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Effects of inert fuel diluents on thermoacoustic instabilities in gas turbine combustion

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Title: Effects of inert fuel diluents on thermoacoustic instabilities in gas turbine combustion
Authors: Karlis, E
Hardalupas, Y
Taylor, AMKP
Item Type: Journal Article
Abstract: The effects of inert diluents in the fuel mixture of a model swirl stabilized gas turbine combustor, under thermoacoustically unstable limit cycle operation, were studied experimentally. The measurements included particle image velocimetry (PIV), high-speed CH* chemiluminescent imaging, and dynamic pressure signals. The paper focuses on the dynamic phenomenon of the period doubling bifurcation, which came about when the equivalence ratio ϕ of undiluted flames was enriched from 0.55 to 0.60 under constant Reynolds number (Re=18,000). The bifurcation featured an emergence of an aerodynamically related timescale in addition to the fundamental timescale that was induced from an unstable acoustic eigenmode. The aerodynamic timescale is introduced by azimuthal convection of a high-heat-release-rate region and is linked in the literature with a precessing motion of the recirculation zone. It was found that on increasing the diluent molar fraction up to 50%, the amplitude and the frequency of the limit cycle fundamental acoustic mode decreased. A mechanism to interpret this suppression is that increasing the diluent molar fraction of the fuel makes the flame more susceptible to quenching because the extinction strain rate of the mixture is decreased. The paper argues that the existence of inert diluents in the fuel can significantly alter the dynamic state of the combustor, because the anchoring locations of the flame greatly depend on the composition-sensitive extinction strain rate of the mixture.
Issue Date: 20-Apr-2020
Date of Acceptance: 20-Feb-2020
URI: http://hdl.handle.net/10044/1/80274
DOI: 10.2514/1.J058312
ISSN: 0001-1452
Publisher: American Institute of Aeronautics and Astronautics
Start Page: 2643
End Page: 2657
Journal / Book Title: AIAA Journal: devoted to aerospace research and development
Volume: 58
Issue: 6
Copyright Statement: © 2020 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the eISSN 1533-385X to initiate your request. See also AIAA Rights and Permissions www.aiaa.org/randp.
Sponsor/Funder: Engineering & Physical Science Research Council (E
Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: J13878
EP/M015300/1
Keywords: Science & Technology
Technology
Engineering, Aerospace
Engineering
HEAT RELEASE FLUCTUATIONS
COHERENT STRUCTURES
EQUIVALENCE RATIO
SWIRLING JET
FLAME
OSCILLATIONS
EXTINCTION
MECHANISMS
STABILITY
DILUTION
Science & Technology
Technology
Engineering, Aerospace
Engineering
HEAT RELEASE FLUCTUATIONS
COHERENT STRUCTURES
EQUIVALENCE RATIO
SWIRLING JET
FLAME
OSCILLATIONS
EXTINCTION
MECHANISMS
STABILITY
DILUTION
Aerospace & Aeronautics
0901 Aerospace Engineering
0905 Civil Engineering
0913 Mechanical Engineering
Publication Status: Published
Online Publication Date: 2020-04-20
Appears in Collections:Mechanical Engineering
Faculty of Natural Sciences