Effect of turbulence intensity on flame propagation and extinction limits of methane/coal dust explosions

Methane/coal dust explosions pose a serious threat to the safety of coal mining. Since the flow field in the tunnel is unsteady, the effect of turbulence on flame propagation is essential for the disaster risk assessment and safety protection. In this study, the effect of turbulence intensity (u′) on flame propagation characteristics and extinction limits of methane/coal dust explosions is investigated. The turbulence parameters of the flow field and the turbulence-flame interaction are estimated by Particle Image Velocimetry. Luminous flame (raw image) and reaction front (OH radical image) of methane/coal dust mixture are captured. The results reveal that the flame propagation velocity increases by 78–200%, when the u′ increases from 1.86 to 2.66 m/s. The acceleration of flame propagation velocity is due to the increase of the release of volatile matter and the flame folded regions caused by the turbulence. When the characteristic time of the turbulence disturbance becomes shorter than that of the chemical reactions, the heat sink effect of turbulence will dominate the combustion process. In this case, the extinction limits of CH4/coal flames increase with the u′. When the u′ increases from 1.86 to 2.66 m/s, the extinction limits of CH4/coal flames increase by 14–60%.