Microscopic Research Of Flame Propagation On Methane-Air Explosion

Combustible gas explosion is one of the main explosion disasters in the field of industrialproduction in China, especially that gas explosion accident in the coal mine is the mostcommon, which causes great damage to people’s lives and property, both the frequency ofexplosion and the casualty it induces exert a huge shadow on juried mass psychology.Therefore, the study on characteristics and mechanism of gas explosion in pipeline is helpfulfor better preventing and controlling of gas explosion disasters in pipeline. In recent years,researches on the process of gas explosion propagation has been paid more and more attention,and the research contents are more widely.Utilizing the transparent pipeline gas explosion experimental appliance created bySecurity technology research center for fire and explosion prevention in North University ofChina and high-speed photography technology to measure the gas explosion flamepropagation, the gas methane-air mixture explosion process were experimentally studiedunder the normal temperature and normal pressure. Research contents are as follows:(1) The dynamic microcosmic propagation of Methane explosion flame in a horizontalpipeline was clearly recorded by high-speed cameras, and the flame front instant velocity wascalculated using MATLAB software programming.(2) Flame propagation conditions, such as the appearing, ending and duration in the pipewere experimental studied when the methane concentration ranged from7%to13%, analysisof different concentrations of methane on flame propagation speed and on the microcosmicstructure of the flame were made. The experimental results show that the flame propagationspeed does not change significantly when the methane concentration is between7-8%, thebiggest speed is about70m/s. After that the flame speed rises rapidly, with the maximumspeed of about130-140m/s. When the increasing methane concentration is more than10%,the normal concentration, the flame speed propagation startes to slow down, expect12% when the speed improves slightly. Methane explosion flame appears at about32ms afterignition with the equivalent concentration, and spreads fast, lasting a short duration, about30ms. The flame has a spherical face when it appears, then the regular shape is terminated intothe flame acceleration on the wall directions respectively, Flame surface inclines and deforms,at50ms tulips-shaped flame eventually generates. When the methane concentration comes to8%and12%the flames both appear more than100ms after ignition, and with a longerduration, that is60and80ms. The change of flame shape is similar to that of equivalentconcentration methane.(3) The flame propagation characteristics was experimental studied of three differentpipe length of1.3m,2.3,3.3m, the influence law of different tube length on the flamepropagation speed, the flame structure were conducted. The pipe length has a great influenceon flame propagation, when the length increased from1.3to2.3m the explosion happensdifficult, only8%,9%and10%methane show explosive, but the flame put out halfway.When the tube length continue to increase to3.3m, all the methane concentration are notexploded, only10%concentration had weak combustion phenomenon. After the pipe isextended, flame appears ahead of time and is earlier than80ms with a duration of80ms also.