Experimental characterization of the electrospray propulsive performance for ionic liquid propellants [EMIm][DCA] and [BMIm][DCA

Abstract

A chemical-electrospray dual-mode propulsion system is significant in improving mission capability and flexibility of a spacecraft. Hypergolic ionic liquids are potential propellants of chemical and electrospray propulsion systems. In this work, the electrical propulsive performance of two hypergolic ionic liquids 1-ethyl-3-methylimidazolium dicyanamide ([EMIm][DCA]) and 1-butyl-3-methylimidazolium dicyanamide ([BMIm][DCA]) are experimentally characterized using two array-emitter electrospray thrusters. Compared with a commonly used ionic liquid propellant 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]), the current magnitude and current steadiness of the electrospray thruster with [EMIm][DCA] and [BMIm][DCA] are efficiently improved, especially with [EMIm][DCA] as propellant. The results show that the low viscosity is beneficial for steady and sufficient flow supply and thus favors a long-time steady operation of the thruster. For the propellant [EMIm][DCA], the maximum specific impulse is 1791 s, i.e., 27.8% higher than that of [EMIm][BF4], while the maximum thrust 32.5 μN is 128.9% greater than that of [EMIm][BF4]. For the propellant [BMIm][DCA], the thrust-to-power ratio of the thruster is approximately 82.8% higher than that of [EMIm][BF4] at a similar specific impulse of about 1120 s resulting from a much greater thruster efficiency. These results demonstrate that [EMIm][DCA] has a better performance than [EMIm][BF4] in both maximum thrust and specific impulse, and [BMIm][DCA] performs best in the aspect of thrust-to-power ratios. This work highlights the prospect of hypergolic ionic liquids and is valuable to promote their application in chemical and electrical propulsion communities.