This study provides detailed temperature and physical structure measurements for liquid pool fires supported on water within both the liquid fuel layer and the supporting water sublayer from ignition to the onset of the boiling water sublayer, WSB. Understanding the mechanism of WSB is important to predict the so-called “boilover phenomenon,” which is associated with an intense spattering of water and fuel droplets. The in-depth physical structure and temperature profiles were obtained using a holographic interferometer for n-decane supported on water in rectangular Pyrex containers with large aspect ratios to provide two-dimensional conditions. The experiments demonstrated that: maximum temperature was achieved 0.1–0.15 cm below the fuel surface due to the combined effect of evaporation heat loss at the fuel surface and in-depth radiation absorption. As a result, Rayleigh convection was generated in the fuel near the fuel surface, and the total heat transfer rate to the fuel-water interface increased by approximately 30 percent. Hence, the water at the fuel-water interface was superheated, so that sporadic spattering of water and fuel droplets (boilover) resulted. To check the applicability of those results to a larger pool fire system and to different fuels, a rectangular container (10 cm long × 5 cm wide × 9 cm high) was designed and eight different liquid hydrocarbon fuels were tested; for all fuels the occurrence of Rayleigh convection was confirmed using fine thermocouples and a streak shadowgraph technique.

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