离散分布多火源耦合燃烧动力学特性与规律研究

Group fires, generated by the burning of discrete combustible materials, can easily develop into urban or wildland mass fires in practice,with great growth of burning intensity. Multiple fires burning is the fundamental process involved in group fires, in which the fires generally have significant influence on each other due to two major fire interaction effects -the air entrainment restriction and radiation heat feedback enhancement. Due to the fire interaction effects, multiple fires burning may lead to extreme fire behaviors such as fire merging and fire whirl, and especially, the data and theory for single fires cannot be directly extra polated to multiple fires. For specific fire source conditions, the interaction effects among fires mainly depend on the fuel distribution conditions such as fire spacing and number of fire points. Therefore, the experiments of multiple discrete fires are designed to study the development and mutation of free burning group fires. For specific fire source conditions, the combustion characteristics, such as burning rate of each fire point, temperature, radiation flux and flame height, will be measured under different fuel types and distribution conditions such as fire spacing and number of fire points. Fire merging phenomenon also will be observed from the video. Based on these experimental data, the time variation and spatial distribution of multiple fires burning behavior can be analyzed. Radiation heat feedback enhances the flame length and burning rate of each fire point and also is affected by the flame state and burning intensity. The dynamic coupling mechanism can be discussed according to the analysis of multiple fires burning behavior and a experimental model to calculate the total radiation heat of burning area will be developed founded on combustion models of single pool fire. Further, based on the experiments and thermal radiation model, numerical simulation is intended to explore the key factors controlling the developing process of multiple fires burning, and some new criteria will be developed to identify the conditions for fire merging and identifying the conditions for fire spreading from burning multiple fire points to nearby discrete fire sources due to thermal radiation. This project is very significant to understand the combustion dynamics of multiple fires in depth, and can provide scientific support for the preventing and controlling of group fires.

群发性火灾，是离散分布的可燃性材料同时燃烧而形成的火灾场景，此类火灾的发展过程中，易发生多火源耦合燃烧现象，引起火灾强度的剧烈变化，形成城市或森林区域大火，造成重大火灾损失。因此，针对群发性火灾的发展与突变问题，以散布火源为研究对象，开展火阵列自由燃烧模拟实验。对于既定的火源，获取不同燃料种类和离散分布特征（火源数目和火源间距）条件下燃烧域内各火源燃烧速率、温度场、辐射热流和火焰高度等燃烧特性表征量，并以此分析各特征量随燃烧时间的变化趋势和在燃烧空间上的分布特征，揭示燃烧区域辐射热流、火焰形态、燃烧速率间耦合作用机制，并基于池火燃烧模型构建多火源燃烧总热辐射经验模型，开展数值模拟并结合实验和辐射模型探讨多火源燃烧时空演化过程关键影响因素，从而提出火焰融合现象和热辐射导致燃烧蔓延的临界条件。本项目对于深入理解多点火源耦合燃烧动力学演化规律有重要意义，可为群发性火灾的预防与控制提供科学指导。

群发性火灾，是当空间多处区域离散分布可燃性材料由其他类型的灾害或火灾蔓延诱发而发生燃烧的火灾场景，此类火灾发展过程中，易发生多火源耦合燃烧现象，引起火灾强度剧烈变化，形成城市或森林区域大火，造成严重的损失。离散多火源燃烧描述的是群发性火灾基本燃烧过程，考察的重要问题是群发性火灾如何向城市和森林区域大火突变。.因此，针对群发性火灾的发展与突变问题，本项目以离散分布火源为对象，主要采用小尺度离散火阵列自由燃烧实验模拟方法对其燃烧特性进行研究，分析不同火源中心距离和阵列大小条件下火源燃烧速率、温度和辐射热流随燃烧时间变化趋势及在空间域上的分布特征，探索火焰融合现象诱发临界判别方法和条件，并基于单一池火燃烧理论发展离散火源总辐射热和各火源燃烧速率计算方法，重要研究结果如下。.本研究首先对离散多火源燃烧特征量变化规律进行了定性分析。对火源燃烧速率、温度和辐射热流密度随燃烧时间变化趋势的分析结果表明，燃烧速率存在近似平稳段，而受燃烧环境变化影响，燃烧区域温度和对外辐射热流密度随燃烧发展达到峰值后逐渐衰减。对火源燃烧速率随离燃烧中心距离及不同大小阵列内中心火源燃烧速率随燃料面比率变化规律的分析结果表明，受所处阵列空间方位影响，中心火源燃烧速率远大于边缘火源；受火焰融合程度和燃烧耦合作用机制竞争影响，燃烧速率随空间位置变化幅度存在突变点。研究还发现对于给定大小火阵列，燃烧周围任意点所受辐射热与燃料面比率成正比。.本研究提出了基于无量纲火源间距和燃烧区域温度场分布特征的两种火焰融合现象判别方法，离散火源中心间距是火焰融合诱发及融合程度主要影响因素，D*=4是等距多火阵列火焰融合临界点，但该条件与火源数目有关，火源越多，其值越大。.本研究发展了基于池火热辐射理论的离散火源总辐射热计算方法并通过实验和数值模拟进行了验证。研究认为离散多火源周围任意点所受辐射热流密度qm=Qtotal(4πlm-2)，燃烧总辐射热Qtotal=0.279HcBRtotal。该研究还基于燃烧传热阻碍理论，将多火源耦合燃烧分解成外加辐射热流使各自由燃烧火源燃烧速率增大过程，并推导出离散分布各火源燃烧速率定量计算方法，该方法目前正在通过实验结果总结验证中。.本研究定性和定量描述了离散分布多火源燃烧特性，丰富了燃烧基础理论，进一步理解了群发性火灾基础燃烧过程和发展突变规律，对这类火灾预防、控制与扑救有重要意义。