| 1. |
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| 2. |
- Koegl, Matthias, et al.
(författare)
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3D LIF/Mie planar droplet s izing in IC engine sprays using single-droplet calibration data
- 2020
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Konferensbidrag (refereegranskat)abstract
- This paper reports on the quantitative 2D and 3D droplet sizing based on the LIF/Mie ratio in ethanol DISI (Direct Injection Spark Ignition) sprays, where the required calibration is performed using quantitative micro and macro LIF/Mie ratio imaging of individual microdroplets. The droplets are generated from a monodisperse droplet generator in a diameter range from 16 µm to 60 µm. First, the liquid LIF (laser-induced fluorescence) and Mie scattered light (Mie) intensity from the dye-doped ethanol droplet illuminated by the 532 nm laser sheet are simultaneously recorded using a microscopic and a macroscopic imaging objective. The light intensity of the LIF and Mie optical signals are evaluated as a function of droplet diameters (d). The LIF and Mie intensity is found in a good agreement with volumetric (d3) and surface (d2) dependencies, respectively. Both micro and macro LIF/Mie intensity ratio show a linear dependence on d. The deduced calibration curve showing a correlation between LIF/Mie intensity ratio and droplet diameter is then used for the calibration of LIF/Mie ratio for 3D droplet size (Sauter Mean Diameter: SMD) in sprays. For 3D sizing, two-phase SLIPI-(Structured Laser Illumination Planar Imaging) based droplet sizing is applied in combination with laser sheet scanning for probing the spray in several two-dimensional (2D) slices. These 2D layers are combined together to reconstruct a quantitative 3D map of droplet SMD. Droplet SMD in the spray is found in the range between 10 µm and 50 µm.
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| 3. |
- Koegl, Matthias, et al.
(författare)
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Analysis of ethanol and butanol direct-injection spark-ignition sprays using two-phase structured laser illumination planar imaging droplet sizing
- 2018
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Ingår i: International Journal of Spray and Combustion Dynamics. - : SAGE Publications. - 1756-8277 .- 1756-8285. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on the spray structure of the biofuels, ethanol, and butanol generated by a multihole direct-injection spark-ignition injector, which is studied in a constant volume chamber. The spray shape and structure are analyzed using two-phase structured laser illumination planar imaging where both laser-induced fluorescence and Mie-scattering light are recorded simultaneously for the extraction of instantaneous laser-induced fluorescence/Mie-scattering ratio images. Quantitative planar measurements of the droplet Sauter mean diameter are conducted, using calibration data from phase-Doppler anemometry. The resulting Sauter mean diameters are presented for ethanol and butanol at various fuel temperatures at different times after the start of injection. It is found that an increase in fuel temperature results in a faster atomization and higher evaporation rate, which leads to reduced spray tip penetration and smaller droplet Sauter mean diameter. At equivalent conditions, butanol consistently showed larger spray tip penetration in comparison to ethanol. This behavior is due to the higher surface tension and viscosity of butanol resulting in the formation of larger droplets and larger Sauter mean diameters in the whole spray region. Finally, the butanol injection also shows larger cyclic variations in the spray shape from injection to injection which is explained by the internal nozzle flow that is influenced by larger fuel viscosity as well. The Sauter mean diameter distribution is also compared to phase-Doppler anemometry data showing good agreement and an uncertainty analysis of the structured laser illumination planar imaging-laser-induced fluorescence/Mie-scattering technique for planar droplet sizing in direct-injection spark-ignition sprays is presented.
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| 4. |
- Koegl, Matthias, et al.
(författare)
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Analysis of LIF and Mie signals from single micrometric droplets for instantaneous droplet sizing in sprays
- 2018
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Ingår i: Optics Express. - 1094-4087. ; 26:24, s. 31750-31766
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Tidskriftsartikel (refereegranskat)abstract
- Planar droplet sizing (PDS) is a technique relying on the assumption that laser-induced fluorescence (LIF) and Mie scattering optical signals from spherical droplets depend on their volume and surface area, respectively. In this article, we verify the validity of this assumption by experimentally analyzing the light intensity of the LIF and Mie optical signals from micrometric droplets as a function of their diameter. The size of the droplets is controlled using a new flow-focusing monodisperse droplet generator capable of producing droplets of the desired size in the range of 21 µm to 60 µm. Ethanol droplets doped with eosin dye and excited at 532 nm are considered in this study, and the individual droplets were imaged simultaneously at microscopic and macroscopic scale. The effects of laser power, dye concentration, and temperature variation are systematically studied as a function of LIF/Mie ratio in the whole range of droplet sizes. Finally, a calibration curve at tracer concentration of 0.5 vol% is deduced and used to extract the droplet Sauter mean diameter (SMD) from instantaneous images of a transient ethanol spray. This droplet size mapping is done using structured laser illumination planar imaging (SLIPI), in order to suppress the artifacts induced by multiple light scattering.
