| 1. |
- Berrocal, Edouard, et al.
(författare)
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Analysis of the SLIPI technique for multiple scattering suppression in planar imaging of fuel sprays
- 2009
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Ingår i: 11th Triennial International Annual Conference on Liquid Atomization and Spray Systems. - 9781617826535
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Konferensbidrag (refereegranskat)abstract
- Structured Laser Illumination Planar Imaging (SLIPI) is a new laser sheet based diagnostic able to significantly increase the contrast of spray images by removing the multiple scattering noise contribution. The technique has been recently developed and applied to the study of a conventional hollow-cone water spray, where the transmission through the near-field spray was 26%. In such condition, it has been shown that 44% of the total optical signal, corresponding to multiply scattered photons, could be removed. In order to now employ the technique to more challenging sprays, such as air-blast atomizer and Diesel sprays, where the transmission can be reduced down to ~0.25%, further investigations and refinements of the approach are required. This article focuses on the analysis, optimization and application of SLIPI for fuel sprays by means of a modern 3-dimensional computational model. The simulation is performed via a validated Monte Carlo code in association with a ray-tracing approach, to simulate the propagation of the incident laser radiation through the spray and the collection optics respectively. This computational work aims to quantify the amount of multiple light scattering detected by both the conventional Mie laser sheet imaging and the SLIPI technique. Results are compared for two hollow-cone fuel sprays of different transmission and droplet size properties. In the first spray the laser transmission, at λ = 532 nm, is 5% in the dense region and 27% in the dilute region, with a droplet size distribution ranging from 8 to 68 µm. The second spray is assumed to be more highly atomized, with a transmission of only 0.17% in the dense region and 7.5% in the dilute region, and with a droplets size distribution ranging from 4 to 34 µm. From these numerical calculations, it is observed that the resultant SLIPI signal tends to be closer from the pure single scattering signal when reducing the spatial period of the incident modulated light. We demonstrate here that the technique should be able to suppress an unwanted light contribution up to 91%, of the light intensity detected in the conventional planar imaging.
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| 2. |
- Berrocal, Edouard, et al.
(författare)
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Multiple Scattering Suppression In Planar Laser Imaging Of Dense Sprays By Means Of Structured Illumination
- 2010
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Ingår i: Atomization and Sprays. - 1044-5110 .- 1936-2684. ; 20:2, s. 133-139
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Tidskriftsartikel (refereegranskat)abstract
- A novel method to reduce the multiply scattered light contribution to images recorded with planar laser imaging is demonstrated. The technique, structured laser illumination planar imaging (SLIPI), is based on spatially modulated excitation light and is tested here within the dense region of a hollow-cone spray. The main idea is to use a laser sheet that is spatially modulated along the vertical direction. By both shifting the spatial phase of the modulation and using adequate image post processing of the successive recorded images, it is possible to remove a significant amount of the multiply scattered light detected. In this paper, SLIPI is applied for imaging within a typical hollow-cone water spray generated in ambient air at 50 bars injection pressure from a pressure-swirl nozzle. Because this type of spray has a known inner structure, the method can be evaluated, demonstrating that 47% of the detected light arising from multiple scattering can be suppressed, resulting in an increase from 61% to 89 % in image contrast. Such an improvement allows more accurate interpretation and analysis of the near-field region of atomizing sprays. The possibility of extracting instantaneous flow motion is also demonstrated for the case of a dilute nebulizer. All these results indicate promising applications of the technique in denser turbid media, such as air-blast atomizer or diesel sprays.
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| 3. |
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| 4. |
- Ehn, Andreas, et al.
(författare)
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Electrochemical Investigation of Model Solid Oxide Fuel Cells in H2/H2O and CO/CO2 atmospheres using Nickel Pattern Electrodes
- 2010
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 157:11, s. B1588-B1596
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Tidskriftsartikel (refereegranskat)abstract
- In this study, nickel pattern electrodes were electrochemically investigated in a three-electrode setup, operating both with H 2 / H 2 O and CO/ CO 2 atmospheres. Heating introduced structural differences in the nickel layer among the pattern electrodes, which appear to affect the electrode performance. Both dense and porous nickel pattern electrodes were formed by heating. Holes appeared in the nickel layer of the porous pattern electrodes, where the open cavity triple phase boundaries exhibited different limiting processes than open triple phase boundary electrodes of the dense electrode. As the temperature was raised in the experiment, the electrodes stabilized, with a degraded behavior that seemed to be strongly coupled to the structural changes in the electrode. It was possible to compare literature results with high temperature impedance measurements in H 2 / H 2 O presented here, while new results at lower temperatures in H 2 / H 2 O are also presented. Impedance spectroscopy measurements were performed, and the gas dependence of the polarization resistance was observed as the mixture ratios and temperatures were varied in both atmospheres. A positive relation between the polarization resistance and the partial pressure of CO was determined for the dense nickel pattern electrode, which agrees with previous results using nickel point electrodes. © 2010 The Electrochemical Society.
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| 5. |
- El Gabaly, Farid, et al.
