Sulphur-dioxide-catalyzed recombination of radicals in premixed fuel-rich hydrogen + oxygen + nitrogen flames

Abstract

The rate of recombination of hydrogen atoms has been measured in a group of hydrogen + oxygen + nitrogen flames at 2000 K containing up to 1 % vol. sulphur dioxide. The catalysis of the rate of recombination by sulphur dioxide^1–3 is confirmed and at ∼2000 K is second order with respect to hydrogen atom concentration in agreement with ref. (3). The rate of catalysis is in accord with the reaction scheme: H + SO₂+ M ⇌ HSO₂+ M, equilibrium constant K₃(3) HSO₂+ H → H₂+ SO₂, rate constant, k₄(4) HSO₂+ OH → H₂O + SO₂, rate constant, k₅(5) in which the rate-determining steps are (4) and (5). Values for K₃k₄ and K₃k₅ are derived which, with an estimate for K₃, give k₄∼5 × 10^–12 and k₅ < 8 × 10^–12 ml molecule^–1 s^–1. Calculations on the effect of temperature on the overall rate of reactions (3), (4) and (5) show that the order of reaction with respect to hydrogen atom concentration changes to first order at lower temperatures in agreement with the interpretation of ref. (2) and probably also with that of ref. (1).