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

Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

[+] Author and Article Information
Andrew P. Shroll, Santosh J. Shanbhogue

Department of Mechanical Engineering Massachusetts Institute of Technology 77-Massachusetts Avenue, 3-342 Cambridge, MA 02139

Ahmed F. Ghoniem1

Department of Mechanical Engineering Massachusetts Institute of Technology 77-Massachusetts Avenue, 3-342 Cambridge, MA 02139

1

Corresponding author.

J. Eng. Gas Turbines Power 134(5), 051504 (Mar 01, 2012) (10 pages) doi:10.1115/1.4004737 History: Received June 21, 2011; Revised June 29, 2011; Published March 01, 2012; Online March 01, 2012

This work explores the dynamic stability characteristics of premixed CH4 /O2 /CO2 mixtures in a 50 kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different dilution levels of carbon dioxide used to control the flame temperature (Tad ). For the highest Tad ’s, the combustor is unstable at the first harmonic of the combustor’s natural frequency. As the temperature is reduced, the combustor jumps to fundamental mode and then to a low-frequency mode whose value is well below the combustor’s natural frequency, 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.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Model of axisymmetric swirl combustor

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Figure 2

Adiabatic flame temperature as a function of equivalence ratio for air combustion and of CO2 reactant mole fraction or O2 mole fraction in O2 plus CO2 for oxy-combustion

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Figure 3

Comparison of consumption speed for air and oxy-combustion at 1800, 2000, and 2200 K. Instances where Sc drops to zero indicate extinction.

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Figure 4

(a) OASPL and (b) spectrum of oscillations as a function of adiabatic flame temperature for CH4 /O2 /CO2 mixtures at Re = 20,000

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Figure 5

Sequence of images in a cycle during the first-harmonic wave mode for CH4 /O2 /CO2 flames with XCO2 = 0.594 (Tad  = 2200 K) at Re = 20,000. Images are 2 ms apart.

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Figure 6

Sequence of images in a cycle during the fundamental mode for CH4 /O2 /CO2 flames with XCO2 = 0.659 (Tad  = 2000 K) at Re = 20,000. Images are 2 ms apart.

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Figure 7

Sequence of images in a cycle during the low-frequency mode for CH4 /O2 /CO2 flames with XCO2 = 0.686 (Tad  = 1900 K) at Re = 20,000. Images are 4 ms apart.

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Figure 8

(a) OASPL and (b) spectrum of oscillations as a function of adiabatic flame temperature for CH4 /air mixtures at Re = 20,000

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Figure 9

Sequence of images (images are 2 ms apart) in a cycle during the fundamental mode for CH4 /air flames for XCO2= 0.798 (Tad  = 2000 K) and Re = 20,000. The conditions were chosen to match those in Fig. 6.

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Figure 10

Sequence of images (images are 4 ms apart) in a cycle during the low-frequency mode for CH4 /air flames for XCO2= 0.734 (Tad  = 1900 K) and Re = 20,000. The conditions were chosen to match those in Fig. 7.

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Figure 11

OASPL as a function of adiabatic flame temperature for (a) Re = 15,000; (b) Re = 20,000; (c) Re = 25,000; (d) Re = 30,000

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Figure 12

Sound pressure level spectrum maps as a function of adiabatic flame temperature for stoichiometric oxy-combustion at different Reynolds numbers

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Figure 13

Sound pressure level spectrum maps as a function of adiabatic flame temperature for air combustion at different Reynolds numbers

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Figure 14

Acoustic model of the combustor

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Figure 15

Comparison between frequencies predicted by the acoustic model (continuous lines, — = CH4 /air, -.- = CH4 /O2 /CO2 ) and measurements (discrete points, = CH4 /air, • = CH4 /O2 /CO2 )

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Figure 16

Demonstration of hysteresis by comparing experiments where the mixture adiabatic flame temperature is increased to previously shown tests for decreasing temperature at Re = 20,000

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Figure 17

Mode history dependence for air combustion at Re = 20,000. For the decreasing sweep, the test was conducted by igniting the flame at Tad  = 2030 K and then decreasing gradually.

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