Borner Arnaud, Wang Pengxiang, Levin Deborah A
Department of Aerospace Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Dec;90(6):063303. doi: 10.1103/PhysRevE.90.063303. Epub 2014 Dec 2.
Molecular dynamics (MD) simulations are coupled to solutions of Poisson's equation to study the effects of the electrical boundary conditions on the emission modes of an electrospray thruster fed with an ionic liquid. A comparison of a new tip boundary condition with an analytical model based on a semihyperboloidal shape offers good agreement, although the analytical model overestimates the maximum value of the tangential electric field since it does not take into account the space charge that reduces the field at the liquid surface. It is found that a constant electric field model gives similar agreement to the more rigorous and computationally expensive tip boundary condition at lower flow rates. However, at higher mass flow rates the constant electric field produces extruded particles with higher Coulomb energy per ion, consistent with droplet formation. Furthermore, the MD simulations show that ion emission sites differ based on the boundary condition and snapshots offer an explanation as to why some boundary condition models will predict emission in a purely ionic mode, whereas others suggest a mixed ion-droplet regime. Finally, specific impulses and thrusts are compared for the different models and are found to vary up to 30% due to differences in the average charge to mass ratio.
分子动力学（MD）模拟与泊松方程的解相结合，以研究电边界条件对以离子液体为燃料的电喷雾推进器发射模式的影响。将一种新的尖端边界条件与基于半双曲面形状的解析模型进行比较，结果显示两者吻合良好，不过该解析模型高估了切向电场的最大值，因为它没有考虑到在液体表面降低电场的空间电荷。研究发现，在较低流速下，恒定电场模型与更严格且计算成本更高的尖端边界条件给出的结果相似。然而，在较高质量流速下，恒定电场会产生每个离子具有更高库仑能量的挤出粒子，这与液滴形成一致。此外，MD模拟表明，离子发射位点因边界条件而异，快照解释了为何一些边界条件模型会预测纯离子模式下的发射，而其他模型则表明是混合离子 - 液滴状态。最后，对不同模型的比冲和推力进行了比较，发现由于平均荷质比的差异，它们的变化幅度高达30%。
