Investigation of the Suppression of Methane Explosions by N2/CO2 Mixtures in Different Proportions

To characterize the inerting effect of N2/CO2 mixtures containing various proportions on methane-air explosions, a series of experiments were conducted in a 20 L spherical vessel under the normal temperature (25 degrees C) and normal pressure (101 kPa). Six concentrations (10, 12, 14, 16, 18, and 20%) of N2/ CO2 mixtures were selected to analyze the suppression of methane explosion by N2/CO2 mixtures. The results indicated that the maximum explosion pressure (pmax) of methane explosions was 0.501 MPa (17% N2 + 3% CO2), 0.487 MPa (14% N2 + 6% CO2), 0.477 MPa (10% N2 + 10% CO2), 0.461 MPa (6% N2 + 14% CO2), and 0.442 MPa (3% N2 + 17% CO2) in the presence of the same N2/CO2 concentration, and similar decreases in the rate of pressure rise, flame propagation velocity, and production of free radicals were observed. Therefore, with the increase of CO2 concentration in the gas mixture, the inerting effect of N2/CO2 was enhanced. Meanwhile, the whole process of the methane combustion reaction was affected by N2/CO2 inerting, which was mainly attributed to heat absorption and dilution of the N2/CO2 mixture. N2/CO2 with a greater inerting effect leads to lower production of free radicals under the same explosion energy and a lower combustion reaction rate at the same flame propagation velocity. The findings of the current research provide references for the design of safe and reliable industrial processes and the mitigation of methane explosions.