Modelling soot formation in a premixed flame using an aromatic-site soot model and an improved oxidation rate Matthew S. Celnik, Markus Sander, Abhijeet Raj, Richard H. West, Markus Kraft * Department of Chemical Engineering, University of Cambridge, New Museums Site, Pembroke Street, Cambridge, CB2 3RA, UK Abstract An updated rate of O 2 oxidation of one to four ring polyaromatic hydrocarbons in premixed flames is presented based on density function theory simulations of oxygen attack at different radical sites on various PAHs. The rate is in agreement with other rates found in the literature; however, it is several orders of mag- nitude lower than the currently accepted oxidation rate of multi-ring aromatic species, including soot. Sim- ulations are presented of a premixed flame using this improved rate and a new advanced soot particle model, which is developed in this paper. This model includes unprecedented detail of the particles in the ensemble, including the aromatic content, C/H composition and primary-particle aggregate structure. The O 2 oxidation rate calculated in this paper is shown to give a better prediction of particle number den- sity and soot volume fraction for a premixed flame. The predicted particle size distributions are shown also to describe better the experimental data. Predicted C/H ratio and PAH size distributions are shown for the flame. Computed TEM-style images are compared to experimental TEM images, which show that the aggregate structure of the particles is well predicted. Ó 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Soot; Stochastic; Modelling; Oxidation; DFT 1. Introduction Soot formation is an important process for industry and for the environment. It is generally acknowledged that polyaromatic hydrocarbons (PAHs) are the precursors to soot particles. This has been inferred from the essentially graphitic nature of nascent soot [1]. The soot model proposed by Frenklach & Wang [2], generally referred to as the ABF model, remains the basis for most soot models currently in use for premixed flames. The ABF model considers soot growth by addition of acetylene via the hydrogen- abstraction–carbon-addition (HACA) mechanism and by condensation of PAHs. The ABF model includes O 2 and OH oxidation of soot particles, however, the rates of these pro- cesses are questionable. The gas-phase mechanism of Wang & Frenklach [3] treats the rate of O 2 oxida- tion of one to four ring aromatic species as equal to the rate for phenyl. They also indicate that there are 1540-7489/$ - see front matter Ó 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.proci.2008.06.062 * Corresponding author. Fax: +44 (0) 1223 334796. E-mail address: mk306@cam.ac.uk (M. Kraft). Available online at www.sciencedirect.com Proceedings of the Combustion Institute 32 (2009) 639–646 www.elsevier.com/locate/proci Proceedings of the Combustion Institute