Lean Blowout and its Sensing in the Presence of Combustion Dynamics in a Premixed Swirl Combustor

Correlations based on design database, combined with multidimensional computational combustion dynamics (CCD) models are used in the combustion design process. However, because of limitations in the current turbulent combustion models, numerics, and boundary conditions, CCD has provided mainly qualitative trends for aerothermal performance, emissions, and liner wall temperature levels and gradients. To overcome these deficiencies, hybrid modeling approaches have been proposed to analyze existing combustors. A typical hybrid modeling approach combines empirical and semianalytical correlations with CCD to give quantitatively accurate predictions of NOx, CO, HC, smoke, lean blowout, ignition, pattern factor, and liner wall temperatures. An alternate approach, anchored CCD, is described in this paper. First, the models were anchored with one of the five modern turbopropulsion engine combustors. The anchored models were then run for the other four combustors. The predicted results correlated well with measured NOx, CO, HC, LEO, and exit temperature quality data, demonstrating a broader applicability of the anchored method. The models were also used for designing a new combustion concept. The pretest prediction agreed well with sector rig data from development hardware, showing the feasibility of using the anchored methodology as a design tool.

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Dynamics and Stability Limits of Syngas Combustion in a Swirl-Stabilized Combustor

Volume 3: Combustion, Fuels and Emissions, Parts A and B ◽

10.1115/gt2008-51023 ◽

2008 ◽

Cited By ~ 2

Author(s):

Raymond L. Speth ◽

H. Murat Altay ◽

Duane E. Hudgins ◽

Ahmed F. Ghoniem

Keyword(s):

High Speed ◽

Equivalence Ratio ◽

Fluid Dynamic ◽

Flame Structure ◽

Low Frequency ◽

Operating Conditions ◽

Video Data ◽

Combustion Dynamics ◽

Lean Blowout ◽

Operating Modes

The combustion dynamics, stability bands and flame structure of syngas flames under different operating conditions are investigated in an atmospheric pressure swirl-stabilized combustor. Pressure measurements and high-speed video data are used to distinguish several operating modes. Increasing the equivalence ratio makes the flame more compact, and in general increases the overall sound pressure level. Very close to the lean blowout limit, a long stable flame anchored to the inner recirculation zone is observed. At higher equivalence ratios, a low frequency, low amplitude pulsing mode associated with the fluid dynamic instabilities of axial swirling flows is present. Further increasing the equivalence ratio produces unstable flames oscillating at frequencies coupled with the acoustic eigenmodes. Additionally, a second unstable mode, coupled with a lower eigen-mode of the system, is observed for flames with CO concentration higher than 50%. As the amount of hydrogen in the fuel is increased, the lean flammability limit is extended and transitions between operating regimes move to lower equivalence ratios.

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Controlling Combustion Dynamics in a Swirl Combustor via Spray Optimization

39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit ◽

10.2514/6.2003-4517 ◽

2003 ◽

Author(s):

Mihir Lal ◽

Miodrag Oljaca ◽

Eugene Lubarsky ◽

Dimitriy Shcherbik ◽

Suresh Menon ◽

...

Keyword(s):

Swirl Combustor ◽

Combustion Dynamics

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Combustion dynamics of a low-swirl combustor

Combustion and Flame ◽

10.1016/j.combustflame.2007.07.017 ◽

2007 ◽

Vol 151 (3) ◽

pp. 412-425 ◽

Cited By ~ 90

Author(s):

D.M. Kang ◽

F.E.C. Culick ◽

A. Ratner

Keyword(s):

Swirl Combustor ◽

Combustion Dynamics

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Studies of Lean Blowout in a Step Swirl Combustor

Volume 3: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

10.1115/94-gt-216 ◽

1994 ◽

Cited By ~ 1

Author(s):

Mark D. Durbin ◽

Dilip R. Ballal

Keyword(s):

