Plasma propellant jet ignition

Abstract

A high energy plasma jet plug fed with liquid propellant, capable of releasing up to 50J of chemical energy from its 30μl internal cavity, is described. Potential applications range from igniters for enhanced oil recovery burners, over liquid propellant gun ignition, to a tool for optical diagnostics of burning propellant jets which requires no high pressure optical facilities. While some applications call for massive shock waves, however, others demand ejection of a burning liquid jet, and the dependence on plug geometry and electrical parameters of the violence of the process is therefore investigated. To this end, a high speed optical system and model plugs with optically accessible cavities are constructed. These allow the evolution of gas and the development of the discharge in the cavity as well as the ejection behaviour of the plume to be studied in great detail. Depending on the charge on the capacitors and on the plug geometry, a wide variety of events—ranging from slow ejection of unchanged propellant to very violent and complete expulsion associated with the emission of light and a sharp crack—can be produced. The relative contributions of the three electrical components of the event: resistive heating, electrolysis and plasma formation, are examined. A precursory electrolytic phase causes bubble formation at the electrode, leading to plasma formation in the gas. Small electrode separation, area, and charging capacitors to high potentials, concentrates most of the energy into a violent discharge. The tailoring of plug design to particular ignition requirements is discussed in terms of these findings.