【作者】 田章福；

【导师】 周进；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2007， 博士

【摘要】 本文采用理论分析、试验和数值仿真等方法,深入研究了低浓度酒精的雾化与蒸发、过氧化氢催化分解及低浓度酒精在低浓度过氧化氢催化分解产物中的点火和燃烧等过程,研究结果对低浓度酒精/过氧化氢燃气发生器的设计和性能改进有重要意义。对五种不同结构燃气发生器喷嘴的流量和雾化特性开展了试验研究。主要研究了喷嘴结构和工作参数对流量和雾化特性的影响,并利用自行设计的反压罐研究了反压对雾化的影响。结果表明:外混式喷嘴有独立的气体和液体通道,气体和液体流量系数受喷嘴结构影响较大,但受工作参数影响较小,而内混式喷嘴两相流流量系数受喷嘴结构和工作参数影响均较大;反压通过改变气体喷注速度影响雾化过程,高反压下,气体喷注速度为亚音速,反压增加使气体速度降低,从而导致雾化性能下降。建立了多组分液滴蒸发模型,并且通过试验验证了该模型的正确性。应用该模型对燃气发生器燃烧过程进行了数值仿真,结果表明:在低浓度酒精喷雾蒸发过程中,由于组分挥发性的差异,液滴中酒精的蒸发速度比水快,导致燃烧室的气相温度沿燃烧室轴线先增加后降低,喷注面板附近较高的燃烧温度有利于火焰稳定。设计了开窗模型燃气发生器,对喷雾燃烧过程进行了观测和拍照,研究了喷嘴结构、酒精浓度等因素对火焰和燃烧效率的影响,并对比了冷/热试中的喷雾和火焰。结果表明:增加同轴直流式喷嘴的缩进长度和内喷嘴出口角度,提高了混合性能,从而提高了燃烧性能。燃烧强度较低时,燃烧对雾化过程影响较小,火焰锥与冷试喷雾锥的宽度和张角相当;燃烧强度较大时,燃烧对雾化过程影响较大,火焰锥的张角明显大于冷试喷雾锥的张角。通过试验和仿真研究了不同浓度过氧化氢的催化分解性能、催化剂床低频不稳定性产生原因及消除方法。结果表明催化剂床及催化剂的吸热对过氧化氢分解过程影响很大,对催化剂床进行预热或采用热导率低的材料制造催化剂床等措施,可以降低催化剂床壁面吸热对催化分解过程的影响,提高催化剂床的响应特性和催化分解效率;催化剂床的低频不稳定是催化分解过程与供应系统耦合产生的,催化剂床气体界面的波动过程中,液体过氧化氢穿透催化剂床形成过氧化氢液体通道,过氧化氢液体通道的产生和扩大是催化剂床不稳定的主要原因,也是消除催化剂床不稳定的关键,试验中在催化剂床内加入分流板成功地抑制了催化剂床的低频不稳定。在以上研究的基础上,系统地研究了低浓度酒精/过氧化氢燃气发生器的点火性能和燃烧性能,分析了余氧系数、燃烧室特征长度和过氧化氢喷注速度等参数对燃气发生器点火性能和燃烧效率的影响。降低过氧化氢分解产物的流量和喷注速度或采用部分过氧化氢催化分解方案,能有效地提高燃气发生器的点火性能;燃气发生器的燃烧效率随特征长度和余氧系数的增加而增加。更多还原

【Abstract】 Diluted ethanol spraying and evaporation, hydrogen peroxide catalytic decomposition, ignition and combustion of diluted ethanol in decomposed hydrogen peroxide were studied in detail by means of theoretic analysis, experimental investigation and numerical simulation. And many significant results, which are important to design and optimize diluted hydrogen peroxide/ethanol gas generator, have been acquired.The discharge and atomization characteristics of five types of gas generator injectors in different configurations were tested. The influences of injector configurations and test parameters on the discharge and atomization characteristics were experimentally studied in detail. The pressured container was designed to study the atomization performance under high pressure environment. Some important conclusions have been obtained from experimental results. Firstly, the discharge coefficient of gas and liquid in external-mixing injectors, which have gas channels and liquid channels separately, is affected obviously by injector configurations but rarely by test parameters. Secondly, the discharge coefficient of two phase flow in internal-mixing injectors is affected distinctly by both injector configurations and test parameters. Finally, the pressure affects the atomization through the velocity of gas. In the high pressure environment, the velocity of gas is subsonic, and the velocity decreases while the pressure rises, which worsens the atomization performance.The evaporation model of multi-composition droplet was presented, which was validated by experiments. The process of combustion in the model gas generator was simulated using the evaporation model, and the results showed that during the evaporation of diluted ethanol droplet, ethanol evaporates faster than water on the droplet surface because of different distillation characteristics, which makes the temperature of the combustion chamber increase at the beginning and then decrease along the axis. The high temperature around the injection panel is good to flame stabilization.The combustion experiments of model gas generator equipped with quarts windows were conducted. The law of flame propagation during ignition and stable combustion, and infuences of the ethanol concentration and the injector configuration on the flame and the combustion performance were investigated. The results showed that the coaxial shear injector with larger indent distance or exit angle has better mixing performance and higher combustion efficiency. When the intensity of combustion is low, combustion has little effect on the spraying and atomization, and the angles of the flame taper and non-reacting spraying taper are almost the same. When the intensity of combustion is high, combustion has obvious effect on the spraying and atomization, and the angle of flame taper is larger than that of non-reacting spraying taper.Hydrogen peroxide catalytic decomposition performance and the low frequency instability of catalyst bed were investigated by numerical simulations and experiments. The results show that the decalescence of catalyst bed affects the process of hydrogen peroxide catalytic decomposition greatly. If the catalyst bed is preheated or made up of materials with low thermal conductivity, that influence can be depressed. At the same time, the response characteristic of catalyst bed and the efficiency of catalytic decomposition can be improved. The low frequency pressure instability of catalyst bed occurs because of the coupling of catalytic decomposition and supplying. The decomposition plane pushes all the way through the catalyst bed during pressure oscillations, causing unreacted liquid hydrogen peroxide to be exhausted from the bed and leading to the appearance of liquid hydrogen peroxide channeling. Consequently, how to prevent or at least limit this channeling is the key to eliminate the pressure instability of catalyst bed. It was found that adding clapboard to the catalyst bed can depress the pressure instability efficiently.On the basis of the investigations above, the ignition and combustion performances of the diluted hydrogen peroxide/ethanol gas generator were studied systematically. Furthermore, the influences of the oxygen coefficient, the combustor character length and the injection rate of hydrogen peroxide on the performance of gas generator were analyzed. Adopting part of hydrogen peroxide through catalytic bed or reducing the flux and injecting rate of decomposed hydrogen peroxide can improve the ignition performance of this gas generator. Increasing the oxygen coefficient and the combustor character length can enhance the combustion efficiency likewise.更多还原