Pressure-Driven Operation of Microfabricated Multiplexed ElectroSprays of Ionic Liquid Solutions for Space Propulsion Applications

The performance of a Multiplexed ElectroSpray (MES) system for space propulsion is studied. The need for multiplexing, i.e., operating several emitters in parallel, stems from the thrust requirements of small satellites for which such a system is well-suited. The device is composed of a microfabricated Si array of nozzles whose hydraulic impedance is increased by packing them with 2.01- $\mu{\rm m}$ silica microbeads. An extractor electrode creates a sufficiently intense electric field to establish multiple electrosprays in the cone-jet mode. Two high electric conductivity ionic liquid solutions are tested in the colloidal (drop) regime: 1) a solution of 21.5% by volume of methylammonium formate (MAF) in formamide (FA), with electric conductivity ${K}={\rm 1.8}~{\rm S}/{\rm m}$ and 2) pure ethylammonium nitrate (EAN), with ${K}={2}~{\rm S/m}$ . Using a seven-nozzle (7-MES) system, we can achieve uniformity of operation of all emitters when the viscous pressure drop in each nozzle dominates the electrodynamic pull at the capillary outlets. Time-of-flight mass spectrometry measurements and comparison of a single-nozzle (1-MES) emitter and the 7-MES system confirm that all seven emitters operate in unison, with the same average propulsive efficiency $\eta_{p}$ as a 1-MES system: $\eta_{p}=85\%$ for FA/MAF and 62% for pure EAN. $\hfill[2013\hbox{-}0170]$