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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Measurements of Stretch Statistics at Flame Leading Points for High Hydrogen Content Fuels

[+] Author and Article Information
Andrew Marshall

School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: andrew.marshall@siemens.com

Julia Lundrigan

Delta Airlines,
Atlanta, GA 30320
e-mail: jslundrigan@gmail.com

Prabhakar Venkateswaran

Milwaukee School of Engineering,
Milwaukee, WI 53202
e-mail: prabhakar.venkateswaran@trincoll.edu

Jerry Seitzman

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

Tim Lieuwen

School of Aerospace Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: tim.lieuwen@aerospace.gatech.edu

1Present address: Siemens Energy, Inc., Charlotte, NC 28273.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 24, 2015; final manuscript received January 3, 2017; published online July 6, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(11), 111503 (Jul 06, 2017) (11 pages) Paper No: GTP-15-1502; doi: 10.1115/1.4035819 History: Received October 24, 2015; Revised January 03, 2017

Fuel composition has a strong influence on the turbulent flame speed, even at very high turbulence intensities. An important implication of this result is that the turbulent flame speed cannot be extrapolated from one fuel to the next using only the laminar flame speed and turbulence intensity as scaling variables. This paper presents curvature and tangential strain rate statistics of premixed turbulent flames for high hydrogen content (HHC) fuels. Global (unconditioned) stretch statistics are presented as well as measurements conditioned on the leading points of the flame front. These measurements are motivated by previous experimental and theoretical work that suggests the turbulent flame speed is controlled by the flame front characteristics at these points. The data were acquired with high-speed particle image velocimetry (PIV) in a low-swirl burner (LSB). We attained measurements for several H2:CO mixtures over a range of mean flow velocities and turbulence intensities. The results show that fuel composition has a systematic, yet weak effect on curvatures and tangential strain rates at the leading points. Instead, stretch statistics at the leading points are more strongly influenced by mean flow velocity and turbulence level. It has been argued that the increased turbulent flame speeds seen with increasing hydrogen content are the result of increasing flame stretch rates, and therefore, SL,max values, at the flame leading points. However, the differences observed with changing fuel compositions are not significant enough to support this hypothesis. Additional analysis is needed to understand the physical mechanisms through which the turbulent flame speed is altered by fuel composition effects.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

(a) Variations of the turbulent flame speed, ST,GC, with turbulence intensity, u′rms, normalized by SL,0 at various mean flow velocities for several H2:CO ratios and pure CH4. (b) Turbulent flame speed data, ST,GC, from (a) normalized by SL,max. Legend presented in Table 1. Data reproduced from Ref. [14].

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Fig. 2

Stretch sensitivity calculations of H2:CO fuel blends and CH4 [14], all with nominally the same SL,0 value

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Fig. 3

Detail view of the: (a) LSB nozzle and (b) swirler model. Dimensions in mm.

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Fig. 4

Mean velocity normalized by U0 for (a) nonreacting and (b) reacting (100% CH4, ϕ = 0.9) cases at STP. U0 = 20 m/s, S = 0.57, and BR = 69%.

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Fig. 5

Mean velocity normalized by U0 in the axial direction along the burner centerline for (a) nonreacting and (b) reacting (100% CH4, ϕ = 0.9) cases at STP. U0 = 20 m/s, S = 0.57, and BR = 69%.

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Fig. 6

RMS velocity normalized by U0 in the axial direction along the burner centerline for (a) nonreacting and (b) reacting (100% CH4, ϕ = 0.9) cases at STP. U0 = 20 m/s, S = 0.57, and BR = 69%.

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Fig. 7

Demonstration of the postprocessing procedure used to identify the flame edge from PIV images: (a) raw image, (b) median-filtered image, (c) thresholded image used to identify reactants and products and find the flame edge, and (d) flame edge, fitted spline curve, instantaneous leading point (x) and average progress variable, 〈c〉, overlaid onto raw image. Data presented are for a 50/50 H2:CO fuel mixture at STP for a swirl number of S = 0.58, mean flow velocity U0 = 30 m/s, and equivalence ratio ϕ = 0.55.

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Fig. 8

Average progress variable 〈c〉 along the axial centerline of the burner. The red line is an error function fit to the data. Conditions are the same as in Fig. 7 (see color figure online).

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Fig. 9

Probability density function (PDF) of locations of instantaneous leading points in 〈c〉-space for three different fuel compositions

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Fig. 10

Borghi–Peters diagram showing regime of experimental data

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Fig. 11

(a) Curvature and (b) tangential strain rate PDFs for varying fuel compositions at U0 = 50 m/s

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Fig. 12

(Top) curvature and (bottom) tangential strain rate PDFs for (a) 50:50 H2:CO and (b) 100% H2

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Fig. 13

Instantaneous leading point: (a) curvature and (b) tangential strain rate PDFs at U0 = 50 m/s

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Fig. 14

Instantaneous leading point (top) curvature and (bottom) tangential strain rate PDFs for (a) 50:50 H2:CO and (b) 100% H2

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Fig. 15

Flame brush leading point: (a) curvature and (b) tangential strain rate PDFs at U0 = 50 m/s

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