Study On The Heat Release Rate Of The High-speed Train Fire

With the rapid development of China’s high-speed railway,high-speed railway and high-speed train have become an essential part of China’s modern transportation and essential infrastructure for economic development.The heat release rate is an essential technical parameter for high-speed train fire protection design,fire safety assessment,and tunnel ventilation system design.However,many factors affect the heat release rate of high-speed train fire,such as train materials,components,fire source positions,fire source power,carriage vent area,tunnel ventilation velocity,etc.The existing theoretical calculation methods of heat release rate can not accurately get the heat release rate of high-speed train fire.Although the numerical simulation and full-scale train fire test can get a more accurate heat release rate value,it takes a lot of time,and the cost of a full-scale train fire test is high.Therefore,how to calculate the heat release rate of high-speed train fire simply,quickly,and accurately has become an urgent problem.In this paper,the heat release rate of the high-speed train fire is studied by theoretical analysis,numerical calculation,and experiment.Through the combustion test of cone calorimeter and ignition temperature tester,the detailed data of the heat release rate,smoke production,and ignition temperature of the main components of the carriage of new high-speed trains in China are obtained.Then,the numerical calculation model of high-speed train fire is established based on the structure and combustion test results of high-speed train materials.The influence of grid size on the numerical calculation results is analyzed.Moreover,the effectiveness of the numerical calculation method in this paper is verified by the local component combustion test of high-speed trains and the full-scale train fire test data in the literature.Then,the essential characteristics of flame spread in high-speed train carriage are studied by numerical calculation method,and the law of flame spread in the high-speed train carriage is revealed.In the early stage of the development of high-speed train compartment fire,the flame spread along with the ceiling above the fire source to both ends of the high-speed train carriage,causing the material to burn at the end of the train and then causing the seat and floor burning under the effect of thermal radiation from the ceiling.In the process of fire development,the average spread rate of flame in the high-speed train carriage is 2.21 m/min,which is slightly higher than the average spread rate of flame in the subway train carriage.The flame spreading process in the carriage is affected by the fire source power,fire source position,and tunnel longitudinal ventilation’s velocity.The fire source power and tunnel longitudinal ventilation’s velocity have little effect on the flame spreading rate.However,the higher the fire source power is,the earlier the flame starts to spread along the length of the carriage.When the longitudinal ventilation velocity exceeds 4m/s,the flame is difficult to spread in the train carriage.Due to the difference in the spatial location of the components in the high-speed train,the surface temperature distribution of the components is quite different.The temperature of the ceiling material surface is the highest,and its combustion intensity and influence on the fire heat release rate are also the largest,while the temperature of the floor material surface is the lowest,and its combustion intensity and influence on the fire heat release rate are the smallest.Therefore,the influence of component combustion intensity on the fire heat release rate should be considered when establishing the calculation method of high-speed train fire heat release rate.The criterion of flashover is that the temperature of the smoke layer on the top of the car reaches 600 ℃.Then,the flashover characteristics of high-speed train carriage fire are studied.In the process of fire development,the flashover extends uniformly along the length of the carriage,with an average expansion rate of 1.85 m/min.The farther away from the fire source,the higher the flashover intensity is.Then,the effects of fire source power,fire source position,and tunnel ventilation velocity on flashover time are analyzed.The results showed that the expansion rate of fire flashover increases with the increase of fire source power and decreases with the increase of tunnel longitudinal ventilation’s velocity.By comparing the flame spread,window rupture time,and flashover time under different fire source positions,it can be concluded that the most unfavorable fire source position is the end wall corner of the carriage(fire source position 1),so fire source position 1 can be regarded as the most unfavorable fire source position in the design fire of high-speed train.The heat release rate curve of high-speed train fire is obtained by numerical simulation.The time for the fire to reach the peak heat release rate is 1040 s,which is close to the research results of SP in Sweden.By monitoring the heat release rate curve of high-speed train carriage fire in sections,it is found that the peak time of heat release rate of the carriage in the fire source section is the same as that of the whole vehicle.Then,the influence of the carriage vent area of the high-speed train on fire heat release rate is analyzed.The results showed that the peak heat release rate of high-speed train fire increases exponentially with the carriage vent area.When the window glass of the high-speed train can break naturally in the fire,the fire type of high-speed train is closer to the Fuel-control type.Moreover,the influence of fire source power,fire source position,and tunnel longitudinal ventilation’s velocity on the fire heat release rate are also analyzed.The maximum difference of peak heat release rate under different fire source power is about 7.7%.The maximum difference in peak heat release rate under different fire source positions is about 16.5%.The relationship between the peak heat release rate and the longitudinal ventilation velocity is exponential decreasing.The cooling effect of longitudinal ventilation velocity on the combustion surface of materials in the carriage is greater than that of oxygen supply.In the process of fire development,the burning area of materials is the key to calculate the heat release rate.In this paper,the heat release rate calculation method is established based on the flame spread rate of material combustion.That is the spatial time-series superimposed method.Then,according to the heat release rate per unit area of materials in the high-speed train carriage and the spatial time-series superimposed method,the calculation model of heat release rate in high-speed train fire is obtained.Then,the calculation model is modified according to the change of material combustion intensity and fire flashover intensity.Finally,the heat release rate calculation method established in this paper is compared with several existing high-speed train fire heat release rate calculation methods.The results showed that the heat release rate curve obtained by the calculation model is consistent with that obtained by the FDS simulation,and the maximum relative error is less than 25%.