Modeling of NOx and soot formation in diesel combustion

An approach to model the formation and oxidation or reduction of soot and N O in turbulent diffusion flames is presented. The model is based on the fla melet library approach and extended to account for radiative heat losses in the flame. Due to the rather slow processes leading to soot and NO a modif ied flamelet library approach is used. Instead of taking the mass fractions directly from flamelet libraries the different source terms for soot and N O formation are calculated and a transport equation for the mean mass fract ions is solved in the CFD calculation. The source terms are obtained from l aminar counterflow-flame calculations using a detailed chemistry model for the gas phase species and the formation and oxidation of soot. Transport eq uations for the mean mixture fraction and the mixture fraction variance are solved and the chemical source term is closed by presuming a beta-function like distribution of mixture fraction and a log-normal distribution of the scalar dissipation rate. The model was first tested in laminar and turbulent jet flames. By applying a reduction strategy for the flamelet libraries of the source terms it was made applicable to the simulation of soot formation in a Diesel spray taki ng different oxidizer temperatures and pressures into account. Additionally , different formulations of the flamelet equations have been tested and the ir accuracy has been evaluated by comparing them to turbulent flame experim ents.