Influence of pressure and dilution gas on the explosion behavior of methane-oxygen mixtures

Abstract

This study investigates the influence of initial pressure (P0) and dilution gas (N2, CO2, He, or Ar) on the explosion behavior of CH4-O2 mixtures. Spherical premixed flames in a 20 L spherical vessel are recorded by high-speed schlieren photography. The explosion parameters, explosion duration (τe), maximum explosion pressure (Pmax), maximum explosion pressure change rate ((dP/dt)max), flame speed, burning velocity, and Markstein length, are experimentally investigated at various pressures up to 250 kPa and at room temperature (280 ± 3 K). The experimental results show that Pmax and (dP/dt)max increase linearly with P0. The influence on the explosion intensities, (dP/dt)max, and flame speed, from high to low with the dilution is in the order of CO2, N2, Ar, and He, which indicates that CO2 and N2 more significantly inhibit CH4-O2 explosion. The results suggest that CO2 not only has a strong endothermic ability and reacts with H, but also changes the active free radicals to molecules due to three-element collision. The experimental phenomena are explained and validated by the results from the Chemkin package using two detailed mechanisms, indicating that (dP/dt)max is closely related to the content of H, O, OH, and CH3. The cellular instability is analyzed by the flame thickness and Markstein length, and it becomes more obvious as the flame thickness and Markstein length decrease. The buoyancy instability, Rayleigh-Taylor instability, and a series of phenomena due to the dilution of CO2 are analyzed. The maximum explosion pressure and flame speed decrease significantly with the addition of CO2 into CH4-air mixtures, and CO2 affects the generation of flame. The buoyancy instability of CH4-air mixtures with CO2 addition is examined. The experimental results contribute to a deeper understanding of the explosion behavior of CH4-O2 mixtures and the dilution effect of other gases on it.