A method of shutting down a fuel cell engine

Abstract

The application discloses a fuel cell engine shutdown method, and belongs to the technical field of fuel cell engines. First, the fuel cell engine shutdown process is determined, and the structural parameters, operating conditions and auxiliary load current of the fuel cell stack are obtained. Then, the total oxygen amount of the cathode closed area when the air supply is closed and the air inlet and outlet throttle valves of the stack are closed and the consumed oxygen amount of the cathode after the auxiliary load is applied are calculated to obtain the minimum hydrogen amount. If the minimum hydrogen amount is greater than or equal to the total hydrogen amount of the anode closed area when the hydrogen supply is closed and the hydrogen upstream and downstream valves of the stack are closed, the fuel cell engine shutdown process is directly executed. Otherwise, at least one parameter in the structural parameters, operating conditions and auxiliary load current of the fuel cell stack is adjusted until the condition is met, and then the fuel cell engine shutdown process is executed, so that the hydrogen-air interface generated in the current shutdown process and the next startup process is avoided, the fuel cell engine shutdown process is optimized, and the durability of the vehicle fuel cell engine is improved.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell engine technology, and specifically relates to a method for shutting down a fuel cell engine. Background Technology

[0002] In a proton exchange membrane fuel cell (PEMFC), hydrogen-rich gas enters from the anode side. Hydrogen atoms lose electrons at the anode and become protons. The protons pass through the proton exchange membrane to the cathode, while electrons also reach the cathode via an external circuit. At the cathode, protons, electrons, and oxygen combine to generate water. It is an environmentally friendly and efficient power generation device.

[0003] A fuel cell engine mainly consists of three subsystems: hydrogen, air, and thermal management. Its workflow is as follows: Figure 1 As shown. Specifically:

[0004] a) Hydrogen Subsystem: Hydrogen enters the ejector via a shut-off valve. After pressure regulation within the ejector, it is fed into the battery stack to supply the electrochemical reaction. A pressure sensor is installed on the hydrogen inlet line for ejector pressure feedback control. Unreacted exhaust gas is drawn into the ejector's hydrogen return port, mixed with fresh hydrogen, and then reintroduced into the battery stack to participate in the reaction, achieving hydrogen recovery and utilization, thereby improving hydrogen efficiency. An exhaust valve is installed on the line after the condensate drain valve to effectively control the concentration of impurity gases in the anode exhaust gas.

[0005] b) Air Subsystem: Ambient air is drawn into the air compressor inlet after passing through a filter. It is then pressurized by the air compressor, cooled by the intercooler, and enters the humidifier. The humidified air then enters the battery stack to participate in the reaction. Exhaust gas from the humidifier is discharged into the ambient atmosphere after passing through a muffler. A throttle valve is installed on both the air inlet and outlet pipes of the battery stack, which completely closes after the engine stops to prevent outside air from entering the battery stack. A pressure sensor is installed on the air inlet pipe.

[0006] c) Thermal Management Subsystem: Stable operation of the fuel cell engine requires controlling the stack temperature within a reasonable range. The cooling circuit is equipped with both large and small circulation loops. Temperature sensors are installed on the coolant inlet and outlet pipes of the stack for feedback control of pump speed and cooling fan speed.

[0007] In actual vehicle operation, fuel cell engines need to frequently perform start-up and shutdown cycles. Related studies ([1] Pei P, Chang Q, Tang T. A quick evaluating method for automotive fuel cell lifetime[J]. International Journal of Hydrogen Energy, 2008, 33(14): 3829-3836. [2] Shimoi R, Aoyama T, Iiyama A. Development of fuel cell stackdurability based on actual vehicle test data: current status and future work[J]. SAE International journal of engines, 2009, 2(2009-01-1014): 960-970.) have confirmed that the performance degradation caused by start-up and shutdown cycles accounts for more than 1 / 3 of the total life cycle performance loss. During the start-up and shutdown process, the hydrogen-air interface formed at the anode of the fuel cell stack leads to the formation of a high potential at the interface of the cathode membrane electrode catalyst layer, causing corrosion of the catalyst carbon support and an increase in the particle size of the platinum catalyst, resulting in a decrease in the effective reaction area, which leads to a serious and irreversible degradation of the fuel cell engine performance.

