Soot Precursor Particles in Flames

Abstract

Thermophoretic sampling was conducted in buoyancy dominated diffusion flames fueled by ethene, methane and acetylene and in the laminar ethene flame. Small polydisperse singlet particles which are more transparent to the electron beam are found at intermediate temperatures on the fuel side of the flame front in these flames. The particles form agglomerates at the flame front or in the upper regions of the flame. The microparticles conform to the description that has been provided by Wersborg et al. of similar species found in the premixed acetylene flame at low pressures which suggests that they are a common particulate precursor to carbonaceous soot in hydrocarbon flames. It is concluded that the particles are likely to be composed of polyaromatic hydrocarbon compounds, which have been found by others to be present in hydrocarbon flames, and that the precursor particles undergo annealing to form a partially graphitic soot upon exposure to elevated temperatures at the flame front.