液氧煤油超临界富氧燃烧中的低频振荡特性实验研究

Experimental Investigation on Low Frequency Oscillation of Supercritical Combustion of LOX/Kerosene Oxidizer-Rich Mixture

关键词:  液体火箭发动机  液氧煤油  超临界  燃烧  低频振荡  离心喷嘴

Key words:  Liquid rocket engine  LOX/kerosene  Supercritical  Combustion  Low frequency  Centrifugal injector

摘要:

为了研究液氧煤油在高混合比下的燃烧特性，在模拟燃烧室中开展了液氧煤油在超临界压力环境下的富氧燃烧实验，燃烧室中采用了双离心喷嘴。实验过程中燃烧室压力额定值为6.4MPa，高于液氧和煤油的超临界压力。燃烧室直径为50mm，燃烧室长度约为345mm，燃烧室喉部直径10.5mm。用压力传感器记录液氧喷前压力、煤油喷前压力和燃烧室压力，压力数据的采样频率为2kHz。实验中发现：当混合比为10时，液氧煤油发生较为稳定的燃烧；当混合比为14.5时，燃烧室内出现了20~30Hz的低频燃烧振荡；在燃烧的启动和关机阶段，也出现了相近频率的低频燃烧振荡。液氧和煤油的喷前压力振荡相位均滞后于燃烧室压力振荡，表明振荡的源头在燃烧室。系统幅频特性分析结果表明，燃烧振荡频率与系统频率不耦合。液氧煤油低频燃烧振荡的主要诱发因素可能是高混合比燃烧下的温度效应。富氧燃烧温度低于2200K易诱发低频燃烧不稳定。

Abstract:

In order to research the combustion characters of LOX/kerosene oxidizer-rich mixture with high mixture ratio， the combustion experiment in a model combustor at supercritical pressure was carried out with such mixture. A dual centrifugal injector was used for liquid propellants atomization in the combustor. The rated chamber pressure during experiment is 6.4MPa， which is higher than the critical pressures of LOX and kerosene. The geometry of the combustion chamber is 50mm in diameter， 345mm in length and 10.5mm of chamber throat diameter. The LOX injection pressure， kerosene injection pressure and chamber pressure were recorded by pressure sensors with sampling rate of 2kHz. In the experiment it is found that combustion is stable at mixture ratio of 10， while unstable of 20~30Hz low frequency oscillation at mixture ratio of 14.5. There is also low frequency combustion oscillation with similar frequency during combustion initiation stage and combustion shut-off stage. The injection pressure oscillation phases of LOX and kerosene are both behind the phase of chamber pressure oscillation， which indicates the oscillation source may be in the combustor. The amplitude-frequency analysis result of experiment system shows that the combustion oscillation frequency is not coupled with the system frequency. The main factor which guides the low frequency combustion oscillation of LOX and kerosene may be temperature effect caused by high mixture ratio combustion. The low frequency combustion instability is easy to be induced when the oxidizer-rich combustion temperature was below 2200K.