A Comparison Between Direct-Methanol and Direct-Hydrogen Fuel Cell Vehicles 1999-01-2914
For an automotive application of a fuel cell power system, it is important to maximize the fuel conversion efficiency, while also providing the required peak power levels for vehicle performance. This paper first compares the fuel conversion efficiency and power density of a state-of-the-art direct-methanol fuel cell (DMFC) with the equivalent parameters of a state-of-the-art direct-hydrogen fuel cell (DHFC). The cell level comparison is then extended to the system level for a potential ZEV automotive application. It is concluded that a DMFC-powered vehicle can become directly competitive with a DHFC-powered ZEV (Zero Emission Vehicle) in any localities or market niches where ZEVs are “a condition of doing business” as a vehicle manufacturer.
Following a brief outline of the experimental conditions used to generate the DMFC data reported and analyzed in this paper, a technique for optimizing the conversion efficiency of a DMFC is briefly reviewed. The technique is then applied to the DMFC state-of-the-art data, and compared with the efficiency and power density of the DHFC state-of-the-art. Next a “system” level comparison is introduced that captures the major differences between the DHFC and DMFC systems for automotive applications. This system level comparison is then used to evaluate the attributes of a DMFC-powered vehicle against the “benchmark” of a DHFC-powered vehicle.
Overall, the conclusion is that a DMFC powered FCV could meet the requirements for a general-purpose ZEV, and could be an effective competitor to a DHFC-based FCV. It would have an range of 350 miles, and provide the same class of performance (acceleration) as a light-weight purpose-built hydrogen-fueled FCV, if two key criteria were met:
DMFC cell/stack power density of 0.35 kW/L,
DMFC stack conversion efficiency over the required dynamic power range of 50% of the equivalent DHFC stack efficiency.
In fact, these criteria are marginally met for the present state-of-the-art in laboratory DMFC performance. However, for implementation of a DMFC power system in an FCV, the development of a commercial DMFC stack technology and fuel control system is also required, and a number of R&D advances are needed before the DMFC cell, stack and system can fully realize its great promise. Even so, because of this promise there are significant worldwide R&D efforts underway to address the technical and commercialization barriers for direct-methanol fuel cell vehicles.