Calculations with a numerical model incorporating detailed chemical kinetics, hydrodynamic motion, and energy transport in a turbulent flow reactor have been compared with experimental results of Dryer and Classman. A reaction mechanism, including 19 chemical species and 56 reactions, for the reaction of dilute moist carbon monoxide in air and of dilute methane in air was established for the temperature range 1000-1350 K. H02 and H202 were found to be important in the mechanism for both carbon monoxide and methane oxidation, and CH20, CH30, C2H6, and C2H4 were found to be important in methane oxidation. Important steps in the reaction mechanisms have been identified, and optimal values for some key reaction rates have been determined.The branching ratio between reaction 3, H + 02 = OH + O, and reaction 17, + 02 + = H02 + M, was found to be important in determining the length of the induction period in each experiment. At 1100 K the value determined for fc17 was 2.6 X 1016 cm6/(mol2 s). Decomposition reaction 7 for HCO, HCO + = + CO + M, was found to play a key role in methane oxidation, providing the major path for production of carbon monoxide. At 1100 K, k7 was found to be 2.4 X 1010 cm3/(mol s). Even though the reaction studied was extremely oxygen rich, recombination of methyl radicals and subsequent oxidation of the ethane thus formed was found to provide a major route for methyl radical destruction. The assumption that plug flow conditions prevail in the turbulent flow reactor was examined and found to be valid under most practical conditions.
The results of numerical calculations of methane oxidation are discussed and analyzed. A simple mathematical model of CO oxidation accounts for the superequilibrium concentrations of OH at late times. A similar model for the induction period shows that the equivalent activation energy does not equal that of any one elementary reaction, in agreement with experiment. The reactions during methane consumption are shown to be controlled by a balance between the rates of creation and consumption of radicals. This balance helps explain the importance of C2H6 formation and allows prediction of the sensitivity of the reaction mechanism to variation of rate constants.
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