Mg-O2和Mg-CO2预混气燃烧特性及热声振荡的数值模拟研究

Numerical Simulation on Combustion Characteristicsand Thermoacoustic Oscillations for

关键词:  金属燃料  镁  燃烧机理  热声振荡

Key words:  Metal fuel  Magnesium  Reaction mechanism  Thermoacoustic oscillations

摘要:

基于金属镁在高超声速飞行器及火星探测器上的应用，为探讨金属燃料在不同氧化剂环境中的燃烧特性及热声不稳定性机理，开展了数值模拟研究。考虑镁蒸气与O₂和CO₂两种氧化剂的剧烈反应区，构建了预混燃烧的二维燃烧室模型，详细探讨了预混气当量比、预混气初温及入口速度等对燃烧特性及热声振荡特性的影响规律，并与CHEMKIN计算结果进行了比较分析。结果表明，较高的当量比下燃烧室的燃烧速率更快，燃烧平衡温度更高，此外增加预混气初温能加快燃烧室燃烧速率，而更高的入口速度会使燃烧室的压力振荡从低频高振幅振荡向高频低振幅振荡转化。燃烧室的压力振荡同时存在轴向振荡和径向振荡，振荡曲线为高频振荡和低频振荡的不同组合。入口速度对燃烧室压力振荡有较大影响，入口速度越快，振荡频率越高，而声压级越低。此外，预混气当量比和预混气初温对燃烧室的压力振荡也有一定影响。

Abstract:

Based on the application of magnesium fuel in hypersonic vehicle and Mars explorer， the combustion characteristics of magnesium vapor in O₂ and CO₂ environment were investigated. In numerical simulation， the reaction mechanism for Mg-O₂ and Mg-CO₂ were considered， the flow field distribution and thermoacoustic oscillation in combustion chamber were studied based on a 2D model， and the results were compared with the calculation results in CHEMKIN. Simulation results show that: Equivalent ratio， initial temperature and inlet velocity affect the combustion characteristics in combustor， the fuel rich premixture has a better combustion performance than the lean premixture. The burning rate is accelerated with the increase of the initial temperature of the premixed gas， and higher inlet velocity will change the pressure oscillation in combustor from low frequency and high amplitude oscillation to high frequency and low amplitude oscillation. Besides， the pressure oscillation mode in combustor is a combination of axial oscillation and radial oscillation. The higher the inlet velocity is， the higher the oscillation frequency is， but the sound pressure level is lower. Besides， the pressure oscillation is also influenced by equivalence ratio and initial temperature.