Third-body interactions in the oscillatory oxidation of hydrogen in a well stirred flow reactor

Abstract

Stationary and oscillatory ignition states have been studied in mixtures of hydrogen and oxygen under flowing conditions in a non-adiabatic, well stirred vessel. The conditions bridge the region between ‘slow reactions’ and ignition at the second (p–T_a) limit. An oscillatory mode of ignition is observed at the boundary; it gives way to a stable state corresponding to complete reactant consumption at higher temperatures within the ignition peninsula. The period of oscillations is governed by the composition of the reaction mixture. The effects on the period of addition of diluents (He, Ar, N₂, CO, CO₂ and C₃F₈) and changes in the H₂/O₂ ratio have been studied by monitoring changes in temperature and light output from the system. The global behaviour of these systems can be modelled successfully using the accepted H₂/O₂ reaction scheme. Comparison of model predictions and experimental findings leads to values of the third-body efficiencies of He, Ar, N₂, CO, CO₂ and C₃F₈ relative to H₂ of 0.35, 0.35, 0.45, 0.40, 0.90 and 2.90, respectively, in the reaction H + O₂+ M → HO₂+ M. With some mixtures hysteresis and birhythmicity are observed in their oscillatory behaviour; these effects too can be modelled successfully.