Experimental Study on Foam Spreading on Fuel Layers with Different Thicknesses

Fire-fighting foam has been widely used as a kind of efficient clean liquid fire extinguishing agent. The spreading of foam is an important index to evaluate the fire suppression performance of foam, which determines whether the foam can quickly cover the whole pool surface in the fire extinguishment process, effectively inhibit evaporation and isolate oxygen. In this work, the foam spreading experiments on the surface of fuel layer with different thicknesses (3-15 mm) were carried out. The results indicate that the decrease of the thickness of the fuel layer could slow down the foam spreading. There is a saturation thickness, beyond which the fuel layer thickness no longer affects foam spreading, because the flow in the fuel layer is transformed from Couette flow to boundary layer flow. Meanwhile, both the increase in the foam flow rate and decrease in the expansion ratio reduce the effect of fuel layer thickness on foam spreading. And at a foam flow rate of 14 L/min or expansion ratio of 5.5, the foam spreading is scarcely affected by the thickness of the fuel. Furthermore, it was found that the foam with smaller expansion ratio spreads faster than that of the lager expansion ratio due to larger pressure gradient at the same foam thickness. The work presented here enhances the understanding of the spread of foam over fuel.