To reveal the combustion mechanism of coal mine methane with different oxygen concentration, a series of combustion experiments on the CH₄/O₂/N₂ blends were conducted at a cylindrical chamber. The influences of oxygen concentration on the flame structure, combustion pressure and flame instability of methane blends with different concentrations were analysed. The results show that lower oxygen concentrations cause inversions formed in the lower flame fronts of methane spherical flames by buoyancy effect. Since the effective Lewis number of CH₄/O₂/N₂ blends is always greater than 1 at different oxygen and methane concentrations, the Thermal-Diffusion instability does not promote spherical flame inversion. Moreover, the thinner flame thickness can promote the flame front sensitivity to stretching rate, which indicates that the thinner flame thickness the more easily to form a flame winkle affected by flame instability. The increase of oxygen concentration significantly enhances the combustion pressure and pressure rise rate of methane blends, while the reduction in methane concentration weakens the sensitivity of combustion pressure to oxygen concentration. In addition, spherical flame inversion attenuates the generation of quench expansion waves, thereby suppressing the methane pressure rise and maximum combustion pressure.

Coal mine methane; Spherical flame; Combustion pressure; Flame instability; Chemical kinetics