Numerical study of a hydrogen ejector with regulated inlet for extended PEMFC operating range in automotive application

Hydrogen recirculation is a key requirement for enhancing fuel efficiency and anode stability in Proton Exchange Membrane Fuel Cell (PEMFC) systems, particularly in automotive applications. Effective hydrogen recirculation is critical for maintaining high efficiency and fuel utilization. A hydrogen recirculation ejector equipped with a regulated pressure inlet, aimed at eliminating the need for mechanical pumps while maintaining optimal hydrogen utilization. The passive operation of the ejector eliminating the need for rotary components which significantly improves system reliability and reduces failure modes commonly associated with moving parts. This work presents a numerical investigation of a hydrogen recirculation ejector featuring a regulated pressure inlet, with the objective of extending its operating range across varying fuel cell power levels. A combination of 1D system-level modelling and 2D multi-species Computational Fluid Dynamics (CFD) simulations was employed to evaluate ejector performance under dynamic operating conditions. The 1D model enabled rapid system behaviour assessment, while the CFD analysis, incorporating hydrogen, nitrogen, and water vapour species, provided detailed insights into flow behaviour, mixing, and entrainment characteristics. Key design parameters such as primary nozzle geometry, secondary inlet positioning, and pressure regulation strategy were studied to optimize ejector efficiency. The simulations explored various power levels of fuel cell net power output, which is representative of real-world drive cycles, ensuring adaptability of the ejector across transient power demands by vehicle powertrain. Results indicate that regulated pressure inlets significantly enhance entrainment ratio, maintain stable flow regimes, and reduce the risk of anode starvation during load changes. The findings support the application of pressure-regulated ejectors as compact, passive, and robust solutions for hydrogen recirculation in automotive PEMFC systems, contributing to improved reliability and reduced balance-of-plant complexity.