Chemical characterization of soot precursors and soot particles produced in hexane and diesel surrogates using an inverse diffusion flame burner

In this study, we present information of the chemistry and morphology of soot particles and precursors generated in inverse diffusion flames of liquid fuels. It was found that diesel surrogate fuel (SF) produces five times more soot than the aliphatic hexane flame (H). This difference is mainly due to the high contribution of both aromatic and cyclohexane fraction of the initial SF, which could significantly influence the early evolution of the first soot particle. For example, the alicyclic component that makes part of SF can suffer fast dehydrogenation processes as flame height increases due to thermal effects. As result, benzene is produced and therefore a declining in the CH stretching mode of the aliphatic groups is observed by FTIR and corroborated by 1H-NMR. Soot particle morphology of both flames becomes chain-like aggregates covered with liquid material; characteristic that induces irregular boundaries of the particles. However, the primary particle size is shifted to small ranges compared to the ones obtained at low flame positions mainly due to thermal and oxidation processes, which in turn caused a reduction in the amount of covering tar material, being more drastic for hexane soot particles than for SF soot, probably because the temperature was higher.