Experimental study on temperature decay and smoke control in tunnel fires with combination of multi-point smoke exhaust and longitudinal ventilation

This paper investigates the longitudinal temperature distribution characteristics beneath the ceiling and smoke control of the tunnel with combination of multi-point smoke exhaust and longitudinal ventilation. Experiments are carried out in a model tunnel with dimensions of 60 m × 1.3 m × 0.67 m. The longitudinal wind speed is set to 0–0.5 m/s, the exhaust air volume to 0.34–1.09 m³/s and the fire heat release rates (HRR) are 30.7 kW and 61.4 kW. The results show that the tunnel fire with combination of multi-point smoke exhaust system and longitudinal ventilation mode (the exhaust fan is installed on the upstream side of the tunnel) causes the offset of flame, and the maximum temperature point beneath the tunnel ceiling appears in the upstream direction from the fire source. The large smoke exhaust air volume will cause smoke layering plug-holing at the smoke exhaust vents, and the temperature of the vents where plug-holing occurs is lower. Longitudinal ventilation combined with the top multi-point smoke exhaust system has a better smoke control effect, but the longitudinal wind speed cannot be greater than 0.5 m/s. The temperature decay beneath the tunnel ceiling is in accordance with the exponential attenuation law in a tunnel with combination of multi-point smoke exhaust system and longitudinal ventilation mode (the exhaust fan is installed on the upstream side of the tunnel), and the longitudinal temperature decay rate of the side close to the exhaust fan is smaller than that of the other side.