Modelling of Hydrocarbon Fuel Droplet Heating and Evaporation: Recent Results

The most recent developments in the modelling of heating and evaporation of hydrocarbon automotive (biodiesel, Diesel, gasoline) fuel droplets at the University of Brighton are reviewed. Analyses of hydrodynamic, kinetic and molecular dynamic models, taking and not taking into account quantum-chemical
effects, are presented. New results in modelling the heating and evaporation of non-spherical (spheroidal) droplets are summarised. In contrast to the models used in most engineering applications, the effects of temperature gradient within spherical droplets were taken into account based on the analytical solution to the one-dimensional heat transfer equation, assuming that the heating process is also spherically symmetric. It was shown that this approach is particularly useful for practical applications in CFD codes. In the case of multi-component droplets we need to take into account that different components evaporate at different rates, creating concentration gradients in the liquid phase. In contrast to the models used in most previous publications, our approach was based on the analytical solution to the species diffusion equation in the liquid phase. These models were implemented into the ANSYS Fluent CFD code using User-Defined
Functions (UDF). The predictions of this code with the new models were verified against the results predicted by the in-house research code. In the case of hydrocarbon fuels with large numbers of components a new multi-dimensional quasi-discrete model has been developed. In this model, the contributions of
individual components are replaced with the contributions of the group of components with close transport and thermodynamic properties, called quasi-components. New approaches to modelling fuel droplet heating, evaporation and ignition, based on the method of integral manifolds, and related problems are discussed. Prospects for future research are highlighted.