Experimental and numerical study of the effects of ullage height on plume flow and combustion characteristics of pool fires

Pool fires are frequently reported to trigger domino effects in oil storage farms and chemical factories. Fire plume is the vehicle of damage caused by pool fires. This study aims to study the effects of ullage height (distance between the fuel surface and the upper pool rim) on fire plume flow and combustion characteristics were conducted by experimental and numerical studies. Ullage heights were systematically changed from zero to the value at which the flame is self-extinguished. Simulations were validated against both time-averaged and instantaneous experimental measurements. In terms of the dynamic of the flame base with respect to the pool outlet, three classes were identified as follows. Class I: Flame base anchored near the upper pool rim, and the combustion was mainly of classic non-premixed flame type; Class II: Flame base entered into the pool but not merged; Class III: Flame base entered into the pool and merged along the middle axis. It was shown that the decreasing pressure near the pool
outlet driven the flame to enter into the pool, as ullage height increased. According to the time-history of plume flow, three plume flow patterns were revealed at different ullage height conditions, which explained the evolutions of flame structures. It was shown that the percentage of premixing combustion was increased with ullage height. This behavior was attributed to the enhanced fresh air entrainment and mixing at the flame base.