Extinguishing the dripping flame by acoustic wave

Abstract

Dripping of molten fuels is a widely observed phenomenon in the wire fire and façade fire, which promotes the fire spread and increases the fire hazard. The flame attachment to drip is a necessary condition for dripping ignition, so that extinguishing the dripping flame can effectively reduce the dripping fire hazard. In this work, we investigated the use of acoustic wave to extinguish the fast-moving dripping flame. Continuous drips, with a mass of 6.2 mg and a diameter of 2.6 mm, were produced from a burning polyethylene tube, and two fall heights, 0.3 m and 0.7 m with velocities of about 2 m/s and 3 m/s, were selected as the targets. The sound source varied in pressure from 80 to 114 dB and frequency from 90 to 110 Hz. Results showed that the effectiveness of flame extinction by acoustic wave decreases as the dripping velocity increases, so the acoustic wave is more effective to extinguish the dripping flame in the early stage. An extinction criterion was formulated based on a characterized Damköhler number to describe the underlying mechanism. This work provides important information on the acoustic effect on a moving flame and helps mitigate the fire hazard of dripping phenomena.