多孔介质内贫预混气体燃烧热斑不稳定性机理研究

Filtration gas combustion (FGC), also known as porous media combustion (PMC), has the advantages of high combustion efficiency, ultra-lean flammability limitation, low emissions of pollutants, etc. And it has a widespread application prospect. However, the hot-spot instability often occurs for low-velocity filtration combustion with lean premixed hydrogen/air mixtures. As one of PMC instabilities, it is necessary to systematically clarify the mechanism of hot-spot instability. In this project, the mechanism for the hot-spot instability of low-velocity filtration combustion will be studied using the experimental, theoretical, and numerical methods. The experimental way combined with high-speed camera, thermal infrared imager, and thermocouples system will be taken to observe and measure the hot-spot instability emergence and dynamic evolution. The main influencing factors will be determined for the hot-spot instability. And the principles and features of hot-spot emergence will also be showed. According the experimental results, the mathematical model of a single hot spot will be proposed. The dimensionless Nusselt number, Sherwood number relations of a single hot-spot heat and mass transfer will be determined. The Lewis number relation for the criteria of the development of hot-spot instability will also be modified by comparison to the experimental results. Furthermore, the flame structure of a hot spot will be calculated with chemical reaction kinetics model, the chemical reaction mechanism of hot spot will be further clarified. Based on the above researches, it is significantly meaningful to construct the theory system of PMC, and to utilize the PMC technology.

过滤气体燃烧，亦即多孔介质燃烧，具有高燃烧效率、极贫燃极限、低污染物排放等优点，应用前景广泛。然而，贫氢气/空气预混气体低速过滤燃烧过程中，常出现热斑不稳定性现象，热斑不稳定性机理作为多孔介质燃烧不稳定性研究内容之一亟待系统地阐明。本课题拟通过实验、理论、数值手段对低速过滤燃烧热斑不稳定性机理进行研究。实验研究拟采用高速摄像机、红外热像仪、以及热电偶测温系统相结合的方式对热斑不稳定性的发生及其动态演变进行观测，确定热斑不稳定性的主要影响因素，揭示其发生的规律与特点。根据实验结果，建立单个热斑的数学模型，确定其传热、传质准则关联式，并将理论解与实验结果进行比较，确定判定热斑不稳定性发生的修正Lewis准则表达式。此外，通过化学反应动力学方法计算热斑火焰结构，阐明热斑不稳定性发生的化学反应动力学机理。基于以上研究，阐明低速过滤燃烧热斑不稳定性机理对多孔介质燃烧的理论体系构建及应用具有重要意义。

多孔介质燃烧可以被认为是一项很有前景的技术，该项技术具有降低燃料/空气贫预混可燃极限、提高燃烧效率、低热值气体利用、低CO和NOx污染物排放等优点。然而，多孔介质燃烧器内低速过滤气体燃烧常出现火焰面倾斜、热斑等不稳定性现象。本项目通过实验、数值模拟分别研究了惰性多孔介质内贫预混气体低速过滤燃烧波火焰面倾斜与热斑不稳定性，理论上分析了这两种不稳定发生及发展的动力学因素。研究结果表明，初始预热不均匀性被确认为低速过滤燃烧波面倾斜不稳定性发生的初始热扰动因素，并且发现火焰面倾斜发展速度与初始热扰动大小成正相关性。当初始扰动达到300K以上时，在较低当量比和较高入口过滤速度条件下，会有火焰面破裂和火焰面偏移不稳定性的发生，与实验结果能够定性上吻合的很好。因此，初始热扰动300K的预热不均匀性是上述不稳定性发生的关键扰动参数，并确定火焰面倾斜、破裂、偏移三种不稳定性机制在过滤速度和当量比条件下发生的参数范围。此外，通过实验确定了多孔介质燃烧器内氧化铝小球堆积床孔隙率、燃烧器尺寸、入口过滤速度、预混燃料浓度等因素显著影响热斑不稳定性的发生及发展。实验结果分析表明，热斑燃烧点在多孔介质堆积床内具有随机分布的特征，并且堆积床孔隙率越大，热斑点尺寸越大，燃烧浓度越高，热斑点数越多。理论上分析表明，在堆积床局部孔隙内，当热斑燃烧点与周围未燃烧预混气流达到动量、热质交换动态交换平衡时，热斑点注定在孔隙内维持稳定地燃烧。同时，热斑不稳定性的发生显著影响主燃烧波传播的稳定性，由于部分燃料提前燃烧，这将导致主燃烧波传播速度的降低。.通过以上多孔介质内燃烧不稳定性研究，确认了影响因素的显著性，揭示这些燃烧不稳定性发生的影响因素及发展规律，为未来多孔介质燃烧技术的工业化应用提供理论和参数支撑。