Effect of Vent Area on Dynamic Characteristics of Premixed Methane/Air Explosions in End-vented Channels with Different Length/Diameter Ratios

Further elucidate the interaction mechanism of pressure-flame-wall in channels under the effects of length/diameter ratio (L/D) and vent area, which helps to propose more effective decompression means. Experiments of premixed methane-air explosions in end-vented channels with L/D of 10, 15 and 20 were conducted under initial conditions (301 +/- 2 K and 1 atm). The results demonstrate that L/D and vent area are critical external factors causing tulip flames and distorted tulip flames. When the vent area is 60 mm x 60 mm similar to 40 mm x 40 mm, the distorted tulip flame can be generated at L/D of 20. Notably, the critical intrinsic factor causing distorted tulip flame is the interaction of reflected pressure waves-flame. It is deduced that flames stagnate or decelerate during the initial stages of irregular flames because rarefaction waves attenuate the driving force of flames. The new overpressure peaks (P-tulip, Pdis-tulip, and Pirr-tulip) induced by tulip flames, distorted tulip flames and irregular tulip flames are identified. Moreover, the drop size and drop ratio of the maximum overpressure decrease with increasing L/D.