Formation of low- and high-molecular-weight hydrocarbon species in sooting ethylene flames

The concentration profiles of the main oxidation and pyrolysis gaseous products (CO, CO2 , H-2 , C-1-C-6) and of soot and high-molecular-weight species were measured inside sooting ethylene/oxygen premixed laminar flames with two different equivalence ratios, phi=2.42 and phi=3.03. As expected, low and high molecular weight hydrocarbon species, such as C-1-C-6 , polycyclic aromatic hydrocarbons (PAHs), and condensed species, were formed in larger amounts in phi=3.03 flame with respect to phi=2.42 flame. In richer conditions, aromatic species including benzene, PAHs, and condensed species reached aconcentration level about three times as large as in leaner conditions. In spite of the much larger amount of PAH and, in general, of high molecular weight species considered soot precursors, in richer conditions soot concentration was only about twice the soot concentration measured in relativelyleaner conditions. PAH distribution and condensed species chemical properties were found to be unaffected by equivalence ratio increase under the investigated conditions.