Study of plasma-propellant interaction during normal impingement

This paper describes an effort to investigate the transient process of an electrothermal plasma normally impinging on a plate or a solid propellant. The objective of this effort was to develop a better understanding of the fundamental aspects of this process to facilitate the development of the plasma ignition system for use in electrothermal chemical propulsion applications. The plasma is produced through an electrical discharge occurring within a polyethylene capillary. The high-temperature and high-pressure plasma exited from the capillary into an ambient air environment and impinged normally onto a plate. Pressure transducers mounted on the plate were used to obtain the stagnation pressure of the plasma jet, and a multiple CCD imaging system was used to visualize this highly transient process. Tests were also performed with the stagnation plate replaced by a solid propellant sample. Plasma-induced surface changes were examined using a scanning electron microscope, mass loss of the propellant was measured, and decomposition species were analyzed using a triple quadrupole mass spectrometer. The results show that when the distance between the capillary exit port and the plate was varied, changes in plasma jet structure, stagnation pressures, and mass losses of the propellant were significant.