【作者】 朱平；

【导师】 侯丽雅； 章维一；

【作者基本信息】 南京理工大学 ， 仪器科学与技术， 2011， 博士

【摘要】 电推进系统以其优越的性能逐步取代传统的化学推进系统,被广泛用来为航天器提供机动和控制推力。作为电推进的一种方式,脉冲等离子体推进器以高比冲、结构简单、重量轻、良好系统继承性和可靠性等特点,成为当前国际电推进研究的热点之一。典型脉冲等离子体推进器使用Teflon作为工质。然而,Teflon脉冲等离子体推进器存在一些问题,如：主放电期间的低速蒸汽和大粒子的发散造成推进性能低、Teflon烧蚀后产生的碳和氟污染飞船上的设备等,限制了脉冲等离子体推进器的实际应用。为此,无污染、性能高、具有广泛适用性的脉冲等离子体推进器技术是值得研究的重要课题。本文从器件研制、推进性能的理论分析、机制实验入手,以低功率水工质脉冲等离子体推进器为研究对象,从外部电路和本体结构的设计与制造、工作特性和性能、提高性能的途径等方面对水工质脉冲等离子体推进器的推进机制进行系统研究,取得了以下成果：推导出基于磁流体动力学的质量流率方程,进而得以从一维准稳定等离子体流场的角度对Teflon、H2O、Argon这三种工质在作用于系统时的质量流率和磁声速进行了比较分析,得出采用水作为工质对低功率脉冲等离子体推进器性能的提高最有利的结论；以水工质脉冲等离子体推进器物理模型的分析为前提,对推进器本体结构、主放电电路、触发装置的设计方法进行研究,研制出了水工质脉冲等离子体低功率推进器实验系统。从脉冲等离子体推进器基本性能关系式(推力、比冲、效率等)入手,把工作过程近似为LCR电路,建立了零维模型。打破了采用不可变电路参量的传统解算零维模型的束缚,提出了采用可变电路参量来解算模型,实现了解算精确性的提高。结合不可变电路参量和可变电路参量的零维模型对电磁加速模式的低功率水工质脉冲等离子体推进器的工作过程分别进行了理论分析,对外部电路结构参数对性能的影响进行了研究；在搭建的放电回路测量系统上,通过放电回路测量实验,结合零维模型研究了水工质脉冲等离子体推进器的放电类型、工作能量阂值等工作特性及放电参数对性能的影响,得出了水工质脉冲等离子体低功率推进器具有良好的工作特性的结论。从推力产生机制的角度(即推力由电热和电磁力制造),以零维模型为理论基础,通过对低功率水工质脉冲等离子体推进器的微冲量和等离子体中等效电阻的测量和理论分析,研究了推功比、能量分配和效率对推进机制的影响。在搭建的低功率水工质脉冲等离子体推进器的微冲量测量实验系统上,测量了羽流撞击水平靶的振动速度,并通过建立的冲量平衡模型得出实测冲量和实测推功比；对放电电流与冲量理论公式相结合计算出的理论推功比与由实测冲量值计算出的推功比进行了比较分析,从推功比的角度研究了电磁加速和电热加速在冲量制造过程中的变化趋势。把水工质PPT放电过程近似为一维准稳态MHD流动,将LCR电路的零维模型与一维准稳态MHD模型相结合,在水工质脉冲等离子体低功率推进器放电时的等离子体产生和膨胀扩散方式进行理论分析的基础上,结合不可变电路参量的零维模型推导出水工质脉冲等离子体推进器在运行过程中的能量分配关系和储能转换为电热和电磁加速的能量转换率公式。通过对放电电流的测量和分析,得到等离子体中的等效电阻分布情况,从能量分配的角度研究了电磁加速和电热加速在冲量制造过程中的变化趋势。针对水工质脉冲等离子体低功率推进器的推功比低是由等离子体的高电阻造成这一特点,在推进机制理论分析和实验研究的基础上,对易电离元素的基体干扰机理及对等离子体电磁加速影响进行了研究,并提出在水工质中添加低电离势的易电离元素Na和K来提高推进器性能的新方法。通过对采用NaCl水溶液、KC1水溶液的低功率水工质脉冲等离子体推进器的放电电流测量和等离子体发射谱线测量和识别,验证了新方法的有效性。更多还原

【Abstract】 Pulsed Plasma Thruster (PPT), as one of the electric propulsion systems which, for its excellent properties, is increasingly taking the place of the traditional chemical prolusion system and being widely used in maneuvering and controlling thrust of spacecrafts, has the characteristics of higher specific impulse, lower power dissipation, structure simplicity, light weight, good system inheritance and reliability, etc. and becoming one of the hot spots in international electric propulsion research. However, in the typical Pulsed Plasma Thruster which uses Teflon as the refrigerant, there exist some problems such as low velocity steam, low propulsive performance caused by large particle divergence, the pollution of spacecraft equipment by carbon and fluorine produced by Teflon ablation, which limit the PPT’s practical application. As a result, it is worthwhile to develop a PPT with free pollution, high performance and extensive applicability.The dissertation studies the propulsive mechanisms of the low-power water propellant PPT from its external circuit, the design and manufacture of noumenon structure, the working characteristics and performance, and the approach of improving the performance, etc. and achieves the following results:The mass flowrate under the magneto-acoustic condition and speed function of magneto-acoustic point are established. By discussing the influence of the propellants of gas-liquid-solid morphologies on PPT’s performance, the dissertation points out that water is the optimum propellant for improving the performance of low power PPT. Based on analyzing the physical models of water propellant PPT, the noumenon structure, main discharge electric circuits, the design of triggering device, the experimental system of water propellant PPT is set up.The numerical analysis of working process of water propellant PPT in the electromagnetic acceleration model is carried out by combining the circuit model of the fixed parameter and that of the variable parameter; the influence of the structure parameter of external circuit on performance is discussed; the measurement system of discharge circuit is built; by the measurement of discharge circuit the working characteristics such as the electric discharge type, work energy threshold etc. and the influencing factors of discharge parameters on performance are analyzed. From the angle of thrust generating mechanism--the thrust is manufactured by the Joule heat and the electromagnetic force, based on zero-dimensional model and by the measurement and theoretical analysis of the micro-impulse and plasma equivalent resistance of low-power water propellant PPT, the impact of thrust-to-power ratio, energy distribution and efficiency on the promotion mechanism is studied. The micro-impulse measurement experimental system of water propellant PPT is built; the impulse equilibrium model is set up; the vibration velocity of plume crashing on horizontal is measured and its impulse is calculated; the comparative analysis between the thrust-to-power ratio calculated by applying impulse theoretical formula to discharge current value and that calculated by practical measurement of impulse value is carried out. The theoretical analysis of dispersal behavior of the production and expansion of the plasma in the discharge process of water propellant PPT is carried out. Combining with the circuit model of the fixed parameter, the energy balance relation, the conversion of Joule heat from energy storage and the conversion rate of electromagnetic acceleration in the operating process of water propellant PPT are derived; the conversion rate of energy storage conversing into Joule heat and the electromagnetic acceleration in the operating process of water propellant PPT is obtained by the measurement of discharge current.The mechanism of easily ionized elements Matrix interferences and its impact on plasma electromagnetic acceleration is studied, and a new approach is put forward for the improvement of the propellant performance by the addition of easily ionized elements Na and K into the water propellant, and its feasibility is verified by the measurement of discharge current and the analytical experiment of emission spectrum.更多还原