Fuel Droplet Heating and Evaporation: Analysis of Liquid and Gas Phase Models

Recently developed liquid and gas phase models for fuel droplet heating and evaporation, suitable for implementation into computational fluid dynamics (CFD) codes, are reviewed. The analysis is focused on the liquid phase model based on the assumption that the liquid thermal conductivity is infinitely large (infinite thermal conductivity (ITC) model), and the so called effective thermal conductivity (ETC) model. Seven gas phase models are compared. It is pointed out that the gas phase model, taking into account the finite thickness of the thermal boundary layer around the droplet predicts the evaporation time closest to the one based on the approximation of experimental data. In most cases, the droplet evaporation time depends strongly on the choice of the gas phase model. The dependence of this time on the choice of the liquid phase model, however, is weak if the droplet break-up processes are not taken into account. Corrections to Newton's law for droplet transient heating are discussed. For the values of parameters relevant to diesel engines, the values of these corrections were shown to be significant. Recent kinetic models for droplet evaporation into a high pressure background gas are reviewed. It is recommended that the kinetic effects are taken into account when accurate analysis of diesel fuel droplet evaporation is essential. A new dynamic decomposition technique for a system of ordinary differential equations is reviewed.