Instability Characteristics of a Gaseous-Oxygen/Methane Pentad Injector

摘要

This experimental research characterized the modes of combustion instability produced by an impinging-jet pentad injector burning in an open cylindrical chamber. The device is being explored as a laboratory analog for unsteady mixing processes in supercritical rocket injectors. The injector burned gaseous oxygen and gaseous methane at equivalence ratios from 0.5 to 2.0 and total mass flow rates from 0.33 to 4.9 grams per second. The radial position of the injector was also varied from 0 to 76% of the chamber radius. Six high-frequency pressure transducers located around the circumference and end of the chamber simultaneously recorded pressure fluctuations at each operating point A detailed phase analysis among the transducers allowed determination of the modes of instability. Fast Fourier transforms determined the amplitude and frequency of the primary instability at each operating point The results show that this single-element injector exhibits spontaneous first radial, first radial-first tangential, or second tangential modes at fluctuation amplitudes up to 17% of chamber pressure. Changing the radial location of the injector changed the operating points at which maximum instability occurred. The tangential instability modes occurred with only one injector element operating under the conditions described and therefore were not driven by injector-to-injector interactions.