A study on the maximum temperature of ceiling jet induced by rectangular source fires in a tunnel using ceiling smoke extraction

This study analyzes the physics characteristics of the flame plume temperature, induced by a ceiling jet and their coupling with an extraction flow. As it is knows, the maximum increase in the temperature of a ceiling jet is a key parameter for tunnel fire safety. The ceiling maximum temperature has been analyzed and its evolution model has also been correlated in the past. However, those previous suggested correlations had considered the fire source shape is square or circular. Actually the van shape is rectangular, the corresponding fire source may be rectangular, which is necessary to extend it to other conditions of rectangular fire sources. It has also been noted that the smoke transport characteristics changed by the ceiling smoke extraction. The aim of this experimental work is to study the maximum increase in the temperature of a ceiling jet induced by rectangular-source fires with different burner aspect ratios (ranging from 1 to 8.2) in a tunnel, using a ceiling smoke extraction. The effects of different burner aspect ratios on the ceiling maximum smoke temperature increase were studied with and without a ceiling smoke extraction. The change of the burner aspect ratios, the ceiling mechanical extraction rate, and the heat release rate were also analyzed. The evolution characteristics of the ceiling maximum plume temperature rise, considering the different burner aspect ratios, with the change in the aspect ratios of burners without the ceiling extraction were firstly obtained. A new normalized equation of the ceiling maximum plume temperature, through the addition of an impact factor for the ceiling smoke extraction rate, of a ceiling jet induced by rectangular-source fires was established. The results indicated that the new global model can effectively predict experimental data.