Study on the electrowetting and beam current characteristics of externally wetted ionic liquid electrospray thruster

Abstract

It is the theoretical basis to analyze the hydrodynamics mechanism of ionic liquid in an electrostatic field to ensure that the ionic liquid electrospray thruster possesses good wettability. Stable and continuous electrowetting emitters are closely related to thrust noise, resolution, and stability. Therefore, it is urgent to explore the law of ionic liquid electrowetting emitters in an electrostatic field to improve the performance of thrusters. The article proposes a new hybrid emitter structure, which consists of a V-blade emitter and a square capillary. It also carries out numerical simulation of emitter electrowetting under normal gravity and atmospheric conditions and emission experiments to explore the process of ionic liquid layer spreading on the external surface of the emitter. The dimensions of the emitter d1, d2, and θ and the physical properties of ionic liquids jointly determine the electrowetting velocity, the threshold of wetting voltage, and the liquid layer thickness. By analyzing the influence of various variables on electrowetting, a complete emitter electrowetting law of ionic liquid electrospray thrusters is summarized, which provides an important basis for the optimization of the emitter structure. Considering the scale of the emitter and bond ≈1, the meniscus in the electrostatic field is mainly affected by gravity, surface tension, viscous force, and electrophoretic force. Accordingly, it is worth noting that electrophoretic force is calculated by the Maxwell stress tensor method that treats ionic liquids as a dielectric to ensure the continuity of the meniscus. Although it can satisfy the electrowetting study at the macroscale, the interaction between anions and cations at the micro-scale is ignored. The numerical simulation results and the experimental results are correlated. It is proved that the method used in this article is accurate enough to simulate electrowetting before the liquid layer breaks up to form ion emission.