A modeling evaluation of the effect of chlorine on the formation of particulate matter in combustion

The effect of chlorine on the fuel-rich oxidation of hydrocarbons and on th e molecular weight growth of aromatics is analyzed by simulating experiment s featuring a model chlorinated additive CH3Cl in a jet-stirred/plug-flow r eactor and premixed flames. The kinetic model used in this work emphasizes the role of resonantly stabilized radicals in the formation and growth of a romatics, and considers soot inception as the net effect of molecular weigh t growth and graphitization of aromatic structures. Chlorinated hydrocarbon s decompose at temperatures significantly lower than hydrocarbons, producin g reactive Cl-atoms, which have a strong tendency to go to HCl. The HCl, ty ing up the H-atoms, inhibits hydrocarbon oxidation. The model is able to pr edict not only the levels but the shape of the experiments quite well and a lso the surprising finding of an increased soot formation associated with l ower PAH levels found in rich flames with significant levels of chlorine. B ased on reaction kinetic analysis, chlorine addition to the fuel enhances s oot formation by promoting the formation of aromatic-ring compounds and acc elerating the abstraction of aromatic H-atoms from stable PAH molecules. Th is process activates the transformation of aromatics to soot. (C) 2001 Else vier Science Ltd. All rights reserved.