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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

High Resolution Particle Image Velocimetry and CH-PLIF Measurements and Analysis of a Shear Layer Stabilized Flame

[+] Author and Article Information
C. W. Foley

School of Mechanical Engineering,
Ben T. Zinn Combustion Lab,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: cfoley3@gatech.edu

I. Chterev

School of Aerospace Engineering,
Ben T. Zinn Combustion Lab,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: ianko@gatech.edu

J. Seitzman

School of Aerospace Engineering,
Ben T. Zinn Combustion Lab,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: jerry.seitzman@ae.gatech.edu

T. Lieuwen

School of Aerospace Engineering,
Ben T. Zinn Combustion Lab,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: tim.lieuwen@ae.gatech.edu

Contributed by the Controls, Diagnostics and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 14, 2015; final manuscript received August 12, 2015; published online September 29, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(3), 031603 (Sep 29, 2015) (13 pages) Paper No: GTP-15-1308; doi: 10.1115/1.4031367 History: Received July 14, 2015; Revised August 12, 2015

Understanding the mechanisms and physics of flame stabilization and blowoff of premixed flames is critical toward the design of high velocity combustion devices. In the high bulk flow velocity situation typical of practical combustors, the flame anchors in shear layers where the local flow velocities are much lower. Within the shear layer, fluid strain deformation rates are very high and the flame can be subjected to significant stretch levels. The main goal of this work was to characterize the flow and stretch conditions that a premixed flame experiences in a practical combustor geometry and to compare these values to calculated extinction values. High resolution, simultaneous particle image velocimetry (PIV) and planar laser induced fluorescence of CH radicals (CH-PLIF) measurements are used to capture the flame edge and near-field stabilization region. When approaching lean limit extinction conditions, we note characteristic changes in the stretch and flow conditions experienced by the flame. Most notably, the flame becomes less critically stretched when fuel/air ratio is decreased. However, at these lean conditions, the flame is subject to higher mean flow velocities at the edge, suggesting less favorable flow conditions are present at the attachment point of the flame as blowoff is approached. These measurements suggest that blowoff of the flame from the shear layer is not directly stretch extinction induced, but rather the result of an imbalance between the speed of the flame edge and local tangential flow velocity.

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References

Figures

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Fig. 1

Illustration of a normal propagation stabilized flame (left) and an edge flame stabilized flame (right)

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Fig. 2

Time averaged chemiluminescence image of ISL stabilized flame with interrogation region for stretch measurements shown (left) and corresponding coordinate system, flame angle, and flame normal definitions (right)

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Fig. 3

Profile of opposed jet flame structure obtained from OPPDIF module in CHEMKIN for methane–air flame ϕ = 1.0, Tph = 533 K

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Fig. 5

Calculated dependence of κextph (solid line) and κextCH (dashed line) upon ϕ for methane–air mixtures with a preheat temperature of 533 K

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Fig. 4

Laminar flame speed sensitivity to fluid strain for methane–air mixtures defined at preheat zone (bottom) and location of YCHmax (top) for Tph= 533K and ϕ = 0.8 and ϕ = 1.0

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Fig. 6

Maximum CH mass fraction, all cases normalized by maximum of YCHmax(κsph) for ϕ = 1.1, as a function of stretch at atmospheric conditions and a preheat temperature of 533 K

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Fig. 7

Typical OH-PLIF images in the r-θ plane ∼4 mm downstream of the dump plane for ISL stabilized flame (upm = 35 m/s at Tph = 366 K, ϕ = 0.65, 1.42 in. centerbody, 45 deg swirler vanes, 4.2 in. combustor). White line indicates location of centerbody relative to flame.

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Fig. 15

Mean uz,r strain field (1/s) with mean CH-layer center line position (dashed line) and flame normal (arrows) overlaid (ϕ = 1.0, upm = 35 m/s)

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Fig. 16

Mean uz,z strain field (1/s) with mean CH-layer centerline position (dashed line) and flame normal (arrows) overlaid (ϕ = 1.0, upm = 35 m/s). Accelerating flow indicated by light region, decelerating region is shaded gray.

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Fig. 10

CH-layer flame brush images for ϕ = 0.8−1.1 at upm = 35 m/s, centerbody location shown as gray rectangle

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Fig. 17

Transverse profiles of mean, axial velocity at various axial locations schematically demonstrating the strain field structure of the near field shear layer and jet

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Fig. 11

Mean flame angle for ϕ = 0.8−1.1 at upm = 35 m/s with error bars in the mean value shown for one standard deviation

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Fig. 12

Mean flame position (dashed line) and flame normal (arrows) with contours of u¯z (solid lines) and u¯r=0 (dashed). Regions of u¯r>0 and u¯r≤0 shown in white and gray, respectively (ϕ = 1.0, upm = 35 m/s).

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Fig. 8

Sample instantaneous images of CH-PLIF and velocity vectors for ϕ = 1.0, upm = 35 m/s

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Fig. 9

Sample instantaneous images of CH-PLIF and velocity vectors for ϕ = 0.8, upm = 35 m/s

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Fig. 13

Instantaneous flame stretch profile as a function of CH-layer arc length by source (ϕ = 0.9, upm = 35 m/s)

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Fig. 14

Mean flame stretch axial dependence by source, normalized by extinction stretch rate (ϕ = 0.9, upm = 35 m/s)

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Fig. 18

Axial dependence of mean flame stretch rates at four equivalence ratios (upm = 35 m/s)

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Fig. 19

Sensitivity of mean stretch rates to equivalence ratio with κsCH normalized by κextCH (upm = 35 m/s)

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Fig. 23

Mean velocity conditions along the CH-layer for ϕ = 0.9, upm = 35 m/s case as a function of downstream distance

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Fig. 24

Normalized tangential and normal flow velocities at flame edge as a function of ϕ for upm = 35 m/s

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Fig. 25

Mean flame position (dashed line) and flame normal (arrows) overlaid on top of u¯z contours (solid lines) and u¯r=0 contours (dashed) with regions of u¯r>0 and u¯r≤0 shown in white and gray, respectively (ϕ = 0.8, upm = 35 m/s)

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Fig. 20

Cumulative distribution plot of flame stretch measurements, κsCH, for ϕ = 0.8 and upm = 35 m/s at an 1 mm axial bin centered at Z = 6 mm, with the mean value shown as the vertical line. Gaussian probability function with same standard deviation as sample standard deviation is indicated for reference by the dashed line.

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Fig. 21

Schematic of flame structure and reference locations of interest

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Fig. 22

Probability density function of flame leading edge angle with respect to the flow, θrel (ϕ = 1.0, upm = 35 m/s)

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