高温伴流中燃料射流不稳定自着火特性研究

Unsteady Autoignition Characteristics of Fuel Jet in Hot Coflow

现代燃气轮机贫预混燃烧室入口温度的升高增加了预混段中不稳定自着火的风险.为探究高温伴流中燃料射流不稳定自着火特性,采用高灵敏度动态压力传感器和高速摄像机观测了自着火的回火过程和自着火频率特性.结合回火速度特征分析了回火机理,并重点研究了燃料摩尔分数、射流速度、伴流温度和伴流速度对不稳定自着火频率的影响.回火过程结果表明,自着火核通过火焰传播向上游的扩展是导致回火的主要原因.根据高速图像和幅度谱发现,当燃料摩尔分数低于临界值时不稳定自着火表现出间歇性.对比不同伴流温度和伴流速度下的幅度谱进一步揭示了该间歇性由化学反应和湍流耗散决定的自着火区域自由基浓度主导.

The rise of inlet temperature of the lean-premixed combustion chamber of the modern gas turbines increases the risk of unsteady autoignition in the premixed ducts.To study the unsteady autoignition characteristics of fuel jet in hot coflow,the flashback process and autoignition frequency were observed using a pressure probe and a high-speed camera.The flashback mechanism was determined based on the correlation of flashback speed.The effects of fuel mole fraction,jet velocity,coflow temperature,and coflow velocity on the unsteady autoignition frequency were mainly studied.The flashback process shows that the upstream expansion of the autoignition kernel through flame propagation is the main reason for the flashback.Based on the high-speed images and amplitude spectrums,the unsteady autoignition shows intermittency when the fuel mole fraction is lower than the critical value.The comparison of amplitude spectrums at different coflow temperatures and velocities further reveals that the concentration of free radicals in the autoignition region,determined by chemical reaction and scalar dissipation,dominates the intermittency.