LAUSR

Abstract The dripping of thermoplastic fuels is a significant fire hazard, but the complex dripping-ignition process is still not fully understood. In this work, we investigate the ignition capability of continual polyethylene drips with the size of 2.6-4.6 mg and the frequency of 0.3-1 Hz. These flaming drips land on four groups of materials, cardstock papers (>0.1 mm), thin papers (≤0.1 mm), cotton, and porous mineral materials. For igniting cardstock papers, the minimum drip number decreases with the drip size and frequency, and the ignition time follows the piloted-ignition theory. The thin permeable paper and cotton are soaked by drips, so ignition only requires a small and fixed number of drips. The soaking effect also helps anchor the flame on drips absorbed by other porous mineral materials, showing a notable fire risk. Theoretical analysis of the ignition limit and delay time is proposed to identify the boundary between the piloted dripping ignition and the flame anchored on drip-soaked material. This research reveals different ignition mechanisms of dripping fire and helps understand the fire hazard regarding the transport and soaking effect of molten fuels.