Experimental Validation of Off-design Combustion for Liquid-propellant Rocket Engine High-frequency Instability

Abstract

The mechanism causing high-frequency combustion instability was presumed to be the progression of combustion at an off-design location; that is, in the vicinity of the faceplate. Experiments were carried out to prove this. In the experiments, water was used to simulate the propellant and the increase in pressure caused by off-design combustion was simulated by injecting nitrogen gas. Pressure increase and decay were measured to within approximately 1 ms, and the maximum local pressure was approximately twice the pressure prior to increasing the pressure. To estimate the pressure change in actual engines, a simplified simulation calculation model was constructed. After calibration using the experimental results, the time and amplitude of pressure change were on the same order of magnitude of those of the engines. The present study results show that the off-design combustion model can be a cause of the high-frequency combustion instability experienced when using liquid rocket engines.