Control of Instability on Premixed Lean Combustion using Pyragas method

预混稀薄燃烧由于火焰温度低于化学计量燃烧，具有NOx排放量低、燃烧效率高的特点。然而，由于在火焰中引入了过量的O2，预混稀燃烧往往不新鲜。本研究的目的是利用混沌控制理论，即Pyragas方法，来提高燃烧器的燃烧效率。无论是工业应用还是学术研究，燃烧状态的感知或O2过剩比的测量都不是一件容易的事情。研究了三种定位高温燃烧蓝色火焰的光学方法。第一种方法是利用高速CCD相机和高分辨率A/D转换器进行光谱分析。它不适合工业应用，但有利于了解火焰动力学，因为火焰的形状和蓝色部分的位置很容易再现可视化。第二种方法也是利用光电二极管阵列系统的光谱学，该系统需要光纤来引导火焰的某一部分光线。虽然与第一种CCD相机方法（约100ms）相比，这种方法需要更短的处理时间（约10ms），但它不被认为是实际的工业应用。为此，采用单色滤光片和高灵敏度光电二极管进行高速处理。结合火焰传感系统，采用扬声器合成射流致动器和Pyragas控制方法对不稳定升力火焰进行了稳定。

Premixed lean combustion is known for low NOx emission and high-efficiency combustion process, because flame temperature is lower than stoichiometric combustion. However, premixed lean combustion tends to be unstale due to introduction of excessive amount of O2 into flame. Aim of this research was improving efficiency of combustors applying a Chaos control theory, known as Pyragas method, for unstable combustion dynamics.Sensing of combustion state or measuring of O2 excess ratio is not easy task for industrial application nor academic research. We investigated three optical methods for locating blue flame, which represents high temperature combustion. First method is spectroscopy using high speed CCD camera and high resoltion A/D converter. It is not suit for industrial application but beneficial to understand the flame dynamics, because shape of the flame and location of blue part is easily reproduced for visualization. The second method is also spectroscopy using photo-diode array system, with which optical fiber is necessary to guide ray of a certain part of flame. Though this method requires shorter process time (about 10ms) compared to the first CCD Camera method(about 100ms), it is not conceived to be practical for industrial application. Therefore, monochroic optical filter and high sensitivity photo-diode were assembled for high speed processing.Loud speeker synthetic jet actuator and Pyragas control method was shown to be effective to stabilize unstable lift flame, coupled with flame sensing system tested in this research.