Experimental And Numerical Simulation Study On Combustion Characteristics Of Tunnel Fire On The Basic Of Two Fire Sources Interaction

With the acceleration of the urbanization process,China's transportation industry develops rapidly,and the mileage of tunnels continuously extend,and the risk of tunnel fire continues to increase.At the same time,the hazard of tunnel fire is also increasing.The traffic flow of highway tunnel is large,and there are many large vehicles,and the vehicles are easy to jam.In the subway tunnel,the running interval of vehicles is short and the cars are connected with each other.Once a fire occurs,these are likely to cause multiple sources fire,increase the degree of fire hazard,and seriously endanger life safety and vehicle operation safety.Studying multiple sources fire in a tunnel is of great significance for reducing the degree of fire hazard.In view of the fact that tunnel fire is mostly multiple sources,and the research of multiple sources in a tunnel is mostly based on two fire sources,In this paper,by means of small-scale experiments and Fire Dynamics Simulator(FDS),the combustion characteristics of two fire sources in a tunnel under different fire size and spacing are studied,which provides data support for the study of tunnel multi fire sources.The main research contents and achievements are as follows:(1)With a 1:10 tunnel model,five groups of small-scale experiments are conducted and FDS numerical simulation is carried out on one of the groups to study the effect of spacing and size on mass loss rate,ceiling maximum temperature and ceiling temperature distribution.The results show that the mass loss rate in the fully developed stage is affected by fire source spacing and is non-monotonic.S/D=1 is the critical point for the change on the competition mechanism of the air entrainment limited effect and radiant heat feedback.When S/D<1,the air entrainment limited effect plays a leading role;when S/D>1,radiant heat feedback plays a leading role.When S/D<1,the ceiling maximum temperature decreases due to air entrainment limitation;when S/D>1,the rate of decrease gradually slows down due to the increase of fire source size.The ceiling longitudinal temperature distribution in the far field follows the exponential decay law;the fire source spacing affects the attenuation speed,which is shown as the ceiling longitudinal temperature attenuation coefficient in the far field showing opposite changes on both sides of S/D=2(2)Combined with the small-scale experimental data,the ceiling longitudinal temperature prediction model of the tunnel single-source fire is revised,and the ceiling longitudinal temperature prediction model for the far field suitable for the case of two fire sources is derived.The results show that when S/D<2,the pre-finger coefficient is greatly affected by the change of fire source size;When S/D>2,it is less affected by the change of fire source size,and tends to be stable as the spacing increases.For the correction of the model,when S/D<2,only the pre-finger coefficient needs to be corrected;when S/D>2,the attenuation coefficient also needs to be corrected based on the correction of the pre-finger coefficient.The revised model prediction results agree well with the experimental results(3)Based on the correction of the ceiling maximum temperature model for tunnel single-source fire,the single fire source equivalent of two fire sources is studied.The results show that the experimental value of the ceiling maximum temperature of the tunnel single-source fire is lower than the predicted value of the classic model,and the model coefficient is 18.1 after correction.According to the relationship between the ratio of the heat release rate of the equivalent single fire source and the fire source 1 and the dimensionless spacing S/D,the single fire source equivalent model is obtained to realize the single fire source equivalent of two fire sources.It has been verified that the equivalent model of single fire source has reliability.