A STUDY OF THE COMBUSTION INSTABILITY IN A MODEL GAS TURBINE COMBUSTOR

Abstract

Combustion instability is a serious obstacle for the lean premixed combustion of gas turbines, and can even cause fatal damage to the combustor and the entire system. Thus, improved understanding of the mechanisms of combustion instability is necessary for designing and operating gas turbine combustors. In this study, in order to understand the instability phenomena, an experimental study was conducted under the moderate pressure and ambient temperature. We investigated the cause of combustion instability in a rearward-step dump combustor with respect to the modulation of the fuel flow—that is, the choked fuel flow and the unchoked fuel flow. The fluctuation of pressure, heat release and equivalence ratio were measured by piezoelectric pressure sensor, high speed Intensified Charge Coupled Device (ICCD) camera and gas chromatography respectively. Various types of combustion instabilities occurred in relation to changes of the equivalence ratio and the fuel flow conditions. Two representative instability modes were self-excited instabilities at the resonance of combustion chamber (200 Hz) and instabilities related to the fuel flow modulation (10 Hz). In this experiment, combustion instability results mainly from thermoacoustic instability, and the modulation of the fuel flow affects the instability mode. It is founded that the causes of heat release rate fluctuation are not only equivalence ratio fluctuation due to the fuel and air flow modulation but also large vortical motion of the mixture flow and the unmixedness of the fuel and air.