Influence Of Multiple Pore Obstacles On Flammable Gas Explosion In Pipeline

In the process of coal mining,the environmental conditions in the roadway have a great influence on the gas explosion.Due to the needs of coal mining and safety protection,underground roadways are usually equipped with a large number of equipment and facilities,and these equipment and facilities are often scattered,forming intervals and pores between each other,and these intervals and pores are important for roadways.Like obstructions in long and narrow pipes,there are different effects on blast propagation.Therefore,studying the influence of obstacles on explosion propagation and understanding the characteristics of gas explosion characteristics are of great significance to the design and protection of gas safety.In this study,a series of explosion experiments were carried out in a closed pipeline with a length of 4 m and a cross-sectional size of 80 mm×80 mm by selecting obstacles with different blocking rates,setting them in different positions,and using 10%methane/air mixture gas.The effects of different blocking rates and multiple pore obstacles at different positions on the explosion of flammable gas in closed pipelines are studied,in order to provide a theoretical basis for gas explosion protection and mine safety design.The main research results are as follows:（1）When a single obstacle is set in a closed pipeline,the closer the obstacle is to the ignition source,the earlier the excitation effect on the explosion intensity will be,the more obvious the excitation effect on the explosion propagation will be,and the greater the flame front propagation speed and the pipeline overpressure will be.When a single obstacle is set at 0.9 m from the ignition source,the propagation speed of the flame front is generally greater than that in the unloaded pipeline,and it tends to increase with the increase of the blocking rate;when the single obstacle is set at 1.9 meters or 2.9 meters,the propagation velocity of the flame front is lower than that of the flame in the unloaded pipeline,but the high blocking rate（BR=75%,86%）obstacle has a more significant acceleration effect on the flame.（2）There is a similar rule in the double obstacle pipeline.The closer the first obstacle is to the ignition source,the earlier the excitation effect on explosion propagation will be,and the downstream explosion propagation will be promoted.The closer the position of the object is to the end of the pipe,the more obvious the effect of the overpressure downstream of the obstacle is because the obstacle has a certain blocking effect on the airflow.When the double obstacle is set at the front end,it has a significant stimulating effect on the explosion propagation in the pipeline;when the double obstacle is set at the end,it has a certain inhibitory effect on the explosion propagation in the pipeline;when the double obstacle is set at both ends,the effect on the explosion propagation It is affected by the size of the blocking rate of the obstacles.When the blocking rate is the same,the closer the position of the double obstacle is to the ignition source,the more obvious the excitation effect on the explosion propagation,and the closer the position is to the end of the pipeline,the more obvious the inhibitory effect on the explosion propagation.In the front-end double obstacle experiment with a blocking rate of 75%,the flame front propagation speed reached 2000 m/s after the excitation of the double obstacle,and it turned into a detonation state.（3）When the double obstacles are set at the front end,due to the close distance between the two obstacles,the influence of the double obstacles at the front end on the explosion propagation in the pipeline with different blocking rates is different from that of a single obstacle at 0.9 m on the explosion propagation in the pipeline.The laws are close to each other.With the increase of blocking rate,the stimulating effect of front-end double obstacles on explosion propagation in the pipeline shows a fluctuating upward trend,and the stimulating effect on explosion propagation is most significant when the blocking rate is 75%.When the double obstacles are set at both ends,the propagation speed of the flame front and the explosion overpressure are mainly affected by two factors.On the one hand,the excitation effect of the first obstacle on the explosion is caused by the second obstacle.The blocking effect of the reflected pressure wave on the flame shows different trends with the increase of the blocking rate.Therefore,the influence of different blocking rates on the explosion propagation is more complicated under this blocking condition.The maximum flame front propagation velocity increases first and then decreases with the increase of the obstacle blocking rate,and the maximum peak overpressure first decreases and then increases with the increase of the obstacle blocking rate.When the double obstacle is set at the end,because the position of the obstacle is closer to the end of the pipeline,it cannot stimulate the explosion propagation during the explosion development stage.The effect of terminal overpressure is obvious,and the peak overpressure at the terminal first decreases and then increases with the increase of the obstruction rate of obstacles.（4）In the triple obstacle experiment,when the blocking rate is 35%-55%,only the first two obstacles have an accelerating effect on the propagation of the flame front;when the blocking rate is 65%-86%,the triple obstacles can accelerate the flame front.The propagation has an accelerating effect,but in the triple obstacle experiment,the maximum flame front propagation speed is obtained between the second and third obstacles,and the triple obstacle with a blocking rate of 65%has the most significant effect on the flame acceleration in the closed pipeline.In the triple obstacle experiment,when the blocking rate is 35%and 45%,the maximum peak overpressure is obtained between the second and third obstacles,the peak overpressure will increase,and finally reach the maximum value at 3.1 meters from the ignition source after the third obstacle.The triple obstacles with the blocking rate of 86%and 65%have the most significant excitation effect on the peak overpressure in the closed pipeline.（5）A single obstacle at 0.9 meters,double obstacles at the front,double obstacles at both ends and triple obstacles are more likely to stimulate the flame propagation in the pipeline.The closer the first obstacle is to the ignition source,the earlier the excitation effect on explosion propagation,and the greater the maximum flame propagation speed.With the increase of the blocking rate,the gap between the peaks v_0.9m,v_f（“f”means double obstacles at the front）,v_e（“e”means double obstacles at both ends）and v_tr（“tr”means triple obstacles）of the flame front propagation velocity gradually decreases.