A plasma igniter has been developed for initiating combustion in liquid-propellant rocket engines. The device propels a hot, dense plasma jet, consisting of elemental fluorine and fluorine compounds, into the combustion chamber to ignite the cold propellant mixture. The igniter consists of two coaxial, cylindrical electrodes with a cylindrical bar of solid Teflon plastic in the region between them. The outer electrode is a metal (stainless steel) tube; the inner electrode is a metal pin (mild steel, stainless steel, tungsten, or thoriated-tungsten). The Teflon bar fits snugly between the two electrodes and provides electrical insulation between them. The Teflon bar may have either a flat surface, or a concave, conical surface at the open, down-stream end of the igniter (the igniter face). The igniter would be mounted on the combustion chamber of the rocket engine, either on the injector-plate at the upstream side of the engine, or on the sidewalls of the chamber. It also might sit behind a valve that would be opened just prior to ignition, and closed just after, in order to prevent the Teflon from melting due to heating from the combustion chamber.

The plasma jet deposits the energy required to initiate combustion, while highly reactive fluorine and fluorine compounds create free-radicals in the flow-field to further promote rapid ignition. The plasma jet is created and accel-

erated electrically, and the feedstock for the plasma is maintained in a solid, inert form, leading to a rugged, reliable and compact design. The device should promote rapid and reliable ignition in LOX/LCH4 engines in particular, and in liquid propellant engines in general. It could also be used in gas-turbine engines where prompt and reliable restart is critically important; for example, in helicopter and jet aircraft engines.

This work was done by Adam Martin and Richard Eskridge of Marshall Space Flight Center. For further information, contact Sammy Nabors, MSFC Commercialization Assistance Lead, at This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to MFS-32557-1.

NASA Tech Briefs Magazine

This article first appeared in the January, 2011 issue of NASA Tech Briefs Magazine.

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