Experimental Investigation About The Effect Of Obstacles On Gas Explosion Flame Propagation Process In Duct

Gas explosion is one of the most serious accidents in coal mine, which brings greatlosses to people’s life and property. With the increase demand of coal, serious gas explosionaccidents occurred frequently and the number of deaths due to gas explosion accounted forthe proportion of coal mine accident death toll rises year by year. So the prevention andcontrol of gas explosion is a major issue to be solved in the coal mine safety production.This dissertation takes the gas explosion in a long and straight duct as research object, toconduct the research on gas explosion flame propagation law with obstacles in the duct,which provides theoretical basis for safety production in coal mine. Main research work ofthis dissertation includes:(1) A large-scale horizonal experiment duct system is set up, which includes ductsystem, data acquisition system, high-speed photography system, ignition system andvacuum system. An external trigger device is designed, which can ensure the ignitionsystem, high speed camera and data acquisition system can be triggered simultaneously.(2) Flame propagation process with and without obstacles is compared, results showsobstacles can significantly increase flame velocity that it can make flame accelerate tohundreds of meters and deflagration to detonation transition can even happen. Effect ofobstacle number, spacing, block ratio and shape on flame acceleration is investigated. It isdiscovered that, more obstacles can increase flame disturbance and make flame velocitypresents increasing trend. For the gas concentration of8percent, flame propagates fasterwith the increase of the interval of obstacles, and flame propagates fastest under semicircleobstacles while lower under other obstacle shapes. For the gas concentration of10percent,flame propagates fastest when obstacle spacing is one time the diameter of duct and flamepresents relative slow propagation under four circle holes and baffle obstacles. Theinteraction of unburned gas and shock wave becomes stronger with the increase of blockratio, while more heat is dissipated when flame passes the obstacles, so flame accelerationis finally determined by the two competition mechanism.(3) Gas explosion overpressure measured in duct is generally less than1MPa. Duringthe propagation of shock wave, part of energy dissipates to the wall of duct and unburnedgas, so explosion overpressure shows a slight decline trend along the duct. Flame has littleeffect on shock wave and overpressure distribution shows a similar trend in different experiment conditions.(4) Complicated process of flame propagation in closed duct is investigated inexperiment and it has shown several characteristics such as many oscillations, differentfinal acceleration states and different extinguish locations. Flame propagates in the form ofturbulence after obstacles and shock wave induced by flame acceleration moves forth andback under the effect of solid wall in duct. At the same time, unburned gas may change itsmoving direction under the effect of shock wave, so flame may also change its propagationdirection with unburned gas in duct and shows oscillation phenomenon.(5) Based on Matlab software, the explosion flame images are processed with averageflame interface approach and largest similarity coefficient approach. The flame propagationvelocity at the observation window is figured out. The flame velocity calculated by imageprocessing is in good agreement with the experimentally measured one. The flame velocitycalculated by largest similarity coefficient approach validates complicated characters offlame propagation phenomenon.