Explosion behavior of non-uniform methane/air mixture in an obstructed duct with different blockage ratios

Abstract

An experimental investigation on explosion behavior of non-uniform methane/air explosion in obstructed duct with different blockage ratios is conducted. The methane/air mixture that the methane concentration decreases from top to bottom and from ignition end to opposite end of duct is tested. The results show that the vertical concentration gradient of methane upstream along the obstacle increases with blockage ratio. After ignition, the flame speed and overpressure increase exponentially when the flame propagates with a finger-liked shape. In the poorly mixed methane/air, the flame speed and overpressure reduce with the appearance of pronounced triple flame. The flame in duct without obstacle propagates with triple shape until it approaches the vent. In the obstructed duct, the flame speed increases again after the flame passes the obstacle and then the triple flame disappears as the flame becomes turbulent. In the more evenly mixed methane/air, the flame speed decreases with the disappearance of finger shaped flame. The flame speed decreases continuously in duct without obstacle but increases again when the flame passes the obstacle in obstructed duct, in which an incomplete mushroom-shape flame forms downstream the obstacle. Generally, both the flame speed and overpressure are larger in methane/air that mixes more fully.