Optimization of arc constrictor sizes in low power arcjet thrusters

Abstract

It is known that the performance of a low power arcjet is influenced by the geometry of the constrictor. The merging of the arc with the propellant gas in the constrictor is a complex process involving electrical and non-equilibrium chemical phenomena with high energy transport rate to the wall. An experimental investigation was performed to investigate the effect of the constrictor geometry on the characteristics of arc discharges and the heat transport rate to the wall, using quartz glass constrictors with different geometries. Following results were obtained. 1) The discharge voltage of the arc increases with the constrictor length (/con) almost linearly, though no distinct effect of the constrictor diameter (cfcon) is observed on it. 2) The thermal efficiency, defined as the ratio of the power of gas ejected from the constrictor (Peject) to the input electrical power (Pin), increases with increasing gas pressure (Peon) and with decreasing /con generally, while with decreasing rfcon the efficiency takes a maximum value at a middle length of dcon. 3) The diameter of arc column decreases with increasing Peon, with increasing /con, and with decreasing rfcon by the thermal pinch effect. 4) The main feature of the variation of constrictor gas temperature with /con and fifcon coincides with that of ejected power and thermal efficiency. It is suggested that the existence of the maximum in the thermal efficiency for the change of cfcon, at a fixed Peon and a fixed mass flow rate of propellant, is due to the coexistence of two type processes, one suppresses heat transport to the constrictor wall and another promotes it.