Optimization of Multi Stage Direct Injection-PSCCI Engines

The more and more stringent regulations on emissions lead the automotive companies to develop innovative solutions for new powertrain concepts, including the employment of advanced combustion strategies and mixture of fuels with different thermochemical properties. HCCI combustion coupled with the partial direct injection of the charge is a promising technique, in order to control the performance and emissions and to extend the operating range. In this work an in-house developed multi-dimensional CFD software package has been used to analyze the behavior of a multi stage direct injection - partially stratified charge compression ignition engine fueled with PRF97. A combustion model based on the partially stirred reactor concept to include the influence of turbulence on chemistry has been employed. Specifically, a skeletal kinetic reaction mechanism for PRF oxidation, with a dynamic adaptive chemistry technique to reduce the computational cost of the simulations has been used. Most of the fuel is injected during the intake stroke, in order to get a homogeneous mixture of fuel and air, whereas the remaining part is injected at the end of the compression stroke, in order to stratify fuel and temperature distributions in the chamber. The delay of fuel injection leads to a lower average temperature in the chamber, thus controlling the heat release rate and NOx emissions. The numerical model has been validated by comparing the results with experimental data available in the literature. Several simulations were performed to optimize the operations of the engine by changing the timing and duration of DI into the chamber and the ratio between the amount of fuel injected during the delayed stage and the amount of early-injected fuel.