Study On The Characteristics Of Flame Morphology And Ceiling Temperature In Tunnels With Dual Fire Sources

With the economic development of the times,tunnels are widely used.Due to the long and narrow closed structure of the tunnel,it has the characteristics of high fire smoke concentration,high temperature,fast spreading speed,difficulty in evacuation,and difficulty in rescue in the fire environment.In addition,multiple fire sources are easily formed in the tunnel due to multiple collisions and flame spreading.Due to the interaction between multiple fire sources,the temperature of the tunnel ceiling will change accordingly,and the flame will tilt and merge,which will change the flame height and inclination of multiple fire sources,which will lead to further spread of the fire.These will pose a great threat to the evacuation of people and the safety of the roof structure.Therefore,it is very necessary to study the flame shape characteristics of dual fire sources and the change of ceiling temperature in the tunnel.Based on these,this article carried out a dual fire source experimental study in a scaled-down experimental platform of 1:10.By changing the heat release rate of the fire source,the spacing of the fire source,and the longitudinal ventilation speed,the flame shape characteristics of the dual fire source in the tunnel and the change law of tunnel ceiling temperature were studied.For the experimental study of the maximum temperature under the tunnel ceiling in the condition of dual fire sources,it is found that:(1)Under the condition without longitudinal ventilation,at smaller fire source pitches,there is a flame merging phenomenon between the two fire sources.While the fire source pitches become larger,the flame merging phenomenon basically disappear.And,the maximum temperature beneath the tunnel ceiling gradually decreases with the increase of the fire source pitch.Larger fire source pitch resulted in less impact on maximum temperature beneath tunnel ceiling.(2)With the effect of longitudinal ventilation,the maximum temperature beneath the tunnel ceiling is significantly reduced.At lower longitudinal ventilation velocity,the fire source pitch has little influence on the maximum temperature beneath the tunnel ceiling.When the longitudinal ventilation velocity increases,the fire source pitch influence on the maximum temperature beneath the tunnel ceiling is only reflected in the conditions with higher fire heat release rates.(3)Based on the experimental results,considering the influence of the double fire source pitch on the maximum temperature beneath the tunnel ceiling,the single fire source prediction model by Kurioka and Y.Z.Li are modified,respectively.The established modified model can well predict maximum temperature of tunnel ceiling under the condition of double fire sources.For the study of the flame shape characteristics of the dual fire sources in the tunnel under the condition of longitudinal ventilation,it is found that:(1)The flame height increases with the power of the fire source.When there is no wind,the flame height will increase as the fire source spacing increases.When there is longitudinal ventilation,the flame height decreases first and then increases as the fire source spacing increases.(2)The flame inclination angle increases as the power of the fire source increases.When there is no wind,the flame inclination angle decreases with the increase of the fire source spacing.When there is longitudinal ventilation,as the fire source spacing increases,the flame inclination angle decreases first and then increases.For the working conditions of smaller fire source power and larger fire source spacing,the phenomenon of flame fusion gradually decreases.