Effect of flammable gases produced from coal smoldering on methane explosion limits under nitrogen dilution in coal mines

The methane released from the coal combines with the air to form a very dangerous explosive mixture, which will be aggravated by the combustible gases of CO and H₂ produced from the coal smoldering in coal mine. In this work, the effect of binary CO-H₂ mixtures on methane explosion limits is investigated, and the inhibitory effect of N₂ dilution on mixed combustible gases is analyzed via experiments and simulations subsequently. The methane explosion limits under different operating conditions are studied using a standard 20-L spherical chamber. The addition of the binary gas of CO-H₂ mixtures exhibit a reduction for LEL and UEL of methane explosions, and remarkably enhance methane explosion risk. Moreover, the addition of binary gas mixture leads to a larger expansion range of the explosion triangle, compared to single CO conditions. In the simulations, the sensitivity of dominant elementary reactions on the H, O, and OH free radicals are analyzed based on the GRI mech 3.0 mechanisms. The inerting effect of N₂ in CH₄/CO/H₂ component system is manifested in the combustion reaction kinetics of R53, R98, and R158, showing a significant inhibitory effect on the generation of these radicals during explosive process. The research results are helpful to understand the hazards of methane explosion in the coal fire area, and have certain guidance for the treatment of methane explosion in coal mine.