A Physical Model and Improved Experimental Data Correlation for Wind Induced Flame Drag in Pool Fires

The flames over a burning liquid fuel are observed to spill over the downwind edge of the liquid pool in a wind. Empirical correlations in the literature relate the total base dimension of the fire (diameter + the spill over) with the wind Froude number. This leads to erroneous and physically incorrect (negative) value for the flame spillover at low wind speeds and/or in large diameter fires. The data from laboratory scale (0.1-0.6 m) to field scale (up to 35 m) fires of different hydrocarbon fuels on the wind induced flame "drag" or "spillover" were re-examined. The ratio of the flame spillover distance with the pool diameter is seen to vary in direct proportion to the square root of the Froude number but with different proportionality constants for different fuels. A physical model was developed to analyze the phenomena that occur at the base of a pool fire subject to a wind. This model indicates that the non-dimensional downwind flame spillover distance is directly proportional to the square root of the Froude number, inversely proportional to the square root of the dimensionless heat of combustion of the fuel and directly proportional to the 1/4th power of the ratio of vapor density to air density. Available experimental data are synthesized into a single correlation when plotted on the basis of the non-dimensional parameters from the model. This correlation includes the Froude number, the Damkohler number (dimensionless heat of combustion of the fuel), the wind flow Reynolds number and the fuel vapor-to-air density ratio.