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

Comprehensive analysis of the effect of the presence of excited singlet oxygen molecules O-2(a(1) Delta g) 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+O-2(X-3 Sigma(-)(g)) and H2S+O-2(a(1) Delta(g)) 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 O-2(a(1) Delta(g)) 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 (T-0 = 600-800 K), and to increase the flame speed. The major effect is observed for the fuel-lean and stoichiometric mixtures. So, at phi = 0.6, the presence of 5% O-2(a(1) Delta(g)) 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. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.