同轴剪切喷嘴高频喷注耦合燃烧不稳定分析

Instability analysis on high-frequency injection-coupled combustion of shear coaxial injector

同轴剪切喷嘴在大推力氢氧发动机及液氧甲烷发动机上得到了广泛的应用,研究表明,当同轴剪切式喷嘴的中心氧喷嘴喷注过程与燃烧室的声学振荡发生耦合时,容易发生高频喷注耦合燃烧不稳定。高频喷注耦合燃烧不稳定一般无法通过隔板、声腔等传统燃烧稳定装置解决,需要在设计喷注器时采取相应措施。通过求解喷嘴导纳得到了喷嘴的固有声学频率,并与冷态声学试验结果和缩比喷注器热试结果进行了对比,表明吻合较好。研究了氧喷嘴长度、氧喷孔环直径、氧喷前温度和氧喷前压力等因素对氧喷嘴声学频率的影响,结果表明:增大氧喷孔环直径、提高氧喷前压力以及减小氧喷嘴长度、降低氧喷前温度可以提高氧喷嘴声学频率。

Shear coaxial injector is widely used in high thrust hydrogen/oxygen and LOX/LCH4engines.According to investigation,the high-frequency injection-coupled combustion instability is easy to happen when the injection process of the central oxygen injector is coupled with acoustic oscillation in chamber.This instability can not be eliminated with baffle or acoustic cavity,but can be avoided by clever design of injector.Inherent acoustic frequency of oxygen injector was obtained by computing admittance of injector,and compared to the results of cold state acoustic experiment and subscale injector hot-fire test.Their consistency is quite good.The effects of oxygen injector length,oxygen injector orifice diameter,oxygen temperature,oxygen pressure on acoustic frequency of oxygen injector are investigated on this basis.The results indicate that the acoustic frequency of the oxygen injector can be improved if the oxygen injector orifice diameter is enlarged,the oxygenpressure is increased,the oxygen injector length is decreased or the oxygen temperature is lowered.Some suggestions on injector design are given.