Multiplexed Electrospray Emission of Green Energetic Ionic Liquids from Wedge-Shaped Porous Emitters

Dual-mode propulsion using energetic ionic liquids (EILs)amalgamatesthe merits of wide-range thrust and high specific impulse, significantlyenhancing the mission flexibility of a single spacecraft. However,EIL electrospray, as a high specific-impulse electric mode, is stillin its infancy when compared to conventional electrospray. In thispaper, we intensively investigate the voltage-current characteristics,plume distribution, beam extraction efficiency, and glowing patternof an EIL electrospray thruster equipped with a porous wedge-shapedemitter. We demonstrate that the emission current generated by usinga porous titanium emitter is one order of magnitude higher than thatof a porous ceramic emitter under unsaturated infiltration. As faras the beam extraction efficiency is concerned at a wide electrodedistance, it mainly depends on the dimensionless plume angle and characteristictime of charged species in the electric field. The stable emissioncurrent and peak extraction efficiency in the examined cases can exceed500 & mu;A and 90%, respectively. Further, we find that the erraticarc discharge caused by the overspray behavior primarily occurs atnegatively high voltages. In contrast, at positively high voltages,the stable muted blue, dazzling white, and hazy violet light graduallyemerge with increasing the amount of propellant loaded into the reservoir.Not only does the amount of filling into the porous reservoir affectthe glowing pattern but it also has a substantial influence on theplume current mode. Especially when a thin liquid film is formed onthe emitter surface, it may lead to a consistent pulse frequency ofthe plume current across various emission sites. The above-mentionedfundamentals are of significance for the advancement of a dual-modethruster in the future.