Detailed explanation of fuel cell hydrogen ejector

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During the operation of the fuel cell, in order to ensure that the electrode sidewall can diffuse uniformly in the active area, the gas must be supplied in excess, and the excess gas cannot be directly discharged after reaction to avoid waste. Therefore, there must be a circulation device to remove the excess carbon dioxide from The exit is circulating to the entrance.

Common circulation devices are mainly divided into active form of turbo circulating pump and passive form of turbo ejector, hybrid turbo circulating pump, turbo ejector has no moving parts, simple structure, reliable operation, and no parasitic power, which is the realization of fuel cell Ideal device for fluorination recycling.

From Bernoulli's law, it is known that low pressure will be generated near the fluid flowing at high speed, which will cause adsorption. Using this effect, a venturi tube can be made. As shown in the figure below, the port A is connected to the hydrogen source, one high-pressure jet is ejected from the nozzle 2 at a higher speed, and the low pressure is generated in the three shaped cavities to make the stack outlet B Excessive wind is injected here, and finally the air that enters at A is mixed and ejected from port C into the stack inlet.


Schematic diagram of fuel cell fluorinated ejector

Generally speaking, the low pressure generated in the higher area sucks the condensation in the high pressure area. The figure clearly shows the corresponding relationship between the volume variable and the pressure of each position in the ejector.


△ Schematic diagram of pressure and change distribution in fluorine ejector

The biggest advantage of the ejector is to save costs. Because there are no complicated moving parts, it is simpler and more reliable, and its volume can achieve the volume of an air circulation pump, and the actual cost is less than half of the air circulation pump.

However, the ejector also has obvious defects. Because the ejector is a passive suction cycle, it is difficult to cover the entire working condition of the fuel cell. Generally, the non-adjustable flow ejector is only designed for the rated operating point of the fuel cell engine. This will cause the ejector to have a poor ejection effect under low-power loads. In order to make up for this shortcoming and cover the entire working range of the fuel cell engine, both domestic and foreign are exploring the use of additional ejector moving parts or the use of ejector. The method in parallel with the circulating pump achieves the above design goals.

Honda adopted the variable nozzle ejector on the 2009 fuel cell vehicle, and then cancelled the variable nozzle function of the implicit injector on the definition fuel cell vehicle, and adopted the integrated air intake of fixed nozzle implicit injector + jet injection Cycle mode.


Schematic diagram of Honda Clarity turbo intake and circulation system

△Honda Clarity Fixed Nozzle Ejector and Air Jet System Integrated Design Structure Sectional View

The core part of the ejector lies in the design and control logic scheme of the venturi. Different companies have different design ideas and solutions. Currently, they are customized based on the needs of customers. Great Wall Motors also introduced the coverage of rated power. 8%~100% full power ejector, using proportional solenoid valve + single ejector" hydrogen circulation module, can effectively replace the shortcomings of the narrow working range of the ejector and improve the efficiency of the ejector.

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