Study on the instability and suppression mechanism of methane/air deflagration flame by inert gas-halogenated hydrocarbons.

• Compound inhibition mechanism of CF 3 I and CO 2 on CH 4. • Effects of CF 3 I and CO 2 on instability of CH 4 flame. • Physical and chemical effects of CO 2 and CF 3 I on CH 4. Natural gas is widely used, but explosions are highly destructive. This work uses a 20L spherical device to study the suppression effect of CF 3 I and CO 2 on 9.5 % CH 4 deflagration flame. The results show that the inhibitory effect of CF 3 I on the laminar burning velocity of methane is significantly better than that of CO 2. Mixing a small amount of CF 3 I into CO 2 can improve the explosion suppression effect. The addition of CO 2 and CF 3 I can inhibit the hydrodynamic instability and enhance the diffusional-thermal instability and the buoyancy instability of the flame. In general, the cellular structure of the flame gradually disappears with the addition of CO 2 and CF 3 I, while the flames float upward. Through numerical simulation analysis, it was found that CO 2 basically does not change the combustion reaction path of methane, but mainly reduces the concentration of active free radicals, rate of production and heat release rate through the inerting effect. CF 3 I can consume H, O and OH free radicals through the HI cycle reaction and CF 3 I decomposition reaction, changing the methane combustion reaction path, reducing the heat release rate and rate of production, especially the inhibition of H free radicals. Through quantitative analysis, the physical inhibitory effect of CO 2 accounts for more than 80 %, and the chemical inhibitory effect of CF 3 I accounts for more than 60 %. When the total amount of explosion suppressant is 8 %, the amount of CF 3 I mixed in CO 2 increases from 0 to 1.5 %, and the proportion of chemical suppression effect increases from 10 % to 60 %. It shows that the inhibition mechanism of CO 2 is mainly physical inerting, and the main inhibition mechanism of CF 3 I is chemical inhibition. Mixing a certain amount of CF 3 I into CO 2 can simultaneously exert the inhibitory effect of CO 2 on reducing oxygen and the effect of CF 3 I on reducing active free radicals. [ABSTRACT FROM AUTHOR]