Low-temperature starting method for fuel cell system

Abstract

The invention discloses a fuel cell system low-temperature starting method which specifically comprises the following steps: S1, detecting environment temperature, judging whether the environment temperature reaches a low-temperature starting condition or not, if so, starting low-temperature starting, and entering step S2; otherwise, circulating the step S1; s2, in the hydrogen loop, the anode supplies hydrogen, an exhaust valve is opened for rapid replacement, and after replacement is completed, the exhaust valve is closed for stable pressure operation; s3, air with the pressure of 10-30 kPa is supplied to the cathode, and the electric density is 500 mA / cm < 2 >, and the air stoichiometric ratio is 3-5; s4, a backflow throttle valve of the backflow pipeline is opened, air on the tail exhaust pipeline flows back to the air inlet end, and the current density is pulled and loaded to 300-500 mA / cm < 2 >; s5, detecting the outlet temperature of the fuel cell stack, and judging whether a low-temperature starting ending condition is met or not; if yes, the low-temperature starting condition is ended; otherwise, circulating the step S5. According to the innovative low-temperature starting method provided by the invention, the reliable and safe low-temperature starting process is realized by regulating and controlling the oxygen concentration under high-flow-rate air on the premise of ensuring normal operation of the fuel cell stack, the limitation of the low-temperature starting process in the prior art is solved, and the low-temperature starting efficiency is improved. And powerful technical support is provided for long-term stable operation of fuel cell automobiles and other application fields.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a low-temperature starting method for a fuel cell system. Background Art

[0002] Fuel cell technology, as an outstanding representative of green energy technology, has shown great potential in the fields of transportation, fixed power supply and portable electronic devices, mainly due to its high energy conversion efficiency and near-zero emission environmental protection characteristics. However, the problem of starting under low temperature conditions has always been one of the key bottlenecks restricting the commercialization of fuel cells. When the ambient temperature drops below freezing, the water in the fuel cell system will form ice crystals, block the airway, corrode the electrode material and hinder the necessary chemical reactions. In severe cases, it may even cause the fuel cell to be completely unable to start.

[0003] Although several existing solutions on the market have alleviated the cold start problem to a certain extent, their respective limitations are also very obvious: Hydrogen-oxygen combustion method: By adding a certain concentration of hydrogen to the cathode air to achieve the heat release of the hydrogen-oxygen combustion reaction to increase the system temperature, in order to counter the impact of the low temperature environment. However, this method is extremely complicated in actual operation and requires precise control of the gas mixing ratio to ensure safety. The slightest carelessness may cause the risk of explosion. In addition, the need for high-precision sensors and control systems increases the cost and maintenance difficulty of the system.

[0004] Interrupt coolant method: Temporarily interrupt the coolant circulation to reduce the heat loss of the system during the cold start phase. Although this can retain more heat in the short term and promote system warming, in the long run, the uneven temperature distribution will cause the ends of the stack to be too cold and the center area to be too hot. This extreme temperature difference accelerates material fatigue and performance degradation, reducing the overall service life of the fuel cell stack.

[0005] High current preheating method: Use the thermal efficiency of fuel cells at low temperatures to combat low temperatures, that is, apply a high current higher than normal operation to the battery at the initial start-up to resist the effects of low temperatures with high thermal efficiency at low temperatures. However, this approach is often counterproductive, as local overheating may not only cause ice blockage inside the battery stack, but also cause battery polarization, that is, an imbalance in the electrode reaction rate, which reduces battery performance and may even cause permanent damage in severe cases.

[0006] In summary, although existing technical means have made some contributions to solving the low-temperature cold start problem of fuel cells, they have not been able to fundamentally overcome core challenges such as operational complexity, safety hazards, accelerated system aging and battery performance degradation. There is an urgent need for a more efficient, safe and reliable cold start solution to promote the widespread application of fuel cell technology. Summary of the invention

[0007] The object of the present invention is to provide a low temperature start-up method for a fuel cell system to overcome the deficiencies in the prior art.

