Performance optimization of a dual-synchronous adjustable ejector for hydrogen recirculation in high-power fuel cell under variable load conditions

Ensuring efficient hydrogen recirculation is essential for maintaining the performance and durability of 200 kW heavy-duty proton exchange membrane fuel cell (PEMFC) systems. To address the limitations of existing ejector optimization studies, which commonly neglect vapor condensation, gas composition variations, and anode pressure fluctuations under actual boundary conditions, a three-dimensional, multi-component, non-equilibrium condensation CFD model has been developed and experimentally validated. The proposed model accurately captures the interactions among load-dependent gas composition (including nitrogen crossover), condensation, and anode pressure variations. On this basis, the overall performance of a newly developed dual-synchronous adjustable ejector is comprehensively evaluated, and its key geometric parameters are optimized under actual boundary conditions. Results indicate that the nozzle throat width has a significant impact on the entrainment performance at low-power operation. Neglecting load-dependent gas composition variations consistently overestimates the hydrogen entrainment ratio, with a maximum deviation rate of 29.63% and an average deviation rate of 16.46%. After optimization, the ejector achieves a mixing chamber diameter (dt) of 7.5 mm, a mixing chamber length (lt) of 45.0 mm, and a nozzle throat width (lnt) of 1.6 mm, delivering stable and efficient performance over 13–200 kW. The hydrogen entrainment ratio increases by an average of 14.02%, and ejector efficiency improves by 26.77% across the full load range. The proposed methodology provides a practical route for wide-range, high-efficiency hydrogen recirculation design for heavy-duty PEMFC applications.