Effects of Unmixedness on Combustion Instabilities in a Lean-Premixed Gas Turbine Combustor |
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Authors: | Seonghyeon Seo Seong-Young Lee |
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Institution: | 1.Combustion Chamber Department,Korea Aerospace Research Institute,Daejeon,Republic of Korea;2.MEEM,Michigan Technological University,Houghton,USA |
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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. |
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Keywords: | |
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