中文摘要：

为研究热声不稳定的自激机理，搭建了mjke型预混燃烧器热声不稳定试验台架，研究了其热声不稳定起振过程的频率特性。Rijke型燃烧器为两个不同尺寸的方管，下端封闭，上端开口，多孔介质稳燃体位于燃烧器下端四分之一管长处，甲烷与空气的预混气体在稳燃体上方燃烧，形成平面火焰。试验发现了Rijke型预混燃烧器内热声不稳定的起振过程中存在着频率跳跃：燃烧热释放脉动与燃烧器声场的耦合首先激发低阶的热声振荡，然后此低阶热声振荡逐步消退，再度激发起更高阶的热声不稳定，依次类推，直至激发起适合当前燃烧器结构的稳定持续的压力振荡。

英文摘要：

In order to study the mechanism of self-excited thermoacoustic instability, experimental setup has been built. The characteristics of oscillation frequency during the start-oscillation of thermoacoustic instability were studied, using two closed-open Rijke-type combustors with different dimensions. Porous flame holders were installed inside the quarter place from the bottom of the combustors, over which the premixed gas of methane and air was ignited to form a flat flame. It is found that the frequency of pulsations hops from one resonant mode to another during the start-oscillation of thermoacoustic instability in these two premixed Rijke-type combustors, as follows： acoustic waves with lower resonant frequency were triggered because of the coupling between fluctuations of combustion heat release and the sound field of the combustors, then these acoustic waves damped quickly, and pressure oscillations with higher frequency were re-triggered, so on and so forth, ultimately a suitable resonant frequency of pulsations corresponding to the structural of the combustor was reached.