Effect of propagation behaviour of expanding spherical flames on the blast wave generated during unconfined gas explosions

In the present study, the flame propagation behaviour and a blast wave of homogeneous premixed combustible gas/air mixtures in unconfined areas were experimentally investigated. The tests of hydrogen/air, methane/air, propane/air and hydrogen/methane/air mixtures conducted using a soap bubble method at room temperature and atmospheric pressure. The results demonstrate that the flame for an Le < 1 mixture was wrinkled by diffusional-thermal instability, accelerating the flame speed and consequently increasing the overpressure with time. The flame for rich mixtures was intensively wrinkled and accelerated in the later stage by the non-uniformity of the concentration distribution, which was induced by the bursting of a soap bubble. This result indicates that rich mixtures have the potential for severe explosion because this phenomenon can generate flame acceleration. The results from the experiments with hydrogen addition in methane/air mixtures indicate the flames were intensively wrinkled and accelerated with the hydrogen addition, and consequently, the overpressure also increased. The results demonstrate that the overpressure increases with the absolute value of the burning velocity, as well as the acceleration of the burning velocity, due to diffusional-thermal instability and heterogeneous concentration areas for rich mixtures.