Merging behavior of facade flames ejected from two windows of an under-ventilated compartment fire

This paper investigates the merging behavior of flames ejected from two parallel windows of an under-ventilated compartment fire using a LPG gas burner. A reduced-scale model (about 1:4) of a compartment fire with a facade wall has been constructed where the window dimensions and the separation distance between them varied during the experiments. The flames ejected from the windows were recorded by a CCD camera. The excess heat release of the fuel burning outside the windows was high enough to produce flames controlled by three-dimensional entrainment. Temperatures inside the compartment, the flame merging probability, the distance from neutral plane to flame lowest merging point, and the height of the facade flames before and during merging were measured. The temperature measurements inside the under-ventilated compartment fires do not change with total heat release rate or the window separation distance, thus indicating that the same heat is produced inside the compartments. The flame merging probability and the flame merging point distance are normalized and well correlated using the facade flame height for completely non-merging flames and the separation distance between the windows. Finally, the facade flame height normalized by the facade flame height for completely non-merging flames is well correlated with the ratio of surface of the air entrained between the windows as the separation distance changes divided by the total surface area from all sides available for entrainment. For the present case this ratio is a function of the ratio of the flame merging point distance over the facade flame height for completely non-merging flames which is finally used for the correlation of merging flame heights.