Benzene formation in premixed fuel-rich 1,3-butadiene flames

Detailed kinetic modeling and flame-sampling molecular-beam time-of-flight mass spectrometry are combined to unravel important pathways leading to the formation of benzene in a premixed laminar low-pressure 1,3-butadiene flame. The chemical kinetic model developed is compared with new experimental results obtained for a rich (ϕ = 1.8) 1,3-butadiene/O2/Ar flame at 30 Torr and with flame data for a similar but richer (ϕ = 2.4) flame reported by Cole et al. [Combust. Flame 56 (1) (1984) 51-70]. The newer experiment utilizes photoionization by tunable vacuum-ultraviolet synchrotron radiation, which allows for the identification and separation of combustion species by their characteristic ionization energies. Predictions of mole fractions as a function of distance from the burner of major combustion intermediates and products are in overall satisfactory agreement with experimentally observed profiles. The accurate predictions of the propargyl radical and benzene mole fractions permit an assessment of potential benzene formation pathways. The results indicate that C6H6 is formed mainly by the C3H3 + C3H3 and i-C4H5 + C2H2 reactions, which are roughly of equal importance. Smaller contributions arise from C3H3 + C3H5. However, given the experimental and modeling uncertainties, other pathways cannot be ruled out.