Oxidation of Carbon Monoxide Mixtures with Added Ethane or Azomethane Studied in Incident Shock Waves

Abstract

CO/O₂/Ar mixtures of varying composition containing small concentrations of ethane or azomethane were investigated in incident shock waves at about ${\text{5.0× 10}}^{17}$ particle/cc total concentration. The reaction was followed by measuring the infrared emissions from CO₂ and CO for about 1700-μ sec particle time over a temperature range 1400–2200°K. For all mixtures, the rate of CO₂ production initially increases exponentially and then becomes constant after several percent conversion. The observed $[{\mathrm{CO}}_2\mathrm{]-}$ time profiles were compared to those obtained by numerical calculation. For the CO/O₂Ar mixtures containing either ethane or azomethane it was possible to describe the observations quantitatively in terms of a mechanism with the following main reactions (rate constants are in units of cubic centimeters/particle·second): $${\mathrm{CO+O}}_2\to {\mathrm{CO}}_2\mathrm{+O}{\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}k}}_1{\text{=2.0× 10}}^{\text{−11}}\exp \text{(−60\hspace{0.17em}000/RT),}$$ $${\mathrm{C}}_2{\mathrm{H}}_6\mathrm{+M}\text{→2}{\mathrm{CH}}_3\mathrm{+M}{\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}k}}_2{\text{=4.0× 10}}^{\text{−3}}\exp \text{(−88\hspace{0.17em}000/RT),}$$ $${\mathrm{CH}}_3{\mathrm{+O}}_2\to {\mathrm{CH}}_2\mathrm{O+OH}{\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}k}}_4{\text{=2.0× 10}}^{\text{−12}}\exp \text{(−12\hspace{0.17em}500/RT),}$$ $${\mathrm{CH}}_3\mathrm{+O}\to {\mathrm{CH}}_2\mathrm{O+H}{\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}k}}_5{\text{=5.75× 10}}^{\text{−11}}\exp \text{(−3\hspace{0.17em}200/RT),}$$ $${\mathrm{CH}}_2\mathrm{O+O}\to \mathrm{CO+H+OH}{\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}k}}_6{\text{=1× 10}}^{\text{−10}},$$ $$\mathrm{CO+OH}\to {\mathrm{CO}}_2\mathrm{+H}{\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}k}}_7{\text{=1.5× 10}}^{\text{−12}}\exp \text{(−1\hspace{0.17em}000/RT),}$$ $${\mathrm{H+O}}_2\to \mathrm{OH+O}{\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}k}}_8{\text{=4.2× 10}}^{\text{−10}}\exp \text{(−16\hspace{0.17em}790/RT),}$$ in addition to several relatively unimportant reactions involving chain carriers, O₂ and C₂H₆. The values for k₁, k₅, and k₈ were taken from the literature and the others were determined by finding the best fit of the $[{\mathrm{CO}}_2\mathrm{]-}$ time profiles to the experimental data.