Studies On Temperature Characteristics Of Fire In High-Speed Train Carriage With Lateral Opening Under Ambient Wind

Today,the development of high-speed railways in China ranks first in the world,and the total operating mileage of high-speed railways exceeds 40,000 kilometers,which promotes the rapid development of society and economy.This also puts forward higher requirements for the safety performance of high-speed trains.Among many safety issues,the fire problem that deserves the most attention.Fire is one of the disasters that are most likely to occur,the most dangerous,and cause the greatest losses in all aspects during the operation of high-speed rail.The rapid development of high-speed railway requires a more in-depth and systematic study of the temperature characteristics of fires in high-speed train compartments,and the exploration of the temperature profile and evolution law of train opening fires in complex wind environments,so as to master the fire safety evacuation problems of high-speed trains.The best strategies and scientific assessment methods for fire safety risks also provide strong technical support for the high-quality development of China’s high-speed railways in the future.In this paper,a simplified model experiment with a scale of 1:8 is designed and made to study the regularity of the internal temperature profile characteristics of the fire in the long-narrow compartment.Based on the similarity theory,the key parameters of the model train fire,such as the ambient wind speed,the size of the opening and the heat release rate of the fire source,were designed,and a series of fire experiments were carried out.Then,based on the classical fire dynamics theory and the dimensionless model proposed by predecessors in fire research,the indoor fire temperature characteristics of high-speed trains are analyzed,and the factors such as ambient wind speed,opening size and fire source heat release rate are understood to affect the long-narrow carriages of high-speed trains.The influence mechanism of the internal temperature evolution of the chamber opening fire,the results show that:The maximum temperature rise develops in three stages with the increase of the heat release rate of the ignition source.In the first stage,the maximum temperature rises linearly with the increase of the heat release rate of the fire source,and the flame burns stably inside the cabin.This stage is the fuel-control stage;in the second stage,the heat release rate of the fire source is increased on the basis of the first stage.The maximum temperature in the carriage no longer rises but slowly decreases,the flame oscillates at high frequency in the carriage,and there is no flame at the opening;it is named the oxygen-deficient combustion stage.In the third stage,on the basis of the second stage,the heat release rate of the fire source continues to increase,the maximum temperature rises sharply,the flame in the cabin is extinguished,and a continuous fire spill plume occurs at the opening,which is named the continuous fire spill plume stage.The second and third stages are ventilation controls.In the longitudinal temperature attenuation,its changing law is the same in the fuel-control stage and the oxygen-deficient combustion stage,but is different from the first two stages in the open continuous fire spill plume stage.In the fuel-control stage,the maximum temperature rise in the cabin has nothing to do with the ventilation factor and wind speed.According to the model of the maximum temperature rise of the chamber fire in previous studies,the prediction formula of the maximum temperature rise in the fuel-control stage is proposed;In the oxygen-deficient combustion stage and the open continuous fire spill plume stage,the maximum temperature rise changes with the heat release rate of the fire source is similar.According to the previous empirical formula,a dimensionless formula is established.The index is negative in both stages,and the dimensionless wind speed index is negative in the oxygen-deficient combustion stage,but positive in the continuous fire spill plume stage.Temperature rise dimensionless relation.Longitudinal temperature distribution models based on ventilated confined spaces have been widely studied,but they are not fully applicable to fires in long-narrow structures with openings,and the experimental data under various opening conditions are also scattered.Considering the phenomenon,it is necessary to analyze the temperature attenuation law in sections.In the fuel-control stage and the oxygen-deficient combustion stage in the vehicle,the longitudinal temperature attenuation inside the fire along the long-narrow space structure has nothing to do with the heat release rate of the fire source,and follows the exponential relationship between the temperature rise under the dimensionless roof and the dimensionless horizontal distance;In the continuous fire spill plume stage,an exponential function was established that could describe the longitudinal temperature distribution inside the fire along the long-narrow structure,and it was found that the attenuation rate had a power function relationship with the aspect ratio of the opening.This research focuses on the internal temperature profile and evolution law of train fires with side openings in wind environment,enriches the research results of fire safety in trains with side openings,and has important implications for improving public safety systems,reducing loss of life and property,and improving disaster prevention.The ability to reduce disasters and ensure people’s daily travel is of great significance.