Study on Dynamic Responses of a Screw-Type Pressure-Swirl Injector under Low Frequency Pressure Oscillation

Abstract

Perturbations in the rate of fuel flow from the injector into the combustor can directly affect unsteady motions in the combustor. Therefore, understanding the dynamic characteristics of the injector is important in the effort to control these phenomena. An experimental study on the dynamic response of a pressure-swirl injector under low frequency pressure oscillation conditions was carried out using a pulse valve and the three-microphone technique. Liquid kerosene was used as the fuel and the fuel feed line was designed for fuel flow modulations up to 200 Hz. Acoustic pressure and specific acoustic impedance were obtained within the fuel feed line. The magnitude of the specific acoustic impedance with respect to frequencies was varied by the static pressure in the fuel tubing. A normalized fuel transfer function between mass flow rate and acoustic pressure fluctuations was obtained in the frequency range between 10 and 200 Hz. Its gain shows a tendency to increase with frequency. The phase of the normalized fuel flow rate fluctuation at the injector exit was also measured. The phase tends to decrease with increase in frequency, and it approaches 180 degrees out of phase with the pressure fluctuations at 200 Hz within the fuel feed line.