Experimental study on ejector performance and control strategy optimization in fuel cell systems through heat exchanger positioning

Ejectors are critical components of fuel cells in renewable energy systems. While previous research has primarily focused on optimizing ejector structural parameters to improve their entrainment performance, issues related to liquid water management and control strategies have not been adequately addressed. Furthermore, evaluating the entrainment ratio and expanding the working range of ejectors presents significant challenges. This study integrates a heat exchanger at key ejector positions to mitigate these challenges. Additionally, we propose a novel mathematical model to evaluate the sensitivity of three parameters. Experimental results show that elevated ejector outlet pressure negatively impacts the entrainment ratio, whereas increased secondary flow inlet pressure significantly improves it. At the rated power of 120 kW, the anode stoichiometry ratio increases by 14.2 % and 12.3 % for the secondary and primary flow inlet heat exchanger configurations respectively, compared to the reference configuration with the heat exchanger at the ejector outlet. However, positioning at the secondary flow inlet limits the operational range of the ejector to 23 %–100 % of the rated power condition, whereas the primary flow inlet configuration significantly extends this range to 7 %–100 % of the rated power load. Finally, we propose a constant anode stoichiometry ratio control strategy for the hydrogen recirculation system.