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.