Flow structures in a lean-premixed swirl-stabilized combustor with microjet air injection

LaBry, Zachary A.; Shanbhogue, Santosh J.; Speth, Raymond L.; Ghoniem, Ahmed F.

doi:10.1016/j.proci.2010.06.092

Cited by 36 publications

(23 citation statements)

References 13 publications

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“…As the dilution levels were increased from χ CO2 = 0.63 (T ad = 2100 K) to χ CO2 = 0.67 (T ad = 1970 K), the flame lengths increase commensurate with what is expected for decreasing flame temperatures. The flame dynamics are controlled by the fluid-mechanics of the inner recirculation zone as was reported in our previous work on propane-air mixtures [15]. The next abrupt transition is seen at χ CO2 = 0.67 (T ad = 1970 K) where the instability jumps from the three-quarter wave mode to the quarter wave mode with a slightly lower limit-cycle amplitude.…”

Section: B Dynamic Characteristics Of Oxy-fuel Mixturesmentioning

confidence: 56%

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Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

Shroll

Shanbhogue

Ghoniem

2011

Volume 2: Combustion, Fuels and Emissions, Parts a and B

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This work explores the dynamic stability characteristics of premixed CH4/O2/CO2 mixtures in a 50kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different fractions of carbon dioxide used to control the flame temperature (Tad). For the highest Tad’s, the combustor is unstable at the five-quarter wave mode. As the temperature is reduced, the combustor jumps to the three quarter mode and then to the quarter wave before eventually reaching blowoff. Similar to the case of CH4/air mixtures, the transition from one mode to another is predominantly a function of the Tad of the reactive mixture, despite significant differences in laminar burning velocity and/or strained flame consumption speed between air and oxy-fuel mixtures for a given Tad. High speed images support this finding by revealing similar vortex breakdown modes and thus similar turbulent flame geometries that change as a function of flame temperature.

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Section: B Dynamic Characteristics Of Oxy-fuel Mixturesmentioning

confidence: 56%

“…Premixed CH 4 /O 2 /CO 2 or premixed CH 4 /air enters the combustor through a 38 mm diameter inlet pipe. The swirler is located 5 cm upstream of the expansion plane and has 8 blades with an estimated swirl number of 0.7 [15]. From the expansion plane downstream, the inner diameter is 76 mm.…”

Section: Methodsmentioning

confidence: 99%

Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

Shroll

Shanbhogue

Ghoniem

2011

Volume 2: Combustion, Fuels and Emissions, Parts a and B

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“…The combustor discharges into a plenum at near atmospheric pressure. The experimental setup is similar to the ones previously investigated by our research group [15][16][17][18]. The swirl number is fixed and estimated at S $ 0.7 based on the swirler's vanes angle, the Reynolds number based on the inlet diameter is Re Din ¼ 20; 000, and the pressure is atmospheric.…”

Section: Introductionmentioning

confidence: 99%

Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion

Taamallah¹,

LaBry²,

Shanbhogue³

et al. 2015

Journal of Engineering for Gas Turbines and Power

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In this paper, we conduct an experimental investigation to study the link between the flame macroscale structure-or flame brush spatial distribution-and thermo-acoustic instabilities, in a premixed swirl-stabilized dump combustor. We operate the combustor with premixed methane-air in the range of equivalence ratio (/) from the lean blowout limit to / ¼ 0:75. First, we observe the different dynamic modes in this lean range as / is raised. We also document the effect of / on the flame macrostructure. Next, we examine the correspondence between dynamic mode transitions and changes in flame macrostructure. To do so, we modify the combustor length-by downstream truncationwithout changing the underlying flow upstream. Thus, the resonant frequencies of the geometry are altered allowing for decoupling the heat release rate fluctuations and the acoustic feedback. Mean flame configurations in the modified combustor and for the same range of equivalence ratio are examined, following the same experimental protocol. It is found that not only the same sequence of flame macrostructures is observed in both combustors but also that the transitions occur at a similar set of equivalence ratio. In particular, the appearance of the flame in the outside recirculation zone (ORZ) in the long combustor-which occurs simultaneously with the onset of instability at the fundamental frequency-happens at similar / when compared to the short combustor, but without being in latter case accompanied by a transition to thermo-acoustic instability. Then, we interrogate the flow field by analyzing the streamlines, mean, and rms velocities for the nonreacting flow and the different flame types. Finally, we focus on the transition of the flame to the ORZ in the acoustically decoupled case. Our analysis of this transition shows that it occurs gradually with an intermittent appearance of a flame in the ORZ and an increasing probability with /. The spectral analysis of this phenomenon-we refer to as "ORZ flame flickering"-shows the presence of unsteady events occurring at two distinct low frequency ranges. A broad band at very low frequency in the range $(1 Hz-10 Hz) associated with the expansion and contraction of the inner recirculation zone (IRZ) and a narrow band centered around 28 Hz which is the frequency of rotation of the flame as it is advected by the ORZ flow.

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“…All frequencies are filtered except for the one related to the subharmonic frequency of instability, in order to isolate the coherent structure associated explicitly with the timescale of interest. Details of the DMD algorithm can be found in [37] and an application on a gas turbine combustor can be found in [38] and in [12]. The results of the reconstruction show an azimuthally convected high heat release rate region.…”

Section: Casementioning

confidence: 99%

Effects of Inert Fuel Diluents on Thermoacoustic Instabilities in Gas Turbine Combustion

2020

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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). The bifurcation featured an emergence of an aerodynamically related timescale in addition to the fundamental timescale which 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. Prior to the bifurcation, the flame anchored between the wall and the outer shear layers of the recirculation zone assuming a V-shape. The dynamics were attracted to a Period-1 limit cycle. Post the bifurcation the flame expanded in the inner shear layers of the recirculation zone assuming an M-shape, while the dynamics were attracted to a Period-2 limit cycle. The latter operational condition was subject to nitrogen dilution in order to parametrically increase the molar fraction of inert diluent in the fuel stream. It was found that on increasing the diluent molar fraction the amplitude and the frequency of the limit cycle fundamental acoustic mode decreased. Also, inert dilution suppressed the aerodynamic timescale and the flame assumed a V-shape again. A mechanism to interpret this mechanism is suggested. Increasing the diluent molar fraction of the fuel makes the flame susceptible to quenching because the extinction strain rate of the mixture decreased. Thus, the flow imposed strain rates quenched the flame when it attempted to anchor on the inner shear layers of the vortex breakdown induced recirculation zone. The inability of the flame to anchor on the shear layers suppressed the aerodynamic mode. The paper argues that the existence of inert diluents in the fuel can significantly alter the dynamic state of the combustor, since the anchoring locations of the flame greatly depend on the composition-sensitive extinction strain rate of the mixture.

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Flow structures in a lean-premixed swirl-stabilized combustor with microjet air injection

Cited by 36 publications

References 13 publications

Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion

Effects of Inert Fuel Diluents on Thermoacoustic Instabilities in Gas Turbine Combustion

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