Kinetic Characteristics Of Gas Explosion For Complex Structure Of Coal Mine

Coal mining is the pillar industry of our country, and gas explosion is the mainfactor which threatens coal-mine safety production. Most of coal mines in our countrywere considered to be high methane mines. Limited by the special geologic condition andthe demand for production,coal mines usually were designed and distributedcomplicatedly,therefore,the formation and development process of gas explosion may beinfluenced by complicated structures and conditions. Besides gas explosion itself showsthe characteristics of complicacy and particularity, which make it more difficult toprevent gas explosion. Thus，research on the characteristics and causes of gas explosionunder complicated structures and conditions is the key to the prevention and control ofgas explosion.According to the real problem,the multidisciplinary knowledge, such as combustionand explosion, chemical reaction kinetics, fluid mechanics, engineering mechanics wereused comprehensively,620simulation experiments in tube were carried out,50high-speed photographies and80high-speed schlierens were taken, and a variety ofmethods were adopted to comparatively study gas explosion mechanism in severalcomplicated structures and conditions underground coal mine. Thus, the followinginnovative results were obtained.(1)Influence of grid-shape obstacles on gas explosion in coal mineThe flame shows a lower speed, expand more easily and induced a smaller pressurewhen it passes through a round hole obstacle compared to a square hole one.If the size ofthe obstacle hole was less than the critical misfire diameter, or even less than the criticalsafety gap, the flame would extinguish and reignite again beyond the obstacle afterinduction periods of gas explosion. And because of the lag between airstream erupts fromthe obstacle and induction periods of gas explosion, a series of small explosions emergedafter airstream passing through the obstacle, and the smaller the grids were, the moreexplosions would be. As the result of jets and impacts of airstream while it goes thoughthe holes of the obstacle, together with the combing perturbation effect of the obstacle,intense turbulence will be generated.Therefore, flame speed will increase rapidly, andpressure will also rise sharply.According to high-speed photographs and high speed schlieren photographs, theflame was badly deformed and flame front moved upward due to the buoyancy effect ordownward owning to the increased concentrations when the flame get through the obstacles of different shapes, and evolved into tulip structure soon.(2) Effect of damper or airtight wall on gas explosionAluminum film was shaped to simulate the damper or airtight wall, the resultsshows that when the flame breaks through the film, the flame speed and pressuredescends temporarily with considerable energy loss,but explosion will be more powerfuland destructive because of preloading and preheating effect, which promoted a higherexplosion pressure and flame speed. The rupture of the film may lead to “allopatrysecondary explosions” as a result of flame propagation, and also” autochthonoussecondary explosions” caused by recoil and counterattack effects of the flame. Inaddition, the most incentive role of obstacles was to enhance explosion effect bycomparing with the situation with different kinds of obstacles, which proved thenecessity and importance of reinforced related structures.(3) Influence of gas explosion on mine chamberDifferent diameter of tubes was used to simulatively study gas explosion in thechamber. The results shows that,whether the tubes were open or closed, gas explosion inchamber would produce a considerably higher pressure and rate of pressure rise than thatin the trunk tube,and a strong backwash was occurred, which may cause a secondarydamage or the ignition source of secondary explosion. The flame would extinguish andreignite when flame arrived the simulated cracks or holes in the chamber,and it wouldextinguish and reignite again when the flame rushed back The repeated incentive resultedin more powerful explosions. Therefore,great importance must be attached to intensity,material, sealing and some other aspects to insulate from heat and flame when designingthe chamber.(4)Explosion propagation law of various filling-ratio gases at the bend of tubeExplosion propagation law of various filling-ratio gases at the bend of tube wasstudied by the experiment and the theory of hydromechanics.The results shows that, withthe increase of the turned angle of the tube, there is an evident uptrend of the pressure inthe trunk tube and a severely attenuation trend of the flame speed and pressure after thecorner of the tube. When the angel turns to certain extent, the flame is partially or totallyextinguished,and further leads to a even steeper attenuation of the flame speed andpressure. Moreover rarefaction wave and the resistance of the tube corner which causedloss in energy could partly account for the attenuation as well.Generally, explosion pressure and flame speed of more than60%filling-ratio gas isbasically the same as those of100%filling-ratio gas in the straight tube. However, in a bend tube, backwash shock wave generated by reflection greatly reduces methane flamepropagating speed and produces pressures superposition as well. At the same time,backwash shock wave would push back the air in front of the straight tube to dilute themoving methane, which has significant impact on gas combustion, making the flamespeed even lower,and pressure drop relatively.If flame speed before the tube corner increases to the supersonic state, flame speedafter the corner in concave wall side is less than that in convex wall side, while pressurein concave wall side is larger than that in convex wall side. If flame before the tubecorner is a subsonic flow, conclusions were completely opposite.The research findings would further enrich gas explosion theory, offer beneficialenlightenment and reference to the layout of the structure of roadway and some facilitiesunderground coal mine, and play a guiding role for gas explosion prevention under manycomplex structures and conditions.In addition,9papers were published based on the results of the study, including2SCI and3EI papers,3international conference papers and1article published in nationalcore periodical.