Hölzer, Jonas Immanuel
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Publication Access status: Open Access , ATHENA Research BookThe ATHENA European University is an alliance of nine Higher Education Institutions with the mission of fostering excellence in research and innovation by facilitating international cooperation. The ATHENA acronym stands for Advanced Technologies in Higher Education Alliance. The partner institutions are from France, Germany, Greece, Italy, Lithuania, Portugal, and Slovenia: the University of Orléans, the University of Siegen, the Hellenic Mediterranean University, the Niccolò Cusano University, the Vilnius Gediminas Technical University, the Polytechnic Institute of Porto, and the University of Maribor. In 2022 institutions from Poland and Spain joined the alliance: the Maria Curie-Skłodowska University and the University of Vigo. This research book presents a selection of the ATHENA university partners' research activities. It incorporates peer-reviewed original articles, reprints and student contributions. The ATHENA Research Book provides a platform that promotes joint and interdisciplinary research projects of both advanced and early-career researchers.Source Type:Book1 404 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Experimental Determination of the Temperature‐Dependent Broadening Effect of Water Vapour on the S‐Branch Raman Linewidths of Nitrogen(2024); ; ABSTRACT This work reports the S‐branch Raman linewidths of N 2 broadened by H 2 O vapour at temperatures 870–1900 K determined using the picosecond time‐resolved pure rotational coherent anti‐Stokes Raman scattering (RCARS) approach. The coherent dephasing time constant of nitrogen in a binary mixture was determined from the time trace fitting of the RCARS signal. Raman linewidths of N 2 for four different binary mixture compositions up to 20% H 2 O were obtained for each temperature and the N 2 ‐H 2 O broadening coefficient was determined. The decay of nitrogen broadened by water vapour is faster than that of self‐broadened nitrogen for all temperatures leading to a higher Raman linewidth. Respectively, the S‐branch Raman linewidths of N 2 ‐H 2 O deviate significantly in magnitude and slope from the Q‐branch Raman linewidth calculated by the modified energy gap (MEG) law. Therefore, taking into account the broadening effect of water molecules in nitrogen has the potential to significantly improve thermometry and species concentration determination. The determined S‐branch Raman linewidths and broadening coefficient will therefore find application in combustion and reactive flow diagnostics.Source Type:ArticleDOI:10.1002/JRS.67424 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Optimierung nicht-linearer laserbasierter Messmethoden zur Charakterisierung von reaktiven Strömungen(2024)In this work advancements of two four-wave mixing based laser measurement techniques, the rotational coherent anti-Stokes Raman spectroscopy (RCARS) and the laser-induced grating technique (LIG), for the diagnostic of reactive flows are presented. The developed approaches aim at optimizing the diagnostic techniques regarding applicability and accuracy as compared to the so far available methods. For the study of oxygen as a probe molecule in combustion processes using the RCARS-technique the temperature and collider dependent S-branch Raman linewidths are determined. These are required in contour-fitting algorithms for the determination of temperature, species concentration and pressure. So far, the use of the only available Q-branch linewidths and the neglection of the proper gas phase collision partners result in deviations and inaccuracies of the obtained thermodynamic conditions. Therefore, the S-branch Raman linewidths of pure oxygen, oxygen in air and a defined mixture with CO2 are determined in a temperature range from 295K to 1900K applying the time resolved RCARS-technique. To this end the influence of the triplet electronic ground state of oxygen on the temporal evolution of the signal intensity need to be considered and a novel evaluation procedure needs to be developed. Furthermore, the S-branch linewidths of CO2 in the mixture with oxygen are to be determined to allow for accurate diagnostics of oxyfuel-combustion processes using RCARS-diagnostics in the future. In application of the LIGS-technique for the diagnostics of reactive flows and mixture formation processes, the evaluation is often based on the easily obtainable sound velocity. The sound velocity, however, exhibits multiparametric dependences on substance data and thermodynamic conditions, which are included in the same LIG signal profile, but are tedious to extract. Hence, in this work procedures are developed, which make use of additional signal contributions recorded within the same LIGS-measurement, to facilitate simultaneous determination of multiple thermodynamic parameters. These are on the one hand a direct two-color four-wave mixing (TCFWM) signal contribution in CO2 in mixture with nitrogen and on the other hand a thermal signal contribution which is generated by pump-laser absorption and subsequent heat release in ammonia-nitrogen gas mixtures. For both process a physical model is developed, which allows application of these methods for different gas mixtures by inserting the respective substance data into the model.Source Type:Doctoral ThesisSeries:Schriftenreihe der Lehrstühle für Strömungsmechanik und technische ThermodynamikVolume number:11245 153 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Two-color four-wave mixing contribution to an electrostrictive laser-induced grating signal in CO<sub>2</sub>–N<sub>2</sub> mixtures and gas diagnostics(2023); ; Multiparameter determination in the gas phase using the versatile laser-induced grating (LIG) technique is a challenging task due to interdependence of observables on multiple thermodynamic parameters. In CO 2 -N 2 mixtures, simultaneous determination of species concentration and gas temperature can be achieved by using an additional CO 2 concentration-dependent contribution to the LIG signal, which appears if 1064 nm pump pulses are employed. This contribution can be attributed to a direct, quasi-resonant two-color four-wave mixing (TCFWM) of the pump and probe radiations in CO 2 . A detailed study of the laser power and beam polarization, as well as mixture composition, pressure, and temperature dependencies of the TCFWM intensity relative to that of the LIG signal, allowed for the formulation of analytical relations enabling simultaneous mixture composition and temperature determination.Source Type:Article3
