【作者】 韩超；

【导师】 夏智勋；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2011， 博士

【摘要】 水冲压发动机性能随着水反应金属燃料中金属含量的增加而显著提高。开展高金属含量水反应金属燃料与水反应机理研究、探索水冲压发动机稳态燃烧特性,对提高水冲压发动机性能、实现高金属含量水反应金属燃料水冲压发动机持续稳定工作具有重要的理论和实际意义。本文采用实验研究、理论分析和数值模拟相结合的方法,对高金属含量镁基燃料水冲压发动机稳态燃烧机理进行了系统研究。提出并建立了水反应金属燃料燃烧机理实验研究方法,采用蒸汽发生器提供高压水蒸气环境,开展水反应金属燃料与水反应机理研究;设计了可进行燃烧现象观察和参数测量的开窗式燃烧器,建成了水冲压发动机燃烧机理研究实验系统,可扩展用于多种燃料在不同环境下的燃烧过程研究。采用DSC、TG-DTA等热分析方法,研究了金属镁含量分别为60%和73%的镁基水反应金属燃料(简称60型、73型镁基燃料)的热分解历程。研究发现,两种燃料的热分解过程均由其组分的热分解叠加而成;73型镁基燃料中氧化剂AP的分解峰温相对提前。开展了60型镁基燃料在氩气和水蒸气环境下的稳态燃烧实验研究。研究表明,60型镁基燃料燃烧时,燃面温度高于金属镁的熔点,镁液滴在燃面着火并进入气相燃烧;与氩气环境下的自维持燃烧相比,水蒸气环境下稳态燃烧的火焰亮度增加,凝相燃烧产物中的氧化镁含量增加,单质镁含量减少。根据60型镁基水反应金属燃料稳态燃烧实验结果,明确了60型镁基燃料稳态燃烧过程,揭示了其稳态燃烧机理,建立了60型镁基燃料稳态燃烧模型。60型镁基燃料稳态燃烧时,燃料中的镁颗粒在燃面熔化成为镁液滴,并在氧化剂和粘合剂热解气体产物的拖拽作用下进入气相;燃料在燃烧区热反馈的作用下进行热分解,氧化剂AP的热分解过程控制着燃速;燃面附近气相火焰由AP预混火焰、AP/HTPB初始扩散火焰、AP/HTPB最终扩散火焰组成;Mg液滴进入气相后,首先与AP氧化性热解产物反应,剩余镁液滴继续与水蒸气反应放热。在发动机工作压强下,燃面获得的热反馈主要来自AP预混火焰、AP/HTPB最终扩散火焰和Mg液滴与AP氧化性热解产物的反应放热,Mg液滴在水蒸气中的燃烧放热对燃面热反馈贡献较小。分析了宏观因素对燃料稳态燃烧特性的影响规律,结果表明,工作压强升高、水蒸气浓度增加和环境温度的升高有利于提高燃料燃面温度和燃速。开展了73型镁基燃料在氩气和水蒸气环境下的稳态燃烧实验研究。研究表明,73型镁基燃料燃烧时,燃面温度高于金属镁的熔点,熔化的镁液滴粘附在燃料热解后的碳骨架上,基本上不进入气相。与自维持燃烧相比,水蒸气氛围下稳态燃烧的火焰亮度和火焰高度增加,凝相燃烧产物中镁颗粒破损程度加剧,氧化镁含量增加,单质镁含量减少。根据73型镁基水反应金属燃料稳态燃烧实验结果,明确了73型镁基燃料的稳态燃烧过程,揭示了其稳态燃烧机理,建立了73型镁基燃料稳态燃烧模型。73型镁基燃料稳态燃烧时,燃料中的镁颗粒在燃面熔化成为镁液滴,由于燃料中氧化剂和粘合剂含量较低,燃料热解产气量较少,无法将镁液滴带入气相;镁液滴在气相火焰热反馈的作用下,在燃面蒸发,并且其蒸发过程控制着燃速;AP、HTPB热解气体产物及镁液滴蒸发产生的镁蒸气在燃面附近形成AP预混火焰、AP/HTPB/Mg初始扩散火焰、AP/HTPB/Mg最终扩散火焰;氧化剂AP消耗完后,剩余镁蒸气继续与水蒸气反应放热,燃料中金属镁的燃烧放热是燃面热反馈的主要来源。分析了宏观因素对73型镁基燃料燃料稳态燃烧特性的影响规律,结果表明,稳态燃烧燃面温度和燃速随着工作压强、水蒸气浓度和环境温度的升高而增大。考虑了燃料与一次进水之间的耦合燃烧对发动机燃烧过程的影响,建立了高金属含量镁基燃料水冲压发动机稳态燃烧与流动数值计算模型,并通过发动机实验数据验证了模型的正确性。系统研究了燃面退移、一次进水水燃比、一次进水角度、一次进水雾化粒径及喷射速度等参数对水冲压发动机稳态燃烧特性的影响,获得了燃面温度和燃速随一次进水参数变化规律,提出了有利于改善水冲压发动机工作性能和维持高金属含量镁基燃料水冲压发动机稳定燃烧的工作方式。更多还原

