Effects of distribution form and location of different branch tunnels on overpressure characteristics of ventedgasoline-air mixture explosion in closed vessels

The branch structure of the tunnel significantly affects the overpressure characteristics of combustible gas explosions in confined space. However, most of previous studies involved explosions in branch vessels were limited to single branch structure, effects of the distribution form and location of the branch structure were rarely considered. In order to explore the influence of various branch distribution forms and locations on overpressure characteristics of vented gasoline-air mixture explosion in closed vessels, the experiments were carried out using three kinds of branch tunnel distribution forms (linear/staggered/symmetrical) and three kinds of branch tunnel locations (near to the spark plug/far from the spark plug/evenly distributed along the main tunnel), under the condition of the same tunnel volume (0.24m3), initial fuel volume concentration (1.2%) and ignition energy (5J). The maximum explosion overpressure pmax, the time to reach maximum explosion overpressure, the maximum rates of pressure rise (dp/dt)max, and the deflagration index KG were examined. Moreover, the effects of distribution form and location of branch tunnels on overpressure characteristics were discussed. Results show that explosion overpressure characteristics are strongly influenced by branch tunnels' distribution form and location. In terms of the symmetrical distribution, the maximum explosion overpressure, the maximum rates of pressure rise, and the deflagration index KG are the lowest among the three types of distribution forms of branch tunnel. Linear and staggered distributions have similar overpressure characteristics, whose explosion overpressure, maximum rates of pressure rise, deflagration index KG are 1.14,1.52and 1.52 times of those in the symmetrical situation respectively. Time to reach the maximum explosion overpressure and time to reach the maximum rates of pressure rise in the symmetrical situation are delayed, which are 1.31 and 1.30 times of those in the linear and staggered situations respectively. The maximum rates of pressure rise and the deflagration index KG descend in the following distribution locations: far from the spark plug, near to the spark plug, evenly distributed along the main tunnel. The results indicate that the farther the branch tunnel from the ignition end, the larger the explosion intensity index, and the closer the branch tunnel from the ignition end, the earlier the time to reach the maximum explosion overpressure rising rate.