A fuel cell system hydrogen leakage diagnosis method

Abstract

The application discloses a hydrogen leakage diagnosis method for a fuel cell system. During the operation of the fuel cell system, the tail hydrogen concentration is monitored in real time. When the hydrogen concentration of the exhaust pipeline is greater than or equal to a second concentration threshold without the opening of the exhaust valve, the fuel cell system is stopped. If the hydrogen concentration of the exhaust pipeline is less than the second concentration threshold, it is determined whether the single cell voltage is low. If the single cell voltage is low, the diagnosis is ended. If the single cell voltage is not low, the hydrogen concentration change rate of the exhaust pipeline is calculated. It is determined whether the tail hydrogen concentration change rate of the exhaust pipeline is greater than a preset change rate threshold. If yes, the diagnosis is that the exhaust valve leaks. If no, the diagnosis is that the stack leaks. The application can quickly distinguish between the stack hydrogen leakage and the exhaust valve hydrogen leakage, thereby accurately locating the fault position and maintaining the safe operation of the fuel cell system.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a method for diagnosing hydrogen leakage in a fuel cell system. Background Technology

[0002] A fuel cell stack is composed of multiple individual cells stacked together and housed within a stack housing. During operation, hydrogen at the anode and air at the cathode undergo an electrochemical reaction to generate electricity. Due to the small size of hydrogen molecules, leakage is common. Hydrogen leakage occurs primarily through: internal leakage from the anode to the cathode (cross-leakage); leakage from the anode to the outside of the stack (external leakage); and external leakage from the anode-side exhaust valve or piping. Therefore, to prevent hydrogen accumulation, the stack housing must be continuously purged. Furthermore, hydrogen emitted through the exhaust valve must be diluted with cathode exhaust gas before being released into the environment.

[0003] When an excessively high hydrogen concentration is detected in the exhaust, indicating a hydrogen leak in the fuel cell system, it is crucial to promptly identify the cause of the leak in order to handle it correctly and ensure the safe operation of the fuel cell system. Therefore, accurately and promptly diagnosing the cause and locating the leak is of paramount importance for the safe operation of the fuel cell system.

[0004] Currently, there are clear diagnostic methods for cross-leakage in fuel cell systems because when cross-leakage occurs, the voltage of the corresponding single cell will decrease. However, there is no effective way to distinguish whether the leakage is external to the fuel cell stack or to an anode valve. Summary of the Invention

[0005] To address one of the aforementioned technical problems, this invention provides a method for diagnosing hydrogen leaks in a fuel cell system. This method can quickly distinguish between external hydrogen leaks from the fuel cell stack and hydrogen leaks from the exhaust valve, thereby accurately locating the fault and maintaining the safe operation of the fuel cell system.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for diagnosing hydrogen leakage in a fuel cell system, characterized by comprising the following steps:

[0007] During the operation of the fuel cell system, the hydrogen concentration in the exhaust is monitored in real time. When the exhaust valve is not open, the hydrogen concentration in the exhaust pipe is checked to see if it is greater than or equal to the second concentration threshold. If it is, it is determined that the hydrogen leakage is too large, the fuel cell system is shut down, and the diagnosis ends. If the hydrogen concentration in the exhaust pipe is less than the second concentration threshold, the next step is performed.

[0008] Determine if a single cell voltage is low in the fuel cell stack. If a single cell voltage is low, end the diagnosis. If no single cell voltage is low, proceed to the next step.

[0009] Calculate the rate of change of hydrogen concentration in the exhaust pipe and determine whether the rate of change of hydrogen concentration in the exhaust pipe is greater than the preset rate of change threshold. If it is, it is diagnosed as exhaust valve leakage; otherwise, it is diagnosed as external leakage of fuel cell stack.

[0010] Furthermore, the calculation of the tail-end hydrogen concentration change rate specifically involves: recording the hydrogen concentration in the exhaust pipe before increasing the anode pressure of the fuel cell stack as concentration value A; increasing the anode pressure of the fuel cell stack by an increment of ΔP; when the hydrogen concentration reaches concentration value B, recording the time Δt from concentration value A to concentration value B; and calculating the hydrogen concentration change rate in the exhaust pipe, wherein the tail-end hydrogen concentration change rate = (concentration value B - concentration value A) / Δt.

