燃烧系统中拍振产生机理及其抑制方法研究

The beating phenomenon in combustion system is a patten of self-excited nonlinear thermo-acoustic instability, which is characterized from conventional limit cycle oscillation by the spontaneous periodic modulation of oscillation amplitude. The appearance of beat is likely related to several processes including modulation of acoustic boundary influenced by the fuel gas jet flow, unsteady heat transfer between flame and the stabilizer, flame pulsating instability caused by Kelvin-Helmholtz instability or thermo-diffusive instability and so on, which have not been investigated experimently and theoretically at present, and their influence mechanisms in thermo-acoustic systems are unclear. This research project aims to investigate mechanisms how the processes mentioned above couple with pressure oscillation or heat release rate oscillation, and then to establish nonlinear dynamic model for simulation of beat oscillations and systematic analysis of subcritical instability in combustion oscillations which is one of the most challenging problems in this area. And control theory for combustion instabilities will be further developed with the special consideration of beating phenomenon. The results of the project will help to extend stability boundary of combustors in fundamental research aspect, and in industrial application aspect to realize effective early warning and control of combustion oscillations,therefore allowing the develop of safe, clean, and highly efficient safe combustion technology for heavy power and propulsion systems.

燃烧系统中的"拍振"是一类由非线性热声耦合导致的燃烧振荡现象，其区别于一般谐波振荡的特点在于：振荡幅值会自发的、有规律的周期性变化。这类现象的发生可能与流动导致的声学边界特性改变、火焰与稳焰结构之间的非稳态传热过程、由流动或扩散过程引起的火焰自身脉动等过程有关，但目前对此还缺乏相关实验研究与理论分析，对这些过程在热声系统中的作用机理也不明确。本项目将从热声耦合系统和火焰动力学两个层面，研究上述过程与压力脉动、放热率脉动的耦合机制，建立可预测拍振的非线性动力学模型，并据此分析目前困扰研究者的燃烧振荡亚临界不稳定现象；同时进一步发展燃烧振荡控制理论以抑制拍振现象。研究结果不仅有助于拓展对于燃烧振荡现象中非线性现象的认识，也将有助于在工业应用中拓宽稳定燃烧工况边界，实现对燃烧振荡现象的有效预警和控制，为发展应用于大型动力与推进系统中的清洁高效安全的燃烧技术提供条件。

燃烧振荡是发展干式低污染燃气轮机燃烧室难以回避的问题之一。燃烧振荡过程中会形成剧烈的压力脉动和火焰不稳定现象，严重危害燃气轮机的安全稳定运行。这种振荡现象是热声耦合导致的燃烧系统固有的不稳定性，也称为热声不稳定。本文针对一类特殊的热声不稳定现象——拍振开展实验研究与理论分析，并对燃烧系统中的拍振进行主动控制研究。本项目系统地对黎开管燃烧器和工业模型燃烧室开展实验研究与理论分析。通过拍振条件下的火焰动力学分析，认为低频的火焰脉动过程是导致拍振的幅值调制现象的主要原因，而这种低频火焰脉动与层流火焰固有的扩散-热不稳定性有关。考虑不同时间尺度上的火焰动力学特性，建立了能够预测拍振的热声耦合模型，利用此模型可以对拍振现象的发生规律与时变特性进行预测与分析。通过黎开管燃烧器主动控制的数值仿真与实验研究，比较了不同控制算法的控制效果。旋流预混燃烧室中的实验研究表明，湍流条件下的拍振现象其基本特征与层流燃烧器中类似，但是其拍振特征随工况条件的变化较明显。针对旋流预混燃烧室中的主动控制，提出了一种通过实验测量建立热声耦合系统的非线性模型的方法，并对旋流预混燃烧室中燃烧振荡的主动控制进行了实验研究。