液氧/液甲烷双离心式喷嘴富氧低频燃烧不稳定性研究

Low Frequency Combustion Instability of LOX/LCH4 Bi-Swirl Injector under Oxygen Rich Conditions

关键词:  富氧燃烧  双离心喷嘴  缩进长度  熵波  低频燃烧不稳定性

Key words:  Oxygen rich combustion  Bi-swirl injector  Recess length  Entropy wave  Low frequency combustion instability

摘要:

为了研究液氧/液甲烷双离心式喷嘴在富氧条件下的低频燃烧不稳定性，在模型燃烧室中开展了喷嘴相对缩进长度为1.5，2.0和2.7的高压燃烧实验和数值模拟研究，描述了低频燃烧不稳定现象，获得了振荡频率特性和喷嘴缩进长度对振荡频率的影响规律。结果表明：燃烧室压力在起动过程中从稳定转为不稳定，压力振荡经历振幅增长阶段后，达到极限环振幅阶段，最终表现为燃烧室和供应路的耦合共振。燃烧室低频振荡频率主要受到熵波传播的影响，基于数值模拟方法获得了燃烧状态下甲烷质量分数空间分布特征，再根据熵波对流模型预测了室压振荡频率，预测频率和实测频率的趋势一致，误差范围是7.4%～9.8%。随着相对缩进长度的增加，甲烷消耗完全所需时间缩短，燃烧室熵波频率增大，因此燃烧室振荡频率也随之增大。

Abstract:

In order to investigate the low frequency combustion instability of LOX/LCH₄ bi-swirl injector under oxygen rich conditions， the high pressure combustion testing and numerical simulation were carried out in a model combustor with injector relative recess lengths of 1.5， 2.0 and 2.7， the phenomenon of low frequency combustion instability is described， otherwise the characteristic of oscillation frequency and the influence of injector recess length are obtained. The results show that the combustor pressure transfers from steady to unsteady in the start process， and the pressure oscillation goes through the stage of amplitude increasing and then reaches the stage of limited cycle amplitude， which finally manifests as the coupled resonance between the combustor and the supply circuit. The low oscillation frequency of combustor is mainly affected by the propagation of entropy wave， the spatial distribution characteristics of methane mass fraction were obtained by numerical simulation methods， and then the combustor pressure oscillation frequency is predicted according to the entropy wave convection model. The trend of predicted frequency is consistent with that of measured frequency， and the error range is 7.4%~9.8%. As the increasing of recess length， the methane consumption time becomes shorter， and the frequency of entropy wave becomes higher， thereby the frequency of combustor pressure oscillation also increases.