Influence of length-to-diameter ratio and static activation pressure on pressure generation and flame propagation in vented gas explosions

On drafting a new European standard Gas Explosion Venting Protective Systems a lack of data has been identified for venting at low activation pressures. Therefore, experiments have been performed on vented gas explosions using bursting foils of different strength. Cylinders of different volumes and length-to-diameter ratios (L/D) have been used as explosion vessels. The vessels were made from glass to make the flame propagation observable by a high-speed video system. For the dependence of the reduced explosion pressure p red on L/D a maximum occurred for L/D about 3. This could be shown for vessels of different volumes and for different vent sizes. Using bursting foils of different strength it could be shown that the pressure evolution after the vent had opened, depended on the activation pressure only, when the vent size was to small to prevent a second peak in the pressure-time curve.