[0008] After the fuel cell engine is shut down, hydrogen, oxygen, and nitrogen undergo transmembrane permeation and hydrogen-oxygen catalytic reactions within the fuel cell stack's internal reaction zone. This leads to concentration and pressure differences in mass transfer between the stack manifold / external piping and the reaction zone, thus affecting the formation of the hydrogen-air interface. Therefore, a reasonable shutdown strategy is needed to prevent the formation of the hydrogen-air interface after shutdown and upon the next startup, thereby improving the durability of the fuel cell system.

[0009] Chinese patent application number 202411006933.1 discloses a shutdown method and apparatus for a fuel cell. Specifically, it first shuts off the air supply, closes the cathode circuit, lowers the cathode potential by consuming cathode oxygen through the application of a load, and then shuts off the hydrogen supply. By lowering the cathode potential through the gas shutdown sequence and auxiliary load, it ensures that a hydrogen-air interface does not appear at the anode, or if a hydrogen-air interface does appear, the corrosion rate of the carbon support is reduced due to the lower cathode potential, thereby avoiding or greatly reducing the degradation caused by the hydrogen-air interface.

[0010] The above technical solution does not consider the impact of shutdown operating parameters (cathode and anode pressure, anode nitrogen content, gas humidity, stack temperature, etc.), stack and system structural parameters (proton exchange membrane thickness, flow channel structural characteristics, stack manifold design, engine piping design, etc.), and auxiliary load parameters (current, duration, etc.) on the internal reaction and mass transfer processes of the battery stack after shutdown (intermembranous interperfusion of hydrogen, oxygen, and nitrogen within the stack, as well as the concentration and pressure difference mass transfer processes caused by the hydrogen-oxygen catalytic reaction). These parameters will couple and affect the dynamic process of the formation and dissipation of the hydrogen-air interface during shutdown, and will also directly determine the equilibrium state of various gas components at the anode and cathode, thus affecting the formation of the hydrogen-air interface during the next startup process.

[0011] However, there is currently no quantitative method for determining the relationship between commercial fuel cell engine-level shutdown conditions, stack and system structural parameters, auxiliary load reduction parameters, and the effectiveness of start-up and shutdown hydrogen-air interface suppression strategies. This makes existing start-up and shutdown processes largely dependent on experience, making it difficult to achieve optimal control. Summary of the Invention

[0012] To address the technical problems existing in the prior art, the present invention provides a method for shutting down a fuel cell engine. By systematically considering the impact of shutdown operating conditions, auxiliary load parameters, and stack and engine structural design parameters on the effectiveness of the shutdown strategy, the method avoids the hydrogen-air interface and achieves global optimization of the shutdown strategy.

[0013] The technical solution adopted in this invention is as follows:

[0014] A method for shutting down a fuel cell engine includes the following steps:

[0015] Step 1: Determine the fuel cell engine shutdown procedure. Specifically, first reduce the stack auxiliary load current to 0, shut off the air supply and the stack air inlet and outlet throttle valves to form a cathode closed area; then apply the auxiliary load to quickly reduce the stack potential; finally shut off the hydrogen supply and the stack hydrogen upstream and downstream valves to form an anode closed area.

