Sooting structure of a premixed toluene-doped methane flame

The structure of a sooting premixed methane/oxygen flame doped with toluene (C/O = 0.66) was studied by means of sampling and chemical and spectroscopic analysis of gas and condensed phases. It was found that the addition of toluene in small amounts (0.8 mol%) to the methane flame (C/O = 0.6) used as reference did not affect the maximum temperature level and the distribution of the main combustion products and C1-C4 hydrocarbons. The main differences observed regarded the higher yield of soot and C5-C6 hydrocarbons as cyclopentadiene and benzene. Some insights on soot structure were obtained by means of spectroscopic tools, i.e. Raman and UV-Visible spectroscopy. Spectral features of toluene-doped soot indicated that toluene doping not only enhances soot production, but also changes its structural properties in terms of aromatic character of soot particles. These features could be of concern about the use of practical fuels rich in aromatic components possibly leading to higher environmental and health impact of aromatic-derived soot in respect to aliphatic-derived soot.