Numerical Studies on Temporal and Spatial Distribution of Equivalence Ratio in Diesel Combustion Using Large Eddy Simulation

To identify ways of achieving good mixture formation and heat release in diesel spray combustion, we have performed Large Eddy Simulation (LES) using a detailed chemical reaction mechanism to study the temporal and spatial distribution of the local equivalence ratios and heat release rate. Here we characterize the effect of the fuel injection rate profile on these processes in the combustion chamber of a diesel engine. Two injection rate profiles are considered: a standard (STD) profile, which is a typical modern common rail injection profile, and the inverse delta (IVD) profile, which has the potential to suppress rich mixture formation in the spray tip region. Experimental data indicate that the formation of such mixtures may extend the duration of the late combustion period and thus reduce thermal efficiency. Analyses of the heat release per unit fuel mass and unit entrained O₂ mass under the two injection regimes indicate that IVD injection reduces the density of the fuel-air mixture in the spray tip region, increases the leanness of the spray core region, and enhances O₂ entrainment, improving the heat release process.