Numerical and experimental analysis of soot formation in laminar diffusion flames along selected particle tracks

We present an application of the flamelet approach combined with computational fluid dynamics calculations to compute the flow field, temperature, mixture fraction, and scalar dissipation rate of laminar, sooting acetylene/nitrogen/air diffusion flames, followed by a comparison with experimentally measured soot volume fraction and net appearance rates. The comparison is performed along selected particle tracks which are based on data from the calculated flow field. The investigation shows that, for different tracks, different trends exist in the net appearance rate of soot in the soot-formation zone of the flames. These differences can be correlated with the local scalar dissipation rate along these tracks. In addition to this important influence of scalar dissipation rate on soot formation, there is an influence of mixture fraction and temperature. Scalar dissipation rate, mixture fraction, and local flame temperature have to meet certain conditions for initiating soot formation and growth reactions. The impact of scalar dissipation rate on soot-particle oxidation is overweighed by the influence of local flame temperature. The results suggest that future numerical simulation of soot formation and oxidation in laminar diffusion flames based on the flamelet approach needs a thorough description of locally varying scalar dissipation rates as well as mixture fractions and local temperature.