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Stirling Thermal Motors, Inc. (STM) has been developing and testing a general purpose Stirling engine, designated the STM4-120. The engine was optimized to produce 25 kW at 1800 RPM and features a four-cycle, double-acting configuration, resulting in high specific power with variable displacement power control for high efficiency over a wide power range. During the last year, Stirling Thermal Motors, Inc. (STM) and Detroit Diesel Corporation (DDC) began a cooperative effort to develop this engine for commercial applications. This engine has demonstrated performance and fuel efficiency equivalent to a diesel with superior emission and noise characteristics. These qualities, in addition to the engine's multifuel capability and the potential for long service free life, have generated interest in manufacturing and marketing this engine for commercial applications where operating requirements are not attainable with today's diesel engine.

A diesel exhaust sampling system was specially designed to measure and collect emissions from a ceramic wall-flow particulate trap during periods of controlled electric regeneration with the exhaust emissions bypassing the trap. This resulted in the regeneration emissions being independent of those produced during either baseline (no control) or trap (exhaust filtration) sampling conditions. This system provided data regarding the physical, chemical, and biological character of regeneration emissions relative to baseline and trap emissions. Selected emission levels measured continuously during the regeneration process were also used to define the particle combustion process in the trap core. Variations in hydrocarbons (HC), oxides of nitrogen (NOx), and particulate volume concentrations during the regeneration process were used to define four stages of the combustion process: preheat; combustion wave formation; combustion wave propagation; and combustion wave extinction.