Smoke Control Characteristics in Tunnel Fires under the Combined Effect of Air Curtains and Shafts

Based on the characteristics of tunnel fires, numerical simulations using the Fire Dynamics Simulator (FDS) were conducted to explore the distribution characteristics of temperature, visibility, and carbon monoxide (CO) concentration, as well as smoke control effectiveness, by combining natural smoke extraction through shafts with smoke control via air curtains.The influence of air curtain jet velocity and angle and the distance between the air curtain and the shaft on these parameters was investigated.Results indicate that the natural smoke extraction of shafts and smoke control via air curtains work synergistically.However, the smoke control efficiency of the air curtain decreases as the distance between the air curtain and the shaft decreases, while the smoke extraction efficiency of the shaft follows an opposite trend.The smoke control efficiency of the air curtain was found to improve by 96.5% compared to conditions without a shaft.When the fire power was set at 12 kW, optimal angles for smoke control and extraction were identified as 30, 20, and 0 for air curtain jet velocities of 6 m/s, 8 m/s, and 10 m/s, respectively.In comparison to conditions without an air curtain, the shaft extraction efficiency increased by 140%.The temperature under the tunnel ceiling within the shaft distance increased with the air curtain jet velocity, while the temperature distribution in the areas outside the shaft distance exhibited the opposite trend.At eye level within the tunnel space, temperature and CO concentration increased with the air curtain jet velocity.Visibility in the smoke control area improved with increasing air curtain jet velocity, while visibility in the evacuation area showed an opposite trend.The temperature in the tunnel evacuation area stabilized below 60, with visibility remaining above 10 m and CO concentration below 50 ppm, thereby meeting the escape requirements for personnel.These findings further validate the feasibility of the combined air curtain and shaft smoke extraction model, providing a foundation for the design of smoke control systems in complex tunnel fire scenarios.