Cold-start effects on performance and efficiency for vehicle fuel cell systems

In recent years government, academia and industry have been pursuing fuel cell technology as an alternative to current power generating technologies. The automotive industry has targeted fuel cell technology as a potential alternative to internal combustion engines. The goal of this research is to understand and quantify the impact and effects of low temperature operation has on the performance and efficiency of vehicle fuel cell systems through modeling. More specifically, this work addresses issues of the initial thermal transient known to the automotive community as "cold-start" effects. Cold-start effects play a significant role in power limitations in a fuel cell vehicle, and may require hybridization (batteries) to supplement available power. A fuel cell system model developed as part of this work allows users to define the basic thermal fluid relationships in a fuel cell system. The model can be used as a stand-alone version or as part of a complex fuel cell vehicle model.

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 of a fuel cell, which governs the efficiency and performance of the system.

This work revealed that the impact on efficiency of a cold-start yielded a 5 % increase in fuel use over a regulated drive cycle for the converted sport utility vehicle. The performance of the fuel cell vehicle also suffered due to operation at low temperatures. Operation of the fuel cell at 20 C yielded only 50% of the available power to the vehicle system.