Cold Start Fuel Economy and Power Limitations for a PEM Fuel Cell Vehicle

Fuel cells are being considered for transportation primarily because they have the ability to increase vehicle energy efficiency and significantly reduce or eliminate tailpipe emissions. A proton exchange membrane fuel cell is an electrochemical device for which the operational characteristics depend heavily upon temperature. Thus, it is important to know how the thermal design of the system affects the performance and efficiency of a fuel cell vehicle. More specifically, this work addresses issues of the initial thermal transient known to the automotive community as “cold start” effects for a direct hydrogen fuel cell system. Cold start effects play a significant role in power limitations in a fuel cell vehicle, and may require hybridization (batteries) to supplement available power. The results include a comparison of cold-start and hot-start fuel cell power, efficiency and fuel economy for a hybrid fuel cell vehicle.

Fuel cell system design can significantly affect the cold start performance of a fuel cell system. Through modeling, it is possible to quantify the impact of thermal mass on warm up time to operating temperature of a fuel cell system. As expected, performance reduction is seen during cold start that affects both available power and fuel use. The overall cold start energy use penalty is relatively small (∼ 5% difference) for the combination of component sizes and control strategy presented here.