Abstract: In order to intensively study the mechanisms of combustion instability in a lean premixed combustor，experiments were carried out to measure the axial distribution of the flame heat release under different conditions with various equivalent ratios and air flow rates. Thus the distribution of the flame transfer function especially the distribution of the phase were obtained and their relevance with all sorts of conditions. Experimental results indicate that the lag time corresponding to the phase of flame transfer function consists of three parts: the time for disturbances to propagate from the position of fuel injector to the dump plane，time lag for the formation of vortex ring near the dump plane，and the transport time of vortex ring from its seminary to the flame front. However，the phase increment resulting from the formation of vortex ring is the key factor as regard to the combustion instability. The phase increment changes from 0.5 to 1.0 while the equivalence ratio varies from 0.6 to 0.73. Two quite large modes exist in this combustor，which are the inlet mode 233Hz with self-locking trait and the transport mode 180 Hz. The frequency of the transport mode alters from 180Hz to 207 Hz with the change of phase increment.

Key words: Combustion instabilities；Self-excited mode；Flame transfer function；Time lag；Vortex ring

摘要： 为了深入研究贫油预混燃烧室中的燃烧不稳定机理，采用实验方法测量火焰沿轴向的热释放分布，研究了不同当量比以及空气流量对自激振荡模态下的分布式火焰传递函数尤其是相位分布的影响。结果表明，火焰传递函数的相位所对应的迟滞时间主要由三部分构成:扰动从燃料喷注点传播至头部所需的输运时间、靠近头部出口突扩面处涡环形成的迟滞时间、涡环输运至火焰锋面的输运时间；而其中漩涡环涡环形成所造成的相位增量是研究燃烧不稳定性的关键因素，当量比由0.6增加到0.73的过程中相位增量相应从0.5增加到1.0。自激振荡较强的两个模态中，进气段模态频率为233Hz具有锁频特性，而输运模态频率为180Hz会随着相位增量的变化而变化，由180Hz增加到207Hz。

关键词: 燃烧不稳定性; 自激振荡模态; 火焰传递函数; 迟滞时间; 漩涡环