Effects of Unmixedness on Combustion Instabilities in a Lean-Premixed Gas Turbine Combustor

Abstract

The present experimental study focuses on the effects of the degree of premixing and swirl strength on combustion instabilities occurring in a lean premixed gas turbine combustor burning natural gas and air. The combustor operated at pressurized conditions with heated air. Major measurements for the investigation of premixed combustion dynamics include pressure fluctuations, flame emissions in reacting flow, and acetone fluorescence in non-reacting flow to assess the degree of premixing between fuel and air. The acetone PLIF results revealed that the degree of premixing improves as mixing time increases. The first and second longitudinal acoustic modes were the dominant excited modes for most cases of interest. Combustion at a lean premixed condition becomes more susceptible to instabilities as the degree of premixing becomes poor, and self-excited pressure oscillations are obviously present under a fully premixed condition, even without equivalence ratio fluctuations in space. For incomplete premixing cases, local equivalence ratio fluctuations caused by poor premixing may initiate instabilities since reaction rate is sensitive to equivalence ratio fluctuations at lean conditions. Phase resolved chemiluminescence measurements show that pressure oscillations are strongly coupled with variations in flame structures. 96 Flow Turbulence Combust (2010) 85:95-112

Effect of ambient pressure oscillation on the primary breakup of cylindrical liquid jet spray

“…They concluded that the modulation of the liquid fuel is crucial to prevent combustion instabilities. Seo and Lee 18 also studied combustion instability mechanisms in a lean premixed gas turbine combustor characterized by large pressure fluctuations and excessive heat transfer. They found that the pressure oscillations are strongly coupled with variations in flame structure.…”