Numerical simulation on the effect of pilot injection on combustion and NOx emission characteristics of light-vehicle diesel engine

Based on KIVA-3V code, the numerical simulation on the combustion process and NOx emission of a light-vehicle diesel engine is carried out, using different injection strategies. The results show that compared with the traditional single injection, pilot injection can decline the ignition delay period and the maximum combustion temperature, which leads to the reduction of the NOx emission; as pre-injection mass increases, NOx emission increases. Fuel of pilot injection must be sufficient for preheating the combustion chamber. Otherwise, NOx emission is deteriorated in the condition of excessive amount of pilot injection. For the light-vehicle diesel engine investigated in this paper, when the proportion of pre-injection mass to cycle-injection mass is 2.5% and the angle between pilot injection to main injection is 15 degrees CA, the NOX emission declines nearly 21.8%.