@article{Dorscht2026,

title = {Optically accessible electrodynamic levitator for in-situ LIBS characterization of iron particles under reactive conditions},

author = {Maximilian Dorscht and Nils Oberndorfer and Benjamin Böhm and Andreas Weinmann and Andreas Dreizler and Dirk Geyer},

url = {https://opg.optica.org/oe/fulltext.cfm?uri=oe-34-6-9652},

doi = {https://doi.org/10.1364/OE.586612},

year  = {2026},

date = {2026-03-10},

urldate = {2026-03-10},

journal = {Optics Express},

volume = {34},

pages = {9652-9668},

abstract = {This study presents an optically accessible electrodynamic levitator that enables quantitative single-particle analysis using laser-based diagnostics. In the context of thermochemical energy storage, the oxidation behavior of individual iron (Fe) microparticles is investigated. Laser-induced breakdown spectroscopy (LIBS) is further developed to determine the particle-specific oxygen-to-iron (O/Fe) ratio in-situ, providing direct insight into the surface composition during oxidation. Diffuse backlight-illumination (DBI) is applied in parallel to visualize the laser pulse-particle interaction and plasma dynamics. The defined, contact-free particle positioning achieved by the electrodynamic levitator ensures reproducible laser coupling, stable plasma conditions, and improved quantitative accuracy compared to previous free particle jet analyses (Fe, Fe2O3). The electrodynamic levitator enables highly repeatable positioning of microparticles (Fe, Fe3O4, Fe2O3), regardless of their morphology and composition, which represents an important step in the diagnostic development for the analysis of reactive particles.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Koschnick2026,

title = {Gas-phase Raman spectroscopy for two-dimensional temperature and concentration profiling in the catalytic oxidative dehydrogenation of ethanol},

author = {Konrad Koschnick and Alison M. Ferris and Marcel Stark and Danny Stark and Jan Welzenbach and Nico Winkler and Andreas Weinmann and Christian Hess and Bastian J.M.Etzold and Alfons Drochner and Tanja Franken and Dirk Geyer and Andreas Dreizler},

url = {https://www.sciencedirect.com/science/article/pii/S0926860X25006696?via%3Dihub},

doi = {10.1016/j.apcata.2025.120767},

year  = {2026},

date = {2026-02-25},

journal = {Applied Catalysis A: General},

volume = {712},

number = {120767},

abstract = {A novel optically accessible catalysis flow channel is introduced that enables quantitative, contiguous, two-dimensional in situ measurements of gas-phase temperature and species concentrations during heterogeneous catalytic reactions. Spatially resolved gas-phase Raman spectroscopy, integral Fourier-transform infrared spectroscopy, and catalyst-resolved infrared thermography establish a well-defined platform for studying coupled reaction–transport phenomena. Applied to the oxidative dehydrogenation of ethanol over iron–molybdenum oxide catalysts, spontaneous Raman measurements yielded two-dimensional profiles of nine gas-phase species – with limits of detection in the tens-to-hundreds-of-ppm range – and gas-phase temperature within 500 µm of the catalyst surface. Transport analysis in the boundary layer yielded a Lewis number of approximately 1.65, indicating dominant thermal diffusion near the surface, while axial Péclet numbers revealed diffusion-controlled heat transport but advection-dominated product transport in a laminar regime. Varying the bulk flow velocity did not significantly alter conversion or product distributions, indicating kinetic and diffusive control under the present conditions. An iron-rich catalyst formulation exhibited higher activity than stoichiometric Fe2(MoO4)3 , whereas temperatures above 511 K reduced selectivity due to increased formation of total-oxidation products. Catalyst-free experiments, supported by kinetic simulations, confirmed partial gas-phase oxidation of acetaldehyde to CO, CO2, acetic acid, methanol, formaldehyde, and peracetic acid. These results highlight the importance of local gas-phase contributions and demonstrate that spatially resolving the gas-phase thermochemistry enables the gas phase to act as a reporter of surface reactions and facilitates the decoupling of chemical processes from transport phenomena.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dorscht2026c,

title = {Atomic composition analysis of iron-based particles via single-shot LIBS and spectral fitting under fluctuating plasma conditions},

author = {Maximilian Dorscht and Marcel Stark and Nils Oberndorfer and Benjamin Böhm and Andreas Weinmann and Andreas Dreizler and Dirk Geyer},

url = {https://iopscience.iop.org/article/10.1088/1361-6501/ae34d1},

doi = {10.1088/1361-6501/ae34d1},

year  = {2026},

date = {2026-01-19},

urldate = {2026-01-19},

journal = {Measurement Science and Technology},

volume = {37},

number = {4},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dorscht2026b,

title = {Single-shot in-situ LIBS-DBI diagnostics for atomic composition analysis of iron particle surfaces in energy storage processes},

author = {Maximilian Dorscht and Nils Oberndorfer and Benjamin Böhm and Andreas Dreizler and Dirk Geyer},

url = {https://www.sciencedirect.com/science/article/pii/S0016236125017181?via%3Dihub},

doi = {https://doi.org/10.1016/j.fuel.2025.135993},

year  = {2026},

date = {2026-01-01},

urldate = {2026-01-01},

journal = {Fuel},

volume = {403},

number = {135993},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Richter.2025c,

title = {A generalized quantification method for bi-directional laser-induced fluorescence},

author = {M. Richter and J. Lill and R. S. Barlow and J. R. Dawson and A. Dreizler and D. Geyer},

