Numerical interpretation of oscillatory glow and ignition during carbon monoxide oxidation in a well-stirred flow reactor

Abstract

Numerical results are presented which give very satisfactory simulations of the oscillatory glow and ignition phenomena that accompany the thermal oxidation of carbon monoxide in a well-stirred flow vessel, when small proportions of hydrogen are present in the reactants. Quantitative comparisons are made with experimental results not only in relation to the amplitudes of oscillations but also the p–T_a regimes in which the different phenomena exist. The origins of oscillatory ignition are traced to the competition between the elementary reactions H + O₂→ OH + O and H + O₂+ M → HO₂+ M, as occurs in the oxidation of hydrogen itself. A change in overall third body efficiencies, that results from changes in composition as reaction proceeds, controls the switch from branching to non-branching reaction. The oscillatory glow originates in a different kinetic competition namely O + H₂→ OH + H and O + CO + M → CO₂+ M. In this case the switch from a branching to non-branching reaction is governed by the change in ratio of [H₂]/[CO] as reaction proceeds. The prediction of the oscillatory phenomenon is sensitive to the magnitude of the rate constant for termination.