Large-scale cold start simulations for automotive fuel cells

In this study, the three-dimensional (3-D) transient cold start model is applied to the real-scale polymer electrolyte fuel cell (PEFC) geometry and transient cold-start simulations are carried out from subzero to normal temperatures. In order to reduce the computational turnaround time involving a large numerical mesh with millions of grid points, the cold start code is parallelized for parallel computing. The simulation results clearly show the evolution of ice, water content, temperature, and current density contours at different cold start stages characterizing freezing, melting, hydration, and dehydration processes. In addition, the model predictions emphasize beneficial influence of vapor phase diffusion from the cathode catalyst layer (CL) to gas diffusion layer (GDL) during cold start, which can contribute to reducing the amount of ice accumulation in the cathode CL. As the effect of vapor phase diffusion is substantial, more ice is accumulated in the cathode GDL rather than in the cathode CL. Therefore, the total amount of ice accumulated inside a cell is not always proportional to the amount of ice in the cathode CL, depending on the strength of vapor phase diffusion.