Research On The Explosion Propagation And On The Gas Explosion Induced Coal Dust Explosion With Influence Of Gas Concentration

The gas explosion pressure, flame propagation and coal dust explosion induced by gas explosion with influence of gas concentration were studied by theoretical analysis, experimental research and numerical simulation.Based on the theoretical analysis on the explosion of gas and coal dust, gas explosion experiments of different gas concentration and those of coal dust induced by gas explosion have been performed respectively in the pipeline with 700mm diameter and in the headway with 7.2m2 section area in ChongQing Branch of China Coal Research Institute. Then numerical simulation and verification were preformed by a flow simulation code.The results obtained from the study on the explosion propagation with different gas concentration are as follows:the maximum pressure near the ignition point is not the maximum pressure of whole process, maximum pressure of shock wave decreases in the ignition nearby, and then rises to some peak value and weakens gradually. The variation of gas concentration influence evidently the peak pressure and flame propagation, both the peak pressure and the reciprocal of flame propagation velocity in same test point are quadratically functional to gas concentration, and the flame propagation velocity is small in the ignition point nearby, then rises to some peak value and decays gradually.The rising of deposited coal dust is mainly caused by shock wave and the turbulence effect after the wave. During the process of coal dust rising, the surface shear force of coal dust maintains a threshold, therefore the deposited coal dust can keep the rising speed in a certain range. By the analysis on velocity field of coal dust particles, it is regarded that the rising process can be divided into three steps which are startup, acceleration and deceleration.Compared to the pure gas explosion, the hybrid explosion involving gas and coal dust owns characteristics of slower attenuation of shock wave and flame front, faster propagation velocity, longer duration, higher pressure peak and longer propagation distance. In the beginning stage of the process of deposited coal dust explosion ignited by gas explosion, the explosion overpressure lasts longer duration, and a phenomenon of sustaining pressure rising in a long period is found, which enhance its damaging capacity. The exposure time of maximum pressure peak is not postponed with the increase of propagation distance, and does not appear with the level sequence of maximum pressure. The process of deposited coal dust explosion induced by gas explosion can be divided into 4 stages, which are pure gas explosion stage, dust rising and ignition stage (i.e, the blast wave of gas explosion contacts coal dust, dust rising and ignition), spreading stage of hybrid explosion of gas and coal dust, and explosion attenuation stage. It is obtained that the pressure peak appeared earlier in the first stage, the exposure time of pressure peak in the second stage is much later than that in the third stage which was caused by the characteristic of rising deposited coal dust dedicated itself into explosion reaction, and appeared most lately in the last stage.The results obtained in the paper are of great importance to the effective prevention and protection, loss decreasing and investigation of gas and coal dust explosion accidents.