Experimental and numerical investigation of liquid fuel mixing effect on PAH and soot formation in counterflow ethylene diffusion flames

The characteristics of the formation of polycyclic aromatic hydrocarbon (PAH) and soot in counterflow diffusion flames of n-Heptane/ethylene, ethanol/ethylene, benzene/ethylene, and toluene/ethylene mixtures were investigated experimentally. Laser-induced fluorescence (LIF) and laser-induced incandescence (LII) techniques were used to measure relative soot volume fractions and PAH concentrations, respectively. The experimental results show that the PAH and soot formation was greater for the toluene/ethylene mixture flame than for the other combinations. This implies that a small amount of toluene has an effect on PAH and soot. Numerical analysis of the reaction path shows that the addition of n-Heptane and toluene increases the methyl and H radical production rate, resulting in higher levels of C₆H ₆ formation. For the toluene mixture flames, the concentration of methyl (CH₃) radical was greater than that of the benzene mixture. The results imply that benzene (C₆H₆) is important for soot formation, whereas C1-chemistry is crucial for enhanced benzene formation in the mixture flames.