The effect of liquid fuel doping 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 incandescence (LII) and laser-induced fluorescence (LIF) techniques were used to measure the relative soot volume fractions and PAH concentrations, respectively. The experimental results show that the PAH and soot formation in toluene/ethylene mixture flame was larger than the other combinations, which implies that a small amount of toluene doping can effectively promote the PAH and soot formation in ethylene flames. Numerical analysis shows that the addition of liquid fuel can lead to higher levels of aromatic ring formation, and the higher aromatic ring formation in the toluene mixture than the benzene doping flame was successfully predicted. The reaction path analysis showed that the toluene route facilitates the pyrene production which promotes larger PAH production in toluene doping flame.