Effects of fuel droplet break-up, heating and evaporation in diesel engines

The results of modelling fluid dynamics, heat/mass transfer and combustion processes in Diesel enginelike conditions are presented with the emphasis on the effects of droplet break-up, heating and evaporation on the predicted spray penetration, in-cylinder gas pressure and the amount of fuel vapour, O ₂, CO₂, CO and NO. The following models have been studied: the Infinite Thermal Conductivity (ITC) and Effective Thermal Conductivity (ETC) liquid phase models, the basic gas phase model, the gas phase model suggested by Abramzon and Sirignano (1989), and three droplet break-up models - the model suggested by Reitz and Diwakar (1987), the KH-RT conventional WAVE model, and the TAB model. It is pointed out that the ETC model leads to the prediction of shorter spray penetration, in agreement with experimental data, when compared with the ITC model. The effect of the liquid phase model on predicted gas pressure in Diesel engines is shown to be relatively weak. The predicted amounts of fuel vapour, O₂, CO₂, CO and NO, are strongly affected by the choice of the liquid phase model but practically unaffected by the choice of the gas phase model. The predicted amounts of all these substances are strongly affected by the choice of the droplet break-up models. All these observations are related to the effect of droplet vaporization rate, controlled by the droplet surface temperature (mainly via the choice of the liquid phase model), and to droplet size distributions, mainly controlled by droplet break-up models.