Abstract: The suppression effect of ultra-fine water mist on methane-coal dust compound explosions was systematically studied in a confined space dust apparatus. Flame propagation velocities, explosion overpressure, pressure rising rate were measured owing to the suppression effect of variously concentrations of ultra-fine water mist. The mechanism of explosion suppression and the behaviors of flame propagation after the addition of ultra- fine water mist were further investigated. Moreover, the critical mist concentration of suppression was decided under different particle sizes and concentrations of coal dust. The results show that the ultra- fine water mist delays the start of the explosion overpressure significantly. Flame experiences four development stages: point flame, partial powerful flame, continuous non- smooth flame and stable layered flame. Therefore, inhibiting the appearance of partial powerful flame is the key reason for suppressing explosion. As the concentration of ultra-fine water mist increases, the secondary accelerating rise of the overpressure disappears gradually, and the correlation between the heat release rate of the explosion and the combustion rate of the flame front is enhanced. The critical mist concentration first increases and then decreases with the increase of coal dust concentration, and decreases with the increase of coal dust particles size.

Key words: ultra-fine water mist, methane-coal dust compound explosion, explosive behavior, flame structure, the critical mist concentration of suppression