Oxidation of CO. II. Influence of H2 on the Induction Period Preceding Rapid CO2 Formation in Shock-Heated CO–O2–Ar Mixtures

Abstract

The influence of small amounts of hydrogen on the induction period, τ_i, preceding rapid CO oxidation in argon‐diluted CO–O₂ mixtures, has been studied at temperatures between 1500° and 3300°K and at pressures between 0.4 and 1.6 atm behind incident shock waves. The initial reaction regime was investigated by using spectral portions of the CO₂‐ν₃ fundamental and CO‐fundamental infrared bands and spectral portions of the ``CO flame emission.'' Up to 0.13% hydrogen was used in dilute mixtures containing between 5% and 20% O₂ and between 10% and 20% CO. For constant temperature and hydrogen concentration, τ_i is inversely proportional to the square root of the product of the mole concentrations of (CO)_i and (O₂)_i of the unreacted gas behind the shock front. The induction period is generally decreased with increasing amounts of hydrogen present; however, above 2400°K for an initial hydrogen concentration of 0.011%, this effect becomes negligible. Under the latter conditions, the dependence on temperature of τ_i can be represented by $${\tau }_i{\mathrm{=k̄}}^{\text{−1}}\mathrm{([}{\mathrm{O}}_2{]}_i[\mathrm{CO}{]}_i{)}^{-\frac{1}{2}},$$ with $${\mathrm{k̄}}^{\text{−1}}{\text{=6.4×10}}^{\text{−15}}\text{(±25\%)×}\exp \text{[40 000(±15\%)/RT]}\mathrm{mole}·{\mathrm{sec\; cm}}^{\text{−3}}.$$ It is demonstrated that a modified Haber—Semenov mechanism can be used to account qualitatively for the observed dependence on hydrogen of the induction period.