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TECHNICAL PAPERS

Combustion Control by Vortex Breakdown Stabilization

[+] Author and Article Information
Christian Oliver Paschereit

Hermann-Fottinger-Institute of Fluid Dynamics, Technical University Berlin, 10623 Berlin, Germany

Peter Flohr

 ALSTOM (Switzerland) Ltd., CH-5405 Baden, Switzerland

Ephraim J. Gutmark

Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati, Cincinnati, OH 45221

J. Turbomach 128(4), 679-688 (Feb 01, 2002) (10 pages) doi:10.1115/1.2218521 History: Received October 01, 2001; Revised February 01, 2002

Flame anchoring in a swirl-stabilized combustor occurs in an aerodynamically generated recirculation region which is a result of vortex breakdown (VBD). The characteristics of the recirculating flow are dependent on the swirl number and on axial pressure gradients. Coupling with downstream pressure pulsations in the combustor affects the VBD process. The present paper describes combustion instability that is associated with vortex breakdown. The mechanism of the onset of this instability is discussed. Passive control of the instability was achieved by stabilizing the location of vortex breakdown using an extended lance. The reduction of pressure pulsations for different operating conditions and the effect on emissions in a laboratory scale model atmospheric combustor, in a high pressure combustor facility, and in a full scale land-based gas-turbine are described. The flashback safety, one of the most important features of a reliable gas turbine burner, was assessed by CFD, water tests, and combustion tests. In addition to the passive stabilization by the extended lance it enabled injection of secondary fuel directly into the recirculation zone where the flame is stabilized. Tests were conducted with and without secondary fuel injection. Measurements and computations optimized the location of the extended lance in the mixing chamber. The effect of variation of the amount of secondary fuel injection at different equivalence ratios and output powers was determined. Flow visualizations showed that stabilization of the recirculation zone was achieved. Following the present research, the VBD stabilization method has been successfully implemented in engines with sufficient stability margins and good operational flexibility. This paper shows the development process from lab scale tests to full scale engine tests until the implementation into field engines.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the atmospheric test facility

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Figure 2

Schematic of the high pressure test facility

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Figure 3

Flame motion in and out of the burner during a pilot instability cycle. Phase averaged pictures taken through a glass window in the burner are shown at intervals of 30deg.

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Figure 4

CFD simulation of the pilot instability

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Figure 5

Burner with extended lance

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Figure 6

Suppression of pressure pulsations for different lance lengths

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Figure 7

NOx emissions for different lance lengths

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Figure 8

Atmospheric startup test. Power variation.

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Figure 9

Atmospheric start-up tests. Flame temperature variation.

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Figure 10

Schematic of the configuration used for annular breakdown analysis

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Figure 11

Critical swirl for a single vortex (w1=u1). Present design shown to be in stable region.

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Figure 12

Normalized velocities near the lance tip measured in the water tunnel

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Figure 13

Critical swirl for two superimposed potential vortices with the geometric parameters (r1∕rL=2, rT∕rL=3.4)

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Figure 14

CFD calculations of the axial flow field around the extended lance compared with water tunnel measurements

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Figure 15

CFD calculations of the flow field downstream of the lance compared with water tunnel measurements

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Figure 16

Video image of combustion in the high pressure rig, indicating that the flame is stabilized downstream of the extended lance

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Figure 17

Atmospheric hydrogen flashback tests

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Figure 18

Forced atmospheric hydrogen flashback test

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Figure 19

Baseline start-up test in the test engine with the original burner configuration

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Figure 20

Reduced pulsations in a start-up test in the test engine using the long lance

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