How Far does the Liquid Penetrate in a Diesel Engine: Computed Results vs. Measurements?

Abstract

A multidimensional model is used to study the penetration of the liquid fuel in a constant volume chamber under normal Diesel engine conditions. Comparisons of the liquid fuel penetration as predicted by the model with results from recent experiments show inadequate agreement but, more importantly, a sensitivity to the numerical resolution. A possible origin of this sensitivity is identified through a series of systematic studies of the different components of the spray model. These studies show that the sensitivity of the liquid penetration to the numerical resolution may be related to a dependence of the computed Sauter Mean Radius (SMR) of the drops on the grid resolution. A detailed study of this dependence relates it to the non-uniformity of the spatial distribution of drops in the chamber, in particular, within about 100 diameters of the injector orifice. This non-uniformity leads to the estimate of different number densities and, hence, different collision frequencies, on different grids. The non-uniformity of drop distribution is shown to be a function of time during the transient injection process and dependent on the vaporization rate. The work also leads to a conclusion about the possible size of injected drops in the Diesel spray.