Proton exchange membrane (PEM) fuel cell systems using steam-reformed methanol are currently under consideration for first generation commercial fuel cell vehicles. Proper water and heat management of such a system is critical in achieving high overall efficiency and maintaining water self-sufficiency.
The first part of the paper briefly describes the key aspects of the water and thermal management (WTM) model developed as part of the Fuel Cell Vehicle Modeling Program (FCVMP) at the University of California – Davis. The main purpose of this model was to determine the water self-sufficiency and temperature management requirements of the indirect methanol fuel cell system and to evaluate the associated parasitic losses. This model has imbedded in it the main components of the fuel cell system, such as the fuel cell stack, air compressor, and fuel processor as seen by the WTM system.
The second half of the paper discusses the results obtained from the model and their implications. We find that the cooling and humidification of the anode and cathode inlet streams can be accomplished with water injection and therefore, a separate heat exchanger is not needed for additional cooling. Additionally we find that the instantaneous and cumulative excess water is determined by factors such as air supply characteristics, condenser efficiency, ambient air humidity, and stack attributes. We find that these factors can affect the ability of the vehicle to achieve true water self-sufficiency.