Effect of mixing methane, ethane, propane and propene on the synergistic effect of PAH and soot formation in ethylene-base counterflow diffusion flames

To elucidate the effect of fuel mixing on the formations of PAH and soot, four different types of fuels (methane, ethane, propane, and propene) were mixed to counterflow ethylene-base diffusion names. Planar laser-induced incandescence and laser-induced fluorescence techniques were employed to measure relative soot volume fractions and PAH concentrations, respectively. Small amount of ethane mixing in ethylene diffusion flame also exhibited the synergistic effect on PAH and soot formations. The mixing of propane in ethylene diffusion flame had more pronounced synergistic effect as compared to the propylene mixing when the mixture ratio was small. Since the decomposition reactions of ethane or propane could be the source of methyl radicals, such behaviors emphasize the role of methyl radicals on the formation of PAH and soot. Propargyl formation could be additionally enhanced by the reactions related to methyl radical, which can be the reason for the synergistic effect in the mixture flames of ethylene with propane or ethane. Numerical results on the concentrations of CH₃, C₂H₂, and C₃H₃ substantiated the importance of methyl radical on the formation of propargyl and thereby the synergistic effect in the formation of PAH and subsequent soot growth.