Study On The Influence Of Tunnel Fire Smoke Characteristics Under The Synergistic Effect Of Longitudinal Ventilation And Shaft Exhaust

With the rapid development of traffic construction in China,tunnel fire safety has been widely concerned by the society and researchers.Compared with urban road tunnels,mountain tunnels are more difficult to control fire smoke,evacuate and rescue.Therefore,vertical shafts are generally used to ventilation and smoke extraction.This study relies on the Shenzhen Maluanshan Tunnel and builds a 1/10 small-scale shaft tunnel model based on the Froude similarity criterion.The experiment uses 0# diesel as the fire source fuel.And by changing the longitudinal position of the fire source,the heat release rate,the longitudinal ventilation velocity,and the ventilation velocity of the shaft mechanical exhaust to study on the influence of tunnel fire smoke characteristics under the synergistic effect of longitudinal ventilation and shaft exhaust,which has important practical significance for the evacuation of trapped people and the safe operation management of the tunnel.(1)Study on the influence of tunnel fire smoke movement characteristics under the effect of tunnel longitudinal ventilation and shaft natural exhaustA total of 126 experimental conditions were designed in this study,and the conclusions are as follows:(a)The smaller longitudinal ventilation velocity promotes the combustion rate of the fire source,but with the increase of ventilation velocity,the combustion rate decreases gradually.(b)The temperature beneath tunnel ceiling variation law with and without shaft is basically the same.However,with the location of the fire source away from the shaft,the maximum temperature rise position beneath tunnel ceiling moves synchronously,and the maximum temperature increases gradually.(c)Considering the influence of the shaft,the maximum temperature rise prediction model and the longitudinal temperature decay prediction model of beneath the shaft tunnel ceiling are obtained.(d)The CO concentration change in the downstream of the shaft and inside the shaft are basically opposite,and the position of the fire source has a greater influence on the smoke exhaust characteristics of the shaft due to the strength of the shaft stack effect.(2)Study on the influence of tunnel fire smoke temperature under the effect of tunnel longitudinal ventilation and shaft mechanical exhaustA total of 99 experimental conditions were designed and carried out in two stages.The first stage,under the condition without longitudinal ventilation,the study on the influence of smoke temperature under the effect of mechanical exhaust in a total of 27 experimental conditions.The second stage,the study on the influence of smoke temperature under the effect of longitudinal ventilation and mechanical exhaust in a total of 72 experimental conditions.The conclusions of the first stage study are as follows:(a)The small size fire source combustion belongs to the fuel control type,and the large size fire source combustion belongs to the ventilation control type.(b)Without the shaft mechanical exhaust system,the maximum temperature rise beneath tunnel ceiling is significantly lower than the conclusions of shaft natural exhaust.Small mechanical exhaust ventilation velocity cannot control the spread of smoke to the downstream of the shaft.Therefore,considering the actual situation,the fire smoke control can be carried out by appropriately increasing the shaft mechanical exhaust ventilation velocity.(c)The temperature of the smoke inside the shaft increases with the increase of the shaft mechanical exhaust ventilation velocity,and the temperature of the smoke decreases gradually in the upward movement of inside the shaft.The conclusions of the second stage study are as follows:(a)Owing to the effect of double ventilation,the mass loss rate of the fire source varies considerably,the stable combustion time becomes shorter,and the stable heat release rate is difficult to measure.(b)When the size of the fire source is small,all the smoke is discharged into the shaft under the effect of mechanical exhaust,and there is no smoke in the downstream of the shaft;when the size of the fire source is large,the longitudinal ventilation velocity can blow the smoke to the downstream of the shaft.Therefore,considering the actual situation,the shaft mechanical exhaust system should be opened first,and then the longitudinal ventilation system should be opened to control the backflow of smoke.