A Pulsed Plasma Thruster Using Dimethyl Ether as Propellant

Abstract

The pulsed plasma thruster (PPT), has attracted attention again as a micro-thruster because of its compactness, light weight, and comparatively low power consumption. On the other hand, the propellant utilization efficiency of a conventinal Teflon PPT is relatively low among electric propulsion devices because a propellant that originates from late-time ablation produces negligible thrust. The liquid propellant PPT (LP-PPT), in which water or ethanol is fed with an injector, was proposed to overcome these difficulties. Thrust measurements show that a LP-PPT provides higher specific impulses than a conventional PPT. However, water requires temperature management for propellant storage due to its relatively high freezing point. Moreover, even if ethanol, which has a sufficiently low freezing point, is used as propellant, a pressurant is necessary, as well as water, because the vapor pressures are insufficient for self-pressurization. In this study, we propose to use dimethyl ether (DME) as the propellant. DME, which has a freezing point of 131 K at 1 atm and a vapor pressure of 6 atm at 298 K, can be stored in tanks as a liquid, and requires no feeding pressurant. We designed a DME pulsed plasma thruster to evaluate performance. Thrust measurement yielded a specific impulse of 430 s for a coaxial type at a capacitor-stored energy of 13 J.

Characterization of a Liquid-propellant Pulsed Plasma Thruster Using Various Nozzle Configurations

“…Ethanol was used as the propellant even though there is a possibility of inducing charring, and therefore may not be suitable for the actual PPT use. Nevertheless, since water and ethanol have the same dependence of performance, 15) ethanol can be used as alternative propellant for water to clarify the performance of a co-axial electrode LP-PPT.…”

“…In thrust measurements, an LP-PPT with paral-lel-plate electrodes yielded a specific impulse of 4,300 s, higher than that of conventional PTFE PPTs, at a capacitorstored energy of 20 J. 16) Although thruster configurations of LP-PPTs are surely expected to affect the performance, characterizations through systematic measurements using various nozzles have not been reported yet. In this study, we experimentally characterized the performance of an LP-PPT using various types of nozzles with coaxial electrodes and different configurations of electrode type, cavity size, area ratio, and divergent nozzle angle.…”

“…To increase the propellant utilization of PPTs and match the impulse bit and capacitor-stored energy levels of conventional PPTs, Kakami et al proposed a liquid propellant PPT (LP-PPT). 14,15) In this LP-PPT, droplets are injected into an electrical-discharge channel just before initiation of the pulsed-arc discharge and become ionized, thereby producing thrust by both electromagnetic and electrothermal acceleration. A pulsed droplet injection system that is synchronized with the pulsed-arc discharge would allow LP-PPTs to utilize most of the injected propellant and produce small discrete thrusts at arbitrary times.…”

“…Such a coaxial electrode LP-PPT potentially offers a thrust-power ratio higher than those of parallel-plate electrode LP-PPTs because of the assistance provided by electrothermal acceleration. 16,17) 2. Coaxial LP-PPT Prototype Figure 1 shows a schematic of our coaxial-electrode LP-PPT prototype.…”

Low-Energy Electron Scattering from Dimethyl Ether

“…Moving to its usage in the plasma field, it is found to be suitable for plasma ignition in high speed flow and thus is a promising replacement for hydrocarbons in such applications. Furthermore, DME is also recognized as a propellant in pulse plasma thruster (PPT), − hence making it pertinent for space propulsion systems.…”