Optimization of the ejector parameters for anodic recirculation systems in high-performance dual-stack proton-exchange membrane fuel cells

Abstract

The anodic recirculation system (ARS) is critical in designing modern proton-exchange membrane fuel cells (PEMFC). Although the flow-through approach can outperform the dead-end approach, it yields excess residual hydrogen during the operation of the fuel-supply system. This residue can reduce the fuel mileage and be explosive when discharged into the environment, particularly in the multi-stack configuration where multiple PEMFCs are connected for high-power purposes. Therefore, it is desirable to develop an appropriate ARS design that facilitates the recycling of this excess hydrogen. This study aimed to develop a one-dimensional ARS model for dual-stack PEMFCs to optimize the recirculation performance, as well as analyze the effect of ARS on fuel cell (FC) stacks. Subsequently, the dual-ejector concept was adopted, having demonstrated higher efficiency than the single-ejector concept in high-performance PEMFCs. In the designing step, ejector geometries were determined based on the sensitivity analysis of the nozzle throat and mixing chamber diameters. The filtering conditions were set for four parameters: hydrogen unrecoverable percentage (4,1% and 5%), stoichiometry (1.5–3), recirculation ratio, and anode inlet pressure (<1.5 bar). Hence, the minimum hydrogen unrecoverable value the system can achieve by optimization was 4.073%. Due to other filtering conditions being close to the upper limit of the requirements, expanding the unrecoverable condition was recommended despite higher hydrogen emissions. Additionally, the performed methodology demonstrated great potential in providing benefits related to simulation speed, accuracy, and the mapping of system-level interrelationships. Through this method, the optimized geometries ensured that filtering parameters were under control during operation. Moreover, this concept could reveal the direct effect of the anode inlet on the working pressure of each FC stack during dynamic simulation with changes in the Nernst voltage and losses.