A detailed modelling of the spray ignition process in diesel engines

The Shell autoignition model with the value of the pre-exponential factor i n the rate of production of the intermediate agent (A(f4)) in the range bet ween 3 x 10(6) and 6 x 10(6) has been applied to the detailed modelling of the ignition process in monodisperse and polydisperse sprays based on a com putational fluid dynamics (CFD) code. The mass balance in the Shell model h as been improved to ensure better physical consistency and more effective n umerical implementation. Based on the analysis of the ignition in a monodis perse spray it is pointed out that in the case of droplets with the initial radius (R-d0) about or greater than 6 mum the physical ignition delay domi nates over the chemical ignition delay, while for the smaller droplets with R-d0 less than or equal to 2.5 mum the opposite is true. The start of the ignition process is predicted near the periphery of both monodisperse and p olydisperse sprays in agreement with current understanding of this phenomen on. The observed ignition delay for a monodisperse spray agrees with the av ailable experimental data. The ignition stage of the polydisperse Diesel co mbustion predicted by the model agrees with available experimental data for a medium duty truck Diesel engine, provided that the fine tuning of the pa rameter A(f4) is performed and additional constants, such as concentration limits. are introduced.