飞火颗粒点燃的实验及机理研究
发布时间：2018-07-31 14:52
【摘要】：森林植被或建筑木质结构燃烧、亦或是高压电线与树木的相互作用会产生木质飞火颗粒,还有烟花燃放(燃烧的微小颗粒)、电焊操作(高温不燃烧的热颗粒)、工业磨削或高压电线碰撞等会产生高温金属颗粒,均可在外界火焰流场及环境风作用下,运动到其源头之外相对远的区域,形成新的点火源,点燃森林可燃物、建筑屋顶等建筑外部材料或建筑外立面保温材料等,导致新的火灾事故或加速跳跃式火势蔓延。此类火灾现象称为飞火。飞火是大尺度森林火灾及森林-城镇交界域火灾中常见的火灾现象,飞火颗粒点燃森林可燃物或建筑结构是导致森林大火及森林-城镇交界域大火发生的重要潜在蔓延途径。与大量研究的传统火蔓延(直接明火接触点燃和火焰辐射点燃)相比,飞火颗粒点燃森林可燃物或建筑结构的点燃方式有很大不同,因此亟需研究飞火颗粒的点燃过程进而填补该研究领域的空白。本论文研究目的是认识高温飞火颗粒点燃建筑外立面保温材料和森林可燃物的基本点燃过程,并建立物理模型揭示其点燃现象及机理。本文的具体工作如下：采用非等温热重和差式扫描量热法,研究低密度建筑外墙保温材料的点燃及燃烧过程中的热解动力学特性。基于固体材料的热解失重曲线,采用等转化率方法和模式函数法,研究了典型建筑保温材料在空气气氛条件下的热解动力学规律,并通过DSC曲线获得了各个热解失重阶段的放热量。基于上述热解动力学研究获得的聚氨酯泡沫和聚苯乙烯泡沫氧化热解阶段的动力学参数及反应放热量,结合经典热点理论,分别以氧化铝颗粒和金属镁颗粒为例,建立了高温颗粒点燃聚氨酯泡沫和聚苯乙烯泡沫的临界条件,模型初步预测了理想情况下热颗粒对保温材料的点燃规律。为深入研究热颗粒的点燃行为,我们建立了热颗粒点燃保温材料的实验平台。实验研究了惰性金属热颗粒(直径6mm至14mm,温度900℃至1100℃)点燃低密度聚苯乙烯泡沫(18或27kg/m3)的过程。实验研究表明：热颗粒对聚苯乙烯泡沫的点燃过程仅发生于颗粒在材料表面的滚动过程及颗粒在材料表面滚动停止且未完全进入燃料床的时间间隔内。金属热颗粒对低密度聚苯乙烯泡沫的临界点燃温度与临界颗粒尺寸呈现双曲线关系,即颗粒直径从6mm升高至14mm时,临界点燃温度将从1030℃降至935℃。与文献中高密度森林可燃物对比发现,聚苯乙烯泡沫的临界点燃温度较高,且点燃转变区域较窄,导致热颗粒点燃对颗粒尺寸呈现弱的依赖关系。实验结果表明,燃料床的密度和厚度对点燃概率和质量损失速率的影响较弱。理论分析表明,热颗粒在聚苯乙烯泡沫的点燃过程中不仅充当加热源的作用,而且充当先导点燃源的作用；热颗粒对聚苯乙烯泡沫的点燃过程是材料热解气和周围空气的混合时间与颗粒在材料表面的滞止时间相互竞争作用的结果。基于热颗粒点燃保温材料的实验现象,我们建立了描述热颗粒点燃聚苯乙烯泡沫的气相点燃数值模型,该模型耦合固相热解反应、气相化学反应及可燃热解混合气的自然对流作用。数值模型获得了不点燃、不稳定点燃及稳定点燃三种点燃机制。数值模型可以较好地预测实验获得的热颗粒点燃的临界条件。鉴于建筑外立面保温材料和森林可燃物的热解、燃烧特性的差异,通过改造热颗粒点燃的实验平台,进行标准化实验操作,研究在环境风(O～4m/s)作用下,惰性金属热颗粒(直径6mm至14mm,温度600℃至1100℃)对不同含水率的松针燃料床(6%至35%)的点燃过程。研究主要关注和讨论热颗粒直接明火点燃、阴燃点燃、阴燃向明火转变的点燃过程。持续点燃的临界颗粒温度(Tp.crt=1800(1+4FMC)/d+500[℃]关系式)随颗粒尺寸的降低和燃料床含水率的增加而减小,热颗粒的最大加热效率近似ηsp=10%。随着热颗粒尺寸的增加,燃料床含水率的影响会变弱。实验测量了金属热颗粒对松针燃料床的两种明火点燃时间。该时间随颗粒尺寸和风速的增加而减小,随燃料床含水率的增加而增加。理论分析解释了临界点燃条件、点燃延滞时间以及直接点燃与阴燃之间的关系。理论分析也表明：在快速的热颗粒直接明火点燃过程中,热颗粒不仅充当加热源的作用,而且充当先导点燃源的作用。而在阴燃点燃和阴燃向明火的转变过程中,热颗粒仅充当加热源的作用,明火点燃的转变过程是易燃混合气体的自发点燃过程。
[Abstract]:The interaction of forest vegetation or building wood structure, or the interaction of high voltage wires and trees, can produce wood fire particles, and fireworks (small particles burning), electric welding (hot particles not burning at high temperature), industrial grinding or high pressure wire collisions, which produce high temperature metal particles, which can be used in the external flame flow field and environment. Under the action of the wind, a new fire source is formed, a new ignition source is formed, the forest combustibles are ignited, the exterior materials of building roofs or building exterior insulation materials, etc., lead to new fire accidents or accelerate the sprawl of jumping fire. This kind of fire is called flying fire. Fire is a large scale forest fire and forest town. Fire particles or building structures are an important potential spread way to cause forest fires and forest fires. Compared with the traditional fire spread (direct fire contact ignition and flame radiation point burning), flying fire particles ignite forest combustibles. The lighting process of building structure is very different. Therefore, it is urgent to study the ignition process of flying fire particles to fill the blank of the research field. The purpose of this paper is to understand the basic ignition process of high temperature fly fire particles to ignite the exterior insulating materials and forest combustibles, and to establish a physical model to reveal the ignition phenomena and mechanism. The specific work of this paper is as follows: using non isothermal thermogravimetry and differential scanning calorimetry, the pyrolysis dynamic characteristics of low density building external wall thermal insulation materials are studied. Based on the weight loss curve of solid material, the atmosphere atmosphere of typical building insulation materials is studied by using the equal conversion method and mode function method. The thermal kinetics of the pyrolysis was obtained by the DSC curve. The kinetic parameters and the reacting heat of the polyurethane foam and polystyrene foam were obtained by the kinetic study of the pyrolysis kinetics. For example, the critical conditions for high temperature particles to ignite polyurethane foam and polystyrene foam are established. The model has preliminarily predicted the ignition law of thermal particles under ideal conditions. In order to study the ignition behavior of hot particles, we set up an experimental platform for heat particles to ignite the thermal insulation materials. The process of ignition of low density polystyrene foam (18 or 27kg/m3) from 6mm to 14mm in diameter and temperature from 900 to 1100 C. Experimental study shows that the ignition of polystyrene foam by hot particles occurs only in the rolling process of the