机械通风环境中细水雾抑制地下停车库火灾轰燃的机理及有效性

Because of the low floor height and huge area, as well as the complicated ventilation surroundings in underground garage, the fire flashover hazard that may be caused by combustible liquid, gas and electricities,is very serious. Previous studies mainly concentrated on the fire flashover in small scale compartments with equivalent length and width under natural ventilation surroundings or long and narrow underground spaces,such as tunnels. The underground garage under mechanical ventilation surroundings is selected as the research object in this proposal. Full scale laboratory experiments on fire flashover control by water mist in underground garage are undergoing on the underground laboratory of 18m×6.9m×2.9m（height）.Together with small scale model experiments, computational simulations, as well as theoretical analysis, the similarity laws on fire flashover control by water mist in underground garage will be established and improved. The following parameters are to be monitored and measured, such as the mist field fluid characteristics, fire temperature,thermal heat flux,convection heat exchange,flue gas composition, as well as the evaporation rate of the liquified combustible materials. Based on the data analysis mentioned above, the thermal instability betweent water mist, flame and smoke are analyzed, as well as the energy feedback from the building enclosure to the flame and the surface of fire source. The dynamics of fire plume and smoke at the time of flashover under the coupling effect of mechanical ventilation and water mist in the underground garage is analyzed. Furthermore, the fire flashover control mechanisms and critical conditions by water mist is deduced to establish the flashover control prediction model by the coupling effect of mechanical ventilation and water mist in the underground garage.As a result, the optimal operation mode of the coupling system is analyzed and established. The research can provide scientific support to the development of water mist technology on the fire prevention and control technology field in the large scale underground engineering project.

地下停车库层高低、面积大、通风环境复杂，可燃液（气）体及带电火灾轰燃危险性严重。前人的研究主要关注自然通风条件下长宽比相当的腔室及地下狭长空间火灾轰燃机理。本课题利用18m×6.9m×2.9m（高）地下工程火灾实验室，进行机械通风环境中细水雾抑制地下停车库火灾轰燃全尺寸现场试验，结合缩尺寸模型实验、计算机模拟和理论分析，建立完善细水雾抑制地下停车库火灾轰燃实验的相似律；通过对雾场特性、火场温度、辐射热通量、对流换热量、烟气成分及燃料气化率等参数的监测，分析机械通风环境中，细水雾与火焰烟气和火源表面相互作用的热不稳定性，围护结构与火焰烟气及火源表面的能量反馈；分析地下停车库火灾轰燃时火焰烟气蔓延的动力学规律，分析机械通风和细水雾耦合系统抑制火灾轰燃的内在机理及临界条件，建立耦合系统抑制地下停车库火灾轰燃的预测模型，分析耦合系统最优化运行模式，为地下工程火灾细水雾防治技术的发展提供科学依据。

由于层高低、面积大、通风环境复杂，地下停车库火灾轰燃危险性严重。本课题以通风环境中地下停车库可燃液体池火为研究对象，首先通过全尺寸实验，利用激光粒子测试PIV系统，分析火灾作用下细水雾的雾场和速度场；搭建1:5和1:4缩尺寸实验模型，分别设置酒精和柴油池火作为主火源，酒精燃料作为待引燃火源，调整机械排烟量和排烟口位置，调整细水雾压力、喷头流量及布置方案和启动时间，进行细水雾抑制地下停车库火灾轰燃的实验。通过缩尺寸模型实验、全尺寸实验和计算机数值模拟的对比，分析机械通风和细水雾耦合系统对地下停车库火灾轰燃的抑制作用，得到结论如下：.1）费洛德相似准则适用于地下停车库火灾轰燃演化过程的分析；Heskestad关于细水雾灭火的相似准则适用于细水雾对地下停车库火灾的抑制作用。.2）地面接收到的热辐射通量是判断轰燃发生的主要依据，轰燃发生的临界时间受主燃料发烟量的影响最大。热辐射高于 15.87 kW/m2可以作为地下停车库火灾轰燃发生的临界判据。.3） 机械排烟抑制地下停车库火灾轰燃的有效性受到排烟口位置、排烟量和风速的影响。6次/h机械排烟无法有效抑制14MW部分遮挡的地下停车库火灾轰燃；在300秒时从30次/h增加到40次/h的变风量排烟系统可以有效抑制轰燃的发生。.4）不同压力细水雾对轰燃的抑制作用可以分为加剧轰燃区、过渡区、抑制轰燃区和加剧烟雾蔓延区。当压力低于3MPa时，细水雾加剧轰燃的主要原因可以归结为水煤气气化反应产生的氢气以及细水雾对空气的扰动作用。.5） 随着细水雾施加压力和喷头流量系数的增加，细水雾的粒径减小，雾动量增加，火焰对细水雾的卷吸作用增强，卷吸速度越大，细水雾对火灾轰燃的抑制作用加强。但细水雾压力过大可能造成烟气层高度降低，对人员疏散不利。.6）机械通风环境削弱了细水雾对火灾轰燃的抑制作用。在本课题所建立的14MPa部分遮挡的汽车漏油火灾工况下，10MPa，K=1.5菱形布置细水雾喷头有效抑制了火灾轰燃的发生。施加变风量机械排烟措施后，菱形布置、单喷头流量为30L/min、10MPa的细水雾可以达到最佳的灭火效果。.本课题的研究成果为地下工程火灾细水雾防治技术的发展提供理论依据和技术支持，从而更为有效的保障大型地下空间的火灾安全。