Thermo-acoustic instabilities in lean premixed swirl-stabilized combustion and their link to acoustically coupled and decoupled flame macrostructures

Taamallah, Soufien; LaBry, Zachary A.; Shanbhogue, Santosh J.; Ghoniem, Ahmed F.

doi:10.1016/j.proci.2014.07.002

Cited by 111 publications

(48 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This rotation motion was highlighted in our previous work and associated with the 28 Hz frequency peak. It was also found to be dominated by hydrodynamics and not fuel dependent [24]. The two frequency bands observed here using flame chemiluminescence data were also confirmed based on the velocity field: we performed a dynamic mode decomposition (DMD) of the instantaneous PIV measurements [25] to extract dominant dynamics of the reacting flow for the different flame macrostructures.…”

Section: Transition To Orz Flame (Iii To Iv)supporting

confidence: 66%

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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Transition To Orz Flame (Iii To Iv)supporting

confidence: 66%

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

Self Cite

View full text Add to dashboard Cite

show abstract

“…Configuration III, where the flame is stabilized on the inner shear layer only is found in the air-flame at f = 0.60, whereas configuration IV is found in the oxy-flame at the same equivalence ratio. This is surprising since the laminar burning velocity of the air flame is higher than the oxy flame as shown in Table 1, and hence it should have been expected to be present in the air-flame according to the dependence of the flame configuration on the burning velocity [7][8][9][10]. Meanwhile, when the equivalence ratio is below 0.58, the flame length significantly increases, and a conical flame (configuration III) appears in both air and oxy-flames.…”

Section: Computationmentioning

confidence: 99%

“…The adiabatic temperatures of the oxy-flames were almost the same as those of the air-flames at the same f, whereas the laminar burning velocities of oxy-flames were consistently lower than those of the air-flames. All cases were calculated at atmospheric pressure, and the inlet reactant temperature was 300 K. In our previous work [7][8][9][10], we analyzed premixed air flames in the swirl-stabilized combustor, and observed four different shapes/configurations that appear as the equivalence ratio is raised or the laminar burning velocity of the corresponding flame increases: columnar flame (I); a bubble+columnar flame (II); a single conical flame (III); and a double conical flame (IV). In flame III (e.g.…”

Section: Computationmentioning

confidence: 99%

“…Recently, Shroll et al studied dynamic stability characteristics of premixed CH 4 /O 2 /CO 2 mixtures in the MIT swirl stabilized combustor, and found that the transition between instability modes correlated with the adiabatic flame temperature [6]. Further work in the same group [7,8] showed that the correlation between the flame structure and the dynamic mode, with flames stabilized on the inner shear layer around the inner recirculation zone being stable while flames stabilized in the inner shear layer as well as the outer shear layer being unstable.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Impact of Equivalence Ratio on the Macrostructure of Premixed Swirling CH4/Air and CH4/O2/CO2 Flames

Watanabe

Shanbhogue

Ghoniem

2015

Volume 4B: Combustion, Fuels and Emissions

Self Cite

View full text Add to dashboard Cite

Premixed CH 4 /O 2 /CO 2 flames (oxy-flames) and CH 4 /air flames (air-flames) were experimentally studied in a swirlstabilized combustor. For comparing oxy and air flames, the same equivalence ratio and adiabatic flame temperature were used. CO 2 dilution was adjusted to attain the same adiabatic temperature for the oxy-flame and the corresponding air-flame while keeping the equivalence ratio and Reynolds number (=20,000) the same. For high equivalence ratios, we observed flames stabilized along the inner and outer shear layers of the swirling flow and sudden expansion, respectively, in both flames. However, one notable difference between the two flames appears as the equivalence ratio reaches 0.60. At this point, the outer shear layer flame disappears in the air-flame while it persists in the oxy-flame, despite the lower burning velocity of the oxy-flame. Prior PIV measurements (Ref. 9) showed that the strains along the outer shear layer are higher than along the inner shear layer. Therefore, the extinction strain rates in both flames were calculated using a counter-flow premixed twin flame configuration. Calculations at the equivalence ratio of 0.60 show that the extinction strain rate is higher in the oxy than in the air flame, which help explain why it persists on the outer shear layer with higher strain rate. It is likely that extinction strain rates contribute to the oxy-flame stabilization when air flame extinguish in the outer shear layer. However, the trend reverses at higher equivalence ratio, and the cross point of the extinction strain rate appears at equivalence ratio of 0.64.

show abstract

“…This work is mainly driven by previous studies demonstrating the link between this transition in the flame macrostructure and the onset of thermo-acoustic instabilities [1,2]. Here, we examine the transition mechanism under thermo-acoustically stable conditions as well as the dominant flow and flame dynamics associated with it.…”

mentioning

confidence: 94%

Transition From a Single to a Double Flame Structure in Swirling Reacting Flows: Mechanism, Dynamics, and Effect of Thermal Boundary Conditions

Taamallah

Shanbhogue

Sanusi

et al. 2015

Volume 5C: Heat Transfer

Self Cite

View full text Add to dashboard Cite

We examine experimentally the transition from a single flame stabilized along the inner shear layer (ISL) to a double flame stabilized along both the inner and the outer shear layers (OSL) and spreading over the outside recirculation zone (ORZ) in a fully premixed swirl-stabilized combustor. This work is mainly driven by previous studies demonstrating the link between this transition in the flame macrostructure and the onset of thermo-acoustic instabilities [1,2]. Here, we examine the transition mechanism under thermo-acoustically stable conditions as well as the dominant flow and flame dynamics associated with it. In addition, we explore the role of changing the thermal boundary conditions around the ORZ and its effect on the presence or absence of the flame there. We start by analyzing the two flames bounding the transition, namely the single conical flame stabilized along the ISL (flame III 1 ) and the double conical flames with reactions * Corresponding author -email: sofiene@mit.edu 1 Same flame configuration nomenclature as in [1][2][3][4][5][6] taking place in the ORZ (flame IV). A dual chemiluminescence approach -using two cameras with a narrow field of view focused on the ORZ -is undertaken to track the progression of the flame as it reaches the ORZ. During the transition, the flame front, initially stabilized along the ISL, is entrained by OSL vortices close to where the turbulent jet impinges on the wall, leading to the ignition of the reactants in the ORZ and the ultimately the stabilization of the flame along the outer shear layer (OSL). This ORZ flame is also subject to extinction when the equivalence ratio (φ ) is between values corresponding to flames III and IV. For φ lower than the critical transitional value, the flame kernel originating from the ISL-stabilized flame is shown to reach the ORZ but fails to grow and quickly disappears. For φ higher than the critical value, the flame kernel expands as it is advected by the ORZ flow and ultimately ignites the reactants recirculating in the ORZ. Sudden and extreme peak-to-peak values of the overall heat release rate are found to be concomitant with the ignition and extinction of the ORZ reactants. Finally, Different ther-

show abstract

Thermo-acoustic instabilities in lean premixed swirl-stabilized combustion and their link to acoustically coupled and decoupled flame macrostructures

Cited by 111 publications

References 16 publications

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

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

Impact of Equivalence Ratio on the Macrostructure of Premixed Swirling CH4/Air and CH4/O2/CO2 Flames

Transition From a Single to a Double Flame Structure in Swirling Reacting Flows: Mechanism, Dynamics, and Effect of Thermal Boundary Conditions

Contact Info

Product

Resources

About