Date of Award

Fall 2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Robert L. Ash

Committee Member

Drew Landman

Committee Member

Arthur Taylor

Call Number for Print

Special Collections; LD4331.E535 P47 2011

Abstract

An experimental investigation was conducted to characterize the performance of a small-scale supersonic propulsion system using supercritical CO2 as a propellant intended for Mars surface applications. This research has focused on estimating the specific impulse behavior of high-pressure carbon dioxide propellant that can be produced by condensing dry ice out of Mars's atmosphere and heating it at constant volume to temperatures above its 31.1 ° C critical temperature. Since supercritical fluid was created by heating different dry ice-vapor mixtures to moderate temperatures, the nominal initial density and thermodynamic state within the pressure vessel could be controlled. The instrumented test apparatus consisted of the heated carbon dioxide pressure vessel, a control valve, and a supersonic Mach 2 nozzle. An earlier thesis examined sonic blow down thrust behavior, but improvements to the overall experimental set-up and test procedures, along with the successful fabrication and integration of a Mach 2 nozzle, resulted in new data that can be used to guide future design studies. The supercritical carbon dioxide expansion process was found to be strongly influenced by the initial density temperature state. By altering the initial density of the CO2 charge and controlling the initial temperature, the supercritical initial conditions could be varied to create three different types of trans-critical blow-down behavior: (1) condensing two-phase, (2) evaporating two-phase, and (3) superheated fluid conditions. A high initial temperature (125 ° C) test was performed to investigate the initial high-pressure region of blow-down when tank conditions were still supercritical to more thoroughly characterize the propulsive performance. The differing behavior of stagnation conditions produced noticeably different measured thrust levels yet produced similar mid- to late-stage specific impulse performance. Specific impulse values ranged between 50 and 35 seconds. Measured thrust levels in the high-pressure supercritical region were higher than the thrust levels predicted using several standard, quasi-steady, equilibrium estimation methods, leading to the conclusion that non-equilibrium effects could be at work.

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DOI

10.25777/469s-t647

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