Growth and oxidation of graphitic crystallites in soot particles within a laminar diffusion flame

The growth and oxidation behaviors of graphitic crystallites in soot particles within a laminar co-flow propane diffusion flame were investigated experimentally. Soot was sampled along the flame axis and collected on a quartz–fiber filter. The soot nanostructure, i.e., the graphitic crystallite size and the amorphous carbon content in the soot particles, was characterized by Raman spectroscopy. The spatial distributions of the fuel, PAHs, soot and OH measured by laser diagnostic techniques are presented to examine the effect of the flame structure on the soot nanostructure. The Raman spectra of the soot show that both the graphitic crystallite size and the amorphous carbon content in the soot particles increase during the soot growth process. In addition, the crystallite size and the amorphous carbon content simultaneously decrease during the soot oxidation process by OH. HRTEM images of soot particles support that these findings obtained from the Raman spectroscopy are reasonable. The influences of the soot formation and oxidation history within the flame on the soot nanostructure are validated.