Acceleration characteristics of composite flame in the initial stage of gas/coal dust explosion and analysis of disaster intensification

Abstract

To clarify the strengthening mechanism of gas/coal dust coupling explosion disasters, a 20 L spherical explosion test system, high-speed schlieren, and PIV analysis were used to study the acceleration characteristics and pressure change of composite flames in the initial stage of gas/coal dust explosion, and the flow field characteristics were also analyzed. The results showed that methane concentration had the most important influence on the formation and development of composite flame. When the methane concentration was 7.5% and 9%, the composite flame propagation showed obvious acceleration characteristics and developed spherically, the flame boundary was clear and smooth, with the whole flame being continuous and bright white. Meanwhile, the Markstein length of composite flame is positive, and increased with the increase of methane concentration and dust particle size but decreased with the increase of coal dust mass concentration, the Markstein length for 9% gas concentration was 7 times larger than 6% gas concentration, indicating the increase of gas concentration can obviously inhibit the instability of composite flame, which prolonged the residence time of coal dust particles in the composite flame, resulting in the enhancement of the pyrolysis of coal dust and improvement of explosion intensity. The PIV test results of 9% gas/coal dust explosion showed that due to the high initial explosion intensity, the negative pressure in the center of the composite flame made most of the coal dust particles undergo centripetal movement, and a large number of coal dust particles gathered around the front of the flame. At the same time, a large number of large vortices in opposite directions were formed around the front of the flame, which promoted rapid contact between the coal dust surface and oxygen and intensified the combustion reaction. The research results can provide guidance for the prevention and control of gas/coal dust composite explosion disasters.