Fundamental experiments on electrospray propulsion: Propellants, plumes, and material interactions

Electrospray sources are devices that use electric fields to extract charged particles directly from a liquid surface. Those charged particles may span a large mass range, from single molecular ions (10^2 amu/q) to large droplets (>10^5 amu/q), depending on the type of electrospray source and its operating conditions. Species in electrospray plumes are heavier than most ion sources (e.g., a Hall-effect thruster), making electrospray appealing for applications such as spacecraft propulsion and material etching. The distribution of mass and energy within the plume determines the performance of an ion source for a given application. In a propulsion context, those distributions may be used to calculate thrust, specific impulse, and efficiency. However, accurately measuring those distributions can be challenging. Part 1 of this dissertation describes a tandem energy analyzer/mass spectrometer for measuring the mass and energy distributions in electrospray plumes. The instrument was used to characterize a capillary emitter plume and the plume of an ionic liquid ion source (ILIS). The ILIS data was used to calculate the mean lifetime of ion clusters in the electrospray plume. For the ILIS used here, operated with the ionic liquid EMI-BF4, we calculate that the EMI+[EMI][BF4] dimer mean lifetime ranges from 3.5 ns to 142 ns for electric field strengths ranging from 35 V/µm to 2 V/µm, respectively. Similarly, the EMI+([EMI][BF4])2 trimer has an estimated lifetime of 0.9 ns to 13 ns for electric field strengths ranging from 22 V/µm to 2 V/µm, respectively. From those data, we estimate the temperature and solvation energy of positive EMI-BF4 dimers is T=471±216 K and ΔG=0.62±0.26 eV, respectively. Similarly, for positive trimers we estimate that T=475±422 K and ΔG=0.55±0.43 eV. These results are among the first to use empirical methods to estimate EMI-BF4 cluster lifetimes, temperature, and solvation energy. Part 2 of this dissertation discusses other topics in electrospray propulsion. We present a “Secondary Species Emission" (SSE) probe designed to measure secondary charge emission from surfaces bombarded by electrospray plumes. Further, we demonstrate that the SSE probe can be operated in tandem with the energy analyzer/mass spectrometer to measure SSE yield as a function of the mass and energy of incident plume species. The ability to discriminate between different species and energies is a novel and significant advance in secondary charge emission measurements. Part 2 continues, presenting the first successful demonstration of a prototype thruster that combines electrospray and monopropellant functionality into a single device. Finally, Part 2 concludes with an investigation of water removal from ionic liquid electrospray propellants.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Lyne, Christopher

Contributors dc:contributor

• Rovey, Joshua
• Levin, Deborah
• Elliott, Gregory
• Liu, Thomas

• Electrospray Propulsion
• Ion Beam Diagnostics
• Mass Spectrometry

Statement dc:rights

• Copyright 2023 Christopher Lyne

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/124615

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F124615