Electrospray of 1-butyl-3-methylimidazolium dicyanamide under variable flow rate operations

The ionic liquid 1-butyl-3-methylimidazolium dicyanamide ([Bmim][DCA]) is a propellant candidate for a standalone electrospray thruster or a dual-mode propulsion system. Characterization of positive polarity ions produced by [Bmim][DCA] capillary emitters with a nominal extraction voltage of 2.0 kV is presented, followed by predictions of propulsion performance. Flow rates from 0.27 to 2.18 nL/s are used to investigate the impact variations in the flow parameter have on the electrospray plume. Measurements indicate the presence of Bmim([Bmim][DCA])+n (n = 0, 1, 2, 3, 4) cation species plus droplet contributions. At 0.27 nL/s , the n = 1 species dominates the mass spectrum contributing 56.5% of the total intensity, while at 2.18 nL/s, the dominant species is n = 4, comprising 40.7%. Based on the retarding potential analysis, ions emitted from the capillary are formed below the emitter potential of 500 eV. Angular distributions indicate the broadening of both the beam current and mass distribution for increasing flow rates. As the flow rate increases from 0.30 to 2.18 nL/s, derived thrust and specific impulse change from 0.84 μN and 200 s to 2.90 μN and 80 s, respectively.