[0008] To achieve the above object, the present invention provides the following technical solutions: The present application discloses a low-temperature starting method for a fuel cell system, comprising an air circuit and a hydrogen circuit for the fuel cell system, wherein the air circuit for the fuel cell system is provided with an air filter, an air compressor, an intercooler, a humidifier, a fuel cell stack and a tail exhaust pipeline in sequence from the air inlet end; a return pipeline is provided on the tail exhaust pipeline, and the other end of the return pipeline is connected to the air inlet end of the air filter; a return throttle is provided on the return pipeline; The method specifically comprises the following steps: S1, detect the ambient temperature and determine whether the ambient temperature reaches the low temperature start condition. If so, start the low temperature start and enter step S2; otherwise, loop step S1; S2, in the hydrogen circuit, the anode supplies hydrogen and opens the exhaust valve for rapid replacement. After the replacement is completed, the exhaust valve is closed for stable pressure operation; S3, cathode supply 10 ~ 30kPa pressure air, at 500mA / cm 2 Electrical density, air metering ratio 3~5; S4. Open the reflux throttle valve of the reflux pipeline to return the air on the tail exhaust pipeline to the air inlet end, and increase the electric density to 300~500mA / cm 2 ; S5, detecting the outlet temperature of the fuel cell stack to determine whether the low-temperature startup condition is reached; if reached, the low-temperature startup condition is ended; otherwise, looping step S5.

[0009] Preferably, the low-temperature starting condition in step S1 is as follows: determine whether the ambient temperature is lower than the starting temperature; if so, determine that the low-temperature starting condition is met; otherwise, determine that the condition is not met.

[0010] Preferably, the starting temperature is 0°C.

[0011] Preferably, step S2 specifically includes the following operations: in the hydrogen loop, the anode supplies hydrogen at a pressure of 50-70 kPa, the exhaust valve is opened for rapid replacement for 5-10 seconds, and after the replacement is completed, the exhaust valve is closed for stable pressure operation.

[0012] Preferably, the low-temperature startup termination condition in step S5 is as follows: determine whether the outlet temperature of the fuel cell stack is greater than the stop temperature. If so, determine that the low-temperature startup termination condition is met; otherwise, determine that it is not met.

[0013] Preferably, the stopping temperature is 5°C.

[0014] Preferably, the air filter comprises a physical filter and a chemical filter, the air outlet of the physical filter is connected to the air inlet of the chemical filter, and the other end of the return line is connected to the air outlet of the physical filter.

[0015] Beneficial effects of the present invention: Improved startup efficiency: significantly shortened the startup time of fuel cells in low-temperature environments and improved system response speed. Currently, the systems running on the market usually rely on heaters to heat up the coolant temperature before pulling the load to generate electricity, which generally takes several minutes; the present invention directly pulls the load at low temperatures, relying on the thermal efficiency of the fuel cell itself to generate heat to achieve internal heating, and the speed is very fast, completed within tens of seconds; Enhanced safety: The tail exhaust hydrogen concentration is guaranteed under high pressure difference, the ice breaking ability is improved under high flow rate, and the reflux oxygen concentration increases the thermal efficiency of the fuel cell system, thereby improving operational safety.

[0016] Balanced temperature control: avoids the problems of icing at both ends of the battery stack and overheating in the middle area, extends the service life of the battery stack and improves system stability.

[0017] Reduce the risk of failure: The circulating air path design effectively reduces local icing and electrochemical reverse polarity phenomena, and enhances the overall reliability and durability of the system.

[0018] The innovative low-temperature starting method proposed in the present invention achieves a reliable and safe low-temperature starting process by regulating the oxygen concentration under high-flow air and on the premise of ensuring the normal operation of the fuel cell stack, which solves the limitations of the existing technology in the low-temperature starting process and provides strong technical support for the long-term stable operation of fuel cell vehicles and other application fields.