[0016] Step 2: Obtain the structural parameters, operating conditions, and auxiliary load current of the fuel cell stack. Among them, structural parameters include the number of fuel cell stack sections. Total volume of the cathode enclosed region Total volume of the anode enclosed region Operating conditions include the pressure at the fuel cell stack air inlet and outlet when the throttle valve is closed. With cathode humidity Pressure when upstream and downstream valves for hydrogen in fuel cell stack are closed Anode humidity With anodic nitrogen content and battery stack temperature ;

[0017] Step 3: Calculate the total oxygen content in the cathode closed area when the air supply and the throttle valves of the fuel cell stack air inlet and outlet are closed. :

[0018]

[0019] In the formula, This represents the gas constant, with a value of 8.314 J / (mol×K). Indicates the saturated vapor pressure of water;

[0020] Step 4: Calculate the amount of cathode oxygen consumed after applying the auxiliary load. :

[0021]

[0022] In the formula, This represents the Faraday constant, with a value of 96485 C / mol;

[0023] Step 5: Calculate the total amount of hydrogen in the anode closed area when the hydrogen supply and upstream and downstream valves of the fuel cell stack are shut off. :

[0024]

[0025] Step 6, based on and Calculate the minimum amount of hydrogen. :

[0026]

[0027] Step 7, Judgment Is it greater than or equal to? If so, proceed directly to step 1 to execute the fuel cell engine shutdown procedure; otherwise, proceed to step 8.

[0028] Step 8: Adjust the structural parameters, operating conditions, and auxiliary load current of the fuel cell stack. At least one parameter in, until the following condition is met:

[0029]

[0030] Then, follow the method in step 1 to perform the fuel cell engine shutdown process to avoid the generation of a hydrogen-air interface between the current shutdown process and the next startup process, thereby optimizing the fuel cell engine shutdown process.

[0031] Furthermore, the cathode enclosed area is the enclosed area between the throttle valves of the upstream and downstream cathode pipelines of the fuel cell stack, specifically including pipelines, fuel cell stack cathode manifolds, and fuel cell stack cathode reaction zone chambers.

[0032] Furthermore, the cathode enclosure region also includes the internal volume of components such as a humidifier.

[0033] Furthermore, the anode enclosed area is the enclosed area between the hydrogen inlet valve and the exhaust valve, specifically including pipelines, the fuel cell stack anode manifold, and the fuel cell stack anode reaction zone cavity.

[0034] Furthermore, the anode enclosure area also includes the internal volume of the ejector and the drain valve.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] This invention proposes a method for shutting down a fuel cell engine. By systematically considering the impact of shutdown operating conditions, load reduction parameters, and stack and engine structural design parameters on the effectiveness of the shutdown strategy, the method quantitatively optimizes the system-level fuel cell engine start-up and shutdown control strategy. This effectively suppresses hydrogen-air interface-induced performance degradation, achieves global optimization of the shutdown strategy, and improves the durability of automotive fuel cell engines. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the working process of a fuel cell engine.

[0038] Figure 2 This is a logic block diagram of the fuel cell engine shutdown method proposed in Example 1;

[0039] Figure 3 The measured operating curves are those of the fuel cell engine shutdown process executed in Example 1. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0041] Example 1

[0042] This embodiment proposes a method for shutting down a fuel cell engine to ensure that the interior of the fuel cell stack anode remains composed of hydrogen and nitrogen after shutdown. This prevents the formation of a hydrogen-oxygen interface in the anode reaction zone upon the next startup, thus avoiding irreversible performance degradation of the fuel cell stack. The specific process is as follows: Figure 2 As shown, it includes the following steps:

[0043] Step 1: Determine the fuel cell engine shutdown procedure. Specifically, first, reduce the auxiliary load current of the fuel cell stack to 0, shut off the air supply and the air inlet and outlet throttle valves of the fuel cell stack to form a cathode closed area, which is the closed area between the throttle valves of the upstream and downstream cathode pipelines of the fuel cell stack air, specifically including the pipelines, the fuel cell stack cathode manifold, and the fuel cell stack cathode reaction zone cavity; then, apply the auxiliary load to quickly reduce the fuel cell stack potential; finally, shut off the hydrogen supply and the upstream and downstream hydrogen valves of the fuel cell stack to form an anode closed area, which is the closed area between the hydrogen inlet valve and the exhaust valve, specifically including the pipelines, the fuel cell stack anode manifold, the fuel cell stack anode reaction zone cavity, and the internal volume of the ejector and the drain valve.

