A vaporization model for discrete multi-component fuel sprays

A vaporization model for multi-component fuel sprays is described. The discrete multi-component (DMC) fuel approach was used to model the properties and composition of gasoline and diesel model fuels. Unsteady vaporization of single and multi-component fuel droplets and sprays was considered for both normal and flash-boiling evaporation conditions. An unsteady internal heat flux model and a model for the determination of the droplet surface temperature were formulated. An approximate solution to the quasi-steady energy equation was used to derive an explicit expression for the heat flux from the surrounding gas to the droplet-gas interface, with inter-diffusion of fuel vapor and the surrounding gas taken into account. The density change of the drop as a function of temperature was also considered. In order to treat phase change under trans-critical conditions, a characteristic length was defined to determine the amount of vaporized fuel as a function of time. The present vaporization models were implemented into a multi-dimensional CFD code and applied to calculate evaporation processes of single and multi-component fuel droplets and sprays for various ambient temperatures and droplet temperatures. Differences between representing model fuels using the single and multi-component fuel descriptions are discussed.