Aromatic ring formation in opposed-flow diffusive 1, 3-butadiene flames

This paper is concerned with the formation of one- and two-ring aromatic species in near atmospheric-pressure opposed-flow diffusion flames of 1,3-butadiene (1,3-C₄H₆). The chemical structures of two different 1,3-C₄H₆/Ar–O₂/Ar flames were explored using flame-sampling molecular-beam mass spectrometry with both electron and single-photon ionization. We provide mole fraction profiles of 47 components as function of distance from the fuel outlet and compare them to chemically detailed modeling results. To this end, the hierarchically developed model described by Seidel et al. [16] has been updated to accurately comprise the chemistry of 1,3-butadiene. Generally a very good agreement is observed between the experimental and modeling data, allowing for a meaningful reaction path analysis. With regard to the formation of aromatic species up to naphthalene, it was essential to improve the fulvene and the C₅ chemistry description in the mechanism. In particular, benzene is found to be formed mainly via fulvene through the reactions of the C₄H₅ isomers with C₂H₂. The n-C₄H₅ radical reacts with CH₃ forming 1,3-pentadiene (C₅H₈), which is subsequently oxidized to form the naphthalene precursor cyclopentadienyl (C₅H₅). Oxidation of naphthalene is predicted to be a contributor to the formation of phenylacetylene (C₈H₆), indicating that consumption reactions can be of similar importance as molecular growth reactions.