Title: High specific impulse electrospray propulsion with small capillary emitters Show Chinese title

Title: 高比冲电喷射推进的小毛细管发射器

Abstract: This study demonstrates the feasibility of using smaller capillary emitters to achieve higher specific impulse ($I_\text{sp}$) in electrospray propulsion. Four ionic liquids were characterized using capillary emitters with tip diameters from 15 to 50 $\mu$m. Smaller diameter capillaries produced smaller and more stable Taylor cones. This stabilization enabled steady cone-jet operation at significantly lower flow rates compared to larger emitters. This was unexpected because when the jet diameter is much smaller than far-field geometric features, the minimum flow rate is thought to be solely determined by the physical properties of the propellant. Using the smaller emitters and acceleration voltages of 10 kV, specific impulses up to 3000 s could be achieved with efficiencies above 50%, approximately doubling the $I_\text{sp}$ observed with larger emitters. For one of the liquids and the smallest emitters, the beam consisted solely of ions at the lowest flow rates, similarly to studies using externally wetted and porous emitters. Another important finding was that at sufficiently low flow rates, a significant fraction of the propellant fed to the emitter is not accelerated by the electrostatic field. These propellant losses make the time-of-flight technique unreliable for determining the $I_\text{sp}$. Show Chinese abstract

Abstract: 本研究证明了使用更小的毛细管喷嘴实现电喷推进更高比冲（$I_\text{sp}$）的可行性。四种离子液体通过具有 15 至 50 $\mu$米尖端直径的毛细管喷嘴进行了表征。较小直径的毛细管产生更小且更稳定的泰勒锥。这种稳定性使锥射流模式能够在比较大喷嘴显著更低的流量下稳定运行。这出乎意料，因为当喷射直径远小于远场几何特征时，最小流量通常被认为仅由推进剂的物理属性决定。使用更小的喷嘴和 10 千伏的加速电压，可以实现高达 3000 秒的比冲，并且效率超过 50%，大约是使用较大喷嘴时观察到的$I_\text{sp}$的两倍。对于其中一种液体和最小的喷嘴，在最低流量下，束流仅由离子组成，类似于使用外部湿润和多孔喷嘴的研究。另一个重要发现是，在足够低的流量下，提供给喷嘴的推进剂中有很大一部分不会被静电场加速。这些推进剂损失使得飞行时间技术在确定$I_\text{sp}$时变得不可靠。