Ethylene/polyethylene hybrid explosions: Part 1. Effects of ethylene concentrations on flame propagations

To reveal the explosion regimes in ethylene/polyethylene dust hybrid explosions, flame propagations in ethylene/polyethylene hybrid explosions with different ethylene concentrations were experimentally studied. The results showed that minimum explosible concentration of polyethylene particles significantly decreased with the increase of ethylene concentration due to the synergistic effect of ethylene and polyethylene particles. The MEC was reduced from 200 g/m(3) to 42 g/m(3) with the addition of 2.3% ethylene gas. Flame propagation velocities, maximum flame temperatures, and temperature rising rates obviously increased as ethylene concentration increased. The maximum average flame propagation velocities of 0.5%, 1.2%, and 2.3% mixtures were 6.22 m/s, 8.31 m/s, and 12.91 m/s respectively. With the increase of ethylene concentration, flame propagation mechanism was transited from the devolatilization-controlled regime to the kinetics-controlled regime. Hybrid explosions of ethylene/polyethylene dust mixtures can be identified into four different regimes, which are no explosion, synergistic explosion, gas-driven explosion, and dust-driven explosion. In the synergistic explosion region, maximum flame temperatures were obviously sensitive to the ethylene concentration and dust concentration. Hybrid explosion regime was transited from the dust-driven explosion to the gas-driven explosion with the increase of ethylene concentration (below LFL).