【Abstract】 The performance of water ramjet engines increase with the metal content of their hydro-reactive fuels. It is significant to develop a steady-state combustion mechanism of hydro-reactive metal fuels for performance enhancement and combustion sustainment of high-metal magnesium-based fuel water ramjet engines.Approaches of experimental study, theoretical analysis and numerical simulation were applied for research on the steady-state combustion mechanism of high-metal magnesium-based fuel water ramjet engines.An experimental method for combustion mechanism research was developed. An experimental system was built and a combustor with functions of observation and measurement was designed.Magnesium-based hydro-reactive fuels of Type 60 and Type 73, in which magnesium contents were 60% and 73% respectively, were adopted in the study. The thermal decomposition courses of both fuels were analysed with DSC and TG-DTA method. It was observed that the thermal decomposition of the fuels consist of decompositions of their components, and the maximum decomposition temperature of AP in the Type 73 fuel was higher than that in Type 60.The combustion experiments of the two fuels were carried out in Argon and steam atmospheres respectively. For the Type 60 fuel, results show that the burning surface temperature is higher than the melting point of magnesium, and the magnesium droplets enter the gas zone, along with the decomposed gas products of AP and HTPB. The flame brightness in steam is stronger than that in Argon, and the content of MgO in combustion products is also higher in steam. For the Type 73 fuel, the burning surface temperature is still higher than magnesium melting point, while the magnesium droplets do not leave the burning surface but adhere to the carbon framework of HTPB.A model was built to describe the combustion of the Type 60 fuel. Magnesium particles melt and ignite in the surface temperature. The gas-phase combustion near the burning surface includes AP premixed flame, AP/HTPB primary and final diffusion flame. The magnesium droplets react with the decomposed products of AP prior to the reaction with the steam. Under the working pressure, the thermal feedback to burning surface mainly comes from the reaction of magnesium and AP. It was found that working pressure, concentration of steam and atmosphere temperature have positive effect on the burning rate and surface temperature.A model describing the combustion of the Type 73 fuel was also established. The flame consists of AP premixed flame, AP/HTPB primary and final diffusion flame forms near the burning surface. Under the surface temperature, magnesium particles melt, evaporate and then react with the oxidization products of AP. With the moving of AP/HTPB/Mg flame, water steam diffuses into the burning area and reacts with the remained magnesium. Under the working pressure of water ramjet engines, thermal feedback to the burning surface mainly comes from the combustion of magnesium. The burning rate and surface temperature increase with the working pressure, concentration of steam and temperature of atmosphere.A numerical model was built to simulate the combustion and flow of high-metal magnesium-based fuel water ramjet engines. Influences of the moving of the burning surface, water/fuel ratio, injection angle, atomize diameter and injection velocity of primary water-jet on combustion characteristic were studied. The variation rules of surface temperature and burning rate were obtained. Methods for optimizing the combustion characteristic were put forward.更多还原