CFD Analysis of Combustion and Pollutant Formation Phenomena in a Direct Injection Diesel Engine at Different EGR Conditions

In this work, exhaust gas recirculation (EGR) is varied in a direct injection constant speed diesel engine using extended coherent flame model for 3-zones by CFD. The three zones are unmixed fuel zone, mixed gases zone, unmixed air plus EGR zone. The three zones are too small to be resolved by the mesh and are therefore modeled as sub-grid quantities. The mixed zone is the result of turbulent and molecular mixing between gases in the other two zones, where combustion takes place. Grid and time independent tests are carried out further to find the appropriate space and time steps respectively. The preliminary studies are carried out to validate the model with the experiments. The present study is conducted towards varying the EGR in the cylinder. CFD results indicate that as EGR increases, nitrogen oxides decreases in a general trend observed in diesel engines. The predicted model shows that flame temperature is lowered in the combustion chamber with the increase in EGR. However, as oxides of nitrogen decreases, soot increases due to lowered oxygen concentration. Reaction variable and temperature contours in the cylinder reveal that combustion regresses as EGR is increased.