Study on flame propagation characteristics of deposited coal dust explosion induced by pressure waves of different intensities

In the hope of studying the laws of secondary explosion induced by gas explosion shock waves lifting deposited coal dust (CD) in coal mines, the paper discusses the explosion overpressure, composite flame propagation characteristics and the acceleration mechanism of composite flame with the aid of a self-built gas explosion experiment pipeline. The experimental results demonstrate that under the methane concentrations of 7.5%, 9.5% and 11.5%, the explosion time-overpressure curves present same variation trend at different measuring points. Specifically, they all surge first, then decrease to a negative value and increase in oscillations, ultimately stabilizing at around 0 MPa. The presence of deposited CD in the reaction has an insignificant impact on the explosion overpressure at the measuring points, and the maximum overpressures all appear near the P2 (0.75 m away from the ignition source) measuring point. However, the deposited CD exerts a considerable influence on the flame's instantaneous velocity, especially on the flame structure during flame propagation. In stark contrast, when the methane concentration is 7.5%, the single flame has a larger instantaneous velocity than the composite flame and it exhibits finger flame, flat flame and tulip flame successively. Compared with the blue flame produced by pure methane combustion, the composite flame shows a bright white light strip that is distributed along the pipeline axis, accompanied by more obvious stratified combustion. The high-pressure wave intensity and the flame front temperature jointly promote the overall turbulence intensity in the area where CD is swept up, resulting in continuous acceleration of the composite flame.