Date of Award

Fall 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Engineering and Applied Science

First Advisor

Fernandez de la Mora, Juan

Abstract

A series of electrified nanojets of the ionic liquid EMI-FAP (1-Ethyl-3-methylimidazoliumtris(pentafluoroethyl)trifluorophosphate) are investigated at various liquid flowrates (60- 1000pl/s), and emitter temperatures (25-75C). Time of flight (TOF) and energy analysis in vacuum are used in series to determine jet parameters at the point of breakup, and propulsive properties. At each experimental condition, the jet velocity Uj , diameter dj , electrical potential Vj and energy dissipated ΔV are obtained at the jet breakup point. Additionally, the following propulsive parameters of the spray are measured: specific impulse Isp , propulsive efficiency ηprop and thrust T. These measurements provide an insight into jets featuring variable specific impulse. Increasing the temperature rises the specific impulse and widens the parameter range of stable emission. A considerable effort is devoted to develop a Faraday cup type electrometer, optimized for Time Of Flight (TOF) characterization of the spray of ions and droplets produced by the jet breakup. This device captures the whole electrospray beam. The full spray is periodically gated by a grid held at a high voltage Vg, and received at a collector where the measured flight times provide the distribution of drop speeds u. Varying Vg provides the bivariate distribution of drop energies ξ and velocities. The collector plate, centered with the beam axis, is divided into concentric rings, yielding the angular distribution of the spray current, and high resolution (u, ξ) values (corrected for spherical aberration) in the whole spray. The energies of various particles of given u are all well defined, but depend uniquely on u, even though u and ξ are in principle independent experimental variables. Slow and fast particles have energies respectively well above and below the emitter voltage. As previously shown by Gamero, this behaviour is due to the 2-stage acceleration process, first jointly in the jet for all particles, and then separately for free flying drops or ions of different mass/charge. The measured two-dimensional distributions of u and ξ provide the jet velocity Uj and electrical potential Vj at the breakup point. At all temperatures and liquid flow rates investigated, all molecular ions originate near the breakup point rather than the meniscus neck. Some molecular ions feature smaller than expected energies, likely as a result of fragmentation after emission. A measurable fraction of anomalously fast drops is observed that must come from Coulomb fissions of the main drops. To study ion fragmentation effects, a different multichannel high sensitivity flat Faraday cup type electrometer was developed and installed into a Differential Mobility Analyzer. An isolated cluster ion is fed to this analyzer through a heated pipe. The abundances of the resulting parent and product ions are measured with the DMA, where they land at different isolated detectors. Evaporation of a neutral from the cluster takes place depending on pipe residence time and temperature. This coupled with the quantitative measurement of the concentration of surviving parent clusters yields the pre-exponential factor A and the activation energy Ea governing the Arrhenius kinetics

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