Temperature regulation in an evaporatively cooled proton exchange membrane fuel cell stack

Maintaining proton exchange membrane fuel cell (PEMFC) stack operating temperature across transient current profiles presents a significant challenge for fuel cell vehicles. Liquid cooled systems require active control of coolant temperature and flow rate to match heat rejection to heat generation. Evaporative cooling is an alternative to conventional liquid cooling in automotive sized PEMFC stacks. In an evaporatively cooled system, liquid water is injected directly into the cathode flow channels where it evaporates, both cooling and humidifying the stack. This paper uses a validated simulation to explore the inherent temperature regulation abilities of an evaporatively cooled PEMFC stack across a range of current profiles and drive cycles. Results show that throughout the normal operating current range, stack temperature varies by less than±2.0°C, this is comparable to liquid cooling but without the need for active temperature control. The introduction of variable operating pressure and cathode stoichiometry using proportional integral control, can further reduce temperature variation to±1.0°C and±1.2°C respectively for step increases in current demand. Variable operating pressure is also shown to improve warm up time and reduce heat loss at low operating loads.