On the influence of singlet oxygen molecules on the NOx formation in methane-air laminar flame

• Published in: Proceedings of the Combustion Institute Vol. 34; no. 2; pp. 3277 - 3285
• Main Authors: Starik, A.M., Kuleshov, P.S., Sharipov, A.S., Strelnikova, V.A., Titova, N.S.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 2013
• Subjects: Chain-branching reactions; Excited oxygen molecules; Methane-air mixture; Nitric oxide; Chain-branching reactions; Methane-air mixture; Nitric oxide; Excited oxygen molecules
• ISSN: 1540-7489; 1873-2704
• DOI: 10.1016/j.proci.2012.10.003

Effect of the presence of singlet oxygen molecules O2(a1Δg) on nitric oxide formation in the CH4-air laminar flame is analyzed with the use of extended kinetic model. The developed model is based on the methane oxidation mechanism developed previously for the case of the abundance of excited O2 molecules in the mixture and incorporates new ab initio studies of N+O2(a1Δg) and N2+O2(a1Δg) reaction channels. It was revealed that the reactivity of O2(a1Δg) molecule in the reaction with atomic nitrogen is significantly smaller than that of normal ground state oxygen. Numerical simulations show that, despite this fact, the abundance of singlet delta oxygen in the CH4-air mixture results in an increase in the concentration of nitric oxide in the combustion exhaust. The major relative rise of NO concentration is observed for the fuel-lean mixture and can mount to 30% at the presence of 5% O2(a1Δg) in molecular oxygen. This phenomenon is due to the appearance of additional amount of atomic oxygen in the flame via acceleration of chain-branching in the mixture by adding O2(a1Δg) molecules. It is shown that, due to extending the flammability thresholds via abundance of singlet delta oxygen in the CH4-air mixture, it is possible to reduce significantly the NO emission without diminishing the flame speed.