| Coal mine gas and coal dust explosion accident prevention and control has been an important work of coal mine safety management and supervision,multiphase flow explosion mechanism,propagation characteristics is also a complex problem of explosion mechanics classical.Although a lot of research has been carried out,and many measures have been taken at the government level to strictly investigate and deal with each explosion accident,but accidents occur from time to time,indicating that the mechanism and propagation characteristics of gas and coal dust explosion accidents have not been fully grasped from the essence.Gas and coal dust explosion accident is a thermodynamic process containing a number of complex physical and chemical changes,subject to multiple factors.Due to the presence of a large amount of coal dust in the production process,the explosion accident is mostly after the gas explosion due to the propagation of the impact airflow rolled up the deposition of coal dust to form a gas and coal dust cloud,followed by a gas-solid two-phase flow explosion.Explosion propagation process flow field evolution is extremely complex,pressure,flame rapidly changing,experiments using sensor testing and other traditional measurement means is not sufficient to fully analyze the gas-solid two-phase flow explosion flow field,so this study uses high-speed laser schlieren technology combined with sensor measurement means to analyze the spatial and temporal characteristics of the explosion flow field,analyze the mechanism of coal dust gas explosion and propagation process.This paper is based on the explosion of different concentrations of methane-air premixed gas(9.5%,8.0%,6.5%)in 60L constant volume vessel,adding different concentrations of coal dust(5g/m~3,10g/m~3,15g/m~3,20g/m~3,25g/m~3)to compare the pressure change after the coal dust involved in the explosion,the flow field changes.The results show that at 9.5%methane concentration,coal dust can make the maximum explosion pressure rise,and the increases then decreases with the increase of coal dust concentration;at 8.0%methane concentration,with the increase of coal dust concentration,it is reflected that the maximum explosion pressure is enhanced first,then decreases;at 6.5%methane concentration,coal dust always decreases the maximum explosion pressure,and the higher the coal dust concentration,the greater the decrease.The ignition in the center of the constant-volume vessel was found to be spherically spread outward by laser schlieren images,and always went through three phases:laminar flame,cellular unstable flame,and turbulent flame.These three stages correspond to three pressure change phases:constant pressure phase(≈0),rising phase,and maximum pressure phase.The addition of coal dust can have a significant effect on the above three flame development processes.In the laminar flow phase,coal dust can reduce the flame propagation speed,and the higher the concentration of coal dust,the stronger the reduction effect,which is reflected in the higher the concentration of coal dust at the same moment,the smaller the radius of the spherical flame.At the same time,coal dust can enhance the flame instability itself,so that the flame in a shorter period of time to reach the cell instability,reflected in the same moment of the schlieren image,the higher the concentration of coal dust,the more dense the flame front cell.In addition,coal dust can significantly increase the explosion flow field self-illumination intensity and explosion duration.Through the experimental data and theoretical analysis of the explosion mechanism of coal-dusted gas,coal dust involved in the reaction through three stages:volatile fraction stage,gas mixing stage,and participation in the explosion stage.From the schlieren image,it can be obtained that the volatile fraction stage is mainly concentrated in the flame laminar combustion stage,the coal dust volatile fraction heat absorption disrupts the flame energy balance process,inhibiting the flame propagation.The gas mixing stage is mainly concentrated in the cellular unstable flame stage,where the gas reaction rate increases and sufficient heat is released,and the coal dust volatile fraction can be fully mixed with methane-oxygen.Participation in the explosion phase is mainly concentrated in the turbulent flame stage,the volatile fraction has been fully precipitated and mixed at this stage,participation in the gas explosion to enhance the flow field self-luminescence,the reaction duration increased. |
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