[0011] Furthermore, before the hydrogen concentration in the exhaust pipe is greater than or equal to the second concentration threshold, it is necessary to detect whether the hydrogen concentration in the exhaust pipe is greater than the first concentration threshold when the exhaust valve is not open. If the hydrogen concentration is greater than the first concentration threshold, it indicates that a hydrogen leak has occurred in the fuel cell system; the first concentration threshold is less than the second concentration threshold.

[0012] Furthermore, the first concentration threshold is 500ppm to 1000ppm.

[0013] Furthermore, the second concentration threshold is 10,000 ppm to 15,000 ppm.

[0014] Furthermore, the pressure increment ΔP is 0.1 bar to 0.3 bar.

[0015] Furthermore, the concentration value B is 2000ppm to 6000ppm.

[0016] Furthermore, the change rate threshold is 1000ppm / s to 1500ppm / s.

[0017] By adopting the above technical solution, the present invention has at least the following beneficial effects: the present invention is simple and reliable, can quickly identify the cause of external hydrogen leakage in the fuel cell system, and ensures the safe operation of the fuel cell system. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the fuel cell system of the present invention.

[0019] Figure 2 This is a flowchart illustrating the steps of the hydrogen leak diagnosis method for a fuel cell system according to the present invention.

[0020] Figure 3 This is a schematic diagram illustrating the changes in anode pressure and exhaust hydrogen concentration over time during the hydrogen leakage diagnosis method for the fuel cell system of the present invention. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] This embodiment discloses a fuel cell system, such as Figure 1 As shown, the device includes a fuel cell stack 11, a fuel cell stack housing 12, an air compressor 21, a back pressure valve 22, a hydrogen concentration sensor 23, a hydrogen supply unit 31, a proportional valve 32, an ejector 33, a gas-liquid separator 34, an exhaust valve 35, a drain valve 36, an exhaust pipeline, and a hydrogen pressure sensor 37. The fuel cell stack 1 includes an air inlet, an air outlet, a hydrogen inlet, and a hydrogen outlet. The gas-liquid separator 34 includes a gas-liquid inlet, an exhaust port, and a drain port.

[0023] The fuel cell stack 11 is built into the fuel cell stack housing 12. The air compressor 21 is connected to the fuel cell stack housing 12 through a branch pipeline. The air compressor 21 periodically purges the fuel cell stack housing 12 to purge the hydrogen gas leaked from the fuel cell stack 11 into the exhaust pipeline.

[0024] Air compressor 21 is connected to the air inlet of fuel cell stack 11, air outlet of fuel cell stack 11 is connected to back pressure valve 22, back pressure valve 22 is connected to exhaust pipe, hydrogen concentration sensor 23 is connected to exhaust pipe, or hydrogen concentration sensor 23 is built into exhaust pipe.

[0025] The hydrogen supply unit 31, proportional valve 32, ejector 33 and hydrogen inlet of fuel cell stack 11 are connected in sequence. The hydrogen outlet of fuel cell stack 11 is connected to the gas-liquid inlet of gas-liquid separator 34. The exhaust port of gas-liquid separator 34 is connected to ejector 33 and exhaust valve 35. The drain port of gas-liquid separator 34 is connected to drain valve 36. Both exhaust valve 35 and drain valve 36 are connected to exhaust pipeline. Hydrogen pressure sensor 37 is connected to hydrogen inlet of fuel cell stack 11.

[0026] When the fuel cell system is running, the air compressor 21 drives most of the air to enter the cathode of the fuel cell stack 11. The exhaust gas from the cathode of the fuel cell stack 11 is depressurized by the back pressure valve 4 and then discharged to the atmosphere through the exhaust pipe. The other part of the air enters the fuel cell stack housing 12 for purging. The purged gas enters the exhaust pipe and mixes with the cathode exhaust gas before being discharged.