Gas Turbine ◽

Flame Length ◽

Air Velocity ◽

Gas Turbine Combustor ◽

Swirl Combustor ◽

Outer Flow ◽

Lean Blowout ◽

Flow Swirl ◽

Wide Range ◽

Air Mixing

The design requirements of a modem gas turbine combustor are increasingly dictated by wide stability limits, short flame length, and uniform mixing. To achieve the best trade-off between the above three factors, flame characteristics (length, shape, mixedness), lean blowout (LBO), and optimum combustor configuration should be investigated over a wide range of inner and outer air velocities, inner and outer vane angles, and co- vs. counter-swirl arrangements. Such an investigation was performed in a step swirl combustor (SSC) designed to simulate the fuel-air mixing pattern in a gas turbine combustor dome fitted with an airblast atomizer. It was found that an increase in the outer vane angle and a decrease in inner air velocity decreased the flame length. LBO was improved when outer flow swirl intensity was increased. An optimum hardware and velocity configuration for the SSC was found for inner swirl = 45°, outer swirl = 60°, co-swirl direction, and inner air velocity = outer air velocity = 16 m/s. This optimum SSC configuration yielded: (i) low values of LBO, (ii) short flame length, (iii) uniformly mixed stable flame, and (iv) little or no variation in these characteristics over the range of operation of SSC. Finally, the co- vs. counter-swirl arrangements and the operation of the optimized combustor configuration were discussed.

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Detection of Lean Blowout and Combustion Dynamics Using Flame Ionization

Volume 1: Turbo Expo 2005 ◽

10.1115/gt2005-68612 ◽

2005 ◽

Author(s):

B. T. Chorpening ◽

D. L. Straub ◽

E. D. Huckaby ◽

K. J. Benson

Keyword(s):

Environmental Conditions ◽

Equivalence Ratio ◽

In Situ Monitoring ◽

Fuel Quality ◽

Combustion Control ◽

Stability Boundaries ◽

Combustion Dynamics ◽

Lean Blowout ◽

Flame Ionization ◽

Lean Premixed

The implementation of sophisticated combustion control schemes in modern gas turbines is motivated by the desire to maximize thermodynamic efficiency while meeting NOx emission restrictions. To achieve target NOx levels, modern turbine combustors must operate with a finely controlled fuel-air ratio near the fuel-lean flame extinction limit, where the combustor is most susceptible to instabilities. In turbine configurations with multiple combustors arranged around the annulus, differences in flow splits caused by manufacturing variations or engine wear can compromise engine performance. Optimal combustion control is also complicated by changes in environmental conditions, fuel quality, or fuel type. As a consequence, engines must be commissioned in the field with adequate stability margin such that manufacturing tolerances, normally expected component wear, fuel quality, and environmental conditions will not cause unstable combustion. A lack of robust combustion in-situ monitoring has limited the ability of modern turbines to achieve stable ultra-low emission performance over the entire load range. Of particular concern is the avoidance of lean blowout (LBO) and combustion dynamics. To minimize combustion temperature and NOx production, it is necessary to approach the LBO boundary. This paper describes continuing work on incipient lean blowout detection using flame ionization, investigating the impact of three different piloting and equivalence ratio reduction strategies applied in a pressurized, lean premixed combustor. This work builds upon previous research in the development of the Combustion Control and Diagnostic Sensor (CCADS). In previous papers, the detection of flashback, equivalence ratio, combustion dynamics, and lean blowout using CCADS has been investigated and described. Previous investigation of lean blowout, however, has been limited to a side pilot configuration. In this paper, lean blowout behavior for a side pilot and a centerbody tip pilot are compared. In addition, two different methods for decreasing equivalence ratio to approach LBO are investigated. These cases are found to have differing lean blowout behavior, and differing CCADS signatures. This paper also reports on the ion signal behavior due to combustion dynamics observed during the equivalence ratio sweeps, including passing through stability boundaries. Tests were performed at 5 atm using an industrial style, lean premixed combustor nozzle, equipped with CCADS electrodes, in a water-cooled, natural gas fueled, acoustically noisy combustor. Testing included sweeps of equivalence ratio from 0.65 to 0.45, crossing one or more stability boundaries. LBO was approached for configurations with a side pilot (on the inlet wall of the combustor, but set away from the premixer) and a centerbody tip pilot. The centerbody tip pilot and the side pilot both helped stabilize combustion, but combustion dynamics still occurred. Incipient LBO was apparent in all cases; however, the different flame structure encountered with each pilot configuration and fuel control strategy made the flame ionization signature differ for each case.

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Robust Lean Blowout Sensing for Turbine Engine Combustors

Volume 3: Controls, Diagnostics and Instrumentation; Education; Electric Power; Microturbines and Small Turbomachinery; Solar Brayton and Rankine Cycle ◽

10.1115/gt2011-46702 ◽

2011 ◽

Author(s):

Ravi K. Bompelly ◽

Jerry M. Seitzman

Keyword(s):

