Experimental study on the ceiling jet characteristics caused by carriage fire in an inclined tunnel: Temperature distribution and flame extension

This work was aimed at investigating the temperature profile and flame extension characteristics of the ceiling jet induced by the fire ejected from a carriage in an inclined tunnel. A series of experiments were conducted in a 1:6 reduced-scale model, including a compartment with a window in an inclined tunnel (from 0 to 10 %). Tests were conducted with various heat release rates (HRRs) and opening dimensions. Results showed that with the decreasing ventilation factor, the mixing of the combustion gases is enhanced with smaller temperature differences inside the compartment and the average temperature at the steady burning stage is also reduced. For a given opening size, the tunnel slope is shown to affect the temperature distribution inside the enclosure only before reaching the steady burning stage, after which the temperature inside the compartment becomes almost uniform independent of the tunnel slope. In the transverse direction, both the temperature profile and flame extension length are found to be insensitive to the tunnel slope, whereas in the longitudinal direction, the flame extension length is increased in the upward direction while decreased in the downward direction due to thermal buoyancy. Based on dimensionless analysis, a new correlation was developed incorporating the effects of HRRs, opening sizes and tunnel slopes for the longitudinal flame extension in both directions, which is found to be in good agreement with the present data and also available data in the literature. The experimental data and the correlation developed are important in understanding the extension behavior of the ejected fire from a carriage in an inclined tunnel, which are essential to assess the thermal hazard and risk of fire spreading to adjacent vehicles.