Study on soot nucleation and growth from PAHs and some reactive species at flame temperatures by ReaxFF molecular dynamics

The transformations from polycyclic aromatic hydrocarbons (PAHs) to polymers and finally to young soot were simulated under different initial conditions at flame temperatures using Reax-FF MD. At low temperatures, PAH heterogeneous nucleation is mainly through physical interactions, but these clusters are not stable at higher temperatures. The molecular dynamics simulation results at 1450 K suggested that soot growth at intermediate temperature and low radical concentration conditions mainly controlled by chemical reactions involving carbon addition directly, without hydrogen abstraction. Some branched chains can be added to the PAH edges and small PAHs grow into dimers, trimers, or larger molecules through combination with unsaturated aliphatic hydrocarbons. At higher temperatures, radical-molecule reactions, such as via the HACA mechanism, reactions of aryl radicals and aryl-acetylene, and radical-radical reactions involving the combination of two aryl radicals, are dominant in soot formation because of high radical concentrations.