A non-dimensional global correlation of maximum gas temperature beneath ceiling with different blockage-fire distance in a longitudinal ventilated tunnel

This paper presents an experimental investigation and non-dimensional global correlation of maximum gas temperature beneath ceiling with blockage (vehicle) at different distance from fire source in a longitudinal ventilated tunnel. Experiments are conducted in a 1/5 model tunnel (72 m long) with a simulated vehicular blockage (1.3 m × 0.4 m × 0.5 m) whose (upstream or downstream) distance from the fire ranged in 1-6 m. It is found that the blockage placed downstream has no effect on the maximum gas temperature. However, as the upstream blockage-fire distance increases, the maximum temperature decreases and then approaches an asymptotic value (similar to that with no blockage). Li model [Y.Z. Li, B. Lei, H. Ingason, The maximum temperature of buoyancy-driven smoke flow beneath the ceiling in tunnel fires, Fire Saf. J. 46 (2011) 204-210] better predicts the measured values than Kurioka model [H. Kurioka, Y. Oka, H. Satoh, O. Sugawa, Fire properties in near field of square fire source with longitudinal ventilation in tunnels, Fire Saf. J. 38(4) (2003) 319-340.] with no blockage. However, they both cannot well predict, even after amended by the (cross-section) blockage ratio proposed by Lee, the measurements with upstream blockage at different distances. Then, a non-dimensional correlation between a modification coefficient α and normalized blockage-fire distance (L) by the hydraulic diameter (D) of the tunnel is further proposed to account for different upstream blockage distances. A global model is finally developed with both blockage ratio and blockage-fire distance included, as shown to well collapse and predict the measured values.