PFPE脉冲等离子体推力器化学反应与流动对碳沉积抑制的影响机理研究

Pulsed plasma thrusters (PPTs) using non-volatile liquid perfluoropolyether (PFPE) propellants are very suitable for use on small satellites weighing less than 10 kg due to the minimal carbon deposition observed during their operation. However, the scientific mechanisms behind the minimal carbon deposition is currently unclear. There are two processes that may be responsible for carbon deposition on the ablation surface: 1) neutral carbon produced directly during the complex ablation process and 2) backflow carbon produced from recombination in the plasma. Therefore, experimental work on carbon deposition will be carried out to determine the conditions behind the carbon deposition and the plasma backflow parameters . A possible scientific mechanism behind PFPE’s minimal carbon deposition may be due to the presence of O atoms in PFPE. This may react with carbon to produce COx compounds. The role of O in the inhibition of carbon deposition will be studied using novel measurements of CO and CO2 within the ablation region, along with the plasma characteristics of PFPE. Finally, measurements of the plasma flow trajectory using long-exposure imaging will be carried out to study the relationship between the plasma flow and carbon deposition. The overall aim of this work is to explain the scientific mechanisms responsible for the minimal carbon deposition observed with PFPE and to provide a technical basis for engineering applications with PPTs.

PFPE(全氟聚醚)脉冲等离子体推力器（PPT）因其优良的碳沉积抑制能力有望成为10kg以下小卫星的微推进技术方案，但其沉积抑制机理尚未开展研究。PPT烧蚀壁面的碳沉积是前次PPT工作等离子体流动中组分离子复合并回流到烧蚀表面形成积碳和后次PPT工作工质烧蚀并发生由O元素引发的化学反应消耗表面积碳的综合作用过程。为此，本研究拟开展PPT碳沉积性能试验研究，获得碳沉积特性状态并为后续的等离子体流动提供电磁场入口条件；其次，开展烧蚀壁面碳沉积机理研究，通过亚mm级设备定位技术开展CO和CO2分子组分和等离子体特性测量试验，并结合理论仿真计算阐明O元素所引发的化学反应在碳沉积抑制中所起的作用；最后，开展基于长曝光摄影的等离子体粒子流动轨迹试验并综合速度信息，厘清等离子体流动对碳沉积的影响机制。本研究可阐释PFPE脉冲等离子体推力器碳沉积抑制的物理和化学机制，为该推力器的小卫星工程应用提供支持。

PFPE（全氟聚醚）脉冲等离子体推力器（PPT）因其优良的碳沉积抑制能力有望成为10kg以下小卫星的微推进技术方案，但其沉积抑制机理尚未开展研究。本项目以阐释PFPE工质PPT烧蚀壁面碳沉积抑制机制为最终目标。为实现这一目标，本项目开展了PFPE和PTFE（聚四氟乙烯）两种工质的PPT沉积试验，利用SEM和EDS等测试分析手段获得不同工质的沉积组分、颗粒分布等沉积特性及其演化过程。开展烧蚀壁面碳沉积机理研究，通过亚mm级设备定位技术、ICCD探测器进行了等离子体组分和等离子体特性测量实验。开展基于长曝光摄影、高速摄影和伪彩色图的等离子体粒子流动轨迹实验，厘清等离子体流动对碳沉积的影响机制。实验结果表明，PFPE工质PPT的推进剂表面存在的C+离子多于PTFE，电离程度较高。PTPE工质烧蚀过程中产生的C+随着向下游流动，容易产生离子复合和回流现象，从而出现碳沉积。本项目为解决PPT碳沉积问题提供参考，为长寿命PPT的研究提供理论依据。