TY  - GEN
Y1  - 2006///
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/7034/
KW  - laserinduzierte InkandeszenzLaser-induced incandescence
AV  - public
ID  - heidok7034
N2  - This work focuses on laser-induced incandescence (LII) at elevated pressure. LII is a laser-based technique for measuring particle sizes and volume fractions of nano-sized particles in aerosols. These particles, as emitted by traffic in the form of soot, cause a significant health risk, as nano-sized particles can penetrate deeply into the lungs and are considered important for causing asthma, fibrosis and the development of tumors [1,2]. Over the past 20 years, LII has been developed and applied mainly for  soot diagnostics in flames. However, only little work has been performed before on LII in sooting flames at elevated pressure. Nonetheless, this is important for applications in technical high-pressure environments, namely Diesel engines. Construction of a sooting high-pressure burner. In order to investigate the ability of LII as a tool for soot diagnostics at elevated pressure, a sooting high-pressure burner was constructed in coopera-tion with the research group of Prof. Dr. Dr. h.c. H. Gg. Wagner and Dr. H. Jander of the Universität Göttingen. Several improvements compared to previous burners were made. The burner produced long-term stable, laminar ethylene/air flames up to 10 bar with pressure fluctuations less than ± 2%. In LII diagnostics, this burner is unique in its performance world wide. Modeling laser-induced incandescence. The LII signal results from the heat-up of particles by a nanosecond laser pulse and subsequent cooling due to near-blackbody radiation and different compet-ing heat-loss paths. This process was modeled by setting up an energy and mass balance for the differ-ent heat- and mass-loss mechanisms. Recent advancements on the different sub-models were com-bined in a numerical model. This model, called LIISim, enables the modeling of LII signals as well as the fitting of experimental LII decay curves with a Levenberg-Marquardt non-linear least-squares fit-ting algorithm. Additionally, a perl script was written which allows the access to the LII model using a web browser. For the first time, an LII model was made available to the scientific community by a web interface. This will simplify the comparison of different LII models and reveal deficiencies in the underlying sub-models. LIISim is available at http://www.liisim.com. Particle sizing with LII at variable pressure. The log-normal size distribution of soot particles was measured in the new high-pressure burner at pressures of 1 ? 10 bar using LII. The flame temperature as well as the peak particle temperature are required as input parameters for the data evaluation with LIISim. These parameters were determined by two-color pyrometry of non-laser-heated soot (flame temperature) and by two-color LII (peak particle temperature). Low laser fluences of 70 ? 115 mJ/cm2 at 1064 nm were used to avoid evaporation. C2 fluorescence within the 550 nm detection channel might interfere with the LII signal. However, spectrally-resolved detection showed no narrow-band interferences in the region of 656 ? 400 nm for the low laser fluences used in this study at all investi-gated pressures. Additional to the LII measurements, soot samples were taken from the flame and the particle-size distribution was determined from transmission-electron microscopy (TEM) images of these samples. For the first time, soot particle-size distributions obtained with LII could be compared with a second, independent method at elevated pressures. Moreover, a first comparison of different heat-conduction models used for the evaluation of experimental LII signals could be performed. The results show excellent agreement between the mean diameter of the particle-size distribution obtained by TEM analysis and LII for all pressures, if the LII data are evaluated with the model of Fuchs taking into account the reduced heat conduction of aggregated particles. This work significantly advanced the understanding of LII at high pressures which further improves the applicability of this diagnostics technique to in-situ particle-size measurements in practical high-pressure combustors like Diesel engines.
TI  - Laser-induced incandescence for soot diagnostics at high pressure
A1  - Hofmann, Arnulf Maximilian
ER  -