A quasi-discrete model for droplet heating and evaporation: Application to Diesel and gasoline fuels

Abstract

The previously suggested quasi-discrete model for heating and evaporation of complex multi-component hydrocarbon fuel droplets is generalised to take into account the dependence of density, viscosity, heat capacity and thermal conductivity of the liquid components on carbon numbers and temperature. This model is applied to the modelling of heating and evaporation of Diesel and gasoline fuel droplets. In agreement with the prediction of the previously reported simplified version of this model in which density, viscosity, heat capacity and thermal conductivity of all liquid components were assumed to be the same as for n-dodecane, it is pointed out that Diesel fuel droplet surface temperatures and radii, predicted by a rigorous model taking into account the effect of all 20 quasi-components, are almost the same as those predicted by the model using five quasi-components. For the Effective Thermal Conductivity/Effective Diffusivity (ETC/ED) model, the number of quasi-components used can be reduced to three. In the case of gasoline fuel, with the maximal number of quasi-components equal to 13, a good approximation for the ETC/ED model can be achieved based on the analysis of just three components. The difference in predictions of the 13 and 1 component models appears to be particularly important when droplets evaporate in gas at a relatively low temperature (450K) and low pressure (0.3MPa). In this case the evaporation time predicted by the one component model is less than half of the time predicted by the 13 component model. The surface mass fraction of the lightest quasi-component in gasoline fuel monotonically decreases with time, while the surface mass fraction of the heaviest component monotonically increases with time. Surface mass fractions of intermediate components initially increase with time, but at later times they rapidly decrease with time.