Combustion and Flame, Vol.135, No.1-2, 171-183, 2003
Investigation of stoichiometric methane/air/benzene (1.5%) and methane/air low pressure flames
Benzene depletion in a laminar premixed flat stoichiometric low-pressure methane/air/benzene (1.5%) flame was investigated using a recently developed kinetic model that has been tested for low-pressure combustion of acetylene, ethylene, and benzene. Experimental flame structures of two stoichiometric methane/air flames (v = 34.2 cm s(-1), 5.33 kPa) with and without the addition of 1.5% of benzene were measured previously by means of molecular beam sampling using mass spectrometry as well as gas chromatography coupled to mass spectrometry as analytic tools. Model computations were conducted using the Premix code within the Cheinkin software package. Experimental temperature profiles were used as input. The analysis of rates of production of selected species allowed for the identification of major formation and depletion pathways. The predictive capacility of the model was assessed in both flames. Good to excellent agreements between predictions and measured mole fraction profiles were obtained for reactants, intermediates, and products such as methane, O-2, methyl, H, OH, CO, CO2. and H2O. Benzene depletion and the formation and consumption of intermediates such as cyclopentadiene were predicted correctly. According to the model, methyl is exclusively formed by hydrogen abstraction from methane and subsequently oxidized by reaction with 0 to fonnyl, (1) CH3 + O reversible arrow HCO + H-2, and formaldehyde, (2) CH3 + O reversible arrow CH2O + H, the latter channel being the dominant one, Benzene consumption occurred mainly by hydrogen abstraction with OH and H as reactant but also the contribution of its oxidation by 0 to phenoxy was significant. Phenol and phenoxy chemistries are strongly coupled, unimolecular decay of phenoxy to cyclopentadienyl radicals and CO is the dominant consumption route. Small PAH are predicted to be formed in the reaction zone, followed by complete depletion in the postflame region. The pressure dependence of the dominant dimethylether formation (32) CH3 + CH3O reversible arrow CH3OCH3 was found to be significant and assessed by means of Quantum Rice-Ramsperger-Kassel (QRRK) analysis. (C) 2003 The Combustion Institute. All fights reserved.