Performance analysis and prediction of ejector based hydrogen recycle system under variable proton exchange membrane fuel cell working conditions

The ejector is a promising candidate in recycling unconsumed hydrogen for proton exchange membrane fuel cell (PEMFC) to increase the fuel utilization. However, due to the multi-operation conditions of stack with reaction water producing, the ejector performance and out flow (i.e. the supply flow) are affected by the secondary flow state which present challenges for PEMFC stable operation and system control. In this paper, a series of numerical research were carried and the flow field distributions were obtained and analyzed to gain further understanding of supply flow pressure and humidity variation under multi-working conditions of PEMFC. Furthermore, a mathematical model for recycle loop was established to build the correlations between PEMFC working conditions and both the hydrogen recycle and supply capacity of ejector. An experimental platform was built and a series of experimental investigations were carried out for recycle system performance research after numerical and mathematical model validation. Both numerical and experimental results indicated that working conditions complexity will result the changes with more than 0.2 bar in pressure and 30% in humidity of supply flow which also could be predicted by theoretical model. It was also observed that along with the secondary flow humidity and temperature increase, the higher entrainment ratio will be achieved and less hydrogen were recycled inversely. In addition, from the research, ejector running under variable conditions may leading poor water management and proton exchange membrane damage risk is also a critical issue for hydrogen recycle application.