Interactive mechanisms of CF3CHFCF3 with H2-CH4-air mixture explosion: A synergistic study using chemical kinetic simulation and density functional theory

[Display omitted] •CF3CHFCF3 reduced the laminar flame speed of H2-CH4-air mixtures.•Low volume fractions of CF3CHFCF3 introduced additional heat in lean-fuel flames.•CF3CHFCF3 prefersed 1,2-HF elimination over C–C cleavage under similar conditions.•The vital intermediate fluorinated olefin CF3CF = CF2 played a crucial role.•Minority fluorinated radicals reacted exothermically with reactive radicals. To ascertain the underlying thermal promotion mechanism of CF3CHFCF3 in H2-CH4-air mixture fires, a comphensive investigation was conducted using chemical knetic simulation and density functional theory (DFT) calculation. The findings indicate that promotion or inhibition effects are determined by both time sequence and thermal characteristics of the main control reactions. As for lean-fuel conditions (Φ = 0.6 and 0.8), CF3CHFCF3 decompose preferentially by 1,2-elimination reaction pathway generating CF3CH = CF2 rather than C–C bond cleavage reaction pathway when CF3CHFCF3 volume fraction is less than 4 %. The low-barrier addition reactions of CF3CH = CF2 double bond generate fluorine-containing radicals (e.g., CF3 and CF2). These fluorine-containing radicals release heat in the reaction with reactive radicals, thereby increasing the adiabatic flame temperature at lean-fuel flames. In the context of stoichiometric and rich-fuel (Φ ≥ 1.0) conditions, the rich reactant concentrations activate fluorine-containing radicals (e.g., CHFO, CHF3, and F) to inhibiting explosion reactions by continueously depleting reactive radicals, absorbing the combustion temperature, and generating stable molecules. Additionally, the results also show that the generated C3F7 presents exothermic properties, which is more apparently under lean-fuel conditions. Furthermore, it was observed that addition of CF3CHFCF3 can retard the explosive chain raction of H2-CH4-air mixture by competing H with CH4. These findings provide theoretical guidance for the selection of halogenation suppressants to address the possible hydrogen-doped natural gas fires.