The PDF-Equation Approach to Diesel Spray Evaporation Computations

A numerical submodel within the PDF-approach is developed for calculation of turbulent evaporation in liquid fuel sprays. This submodel is based on the Monte Carlo simulation of derived PDF transport equation for vapor concentration that accounts for both large scale turbulent air-fuel mixing and small scale turbulence. Evaporation-micromixing interaction is treated within coalescence-dispersion processes where evaporated mass is presented in statistical manner. The submodel is incorporated into KIVA II diesel spray codes. Computations of transient dynamics of vaporizing fuel spray were performed to assess the fluctuating structure of fuel vapor field. Discontinuous distributions of fuel vapor mass fraction are demonstrated in zones were droplets are still not evaporated. Highest intensity of vapor concentration fluctuations at the spray tip was observed. Calculated local PDF distributions of vapor concentration correspond to rather quasi-Gaussian form including Dirac δ-function at the extremities of the concentration space.