Oxidation of Carbon Monoxide/Methane Mixtures in Shock Waves

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Abstract
CO/O2/Ar mixtures with mole fractions of 4%/2%/94% and containing 180 or 500 ppm CH4 were investigated in incident shock waves at about 5×1017 particles/cc total concentration. The reaction was followed by measuring infrared emissions from CO2 and CO for about 1500‐μsec particle time over the temperature range 1750–2575°K. The rate of CO2 production initially increased exponentially and then became constant after several percent conversion. The observed [CO2]–time profiles were compared to those calculated by numerical integration on an IBM 360/65 computer. It was possible to quantitatively describe the observations in terms of a mechanism with the following main reactions (rate constants are in units of cc molecule−1·sec−1): CO+O2=CO2+O; k1 = 2.0 × 10−11exp(− 60 000 / RT), OH+CO=CO2+H; k4 = 1.9 × 10−12exp(− 1030 / RT), H+O2=OH+O; k6 = 4.2 × 10−10exp(− 16 800 / RT), CH4+M=CH3+H+M; k7 = 2.7 × 10−6exp(− 103 000 / RT), O+CH4=CH3+OH; k9 = 2.6 × 10−10exp(− 7950 / RT), O2+CH3=CH2O+OH; k12 = 5 × 10−11exp(− 10 000 / RT), O+CH3=CH2O+H; k13 = 1 × 10−10, O+CH2O=H+CO+OH; k16 = 1 × 10−10, in addition to several relatively unimportant reactions involving chain carriers and O2 with CH4 and trace impurities H2 and H2O. Values of k4 and k6 were taken from the literature; others were determined by finding the best fit of the calculated [CO2]–time profiles to the experimental ones. Consequently, some change of the individual rate parameter values is possible without losing reasonable agreement with experiments. However, a substantial disagreement between the above values of k7 and k12 and literature values is attributed to the earlier workers' use of only the induction period data. Methane was found to be more effective than either H2 or H2O in promoting the branching chain oxidation of CO. Extending these observations, it is pointed out that extremely small concentrations of organic compounds can strongly influence many features of the CO/O2 system.