Damping Device to Reduce the Risk of Injection-Coupled Combustion Instabilities

Abstract

The DLR research combustor ’BKD’ shows self-excited combustion instabilities driven by LOX injection-coupling. This driving mechanism has also been observed for other cryogenic rocket engine experiments up to full-scale engines, as the LE-X or J-2S. A new countermeasure against injection-coupled instabilities, by directly damping the acoustic eigenmodes of the injector instead of chamber pressure oscillations, has been developed and tested at representative operating conditions in BKD. The principle of the damping method is described in this report. Acoustic absorber elements have been integrated into a modified component of the BKD injector head. The absorbers had no measurable influence on thrust chamber performance. Test results are presented which show that flame and pressure oscillations were successfully reduced by the modification.