| Flammable gas explosion accidents are one of the common disasters in industry and mining,resulting in significant financial losses and health risks for employees.Whether in industrial production,transportation,storage and use,or in coal mining where safety protection or work tasks require,there are typically destructible flexible obstacles such as wind curtains,airtight walls,shrubs in green belts,etc.In contrast to rigid obstacles such as large machinery and equipment,these typically flexible obstacles have a significantly different mechanism of impact on combustible gas explosions in confined spaces.Therefore,the study of the mechanism of effect of flexible obstacles on flammable gas explosion properties will provide theoretical reference for disaster prevention and mitigation and safety design in confined spaces.In this paper,a closed explosive pipe with a length of 3000 mm and a crosssection size of 80 mm×80 mm is adopted,and 10% methane/air premixed gas is selected as the typical combustible gas,and experimental parameters such as the thickness,blocking rate and pore shape of flexible obstacles are changed to conduct the explosion experiment,so as to study the effect of flexible obstacles on combustible gas explosion characteristics.The main research results are as follows:(1)In contrast to experiments with empty pipes,flexible obstacles facilitate explosion propagation through a special mechanism.During the early stage of explosion,due to the barrier effect of the obstacle itself,the precursor shock wave accumulates in the upstream of the membrane,resulting in the formation of pressure difference between the upstream and downstream of the membrane,making the obstacle subject to the pressure of the vertical arc plane toward the direction of explosion.The closer to the geometric center of the obstacle,the larger the resulting force,leading to the stretching of the obstacle and conical deformation.When the ultimate pressure strength of the flexible obstacle is reached,the pressure waves accumulated in the upstream of the membrane will gradually break through the obstacle with the geometric center of the obstacle as the weak link,blocking rate gradually drops to 0,and the efflux formed when the membrane breaks will propagate to the downstream direction of the membrane.In particular,in flexible pore obstacle experiments,the precursor shock wave will also form a jet before the membrane breaks due to the confinement effect of the pore.On the one hand,these two jets drive the accelerated propagation of flame,on the other hand,they cut the stable gas field downstream of the film,promote the formation of turbulence,jointly accelerate the propagation of flame,enhance the overpressure in the pipeline,promote the emergence of three-dimensional combustion,and thus promote the propagation of explosion.(2)BR=100% thickness variation of flexible obstacle(0.105 mm,0.210 mm,0.315 mm,0.420 mm,0.525 mm,0.630 mm)affects the reflected wave before film breaking and the jet flow during film breaking,which is an essential factor affecting the explosion intensity.When the obstacle is set upstream of the pipe,the peak overpressure and the peak flame front velocity increase with increasing thickness.The peak flame signal intensity reaches its maximum at an obstacle thickness of 0.315 mm.The intensity of the peak flame signal first increases and then decreases with increasing thickness.?When the obstacle is set downstream of the pipe,the change in the thickness of the obstacle has a slight effect on the peak overpressure.As the thickness of the obstacle increases,the peak flame front velocity increases.The peak flame signal is maximum when the thickness of the flexible obstacle is 0.420 mm.As the thickness increases,the influence of the peak flame signal intensity first increases and then decreases.(3)Blocking ratio changes of flexible obstacles with 0.105 mm thickness(25%,35%,45%,55%,65%,75%,85%,90%)affect the reflected waves generated by obstacles and the jet flow through obstacles,which is an important factor affecting the explosion intensity.When obstacles are set in the upstream of the pipeline,with increasing blocking ratio(25%-55%,65%-85%),the flame front speed increases,but when blocking rate is 55%-65%,85%-90%,the flame front speed decreases.In addition,the peak flame signal is enhanced for blocking rates of25% to 65% and 75% to 85%,but decreases for blocking rates of 65% to 75% and85% to 90%.When obstacles are set in the downstream of the pipe,BR increases(25%-35%,45%-75%),resulting in increased flame front speed,but when blocking rate is35%-45%,75%-90%,flame front speed decreases.In addition,the peak flame signal gradually decreases for blocking rates of 25% to 45% and 55% to 75%,but increases for blocking rates of 45% to 55% and 75% to 90%.(4)The shift of pore shape(BR=75%)leads to the shift of pore irregularity,which affects the jet flow through the obstacle and is an essential factor affecting the explosion intensity.In experiments with circular,square,and triangular pore shapes,the peak flame front velocity and peak flame signal intensity increase with the pore circumference.However,in experiments with 4-tooth,6-tooth and 8-tooth pore shapes,the peak flame front velocity and peak flame signal intensity decrease with the increase of pore circumference.?In particular,unlike the rigid obstacle,the flexible porous barrier is fully broken by the flame as it passes through,which affects the propagation of the explosion mainly through the interaction with the precursor shock wave.According to the analysis of 4-tooth,6-tooth,and 8-tooth experiments,the pore perimeter continues to increase with the obstacle,increasing the pore shape irregularity,enhancing the jet cutting through the obstacle,and combing the membrane downstream of the aura;However,the ultimate pressure strength of the horizontal X-axisymmetry flexible obstacle with pore shape decreases with the pore circumference of the obstacle,resulting in a small pressure difference between the upstream and downstream of the membrane,and the jet generated in the process of bursting has a weak promoting effect on the explosion.Together,these two combinations suppress the explosion. |
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