Mechanism of sulfur chemiluminescent emission in pulsed flames

Time-resolved light emission from an atmospheric pressure hydrogen/air pulsed propagated flame doped with a small concentration of SO2 was measured. The main idea of the pulsed flame approach is to exchange the usual continuous flame with an unstable pulsed propagating flame where flashback occurs repetitively. The use of pulsed flame instead of the usual continuous one allows us to replace space measurements by time-resolved experiments. This approach was very successful in constructing a pulsed flame photometer molecular detector. The emission from electronically excited sulfur molecules is dramatically delayed after the short background pulse associated with OH* radical emission. The mechanism responsible for this delay is proposed and the results of numerical calculations based on a simple model of isotropic explosion are shown. Comarison of the experimental results to calculations indicates that the main reaction which forms the electronically excited sulfur molecules is the recombination of sulfur atoms. The proposed mechanism accounts for the main experimental evidence: a dependence on the sulfur concentration, emission quenching upon the addition of hydrocarbons, and others.