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Exhaust emissions and combustion characteristics from well-characterized diesel test fuels have been measured using two types of single-cylinder HSDI diesel engines. Data were collected at several fixed speed/load conditions representative of typical light-duty operating conditions and full-load performance (smoke-limited maximum torque) points. In addition, in-cylinder soot formation processes of these fuels were investigated via Laser Induced Incandescence (LII) using an optically accessible single-cylinder engine. The test fuels used in this study have been formulated with a sophisticated blending algorithm that systematically varies the hydrocarbon molecular structure in the fuels while maintaining the distillation characteristics of market diesel fuels. The following results have been obtained from this study. (1) The lowest PM emissions were observed with a fuel containing approximately 55% iso-paraffins and 39% n-paraffins with CN=52.5.

Combustion and exhaust emission characteristics were compared among three representative diesel fuels called “Base (corresponding to a Japanese market fuel)”, “Improved” and Swedish “Class-1” using both a modern small and an optically accessible single-cylinder DI diesel engines. In these tests, the relative amount of PM collected in the exhaust was “Base” >“Class-1” >“Improved” at almost all of the operating conditions. This means that “Class-1” generated more PM than “Improved”, even though “Class-1” has significantly lower distillation temperatures, aromatic content, sulfur, and density compared with “Improved”. There was little difference in combustion characteristics such as heat release rate pattern, mixture formation and flame development processes between these two fuels. However, it was found that “Class-1” contained more branches in the paraffin fraction and more naphthenes.

Self-Tuning Regulators, based on both Minimum Variance Control theory and Recursive Extended Least Squares method, are applied to fuel injection/spark ignited automotive engines in order to improve idle speed stability. Simplified mathematical models, with consideration for stochastic combustion variation, are used to describe idle speed dynamics. Model parameters and control gains are calculated in every combustion cycle by using a 16-bit microcomputer. Fuel injection rate and alternator load manipulation are independently examined as control forces. It is founded that (1) these techniques for cotrolling fuel injection rate and alternator load provide over 10% and 30% reduction of engine speed fluctuation, respectively, in comparison with the conventional control systems and (2) this system, in which the control gains are tuned to the appropriate levels, can operate stably in sudden changes of air flow rate and external load.