Experimental modeling study on mechanical smoke exhaust system during tunnel fire

Introduction With the rapid development of transportation infrastructure, highway tunnels have become vital transportation arteries. However, due to their enclosed and narrow structure, they face severe fire risks. Mechanical smoke extraction systems are core fire protection technologies in highway tunnels, among which the unilateral large-spacing point-type system is widely used in long tunnels. The efficiency of this system depends heavily on key parameters such as the distance between smoke vents and the fire source, and the installation position of longitudinal ventilation fans. However, there is insufficient research on the synergistic effects of these parameters and their performance under high-power fires. Method To address this gap, this study optimized the key smoke extraction system by focusing on these two parameters. Based on the Froude similarity criterion, a scaled tunnel model was constructed. Experiments were conducted under both natural and mechanical ventilation conditions, analyzing the smoke exhaust effect with different vent positions and fan locations. Results The results showed that under mechanical ventilation, the smoke flow velocity and temperature increase monotonically decreased with the distance from the vent to the fire. The optimal fan position was found to be around 20 cm upstream of the fire, which maximizes the coupling synergy with near-field smoke. Increasing the fan distance flattened the attenuation of flow velocity and temperature in mid-to-distal vents. Discussion This study provides theoretical support for optimizing tunnel smoke extraction systems and aids efficient fire rescue, thereby contributing to the reduction of casualties and property losses.