On the growth of Polycyclic Aromatic Hydrocarbons (PAHs) in a coflow diffusion flame of ethylene

A wide of range of PAH of different structures were measured along the centerline of a coflow diffusion flame of ethylene using GC/MS, allowing for a previously not possible detailed analysis of potential formation routes. The experimental results showed that the difference in reactivity of the sites of a PAH where growth took place limited the formation of benzenoid PAH at high temperatures. This difference in reactivity led to the formation of PAH with a five-membered ring at high temperatures. The recombination of PAH radicals could not be favored in this flame which explained the small amounts of alkyl-bridged PAH at high temperatures. PAH with an alkyl sidechain were favored only along the free edge. Alkyl substituted PAH were formed in low amounts and decreased with an increase in temperature. Methylene-bridged PAH could led to faster growth of large PAH and become significant at intermediate temperatures. The target flame was simulated using state-of-the-art models. The simultaneous measurements of both PAH and soot allowed for a comprehensive assessment of the chemical mechanisms and soot aerosol dynamics. The assessment suggested that both the chemical mechanisms and the soot aerosol dynamics need further improvements.