Experimental study on the flame characteristics of ceiling jet with various air entrainment conditions and vertical fire positions

Abstract

This paper presents an experimental investigation into the impact of varying the location of the fire source within a tunnel on the temperature and morphology of the ceiling jet in different directions. It proposes a method to predict the longitudinal and transverse flame length based on previous studies about flame morphology. The experiment is conducted on a reduced scale (1/8th) tunnel, with the fire source being a porous gas burner utilizing propane as fuel. It comprised two series of transverse fire source locations (against the wall or at the centerline of the tunnel). Each series included five heights, ranging from 0 m to 0.4 m, and 12 heat release rates, spanning from 5.67 kW to 85.10 kW. The results of the experiments demonstrated that elevating the fire source or positioning it against the wall facilitated the formation of ceiling jets. The limited transverse space of the tunnel leads to greater constraints on the transverse ceiling jets, resulting in a longer longitudinal ceiling jet than a transverse ceiling jet. And the longer longitudinal ceiling jets simultaneously result in a higher longitudinal temperature distribution under the ceiling. This study proposed the effective HRR Q_ef based on the assumption of a constant heat release rate per unit flame volume to analyze the flame length. And the dimensionless flame length L_f/D has been found to scale with the dimensionless effective HRR Q_ef^⁎ by the power of 2/5. This correlation is further validated by comparing it with the previous experimental data.