Investigation on the reaction mechanism of methane combustion near flammability limits at elevated pressures and temperaturaes

Combustible gas explosions may occur at elevated pressure and temperature of wellbore conditions. To better understand and protect against wellbore explosion, it is necessary to study the combustion mechanism of methane at elevated pressure and temperature conditions. In this study, combustion mechanisms near the stoichiometric concentration as well as the flammability limit were investigated using a one-dimensional premixed laminar flame speed model based on the GRI 3.0 mechanism. The effects of initial pressure and initial temperature on flame temperature were analyzed. The main free radicals and reactions at different conditions were determined by sensitivity analysis. The reaction rates of the main reactions were comprehensively analyzed with previous experimental results of the flammability limit at different conditions. The mechanism of how initial pressure and initial temperature affects the flammability limit was determined. The results showed that the radical HO₂ and its involved reaction HO₂+CH₃[dbnd]OH + CH₃O play a crucial role in the methane combustion process at elevated pressure and temperature conditions. The initial pressure and initial temperature quantitatively affect the flammability limit mainly by affecting the reaction rates of the main reactions.