Numerical investigation into effects of ejector geometry and operating conditions on hydrogen recirculation ratio in 80 kW PEM fuel cell system

Ejectors play a crucial role in improving the fuel utilization efficiency of proton-PEMFC systems by recirculating the excess hydrogen discharged from the anode outlet side of the stack. This study has constructed a full MATLAB/Simulink model of an 80 kW PEMFC system consisting of an anode hydrogen gas supply system, a cathode oxygen gas supply system, a fuel cell stack, a terminal exhaust and drainage system, and an ejector-based anodic gas recirculation system. The model has been used to examine the effects of the ejector geometry and PEMFC operating conditions on the hydrogen recirculation ratio and hydrogen stoichiometric ratio. The results show that as the primary flow pressure increases, the primary mass flow rate increases, but the recirculation ratio and secondary mass flow decrease. By contrast, as the secondary pressure increases, the primary mass flow rate remains unchanged, but the secondary mass flow rate and recirculation ratio increase. For a constant primary flow pressure, the recirculation ratio increases with an increasing primary flow temperature. Conversely, for a constant secondary flow pressure, the recirculation ratio reduces slightly with an increasing secondary flow temperature. For a hydrogen stoichiometric ratio of 1.5, the optimal value of the mixing chamber diameter (D2) to nozzle throat diameter (Dt) is found to be D2/Dt = 2.2. (C) 2021 Elsevier Ltd. All rights reserved.