氢体积分数对甲烷-氢贫燃预混钝体火焰燃烧不稳定性影响

Effects of hydrogen volume fraction on combustion instability of methane-hydrogen lean premixed bluff-body flame

通过扬声器创造可调频率和振幅的正弦波声场环境,以甲烷-氢混合气贫燃预混钝体火焰为实验对象,通过火焰传递函数表征整个燃烧系统的燃烧不稳定性特征,借助CH基自发荧光图像描述火焰锋面运动及演化过程,研究了在不同声场频率和速度波动(声场振幅)下氢体积分数的变化(0、10%、20%)对火焰燃烧不稳定的影响。结果表明:随着氢体积分数的提升,在声场频率90～105 Hz区间时,火焰传递函数幅值变小,涡对火焰的影响减弱,火焰稳定性增强,而在115～170 Hz区间时,传递函数幅值增加,火焰长度变短,混合气火焰稳定性差;随着速度波动增加,在160 Hz声作用下甲烷火焰与涡的相互作用程度增强,而随着氢体积分数的提升,涡结构对火焰流场的拉伸和卷吸作用加强,燃烧热释放波动变大,火焰传递函数幅值增加,火焰抵抗外界扰动能力增强。该实验结果可为掌握甲烷-氢混合气燃烧不稳定性机理,发展燃烧不稳定性的主动控制技术提供参考。

In this study,a sinusoidal wave sound field environment with adjustable frequency and amplitude was created by loudspeakers.By taking the premixed blunt-body flame of lean combustion of methane-hydrogen mixture as the research object,the combustion instability of the whole combustion system was characterized by flame transfer functions and the motion and evolution of flame front was described by CH-based autofluorescence image.The effects of hydrogen volume fraction(0,10%,20%)on flame combustion instability under different sound field frequencies and velocity fluctuations(sound field amplitudes)were studied.The results show that,the combustion characteristics are very sensitive to the fraction of hydrogen in the fuel mixture.With an increase in the hydrogen concentration,when the sound field frequency varies within 90~105 Hz,the amplitude of flame transfer functions reduces,the flame-vortex interactions become mitigation,and the combustion instability of the premixed flame becomes weaker;when the sound field frequency changes within 115~170 Hz,the amplitude of flame transfer functions increases,the flame length becomes shorter,and the combustion instability of the premixed flame becomes stronger.With the increase of velocity fluctuation,the flame-vortex interactions become stronger at 160 Hz.As the hydrogen volume fraction increases,the drawing and entrainment of flame flow field by vortex structure improves,the fluctuations of heat release during the combustion enlarges,the amplitude of flame transfer functions increases,and the combustion instability of the premixed flame becomes stronger.These results help to understand the mechanism of combustion dynamics of methane-hydrogen flame,and develop the theory for active control strategies.