Experimental study and physical modeling of ceiling temperature and heat flux profiles by wall-attached fires in inclined tunnels

In this work, the longitudinal heat flux, temperature distribution and flame spread length, beneath a sloping tunnel ceiling caused by fire sources attached to the sidewall were experimentally investigated. The effect of heat release rate (HRR) and tunnel slope on the flame spread length, temperature and heat flux profile were comprehensively considered. The present results show that, in the longitudinal direction, the temperature and heat fluxes under ceiling decrease with increasing distance in the downstream and upstream directions from the flame stagnation point. Thermal and flame buoyancy will change the forces on the ceiling jet caused by a wall-attached fire, resulting in differences in the mass flow rate of fire plumes in upstream and downstream directions. A correlation is developed for the flame extent in the longitudinal upward and downward directions. The temperature and heat flux under ceiling increase in the upstream direction for a given distance in the longitudinal direction compared with the downstream direction and with increasing slopes of the tunnel inclination. This is due to the fact that the upstream thermal flow increases, and the flame extension length becomes larger, while the downstream thermal flow decreases exacerbating the difference of heat flux between upstream and downstream. In addition, the correlation between the dimensionless heat flux and the temperature profile under inclined ceiling in the upstream and downstream directions was further analyzed as a function of the flame length variation. These correlations are well described by physically based models for all the experimental results, including the heat flux under the tunnel ceiling at stagnation point and along the longitudinal flame extension.