Experimental investigation of the self-excited oscillation characteristics of a supercritical aviation kerosene jet in a swirling flow field

As the pressure ratio and the turbine inlet temperature keep increasing in high performance aero-engines, the kerosene injected into the combustion chamber becomes supercritical. Thus, the traditional self-excited oscillations of the kerosene jets in the fuel-gas mixing are much more pronounced because of the drastic changes in the kerosene thermal properties, which may exacerbate the combustion instability and threaten engine efficiency and safety. In this work, an experimental study was carried out on the self-excited oscillation phenomena of supercritical kerosene injected into a swirling flow field. The injection of supercritical kerosene under different operating conditions was studied using the Schlieren technique and the proper orthogonal decomposition method. The results present that the mixing dominated oscillations of the kerosene jet are induced by the fuel-gas interaction. While the condensation dominated oscillations are due to the phase change of supercritical kerosene in the subcritical environment and the swirling flow field. The spatial distribution of the self-excited oscillations is found to be highly related to the velocity magnitude, instead of the variations in the injection temperature and pressure. The self-excited oscillations are easier to be induced in a low velocity flow field and the oscillation region moves closer to the upstream. Thermal properties also show distinct influences on the injection. At the near-critical region, the suppression effects of high injection pressure on the high-frequency (>100 Hz) self-excited oscillations are much more distinct.