热声耦合振荡燃烧的实验研究与分析

Experimental study and analysis of thermo-acoustic instabilities in natural gas premixed flames

关键词:  预混火焰  热声耦合振荡  线性扰动分析  燃烧动力学

Key words:  Premixed combustion  Thermo-acoustic instabilities  Linear perturbation theory  Combustion dynamics

摘要:

热声耦合振荡是在推进系统工作中经常遇到的危害系统工作及安全的现象。它是由非稳定燃烧放热和压力脉动互相耦合产生的系统振荡过程。通过对天然气预混燃烧过程中的热声耦合振荡现象进行了实验研究,分析了不同当量比、热负荷和进出口边界条件下天然气燃烧的动态过程,分析其稳定范围及振荡模态随影响因素的变化规律。结果显示振荡频率随着当量比的减小有所增加,但是没有发生模态变化。在常压条件、接近贫燃熄火极限时,热声耦合振荡现象消失,压力脉动频率跃升至500 Hz或1000 Hz附近的高频。燃烧室出口越接近阻塞条件,燃烧过程的稳定范围越小。同时入口边界位置越接近燃烧段,压力脉动频率越高。热功率变化也会对脉动频率和声压级数值产生影响。另外还采用线性扰动分析方法对天然气燃烧动态过程进行理论分析,进一步研究了不同条件下旋流预混燃烧的热声耦合振荡模态。

Abstract:

Combustion oscillations are phenomenon usually encountering during the engine operation and it is dangerous for engine operation.Combustion oscillations are induced by coupling between unsteady heat release and pressure perturbations.The dynamical processes of natural gas premixed combustion were examined by varying fuel-air equivalence ratio;power loads and boundary conditions.Under each condition,the equivalence ratio range of stable combustion was obtained and the variations of oscillation modes were analyzed.It was shown that the oscillation frequencies would increase with the decrease of equivalence ratio.At the atmosphere pressure,the combustion oscillations will disappear near the lean blow out limits and the frequencies will change in the range between 500 Hz and 1000 Hz.The combustion stable range turns into narrow when the outlet is close to the choking conditions.The shorter length of the inlet boundary,the higher frequency of the pressure oscillations.The power loads also have significant influences on the frequencies of oscillations and their amplitudes.Meanwhile,the dynamical processes of natural gas combustion were also studied by linear perturbation theory.The oscillation modes were analyzed.