Preliminary Results on the Effects of Distributed Aluminum Combustion Upon Acoustic Growth Rates in a Rijke Burner

University of Utah

Distributed particle combustion in solid propellant rocket motors may be a significant cause of acoustic combustion instability. A Rijke burner has been developed as a tool to investigate the phenomenon. Previous improvements and characterization of the upright burner lead to the addition of a particle injection flame. The injector flame increases the burner's acoustic driving by about 10% which is proportional to the injector's additional 2 g/min of gas. Frequency remained fairly constant for all test cases. Preliminary testing shows that the combustion of 17.8 µm or 33.4 µm aluminum powder can triple the acoustic driving in the burner from the "gas only" rate of approximately 135 s^-1 The larger aluminum particles, which burn farther into the burner's exhaust, caused a slightly greater acoustic growth rate. Viscous damping appears to limit the effect of distributed particle combustion for particle loadings greater than 8% of the gas flow rate. The information gained in this preliminary study will direct the planned burner characterization and in-depth particle studies.