[0044] Step 2: Obtain the structural parameters, operating conditions, and auxiliary load current of the fuel cell stack. Among them, structural parameters include the number of fuel cell stack sections. Total volume of the cathode enclosed region Total volume of the anode enclosed region Operating conditions include the pressure at the fuel cell stack air inlet and outlet when the throttle valve is closed. With cathode humidity Pressure when upstream and downstream valves for hydrogen in fuel cell stack are closed Anode humidity With anodic nitrogen content (defined as the molar percentage of nitrogen in the anode dry gas), and the battery stack temperature. ;

[0045] Step 3: Calculate the total oxygen content in the cathode closed area when the air supply and the throttle valves of the fuel cell stack air inlet and outlet are closed. :

[0046] Equation (1)

[0047] In the formula, This represents the gas constant, with a value of 8.314 J / (mol×K). Indicates the saturated vapor pressure of water;

[0048] Step 4: After shutting off the air supply, applying an auxiliary load will consume hydrogen and oxygen at the cathode. Calculate the amount of cathode oxygen consumed after applying the auxiliary load. :

[0049] Equation (2)

[0050] In the formula, This represents the Faraday constant, with a value of 96485 C / mol;

[0051] Step 5: The time interval between shutting off the air supply and the air inlet / outlet throttle valves of the fuel cell stack, and shutting off the hydrogen supply and the upstream / downstream hydrogen valves of the fuel cell stack, is as follows: During this process, oxygen from the anode permeates across the membrane into the cathode, consuming oxygen from the cathode. Oxygen from the cathode also permeates across the membrane back to the anode. Calculate the amount of cathode oxygen consumed in both processes. :

[0052] Equation (3)

[0053] In the formula, This represents the rate of hydrogen permeate across the membrane; This represents the rate of oxygen permeation across the membrane;

[0054] Step 6: Calculate the total amount of hydrogen in the anode closed area when the hydrogen supply and upstream and downstream hydrogen valves of the fuel cell stack are shut off. :

[0055] Equation (4)

[0056] Step 7, based on , and Calculate the minimum amount of hydrogen. :

[0057] Equation (5)

[0058] Due to the interperfusion of hydrogen and oxygen across the membrane, oxygen... The results involve integrals and complex calculations that are difficult to obtain, and the time intervals are also significant. The shorter the membrane, the less cathode oxygen is consumed by hydrogen-oxygen transmembrane interpenetration. The size is negligible. The calculation formula is simplified to:

[0059] Equation (6)

[0060] And ignore Calculated This will make it easier to maintain the hydrogen and nitrogen composition in the anode chamber at any time after shutdown;

[0061] Step 8, Judgment Is it greater than or equal to? If so, proceed directly to step 1 to execute the fuel cell engine shutdown procedure; otherwise, proceed to step 9.

[0062] Step 9: Adjust the structural parameters, operating conditions, and auxiliary load current of the fuel cell stack. At least one parameter, namely the number of fuel cell stack sections. Total volume of the cathode enclosed region Total volume of the anode enclosed region Pressure at the air inlet and outlet of the fuel cell stack when the throttle valve is closed With cathode humidity Pressure when upstream and downstream valves for hydrogen in fuel cell stack are closed Anode humidity With anodic nitrogen content Battery stack temperature and auxiliary load current At least one parameter in, until the following condition is met:

[0063]

[0064] Equation (7)

[0065] Then, follow the method in step 1 to perform the fuel cell engine shutdown process to avoid the generation of a hydrogen-air interface between the current shutdown process and the next startup process, thereby optimizing the fuel cell engine shutdown process.

