Experimental study on explosion pressure variation law of coal dust with different degrees of metamorphism

In order to study the variation law of coal dust explosion pressure with different metamorphic degrees, the maximum pressure p_max and maximum pressure rise rate (dp/dt)_max are characterized. The variation of explosion pressure characteristics of lignite, long flame coal, non-coking coal and gas coal is investigated by using a near-spherical coal dust explosion device. It is found that, among the selected coal dust samples, lignite has the largest p_max and (dp/dt)_max, up to 0.71 MPa and 65.69 MPa/s, respectively. With the increase of metamorphism, the p_max and (dp/dt)_max of long-flame coal, non-coking coal and gas coal are significantly reduced. Characterizing the explosion intensity by the explosion pressure characteristics, the four coal dust explosion strengths are then ranked from lignite, long flame coal, non-coking coal to gas coal. By comparing the volatile matter content of coal dust before and after the explosion, it is concluded that the proportion of volatile matter involved in the explosion is 46.28%−68.19%. At dispersion pressure p₀=2.0 MPa and ignition delay time t₀=100 ms, the p_max values of the four types of coal dust reach the maximum 0.71, 0.60, 0.55 and 0.47 MPa, respectively. However, lignite, non-viscous coal and gas coal have the highest (dp/dt)_max at p₀=2.0 MPa and t₀=80 ms, while long-flame coal reaches the maximum (dp/dt)_max at p₀=2.0 MPa and t₀=100 ms. The results are of significance for mastering explosion pressure characteristics under different test conditions.