Numerical simulation on formation mechanism of pulverized coal cloud and flame dynamic behaviors during the explosion process in an open vessel

The flame propagation process and propagation mechanism of coal dust cloud explosion in a semi-confined space are rather complicated due to numerous influencing factors.Moreover,there exists complex interaction between flame,turbulence and pressure during the explosion process.To reveal the dynamic evolution characteristics of flame behaviors and the formation mechanism of coal dust cloud in an open tube,the open Hartmann pipe was set as the simulation object,the diffusion characteristics and explosion process of coal dust in the open tube were simulated numerically based on the theory of computational fluid dynamics,combustion modeling,and numerical heat transfer.Furthermore,based on physical experimental validation and numerical simulation,the scattering,suspension,and sedimentation characteristics of coal dust in the open pipe were analyzed,the space-moments evolution characteristics of flow field dust diffusion process were obtained,the changing tendency for the temperature of coal dust clouds during the explosion process were acquired,the dynamic behaviors and the variation trend for flame height and flame velocity were revealed,the influence of coal particle size and ignition delay moments on the flame height and flame speed were investigated,finally,the dynamic mechanism for the flame propagation of coal dust cloud explosion in an open tube was put forward.Results showed that:① the formation of coal dust cloud goes through four different stages:fast injection,decelerating dispersion,free diffusion,and sedimentation.② The factors that affect the flame shape are different in various explosion stages; whereas,during the entire explosion process,the evolution trend of flame front plane is described as:“non-spherical-flying and point-shaped fire-mushroom”.③ With the development of the explosion,the flame height presents the Logistic function characteristics,while the flame velocity changes as the opening downward parabola.The coupling effect on homogeneous combustion and heterogeneous combustion from turbulence leads to the instability of flame front.