Characterization of a Rijke Burner as a Tool for Studying Distributed Aluminum Combustion

As prelude to the quantitative study of aluminum distributed combustion, the current work has characterized the acoustic growth, frequency, and temperature of a Rijke burner as a function of mass flow rate, gas composition, and geometry. By varying the exhaust temperature profile, the acoustic growth rate can be as much as tripled from the baseline value of approximately 120 s-1• At baseline, the burner operated in the third harmonic mode at a frequency of 1300 Hz, but geometry or temperature changes could shift operation to a second mode. During oscillatory combustion, centerline temperatures in the exhaust rose by as much as 80 K when compared to the nonoscillating case. With oscillations, the mean flow of gases in the boundary slowed with a consequent decrease in heat transfer to the walls. The information gained in this study will aid in refining burner modeling efforts and allow interpretation of planned aluminum combustion studies in hopes of gaining a greater understanding of distributed combustion as a driving mechanism in the combustion instability of solid propellant rocket motors.