Moore, Robert M., Shimshon Gottesfeld, P. Zelenay (1999) Control Strategy to Optimize the Efficiency of a Direct-Methanol Fuel Cell for Automotive Applications. Institute of Transportation Studies, University of California, Davis, Presentation Series UCD-ITS-RP-99-06
For automotive applications, it is necessary to maximize the conversion efficiency of a PEM direct-methanol fuel cell (DMFC) over the broadest possible dynamic range of power. The research presented here provides the framework for a control strategy that provides such an optimization. This framework leads into a system level optimization of efficiency vs. power, and an operational strategy for controlling a direct-methanol fuel cell for maximum efficiency from minimum to maximum power. Contrary to the conventional wisdom regarding DMFCs, the research reported here shows that, if such operational strategy can be implemented, DMFCs can be considered for highly dynamic applications – including automotive use – without resorting to "hybrid" power systems.
The potential range of application for the direct-methanol fuel cell (DMFC) depends on its conversion efficiency across a broad spectrum of power density levels. Certainly there are potential niche applications for DMFC power systems that can only be operated efficiently at relatively fixed power, or in "hybrid" power systems. However, if the potential use of the DMFC is limited to such niches, this greatly restricts the eventual markets for the DMFC.
The objective of the research reported here is to critically examine the limitations on the efficiency of the DMFC – when operated over a broad power range. The conventional wisdom was that the DMFC could not efficiently operate across the range of power levels demanded in applications such as automotive power systems. It is shown here that this conclusion is incorrect.
This paper is organized into four sections, followed by a summary of the results. First, there is an explanation of the experimental conditions used to obtain the DMFC data reported and analyzed here. Next, unique features of the DMFC are discussed focusing on the methanol crossover phenomenon. This is followed by the presentation of the conceptual framework for the optimization of conversion efficiency, which introduces the idea of the Maxium Conversion Efficiency Curve. Finally there is a discussion of the optimized conversion efficiency in terms of the familiar concepts of voltage efficiency and fuel utilization.