The overall propulsion efficiency for ion-mode electrospray thrusters has been predicted to be as high as 90%; however, experimental measurements currently fall far short of these predictions. Further complicating this is that for passively fed electrospray thrusters, the mass flow rate, which is required to obtain the propulsion efficiency and specific impulse, is not directly controlled or measured, and so this parameter is typically estimated by assuming all mass loss is due to the emitted ion current. Presented here is a detailed investigation into the efficiencies associated with a porous-media-based electrospray thruster operated in the purely ionic regime using the ionic-liquid propellant 1-ethyl-3-methylimidazolium tetrafluoroborate in both positive and negative ion emission modes. Measurements of performance metrics that affect thruster efficiency are discussed, including the transmission, angular, polydispersive, energy, and mass utilization efficiencies, in order to determine their impact on overall efficiency. The overall propulsion efficiency and specific impulse are also calculated using a variety of methods to better investigate how the assumptions made to estimate the mass flow rate affect these parameters. These results suggest that the efficiency of these devices may primarily be limited by the presence of additional mass loss mechanisms other than ion emission occurring during thruster operation.

预计离子模式电喷雾推进器的总推进效率将高达90％。但是，目前的实验测量结果远未达到这些预测。更为复杂的是，对于被动式电喷雾推进器而言，获得推进效率和比冲所需要的质量流率无法直接控制或测量，因此该参数通常通过假设所有质量损失是由于发射的离子电流。本文介绍了使用正离子和负离子两种离子液体推进剂1-乙基-3-甲基咪唑四氟硼酸盐在纯离子状态下操作的基于多孔介质的电喷雾推进器的效率的详细研究。讨论了影响推进器效率的性能指标的度量，包括传输效率，角度，多分散性，能量和质量利用效率，以确定它们对总体效率的影响。还使用多种方法来计算总体推进效率和比冲量，以更好地研究为估计质量流量所做的假设如何影响这些参数。这些结果表明，这些设备的效率可能主要受到除推进器运行期间发生的离子发射以外的其他质量损失机制的限制。还使用多种方法来计算总体推进效率和比冲量，以更好地研究为估计质量流量所做的假设如何影响这些参数。这些结果表明，这些设备的效率可能主要受到除推进器运行期间发生的离子发射以外的其他质量损失机制的限制。还使用多种方法来计算总体推进效率和比冲量，以更好地研究为估计质量流量所做的假设如何影响这些参数。这些结果表明，这些设备的效率可能主要受到除推进器运行期间发生的离子发射以外的其他质量损失机制的限制。