PAH laser diagnostics and soot particle dynamics in gasoline co-flow flames doped with n-butanol

As a carbon-neutral fuel, bio-butanol mixed with gasoline has become a potential decarbonization method in transportation field. In this work, the effects of n-butanol addition to gasoline on PAH and soot formation were investigated experimentally and numerically. As n-butanol ratio increases, flame lift-off height, flame height and OH/CH chemiluminescence intensity decrease gradually. The n-butanol addition has inhibitory effect on PAH with different sizes, and the inhibitory effect increases with the increasing aromatic-ring size. As ring size increases, the high concentration region gradually evolves from the center of upper flame to the two wings of downstream flame. The primary particle size and number density show a monotonically decreasing trend with n-butanol ratio, attributing to the significant decrease of nucleation and surface growth rate. For particle surface growth, the decreasing trend of PAH condensation is higher than that of HACA with the n-butanol ratio. The contribution of HACA to particle growth increases with n-butanol ratio, and replaces PAH condensation as the main mechanism when n-butanol ratio exceeds 60%. For particle oxidation, n-butanol addition leads to a slight increase in OH oxidation rate and a significant decrease in O2 oxidation rate, while O2 oxidation is always the dominant mechanism for particle oxidation.