基于火焰图像诊断的模型燃烧室燃烧不稳定特性

Combustion instability characteristics of model combustor based on flame image diagnosis

提出了一种基于火焰图像诊断的旋流燃烧室燃烧不稳定特性研究方法。分析甲基滤镜下高速CCD(charge coupled device)拍摄的火焰面振荡图像,发现不稳定工况下的旋流火焰在以较高频率抖动的同时伴随着周期性的火焰脱落,其脱落信息可由火焰面轴向峰值位置体现。对CCD图像进行数字图像处理获得轮廓线,统计其边缘轴向最远处坐标作为火焰抖动峰值位置。基于图像分析确定火焰脱落阈值,获得不同工况下火焰脱落发生时的脉冲时序信号,统计得各工况火焰脱落频率。研究发现该频率分别与火焰抖动时序、CH*时序及燃烧室压力脉动时序信号各自3阶本征模态函数的傅里叶谱主峰值接近。在多工况下研究了不稳定火焰脱离频率在时序信号中的存在方式和规律,发现对于本模型燃烧室,火焰脱落频率随着油气比的降低而升高,在油气比约0.0096处到达火焰脱落频率临界点,之后呈现缓慢下降趋势。

A method for studying combustion instability of swirl combustor based on flame image diagnosis was proposed.The flame surface oscillation image taken by the high-speed CCD(charge coupled device)under the methyl filter was analyzed.It was found that the swirl flame was jittered at high frequency with periodic flame shedding,and the shedding information can be reflected by the axial peak position of the flame surface.Digital image processing was performed on the CCD image to obtain the contour line.Then the coordinates of the farthest point in the axis of its edge were counted as the peak position of the flame jittered.Based on image analysis,the flame shedding threshold was determined,the pulse timing signals when flame shedding occurred under different working conditions were obtained,and also the flame shedding frequency of each working condition was calculated.The study found that the frequency was close to the main peak of the Fourier spectrum of the respective third-order eigenmode functions of the flame jitter timing,CH*timing,and combustion chamber pressure pulsation timing signals.The existence mode and law of the unstable flame separation frequency in the time sequence signal were verified under multiple working conditions.It was found that for the combustion chamber of this model,the ignition frequency increased with the decrease of the oil-gas ratio.When the oil-gas ratio was about 0.0096,it reached the critical point of flame shedding and then presented a slow downward trend.