Energy analysis and efficiency optimization of a fuel cell passenger vehicle based on energy flow distribution and thermal management under various driving conditions

Fuel cell electric vehicles (FCEVs) are a promising pathway toward low-carbon transportation, yet their complex powertrain architecture poses significant challenges for energy management and thermal regulation. A clear understanding of their energy flow characteristics is critical for optimizing efficiency and guiding system design. A comprehensive experimental investigation was conducted in a climatic wind tunnel to quantify the energy flow distribution and evaluate the thermal management performance of an FCEV under diverse driving conditions. The energy conversion efficiency of the fuel cell system ranges from 47.30 % to 52.96 %, with roughly 85 % of the energy losses arising from reaction heat within the fuel cell stack. The motor efficiency varies by more than 10 % across different vehicle loads, while the transmission system and DC/DC exhibit relatively lower but steadier efficiencies. Approximately 50 % of the total input power is dissipated as thermal energy, while about 37 % is ultimately converted into wheel-side power for propulsion. As vehicle load increases, the fraction of power lost as heat rises while the share of parasitic power declines. Thermal loads in all three cooling circuits grow with rising vehicle speed, road slope, ambient temperature, and relative humidity, with the ethylene glycol circuit showing the greatest sensitivity to environmental conditions. Higher vehicle speeds also improve temperature regulation at steady-state operating points. Based on these findings, targeted measures are proposed to enhance the overall energy utilization efficiency of FCEVs.