[0027] The high-pressure hydrogen from the hydrogen supply unit 31 is reduced in pressure by the proportional valve 32 and then enters the anode of the fuel cell stack 11 through the ejector 33. The exhaust gas from the outlet passes through the gas-liquid separator 34 and then flows back into the ejector 33 to mix with the inlet hydrogen. The drain valve 36 periodically discharges the water accumulated inside the gas-liquid separator 34, and the exhaust valve 35 periodically discharges the hydrogen-containing exhaust gas from the anode outlet to reduce the cumulative nitrogen concentration at the anode. The discharged exhaust gas enters the exhaust pipe and mixes with the cathode exhaust gas before being discharged.

[0028] Hydrogen concentration sensor 23 monitors the hydrogen concentration in the exhaust gas, and hydrogen pressure sensor 37 measures the anode pressure of fuel cell stack 11.

[0029] When cross-leakage occurs in fuel cell stack 11, or hydrogen leaks from fuel cell stack 11, or when exhaust valve 35 leaks, the hydrogen concentration in the tail gas will increase and be detected by hydrogen concentration sensor 23, thus discovering hydrogen leakage in the fuel cell system.

[0030] This embodiment discloses a hydrogen leak diagnosis method for a fuel cell system, mainly employing an external leak diagnosis method, which operates on the fuel cell system described in this embodiment. Figure 2 As shown, it includes the following steps:

[0031] During the operation of the fuel cell system, the hydrogen concentration sensor 23 monitors the hydrogen concentration in the exhaust pipe in real time. When the exhaust valve is not open, if the hydrogen concentration in the exhaust pipe is detected to be greater than the first concentration threshold (e.g., Figure 3 As shown, the first concentration threshold can be selected from 500ppm to 1000ppm. Figure 3 The hydrogen concentration in the tail section (which is the hydrogen concentration in the exhaust pipe) indicates that a hydrogen leak has been detected, and signals that a hydrogen leak has occurred in the fuel cell system.

[0032] The hydrogen concentration sensor 23 continuously monitors the hydrogen concentration in the exhaust. When the exhaust valve is not open, it checks whether the hydrogen concentration in the exhaust pipe is greater than or equal to the second concentration threshold (the second concentration threshold can be selected from 10,000 ppm to 15,000 ppm). If so, it determines that the hydrogen leakage is too large. In order to protect the safety of the fuel cell system, it is shut down to prevent further hydrogen leakage. At this time, the diagnosis ends. If the hydrogen concentration in the exhaust pipe is less than the second concentration threshold, the diagnosis process continues and proceeds to the next step.

[0033] Determine whether a single cell voltage is low in fuel cell stack 11 (a single cell voltage is defined as a single cell voltage less than 0.8 * average voltage). If a single cell voltage is low, end the current external leakage diagnosis and proceed with cross-leakage fault diagnosis (cross-leakage fault diagnosis is performed using other technical detection methods). Otherwise, continue with the external leakage diagnosis to confirm whether the leakage is from the fuel cell stack or from the exhaust valve 35.

[0034] like Figure 3As shown, the hydrogen concentration in the exhaust pipe at this time is labeled as concentration value A. The anode pressure of fuel cell stack 11 is increased by a pressure increment of ΔP (ΔP can be selected from 0.1 bar to 0.3 bar). After the anode pressure is increased, the hydrogen leakage will increase, and the hydrogen concentration in the exhaust pipe will increase. The change in hydrogen concentration in the exhaust pipe is monitored. When the hydrogen concentration reaches concentration value B (selectable from 2000 ppm to 6000 ppm), the time Δt from concentration value A to concentration value B is recorded, and the hydrogen concentration change rate in the exhaust pipe is calculated as follows: hydrogen concentration change rate in the exhaust pipe = (concentration value B - concentration value A) / Δt.

