Numerical Characterization of Fragmentation in Ionic Liquid Clusters

2022

Preprint

Electrospray thrusters are of particular interest for micropropulsion because of their compactness, high specific impulse, and their ability to operate over very long periods of time. However, particles on the periphery of the plume are susceptible to collide with the extractor grid, which may reduce the efficiency and limit the lifetime of the electrospray thruster. Therefore, a good knowledge of the collision process and byproducts is crucial to understanding the long-term surface effects and overcoming the lifetime-limiting mechanisms. This study attempts to investigate particles impingement on the extractor grid using molecular dynamics simulations with two different models. The first model is based on a non-reactive force field and is used to investigate the dissociation of ionic bonds. The second model is based on a reactive force field and is used to investigate the breaking of covalent bonds. In both cases, a statistical analysis is carried out over the initial configuration of the molecule. The major results of this study are: (1) the inference of probability curves of the ionic dissociation in function of the impact energy for temperatures ranging from 300K to 1000K, and (2) the determination of pseudomass spectra of the byproducts post-collision. The probability curves indicate a strong correlation between the impact energy and the ionic dissociation for energies smaller than 60 eV. The pseudomass spectra indicate that strong collisions are more likely to produce light byproducts whereas weak collisions tend to produce heavier molecules.

Section: Resultsmentioning

confidence: 98%

Molecular Dynamics Studies of Ionic Liquid-Surface Interactions for Electrospray Thrusters

Bendimerad

2022

Preprint

“…The zero probability of ionic dissociation in the absence of collisions (i.e., KE = 0 eV) is due to the intrinsic setup of the simulation in which there is no electric field. However, the occurrence of spontaneous dissociation in the presence of an external electric field is not excluded as shown in [16], albeit only observed for dimers and trimers. Therefore, the non-zero Fig.…”

Section: Resultsmentioning

confidence: 98%

Molecular dynamics studies of ionic liquid-surface interactions for electrospray thrusters

Bendimerad

2022

J Electr Propuls

Electrospray thrusters are of particular interest for micropropulsion because of their compactness, high specific impulse, and their ability to operate over very long periods of time. However, particles on the periphery of the plume are susceptible to collide with the extractor grid, which may reduce the efficiency and limit the lifetime of the electrospray thruster. Therefore, a thorough characterization of the collision process and byproducts is crucial to understanding the long-term surface effects and overcoming the lifetime-limiting mechanisms. This study attempts to investigate particle impingement on the extractor grid using molecular dynamics simulations with two different models. The first model is based on a non-reactive force field and is used to investigate the dissociation of ionic bonds. The second model is based on a reactive force field and is used to investigate the breaking of covalent bonds. In both cases, a statistical analysis is carried out over the initial configuration of the molecule. The major results of this study are: (1) the inference of probability curves of the ionic dissociation in function of the impact energy for temperatures ranging from 300K to 1000K, and (2) the prediction of mass spectra of the byproducts post-collision. The probability curves indicate a strong correlation between the impact energy and the ionic dissociation for energies smaller than 60 eV. The predicted mass spectra indicate that strong collisions are more likely to produce light byproducts whereas weak collisions tend to produce heavier molecules.

“…Molecular dynamics (MD) results from the previous work provide the dependence of cluster mean lifetime on total internal energy and electric field strength. 34 Details of the simulation procedures and results are provided in the Appendix. In short, the simulations followed the procedures developed by Coles and Lozano using the Canongia Lopes and Padua force field in LAMMPS.…”

Section: Fragmentationmentioning

confidence: 99%

“…The results of this previous work indicate that the molecular dynamics simulation temperature parameter can be used interchangeably with the total internal energy of the ion cluster. 34 Fragmentation rates are referenced here using the temperature of the MD simulations for ease of comparison with the previous work.…”

Section: Fragmentationmentioning

confidence: 99%

Multiscale modeling of electrospray ion emission

Journal of Applied Physics

Gallud

Hampl

et al. 2022

Self Cite

A multi-scale approach to electrospray ion source modeling has been developed. The evolution of a single-emitter electrospray plume in a pure ionic regime is simulated with a combination of electrohydrodynamic fluids and n-body particle modeling. Simulations are performed for the ionic liquid, EMI-BF4, firing in a positive pure-ion mode. The metastable nature of ion clusters is captured using an ion fragmentation model informed by molecular dynamics simulations and experimental data. Results are generated for three operating points (120, 324, and 440 nA) and are used to predict performance relevant properties, such as the divergence angle and the extractor surface impingement rate. Comparisons to experimental data recorded at similar operating points are provided.