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, τi, 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, τi 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 τi can be represented by τi=k̄−1([O2]i[CO]i)−12,with k̄−1=6.4×10−15(±25%)×exp[40 000(±15%)/RT]mole·sec cm−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.