Visualization of explosion characteristics of methane-air mixtures with different ignition positions and vent areas in a large-scale venting chamber

Explosion venting trials were conducted in a 4.5 m3 stainless chamber to investigate the effects of ignition position and vent area on the explosion characteristics of 9.5 vol% methane-air mixtures using a high-speed camera and three pressure transducers under standard conditions (P0 = 100 kPa, T0 = 298 K). This work provides a basic understanding of the relationship between flame behaviors and internal pressure under different experimental conditions. The results show that hydrodynamic instability, diffusive-thermal instability, and R-T instability stimulate the cellular structure and oscillations of the flame front, and the increase of the internal pressure promotes the instability of the flame front. P1 forms owing to the rate of combustion products and dynamic characteristics of the vented plate. The coupling of the flame front, reflected wave on the walls and the acoustic wave, results in violent flame oscillations during venting, corresponding to P4. Ignition position has almost no effect on the flame front speed before vented plate failure. Helmholtz oscillation process is more violent for ignition near the vent but disappears with decreasing vent area. Central ignition always leads to the maximum pressure peak, only two pressure peaks are observed for front or central ignition, three pressure peaks occur after rear ignition. As the vent area decreases, P1 and P4 are the dominant peak pressures in the cases of rear and central ignitions, respectively. The maximum pressure peak is equal in the front and rear ignition cases when the vent area is greater than, or equal to 0.36 m2.