Effects of an obstacle on the deflagration behavior of premixed liquefied petroleum gas-air mixtures in a closed duct

Abstract This work aims to investigate the influences of an obstacle on the deflagration behaviors of premixed liquefied petroleum gas (LPG)-air mixtures. Experiments were conducted in a closed tube, with a length/diameter ratio of 5.9, at ambient pressure and temperature. The effects of blockage ratios (BRs, 0–0.9) on the flame propagation features, the combustion time, the explosion pressure, the pressure rising rate, and the deflagration index of LPG-air mixture were observed and analyzed. The results indicated that the flow field structure of the unburned gas induced by the obstacle increased the degree of flame front wrinkling and sharply increased the flame propagation speed. During the subsequent propagation, various extremely irregular flame shapes emerged on the flame front, and the flame propagation speed continually accelerated as the distance from the ignition source increased. However, 1.5 m from the ignition source, the flame propagation speed began decreasing, after which the flame alternately accelerated and decelerated. Furthermore, the obstacle drastically changed the LPG explosion pressure dynamics: the maximum explosion pressure increased, the time to reach maximum explosion pressure decreased, and the deflagration index increased, namely, the explosion hazard level increased. When crossing the obstacle, under the action of the Rayleigh-Taylor instability regime, the sudden acceleration of the flame in the duct generated the pressure waves. These pressure waves interacted with the flame front and produced flame disturbances. Thereby the flame front was distorted and deformed, and the flame front area and the local mass and energy transmission were increased.