Impact of propellant temperature on the emission regime of an externally wetted electrospray system using time-of-flight mass spectrometry

Electrospray thrusters operate in different regimes depending on the ejected particles: pure ionic regime, characterized by the presence of only solvated ions; droplet regime; and mixed regime, where both ion and droplets are emitted. The electrospray emission regime is driven by the physical properties of the liquid, the flow rate to the emission site, and the electric field applied. Because of the temperature dependence of the ionic liquid, the emission regime and hence the propulsive performance are sensitive to the liquid temperature. Additionally, in externally wetted electrospray emitters, where the flow rate is passively controlled by viscous forces, temperature plays a crucial role as it drives the hydraulic impedance of the emitter due to the variation of the liquid's viscosity, and therefore the emitter flow rate. The research described in this work is focused on the effect of the propellant temperature on the emission regime of externally wetted emitters. By means of a time-of-flight mass spectrometer the plume composition has been analyzed under different conditions of applied voltage and operating temperature, finding that voltage increases the relative amount of ion species and temperature increases the relative amount of droplets.