Experimental Study on the Flame Characteristics of Temperature and Morphology with Various Fire Source Positions of Restricted Environments

Abstract

Fire releases substantial uncontrolled energy, leading to significant damage. The development of fire becomes more complex in restricted environments, making it crucial to understand combustion behavior in such environments. The unpredictable location of the fire's origin further complicates fire behavior predictions. This study examines how variations in fire source height and transverse position (against the sidewall and at the longitudinal tunnel centerline) influence flame characteristics in tunnels. Experiments were conducted in a 1/8th model scale tunnel, using a porous gas burner to simulate the fire source, with 14 heat release rates ranging from 2.13 kW to 85.10 kW. Results show that sidewall confinement and increased fire source height elevate ceiling excess temperatures and increase the probability of flame impingement. With flame increasing and approaching the tunnel ceiling, three distinct temperature zones were observed: buoyant plume, intermittent flame, and continuous flame impingement. A mirror model was used to simulate sidewall fire behavior. Based on dimensionless analysis, correlations of flame height and ceiling impinging temperature are put forward and verified by comparing them to the previous experimental data. On this basis, a three-stage model is further proposed to predict the probability of flame impingement on the ceiling under different fire positions.

Keywords: Fire source position, Flame height, Ceiling temperature, Flame impingement, Mirror model, Tunnel fire