Chemical kinetic behaviors at the chain initiation stage of CH₄/H₂/air mixture

To intensively investigate chemical kinetic behaviors at the initial stage of CH₄/H₂/air mixture thoroughly, the density functional theory (CAMB3LYP/6-31 G) and a detailed mechanism (GRI-Mech3.0) were used to obtain kinetic and thermodynamic parameters. The reaction paths during the explosion process were analyzed, and the reaction rates of elementary reactions were compared with different ratios of CH₄/H₂/air mixture. The key reactions at the initiation stage of CH₄/H₂/air mixture explosion were determined, and their configurations were optimized. The reaction mechanism, reaction channel and configuration parameters of key reactions were obtained, which was verified by the intrinsic reaction coordinate (IRC) theory. Results show that H₂ addition increases the laminar burning velocity, while it shortens the ignition delay time of H₂/CH₄/air mixture. The addition of hydrogen greatly accelerated the explosion reaction from sample 1 to sample 4. Moreover, CH₄ still plays a key role at the chain initiation stage in H₂/CH₄/air mixture system; the addition of H₂ would not compete with CH₄ for triggering the explosion reaction, nor will it suppress the explosion of CH₄. H₂ could not replace or take precedence over the chain branching reactant (CH₂O) of CH₄ explosion to react with O₂. Besides, H₂ takes precedence over CH₄ in the process of chain transfer after the chain reaction beginning, although CH₄ has a distinct advantage in the chain initiation stage. The present results can provide theoretical guidance for the prevention and control of gas explosion, which may effectively reduce the explosion hazards.