Effect of gravity on puffing phenomenon of liquid pool fires

The flame characteristics of pool fires such as their height and oscillation frequency vary depending on gravity. To improve our understanding of the effects of gravity on flame characteristics, we experimentally investigated small-scale pool fires under conditions of normal to low gravity; using the drop tower at Hirosaki University in Japan to obtain arbitrary low-gravity acceleration, which varied from 1G to 0.55G. Our experiments include analyses of the flame height and oscillation frequency of puffing phenomenon caused by buoyancy under low-gravity environments with a high-speed camera. To clarify the factor of puffing occurrence factor, experiments were performed using eleven different sizes of fuel pan and three different kinds of fuels. It emerged that the flame height and puffing frequency declined with decreasing gravity, whereas the puffing phenomenon which occurred with fuel pan size rose with decreasing gravity. The puffing phenomenon was suppressed with decreasing gravity and the puffing frequency under low-gravity environments was summarized by the relationship between the Strouhal-and Froude numbers. The occurrence of the puffing phenomenon, namely the puffing-limit, was summarized by the relation between the (H/D)limit and Grashof number, and found to be inversely proportional.