Mechanism of influence of water mist in a closed vessel on the explosion overpressure and flame propagation characteristics of magnesium dust

The primary purpose of this paper is to deeply investigate the impact of water mist on the explosive characteristics of magnesium dust and to broaden the inerting and suppression strategies for magnesium dust explosions. The explosion characteristics and flame propagation behaviors of magnesium dust/water mist mixtures were examined in a 16.2-L visualized closed vessel. The explosion products were further analyzed using SEM and XRD. The results indicate that with the addition of water mist, the explosivity of low-concentration magnesium dust (≤600 g/m3) increases. The explosive strength of three higher concentrations of magnesium dust (800 g/m3, 1200 g/m3, 1600 g/m3) notably decreases, with the Pmax dropping by 69.86%, 54.08%, and 46.22% respectively compared to pure magnesium dust. The leading edge of the preheat zone exhibits red radiation, the fluctuation range of the instantaneous flame propagation speed decreases, and cubic particles appear in the explosion products. These changes are mainly attributed to the hydrogen produced in the explosion of the magnesium dust/water mist mixture. Under the combined effects of hydrogen and steam, the preheat zone significantly expands. Moreover, as the concentration of hydrogen increases, its presence weakens the suppressing effect of the water mist, manifested by the evident slowing of the average flame speed, the maximum flame speed, and the rate of decrease in explosive strength. The suppression of magnesium dust explosions by water mist mainly relies on physical actions such as heat absorption, blocking thermal radiation, and diluting oxidizer concentration.