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| 5. |
- Koegl, Matthias, et al.
(författare)
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Analysis of the LIF/Mie ratio from individual droplets for planar droplet sizing : Application to gasoline fuels and their mixtures with ethanol
- 2019
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 9:22
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the possibility of using planar droplet sizing (PDS) based on laser-induced fluorescence (LIF) and Mie scattering was investigated within the framework of measuring the droplet Sauter mean diameter (SMD) of direct-injection spark-ignition (DISI) spray systems. For this purpose, LIF and Mie signals of monodisperse fuel droplets produced by a droplet generator were studied at engine relevant diameters (20-50 μm). The surrogate gasoline fuel Toliso (consisting of 65 vol. % isooctane, 35 vol. % toluene) and the biofuel blend E20 (consisting of 80 vol. % Toliso, 20 vol. % ethanol) were used and which were doped with the fluorescence dye "nile red". The effects of ethanol admixture, dye concentration, laser power, and temperature variation on the LIF/Mie ratio were studied simultaneously at both macroscopic and microscopic scale. The deduced calibration curves of the LIF and Mie signals of both fuels showed volumetric and surface dependent behaviors, respectively, in accordance with the assumptions in the literature. The existence of glare points and morphology-dependent resonances (MDRs) lead to slightly higher LIF and Mie exponents of E20 in comparison to Toliso. In principle, these calibration curves enable the determination of the SMD from LIF/Mie ratio images of transient fuel sprays.
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| 6. |
- Mishra, Yogeshwar Nath, et al.
(författare)
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3D mapping of droplet Sauter mean diameter in sprays
- 2019
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Ingår i: Applied Optics. - 2155-3165. ; 58:14, s. 3775-3783
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we report on the three-dimensional (3D) characterization of a spray in terms of its droplet Sautermean diameter (SMD) using the laser-induced fluorescence (LIF)/Mie ratio technique. The spray structure isanalyzed for a multi-hole direct-injection spark ignition (DISI) injector. A calibration curve to convert theLIF/Mie ratio to droplet diameter is deduced using LIF/Mie imaging and analysis of single droplets generatedby a droplet generator. The DISI spray investigated here is optically sectioned by means of two-phase structuredlaser illumination planar imaging to suppress the intensity of multiple light scattering from LIF and Mie imagesprior to their ratio. A series of calibrated LIF/Mie ratio images of spray is then recorded at several depths along thezdirection following the light sheet scanning of the spray. The droplet SMD ranges from less than 5μmuptoamaximum of 50μm in single-shot images. The averaged SMD results (1–30μm) obtained by using the calibrationcurve from the droplet generator are compared with measurement results from phase-Doppler anemometry.Finally, a 3D map is reconstructed from the successive 2D layers generated from spray scanning. The resulting3D representation of the droplet SMD shows a non-symmetric spray structure produced by the studied multi-hole injector, which cannot be resolved by analyzing only one central plane.
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| 7. |
- Storch, Michael, et al.
(författare)
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Two-phase SLIPI for instantaneous LIF and Mie imaging of transient fuel sprays
- 2016
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Ingår i: Optics Letters. - 1539-4794. ; 41:23, s. 5422-5425
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Tidskriftsartikel (refereegranskat)abstract
- We report in this Letter a two-phase structured laser illumination planar imaging [two-pulse SLIPI (2p-SLIPI)] optical setup where the "lines structure" is spatially shifted by exploiting the birefringence property of a calcite crystal. By using this optical component and two cross-polarized laser pulses, the shift of the modulated pattern is not "time-limited" anymore. Consequently, two sub-images with spatially mismatched phases can be recorded within a few hundred of nanoseconds only, freezing the motion of the illuminated transient flow. In comparison with previous setups for instantaneous imaging based on structured illumination, the current optical design presents the advantage of having a single optical path, greatly simplifying its complexity. Due to its virtue of suppressing the effects from multiple light scattering, the 2p-SLIPI technique is applied here in an optically dense multi-jet direct-injection spark-ignition (DISI) ethanol spray. The fast formation of polydispersed droplets and appearance of voids after fuel injection are investigated by simultaneous detection of Mie scattering and liquid laser-induced fluorescence. The results allow for significantly improved analysis of the spray structure.
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