Ethylene/polyethylene hybrid explosions: Part 2. effects of polyethylene particle size distributions on flame propagations

To reveal clearly the effects of particle size distributions on flame propagations during hybrid explosions, ethylene/polyethylene hybrid explosions with different polyethylene particle size distributions were experimentally studied. Experimental results showed that flame propagation velocities and maximum flame temperatures increased with the decrease of particle size distribution as a whole. Due to the serious agglomeration of polyethylene when the concentration of ethylene was 0.5%, flame propagation velocities and maximum flame temperatures of the <75 μm polyethylene hybrid mixture were lower than those of the 75-100 μm polyethylene hybrid mixture when dust concentration was less than a certain range. The maximum flame temperature of the 100-212 μm polyethylene hybrid mixture was higher than those of the <75 μm and 75-100 μm polyethylene hybrid mixtures when dust concentration >500 g/m3, which was attributed to the combustion behavior of the molten polyethylene particles. The maximum flame temperatures of 2.3% ethylene hybrid mixtures increased slightly as particle size distribution decreased. The maximum flame temperatures of the 2.3% ethylene hybrid mixtures of particle size distributions <75 μm, 75-100 μm, and 100-212 μm were 1776 °C, 1759 °C, and 1758 °C respectively. Ethylene/polyethylene hybrid flame consisted of the premixed gas flame followed by the diffusing dust flame. With the increase of particle size distribution, the large particle pyrolysis zone without visible flame would exist between the premixed flame zone and the dust flame zone.