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Träfflista för sökning "WFRF:(Mishra Yogeshwar Nath) "

Sökning: WFRF:(Mishra Yogeshwar Nath)

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1.
  • Chorey, Devashish, et al. (författare)
  • Simultaneous imaging of CH*, C*2, and temperature in flames using a DSLR camera and structured illumination
  • 2023
  • Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 62:14, s. 3737-3746
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurement of chemical species and temperature mapping in flames is essential to understanding the combustion process. Multiple cameras are conventionally employed for measurement in such scenarios making the experi-mental setup not only cost-intensive but also challenging. To circumvent this, structured illumination (SI)-based methods are reported for multispecies chemiluminescence (CL) imaging using a single camera. In this paper, we demonstrate four-channel SI-based imaging for simultaneous snapshot CH* and C*2 CL imaging and two-color pyrometry for temperature profiles in a butane diffusion flame. We demonstrate our approach using individual species and multiple species imaging. Taking the advantage of the axisymmetric nature of the flame, the Abel trans-form is performed on the line-of-sight averaged images to obtain deconvoluted images. The deconvoluted maps of temperature are compared with the temperature data obtained by using a physical thermocouple probe. (c) 2023 Optica Publishing Group
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2.
  • Koegl, Matthias, et al. (författare)
  • 3D LIF/Mie planar droplet s izing in IC engine sprays using single-droplet calibration data
  • 2020
  • 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)
  • Analysis of ethanol and butanol direct-injection spark-ignition sprays using two-phase structured laser illumination planar imaging droplet sizing
  • 2018
  • Ingår i: International Journal of Spray and Combustion Dynamics. - : SAGE Publications. - 1756-8277 .- 1756-8285. ; 11
  • 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)
  • Analysis of LIF and Mie signals from single micrometric droplets for instantaneous droplet sizing in sprays
  • 2018
  • Ingår i: Optics Express. - 1094-4087. ; 26:24, s. 31750-31766
  • 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.
  • Kögl, Matthias, et al. (författare)
  • Single Shot SLIPI LIF/Mie Ratio for Droplet Sizing in DISI-Sprays
  • 2016
  • Ingår i: ILASS – Europe 2016, 27th Annual Conference on Liquid Atomization and Spray Systems, 4-7 September 2016.
  • Konferensbidrag (refereegranskat)abstract
    • This paper reports on the first realization of two-phase SLIPI (Structured Laser Illumination Planar Imaging) in combination with LIF/Mie ratio imaging for a single shot mapping of relative SMD (Sauter Mean Diameter) in a transient fuel spray. The technique is applied to a non-combusting multi-jet DISI (direct-injection spark-ignition) spray of ethanol fuel injected into an optically accessible constant volume chamber. The organic dye Eosin is added to the fuel as a laser-induced fluorescence (LIF) tracer when illuminated by the 532nm laser sheet. It is found that SLIPI produces more reliable relative SMD distributions in comparison to the conventional LIF/Mie-approach. Multiple scattered light is suppressed by the SLIPI technique and the background spray plumes and artifacts behind the illuminated plane are successfully suppressed. The single-shot SLIPI images give a clear insight into the highly turbulent liquid spray structure and provide reliable information on the spatial droplet distribution.
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6.
  • Mishra, Yogeshwar Nath, et al. (författare)
  • 3D droplet sizing and 2D optical depth measurements in sprays using SLIPI based techniques
  • 2016
  • Ingår i: 18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics. ; , s. 01-01
  • Konferensbidrag (refereegranskat)abstract
    • While imaging optically dense media such as atomizing sprays, the multiple light scattering induces image artifacts and blurring effects which limit visibility.Therefore, extracting quantitative spray information such as droplet size and concentration from qualitative images becomes very challenging. However, multiple scattering effects can be efficiently addressed by means of the SLIPI (Structured Laser Illumination Planar Imaging) technique. Recently, using SLIPI in combination with LIF/Mie droplet sizing (ratio of the liquid Laser Induced Fluorescence (LIF) and Mie scattering signals), a mapping of absolute Sauter Mean Diameter (SMD or D32) could be extracted. It was observed that without SLIPI, reliable measurements of SMD could not be achieved. In another work, a 3D map of the droplet extinction-coefficient (µe) in an aerated spray was extracted using the SLIPI-scan technique. In this article, SLIPI-LIF/Mie droplet sizing is performed in combination with SLIPI-scan in order to construct a 3D representation of droplet SMD in the developed spray region and the corresponding optical depth in 2D.
