低速过滤燃烧非平衡特性的孔隙尺度研究

The combustion mechanism of premixed gas in the pores is the basis and key to study the filtration combustion. It is also the only way to further understand the characteristics of filtration combustion. Based on experimental test, theoretical and numerical studies on pore scale, this project explores the microscopic mechanism and basic rules of low-velocity filtration combustion characteristics in porous media. Based on the non-intrusive combustion visualization measurement and pore scale numerical study, we study the flame of dynamic propagation, shape and evolution rule of flame in characteristic unit. We reconstruct a general geometric model for sphere packed bed suitable for high temperature combustion taking into account of sphere-sphere contact heat transfer. The influence of the working parameters on the nonequilibrium characteristics is revealed. The mechanism of superadiabatic combustion and stabilization combustion is clarified on the pore scale. The energy conservation equation of the flame propagating in the pore is established, and the critical number of the low-velocity filtration combustion transition to the disturbance combustion and the high speed filtration combustion is analyzed. This study helps to promote the recognition of filtration combustion mechanism from macro understanding to mesoscopic scale and present the microscopic mechanism of the filtration combustion which is ignored by the volume-averaged method. At the same time, a more perfect basic theory of flame dynamics for filtration combustion on the pore scale is developed, it is beneficial to formation of new knowledge of filtration combustion, which lays the theoretical foundation for efficient filtration combustion use in the national economy and social development.

预混气在孔隙内的燃烧机理是研究过滤燃烧的基础和关键，也是进一步深入认识过滤燃烧特性的必由之路。本项目通过实验测试、数值研究和理论分析，基于孔隙尺度深入探索低速过滤燃烧的微观机理和基本规律。采用燃烧可视化测量和孔隙尺度的数值研究，探明火焰在特征单元内的细微动态传播、结构形态和演化规律。考虑球-球接触传热，建立适用于燃烧高温场合的小球填充床通用几何模型，阐明工作参数对非平衡特性的影响规律,从孔隙尺度揭示出超绝热机理和火焰驻定燃烧机理。建立火焰在孔隙内传播的能量守恒方程，解析低速过滤燃烧转捩为扰动燃烧和高速过滤燃烧的临界准则数。本申请将过滤燃烧的宏观认识推进到介观尺度，揭示出被以往体积平均法忽略的过滤燃烧的微观机理，建立较为完善的孔隙尺度过滤燃烧火焰动力学基本理论，形成比较系统的过滤燃烧新知识，为过滤燃烧在国民经济和社会发展中的高效利用奠定理论基础。

极低热值燃气的使用促使科学家开发出各种高效、清洁的燃烧技术。多孔介质燃烧器被认为是用于热值范围广泛的各种燃料的最有效的方法之一，与自由空间中的燃烧相比，多孔介质中燃烧具有的优势是：宽广的操作极限、极富与极贫的可燃性极限和较低的污染物排放。本项目主要研究内容包括：火焰动力学、热非平衡、超绝热燃烧机理与调控、两层多孔介质燃烧器驻定燃烧机理，从孔隙尺度揭示热非平衡特性和影响因素，阐明固体基质物性和几何形状对超绝热燃烧效应的影响和调控机制，解析低速过滤燃烧的转捩机理。. 本项目基于实验与孔隙尺度三维数值研究，发现多孔介质燃烧器内的回热机制是通过多孔介质表面逐层传递的；流动非平衡是填充床的本质特性，流动非平衡存在于整个燃烧器内，非平衡从燃烧器入口开始振荡增大，在火焰区域二者达到最大值，随后振荡降低。填充床内表现出很强的非平衡特性，在火焰区域组分、化学反应速度、温度和气体速度的变化非常剧烈，变量在三维空间上的分布是变化的。特别是流速的非平衡分布必然导致当地传热系数的变化，进而影响气体温度分布以及化学反应速度。均方根流速与流速比值达到0.6，而均方根温度值达到120K。这些数据揭示了填充床内的非平衡特性，从本源上探明了多孔介质燃烧器内燃烧的物理机制和真实面目，为燃烧器的优化设计奠定了理论基础。