[0035] If the rate of change of hydrogen concentration in the exhaust exceeds a preset threshold (the threshold can be selected from 1000ppm / s to 1500ppm / s, the specific value being related to the size of the space in the fuel cell stack housing 12), then it is diagnosed as a leak in the exhaust valve 35; otherwise, it is diagnosed as an external leak in the fuel cell stack 11. If it is an external leak, when the leakage increases, the increased leaked hydrogen must first be mixed and diluted with the original gas in the internal space of the fuel cell stack housing 12 before being blown out of the fuel cell stack housing 12 (the hydrogen concentration inside the fuel cell stack housing 12 gradually increases and reaches equilibrium) and enters the exhaust. Therefore, the hydrogen concentration measured by the hydrogen concentration sensor 23 will rise more slowly and eventually stabilize. Figure 3 As shown in (b); if the exhaust valve 35 leaks, the increased leaked hydrogen can directly enter the tailpipe and be measured by the hydrogen concentration sensor 23. The measured hydrogen concentration will then rise more rapidly and stabilize quickly, as shown in (b). Figure 3 As shown in (a); based on this characteristic, external leaks are diagnosed and differentiated.

[0036] Restore the anode pressure to end the diagnostic process.

[0037] The hydrogen leakage diagnosis method for fuel cell systems presented in this embodiment is simple and reliable, and can quickly identify the cause of external hydrogen leakage in the fuel cell system, thus ensuring the safe operation of the fuel cell system.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various equivalent changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for diagnosing hydrogen leakage in a fuel cell system, characterized in that, Includes the following steps: During the operation of the fuel cell system, the hydrogen concentration in the exhaust is monitored in real time. When the exhaust valve is not open, the hydrogen concentration in the exhaust pipe is checked to see if it is greater than or equal to the second concentration threshold. If it is, it is determined that the hydrogen leakage is too large, the fuel cell system is shut down, and the diagnosis ends. If the hydrogen concentration in the exhaust pipe is less than the second concentration threshold, the process proceeds to the next step. Determine if a single cell voltage is low in the fuel cell stack. If a single cell voltage is low, end the diagnosis. If no single cell voltage is low, proceed to the next step. The rate of change of hydrogen concentration in the exhaust pipe is calculated to determine whether it exceeds a preset threshold. If it does, the exhaust valve is diagnosed as leaking; otherwise, the fuel cell is diagnosed as leaking externally. Specifically, the calculation of the rate of change of hydrogen concentration in the exhaust pipe is as follows: the hydrogen concentration in the exhaust pipe before the anode pressure of the fuel cell is increased is recorded as concentration value A; the anode pressure of the fuel cell is increased by pressure increment ΔP; when the hydrogen concentration reaches concentration value B, the time Δt from concentration value A to concentration value B is recorded, and the rate of change of hydrogen concentration in the exhaust pipe is calculated. The rate of change of hydrogen concentration in the exhaust pipe is calculated as (concentration value B - concentration value A) / Δt.

2. The method for diagnosing hydrogen leakage in a fuel cell system according to claim 1, characterized in that, Before the hydrogen concentration in the exhaust pipe reaches or exceeds the second concentration threshold, it is necessary to check whether the hydrogen concentration in the exhaust pipe exceeds the first concentration threshold when the exhaust valve is not open. If the hydrogen concentration exceeds the first concentration threshold, it indicates that a hydrogen leak has occurred in the fuel cell system. Leakage situation; the first concentration threshold is less than the second concentration threshold.

3. The method for diagnosing hydrogen leakage in a fuel cell system according to claim 2, characterized in that, The first concentration threshold is 500ppm to 1000ppm.

4. The method for diagnosing hydrogen leakage in a fuel cell system according to claim 1, characterized in that, The second concentration threshold is 10,000 ppm to 15,000 ppm.

5. The method for diagnosing hydrogen leakage in a fuel cell system according to claim 1, characterized in that, The pressure increment ΔP is 0.1 bar to 0.3 bar.

6. The method for diagnosing hydrogen leakage in a fuel cell system according to claim 1, characterized in that, The concentration value B is 2000ppm to 6000ppm.

7. The method for diagnosing hydrogen leakage in a fuel cell system according to claim 1, characterized in that, The threshold for the rate of change is 1000ppm / s to 1500ppm / s.

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