Analysis of In-flame Soot and Polycyclic Aromatic Hydrocarbons by Laser Raman Spectroscopy

Abstract

In the present study, we introduced into the laminar diffusion flame to a KrF excimer laser to analyze the formation mechanism and characterization of in-flame soot and its precursor such as polycyclic aromatic hydrocarbons (PAHs). The test fuel was hexane, which was a typical paraffin-type hydrocarbon fuel. The spatial distributions of PAHs and soot were measured using laser-induced fluorescence and laser-induced incandescence methods. The graphite structure of soot was analyzed using a Raman spectroscopic method. From these results, a G-band attributed to the vibration mode of the graphitic lattice and a D-band attributed to the disordered graphitic lattice were detected. When the sampling position approached the downstream part of the flame, G/D ratio (ratio of these bands) of the soot increased. Further, the G/D ratio of PAHs was also detected. It was shown that the G/D ratio attributed to the PAHs and soot was in proportion to the flame temperature.