Study on soot evolution under different hydrogen addition conditions at high temperature by ReaxFF molecular dynamics

The physical and chemical properties evolution of soot particles was studied by ReaxFF MD simulation. The dimerization of PAHs, nucleation and coagulation, and graphitization from hydrocarbons to the final soot nanoparticle were investigated, and the chemical effects of the hydrogen addition on the formation mechanism of primary soot nanoparticle was explored by considering important polycyclic aromatic hydrocarbons (PAHs) in ethylene flames under high temperatures. The results obtained reveal that, in the first stage, the activated aliphatic hydrocarbons mainly grow into a large ring through the chain growth reactions, and then gradually form PAH-like molecules with inner ring bridging instead of directly generating the five or six-carbon ring structures. Hydrogenation effectively inhibited the soot nanoparticle nucleation at all stages. Due to a large number of vinyl and acryl groups attacked by the hydrogen to decarbonize and produce methane, a rapid decrease of the formation and growth rate of the PAHs was observed. With the increase of hydrogen, the nucleation and surface growth rate of soot particles are slowed down due to lose activity.