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Title:Exit plane plasma measurements of a low-power hydrazine arcjet
Author(s):Bufton, Scott Allen
Doctoral Committee Chair(s):Burton, Rodney L.
Department / Program:Engineering, Aerospace
Engineering, Mechanical
Discipline:Engineering, Aerospace
Engineering, Mechanical
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Aerospace
Engineering, Mechanical
Abstract:Electric propulsion systems, and electrothermal arcjets in particular, have received considerable attention as viable systems for satellite propulsion applications. Research in this area has been fueled by recent applications of low-power arcjets aboard geosynchronous communications satellites. Recent advances made in low power (1-2 kW) arcjet numerical modeling, coupled with the demonstrated utility of arcjet thrusters, make the validation of computational models through experimentation increasingly important.
In this work, improved understanding of the flow processes in a 1-kW hydrazine constricted arcjet is achieved with multiple electrostatic probe surveys at the exit plane of a laboratory thruster. Quadruple, triple, and single electrostatic probe techniques are utilized for measurements of the electron temperature T$\sb{\rm e},$ electron density n$\sb{\rm e},$ and ratio of ion axial velocity to most probable thermal speed u$\rm \sb{i}$/C$\rm \sb{m,H\sp+}.$ Three thruster specific power levels (19.8, 22.3, and 26.0 MJ/kg) are investigated by varying the thruster current and propellant mass flow rate. Centerline axial profiles of T$\rm \sb{e}$ and n$\rm \sb{e}$ are presented for 2.2-6.2 mm downstream of the exit plane, yielding T$\rm \sb{e}$ $\sim$ 7000 K and n$\rm \sb{e}$ $\sim$ $3.6\times10\sp{12}$ cm$\sp{{-}3}$ near the thruster exit for P/m = 22.4 MJ/kg.
Radial gradients in T$\rm \sb{e}$ and n$\rm \sb{e}$ for off-centerline measurement locations are shown to adversely affect the quadruple probe response in this region of the plume. The uniform plasma quadruple probe theory is modified to account for radial gradients in T$\rm \sb{e}$ and n$\rm \sb{e}$ over the probe radial dimension, and is used to extract exit plane radial T$\rm \sb{e}$ and n$\rm \sb{e}$ profiles from the raw probe data. These results indicate that the T$\rm \sb{e}$ radial profile is much wider than that of n$\rm \sb{e}$ at the thruster exit. Additionally, floating electrostatic probe measurements yield estimates of the radial electric-field profile at the thruster exit, implying the presence of a small amount of the thruster current ($\sim$2%) and ohmic heating downstream of the arcjet exit plane.
A spatially-resolved time-of-flight electrostatic probe technique is developed and employed in this study for measurements of radial profiles of the plasma axial velocity u$\rm \sb{i}$ at the arcjet exit plane. Results indicate that the centerline axial velocities vary from 5.5 to 8.0 km/s over the 19.8-26.0 MJ/kg range of specific powers investigated. The quadruple probe results (T$\rm \sb{e},$ n$\rm \sb{e},$ u$\rm \sb{i}$/c$\rm \sb{m}),$ coupled with these independent measurements of plasma velocity u$\rm \sb{i},$ are used to determine the gas temperature T$\rm \sb{g}.$ These results reveal significant thermal nonequilibrium effects (T$\rm \sb{g}$/T$\rm \sb{e}<1)$ at the thruster exit.
Exit plane probe measurements of n$\rm \sb{e},$ T$\rm \sb{e}$ and T$\rm \sb{g}$ are compared with previously reported experimental data in the nozzle interior and thruster far-field plume. Finally, the results of this study are used to evaluate the performance of a comprehensive nitrogen-hydrogen arcjet model developed recently by Megli (1995). Comparisons of the experimental and predicted results indicate general agreement for the plasma parameters measured in this study.
Issue Date:1996
Rights Information:Copyright 1996 Bufton, Scott Allen
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9625115
OCLC Identifier:(UMI)AAI9625115

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