Multi-scale modeling of ionic electrospray emission

Abstract

The physics of ionic electrospray propulsion spans multiple length scales. This paper combines a molecular dynamics model, a particle–particle model, and a particle-in-cell model to investigate the physics of ionic electrospray propulsion over 9 orders of magnitude in length scale. The combined models are applied to simulate beam emission for an ionic electrospray propulsion system with porous emitter tips and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid propellant from the emission site to the downstream plume. Additionally, the impact of multiple emission sites from a single emitter tip is analyzed with regard to extractor grid interception and overall beam neutralization for bipolar thruster pairs. Results show that beams consisting of species of different masses (i.e., monomer and dimer species) are affected by particle–particle forces during acceleration and should not be treated as a superposition of independently accelerated species in macro-scale plume models. The activation of multiple emission sites also causes a noticeable increase in the beam’s spread, leading to increased intercepted current but relatively little adverse effects in the downstream plume region.

Multiscale modeling of electrospray ion emission

“…The iterative process starts with a guess of the initial equilibrium shape that is used at a first stage to solve the Poisson equation in the liquid (4), the Laplace equation in the vacuum (5), charge conservation (8), and kinetic law for ion evaporation (9) subject to the boundary conditions in Eqs. ( 6) and ( 7).…”

“…The integration of an electrohydrodynamic source model with a discrete plume model presents new opportunities for validation of the meniscus solution. Furthermore, it offers promise to bridge the gap between the macroscale design parameter space (emitter geometry, liquid properties) and the plume evolution via realistic initial conditions in ways that cannot be captured through molecular dynamics or simulations alone, 9 limited to domain size, or constant axial flux, 10 which are usually constrained to a limited set of operating conditions.…”

Study on the plume self-neutralization of ionic liquid electrospray thruster based on median potential

“…Therefore, the spatial distribution mode is a more convenient choice. Wang et al [32][33][34] performed Particle-in-Cell (PIC) simulations to investigate the plume in spatial distribution and found that the bipolar ion beam was almost uncoupled, and the plume exhibited no backflow. Zhang et al [35] conducted PIC simulations of the plume in spatial distribution and observed that self-neutralization of the plume is achieved through temporal and spatial oscillations of the ion beam.…”

Comparison of computational algorithms for simulating an electrospray plume with a n-body approach

“…These electric fields typically span over multiple scales, from the V/m in the emission region to almost vanishing fields in the field-free region, and are a direct byproduct of the geometry of the acceleration region, including the features of the meniscus shape itself [ 6 ] and the curvature of the tip electrodes. The study of these processes affecting ion plume trajectories has motivated the development of multi-scale simulation frameworks at different levels of accuracy: from kinetic approaches [ 7 ] to particle-in-cell (PIC) models [ 8 , 9 ]. The former model improves the accuracy of the electric field estimation by computing the exact Coulomb force between the particles at the expense of an intense computational scalability 1 , where N is the number of particles being simulated.…”