Combustion instability in a small liquid rocket motor

An experimental investigation of high frequency combustion instability in a liquid rocket engine of 3kN thrust was conducted. The diagnostic method of detecting combustion instability was based on the measurement of the dynamic pressure following an artificial disturbance in the combustion chamber. Test data spectral analysis was performed by using the stochastic vibration data processing method. Although the engine has demonstrated an absence of tendency to spontaneous instability, insufficient stability of the original engine design was evident during tests with artificial triggers. A Helmholtz type resonator in form of partitioned cavities tuned to a few different, close frequencies was designed and installed in the combustion chamber wall to avoid spontaneous or triggered combustion instability. The experimental results from hot tests with artificial triggers confirmed the high efficiency of the applied acoustic resonator.