Effects of self-pulsation on combustion instability in a liquid rocket engine

Abstract

The flame oscillation characteristics as well as the relationship between self-pulsation and combustion instability in a combustor burning gaseous oxygen (GOX) and liquid ethanol (LET) through a liquid-centered swirl coaxial (LCSC) injector were investigated experimentally. Data were obtained at pressures from 0.53 to 0.6 MPa and mixture ratios from 0.16 to 0.3. The side-on images of spray and flame were captured synchronously through two high-speed cameras. With the increase of recess length, spray and flame transform from the stable behavior to the self-pulsated behavior with periodic intensity variations of flame emission. When self-pulsation occurs, flame together with the pressure of the LET manifold oscillates at the same frequency, and the peak-to-peak pressure amplitudes of the LET-manifold are greater than 26%. Due to the blocking actions of the conical liquid sheet, spray self-pulsation caused by the periodic fluctuation of pressure in recess chamber is found to be the essential reason of flame and LET manifold pressure oscillation. Furthermore, when the self-pulsation frequency is coupled with the first-longitudinal-mode (1L) natural acoustic frequency of combustor, combustor pressure will be induced to oscillate at the same frequency. This further indicates that self-pulsation may probably be a critical factor inducing combustion instability in liquid rocket engines.