Simulation and experiment of DI diesel engine under transient operations

3D simulations on a DI diesel engine with high pressure common rail injection system under transient operations with EGR were conducted. The in-cylinder parameters of transient operations were analyzed. Experimental results based on time were converted into the discrete points based on cycle. NO_x emissions were analyzed by volume, duration of in-cylinder high temperature area and φ-T diagram. Simulation results of separated transient cycle agree with that of the corresponding experimental data. NO_x emissions decreases under the increasing torque process while soot emissions increase substantially as being explained by φ-T diagram where in-cylinder equivalence ratio and temperature approach to the soot area and retreat to NO_x area when loads increased. Uniformity of cylinder mixture was analyzed by Lorenz curve. Under transient conditions, soot emission deterioration is from the increased heterogeneity of the in-cylinder fuel-air mixture compared with steady condition.