Effect of Obstacles Gradient Arrangement on Non-Uniformly Distributed LPG-Air Premixed Gas Deflagration

The arrangement of obstacles can significantly impact the deflagration behavior of combustible gases. In the actual pipeline accident site, liquefied petroleum gas (LPG) and other gases often show non-uniform distribution after leakage owing to diffusion and gravity, and the deflagration mechanism is also more complex. In this paper, based on the non-uniform distribution of combustible gases, the flame behavior and overpressure characteristics of LPG-air combustible gas deflagration are carried out by a combination of experiments and numerical simulations with obstacles arranged in increasing and decreasing blockage height. The results show that in the increasing blockage height arrangement, the flame forms a "straw hat" cavity, finally forming an elliptical region. In the decreasing blockage height arrangement, the flame appears as a "ribbon-shaped" narrow, blank area, which gradually becomes longer with time. By observing the overpressure and the structure of flame propagation in the coupled state, it is found that the explosion overpressure is maximum when the height of the obstacle is consistent, and the moment of the maximum area of flame appears slightly earlier than the appearance of the maximum overpressure peak. At the same time, without considering the change in height of the obstacle, the three arrangements all have an accelerating effect on the flame of deflagration. And the decreasing blockage height arrangement condition has the most obvious effect on the flame acceleration, which makes the peak of area of flame and the overpressure peak appear at first, and finally leads to the formation of a positive feedback mechanism among the speed of flame propagation, the area of flame and overpressure. In addition, in the case of the non-uniform distribution of combustible gases, the acceleration obtained by the flame at the initial stage is very important for the overall acceleration of the flame. The results of this paper can provide a reference for the placement of equipment and facilities in long and narrow spaces such as various pipe galleries, and to make predictions about the impact of the shape of some objects on the explosion and provide a theoretical basis for the prevention and management of gas explosions.