分布式非预混火焰传递函数的实验研究

Experimental Investigation of Distributed Flame Transfer Function for Non-Premixed Flame

关键词:  燃烧振荡  非预混火焰不稳定性  分布式火焰传递函数  卡塞格林光学测量系统

Key words:  Combustion oscillation  Instability of non-premixed flame  The distributed flame transfer function  Cassegrain optical system

摘要:

非预混燃烧是动力设备和推进系统中常见的燃烧组织形式。为了理解非预混火焰的动力学特性、预测和控制其振荡燃烧现象，有必要获得其火焰传递函数。本文通过实验测量对分布式非预混火焰的传递函数进行了研究，实验对象为甲烷空气同心射流火焰。实验中使用双麦克风技术测量燃烧室出口速度脉动，作为传递函数的输入量；使用CH基自发荧光测量燃烧过程的放热率脉动，作为传递函数的输出量。搭建了卡塞格林光学测量系统，以提升放热率测量的空间分辨率，实现单点测量，进而得到一维分布式火焰传递函数。结果表明，在频域内，实验中测得的传递函数的幅值沿火焰轴向存在两个峰值，在幅值的峰谷处相位角有[180°]翻转，这是热斑以对流速度向下游传播，跨越火焰面时所造成的。

Abstract:

Combustors with non-premixed flames are widely used in propulsion and power systems. To predict and control the combustion oscillation，it is crucial to understand the flame dynamics，which can be described by the flame transfer function. The one-dimensional distributed flame transfer function for a methane-air coflow non-premixed flame was investigated experimentally. The two-microphone technique and [CH*] chemiluminescence intensity measurement were used to determine the inlet-velocity perturbation and heat release oscillation，which are the input and output to the flame transfer function. A Cassegrain optical system was used to improve the spatial resolution so that the local，temporal intensity of chemiluminescence can be measured，therefore the one-dimensional distributed flame transfer function. The results show that in the frequency domain，the amplitude of the distributed flame transfer function has two peaks，and the angle of the distributed flame transfer function has a nearly[π]shift through between two peaks. This is caused by the hot spots propagating downstream across the flame surface.