Flame propagation characteristics of deposited coal dust explosion induced by shock waves of different intensities

In a fully transparent organic glass pipeline,the explosion characteristics and flame propagation characteristics of deposited coal dust explosion induced by gas explosion were studied from explosion over pressure,flame propagation speed,flame temperature and the evolution law of compound flame structure,using synchronous control system,high speed camera system and high speed particle image velocimetry system (PIV).The results showed that under three working conditions,the explosion overpressure and pressure rise rate increased obviously with the increase of methane volume fraction,and the arrival time of pressure peak decreased gradually.When the methane volume fraction exceeded 8.5%,the pressure time curve and pressure rise rate time curve showed some obvious oscillation characteristics.The propagation speed of the compound flame was much greater than that under pure methane explosion condition,and the velocity position curve of compound flame showed the characteristics of fluctuation and rising.The closer the volume fraction of methane to the equivalence ratio,the higher the explosion overpressure,wave front velocity,flame front temperature and its temperature rising rate.When the volume fraction of methane was 9.5% and 8.5%,the compound flame was “barb shaped”,after that,the flame accelerated rapidly.However,when the volume fraction of methane decreased to 8.5%,the brightness of the compound flame was slightly lower,and the structure was broken and discontinuous.The results of PIV test showed that when the volume fraction of methane was 9.5%,due to the high initial explosion intensity and wave front velocity,the coal powder moved rapidly with the shock wave,and the turbulence intensity in the winch area was high,which greatly accelerated the mixing speed of pulverized coal and air,and promoted the combustion of pulverized coal.Therefore,the combination of higher shock wave front velocity and flame surface temperature is the reason for the continuous acceleration of methane/coal dust composite flame.The research results will provide a theoretical support for the prevention and control of gas/coal dust explosion.