Experimental and kinetic modeling evidences of a C7H6 pathway in a rich toluene flame.

The structure of a laminar, premixed, and one-dimensional toluene-oxygen-argon (9.9 mol % C(7)H(8), 44.5 mol % O(2), and 45.6 mol % Ar) flame, with an equivalence ratio of 2 and burning at 36 Torr was analyzed by gas chromatography and molecular beam mass spectrometry (MBMS). Mole fraction profiles of 25 chemical species including permanent gases of combustion and first polycyclic aromatic hydrocarbons as naphthalene, methylnaphthalene isomers, biphenyl, and phenanthrene have been measured. A kinetic model based on recent literature data has been elaborated to compare with measurements. As suggested by recent theoretical studies, benzyl radical (C(7)H(7)) dissociation into fulvenallene (C(7)H(6)) + H and the reaction between C(7)H(6) and H giving cyclopentadienyl radical and acetylene have been included into the model. A comparison between experimental and predicted flame structures have allowed us to validate the kinetic model for rich toluene combustion. Moreover, MBMS measurements of mole fraction profiles corresponding to m/z ratios of C(7)H(7) and C(7)H(6) have permitted a specific validation of the theoretically postulated C(7)H(6) pathway in toluene flames.