Study on flame fractal characteristics of coal dust explosion at the decompression position of Hartmann tube

The explosion of coal dust is powerful and has a wide range of spread, which can easily cause mass death and injury. In this paper, the flame microstructure and propagation characteristics of coal dust explosion are recorded by high-speed photography schlieren technique. The experimental results show that the flame shape of Hartmann outlet is mushroom cloud with obvious fractal characteristics, and the fractal dimension can measure its complexity. When the particle size of coal dust is constant, the fractal dimension increases first and then decreases with the increase of concentration. When the coal dust particle size is less than 53 μm and the initial concentration is 300 g/m³, the flame fractal dimension reaches the maximum value of 1.71. The fractal dimension decreases with the increase of coal dust particle size. The coal dust explosion flame has a cellular structure, and its instability is caused by the combined action of hydrodynamic instability and unequal diffusion instability. These instabilities make the flame front structure develop from wrinkles to cell bodies and change continuously. This study can reveal the complexity of coal dust explosion flame propagation at the outlet position, and provide a new perspective for in-depth understanding of coal dust explosion propagation behavior.