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      Effects of liquid properties on atomization and spray characteristics studied by planar two-photon fluorescence

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          Abstract

          In this work, planar two-photon laser-induced fluorescence (2p-LIF) is applied for the first time to analyze the fluid dependent spray structure and atomization behavior of water and ethanol in a quantitative way. A commercial six-hole DISI (Direct-Injection Spark-Ignition) injector was studied at different injection pressures, operated with liquids containing the LIF dye fluorescein. Specifically for DISI-injectors, the fluid-dependent atomization is very complex and not fully understood due to the cavitating, turbulent nozzle flow that dominates the spray formation. Optical access and analysis of the near-nozzle spray are often challenging due to multiple light scattering in dense regions which is reduced by 2p-LIF measurements using a femtosecond laser. This allows high-contrast spray imaging close to the nozzle, resulting in an improved identification of single liquid structures of the spray. Thus, a higher accuracy of sizing is possible. Compared to water, the ethanol spray shape shows increased cone angles in the nozzle near-field of about 6%, which cannot be explained by classical atomization theory based on aerodynamic breakup. The larger cone angle of ethanol was attributed to its larger viscosity, which could decelerate the flow at the wall of the injection hole, affecting the velocity profile of the emerging jet. The atomization shows a main jet breakup distance of 7–10 mm in which the structure sizes decreased drastically, specifically for water. For the size of the liquid structures in the near-nozzle region, which show dimensions of about 80–130 μm, ethanol exhibited about 2% smaller Feret's diameters than water for the tested time steps at 20 MPa. This effect is even more distinct for other injection pressures and positions at a further distance to the injector. For all investigated conditions and measurement positions downstream of the nozzle, ethanol showed on average about 24% smaller structures compared to the water spray. Although this trend is in accordance with the classical atomization theory based on the aerodynamic breakup mechanism, other effects, such as cavitation and nozzle-flow induced breakup, contribute to this behavior.

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          Most cited references53

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          Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy.

          Intrinsic, three-dimensionally resolved, microscopic imaging of dynamical structures and biochemical processes in living preparations has been realized by nonlinear laser scanning fluorescence microscopy. The search for useful two-photon and three-photon excitation spectra, motivated by the emergence of nonlinear microscopy as a powerful biophysical instrument, has now discovered a virtual artist's palette of chemical indicators, fluorescent markers, and native biological fluorophores, including NADH, flavins, and green fluorescent proteins, that are applicable to living biological preparations. More than 25 two-photon excitation spectra of ultraviolet and visible absorbing molecules reveal useful cross sections, some conveniently blue-shifted, for near-infrared absorption. Measurements of three-photon fluorophore excitation spectra now define alternative windows at relatively benign wavelengths to excite deeper ultraviolet fluorophores. The inherent optical sectioning capability of nonlinear excitation provides three-dimensional resolution for imaging and avoids out-of-focus background and photodamage. Here, the measured nonlinear excitation spectra and their photophysical characteristics that empower nonlinear laser microscopy for biological imaging are described.
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            Mechanism of atomization of a liquid jet

            R. Reitz (1982)
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              High order conservative finite difference scheme for variable density low Mach number turbulent flows

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                Author and article information

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                Journal
                Physics of Fluids
                Physics of Fluids
                AIP Publishing
                1070-6631
                1089-7666
                August 2022
                August 2022
                : 34
                : 8
                : 083305
                Affiliations
                [1 ]Institut für Thermodynamik, Professur für Energiewandlug, Fakultät für Luft- und Raumfahrttechnik, Universität der Bundeswehr München (UniBw M), Neubiberg, Germany
                [2 ]Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
                [3 ]Professur für Fluidsystemtechnik (FST), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
                [4 ]Division of Atomic Physics, Lund University, Lund, Sweden
                [5 ]Division of Combustion Physics, Lund University, Lund, Sweden
                Article
                10.1063/5.0098922
                c397e555-7e0a-44f6-951b-d63724fb6168
                © 2022
                History

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