Enhancement of hydrogen sulfide oxidation via excitation of oxygen molecules to the singlet delta state

Abstract

Comprehensive analysis of the effect of the presence of excited singlet oxygen molecules O2(a1Δg) on the enhancement of ignition and combustion in the H2S–air mixture is conducted on the basis of developed reaction mechanism. This mechanism incorporates the results of ab initio calculations of potential energy surfaces for the H2S+O2(X3Σg−) and H2S+O2(a1Δg) systems. The existing experimental data on the ignition delay and laminar flame speed in the H2S–air mixture are used for the validation of the constructed reaction mechanism. It has been demonstrated that the abundance of O2(a1Δg) molecules even in small amounts (only 1% in total oxygen) could substantially intensify the chain-branching in the H2S–air mixture. This allows one to reduce notably the ignition delay, especially at low initial temperatures (T0 = 600–800K), and to increase the flame speed. The major effect is observed for the fuel-lean and stoichiometric mixtures. So, at ϕ = 0.6, the presence of 5% O2(a1Δg) molecules in total oxygen increases the flame speed by 25%. Kinetic mechanisms, responsible for shortening the ignition delay and for the increase of flame speed, are discussed in a detailed manner.