Successes and Uncertainties in Modeling Soot Formation in Laminar, Premixed Flames

A model for soot formation in laminar, premixed flames is presented. The analysis is based on a simplified inception model, detailed kinetic calculations of soot surface growth, and coalescing particle collisions. A sectional aerosol dynamics algorithm which involves solving a master equation set for the densities of different particle size classes provides an efficient solution scheme. The calculation of surface growth and coalescence sectional coefficients has been simplified and extended to the entire temperature range of interest in flame simulations. In order to test convergence properties, the former geometric limitation on the number of size classes has been relaxed. Convergence of the soot volume fraction typically requires only a few size classes and balance equations. Several possible soot surface growth models have been compared. The inception and surface growth models require profiles of temperature and important species like benzene, acetylene, and hydrogen atoms, and oxidizing species. Extensive comparisons have been made with well-characterized flame data by using experimental temperature profiles and calculating the concentrations of the important species with a burner code. The calculated species concentrations and surface growth/oxidation rates are input to the aerosol dynamics program, which calculates the evolution of various soot size and density parameters. While aspects of the model are highly simplified, on balance it appears to give agreement with experiment that is comparable to that obtained from more elaborate models. The calculated sensitivity of soot growth to temperature and the important inception and coalescence parameters is discussed.