Design of Thermal Management System Based on Phase Change Material for Fuel Cell Hybrid Electric Vehicles: A Numerical Study

Abstract

In this study, a numerical analysis of the thermal management system for a fuel cell hybrid electric vehicle (FCHEV), based onthe second-generation Toyota Mirai, has been conducted. Within the scope of the model, the fuel cell stack, electric motor, high-voltage battery, cabin heating/cooling system, and phase-change material (PCM) based thermal storage unit have been consideredas a single integrated system. Hydrogen consumption, component temperatures, battery state of charge, the effect of regenerativebraking, cabin thermal behavior, and waste heat recovery have been analyzed for summer and winter operating conditionswithin the WLTC Class 3 driving cycle. In the proposed model, while the fuel cell is regarded as the primary energy source, thebattery functions as a secondary energy storage system, used to meet sudden power demands and to store energy recovered fromregenerative braking. The control strategy is designed to recover waste heat energy generated by the fuel cell and electric motorfor cabin heating and PCM charging. The model also considers dynamic battery SOC behavior, fuel-cell load-following operation,cabin thermal behavior, and PCM charge/discharge behavior. The results obtained demonstrate that the proposed integratedthermal management approach can utilize fuel cell and electric motor waste heat to support cabin heating, particularly in winterconditions. The simulated hydrogen consumption is 0.944 kg/100 km under WLTP-like conditions, within 6% of the certified valueof 0.89 kg/100 km, rising to 0.989 and 1.007 kg/100 km under summer and winter HVAC loads, respectively. In winter, 29.2% ofthe powertrain waste heat is recovered; the pre-charged PCM unit delivers 1204 Wh of cabin heat, covers 73.9% of the deliveredheating during the first 10 min of the cold start, and reduces the PTC consumption by 58.4% and the hydrogen consumption by 5.8%compared with the no-PCM baseline In conclusion, the PCM-assisted integrated thermal management system offers a measurableimprovement in energy efficiency and cabin heating performance in fuel cell vehicles, but its effectiveness depends strongly onthe control strategy, the initial thermal state of the storage, and the sizing of the PCM unit.