The flammability limits and explosion behaviours of hydrogen-enriched methane-air mixtures

The effects of hydrogen(H2) on the macroscopic explosion parameters and microscopic chemical kinetics of methane(CH4)-air mixtures were investigated. First, the effect of H2 on the flammable limit of CH4 was studied with a. standard test device. Second, the explosion characteristic parameters of CH4-H2-air mixtures were measured in a standard 20-L spherical chamber, including the maximum explosion pressure, maximum pressure rise rate and combustion time. Finally, based on the GRI mech 3.0 and USC mech 2.0 mechanisms, the effect of H2 on the chemical kinetics of CH4-air mixtures was studied. The results reveal that the flammable limit of CH4 is expanded and the explosion risk value is enhanced with the addition of H2, and more inert gas is required to inertize CH4. The explosion intensity of the CH4-air premixed gas rises after H2 addition in the fuel-lean state. The explosion intensity first increases and then decreases with increasing H2 addition under stoichiometric conditions. The addition of H2 under fuel-rich conditions reduces the explosion intensity of the premixed gas. Moreover, under the three CH4 conditions, the main elementary reactions affecting the sensitivity and production rate of the key free radicals (H, O and OH) are the same, and as the H2 addition amount increases from 0% to 2%, the sensitivity coefficient of the elementary reactions accordingly increases.