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To investigate the mechanisms of haloalkanes in promoting and inhibiting explosions in methane-air mixtures, the halon alternatives of CHF 3 , C 3 HF 7 , and C 3 H 2 F 6 were selected as inhibitors. Experimental research was conducted in a 20-liter spherical explosion vessel to examine the promotional and inhibitory effects of these haloalkanes on methane-air mixtures. The adiabatic flame temperature, heat release rate, and concentrations of the key radicals were calculated. The results showed that C 3 H 2 F 6 , C 3 HF 7 , and CHF 3 all exhibited a dual effect, initially promoting and subsequently inhibiting explosions in fuel-lean methane-air mixtures. The critical explosion suppression volume fractions of C 3 HF 7 and CHF 3 were 1.5 times and 2.25 times that of C 3 H 2 F 6 , respectively, for the suppression of methane explosion at Φ = 1.2. Furthermore, C 3 HF 7 demonstrated a dual impact on the explosion of stoichiometric methane-air mixtures. From the perspective of reaction kinetics, for fuel-lean methane-air mixture (Φ = 0.8), a small volume of halogenated hydrocarbons led to an increase in the adiabatic flame temperature due to the heat release from critical fluorine-containing elementary reactions, thereby promoting the explosion. Under fuel-lean conditions, the introduction of a small volume of halogenated hydrocarbons led to an increase in the adiabatic flame temperature due to the heat release from critical fluorine-containing elementary reactions, thereby promoting the explosion. Simultaneously, these fluorine-containing reactions scavenged the key free radicals of H, O, and OH inhibiting the explosion process. These two effects competed with each other, ultimately determining the direction of the explosion process. [ABSTRACT FROM AUTHOR]

To prevent the explosion hazards of hydrogen energy, in this work, the deflagration behaviors of H 2 -air mixtures at equivalence ratios from 0.6 to 1.4 under the effects of C 3 HF 7 and CO 2 are experimentally investigated. Deflagration pressure and time indexes at ambient pressure and temperature are obtained. The characteristic parameters of chemical kinetics are analyzed according to a detailed mechanism. The results suggest that C 3 HF 7 has dual effects of pressure enhancement and suppression with the rising volume ratio in fuel-lean H 2 -air mixtures. It is the F-involved reactions that govern the exothermic process, facilitate the comprehensive conversion of crucial free radicals, and augment the exothermicity of the principal reaction, leading to the elevation in peak pressure. Dilution of CO 2 would decrease the heat release rate of the F-involved reactions and reduce the explosion enhancement effect of C 3 HF 7. The results of this work are beneficial to the formulation of mitigation measures for hydrogen explosions. [Display omitted] • C 3 HF 7 plays dual effects of explosion promotion and suppression on fuel-lean hydrogen-air mixtures. • This deflagration enhancement effect of C 3 HF 7 is attributed to the F-involved reactions. • CO 2 would decrease the heat release of F-involved reactions and reduce the explosion enhancement effect. [ABSTRACT FROM AUTHOR]

To investigate the effect of venting diameter and static activation pressure on the explosion venting behavior of hydrogen-air mixtures, tests were performed utilizing the explosion venting test platform. The pressure and flame propagation characteristics under different venting diameters (30–70 mm) and pressures (0.1–0.4 MPa) were experimentally examined, and numerical calculation was employed to analyze the explosion venting characteristics of hydrogen at a stoichiometric ratio. Compared to fuel-lean and fuel-rich hydrogen conditions, the first peak pressure within the container is maximal under the hydrogen-air mixtures at a stoichiometric ratio. Under stoichiometric and fuel-rich hydrogen-air mixtures, pressure peak structures inside the container are both bimodal. When D = 30 mm, as P stat is increased from 0.1 to 0.2 MPa, P max11 increases. However, when P stat exceeds 0.2 MPa, with the increase of P stat , P max11 remains at the level of 0.69 MPa, reaching the "venting bottleneck". The discovery of this phenomenon is crucial for the research and development of the venting device for hydrogen storage equipment. Numerical simulations indicate the formation of the second peak pressure inside the container is primarily attributed to the intense obstruction of venting by secondary explosions within the duct. • The pressure in the container appears "venting bottleneck" phenomenon. • The venting diameter affects the "venting bottleneck" phenomenon. • The pressure waves reflected trigger the peak pressures in the duct. [ABSTRACT FROM AUTHOR]