Abstract - Pfefferle This is a study of hydrocarbon growth mechanisms that lead to the formation of soot and soot precursors under diffusion flame conditions; such conditions are relevant to most practical combustion conditions. The objective is to determine the effects of combustion conditions and fuel structure on the formation pathways of aromatic ring compounds and soot. Both single-fuel flames and methane diffusion flames doped with low concentrations of various hydrocarbons are studied. Soot volume fraction to 0.1 ppm, morphology and composition of soot, polycyclic aromatic hydrocarbons (PAH), and stable intermediate species present at levels above 1 ppm and measured. Particular reaction pathways important in the diffusion flames are studies also in a molecular-beam-sampled well-mixed reactor to obtain detailed reaction parameters. This methodology allows fast, quantitative species sampling in diffusion flames with significant soot loadings. Reaction products are detected using vacuum ultraviolet (VUV) photoionization. The soot measurement technique allows detection of sub-ppm soot volume fractions and includes measurement of the translucent particles that may be the direct precursors of mature soot. With this technique, precursor particles can be discriminated from mature soot, their composition analyzed, and the process of graphitization followed. Soot and PAH associated with incomplete combustion are recognized as major health hazards. Detailed studies of the formation and character of these materials can identify which systems pose the greater threats and also suggest control strategies.
