Lehnert B (2025)
Publication Language: German
Publication Type: Thesis
Publication year: 2025
Edited Volumes: Technische Fakultät
Spray processes are used in a wide variety of applications. However, the behavior
of spray processes is difficult to predict due to short time scales, phase changes,
and turbulent flows. The aim of this work is to further develop and validate Diffuse
Backlight Illumination Extinction Imaging (DBIEI) as a quantitative line-of-sight
measurement technique for the spatially three-dimensional and temporally resolved
detection of the liquid volume fraction.
Sprays from different injectors for gasoline direct injection are investigated in constant
flow chambers. Ambient pressure, ambient temperature, fuel pressure, and
fuel temperature can be precisely and repeatably adjusted and controlled in these
chambers. The flow chamber permits an experiment to be performed at a frequency
of one Hertz, and the motorized injector rotation allows measurements to be taken
from different directions. In addition, the control of the test parameters and the experiments
from different angles are automated. The Spray G and Spray M research
injectors of the Engine Combustion Network and commercially available gasoline
injectors with different nozzle geometries are used for the investigation.
To minimize schlieren refraction and the resulting loss of quantifiability, a diffuse
light source is used. The ability to suppress these refractions is mathematically
calculated and experimentally tested using the schlieren technique at up to 74 bar
ambient pressure and up to 700°C ambient temperature. In line-of-sight techniques
using visible light, the optical thicknesses recorded in dense sprays are often strongly
affected by single and multiple scattering. The use of a diffuse light source increases
this effect. To evaluate the influence of single and multiple scattering, a Monte Carlo
simulation of photons in turbid media is performed. This simulation corrects the
optical thickness of the experimental investigations and can account for the error
due to scattering effects. The corrected results of the light transmission measurements
are converted to a projected liquid volume fraction using Lambert-Beer’s law.
By measuring from different directions, the projections are then resolved in three
dimensions using tomographic reconstruction. The tomographic reconstruction mevi
thod is validated using a synthetic spray model. The result is a spatial representation
of the liquid volume fraction in the spray.
To validate the results, the DBIEI is compared with other measurement techniques.
Fourier-filtered Extinction Imaging is used to compare unscattered optical thicknesses
with corrected optical thicknesses. Single-plane velocity profiles measured by
Laser Doppler Anemometry are used to compare the spray target to planes of the
tomographic reconstruction. In addition, the quantitative results of a Laser Plasma
Accelerator are compared with the liquid volume fractions of the DBIEI.
After validation of the measurement method, examples of further applications are
shown. In addition to spray characterization on multi-hole injectors, the DBIEI is also
suitable for hollow cone nozzles. It can also be used to evaluate the spray pattern of
non-rotationally symmetric injectors and to detect damage or defects in production.
It is also shown that the method is stable against different environmental conditions
and can therefore be used flexibly. Finally, the time-resolved injected liquid mass is
calculated with the results of the DBIEI and compared with another injection rate
method to derive the evaporation rate over the injection duration.
APA:
Lehnert, B. (2025). Dreidimensionale Quantifizierung der Flüssigphase in transienten Sprayprozessen (Dissertation).
MLA:
Lehnert, Bastian. Dreidimensionale Quantifizierung der Flüssigphase in transienten Sprayprozessen. Dissertation, 2025.
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