particles on the surface of the material and the stopping of the particles on the surface of the material and in the time interval of not completely entering the fuel bed. The critical ignition temperature of the low density polystyrene foam has a hyperbolic relationship with the critical particle size, that is, when the particle diameter increases from 6mm to 14mm, the critical ignition temperature will be reduced from 1030 to 935. The results show that the density and thickness of the fuel bed have a weak effect on the ignition probability and the mass loss rate. The theoretical analysis shows that the thermal particles not only act as the heating sources but also serve as the pilot igniting sources for the ignition of the polystyrene foam. The ignition process of hot particles on polystyrene foam is the result of the interaction between the mixing time of the material heat and the surrounding air and the lag time of the particles on the surface of the material. Based on the experimental phenomenon of the thermal particles igniting the thermal insulation material, a numerical model of gas phase ignition describing the hot particle point burning polystyrene foam is established. The model coupled the solid phase pyrolysis reaction, gas phase chemical reaction and the natural convection of combustible pyrolysis mixture. The numerical model obtained three kinds of ignition mechanisms, which are non igniting, unstable ignition and steady ignition. The pyrolysis of forest combustibles and the difference of combustion characteristics are carried out by standardized experimental operation by reforming the experimental platform of heat particle ignition. The ignition process of pine needle fuel beds (6% to 35%) with different moisture content of inert metal thermal particles (diameter 6mm to 14mm, temperature 600 to 1100 C) under the action of ambient wind (O to 4m/s) is studied. The direct ignition of hot particles, the igniting of the smoldering and the transition from the smoldering to the open fire. The critical particle temperature (Tp.crt=1800 (1+4FMC) /d+500[C) for continuous ignition decreases with the decrease of the particle size and the increase of the water content of the fuel bed, and the maximum heating efficiency of the hot particles is approximately sp=10%. with the increase of the thermal particle size. The effect of the water content of the fuel bed will become weaker. The time of two kinds of light igniting of the metal heat particles to the pine needle fuel bed is measured. This time decreases with the increase of particle size and wind speed, and increases with the increase of the water content of the fuel bed. The theoretical analysis also shows that heat particles not only act as the heating source, but also act as the pilot igniting sources in the process of quick hot particle direct fire, while the heat particles act only as the heating source during the transition of the smoldering and the smoldering to the open fire, and the transition process of the light ignition is a flammable mixed gas. The spontaneous ignition process.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X932
本文编号：2155932
[Abstract]:The interaction of forest vegetation or building wood structure, or the interaction of high voltage wires and trees, can produce wood fire particles, and fireworks (small particles burning), electric welding (hot particles not burning at high temperature), industrial grinding or high pressure wire collisions, which produce high temperature metal particles, which can be used in the external flame flow field and environment. Under the action of the wind, a new fire source is formed, a new ignition source is formed, the forest combustibles are ignited, the exterior materials of building roofs or building exterior insulation materials, etc., lead to new fire accidents or accelerate the sprawl of jumping fire. This kind of fire is called flying fire. Fire is a large scale forest fire and forest town. Fire particles or building structures are an important potential spread way to cause forest fires and forest fires. Compared with the traditional fire spread (direct fire contact ignition and flame radiation point burning), flying fire particles ignite forest combustibles. The lighting process of building structure is very different. Therefore, it is urgent to study the ignition process of flying fire particles to fill the blank of the research field. The purpose of this paper is to understand the basic ignition process of high temperature fly fire particles to ignite the exterior insulating materials and forest