Soot Particle Growth in Premixed Toluene/Ethylene Flames

Abstract

Surface growth of soot was examined in several premixed flat flames. The fuel was a mixture of toluene and ethylene, with more than half of the carbon supplied by the toluene. We found: (I) Acetylene in the burned gases supplied most of the mass for surface growth, and the growth mechanism in toluene/ethylene flames was the same as in the ethylene flames that we examined previously; i.e., the rate constants that we found in the earlier work predicted the surface growth rates in these flames. (2) In comparing ethylene and toluene/ethylene flames, the fluorescence intensity from polycyclic aromatic hydrocarbons (PAH) was very different for flames with the same C/O ratios but similar for flames with the same soot volume fraction. (3) For a given C/O ratio the amount of soot produced in the particle inception stage in the toluene/ethylene flames was much higher than in the ethylene flames. However, because the acetylene concentrations were higher in the ethylene flames, the rate of surface growth per unit surface area was higher in the ethylene flames than in the toluene/ethylene flames, even though the rate constants were the same.