Study on the formation characteristics of coal dust cloud and dynamic behavior of flame during explosion in a Hartmann tube

A coal dust explosion is one of the most severe mine disasters. An experimental investigation was conducted on coal dust explosions using a semi-closed Hartmann tube with anthracite. The dynamic propagation process of the flame was synchronously recorded using a high-speed camera and the schlieren technique to investigate the flame propagation characteristics in coal dust explosions with different concentrations. The results show that the propagation process can be categorized into three stages: ignition, flame acceleration and flame spreading. The velocity inside the tube exhibits clear symmetry, although the distribution is generally not uniform. The flame shape at the tube outlet is classified into three regions: the unperturbed zone, the preheating zone, and the combustion zone, which are affected by the guiding shock wave. With an increase in concentration, the preheating zone becomes thinner. At the same concentration, the flame propagation velocity at the tube outlet initially increases and then decreases. With an increase in concentration, the peak flame velocity at the tube outlet gradually decreases, resulting in a delayed peak time. The experimental results contribute to process safety and further explore the coal dust explosion mechanism to prevent the occurrence of coal dust explosion accidents.