Experimental study on flame spreading over locally wetted thin combustibles

Abstract

This study proposed a better fire-extinguishing strategy by investigating the effectiveness of wetting operations. It also serves as a first step toward developing physical-based discrete fuel flame spread models using a newly developed small-scale test device. This study examined downward flame spread through a dry narrow path sandwiched by wetted zones formed with thin paper, with different levels of wetting and dried layer width. The dynamic flame behavior and the effect of the presence of adjacent wetting zones were studied both experimentally and numerically. The experimental observations revealed three burning patterns, namely unburned, partially burned, and burned-out regions, depending on various locally wetting fuel arrangements. Additionally, the accelerating flame spread of the wetting case was experimentally reported for the first time. One-dimensional computational simulations suggest that this accelerating phenomenon could be attributed to the chemical reaction triggered by the introduction of water. The reaction rates of OH + CO ↔ H + CO2 and H + O2 + H2O ↔ HO2 + H2O increased due to the water vapor, thereby increasing the heat production rate to further promote the preheating of the downward unburned region and flame spread rate. These findings and conclusions shed more light on the physical and chemical effects of water on flame spreading, highlighting another possibility of water accelerating flame propagation.