference to one of the above embodiments can also be used in combination with other features or steps of other of the above embodiments. Reference signs in the claims are not to be considered as limiting. [Explanation of symbols]

[0072] 10. System 12 Fuel Cell 14 Pressure control module (pressure accumulator) 16 Coolant Circuit 18 Heat exchanger 20 Pump 100 How to reduce temperature peaks 102 Adjustment of the first saturation pressure 104 Fuel Cell Start-Up 106 Adjustment of the second saturation pressure 200 aircraft T B Fuel Cell Maximum Operating Temperature T S Maximum temperature due to delayed boiling

Claims

1. A method (100) for reducing temperature peaks during start-up of a fuel cell (12) using a two-phase cooling system, comprising the steps of: The saturation pressure of the coolant is controlled via a pressure control module (14) to the maximum temperature of the coolant caused by boiling delay (T Ｓ ) is the maximum operating temperature of the fuel cell (T Ｂ (102) adjusting the first saturation pressure to a first saturation pressure less than starting up the fuel cell (104); The maximum temperature of the coolant caused by boiling delay (T Ｓ regulating (106) the saturation pressure of the coolant via the pressure control module (14) to a second saturation pressure higher than the first saturation pressure; A method (100).

2. The method (100) of claim 1, wherein the pressure control module (14) is a pressure accumulator (14).

3. The method (100) of claim 2, wherein the accumulator (14) is connected to an outlet of the fuel cell (12) and configured to separate vapor and liquid phases of the coolant from one another.

4. The method (100) of claim 2 or 3, wherein the accumulator (14) is configured to regulate a temperature of the coolant.

5. The method (100) of any one of claims 2 to 4, wherein the accumulator (14) is configured to regulate the pressure of the coolant.

6. The method (100) of claim 1, wherein the pressure control module (14) is a combination of a pump (20) and a throttle valve.

7. The method (100) according to any one of the preceding claims, wherein the first saturation pressure is in the range of 0 bar to 10 bar, preferably in the range of 0 bar to 5 bar, particularly preferably 1.25 bar.

8. The method (100) according to any one of the preceding claims, wherein the second saturation pressure is in the range of 0 bar to 10 bar, preferably in the range of 0 bar to 5 bar, particularly preferably 3 bar.

9. The method (100) according to any one of the preceding claims, wherein the maximum temperature of the coolant caused by boiling delay is between 50% and 100%, preferably between 60% and 90%, particularly preferably between 70% and 80% of the operating temperature.

10. The method (100) of any one of claims 1 to 9, wherein the coolant comprises methanol and / or ethanol.

11. A system (10) for operating a fuel cell with a two-phase cooling system, the system (10) being configured to implement the method according to any one of claims 1 to 10 in order to reduce temperature peaks during start-up, At least one fuel cell (12); A pressure control module (14); A heat exchanger (18); a coolant circuit (16); the coolant circuit (16) is configured to cool the fuel cell (12) by two-phase cooling via the heat exchanger (18); The pressure control module (14) is configured to regulate a saturation pressure of a coolant contained in the coolant circuit (16), the system (10).

12. An aircraft (200) comprising a system (10) according to claim 11.

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