Study on the flame propagation characteristics of coal-rock mixed dust explosion in semi-coal-rock roadway

Deep coal mines with interbedded strata frequently form semi-coal-rock roadways, where 20–80 % of the section is rock, resulting in the generation of coal-rock mixed dust owing to complex geological features. In this study, the flame propagation characteristics of coal-rock mixed dust are investigated under different ignition energies, ignition delay times, rock dust contents, and particle sizes. The results show that flame height and propagation velocity exhibit a nonlinear "accelerated growth-growth slowdown-stabilization" trend with increasing ignition energy, peaking at 42 J, while flame velocity follows a unimodal "low delay growth-peak stabilization-high delay attenuation" pattern with ignition delay time, peaking at 20 ms. Moreover, the presence of rock powder diminishes flame brightness and disrupts its continuity, transforming the typical mushroom-cloud-shaped flame into an intermittent pattern characterized by fine streaks, point-like spots, and thread-like structures, while also exerting bidirectional regulatory effects. In addition, the flame propagation velocity increases as particle size decreases. A dynamic mechanism for flame propagation was discovered. Specifically, the dust explosion was suppressed by rock powder through a combination of physical isolation, pyrolysis-induced heat absorption, and chemical inerting, as well as three-phase interface interference. These mechanisms operate synergistically to regulate flame propagation stages, reducing both the probability and intensity of coal dust explosions. The results of this study provide a theoretical basis for the prevention and control of coal dust explosions in mines.