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Experiments were conducted in a 2 m large duct with an internal diameter of 70 mm, to investigate the effects of the vent area and ignition position on pressure oscillations with different methane concentrations. The results showed that violent pressure oscillations occurred when methane concentrations were between 9.5 and 12 vol. % in the closed duct. End ignition was shown to dampen the pressure oscillations to a significant extent. In addition, vented explosions could also reduce the pressure oscillations where the amplitude of the pressure oscillations decreases with increasing vented area. For a vent area of 38.5 cm2, no pressure oscillations occurred in all tests. Central ignition produced the larger pressure peak only when the vent area was small. [ABSTRACT FROM AUTHOR]

The dynamic response study of explosion venting components is of great significance for the assessment of explosion disasters and the determination of damage. Based on the self-developed rectangular explosion venting device, a series of experimental investigations on the dynamic response and failure mode of calcium silicate vent plates under the methane explosion loads induced by a detonator were conducted. The results show that the vent plate mainly exhibits brittleness and presents a plastic hinge failure mode under the blasting loads. When the gas concentration is closer to the stoichiometric concentration, P 2 (the peak overpressure generated by the vent plate rupture) and its pressure rise rate dP 2 /dt are higher. Conversely, when the methane concentration is closer to the upper or lower limits of the explosion, the explosion load tends to be static, the yield line of the vent plate is shorter, and there are fewer fragments generated by the failure of the plate. The pressure-displacement curve and the correlation diagram of failure modes proposed provide a reference for predicting the failure mode of light and fragile explosion venting components. • The failure modes of vent plates subjected to methane explosion load in field tests. • Correlation between methane concentration, explosion load characteristics, and dynamic response of vent plates. • The failure mode of the vent plate is predicted by the pressure displacement curves. [ABSTRACT FROM AUTHOR]

Methane-air mixtures initiated by Hexogen (RDX) were experimentally investigated in a custom-designed rectangular venting device. By changing the methane concentration, the overpressure characteristics and flame propagation were studied under the conditions of RDX detonation and electric spark ignition, respectively. The results indicate that, compared with spark ignition, the RDX explosion shock wave leads to the structural vibration and interacts with the flame, shortening the methane reaction time and substantially increasing the explosion overpressure. When the methane concentration is close to the equivalence ratio of unity, only one pressure peak occurs after the vent plate opening. The pressure peak caused by the interaction between acoustic waves and flames, P 3 , appears only at methane concentrations of 8 vol% and 13 vol% under RDX detonation. The acoustic vibration of the structure induced by different masses of RDX has a nonlinear impact on the increase of P 3. The long reaction duration and the weakening of the shock wave result in a relatively small frequency of high-frequency oscillations at high concentrations. [ABSTRACT FROM AUTHOR]

Gas explosion accidents under shock wave stimulation cause more severe hazards than electric spark ignition. To explore the initiation mechanism and explosion characteristics of methane induced by shock waves. A series of experimental investigations of methane-air mixtures initiated by hexogen (RDX) was performed based on a self-developed closed pipeline. The effects of incident shock wave intensity and methane concentration on the characteristics of methane explosion were studied. The results indicate that methane participating in the reaction can significantly increase the positive pressure duration compared with RDX explosion. With the increase of incident shock Mach number (Ma), methane deflagration pressure increases and counteracts the attenuation of RDX detonation pressure. When the ignition distance is 0 cm, the overpressure inside the pipeline is directly proportional to the methane concentration from 5 vol% to 13 vol%. When the concentration approaches the upper explosion limit, the flame velocity exceeds the theoretical detonation velocity, resulting in the unstable detonation of methane in the pipeline. • The methane combustion mechanism initiated by RDX was investigated in a closed pipeline. • The effect of the shock wave intensity on the explosion characteristics was analyzed. • Significant influence of methane concentration on overpressure peak and flame velocity was obtained. [ABSTRACT FROM AUTHOR]

• Large-scale methane vented explosion was conducted. • Explosion pressure oscillations were analysed in terms of oscillation frequency. • Internal flame development was analysed via changes in flame colour and profile. • Initial turbulence effects on pressure and flame development were discussed. The testing of vented explosion of methane-air mixtures was conducted in a custom-designed 4.5-m3 steel chamber. Methane concentrations in the mixed gas varied between 7 and 13 vol% and the static hysteresis time was set as 0, 1, and 5 min to characterize strong, medium and weak turbulence levels. The effects of concentration and initial turbulence on pressure characteristics and flame development were investigated. It is found that the quasi-static pressure in the chamber during vented explosion can be divided into three stages: pressure release, Helmholtz oscillation, and acoustic oscillation. The Helmholtz oscillation at a frequency of about 20–40 Hz is produced after the peak pressure P 1 caused by the pressure release at all concentrations; however, the acoustic oscillation at a frequency of about 300 Hz only occurs after Helmholtz oscillation when the concentration is near the optimum. In the early stage of internal flame development, the cellular structure is generated due to hydrodynamic instability and diffusive-thermal instability, and the flame front is distorted owing to the instability caused by venting. Initial turbulence distorts the flame front, significantly increases the peak pressure, and stimulates the generation of acoustic oscillation at the upper and lower limits of concentration. Under the influence of initial high turbulence, the internal flame propagation distance has a power function relationship with time, and the turbulence acceleration factor and distance also show a power function relationship. [ABSTRACT FROM AUTHOR]