[0066] In this embodiment, the number of fuel cell stack sections used is... The total volume of the cathode enclosed area is 340 units; when the air supply and the fuel cell air inlet / outlet throttle valves are closed, the total volume of the cathode enclosed area is... It is 9.274×10 -3 m 3 ,pressure The pressure is 104 kPa, and the cathode humidity is... The value is 0.8; when the hydrogen supply and upstream and downstream valves of the fuel cell stack are closed, the total volume of the anode enclosed area is 0.8. It is 5.838×10 -3 m 3 ,pressure The pressure is 144.2 kPa, and the anode humidity is... The anode nitrogen content in the anode gas supply is 0.6. The temperature of the fuel cell stack is 0. The temperature is 38℃ (311 K). Refer to the table for the corresponding saturated vapor pressure of water. is 6.63 kPa;

[0067] Under the aforementioned structural parameters and operating conditions of the fuel cell stack, the following calculations were performed:

[0068]

[0069]

[0070]

[0071] because You can directly follow the method in step 1 to perform the fuel cell engine shutdown process, thus avoiding the generation of a hydrogen-air interface during the shutdown process and the next startup process.

[0072] The measured operating curve obtained by executing the fuel cell engine shutdown procedure in this embodiment is as follows: Figure 3 As shown, the voltage drops rapidly to 0 and remains thereafter after shutdown. When hydrogen is introduced during the next startup, the voltage is 0. The voltage only starts to be generated when air is introduced, indicating that no hydrogen-air interface is generated after shutdown or during the next startup.

[0073] It should be noted that this is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for shutting down a fuel cell engine, characterized in that, Includes the following steps: Step 1: Determine the fuel cell engine shutdown procedure. Specifically, first reduce the auxiliary load current of the fuel cell stack to 0, shut off the air supply and the air inlet and outlet throttle valves of the fuel cell stack to form a cathode closed area; then apply the auxiliary load to quickly reduce the stack potential; finally shut off the hydrogen supply and the upstream and downstream valves of the hydrogen in the fuel cell stack to form an anode closed area. Step 2: Obtain the structural parameters, operating conditions, and auxiliary load current of the fuel cell stack. Among them, structural parameters include the number of fuel cell stack sections. Total volume of the cathode enclosed region Total volume of the anode enclosed region Operating conditions include the pressure at the fuel cell stack air inlet and outlet when the throttle valve is closed. With cathode humidity Pressure when upstream and downstream valves for hydrogen in fuel cell stack are closed Anode humidity With anodic nitrogen content and battery stack temperature ; Step 3: Calculate the total oxygen content in the cathode closed area when the air supply and the throttle valves of the fuel cell stack air inlet and outlet are closed. : In the formula, Represents the gas constant; Indicates the saturated vapor pressure of water; Step 4: Calculate the amount of cathode oxygen consumed after applying the auxiliary load. : In the formula, Denotes Faraday's constant; Step 5: Calculate the total amount of hydrogen in the anode closed area when the hydrogen supply and upstream and downstream valves of the fuel cell stack are shut off. : Step 6, based on and Calculate the minimum amount of hydrogen. : Step 7, Judgment Is it greater than or equal to? If so, proceed directly to step 1 to execute the fuel cell engine shutdown procedure; otherwise, proceed to step 8. Step 8: Adjust the structural parameters, operating conditions, and auxiliary load current of the fuel cell stack. At least one parameter in, until the following condition is met: Then, follow the steps in step 1 to perform the fuel cell engine shutdown procedure in order to avoid the generation of a hydrogen-air interface during this shutdown process and the next startup process.

2. The fuel cell engine shutdown method according to claim 1, characterized in that, The cathode enclosed area is the enclosed area between the throttle valves of the upstream and downstream cathode pipelines of the fuel cell stack, specifically including pipelines, fuel cell stack cathode manifold, and fuel cell stack cathode reaction zone cavity.

3. The fuel cell engine shutdown method according to claim 2, characterized in that, The cathode enclosure area also includes, for example, the internal volume of a humidifier.

4. The fuel cell engine shutdown method according to claim 1, characterized in that, The anode enclosed area is the enclosed area between the hydrogen inlet valve and the exhaust valve, specifically including pipelines, the fuel cell stack anode manifold, and the fuel cell stack anode reaction zone cavity.

5. The fuel cell engine shutdown method according to claim 4, characterized in that, The anode enclosure area also includes the internal volume of the ejector and the drain valve.

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