Electrostatic probe measurements in solid- propellant rocket exhausts

Abstract

A stagnation point electrostatic probe that can be used to measure local electrical characteristics of solid-propell ant rocket exhausts has been developed. The probe is a flat-faced insulated cylinder with the collector surface at the tip, and is water-cooled. The probe was tested in a laboratory flame and in small-scale rocket motor exhausts at the Naval Research Laboratory, and performed well both thermally and electrically. The analytical procedure for interpreting probe measurements was based on Lam's generalized continuum theory. The theory was verified in laboratory flames of known ionization levels. Positive ion and electron densities were measured in small-scale aluminized composite solid-propellant rocket motor exhausts at NRL. Tests in full-scale, sea-level rocket motor exhausts were performed, and positive ion densities in general agreement with theoretical predictions were obtained. It is concluded that local values of charged species concentrations in solid-propellant rocket motor exhausts can be obtained with a stagnation point electrostatic probe.