贫燃预混旋流火焰的模态转换燃烧不稳定特性分析

Analysis of Combustion Instability Characteristics of Mode Switching on Lean-Premixed Swirling Flame

关键词:  燃烧不稳定性  旋流火焰  模态转换  本征正交分解法  燃烧室

Key words:  Combustion instability  Swirling flame  Mode switching  Proper orthogonal decomposition  Combustion chamber

摘要:

为进一步研究燃烧室燃烧不稳定特性，通过实验对贫燃预混旋流火焰的燃烧不稳定性模态转换现象进行了研究。在贫燃的情况下进行了甲烷-空气预混旋流燃烧实验，用动态压力传感器测量火焰场动态压力，用光电倍增管捕捉CH*化学发光，用4kHz频率的高速摄像记录火焰图像。发现当量比渐增到0.72附近时，燃烧有明显的模态转换，压力脉动主频由264Hz突变为187Hz，脉动幅值大幅增加。采用本征正交分解法得到各模式空间分布，通过模态系数进行快速傅里叶变换(FFT)分析，得到流场时间分布特征。发现模态转换前平均火焰为喇叭形，转换后为“M”型，模态的转换与涡脱落模式有重要关系。

Abstract:

In order to study the combustion instability characteristics of combustion chamber, the combustion instability of mode switching on lean-premixed swirl flame was investigated by experiments. The experiments were about methane-air lean-premixed swirling flame. The dynamic pressure of flame field was measured by dynamic pressure sensor, and the chemiluminescence of CH* was captured by photomultiplier tube. High speed images with acquisition frequency of 4kHz were recorded to catch flame structure. The experimental results show that when the equivalent ratio of flame increases to 0.72, the combustion has mode switching. During the switching, the pulsating main frequency changes from 264Hz to 187Hz, and significant increase in amplitude. A proper orthogonal decomposition (POD) procedure is used to extract the spatial distributions of modes. The time distribution characteristics of flow can be obtained by Fast Fourier Transform (FFT) analysis of modal coefficients. The results show that the average flame is horn-shaped before mode switching and “M” after that. The modal switching is closely related to vortex shedding mode.