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With the coal mining toward depth, there is an increased probability of gas explosion accidents. While the propagation characteristics of gas explosion on account of goaf environment have not been determined yet, which has great significance for the prevention of the goaf fire spreading to working face. This paper investigates the critical void scale of coal piles that allowed for the propagation of gas explosion flames using a closed duct with the dimensions of 100 × 20 × 10 cm. The void ratios of the stacked coals varied in 0.554, 0.521, 0.492, and 0.471. The results show that the increased flame speed in the coal accumulations poses a greater explosion hazard. While the smaller coal particle sizes are more advantageous for the suppression effect on flame velocity. The explosion duration is inversely proportional to the void ratio, which mainly depends on the void diffusion stage and the flame extinction stage. Moreover, the maximum overpressure and (dP/dt) max  of the explosions attenuate with the decrease in the void scale. The critical void ratio of coal accumulation is between 0.47 and0.49 for premixed methane-air flame with an equivalence ratio of 1. The irregular coal geometry makes flame quenching easier. The void-scale effect of accumulations on flame propagation should be fully considered in the explosion prevention works.

Effects of Void Scale of Coal Accumulation on Methane-Air Flame Propagation and Overpressure Dynamics