Modeling and Simulation

In addition to rigorous experimental work, SPL has a strong history of theoretical research. This theoretical work includes computational modeling and numerical simulation. Most recently, our computational work has focused on the development of high-fidelity electrohydrodynamic (EHD) models of electrified liquid menisci. These models are important to investigate for several reasons, including:

  • The meniscus is the most dynamically interesting part of an electrospray.
  • Meniscus dynamics have the largest effect on the output and performance of an electrospray.
  • It’s extremely difficult to take direct measurements of the meniscus, especially for ionic liquid ion sources.

Computational domain of an ionic liquid meniscus.

EHD simulation results.

Multiscale Modeling

One of the factors that makes electrospray sources so difficult to fully understand is the fact that extremely important physical processes occur at vastly different length scales. For instance, interactions and forces between individual molecules on the sub-nanometer scale have significant effects on the emission current and properties of the ion beam that results from electrospray. One method for modeling these processes is through molecular dynamics (MD) simulations.

At the same time, long-range interactions between particles in the relatively diffuse ion beam that emanates from a meniscus or full thruster determine the dynamics and evolution of the plume. The length scale for these dynamics can be on the order of meters. One method for simulation these kinds of environments is particle-in-cell (PIC) modeling. No single tool or method can be used to cover both these length scales and everything in between, so we must use various techniques to build different models, but these models must be compatible so that information can be seamlessly passed between them and the full behavior of the device can be understood.

Molecular dynamics simulation of an ionic liquid meniscus.

PIC simulation of an electrospray ion plume.

Relevant Publications

X. Gallud Cidoncha, B. Kristinsson, and P. Lozano, “Informing the Design of Pure-Ion Electrospray Thrusters via Simulation of the Leaky-Dielectric Model with Charge Evaporation,” Proceedings of the 36th International Electric Propulsion Conference, Vienna, Austria, 2019

X. Gallud Cidoncha, “A Comprehensive Numerical Procedure for Solving the Taylor-Melcher Leaky Dielectriic Model with Charge Evaporation,” Master’s thesis, Massachusetts Institute of Technology, Cambridge, MA, 2019

C. Coffman, M. Martinez-Sanchez, and P. Lozano, “Electrohydrodynamics of an Ionic Liquid Meniscus During Evaporation of Ions in a Regime of High Electric Field,” Physical Review E., vol. 99, p. 063108, 2019

C. Coffman, “Electrically-Assisted Evaporation of Charged Fluids: Fundamental Modeling and Studies on Ionic Liquids,” Master’s thesis, Massachusetts Institute of Technology, Cambridge, MA, 2016