Simulation of ignition and combustion of a homogeneous methane-air mixture under local thermal and photochemical actions

Ignition and combustion of a homogeneous stoichiometric methane-air mixture under simultaneous local thermal and photochemical actions, resulting in the formation of either $\mathrm{O}_2(a^1\Delta_g)$ molecules or $\mathrm{O}$ atoms, are numerically simulated. A two-dimensional unsteady multicomponent approach with the use of the known detailed kinetic mechanism of methane oxidation, which takes into account reactions with participation of electronically excited oxygen molecules $\mathrm{O}_2(a^1\Delta_g)$ and $\mathrm{O}_2(b^1\Sigma_g^+)$, is applied. It is shown that an additional photochemical action ensures ignition of the mixture in situations where the thermal action alone is insufficient. Moreover, for identical energy inputs, a higher burning rate at the initial stage is observed in the case of generation of oxygen atoms. This method of the photochemical action seems to be more effective from the viewpoint of combustion initiation. The computed results on propagation of turbulent combustion are in reasonable agreement with available experimental data.