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Atomization and Sprays
Facteur d'impact: 1.262 Facteur d'impact sur 5 ans: 1.518 SJR: 0.814 SNIP: 1.18 CiteScore™: 1.6

ISSN Imprimer: 1044-5110
ISSN En ligne: 1936-2684

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Atomization and Sprays

DOI: 10.1615/AtomizSpr.2018024340
pages 565-578

ULTRASHORT PULSE OFF-AXIS DIGITAL HOLOGRAPHY FOR IMAGING THE CORE STRUCTURE OF TRANSIENT SPRAYS

Marco Minniti
Department of Mechanical and Aerospace Engineering, University of California, Irvine, Irvine, California 92697, USA
A. Ziaee
Department of Mechanical and Aerospace Engineering, University of California, Irvine, Irvine, California 92697, USA
J. Trolinger
Metrolaser Inc., Laguna Hills, California 92653, USA
Derek Dunn-Rankin
Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA 92697, USA

RÉSUMÉ

A single-shot Ultra-short Pulse Off-axis Digital Holography (UPODH) system successfully images microscopic details of fuel injection phenomena that are hidden from view by a dense cloud of droplets surrounding the near-nozzle region. The experiment approximates the optically dense conditions typical of fuel injection in modern diesel engines. Under these conditions an outer layer of small droplets can hide a core of larger droplets or liquid ligaments; this core is inaccessible to most imaging techniques due to multiple-scattering in the outer layer. These conditions are mimicked by intentionally surrounding a core spray with a fine mist. The mist has a Sauter mean diameter of 4.28 microns. The core spray comes from driving water, with pressure ranging from 1 to 13.8 Bar, through single orifices of 0.1 and 0.3 mm diameter. The whole spray field shows nearly opaque transmissivities as low as 6×10-6. Transient phenomena, such as sheets of liquid becoming ligaments and their further break up into small particles are easily visible even when surrounded by the opaque mist with an optical density (OD) of 12. Holographic reconstruction allows these phenomena to be clearly observable in 3-D, and single droplets as small as 25 μm are resolved. The 3-D capability allows UPODH to bring into focus small particles and ligaments at different depth planes, even centimeters apart.


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