Flame propagation of local LDPE dust cloud in a semi-open duct

High-speed camera technology are used in experimental studies for flame propagation of the local dust cloud of low density polyethylene (LDPE) in a semi-open duct, to examine the impacts of dust cloud concentration and particle size on flame propagation. This proves that the dust cloud concentration exerts significant impact on flame propagation. Both the maximum and average flame speeds follow a general trend of increasing at first and then decreasing with concentration. The continuous acceleration distance of the flame increases at first but then levels off with the concentration. The flame developing processes between the fuel-lean and fuel-rich states are completely opposite. The particle size also exerts significant impact on the flame speed and shape. The smaller the particle size and the larger the specific surface area, the larger the total reaction area and the combustion rate, the longer the continuous acceleration distance of the flame, the higher the maximum and average flame speeds, the clearer the flame contour, and the smoother and brighter the front surface. The flame of a larger particle size is likely to segment in the second half of propagation, and the front surface is easily narrowed along the radial direction of the duct. Moreover, the flame propagates far beyond the original dust cloud range in a manner proportional to dust cloud concentration and inversely proportional to particle size. These conclusions can be used as a scientific reference for explosion hazard analysis and process safety design of LDPE powders.