Flame lengths in two directions underneath a ceiling induced by line-source fire: An experimental study and global model

The present study investigates experimentally flame lengths in the two directions underneath a horizontal ceiling (x-direction: parallel to the longer side of the burner; y-direction: perpendicular to the longer side of the burner) produced by line-source fire. It is noted that the previous classical equations are limited for axisymmetrical sources where only one-dimensional radial flame length is considered. They are non-applicable for the two-dimensional impinged ceiling flow induced by non-axi-symmetrical line-source in despite that it is also a basic source condition in fire science essentially and practically. Experiments are conducted employing a line-source gas burner using propane as fuel. The flame lengths due to impingement upon the ceiling in the two directions are measured, and their difference are quantified, at various heat release rates and ceiling heights. Experimental results show that the flame length in x-direction is shorter than that in y-direction. Their difference decreases with increasing of ceiling height, meanwhile increases with increasing of heat release rate. A new global formula is derived to describe the flame lengths underneath the ceiling based on the analysis of un-symmetrically distributed un-burnt fuel mass flows after impingement in the two directions reflected by their characteristic lengths, which are proposed to be the fire plume impinging zone characteristic dimensions in the two directions determined by the initial source dimensions, ceiling height and air entrainment. The proposed new function well represents the flame lengths globally in both directions. It provides for the first time a general model for describing the flame lengths underneath a ceiling of line-source fire plume impingement. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This experimental study investigates flame lengths in two directions beneath a horizontal ceiling, finding that the flame length in the x-direction is shorter than in the y-direction. The difference decreases with increasing ceiling height and increases with increasing heat release rate. A new global formula is derived to describe the flame lengths underneath the ceiling, providing a general model for line-source fire plume impingement.