CFD modeling of a mixed mode boosted GDI engine and performance optimization for the avoidance of knocking

The paper applies simulation techniques for the prediction and optimization of the thermo-fluid-dynamic phenomena characterizing the energy conversion process in a GDI engine. The 3D CFD model validation is realized on the ground of experimental measurements of in-cylinder pressure cycles and optical images collected within the combustion chamber. The model comprehends properly developed submodels for the spray dynamics and its impingement over walls. This last is particularly important due to the nature of the mixture formation mode, being wall-guided. Both homogeneous stoichiometric and lean stratified charge operations are considered. In the case of stoichiometric mixture, the possible occurrence of knocking is also accounted for by means of a submodel able to reproduce the preflame chemical activity. The CFD tool is finally included in a properly formulated optimization problem aimed at minimizing the engine-specific fuel consumption with the avoidance of knocking through a non-evolutionary algorithm.