Abstract: The acoustic characteristics of the combustion system，as well as the response of the flame to the fluctuations of incoming fluid，exert a fundamental influence on the conditions in which the instability may occur. Data from low-order thermoacoustic model were used to identify the frequencies，mode shape and nonlinear behavior of thermoacoustic instabilities. Low-order models described the acoustic characteristics of combustor system as a series of subsystems. In the flame model，heat release rate oscillation was written as the linear and nonlinear function of incoming velocity fluctuation. Nonlinearities were introduced into the linear flame model to predict triggering instabilities and limit cycle amplitudes. Several test cases compared with the experiments of laboratory combustor were analyzed in order to invest the effect of nonlinear terms in the flame model. The results agree well with the experiments，showing that the code can be used to describe the characteristics of the combustion instability and predict directly the limit cycle amplitudes from nonlinear flame model.

Key words: Combustion instabilities；Low-order thermoacoustic network；Flame model；Nonlinear；Limit cycle amplitudes

摘要： 为研究预混燃烧的燃烧不稳定性，采用低阶热声网络分析方法确定燃烧不稳定性的模态特征及非线性特性。在热声网络程序中利用声网络来描述燃烧室结构的声学特性，利用速度脉动的函数描述火焰的热释放脉动。在火焰模型中，在线性模型中增加非线性以求解不稳定模态的极限环幅值。分析了钝体模型燃烧室中火焰模型参数对燃烧不稳定性的影响，模拟结果与实验结果符合得很好。结果表明声网络方法结合非线性火焰模型能描述燃烧系统的燃烧不稳定性和直接预测极限环幅值。

关键词: 燃烧不稳定性; 低阶热声网络; 火焰模型; 非线性; 极限环幅值