Multifunctional bypass valve for water management and surge protection in a proton-exchange membrane fuel cell supply-air system

A multifunctional valve for air supply was placed downstream of the compressor in a fuel cell system to manage cathode air characteristics under different load changes and configurations. The advantages of using the fourway valve, with different ports for cathode flow, throttling, and bypassing, were analyzed through modeling and simulation. The model focused on the air supply system, which included a centrifugal compressor, intercooler, membrane humidifier, valve, and mixer. The simulation demonstrated that placing the valve right after the compressor was more effective in controlling the compressor surge than a traditional back pressure valve. During compressor surge, opening the throttling port at 18 degrees could suppress the surge and stabilize the cathode flow. The balance between surge protection and stack performance under transient conditions was also discussed, and an optimal valve opening for throttle flow was presented. Furthermore, bypassing the humidifier by 20% of the supply air reduced the cathode inlet relative humidity by the same percentage, contributing to water management in the stack, particularly under flooding conditions.