Comprehensive analysis of combustion initiation in methane–air mixture by resonance laser radiation

Abstract

The subject of this study is the comparative analysis of the kinetic mechanisms that proceed in a methane–air mixture when O2 molecules are excited to the electronic state by laser photons with wavelength λI = 762.346 nm and when O2 molecules dissociate due to the absorption of laser radiation with λI = 193.3 nm. The efficiencies of both methods of combustion initiation are compared with each other and against the method of laser-induced thermal ignition. Numerical simulation shows that for methane–air mixture the excitation of O2 molecules to the state is more effective in reducing the induction time and in lowering the ignition temperature than the method of photodissociation of O2 molecules by laser radiation at 193.3 nm wavelength. In order to ignite a stoichiometric CH4–air mixture at identical temperature it is needed to supply twofold greater energy upon photodissociation of O2 molecules than in the case of O2 molecule excitation. However, both the laser-induced excitation of O2 molecules to the state and O2 molecule dissociation by laser photons with λI = 193.3 nm are much more effective in combustion initiation than the method based on heating the mixture by laser radiation.

Reaction pathways of producing and losing particles in atmospheric pressure methane nanosecond pulsed needle-plane discharge plasma

“…29 In addition, Starik et al have established the complete reaction mechanisms in CH 4 /O 2 and CH 4 / air. 30,31 Electron densities and electron temperatures calculated by the present model are slightly higher than the simulation results in Ref. 29, which should be attributed to the difference between the needle-plane discharge and the DBD.…”

Theoretical analysis of reaction kinetics with singlet oxygen molecules

“…One of the hot combustion topics today concerns the development of novel approaches to enhance ignition and combustion by means of electric discharge [5][6][7][8][9][10][11] or resonance laser radiation. [12][13][14] In these cases, the excited oxygen O Ã 2 molecules in singlet electronic states a 1 D g and b 1 S + g can sufficiently accelerate the formation of O, H atoms and OH radicals in combustible mixtures due to the lower activation barrier in endoergic reactions as compared to the ground state O 2 molecules, and thus, can intensify the chainbranching in oxy-fuel systems, shorten the induction time, and reduce the ignition temperature. In addition, the singlet oxygen molecules O 2 (a 1 D g ) and O 2 (b 1 S + g ) play a significant role in the middle and upper Earth's atmosphere and are responsible for the ozone formation.…”

O2(b1Σg+) Quenching by O2, CO2, H2O, and N2 at Temperatures of 300–800 K

“…Oxygen in the electronically excited state b 1 Σ g + is involved in various chemical, radiative, and energy-exchange processes in the atmosphere, oxygen-containing gas discharges, combustion, and the active medium of an oxygen–iodine laser (OIL) . Reactions with O 2 (b 1 Σ g + ) can produce chemically active atmospheric species such as odd-hydrogen (HO x ) or odd-nitrogen (NO x ) intermediates. , Airglow emission from the O 2 b 1 Σ g + –X 3 Σ g – transition (762 nm) contributes significantly to the radiation budget of the atmosphere .…”

“…Ignition and combustion enhancements in various mixtures by means of plasma or laser excitation of singlet states of oxygen (a 1 Δ g , b 1 Σ g + ) have been considered. Excitation of the O 2 (b 1 Σ g + ) state by laser radiation with wavelength λ = 762 nm has strong effects on the initiation of detonation in the supersonic flow of a H 2 /O 2 mixture …”