Flame propagation characteristics and overpressure prediction of unconfined gas deflagration

Shock wave and thermal radiation were two main hazards of gas cloud deflagration in the open space. Actually, the overpressure can't be forecast easily, because the deflagration process was often affected by the gas cloud size, ignition energy, combustion mode of the cloud, flame speed. So, the prediction of the gas cloud deflagration overpressure in the open space was relatively difficult. In this study, a series of small-scale gas cloud explosions were made to investigate the deflagration characteristics, flame acceleration process and overpressure distribution. The gas cloud was restricted by different sizes of latex balloon and ignited by different energy sources. High-speed video camera was used to record the flame propagation process. Experimental results showed that the rupture of the balloon can strongly accelerate the flame speed for about 10 times which was about 18 m/s, but the flame speeds at different directions came into different values and the flame speed was higher when the acceleration distance was longer within certain limits. What's more, when the gas cloud was ignited by a weak ignition the distribution of overpressures in the repeated experiments was not stable. Overpressure and maximum flame speed increase with the size of the gas cloud, but not linear dependence and can't be used to predict large-scale gas explosion. A new overpressure prediction model was proposed, which was based on the maximum flame speed. This new model was feasible, but the maximum flame speed prediction model should be corrected basing more experimental data.