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An experimental investigation of partial premixed charge compression ignition (PCCI) in combination with direct fuel injection was conducted on a Caterpillar C-15 heavy-duty diesel engine (HDDE). The intent of the program was to investigate the performance, emissions, and efficiency characteristics of the concept. A portion of the fuel was delivered to the intake manifold using air-assist port fuel injectors. The spray droplet characteristics were measured, for several different injector geometries, over a range of thermodynamic conditions. Subsequently, the optimized port fuel injector (PFI) was utilized in the engine tests. The engine tests were run at conditions ranging from 1200 - 1800 RPM, loads ranging from 25 - 75%, and PFI quantities ranging from approximately 10 - 70%. The tests showed that oxides of Nitrogen (NOX) emissions did not decrease dramatically with partial premixing.

This study focuses on the development of an autoignition model for diesel sprays that is applicable to phenomenological multi-zone combustion models. These models typically use a single-step Arrhenius expression to represent the low-temperature chemistry leading up to autoignition. There has been a substantial amount of work done in the area of n-heptane autoignition in homogeneous mixtures. Reduced kinetic mechanisms with ten reactions or less have been proposed in the literature to represent the complex low-temperature oxidation of n-heptane. These kinetic models are attractive for multi-zone simulations because of the low number of reactions involved. However, these kinetic mechanisms and the multi-zone treatment of the fuel spray do not account for the effect of turbulence/chemistry interactions on the chemical reaction rate.