Study On Combustion And Explosion Characteristics Of Combustible Gas With Non-uniform Concentration Distribution

Coal,known as black gold,is one of the main energy sources used by mankind since the 18 th century.China is a country of large coal production and usage,and coal will occupy a great proportion of China's energy composition in a long time.Gas is an inevitable combustible gas in the process of coal mining,whose main component is methane.More than half of coal mine production accidents are gas explosion accidents,which cause huge casualties and economic losses.Therefore,the prevention of gas explosion is the first thing to do for the safety of coal mining.Starting from the phenomenon of uneven distribution of underground gas concentration,this paper studies the influence of the concentration gradient and the hole type obstacles under the concentration gradient on the characteristic parameters of methane explosion.In this paper,a 6-m-long square explosion experimental pipeline is used,which is divided in three experimental sections,2-m-long for each.Each section is separated by PVC membrane,and different concentrations of methane-air premixed gas are injected in separtedly to create concentration gradients,then study the influence of concentration gradient on the explosion characteristics of methane.After that,hole-type barriers with different opening shape and opening rate are installed between the experimental sections to study the characteristics of flame propagation velocity,explosion pressure and temperature of methane/air premixed gas under the concentration gradient.The results achieved are as followed:(1)Concentration gradient has a significant influence on the combustion and explosion characteristics of methane air premixed gas.When there is the concentration gradient,the average flame velocity,explosion pressure and pressure rising rate of premixed gas are higher than that of uniform methane concentration of9.5%.(2)With the increase of concentration gradient,the average flame velocity,explosion pressure,pressure rising rate and explosion temperature of methane air premixed gas all increase first and then decrease.The average flame velocity,explosion pressure and explosion temperature reach the maximum when the concentration gradient is 1.0%;when the concentration gradient is 1.5%,the pressure rising rate is the maximum.(3)Under the condition of concentration gradient,due to the length/diameter ratio of the pipeline is large enough(L/D=54.5),the methane explosion shock wave in the pipeline is obviously reflected by the wall,and the interface effect exists at the concentration mutation interface,therefore the time to reach the maximum explosion pressure presents a reciprocating trend.(4)The opening shape of the hole-type obstacle has a significant effect on the combustion and explosion characteristics of methane under the concentration gradient,influence degree: square > right-angle sector > circle;the flame propagation velocity,explosion temperature,explosion pressure and pressure rising rate all increase first and then decrease due to the effect of turbulence and concentration gradient,and when the concentration gradient is 0.5%,the parameters of square opening obstacles are all the maximum;when the concentration gradient is 1.0%,the parameters of right-angle sector opening and circular opening reach the maximum,besides the explosion temperature of right angle sector opening is always higher than that of circular opening.(5)Under the concentration gradient,the smaller the opening rate of circular shaped obstacles is,the more obvious the influence is on the combustion and explosion characteristics of methane;the flame propagation speed,explosion temperature,explosion pressure and pressure rising rate with opening rate of 40%decrease with the increase of concentration gradient,and the maximum values of parameters are obtained with the concentration gradient of 0.5%.The parameters of50% and 60% of the opening rate increased first and then decreased with the increase of the concentration gradient,the maximums are acquired at the concentration gradient of 1.0%,and the parameters with 50% opening rate are always higher than those of 60% opening rate.