Experimental investigation on ceiling flame extension subject to relative large area of liquid fuel in a channel-like structure with confined portals

Abstract

This paper provides a quantitative model study for ceiling impinging flame extension behaviors subject to the relatively large area of liquid fuel in channel-like structure with confined portals (eg. tunnel), based on experimental results. The fire tests were conducted in a model tunnel [8 m (Length) × 0.8 m (Height) × 0.6 m (Width)]. Different portal-confined areas and liquid fuel areas were considered. Results show that the ceiling flame extension is non-monotonously varied with the portal-confined area, which can be mainly attributed to the combined influence of two action mechanisms of restricting external air inflow and reducing internal heat loss. And there is a critical confined area determined by fuel area, at which the ceiling flame extension length is maximized. Especially, when fuel area is relatively large, a fuel-rich area appears inside tunnel and the high-temperature combustion region moves towards the portals. This provides a prior condition for the flame overflow phenomenon. Based on the analysis of ceiling impinging flame extension behaviors and experimental observations, a global dimensionless factor is introduced to characterize flame extension. A new empirical correlation for ceiling impinging flame extension is proposed accordingly by considering the portal-confined boundary. This empirical correlation performs well in the prediction of ceiling impinging flame extension in channel-like structure fires.