An experimental estimation of mean reaction rate and flame structure during combustion instability in a lean premixed gas turbine combustor

Lee, Seong-Young; Seo, Seok Bin; Broda, J.; Pal, Snehanshu; Santoro, Robert J.

doi:10.1016/s0082-0784(00)80280-5

Cited by 132 publications

(49 citation statements)

References 27 publications

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“…The flame surface density (FSD) based on OH PLIF was found to agree well with chemiluminescence, which is in agreement with previous works [3,23,24]. The flow field under cold condition was explored using high speed smoke visualization.…”

Section: Discussionsupporting

confidence: 87%

Non-linear Response of Turbulent Premixed Flames to Imposed Inlet Velocity Oscillations of Two Frequencies

Balachandran

Dowling

Mastorakos

2008

Flow Turbulence Combust

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This paper describes an experimental study investigating the non-linear response of lean premixed air/ethylene flames to strong inlet velocity perturbations of two frequencies. The combustor has a centrally-placed bluff body and a short quartz section. The annulus between the bluff body and the flow tube, which also housed the acoustic pressure transducers, allowed the reactants into the combustor. The inlet flow was perturbed using loudspeakers. High speed laser tomography, OH* chemiluminescence and OH Planar Laser Induced Fluorescence (PLIF) have been used for flow visualization, heat release and flame surface density (FSD) measurements respectively. The heat release fluctuations increased initially linearly with inlet velocity amplitude for a single frequency forcing, with saturation occurring after forcing amplitudes of around 15% of the bulk velocity, which was found to occur due to vortex roll up and subsequent flame annihilation. The introduction of energy at the second frequency (i.e, the harmonic) was found to change the vortex formation and shedding frequency, depending on the level of forcing. This resulted in a non-linear flame response transfer function (defined as the amplitude of unsteady heat release divided by the amplitude of velocity perturbation at the fundamental) whose amplitude depended greatly on the amount of harmonic content present in the perturbations. The introduction of higher harmonics reduced the flame 456 Flow Turbulence Combust (2008) 80:455-487 annihilation events, which are responsible for saturation, thus reducing non-linearity in the amplitude dependence of the flame response. These results were further verified using sequential time-resolved OH PLIF measurements. The findings from this study suggest that the acoustic response of the flame was mostly due to flame area variation effected by modulation of the annular jet and evolution of the shear layers.

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Section: Discussionsupporting

confidence: 87%

Non-linear Response of Turbulent Premixed Flames to Imposed Inlet Velocity Oscillations of Two Frequencies

Balachandran

Dowling

Mastorakos

2008

Flow Turbulence Combust

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“…Published by Elsevier Inc. All rights reserved. doi:10.1016/j.combustflame.2010.07.011 from simple, unconfined flames [18,19] to high-temperature, highpressure combustors using complex fuels [20][21][22][23][24][25][26]. However, the simple flame configurations are typically designed to study one particular fundamental process and do not describe the complex flow-flame interactions occurring in practical systems.…”

Section: Introductionmentioning

confidence: 99%

Flow–flame interactions causing acoustically coupled heat release fluctuations in a thermo-acoustically unstable gas turbine model combustor

Steinberg

Boxx

Stöhr

et al. 2010

Combustion and Flame

276

149

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a b s t r a c tA detailed analysis of the flow-flame interactions associated with acoustically coupled heat-release rate fluctuations was performed for a 10 kW, CH 4 /air, swirl stabilized flame in a gas turbine model combustor exhibiting self-excited thermo-acoustic oscillations at 308 Hz. High-speed stereoscopic particle image velocimetry, OH planar laser induced fluorescence, and OH* chemiluminescence measurements were performed at a sustained repetition rate of 5 kHz, which was sufficient to resolve the relevant combustor dynamics. Using spatio-temporal proper orthogonal decomposition, it was found that the flow-field contained several simultaneous periodic motions: the reactant flux into the combustion chamber periodically oscillated at the thermo-acoustic frequency (308 Hz), a helical precessing vortex core (PVC) circumscribed the burner nozzle at 515 Hz, and the PVC underwent axial contraction and extension at the thermo-acoustic frequency. The global heat release rate fluctuated at the thermo-acoustic frequency, while the heat release centroid circumscribed the combustor at the difference between the thermoacoustic and PVC frequencies. Hence, the three-dimensional location of the heat release fluctuations depended on the interaction of the PVC with the flame surface. This motivated the compilation of doubly phase resolved statistics based on the phase of both the acoustic and PVC cycles, which showed highly repeatable periodic flow-flame configurations. These include flames stabilized between the inflow and inner recirculation zone, large-scale flame wrap-up by the PVC, radial deflection of the inflow by the PVC, and combustion in the outer recirculation zones. Large oscillations in the flame surface area were observed at the thermo-accoustic frequency that significantly affected the total heat-release oscillations. By filtering the instantaneous reaction layers at different scales, the importance of the various flow-flame interactions affecting the flame area was determined. The greatest contributor was large-scale elongation of the reaction layers associated with the fluctuating reactant flow rate, which accounted for approximately 50% of the fluctuations. The remaining 50% was distributed between fine scale stochastic corrugation and large-scale corrugation due to the PVC.

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“…Chemiluminescence/emission signals have been considered to assess heat release in the study of combustion instability for many years. The most commonly used species for this purpose are CH* and OH* in hydrocarbon flames [17,18]. A numerical study by Samaniego et al [19] suggests that the detection of CO 2 * emission in hydrocarbon flames can be used to infer a heat release rate.…”

Section: Optical Configurationsmentioning

confidence: 99%

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

Seo

Lee

2010

Flow Turbulence Combust

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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

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An experimental estimation of mean reaction rate and flame structure during combustion instability in a lean premixed gas turbine combustor

Cited by 132 publications

References 27 publications

Non-linear Response of Turbulent Premixed Flames to Imposed Inlet Velocity Oscillations of Two Frequencies

Non-linear Response of Turbulent Premixed Flames to Imposed Inlet Velocity Oscillations of Two Frequencies

Flow–flame interactions causing acoustically coupled heat release fluctuations in a thermo-acoustically unstable gas turbine model combustor

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

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