[0019] The features and advantages of the present invention will be described in detail through embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic structural diagram of the air circuit of the fuel cell system of the present invention; Figure 2 This is a schematic diagram of a low temperature startup method for a fuel cell system of the present invention. DETAILED DESCRIPTION In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below through the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0021] See also Figure 1The embodiment of the present invention provides a low temperature start method for a fuel cell system. The technical solution of the present invention is constructed in a fuel cell system with a precisely controllable air reflow structure, realizing a structure with controllable cathode inlet oxygen concentration, achieving rapid warm-up through a high thermal efficiency mode of the fuel cell under low oxygen concentration, and achieving a reliable low temperature start process. Figure 2 , specifically including: The method specifically comprises the following steps: S1, detect the ambient temperature and determine whether the ambient temperature reaches the low temperature start condition. If so, start the low temperature start and enter step S2; otherwise, loop step S1; Specifically, low temperature start condition: determine whether the ambient temperature is lower than the start temperature. If so, it is determined that the low temperature start condition is met. Otherwise, it is determined that the start temperature is not met. The start temperature is 0°C. S2, in the hydrogen circuit, the anode supplies hydrogen and opens the exhaust valve for rapid replacement. After the replacement is completed, the exhaust valve is closed for stable pressure operation; Specifically, after the system is started, the anode is supplied with hydrogen at an operating pressure of 50-70 kPa, the exhaust valve is opened for rapid replacement for 5-10 seconds, and then the exhaust valve is closed to stabilize the pressure operation; S3, cathode supply 10 ~ 30kPa pressure air, at 500mA / cm 2 Electrical density, air metering ratio 3~5; Supplying high-flow, low-pressure, high-velocity air is conducive to breaking ice and blowing. At the same time, the interior gradually becomes dry under high flow, the internal resistance increases, the thermal efficiency of the fuel cell system gradually increases, and the low-temperature cold start process is accelerated; S4. Open the reflux throttle valve of the reflux pipeline to return the air on the tail exhaust pipeline to the air inlet end, and increase the electric density to 300~500mA / cm 2 ; As the system continues to run, the reflow oxygen concentration gradually decreases, the average voltage gradually decreases, the thermal efficiency of the fuel cell system gradually increases, and the cooling temperature gradually rises. When the cooling outlet temperature is greater than 5°C, the low-temperature start-up process ends and the reflow air is turned off; S5, detecting the outlet temperature of the fuel cell stack to determine whether the low-temperature startup condition is reached; if reached, the low-temperature startup condition is ended; otherwise, looping step S5.

[0022] The present invention is a fast and reliable warm-up strategy for the fuel cell system by intelligently regulating the low-oxygen concentration air at the cathode outlet to flow back to the cathode inlet, with low oxygen concentration and high thermal efficiency. The strategy is particularly suitable for solving the problems of attenuation and start-up failure caused by icing during the low-temperature start-up of the fuel cell system.

[0023] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low temperature start-up method for a fuel cell system, comprising an air circuit and a hydrogen circuit of the fuel cell system, characterized in that: The fuel cell system air circuit is provided with an air filter, an air compressor, an intercooler, a humidifier, a fuel cell stack and a tail exhaust pipeline in sequence from the air inlet end; a return pipeline is provided on the tail exhaust pipeline, and the other end of the return pipeline is connected to the air inlet end of the air filter; a return throttle valve is provided on the return pipeline; The method specifically comprises the following steps: S1, detect the ambient temperature and determine whether the ambient temperature reaches the low temperature start condition. If so, start the low temperature start and enter step S2; otherwise, loop step S1; S2, in the hydrogen circuit, the anode supplies hydrogen and opens the exhaust valve for rapid replacement. After the replacement is completed, the exhaust valve is closed for stable pressure operation; S3, cathode supply 10 ~ 30kPa pressure air, at 500mA / cm 2 Electrical density, air metering ratio 3~5; S4. Open the reflux throttle valve of the reflux pipeline to return the air on the tail exhaust pipeline to the air inlet end, and increase the electric density to 300~500mA / cm 2 ; S5, detecting the outlet temperature of the fuel cell stack to determine whether the low-temperature start-up condition is reached; if reached, the low-temperature start-up condition is ended; Otherwise, the process loops to step S5.

2. A fuel cell system low temperature startup method according to claim 1, characterized in that: The low-temperature starting condition in step S1 is as follows: determine whether the ambient temperature is lower than the starting temperature, if so, determine that the low-temperature starting condition is met, otherwise, determine that it is not met.

3. A fuel cell system low temperature startup method as claimed in claim 2, characterized in that: The starting temperature is 0°C.

4. A fuel cell system low temperature startup method as claimed in claim 1, characterized in that: Step S2 specifically includes the following operations: in the hydrogen loop, the anode supplies hydrogen at a pressure of 50-70 kPa, the exhaust valve is opened for rapid replacement for 5-10 seconds, and after the replacement is completed, the exhaust valve is closed for stable pressure operation.

5. A fuel cell system low temperature startup method as claimed in claim 1, characterized in that: The low temperature start-up termination condition in step S5 is as follows: determining whether the outlet temperature of the fuel cell stack is greater than the stop temperature, and if so, determining that the low temperature start-up termination condition is met; Otherwise, it is judged as not reached.

6. A fuel cell system low temperature startup method as claimed in claim 5, characterized in that: The stop temperature is 5°C.

7. A fuel cell system low temperature startup method as claimed in claim 1, characterized in that: The air filter comprises a physical filter and a chemical filter, the air outlet end of the physical filter is connected to the air inlet end of the chemical filter, and the other end of the return line is connected to the air outlet end of the physical filter.

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