【作者】 刘景华；

【导师】 王振国；

【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】 以过氧化氢为氧化剂的液体火箭发动机具有广泛的应用前景,其动态特性是研制中的难题之一。本文综合采用理论分析、数值仿真和实验研究等多种手段,对过氧化氢发动机的动态特性进行了全面深入的研究。针对液体火箭发动机系统的特点,提出了混合维仿真方法。对静态参数混合、动态参数混合和动态直接混合的三种维度混合方式,分析了其相关理论问题。在静态参数混合中,以过氧化氢喷嘴为例,研究了流量系数随结构参数和工作参数的变化。在动态参数混合中,首先应用有限元方法,分析了弹簧的模态和频响特性,再应用系统辨识的方法,建立了弹簧的二阶模型,指出:由于存在死圈,弹簧的等效质量应为总质量的40%,并据此对压力调节阀进行了仿真;通过对文氏管进行二维CFD仿真,建立了文氏管的黑箱和灰箱模型,计算表明,文氏管在动态反压下,输出流量将有±3.3%的波动。对某发动机的启动过程开展了仿真研究,分析了该发动机隔离阀前出现压力突然下降的原因,特别指出压力降不是与流量变化值相关,而是与流量变化的速率相关。提出了相应的解决措施,包括:(1)改变管路尺寸;(2)调节流量变化曲线;(3)在隔离阀前加装蓄能器。针对某过氧化氢/煤油发动机出现关机爆炸的现象,开展了包含传热、两相流在内的关机过程仿真,对氦气吹除的效果进行了评估,得到了不当的氦气吹除反而造成温升的结论。提出了过氧化氢延时关机方案,通过对过氧化氢冷却和吹除气冷却的效果进行研究,得到了最佳的关机时序。开展了以低浓度过氧化氢/低浓度酒精为推进剂的发动机实验。(1)开展了催化分解实验,对催化分解效率、活化时间、催化剂寿命等进行了研究,得到了催化床的设计准则;利用孔板和隔板,成功消除了过氧化氢催化床中存在的低频不稳定。(2)研究了燃烧室构型、喷注器结构、催化分解效率、工作参数等对燃烧性能的影响,得到了提高燃烧效率的途径。(3)从推进剂浓度、喷注压降、点火能量、点火时序等方面开展了点火研究,突破了低浓度推进剂发动机的点火这一关键技术。(4)过氧化氢发动机中长期存在低频振荡,通过分析影响振荡的各种因素,提出了相应解决方案,攻克了这一技术难关。研制了一系列高效、稳定、快速的过氧化氢发动机,所采用的过氧化氢浓度可以为90%,70%,50%,工作室压为1.9～4.0MPa,发动机流量为0.6～7.7kg/s,理论燃烧温度为900～1800K。这些发动机所生成的高温燃气具有广泛用途。针对实验中的不稳定现象,综合采用各种维度混合方式,建立了过氧化氢发动机的混合维仿真模型。(1)稳态仿真表明:在低浓度酒精发动机中存在着“酒精先蒸发”现象,使局部温度大于理论温度,这一定程度上解释了实验中出现的喷注面板烧蚀现象;燃烧效率的仿真结果与实验结果较为吻合,偏差不超过6%。(2)建立了发动机稳定性的理论分析模型,对实验发动机而言,当燃烧时滞大于13ms时,系统将不稳定。(3)仿真所得到的系统振荡频率与实验的频率接近,趋势一致,说明混合维仿真具有较高实用价值;研究了喷注压降、余氧系数等对发动机不稳定度的影响,表明:过低的喷注压降会引起系统振荡,过高的压降会造成发动机熄火。(4)提出了一种部分催化的单调变推力发动机方案,该发动机具有宽范围的稳定性和良好的调节性。更多还原

【Abstract】 Liquid propellant rocket engine with hydrogen peroxide as its oxidant has prosperious future and one of the most difficult things to develop this type of engine is its dynamic characteristics, as is researched deeply in this thesis by means of theoretical analysis, numerical simulation, and experiment research.A new method used to simulate liquid rocket propulsion system is proposed by the name of mixing-dimensional simulation. And there are three modes of dimension mixing: static parameter mixing, dynamic parameter mixing, dynamic direct mixing, all of which are researched with relative theories. The discharge coefficiency of injector, as is an example of static parameter mixing, is variable with structure parameter and work parameter, considering the injector is so narrow in hydrogen peroxide engine. The modes and frequency response of spring is obtained using 3D CFE method, then spring model is established by means of system identification and the result shows that the equivalent mass occupies 40 percent of total mass because of dead loop. And a pressure adjust valve is simulated based on this spring model. Black-box model and grey-box model of venturi are established based on 2D CFD simulation, results show that the flow rate fluctuates in the range of±3.3% in the conditions of dynamic exit pressure.The starup process of engine is simulated with focusing on the pressure drop before isolation valve. The reasons are found and correlative means to solve this problem are proposed including: (1) change size of supply pipe; (2) regulate the variety of flow rate; (3) install accumulator before isolation valve.The shutdown pocess of hydrogen peroxide/kerosane engine is simulated based on heat transfer and two phase flow aiming at the explosion in experiment. It shows that the peroxide temperature in cooling channel may increases when helium expels in wrong flow rate or in wrong sequence. A scheme of postponing shut of hydrogen peroxide is proposed and the shutdown sequence is optimized through evaluating the effect of peroxide as a coolant or helium as a filling gas on the decrease of temperature.Experiments of engine with low concentration hydrogen peroxide and low concentration ethanol as propellants are conducted. (1) Catalysis decomposition of peroxide is researched especially focused on the catalysis efficiency, activation time and longevity of catalyst bed in order to get the design and use guideline. The low frequency fluctuate in the catalyst bed is elimilated using hole shutter and isolation panel. (2) Combustion performance is researched in different conditions including: different configuration of combustor, structure of injector, efficiency of catalyze and working parameters. Then approachs to improve combustion performance are obtained. (3) The ignition of this low concentration propellant which is very difficult is broken through considering the effect of propellant concentration, pressure drop of injector, ignitor energy and ignition sequence. (4) Low frequency fluctuate which often happens is controlled by analyzing relative factors. Then a series of fast, high efficiency and stable hydrogen peroxide engines are developed with peroxide concentration range of 90%~50%, combustor pressure range of 1.9~4.0MPa, combustion temperature ranges of 900~1800K, flow rate of 0.6~7.7kg/s. And the high temperature gas produced by these engines is very useful in some areas.The mixing-dimension model of experimental propulsion system is established in order to simulate the unstable phenomena. (1) Results from stability simulation show that there is a phenomenon of“ethanol evaporates firstly”, as is the reason why injector panel is burnt in experiment. And the combustion efficiency from simulation is consistent with that from experiment; with the maximum deviation is less than 6%. (2) Stability model is established and researched, results show that the propulsion system gets unstable when combustion-lag is more than 12 millisecond. (3) Oscillation frequency from simulation is approximately equal to that from experiment. Then the factors that influence instability degree are checked, including injector pressure drop, excess oxygen coefficient, etc. Results show that too low injector pressure drop leads to unstable but too high drop leads to flameout. (4) And a new concept variable thrust engine using partially catalyzed peroxide is evaluated mainly on its stability and modulation.更多还原