Soot Formation From Toluene.

Abstract

Synthetic fuels will likely have a higher aromatic content than petroleum-based fuels. This aromatic character will result in increased soot formation and increased flame radiation. Since the kinetics of soot formation is poorly understood, it is very difficult to design combustors using aromatic fuels. A laser beam attenuation technique was utilized to study the kinetics of soot formation from toluene and other selected fuels over the temperature range 1400-2500 K and the pressure range 2.5-10 atmospheres. Detailed soot yield studies show that the aromaticity of the hydrocarbons determines their sooting characteristics. At low temperatures, the condensation, polymerization, and dehydrogenation are the most important soot formation steps for aromatic fuels. At high temperatures, the rings tend to be cracked readily, therefore fragmentation, cyclization, aromatization, polymerization, and dehydrogenation encompass the important sooting steps. Possible routes leading to soot for these two competitive sooting procedures are proposed. Thermochemical equilibrium composition calculations indicate that C(,96)H(,24) appears to be an important soot precursor. Correlation equations for soot formation delay times, apparent soot formation rates, and quasiglobal rate models are obtained. A quasiglobal mechanistic approach using the limited detailed pyrolysis steps of toluene to predict the soot production is also developed. The data presented herein may be used to estimate the effects of sooting in combustors in which highly aromatic, synthetic fuels are used.