combustibles, and to establish a physical model to reveal the ignition phenomena and mechanism. The specific work of this paper is as follows: using non isothermal thermogravimetry and differential scanning calorimetry, the pyrolysis dynamic characteristics of low density building external wall thermal insulation materials are studied. Based on the weight loss curve of solid material, the atmosphere atmosphere of typical building insulation materials is studied by using the equal conversion method and mode function method. The thermal kinetics of the pyrolysis was obtained by the DSC curve. The kinetic parameters and the reacting heat of the polyurethane foam and polystyrene foam were obtained by the kinetic study of the pyrolysis kinetics. For example, the critical conditions for high temperature particles to ignite polyurethane foam and polystyrene foam are established. The model has preliminarily predicted the ignition law of thermal particles under ideal conditions. In order to study the ignition behavior of hot particles, we set up an experimental platform for heat particles to ignite the thermal insulation materials. The process of ignition of low density polystyrene foam (18 or 27kg/m3) from 6mm to 14mm in diameter and temperature from 900 to 1100 C. Experimental study shows that the ignition of polystyrene foam by hot particles occurs only in the rolling process of the particles on the surface of the material and the stopping of the particles on the surface of the material and in the time interval of not completely entering the fuel bed. The critical ignition temperature of the low density polystyrene foam has a hyperbolic relationship with the critical particle size, that is, when the particle diameter increases from 6mm to 14mm, the critical ignition temperature will be reduced from 1030 to 935. The results show that the density and thickness of the fuel bed have a weak effect on the ignition probability and the mass loss rate. The theoretical analysis shows that the thermal particles not only act as the heating sources but also serve as the pilot igniting sources for the ignition of the polystyrene foam. The ignition process of hot particles on polystyrene foam is the result of the interaction between the mixing time of the material heat and the surrounding air and the lag time of the particles on the surface of the material. Based on the experimental phenomenon of the thermal particles igniting the thermal insulation material, a numerical model of gas phase ignition describing the hot particle point burning polystyrene foam is established. The model coupled the solid phase pyrolysis reaction, gas phase chemical reaction and the natural convection of combustible pyrolysis mixture. The numerical model obtained three kinds of ignition mechanisms, which are non igniting, unstable ignition and steady ignition. The pyrolysis of forest combustibles and the difference of combustion characteristics are carried out by standardized experimental operation by reforming the experimental platform of heat particle ignition. The ignition process of pine needle fuel beds (6% to 35%) with different moisture content of inert metal thermal particles (diameter 6mm to 14mm, temperature 600 to 1100 C) under the action of ambient wind (O to 4m/s) is studied. The direct ignition of hot particles, the igniting of the smoldering and the transition from the smoldering to the open fire. The critical particle temperature (Tp.crt=1800 (1+4FMC) /d+500[C) for continuous ignition decreases with the decrease of the particle size and the increase of the water content of the fuel bed, and the maximum heating efficiency of the hot particles is approximately sp=10%. with the increase of the thermal particle size. The effect of the water content of the fuel bed will become weaker. The time of two kinds of light igniting of the metal heat particles to the pine needle fuel bed is measured. This time decreases with the increase of particle size and wind speed, and increases with the increase of the water content of the fuel bed. The theoretical analysis also shows that heat particles not only act as the heating source, but also act as the pilot igniting sources in the process of quick hot particle direct fire, while the heat particles act only as the heating source during the transition of the smoldering and the smoldering to the open fire, and the transition process of the light ignition is a flammable mixed gas. The spontaneous ignition process.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X932
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