Study On The Characteristics Of Strong Plume Fire In Tunnel Under The Restricted Conditions On Both Sides Of Fire Source

To satisfy the travel needs of modern society,a large number of traffic tunnels have appeared.In recent years,a series of tunnel fire accidents have caused a large number of casualties and property losses.As a restricted narrow and long space,when the fire broke out,the high temperature flue will seriously endanger the stability of tunnel structure and the safety of fire rescue personnel.Therefore,when the personnel in the tunnel are safely evacuated,setting blocking facilities on the tunnel section in the area far away from the fire source can not only effectively control the development of the fire,but also ensure the safety of firefighters,which has become a powerful measure to deal with large tunnel fires In order to explore the characteristic law of fire development in the blocked tunnel and provide theoretical basis for the prevention and control of tunnel fire,this paper carried out the fire experiment under the condition of blocking at both ends in a 1:10 reduced size model tunnel,and especially studied the possible middle fracture of the blocking wall when the heat release rate is large.The specific work includes:(1)In the tunnel with limited exits at both ends,the replenishment process of fresh air and the spread process of fire smoke are restricted by the sealing wall,and the amount of smoke exhaust and air supplement in the fire process are dynamic change.Firstly,the dynamic process of smoke spreading in the sealing tunnel is studied.At the initial stage of fire,the temperature inside the sealing wall is low and the amount of smoke accumulation is small,so the pressure inside and outside the wall is basically balanced.When the fire was fully developed,the pressure difference between the inside and outside of the sealing wall increased and the smoke spread dominated.The dynamic process is affected by the opening proportion and position of the sealing wall: in the middle opening condition,the competition between air supplement and flue gas spread through the opening of the sealing wall is more obvious,and the competition phenomenon will be intensified by reducing the opening proportion.(2)The oxygen content inside the sealing wall is constantly changed,which affects the combustion expansion length of the flame.When the distance between the sealing wall and the fire source is 4m,and the total sealing ratio is 75%,the flame spreading length decreases first and then stabilizes due to the relationship of air competition,and the longitudinal spreading length after stabilization is obviously larger than that of the open condition at both ends.Different opening positions have a significant influence on the flame changing trend.When the total ratio is reduced to 50%,the flame spread length is similar to that without sealing.When the distance between the sealing wall and the fire source is 2.5m,the variation trend of flame extension length is small,the total amount of oxygen in the sealing wall is low.At this time,the combustion efficiency is low,and the flame extension length is smaller than that without sealing.Then,combined with theoretical analysis and literature research,the coupling flame propagation length formulas of different sealing ratios and opening positions are obtained through data fitting.Finally,considering the influence of tunnel width on flame propagation,and based on the classical theory of tunnel fire flame propagation,the mathematical model of strong plume flame propagation law in sealing tunnel is established.(3)The characteristics of fire in the sealing wall are studied,and the analysis is carried out from two aspects: the temperature rise law of the ceiling and the heat flow distribution according to the ground height of 0.2m.In terms of the temperature rise law of ceiling driven by strong plume,the maximum temperature rise law above the fire source and the temperature rise distribution along the downstream of the fire source are studied under different sealing conditions,and the prediction model of temperature attenuation law along the fire source is obtained.In terms of the longitudinal heat flow distribution of the tunnel,within the longitudinal range of 1.6m away from the fire source,the heat radiation effect of the strong plume flame is dominant.In the case of symmetrical sealing of the upper and lower parts,when the fire source power is small,there is little difference between the heat flow law of(37.5+37.5)% sealing and(25+25)% sealing.When the heat release rate increases to 35.35 k W.A larger sealing ratio will increase the heat flow in the area near the fire source.Then,the key factors affecting the heat flow effect at the bottom of the tunnel are discussed.Increasing the power of the fire source or decreasing the effective height of the fire source will increase the heat flow effect at the bottom of the tunnel near the fire source,and the heat flow effect gradually decreases as the distance from the fire source increases,meanwhile,the longitudinal along-range heat flow distribution law at the bottom of the tunnel on the central axis under different sealing conditions is given.