Calculation of the size distribution function of soot particles in turbulent diffusion flames

Abstract

The advantages of a combined model approach were exploited to compute piloted natural gas/air turbulent jet diffusion flames with the intention towards a quantitative description of the soot properties (soot volume fraction) as well as the evolution of the size distribution of the soot particles across the flame. The interaction of turbulence and chemistry was described by a probability density approach in combination with the laminar flamelet formulation. Gas-phase chemistry was accounted for by the detailed mechanism of Appel, Bockhorn and Frenklach, which includes the formation of aromatic species up to pyrene. The formation and oxidation of the particulate phase was described by soot particle size population balance equations, which were solved using a modified version of the stochastic particle algorithm developed by Kraft and co-workers. The influence of turbulent fluctuations on particle inception, coagulation and surface reactions is discussed. The predictions of the particulate phase were assessed quantitatively by comparison with measurements of total soot particle concentrations of turbulent diffusion jet flames, which were investigated by Bartenbach et al. The evolution of the size distribution of the primary particles across the turbulent jet flame was visualized. After the region, where particle inception plays the dominating role, shape and extension of the size distribution is governed mainly by coagulation processes until the oxidation reactions are of increasing importance, leading to the consumption and depletion of particles, which significantly alters the distribution.