How far does the liquid penetrate in a diesel engine: Computed results vs.measurements?

A multidimensional model is used to study the penetration of the liquid fue l in a constant volume chamber under normal Diesel engine conditions. Compa risons of the liquid fuel penetration as predicted by the model with result s from recent experiments show inadequate agreement but, more importantly, a sensitivity to the numerical resolution. A possible origin of this sensit ivity 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 depe ndence of the computed Sauter Mean Radius (SMR) of the drops on the grid re solution. A detailed study of this dependence relates it to the non-uniform ity of the spatial distribution of drops in the chamber, in particular, wit hin about 100 diameters of the injector orifice. This non-uniformity leads to the estimate of different number densities and, hence, different collisi on frequencies, on different grids. The nonuniformity of drop distribution is shown to be a function of time during the transient injection process an d dependent on the vaporization rate. The work also leads to a conclusion a bout the possible size of injected drops in the Diesel spray.