Experimental study on high-frequency combustion instability of liquid-propellant rocket engines using off-design combustion model

Combustion tests were conducted to investigate the high-frequency combustion instability of liquid propellant rocket engines using a small experimental model. The model simulates the base space around the propellant injectors of rocket engines. In this study, we presumed that off-design combustion occurred in the base space created by the injected propellants and injector faceplate, and investigated the propagation and repetition of combustion in the base space. The model has two base spaces in which the propagation of combustion was examined. 2-Propanol and gaseous oxygen were used as propellants. 2-Propanol was used as a substitute fuel to study the injection and combustion dynamics of high-density rocket propellants. The test results revealed that (1) the pressure changed up to 20 times higher than the pressure prior to combustion within a millisecond; (2) the flame propagated from one base space to another; (3) combustion was repeated several times, and (4) the pressure outside the base space was dozens of percent to several times greater. The propagated and repeated combustions, as in (2) and (3), can produce a pressure change of a higher frequency than the frequency due to a single combustion. The experimental results indicated that off-design combustion in the base space could be a mechanism for high-frequency combustion instability.