Experimental Study On Temperature Distribution And Flame Extension Length Driven By Strong Plume In A Longitudinal Ventilated Tunnel

With the boom of the economy and transportation,the tunnel plays an increasing important role in road and railway transport.However,with the growth in the number and length of tunnel,the tunnel fire threats people's life and property.Although tunnel fire is a rare event,but due to its special narrow structure and relatively confined space,it is difficult to evacuate when a tunnel fire occurred.Although the tunnel fire has been generally studied by formal researchers,but most classical theories were proposed just for weak plume driven flame condition(flame did not impinge on tunnel ceiling),and the temperature distribution and flame extension length beneath tunnel ceiling for strong plume driven flame condition(flame impinge on tunnel ceiling)has been rarely studied.However,most fire has a high figure of heat release rate and flame height in a real condition.In this paper,a series scaled tunnel fire experiments based on the Froude rule was carried out to study the temperature distribution and flame extension phenomenon beneath the tunnel ceiling.The main factor in the tests includes the heat release rate,ceiling-source distance and longitudinal ventilation velocity.The main research results include:Temperature distribution of strong-plume-driving ceiling jet.(1)When there is no longitudinal ventilation,the maximum temperature changes little with the heat release rate and ceiling-source distance,but the high-temperature range changes large.With the increase of longitudinal velocity,the maximum temperature decreases and the location of high-temperature region moves to downstream.(2)We proposed a hypothesis that the longitudinal ventilation reduces the real heat release rate.Then,we can generate a mathematic model to predict the maximum temperature by theoretical analysis and data fitting.Flame extension length of strong-plume-driving ceiling jet.(1)When there is no longitudinal ventilation,the flame extension length in both sides of fire-source increases under the condition of increase at heat release rate and decrease at ceiling-source distance.With the increase of longitudinal velocity,the flame length in upstream decreases rapidly but changes little in downstream,the total length decreases as well.(2)Based on the hypothesis and data fitting,a mathematic model is proposed to predict the flame extension length beneath the tunnel ceiling.This model has been experimentally verified with the help of cylindrical and ellipse flame shape hypothesis.