Study on the explosion suppression characteristics of ethylene/polyethylene hybrid mixtures by melamine polyphosphate

The characteristics of gas–solid hybrid explosions are heavily influenced by their components and suppressants, making this a critical focus in industrial explosion prevention research. The effects of ethylene (C₂H₄) on the explosion characteristics of polyethylene (PE) dust were investigated using a 20 L explosion sphere apparatus, and the suppressive performance of melamine polyphosphate (MPP) on C₂H₄/PE hybrid explosions was evaluated. The study systematically investigated explosion overpressure, flame propagation, explosion products, and the chemical reaction kinetics. The results indicate that as C₂H₄ concentration increases, the explosion intensity of the gas–solid hybrid mixture initially increases, reaching a maximum at 7 %, before decreasing. The incorporation of 70 wt% MPP reduced the maximum explosion pressure (P_max) and flame propagation speed of the hybrid mixtures by 11.19 % and 37.74 %, respectively. The addition of C₂H₄ significantly accelerated the pyrolysis and oxidation of PE dust, leading to the release of highly reactive free radicals. These radicals enhanced the porosity and induced cracking in the explosion product particles. In contrast, the MPP inhibited the reactions through “HOPO ⇋ PO₂” and “HOPO₂⇋PO₂” suppression cycles, which efficiently consumed H, OH, and O free radicals. This decreased the chain reaction intensity and suppressed combustion by forming phosphorus oxides and nitrogen-containing compounds. Although MPP showed some effect in inhibiting the explosion of the C₂H₄/PE hybrid system, the presence of C₂H₄ significantly altered the reaction kinetics and radical generation pathways of the system, which made the difficulty of explosion inhibition increased compared to the original mixture without C₂H₄.