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

An Experimental Investigation of Kerosene Droplet Breakup by Laser-Induced Blast Waves

[+] Author and Article Information
Gregor C. Gebel

e-mail: gregor.gebel@dlr.de

Manfred Aigner

Institute of Combustion Technology,
German Aerospace Center (DLR),
70569 Stuttgart, Germany

Stéphane Le Brun

Institut Supérieur de l’Aéronautique
et de l’Espace (ISAE),
31055 Toulouse, France

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received September 24, 2012; final manuscript received October 1, 2012; published online January 10, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(2), 021505 (Jan 10, 2013) (10 pages) Paper No: GTP-12-1376; doi: 10.1115/1.4007776 History: Received September 24, 2012; Revised October 01, 2012

The work presented in this paper intends to deepen our understanding of the mechanisms involved in the spark ignition of liquid fuel sprays. An experimental study is presented regarding the ignition of monodisperse droplet chains of Jet A-1 aviation kerosene in a generic model combustor under well-defined boundary conditions. Breakdowns created by focused laser radiation were used as ignition sparks. They featured rapid spatial expansion, resulting in the formation of spherical blast waves in the surrounding air. The focus of this study lay on the effect of the blast waves on the fuel droplets. Blast wave trajectories were investigated by Schlieren imaging. Their interaction with kerosene droplets was observed with a high speed camera via a long distance microscope; the droplets were visualized by laser-induced Mie scattering. Droplets within a distance of 10 mm from the breakdown position were deformed and disintegrated by the aerodynamic forces of the postshock flow field. Different breakup modes were observed, depending on the distance from the breakdown position: Catastrophic breakup was observed at a 5 mm distance, resonant breakup was observed at a 10 mm distance. Breakup by blast waves from ignition sparks is expected to be a crucial mechanism for spray ignition because it supports evaporation. Weber number calculations revealed that the breakup modes observed under lab conditions will also appear in aviation gas turbines at high altitude relight conditions.

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Figures

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Fig. 1

Hypothesis about the mechanisms involved in flame kernel generation out of a laser-induced breakdown

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Fig. 2

Schematic of the model combustor. Scales are given in mm.

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Fig. 3

Setup of the Schlieren experiment

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Fig. 4

Setup of the Mie scattering experiment

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Fig. 5

Schlieren images of the laser-induced breakdown in static air. The center of reference is the focal point of the breakdown.

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Fig. 6

Blast wave trajectory from the Schlieren images and Brode’s numerical simulation

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Fig. 7

Mie scattering of Jet A-1 droplet breakup 5 mm below the breakdown focus

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Fig. 8

Mie scattering of Jet A-1 droplet breakup 10 mm below the breakdown focus

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Fig. 9

Calculated flow velocities and Weber numbers behind the shock front for a spherical blast wave of 93 mJ initial energy and Jet A-1 droplets of 130 μm in diameter

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