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7.
  • Mishra, Yogeshwar Nath, et al. (författare)
  • 3D mapping of droplet Sauter mean diameter in sprays
  • 2019
  • Ingår i: Applied Optics. - 2155-3165. ; 58:14, s. 3775-3783
  • 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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8.
  • Mishra, Yogeshwar Nath, et al. (författare)
  • Application of SLIPI-based techniques for droplet size, concentration, and liquid volume fraction mapping in sprays
  • 2020
  • Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 10:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Structured laser illumination planar imaging (SLIPI)-based techniques have been employed during the past decade for addressing multiple light scattering issues in spray imaging. In this article, SLIPI droplet sizing based on the intensity ratio of laser-induced fluorescence (LIF) over Mie scattering (SLIPI-LIF/Mie) and SLIPI-Scan for extinction-coefficient (μe) mapping are applied simultaneously. In addition, phase Doppler anemometry (PDA) and numerical calculations based on the Lorenz-Mie theory are also employed in order to extract the droplets Sauter mean diameter (SMD), the droplets number density (N), and the liquid volume fraction (LVF) in a steady asymmetric hollow cone water spray. The SLIPI-LIF/Mie ratio is converted to droplets SMD by means of a calibration procedure based on PDA measurements. The droplet SMD for the investigated spray varies from 20 μm to 60 μm, the N values range from 5 to 60 droplets per mm3, and the LVF varies between 0.05 x 10-4 and 5.5 x 10-4 within the probed region of the spray. To generate a series of two-dimensional images at different planes, the spray scanning procedure is operated in a "bread slicing" manner by moving the spray perpendicularly to the light sheet axis. From the resulting series of images, the procedure described here shows the possibility of obtaining three-dimensional reconstructions of each scalar quantity, allowing a more complete characterization of droplet clouds forming the spray region.
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9.
  • Mishra, Yogeshwar Nath (författare)
  • Droplet size, concentration, and temperature mapping in sprays using SLIPI-based techniques
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Structured laser illumination planar imaging (SLIPI) is a technique capable of suppressing multiple light scattering effects in optically dense sprays, resulting in spray images without blurs and with enhanced contrast. The novelty of the work presented in this thesis concerns the applications of a variety of SLIPI-based techniques for the measurement of droplet size, droplet concentration, and liquid temperature in atomizing sprays. Two types of spray systems are investigated here: 1) Steady hollow-cone water sprays using temporally averaged imaging. 2) Transient Direct-Injection spark ignition (DISI) biofuel sprays using instantaneous imaging. The temporally averaged measurements are performed using three-phase SLIPI (3p-SLIPI) with liquid injection pressures in the range of 20–50 bar and at ambient conditions. Droplet sizing is obtained by combining SLIPI with the laser-induced fluorescence (LIF)/Mie ratio approach, where the droplet Sauter mean diameter is deduced after calibration with phase Doppler anemometry measurements. The droplet concentration and liquid volume fraction are obtained by combining the SLIPI-LIF/Mie method with light transmission measurements. This is performed using a laser sheet scanning approach, which provides three-dimensional quantitative reconstructions. Finally, the spray temperature is obtained by combining SLIPI with two-color LIF ratio thermometry for a liquid temperature ranging from 25–55°C. It is found that multiple light scattering induces measurement errors even for sprays having singly scattered photons in majority. This finding, therefore, strongly supports the application of SLIPI for quantitative spray measurements, even for optically dilute sprays. The 3p-SLIPI approach is based on recording a minimum of three modulated sub-images successively, each having a different spatial phase; therefore, it has been primarily used for temporally averaged imaging. To circumvent this limitation, two novel instantaneous imaging approaches, 2p-SLIPI and 1p-SLIPI (corresponding to two-phase and one-phase, respectively), have been developed. In the 2p-SLIPI optical setup, the “lines structure” is optically shifted by exploiting the birefringence property of a calcite crystal. This novel optical approach is used to image spray dynamics in ethanol and butanol DISI sprays at liquid fuel injection pressures of 80 and 160 bar, where the spray chamber is operated at 2-bar air pressure. Finally, the results from instantaneous 2p-SLIPI and 1p-SLIPI imaging have been compared, showing promising applications for the study of spray dynamics.
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10.
  • Storch, Michael, et al. (författare)
  • Two-phase SLIPI for instantaneous LIF and Mie imaging of transient fuel sprays
  • 2016
  • Ingår i: Optics Letters. - 1539-4794. ; 41:23, s. 5422-5425
  • 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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