Divided-Chamber Diesel Engine, Part I: A Cycle-Simulation Which Predicts Performance and Emissions

A model has been developed for a divided-chamber automotive diesel engine which describes the intake, compression, combustion and expansion, and exhaust processes in sufficient detail to permit calculations of pressure, fuel-air ratio distribution, heat release distribution, NO formation, soot mass loading, and soot oxidation processes. The novel feature of this model is the use of a stochastic mixing approach during the combustion and expansion processes to describe the nonuniform fuel-air ratio distribution within the engine. In this approach, the fuel-air ratio distribution during the combustion and emissions formation processes can be followed as it evolves with time. Experimental data generated on a single-cylinder divided-chamber diesel engine were used to verify the accuracy of the model predictions. Agreement between experimental data and predicted values of engine performance and NO_x emissions levels was good. The model is used to examine the origin of NO and soot emissions in a divided-chamber diesel engine. The cycle-simulation results show that NO forms primarily in the pre-chamber. The soot studies show that soot oxidation occurs in the pre- and main-chambers, and soot oxidation mechanism is both kinetically and mixing limited.