Effects of N2/CO2 on explosion characteristics of methane and air mixture

• Explosion strength decreases with the volume fraction of N2/CO2 in the mixture.
• Limiting oxygen concentration decreases linearly with volume ratio of N2 and CO2.
• The flammability limits change with the volume fraction of N2/CO2 in the mixture.
• Volume fraction of CO2 in the mixture has an effect on explosion suppression effect.

An experimental apparatus for the methane and air mixture explosion with N2/CO2 in a closed vessel was set up. A series of experiments have been performed to analyze the effects of N2/CO2 on explosion strength, limiting oxygen concentration, flammability limits and explosion suppression. Results show that explosion strength decreases with the volume fraction of N2/CO2 in the mixture. Limiting oxygen concentration decreases linearly with the volume fraction of N2 in N2/CO2 mixture. The flammability limits change linearly with the volume fraction of N2/CO2 in the mixture. The higher the volume fraction of CO2 in N2/CO2 mixture, the better the explosion suppression effect is. Based on experimental data, fitted equations and diagrams are made to predict methane flammability limits with N2/CO2 under different volume fraction ratio of N2 and CO2. The research results can be used as a reference for the inerting treatment design of methane explosion protection in process industries.