柞木燃烧蔓延规律及释烟特性研究

A Study on Spreading Laws and Smoke Emission Characteristics of Xylosma racemosum Combustion

【目的】灌木林内植被生长连续、多藤蔓附生,在垂直、水平方向分布紧密,可燃物负荷量大,燃烧蔓延速率快、火强度高。柞木是云南省典型灌木林植物代表,开展燃烧蔓延及释烟特征研究可为灌木林火防治提供科学依据,减少灌木林火发生频率,保护森林资源。【方法】以云南省局部山地地形、柞木植被数据为基础,利用Fire Dynamics Simulator(FDS)建立微观山体柞木林模型,设置5种坡度(0°、15°、25°、35°、45°)、2个火源位置(火源1、2分别位于坡度15°、0°),分别模拟4种风速(0 m/s、1.5 m/s、2.5 m/s、3.5 m/s)条件下柞木林火燃烧,研究柞木林火燃烧蔓延规律、温度变化趋势、CO浓度、CO_(2)浓度、烟气流速、烟气热辐射。【结果】微观柞木林模型燃烧约100 s趋于稳定,风速≤2.5 m/s的初始燃烧阶段,坡度15°与25°、35°与45°区域燃烧温度几乎同时达到反应温度300℃,柞木林火在以上连续坡度范围内蔓延速度更快;火源1为起火点时,25 s内,3.5 m/s风速时坡度15°区域为主要蔓延位置;平地内燃烧温度可达2000℃、烟气热辐射量为1500~1700 kW/m^(2)、烟气流速约15 m/s,均高于其它坡度;下山火受逆风影响蔓延较为困难,风速3.5 m/s时下山火发生概率较小;在柞木林火模拟过程中,烟气流速与坡度呈负相关,坡度增加风速降低,烟气流速越小;烟气热辐射的初始上升速率较为缓慢,150 s左右数值变化趋于稳定。【结论】FDS软件模拟微观柞木林模型燃烧与实际火灾发生蔓延状况大致相同,可作为森林火灾燃烧蔓延规律及烟气释放特征研究的有力工具。模拟结果可为柞木林火预防、扑救提供科学指导,有效提高森林防火的工作效率。

[Objective]The vegetation in the shrubby grows continuously and is epiphytic with many vines,the combustibles in shrubbery are closely distributed in space,with a large load,fast burning spread rate,and high fire intensity.Xylosma racemosum is a typical shrub in Yunnan Province.The study of its spreading laws and smoke emission characteristics can provide a scientific basis for prevention and control of shrub forest fire and reduce the frequency of shrub forest fire and preserve forest resources.[Method]The micro-mountain model of Xylosma racemosum was established by FDS software,the data were based on the local mountain topog⁃raphy and Xylosma racemosum vegetation in Yunnan Province.Two fire origins(Fire origins 1,fire origins 2 were located at slope 15°and slope 0°),four wind speeds(0,1.5,2.5,3.5 m/s),and five slopes(0°,15°,25°,35°,45°)were set in this model to study the law of fire spread,temperature change,CO concentration value,CO_(2) concentration value,velocity of flue gas,and radiative heat flux gas of Xylosma racemosum.[Result]The micro Xylosma racemosum model combustion was stable within 100 s.At the initial stage of combustion,when the wind speed was≤2.5 m/s,the temperature reached 300°C in the slope area of 15°and 25°,35°and 45°at the same time,and the spread rate of Xylosma racemosum fire in the above continuous slope range was faster.When the wind speed was 3.5 m/s within 25 s,the Xylosma racemosum fire spread was mainly at the slope of 15°under the fire origin 1.In the flat land,the combustion temperature could reach 2000℃and the radiative heat flux gas was 1500-1700 kW/m^(2),and the smoke velocity was about 15 m/s,which were higher than those at other slopes.It was difficult for downslope fire to spread under the influence of headwinds,and downwind fires rarely occurred when the wind speed was 3.5 m/s.The smoke velocity was negatively correlated with the slope in the simulation process of Xylosma racemosum fire,and it was found that the greater the slope was,the smaller the wind speed was and the lower the smoke velocity was.The initial rise rate of radiative heat flux gas was rela⁃tively slow,and the numerical change tended to be stable around 150 s.[Conclusion]The simulation of the burning of the micro Xylosma racemosum model with FDS software was similar in subsfance to the actual fire.It’s feasible for FDS software to simulate the burning of Xylosma racemosum and study its spreading laws and smoke emission characteristics.The results can provide scientific guidance for the fire fighting and prevention of Xylosma racemosums fire,and can effectively improve the efficiency of forest fire prevention.