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

Characterization of Lean Burn Module Air Blast Pilot Injector With Laser Techniques

[+] Author and Article Information
U. Meier

e-mail: ulrich.meier@dlr.de

C. Hassa

DLR - German Aerospace Center,
Institute of Propulsion Technology,
Linder Hoehe,
Cologne D-51147, Germany

W. Lazik

Rolls-Royce Deutschland Ltd & Co
KG, Eschenweg 11, Dahlewitz,
Blankenfelde-Mahlow 15827, Germany

M. Whiteman

Rolls-Royce plc,
Derby DE24 8BJ, UK

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 16, 2013; final manuscript received July 24, 2013; published online September 23, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(12), 121508 (Sep 23, 2013) (7 pages) Paper No: GTP-13-1264; doi: 10.1115/1.4025148 History: Received July 16, 2013; Revised July 24, 2013

For lean burn combustor development in low emission aero-engines, the pilot stage of the fuel injector plays a key role with respect to stability, operability, NOx emissions, and smoke production. Therefore it is of considerable interest to characterize the pilot module in terms of pilot zone mixing, fuel placement, flow field, and interaction with the main stage. This contribution focuses on the investigation of soot formation during pilot-only operation. Optical test methods were applied in an optically accessible single sector rig at engine idle conditions. Using planar laser-induced incandescence (LII), the distribution of soot and its dependence on air/fuel ratio, as well as geometric injector parameters, was studied. The data shows that below a certain air/fuel ratio, an increase of soot production occurs. This is in agreement with smoke number measurements in a standard single sector flame tube rig without optical access. Reaction zones were identified using chemiluminescence of OH radicals. In addition, the injector flow field was investigated with PIV. A hypothesis regarding the mechanism of pilot smoke formation was made based on these findings. This along with further investigations will form the basis for developing strategies for smoke improvement at elevated pilot-only conditions.

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Figures

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Fig. 1

Rolls Royce LDI fuel injector with concentric arrangement; pilot injector at center. a: main fuel flow; b: pilot fuel flow; c: pilot air flow; d: main air flow. Left: schematics; right: operation in BOSS rig.

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Fig. 2

Schematics of test rig

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Fig. 3

Test section BOSS during operation and schematic

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Fig. 4

Abel-transformed OH chemiluminescence image for test point 4 in Fig. 5

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Fig. 5

Smoke number measured by OSM as function of module FAR for injector A. Solid symbols indicate test conditions shown in Fig. 6.

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Fig. 6

Soot volume fraction distributions for test points shown in Fig. 5

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Fig. 7

Isothermal (left) and reacting flow field (right) of injector A. Top: axial velocity, bottom: radial velocity. Discussion see text.

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Fig. 8

Reaction zones from OH chemiluminescence (gray scale) and velocity field for injector A

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Fig. 9

Flow fields at idle condition for injector A (right half) and B (left half)

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Fig. 10

Reaction regions from Abel-transformed OH chemiluminescence for injector A (right) and B (left)

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Fig. 11

Soot distribution for injector A (right) and B (left) at lean conditions (point 1 in Fig. 5). Contour lines show heat release regions.

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Fig. 12

Soot distribution for injector A (right) and B (left) at rich conditions (point 3 in Fig. 5). Contour lines show heat release regions.

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Fig. 13

Velocity field and soot distribution (gray scale) for injectors A and B at rich conditions (point 3 in Fig. 5). Thick black contour lines show heat release regions.

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