(författare)
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Measuring individual overpotentials in an operating solid-oxide electrochemical cell
- 2010
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12:38, s. 12138-12145
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Tidskriftsartikel (refereegranskat)abstract
- We use photo-electrons as a non-contact probe to measure local electrical potentials in a solid-oxide electrochemical cell. We characterize the cell in operando at near-ambient pressure using spatially-resolved X-ray photoemission spectroscopy. The overpotentials at the interfaces between the Ni and Pt electrodes and the yttria-stabilized zirconia (YSZ) electrolyte are directly measured. The method is validated using electrochemical impedance spectroscopy. Using the overpotentials, which characterize the cell’s inefficiencies, we compare without ambiguity the electro-catalytic efficiencies of Ni and Pt, finding that on Ni H2O splitting proceeds more rapidlythan H2 oxidation, while on Pt, H2 oxidation proceeds more rapidly than H2O splitting.
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| 6. |
- Falgout, Zachary, 1990, et al.
(författare)
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Cavitation Inside High-Pressure Optically Transparent Fuel Injector Nozzles
- 2015
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 656:1
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Konferensbidrag (refereegranskat)abstract
- Nozzle-orifice flow and cavitation have an important effect on primary breakup of sprays. For this reason, a number of studies in recent years have used injectors with optically transparent nozzles so that orifice flow cavitation can be examined directly. Many of these studies use injection pressures scaled down from realistic injection pressures used in modern fuel injectors, and so the geometry must be scaled up so that the Reynolds number can be matched with the industrial applications of interest. A relatively small number of studies have shown results at or near the injection pressures used in real systems. Unfortunately, neither the specifics of the design of the optical nozzle nor the design methodology used is explained in detail in these papers. Here, a methodology demonstrating how to prevent failure of a finished design made from commonly used optically transparent materials will be explained in detail, and a description of a new design for transparent nozzles which minimizes size and cost will be shown. The design methodology combines Finite Element Analysis with relevant materials science to evaluate the potential for failure of the finished assembly. Finally, test results imaging a cavitating flow at elevated pressures are presented.
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| 7. |
- Falgout, Zachary, 1990, et al.
(författare)
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Evidence for supercritical mixing layers in the ECN Spray A
- 2015
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35:2, s. 1579-1586
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Tidskriftsartikel (refereegranskat)abstract
- Prior work on an engine combustion network Diesel fuel injector led to the conclusion that under Diesel engine conditions (combustion chamber pressure and temperature) the jet was transitionally supercritical; meaning that the core of the jet would be condensed liquid while the edge of the jet would be supercritical. We report initial experiments aimed at observing the thickened turbulent mixing layer that would result if the jet were transitionally supercritical. We have applied ballistic imaging to the same Diesel fuel injector, under similar conditions, and we find that the images do indicate a structural change when going from subcritical to supercritical conditions. Under subcritical conditions we observe a well-defined liquid/gas interface, surface wave structure, and formation of ligaments and voids. Under supercritical conditions the interface transitions into a continuous, turbulent mixing layer. Images of this layer include the cellular structure characteristic of gas jets. These changes are consistent with experimental literature on cryogenic supercritical jets and with DNS modeling of supercritical mixing layers.
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| 8. |
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| 9. |
- Falgout, Zachary, 1990, et al.
(författare)
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Gas/Fuel Jet Interfaces Under High Pressures and Temperatures
- 2016
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 168, s. 14-21
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Tidskriftsartikel (refereegranskat)abstract
- We report observations regarding changes in surface morphology for transient fuel jets as the ambient conditionsapproach the critical properties of pure fuels. Both ballistic imaging and ultrafast shadow imaging were applied tofour fuels as they were injected through a single hole Diesel injector into a spray research chamber operated at threedifferent ambient conditions that span the range of critical properties for the pure fuels that were studied. The resultsindicate that the pure fuels (butanol, dodecane, and hexadecane) tend to undergo a change in image structure thatusually scales with estimated mixture critical properties. Commercially available Diesel fuel is not strongly affected,even at the highest pressure and temperature conditions.
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| 10. |
- Falgout, Zachary, 1990, et al.
(författare)
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Novel design for transparent high-pressure fuel injector nozzles
- 2016
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 87:8, s. 085108-
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency and emissions of internal combustion (IC) engines are closely tied to the formation of the combustible air-fuel mixture. Direct-injection engines have become more common due to their increased practical flexibility and efficiency, and sprays dominate mixture formation in these engines. Spray formation, or rather the transition from a cylindrical liquid jet to a field of isolated droplets, is not completely understood. However, it is known that nozzle orifice flow and cavitation have an important effect on the formation of fuel injector sprays, even if the exact details of this effect remain unknown. A number of studies in recent years have used injectors with optically transparent nozzles (OTN) to allow observation of the nozzle orifice flow. Our goal in this work is to design various OTN concepts that mimic the flow inside commercial injector nozzles, at realistic fuel pressures, and yet still allow access to the very near nozzle region of the spray so that interior flow structure can be correlated with primary breakup dynamics. This goal has not been achieved until now because interior structures can be very complex, and the most appropriate optical materials are brittle and easily fractured by realistic fuel pressures. An OTN design that achieves realistic injection pressures and grants visual access to the interior flow and spray formation will be explained in detail. The design uses an acrylic nozzle, which is ideal for imaging the interior flow. This nozzle is supported from the outside with sapphire clamps, which reduces tensile stresses in the nozzle and increases the nozzle's injection pressure capacity. An ensemble of nozzles were mechanically tested to prove this design concept.
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