Study On Effects Of Tunnel Slope And Smoke Extraction Mode On Burning Rate And Heat Feedback Mechanism Of Pool Fire Under Longitudinal Ventilation

The tunnel brings great convenience to people,however,the tunnel fire brings new problems and challenges.Therefore,the prevention and control technology of tunnel fire is becoming more and more important.It is meaningful to explore the combustion characteristics of tunnel fire.The critical velocity is a key parameter in the design of longitudinal ventilation and smoke exhaust.However,the specification mainly designs the critical wind speed based on the heat release rate of the fire source in the tunnel.The effects of smoke exhaust velocity,tunnel structure and blocking conditions on the ignition source itself were not considered.In addition,there is little research on the change of the heat release rate of the ignition source under other ventilation and smoke extraction methods such as semi-horizontal smoke extraction.Therefore,this paper adopts the method of simulation tunnel experiment to study the influence of inclined tunnel,semi-transverse smoke emission and the distance between the obstacle and the ignition source on the combustion characteristics of the ignition source.In the experiment of inclined tunnel,the burning rate and flame title angle were measured under different conditions.The experimental results show that with the increase of the wind speed of longitudinal ventilation,the burning rate in the horizontal tunnel and the tunnel with a slope of 5% decreases first and then increases.However,the burning rate of n-heptane increases monotonously in tunnels with a slope of 10%.The slope of tunnel has little effect on the flame title angle.Semi-transverse smoke exhaust is both longitudinal and transverse ventilation smoke exhaust.Transverse ventilation has little effect on combustion characteristics.The influence of longitudinal ventilation is more obvious.With the increase of wind speed of longitudinal ventilation,the heat convection feedback increases,which leads to the increase of heat feedback.The radiation feedback changes little and the conduction feedback decreases.In the obstacle experiment,when the distance between the obstacle and the ignition source is within a certain range,the burning rate is higher than that without obstacles.However,when the distance between the obstacle and the source of fire is beyond a certain range,the burning rate is not much different.The main reason is that the radiation feedback from the wall of the obstacle increases the burning rate.