Multi-Dimensional Quantitative Laser-based Diagnostics - Development and Practial Applications
Author
Summary, in English
The aforementioned techniques are most often employed on a single shot basis, providing independent snapshots of two-dimensional (2D) data. In some examples, the measurement techniques are extended to the third spatial dimension, and in recent years, studies employing high repetition rate measurements capable of resolving the dynamics in time have become more frequent. In the thesis, a method for simultaneously extending the measurements to the third spatial dimension and to the time dimension, is presented. A high repetition rate laser and detection system is combined with oscillating mirrors, the laser sheet being scanned back and forth throughout the measurement volume. The deflections from two mirrors operated at different frequencies are combined to obtain equidistant laser sheets in the measurement region. The method is demonstrated on the Mie-scattering from a flow of droplets and is used to probe the planar laser induced fluorescence (PLIF) from the OH in a flame. Post processing methods to calculate concentrations and flame-fronts from large data sets are demonstrated.
Measurements of droplet concentration and size distribution in sprays, based on recording the light scattered from a laser sheet, suffer from uncertainties due to multiple scattering (MS) and attenuation of the illuminating and scattered light. A method is demonstrated here, that takes advantage of the ability to suppress the MS light by means of structured illumination. After MS suppression, the attenuation of the laser and signal light can be compensated for by comparing the transmission through the spray with the side-scattered signal. In the process, the local extinction coefficient is calculated from the Beer-Lambert law.
Laser based optical diagnostic techniques are in general developed for atmospheric flames under ideal laboratory conditions. In the application of the same techniques in more realistic situations, such as internal combustion (IC) engines, the harsh conditions involving vibrations, varying pressure, moving parts, limited optical access and a sooty environment have to be taken into account. Several of the measurement campaigns reported in the thesis were conducted in IC engines. Although the main goals of these campaigns were to answer combustion or engine related questions, time has also been invested in improving and adopting the measurement techniques to the existing conditions. By following the spray propagation in a light duty-diesel engine over time, knowledge was gained regarding how early spray injections should be conducted to avoid wall wetting. From high speed laser induce incandescence (LII) measurements in a heavy-duty Diesel engine, conclusions regarding soot formation and oxidation were drawn. The implementation of LII at high repetition rates in IC engines was investigated here. Challenges associated with attenuation of the laser and signal light were also addressed. Visualization of the flame jet propagation in a large-bore gas engine was made possible by means of fuel tracer LIF. Apart from the combustion related conclusions, it was shown that the image quality could be improved substantially by the use of correction optics.
Department/s
Publishing year
2014
Language
English
Publication/Series
Lund reports on combustion physics
Volume
177
Full text
Document type
Dissertation
Publisher
Division of Combustion Physics, Department of Physics, Lund University
Topic
- Atom and Molecular Physics and Optics
Keywords
- Post injection
- Structured illumination
- Mie scattering
- Dense sprays
- Extinction coefficient
- Signal attenuation
- Laser extinction
- Multiple scattering
- Scattering measurements
- Planar laser induced fluorescence
- Time resolved
- Imaging through turbulent media
- Three-dimensional image acquisition
- Diesel particulate filter regeneration
- Wall impingent
- Biodiesel
- LII
- Large-bore gas Engine
- Pre-chamber ignition
- Fysicumarkivet A:2014:Wellander
Status
Published
Supervisor
ISBN/ISSN/Other
- ISSN: 1102-8718
Defence date
9 January 2015
Defence time
09:15
Defence place
Lecture hall Rydbergsalen, Department of Physics, Professorsgatan 1, Lund University Faculty of Engineering
Opponent
- Volker Sick (Professor)