Combustion modeling of diesel and Ng fueled/micro-pilot diesel ignition engines

A complete grid for a 4-valve single cylinder diesel engine CAT3401 was generated by the improved K3PREP. Intake and in-cylinder flows, along with effects of grid types on predictions of in-cylinder flows were investigated in this dissertation. It was also found that it was impossible to account for the complicated in-cylinder flow with a simplified 60° sector grid. However, a simplified full circle grid with initial swirl and the new proposed tumble ratio option compared well to the solution found with the complete grid.; Two different combustion mechanisms for diesel engines, chemically controlled and mixing controlled combustion mechanisms, were compared. A hybrid combustion model combining these two mechanisms as well as a soot model were proposed. Combustion and emissions of both diesel engines and natural gas fueled/micro-pilot diesel ignition engines were modeled. Computations showed that the reaction zones of the two different reaction mechanisms were different. Such a difference has an important effect on the products composition. The hybrid combustion model and the soot model are capable of predicting the combustion and emissions of diesel engines. Studies have shown that the hydroxyl (OH) plays an important role in the soot oxidation in diesel engines.; Reasonable predictions of HC, NO_x and CO emissions were obtained by the dual fuel combustion model. Higher HC and CO, and lower NO_x emissions were obtained in NG (methane) fueled/micro-pilot diesel ignition engines compared to the diesel-fueled engines. It is difficult for the current methods to reduce the unburned methane to an acceptably low level at light loads (&phis; < 0.5) without deteriorating economic performance and NO _x emissions. A new method, split injection, was proposed to reduce unburned methane emissions in a dual fuel engine at light loads. It is found that split injection is a promising method to reduce HC, CO, and NO_x emissions at light loads in NG fueled/micro-pilot ignition engines. With optimal injection timing, HC can be reduced by more than 90%, CO can be reduced 50%, NO _x can be reduced by 70%.