镁基燃料水冲压发动机的热声振荡特性研究

Characteristics of Thermoacoustic Oscillations in MagnesiumBased Water Ramjet

为了探究金属基燃料发动机内的燃烧不稳定性问题,以镁基燃料水冲压发动机为背景,从理论上开展了热声振荡机理及特征频率特性的研究。通过Mg/H2O燃烧化学反应动力学分析,证实了高温环境中水的热分解特性是引起燃烧反应热释放波动的原因,结合不稳定燃烧中的声压振荡,合理解释了热声振荡的发生机理。进一步考虑平均流作用,建立了一维热声振荡计算模型,基于自行开发的热力计算程序,获得了三种选定镁基燃料一次燃烧产物的热力学性质及燃烧水燃比的上限2.0,2.4,2.6,同时结合边界条件、守恒条件求解了声压传播方程,获得了不同工况下的复频特性,实部均在700Hz以内属低频振荡,镁基燃料质量组分配比、进水口位置及水燃比均对特征频率虚部有较大影响,对于既定的燃烧室结构构型及镁基燃料,可通过调节进水量来主动干预热声振荡的发展趋势。

Characteristics of thermoacoustic oscillations in magnesium-based water ramjets are investigat- ed theoretically. The mechanism of thermoacoustic oscillations for magnesium combustion in steam atmospheres has been obtained based on analysis of Mg/H2O chemical reaction kinetics, and the results indicate that water dissociation under high temperature arouse heat release fluctuations, then coupled with pressure fluctuations un- der reliable phase, thermoacoustic oscillations would occure. A one-dimensional calculation model considering a mean flow for calculating eigenfrequency of thermoacoustic oscillations is established, and it is known that ther- modynamic properties of primary combustion products and maximum water/fuel ratio 2.0, 2.4, 2.6 could be achieved based on developed thermodynamic calculation. The pressure wave equation is solved based on these in- let thermodynamic properties coupled with boundary conditions and conservation conditions. The results show that the oscillation model belongs to low-frequency oscillation due to real part of eigenfrequency less than 700Hz, while the imaginary part profile of complex frequency along with water/fuel ratio, water inlet position for three magnesium-based fuels indicate that these three factors hold great influence, and the development trend of oscillations could be transformed by through altering water supply.