High Speed ◽

Probabilistic Approach ◽

Combustion Process ◽

Optical Signal ◽

Combustion Noise ◽

Mode Switching ◽

Occurrence Rate ◽

Single Element ◽

Combustion Dynamics ◽

Lean Blowout

Lean blowout (LBO) proximity detection is demonstrated in a Jet-A fueled, single-element Lean Direct Injection (LDI) combustor operating at conditions intended to simulate supersonic cruise (2–4 atm, ∼700 K inlet air). Detection is based on identifying LBO precursors in the optical radiation produced by the combustion process. The precursors result from short duration partial flame extinction and re-ignition events. Thresholding of the low-pass filtered optical signal provides robust precursor identification in the presence of the moderate levels of combustion dynamics exhibited by the combustor. Acoustic-based precursor sensing was also attempted, but the precursors could not be reliably identified in the presence of the combustion noise and dynamics; likely causes are discussed. The average event occurrence rate in the optical signal provides a reliable measure of the combustor’s proximity to LBO, monotonically increasing as the LBO limit is approached. The precursor events occur intermittently, and the occurrence rate statistics are reasonably modeled with a normal probability distribution. A probabilistic approach is developed to estimate the fastest fuel reduction transients that could be controlled based on the need to detect some events before the blowout conditions are reached. The results from the LDI combustor are also compared to tests in a premixed, swirl- and dump-stabilized gas-fueled combustor with a center body. High-speed flame images of the precursor events indicate the existence of different static stability modes in the premixed combustor, which are absent in the LDI combustor. The absence of mode-switching in the LDI combustor is suggested to be the reason why it produces much shorter but more frequent precursor events compared to the premixed combustor.

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Anchored CCD for Gas Turbine Combustor Design and Data Correlation

Volume 3: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

10.1115/96-gt-143 ◽

1996 ◽

Cited By ~ 2

Author(s):

Allen M. Danis ◽

David L. Burrus ◽

Hukam C. Mongia

Keyword(s):

Turbulent Combustion ◽

Design Tool ◽

Hybrid Modeling ◽

Quality Data ◽

Gas Turbine Combustor ◽

Combustion Dynamics ◽

Lean Blowout ◽

Design Database ◽

Exit Temperature ◽

Temperature Levels

Correlations based on design database, combined with multi-dimensional computational combustion dynamics (CCD) models are used in the combustion design process. However, because of limitations in the current turbulent combustion models, numerics, and boundary conditions, CCD has provided mainly qualitative trends for aerothermal performance, emissions and liner wall temperature levels and gradients. To overcome these deficiencies, hybrid modeling approaches have been proposed to analyze existing combustors. A typical hybrid modeling approach combines empirical and semianalytical correlations with CCD to give quantitatively accurate predictions of NOx, CO, HC, smoke, lean blowout, ignition, pattern factor and liner wall temperatures. An alternate approach, anchored CCD, is described in this paper. First, the models were anchored with one of the five modern turbopropulsion engine combustors. The anchored models were then run for the other four combustors. The predicted results correlated well with measured NOx, CO, HC, LBO and exit temperature quality data, demonstrating a broader applicability of the anchored method. The models were also used for designing a new combustion concept. The pre-test prediction agreed well with sector rig data from development hardware, showing the feasibility of using the anchored methodology as a design tool.

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Thermoacoustic Instabilities of Hydrogen-Enriched Partially Premixed Flames in a Swirl Combustor

10.1115/gt2021-60009 ◽

2021 ◽

Author(s):

Y. Gong ◽

D. Fredrich ◽

A. J. Marquis ◽

W. P. Jones ◽

I. Boxx

Keyword(s):

Field Method ◽

The Self ◽

Chamber Pressure ◽

Stochastic Field ◽

Cross Sectional ◽

Swirl Combustor ◽

Combustion Dynamics ◽

Thermoacoustic Instabilities ◽

Chemical Reaction Mechanism ◽

Swirling Flames

Abstract Large eddy simulations (LES) of premixed hydrogen-enriched swirling flames were performed to investigate the flame topology and combustion instabilities with different hydrogen concentrations. A compressible LES approach is utilised to account for the self-excited combustion dynamics. A transported probability density function (pd f) approach is adopted to account for sub-grid scale (sgs) turbulence-chemistry interaction, and the solution to the joint sgs – pd f evolution equation of the scalars is obtained by the stochastic field method. The chemistry is represented using a reduced chemical reaction mechanism containing 15 reaction steps and 19 species. The results revealed that as the concentration of hydrogen increases, the flame is shortened in the injecting direction and more confined in the cross-sectional direction, which is consistent with experimental observations. The self-excited limit-cycle oscillations for all considered cases were successfully reproduced, with the predicted peak frequencies of the chamber pressure spectra in excellent agreement with the measured values. The feedback loop of the oscillations is successfully captured and analysed with the temporal evolution of axial velocity and heat release presented.

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