Numerical investigations of assisted heating cold start strategies for proton exchange membrane fuel cell systems

To investigate cold start strategies at the system level, an integrated transient system model is developed, consisting of stack, membrane humidifier, electrochemical hydrogen pump, compressor, and radiator. The unassisted startup from -10 degrees C succeeds while it fails when started from -20 degrees C. To achieve the successful startup from -20 degrees C, various assisted strategies are adopted. For reactant gas heating method, the additional heat carried by gases is averaged about 1.2 W for each individual cell when the temperature of humidifier and hydrogen pump are maintained at 60 degrees C. Meanwhile, a large amount of moisture is introduced to the stack, which may lead to accelerated failure. For stack heating method, the startup succeeds if the total heating power reaches 40 W. However, the corresponding temperature difference within stack reaches as large as 22.0 degrees C, which indicates that improving the thermal conductivity of fuel cell materials is of great importance. Under coolant heating method, the startup succeeds if the coolant temperature reaches -5 degrees C, and the ice formation can even be avoided if the coolant temperature is kept at 10 degrees C. However, the power consumption for heating coolant is extremely large, indicating that secondary power sources are necessary. (C) 2021 Published by Elsevier Ltd.