Effect of ion solvation energy on electrohydrodynamic behavior of ionic liquid droplets in electrospray thrusters

The electrospray thruster supplied by ionic liquid is a promising micro-propulsion thruster with small size and precise thrust, which can emit both cations and anions to achieve self-neutralization. In order to further investigate the effect of ion solvation energy on the evaporation of cations and anions from ionic liquid under the action of a uniform electric field, this paper establishes a transient Electrohydrodynamic (EHD) model for free ionic liquid droplets undergoing ion evaporation. The dynamic processes of droplet deformation and ion evaporation are simulated. And the study further focuses on the influence of different ion solvation energies for cations on the droplet morphology and the ion evaporation characteristics at the positively charged end and negatively charged end of the droplet. The results indicate that, when the ion solvation energy for cations is higher than that of anions, it will cause the ion evaporation at the positively charged end of the droplet to lag behind the ion evaporation at the negatively charged end. And the higher the ion solvation energy for the cations, the longer the evaporation lag time at the positively charged end of the droplet, which will lead to a higher peak of surface charge density that can be reached, resulting in a larger evaporation current and sharper droplet stretching deformation. Additionally, the peak surface charge density of the positively charged end of the droplet is linearly related to the ion solvation energy for cations, while the peak surface charge density of the negatively charged end remains almost unchanged and is not significantly affected by the ion solvation energy for cations.