In this study, energy-flow experiments are performed on a fuel-cell (FC) hybrid heavy-duty truck under constant vehicle speeds of 25 and 75 km/h at normal temperature (23 degrees C) and high temperature (35 degrees C), respectively. The vehicle energy consumption and distribution, the efficiency of the main systems and components, and the characteristics of the thermal-management system are analyzed comprehensively to evaluate the vehicle performance. Experiment results show that the energy-conversion efficiency of the FC stack is relatively low (45.6% to 50.25%) and that the output-power fluctuation of the FC system is relatively large, which indicate that the FC stack's control of hydrogen and air may be unreasonable. Moreover, the battery-charging energy occupies a considerable proportion of the FC stack output energy, which results in the high internal resistance of the power battery under low-speed driving conditions. This implies that the vehicle's power-matching and control strategies may not be reasonable. For the thermal-management system, the temperature difference between the inlet and outlet coolant of the FC coolant exceeds 10 degrees C in most cases, thus resulting in high thermal-energy losses. Additionally, the maximum temperature of the power battery core does not decrease significantly once the battery cooling cycle began. This indicates that the tested FC hybrid truck may be inappropriate in terms of structural design, accessory matching, and control of the thermal-management system. Furthermore, the highest difference in temperature between the head of the co-pilot and sleeper exceeds 10 degrees C in most cases, which results in an uncomfortable crew-cabin environment. This implies that the structure of the air duct and the number and position of the crew-cabin air outlets are inappropriate. In general, the efficiencies of the vehicle direct current (DC)/DC, motor, and transmission system are relatively low, particularly at low vehicle speeds (less than 90%). Existing problems associated with the entire vehicle and key components are identified, and the corresponding improvement suggestions are proposed based on experimental results pertaining to the energy-flow and thermal- management characteristics. Thus, this study provides an important reference and basis for the performance and energy-consumption optimizations of FC hybrid heavy-duty trucks in the future. Additionally, this study provides an effective method for evaluating the performance and energy consumption of FC hybrid vehicles.
