Experiments on afterburner combustion performance with self-excited sweeping nozzle in high speed and medium temperature air flow

To further prove the effectiveness of self-excited sweeping nozzles in enhancing afterburner combustion performances under the constraints of practical application conditions, this study first designed an afterburner fuel spray bar containing 10 self-excited sweeping nozzles, and then a plain-orifice spray bar was designed for comparison with the same nozzle number, injection locations, and total flow rate. The flow rate, frequency, and injection angle of both spray bars were measured and analyzed. Then, under the typical bypass airflow conditions of a turbofan engine with an airflow of high speed and medium temperature, combustion efficiency at the exit cross-section, temperature distribution along the path, and dynamic wall pressure fluctuations were measured using on a rectangular afterburner combustion performance test bench with the plain-orifice and self-excited sweeping spray bars respectively. The results showed that the self-excited sweeping spray bar significantly expanded the blowout limit of the combustion chamber compared to the plain-orifice spray bar, and improved combustion efficiency across the entire fuel-to-air equivalence ratio range, with a maximum improvement of 8.5%, and the gas temperature along the path increased by up to 181 ℃. At a higher equivalence ratio, the plain-orifice spray bar induced a low-frequency longitudinal thermoacoustic coupling oscillation at around 140 Hz, with a pressure relative pulsation amplitude of 16.3%. In contrast, under the same conditions, the self-excited sweeping spray bar reduced the pressure relative pulsation amplitude to only 2.3%, effectively suppressing combustion instability. This study fully demonstrates the notable results of self-excited sweeping nozzles in improving combustion efficiency, expanding the blowout limit and suppressing combustion instability of the afterburner.