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Because of the inherent advantageous energy conversion features of a fuel cell power system, it is a prime candidate technology to meet the national needs for a high mileage, low emission automotive engine replacement that can be realized with both near term and future fuels. This paper provides an overview of efforts to develop such an automotive power system and summarizes early data related to system integration efforts to attain U.S. Department of Energy (DOE) program goals for performance, emissions and multi-fuel operation. Efforts to date have led to the first testing of an integrated fuel cell power system utilizing gasoline.

Stirling engines are excellent candidates for the power conversion system in hybrid electric vehicles due to their low emissions levels and high conversion efficiency. Laboratory and vehicle chassis dynamometer test data using natural gas fuel are presented for kinematic Stirling engine emissions levels over a range of air/fuel ratios and exhaust gas recirculation (EGR) levels. Projections are made for emissions levels during a simple, assumed dual operating point driving cycle for which a battery supplies energy during periods of high demand and stores energy during periods of regenerative braking. The projected emissions levels are compliant with the 1995 California Air Resources Board (CARB) Mobile Source Emission Standards for ultra-low-emissions vehicles.

The status of the Mod III kinematic Stirling engine (155 hp at 2800 rpm) is reviewed with emphasis on natural gas emissions test results and manufacturing cost predictions. Laboratory emissions results are presented for an existing upgraded Mod I (UM-I) engine that has volumetric firing rates comparable to the Mod III. Stirling emissions levels are compared with several internal combustion (IC) engines. Preliminary vehicular emissions measurements with natural gas were also obtained from an UM-I engine installed in a Dodge D-150 pickup truck. Cost for commercial manufacture of the Mod III is determined on the basis of a value-engineered design. This analysis indicated that manufacture of engines in sufficient volume to satisfy projected market needs for a stationary application would provide an adequate manufacturing base to produce the engine at a commercially competitive price.

The Stirling engine is an inherently multifuel engine that has been demonstrated to operate on a wide range of alternate fuels. Among the attractive fuel alternatives for the Stirling engine in a variety of applications are methanol/ethanol, natural gas, jet fuels and synthetic fuels.