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Droplet size, concentration, and temperature mapping in sprays using SLIPI-based techniques

Mishra, Yogeshwar Nath LU (2018)
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... (More)
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. (Less)
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author
opponent
  • Professor Hardalupas, Yannis, Imperial College London, United Kingdom
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Sprays, Optical measurements, Laser diagnostic, Droplet size, Temperature, Fysicumarkivet A:2018:Mishra
pages
207 pages
publisher
Division of Combustion Physics, Department of Physics, Lund University
defense location
Rydbergsalen, Fysicum, Professorsgatan 1, Lund University, Faculty of Engineering.
defense date
2018-02-16 10:15
ISBN
978-91-7753-467-9
978-91-7753-468-6
language
English
LU publication?
yes
id
2b05823e-ff48-42f7-8a4d-16db87dc0f02
date added to LUP
2018-01-22 11:33:54
date last changed
2018-05-29 12:22:33
@phdthesis{2b05823e-ff48-42f7-8a4d-16db87dc0f02,
  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. <br/><br/>The temporally averaged measurements are performed using three-phase SLIPI <br/>(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. <br/><br/>To circumvent this limitation, two novel instantaneous imaging approaches, 2p-<br/>SLIPI and 1p-SLIPI (corresponding to two-phase and one-phase, respectively), <br/>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. },
  author       = {Mishra, Yogeshwar Nath },
  isbn         = {978-91-7753-467-9},
  keyword      = {Sprays,Optical measurements,Laser diagnostic,Droplet size,Temperature,Fysicumarkivet A:2018:Mishra},
  language     = {eng},
  month        = {01},
  pages        = {207},
  publisher    = {Division of Combustion Physics, Department of Physics, Lund University},
  school       = {Lund University},
  title        = {Droplet size, concentration, and temperature mapping in sprays using SLIPI-based techniques},
  year         = {2018},
}