Detailed modelling of soot oxidation by O-2 and OH in laminar diffusion flames

A detailed knowledge of soot formation and oxidation processes is desired to reduce the soot emissions in combustion devices. Soot oxidation is one of the most complex processes in the numerical modeling of soot. In this work, the oxidation of soot has been numerically studied in laminar ethylene/air coflow diffusion flames. There has been disagreement in the literature over the rates of soot oxidation by O-2 molecules and OH radicals. A sensitivity analysis has been performed on the roles of O-2 and OH in various parts of the diffusion flame, isolating the effects these species have on soot oxidation. A new oxidation model is developed based on the observation that soot ageing reduces surface reactivity and is primarily based on temperature and residence time. A function for surface reactivity of soot, based on the temperature history a soot particle experiences, has been proposed to model soot oxidation. Using this new model, it is now possible to capture the correct behavior of both smoking and non-smoking flames in various flame configurations. Along with a detailed sectional soot model, the new oxidation model predicts the correct soot volume fractions, smoke emission characteristics, and primary particle diameters for different flames without any variation in model parameters between cases. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.