Experimental and theoretical study on near-floor flame spread along a thin solid

Abstract This paper presents experimental observations and a theory of near-floor flame spread along a thin solid. Experiments were conducted by igniting at the center of a thin circular paper sheet that was held at a given height h from the bottom floor. It was observed that the flame front was corrugated and often broke into separated structures when h was small, and highly disturbed burned areas were obtained for h = 2  mm; flame spread was not possible at h = 1  mm. When h was larger than about 5 mm, on the other hand, nearly axisymmetric spread was observed, and the spread velocity was found to increase with h . Since the front structure showed a similarity with smoldering combustion, an analysis was conducted based on a theory of smoldering spread, in which oxidizer flow velocity and the degree of heat loss are two important parameters. Boundary-layer consideration and PIV measurement showed that the oxidizer flow velocity did not significantly vary under the conditions studied, thereby suggesting the importance of heat loss to the bottom floor. An equation that describes the front normal velocity was then derived, which was numerically solved. Since the tangential velocity does not alter the shape of a curve, it was adjusted such that the grid-point spacing would be asymptotically uniform. Theoretically predicted front-shape evolution for different values of h agreed reasonably well with the experimental observations, validating the theory at least qualitatively.