(Dr. Ben Zinn,  advisor)

"Effectiveness of Pulsed Spray Combustion for Suppression of Combustion Instabilities"

Abstract

 A pulsed spray combustion control source was developed for the purpose of actively suppressing combustion instabilities.  The control source successfully created heat release oscillations by pulsing the flow rate through a pintle type fuel injector.  Its effectiveness was evaluated by determining the percentage of fuel injected that produced heat release oscillations 'useful' for suppression.  CH* emission was used to characterize the heat release experimentally.  The entire flame was characterized in a single test run.  The data was then divided into several slices, and analyzed individually.  The data was processed to determine the percentage of fuel burned that produced oscillations.  The axial phase distribution of the CH* oscillation was also determined. This information was then used with the Rayleigh criterion to determine whether or not the oscillations were useful for suppression.  Square wave control signals were investigated in the 170-800 Hz range at several duty cycles.  The percent duty cycle reflected the amount of time that the pintle spent in the closed position.  The influence of the control signal properties on the effectiveness was then evaluated.  Also, the flame was filmed using high-speed photography, and the fuel spray was characterized using the Phase Doppler Particle Analyzer to better understand its behavior.  The most effective results occurred when the fuel was injected as brief high-pressure bursts.  For the injector used in this study, this corresponded to control signals with low frequencies and high duty cycles. (i.e. 170 Hz, 75 % Duty Cycle)