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In an attempt to increase efficiency and lower critical and highly regulated emissions (i.e., NOx, PM and CO2) many advanced combustion strategies have been investigated. Most of the current strategies fall into the category of low temperature combustion (LTC), which allow emissions mandates to be met in-cylinder along with anticipated reduction in cost and complexity. These strategies, such as homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI), use early injection timings, resulting in a highly lean charge with increased specific heat ratios to improve thermal efficiency and reduce PM emissions. Lower combustion temperatures also avoid the activation of NOx formation reactions.

This paper describes numerical simulations that compare the performance of two combustion CFD models against experimental data, and evaluates the effects of combustion and spray model constants on the predicted combustion and emissions under various operating conditions. The combustion models include a Characteristic Time Combustion (CTC) model and CHEMKIN with reduced chemistry models integrated in the KIVA-3Vr2 CFD code. The diesel spray process was modeled using an updated version of the KH-RT spray model that features a gas jet submodel to help reduce numerical grid dependencies, and the effects of both the spray and combustion model constants on combustion and emissions were evaluated. In addition, the performance of two soot models was compared, namely a two-step soot model, and a more detailed model that considers soot formation from PAH precursors.