A shock tube study of methane decomposition using laser absorption by CH 3

Abstract

The pyrolysis of methane was studied in the temperature range 1790 to 2325K, pressure range 0.56 to 3.76 atm, and CH4 mol fraction range 200 ppm to 1.0% in reflected shock wave experiments. The rate coefficient, k1, for methane decomposition, CH4 + Ar → CH3 + H + Ar was determined by comparing measurements of CH3 concentrations made using a narrowlinewidth CW laser absorption technique with CH3 concentrations calculated using a reaction mechanism adapted from Miller and Bowman (1989). Reactant mixture compositions and the experimental conditions were selected so that the early-time CH3 concentration profiles were sensitive almost exclusively to the rate of reaction (1). The least-squares fit to 25 early-time CH3 profiles yielded a bimolecular rate coefficient expression k1 = 8.17 × 1016 exp (−44030/T[K])[cm3/mol/s]. The measured bimolecular rate coefficients were found to be independent of pressure in the range studied. The present determination is similar to the previously-published values summarized by Cobos and Troe (1990) and differs from the recent determination of Klemm et al. (1991).