The causes and optimization strategies of voltage uniformity fluctuation of fuel cell systems under dynamic loads based on multi-scale, multi-phase fusion methods

Based on a multi-scale, multiphase integration of research methods, including experiments on a 19 kW fuel cell system, single-cell tests of fuel cells, and three-dimensional multiphase single-cell computational fluid dynamics (CFD) simulations, an equivalent analytical model is established to investigate the causes and solution countermeasures of the Voltage Uniformity fluctuation in the start-up-phase of fuel cell systems. The study focuses on investigating the performance characteristics of individual cells under different stoichiometric ratio conditions under heavy load, and conducts flow field dimension optimization to mitigate flooding and low voltage issues under low air inlet conditions. The research findings indicate that during the start-up process at high current density, inadequate gas supply and uneven flow distribution among individual cells result in excessively low voltage of specific cells, ultimately leading to system shutdown. The equivalent analytical model analysis results reveal that under low air inlet conditions, severe flooding occurs in individual cells under heavy load conditions. Inlet flow optimization results show that with increasing flow, the voltage of individual cells first increases and then levels off, and the flooding issue is essentially resolved when the stoichiometric ratio exceeds 1.75. This stoichiometric ratio is selected as the representative condition of high stoichiometric ratio for subsequent performance comparison. Flow field size optimization indicates that, without increasing the inlet flow, significant improvement in individual cell performance and effective flooding prevention can be achieved through flow field size optimization. The results provide important references for the optimization of fuel cells in practical applications.