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Engine hardware modifications, fuel and lube oil properties, electronic controls, and aftertreatment devices may all play a role in meeting future heavy-duty diesel engine emission standards. Detroit Diesel Corporation (DDC) is actively involved in evaluating the contributions of these technologies to reduce emissions as well as evaluating the impact on initial and life cycle system cost, fuel consumption, reliability and durability. This paper focuses on the potential of low emission diesel fuels to contribute to lower engine-out emissions. DDC has been testing low emission diesel fuels with low sulfur and aromatics and higher cetane number, synthetic diesel fuels, and today's fuels with various additives. Other industry programs have generated similar data. These results have led us to the conclusion that a significant contribution can be made by tailoring future diesel fuels to produce low emissions.

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.

An in-cylinder optical sensor has been developed to measure and control the exhaust smoke or soot emission from heavy-duty diesel engines. The sensor directly measures the radiant emission from incandescent soot particles during and after main combustion. Results show a strong correlation between both the measured duration and end of radiant emission, and the amount of soot emitted by the engine. Test results also demonstrated some potential benefits of in-cylinder control using the optical sensor. In one test, the optical signal was used to control high-load soot emission during changes in air intake pressure and temperature. In a second test, the optical signal was used to minimize the variability in exhaust soot levels caused by manufacturing variations in fuel-injector flow characteristics.

In-cylinder sampling appears to be the only available means for obtaining detailed information of the diesel combustion process. This information is necessary to understand pollutant formation because of the intimate relationship between formation rates and local cylinder conditions. This paper discusses efforts to (1) examine and improve sampling valve design, (2) evaluate potential effects of the valve and the sampling system on sample composition, (3) find methods to extract useful information from sampling data. Sampling hardware is currently being used to study combustion in engines, but further work is needed to quantify the influence of hardware and procedures on sample composition and to design experiments to provide data containing maximum information.

The development of a variable valve timing (VVT) camshaft was initiated as a potential means of controlling exhaust emissions from a spark ignition piston engine. This approach was based on the fact that valve overlap influences internal exhaust gas recirculation which in turn affects spark ignition engine emissions and performance. The design, fabrication, bench tests and engine durability tests of a unit incorporating splines to allow the intake cams to move relative to the exhaust cams is discussed. Preliminary test data from a 350 CID (5700 cm3) engine fitted with the VVT camshaft are discussed with regard to durability and emissions.