Application of Soot Formation Model: Effects of Chlorine

Abstract

Soot formation in the combustion of hydrocarbon fuels is the net effect of competition between molecular weight growth and destruction mechanisms involving free radicals. Chlorine addition to the fuel can alter the concentrations of radicals in a manner that enhances soot formation. In diffusion flames and purely pyrolysis systems, the presence of chlorine increases the fractional conversion of carbon to soot, while in premixed flames and well-stirred combustion the presence of chlorine lowers the critical equivalence ratio for the onset of soot formation. These effects tend not to be of major importance in premixed and well-stirred systems unless substantial amounts of chlorine are added. The chlorine has a strong tendency to go to HO, which may or may not significantly lower the concentration of H atoms, and in turn affect the concentrations of OH and O, depending on whether the atomic Cl/H ratio is comparable to or much less than unity. The observed effects of chlorine on soot formation are qualitatively consistent with expectations based on the knowledge of soot formation, the known rate coefficients of the hydrogen and chlorine analogs of the key radical reactions, and calculated equilibrium compositions with and without chlorine present.