CO Oxidation. I. Induction Period Preceding CO2 Formation in Shock-Heated CO–O2–Ar Mixtures

Abstract

The time history of the reaction processes occurring behind shock waves through argon‐diluted mixtures of CO and O₂ containing at most 1 ppm hydrogenous compounds has been studied spectroscopically between 1500° and 3000°K. The initial reaction regime was investigated by using spectral portions of the CO‐fundamental and CO₂−ν₃‐fundamental infrared bands and spectral portions of the ``CO‐flame emission.'' An induction period has been observed which precedes the onset of measurable electronic ground‐state CO<sub>2</sub> formation and atomic oxygen production. The induction period is inversely proportional to the square roots of the initial mole concentrations of CO and O<sub>2</sub>. The temperature dependence of the induction time for the initiation of CO<sub>2</sub> formation can be represented by an ``apparent activation energy'' which varies from 22 kcal/mole at 1500°K to 40 kcal/mole at 3000°K. Addition of 0.1% H₂ results in a decrease of the induction period and a decrease of ``apparent activation energy'' for the induction period. At temperatures above 2400°K, the contamination by hydrogenous species becomes negligible and the induction period is attributed to the mechanism $$\mathrm{CO}+{\mathrm{O}}_2\to {\mathrm{CO}}_2+\mathrm{O},$$ $$(\mathrm{M}\mathrm{+)}\mathrm{CO}+\mathrm{O}\mathrm{\to (}\mathrm{M}\mathrm{+)}{\mathrm{CO}}_2^{*},$$ $${\mathrm{CO}}_2^{*}+{\mathrm{O}}_2\to {\mathrm{CO}}_2\text{+20.}$$ Based upon this mechanism the rate coefficients for Reactions (I) and (II) were determined to be: $$k_{\mathrm{I}}{\text{=(3.5±1.6)×10}}^{12}\exp \text{[−(51 000±7000)/RT]\hspace{0.17em}}{\mathrm{cm}}^3\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}}$$ and $$k_{\mathrm{III}}{\text{=(1.4±1.1)×10}}^{14}\exp \text{[−(39 000±7000)/RT]\hspace{0.17em}}{\mathrm{cm}}^3\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}},$$ respectively, for 2400°K≤T≤3000°K.