doi = {10.1007/s00340-025-08560-6},

year  = {2025},

date = {2025-11-15},

urldate = {2025-11-15},

journal = {Applied Physics B},

volume = {131},

issue = {226},

pages = {14},

abstract = {Quantitative measurements of minor species are essential for understanding flame propagation and emission formation, and for validation of chemical kinetic models. Laser-induced fluorescence-based methods are widely employed due to their ability to selectively excite specific species and achieve high signal-to-noise ratios. However, these techniques are inherently susceptible to collisional quenching, which complicates signal quantification. Bi-directional laser-induced fluorescence (BD-LIF) was proposed decades ago as a promising approach to obtain absolute species concentrations while preserving spatial resolution. Despite its potential, initial measurements showed deviations of 50 – 60 % compared to equilibrium calculations and 1D simulations. We present a generalized quantification strategy for BD-LIF based on the general form of Beer’s law that explicitly accounts for wavenumber-dependent absorption and the resulting spatial evolution of the overlap between laser and absorption line, due to the stronger absorption near the line center. The method is demonstrated by measuring hydroxyl (OH) radicals following excitation in the A–X(1,0) system in the post-flame region of laminar CH4-air flames. The results show very good agreement with simulated OH concentrations, underscoring the robustness of the generalized approach and its potential for broader application in combustion diagnostics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Richter.2025,

title = {Quantification of NO in the post-flame region of laminar premixed ammonia/hydrogen/nitrogen-air flames using laser induced fluorescence},

author = {Richter, M. and Lill, J. and Barlow, R. S. and Gruber, A. and Dreizler, A. and Dawson, J. R. and Geyer, D.},

doi = {10.1016/j.combustflame.2025.114139},

year  = {2025},

date = {2025-04-16},

urldate = {2025-04-16},

journal = {Combustion and Flame},

volume = {277},

number = {114139},

key = {Richter.2025},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lill.2025,

title = {Accurate simulation of spontaneous Raman scattering of CO2 for high-temperature diagnostics},

author = {Johannes Lill and Andreas Dreizler and Gaetano Magnotti and Dirk Geyer},

doi = {10.1016/j.jqsrt.2024.109223},

issn = {00224073},

year  = {2025},

date = {2025-01-01},

journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},

volume = {330},

pages = {109223},

abstract = {Journal of Quantitative Spectroscopy and Radiative Transfer, 330 (2025) 109223. doi:10.1016/j.jqsrt.2024.109223},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Richter.2025,

title = {Measurements of NO in the post-flame region of laminar premixed ammonia/methane-air flames using laser-induced fluorescence},

author = {M. Richter and J. Lill and R. S. Barlow and A. Dreizler and J. R. Dawson and D. Geyer},

doi = {10.1016/j.combustflame.2025.114450},

issn = {00102180},

year  = {2025},

date = {2025-01-01},

urldate = {2025-01-01},

journal = {Combustion and Flame},

volume = {282},

pages = {114450},

abstract = {Combustion and Flame, 282 (2025) 114450. doi:10.1016/j.combustflame.2025.114450},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dorscht.2025,

title = {Single-Shot In-Situ Libs-Dbi Diagnostics for Atomic Composition Analysis of Iron Particle Surfaces in Energy Storage Processes},

author = {Maximilian Dorscht and Nils Oberndorfer and Benjamin Böhm and Andreas Dreizler and Dirk Geyer},

doi = {10.2139/ssrn.5208502},

year  = {2025},

date = {2025-01-01},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Koschnick.2025,

title = {High-Sensitivity Gas-Phase Raman Spectroscopy for Time-Resolved In Situ Analysis of Isotope Scrambling over Platinum Nanocatalysts},

author = {K. Koschnick and A. M. Ferris and B. Zhang and J. Lill and M. Stark and A. Weinmann and H. H. Limbach and T. Gutmann and D. Geyer and A. Dreizler},

doi = {10.1021/acs.analchem.5c02840},

year  = {2025},

date = {2025-01-01},

journal = {Analytical chemistry},

abstract = {In this study, we present a novel approach for time-resolved, in situ analysis of isotope scrambling reactions over platinum nanoparticle catalysts using high-sensitivity gas-phase Raman spectroscopy. A recently developed spectrometer setup enables detection limits in the hundreds of ppm, a dynamic range spanning four orders of magnitude in mole fraction, and a temporal resolution of one second. Experiments were performed by introducing D2 gas to an H2-activated Pt nanoparticle catalyst in a closed sample, resulting in the formation of gaseous HD and H2. The time-resolved gas-phase mole fraction profiles show HD as the dominant product and only minor formation of H2. This observation is consistent with a predominantly associative exchange mechanism, in which D2 reacts directly with surface-bound hydrogen to produce HD. A superimposed exchange involving trace water vapor was also observed, with stepwise conversion of H2O to HDO and D2O via surface-mediated reactions. Mole fractions were quantified using a spectral fitting routine based on simulated Raman spectra derived from literature polarizabilities and energy levels. The reaction quotient of the hydrogen isotopologues converged over time toward literature values of the equilibrium constant, and measurements at defined H2/D2 ratios confirmed relative accuracies better than 2%. This Raman-based quantification method enables simultaneous, in situ detection of all relevant species with high accuracy and is ideally suited for studying transient, catalytic processes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lill.2025b,

title = {Simulated Raman libraries of gaseous CO, H2, N2, O2, CO2, and H2O for high-temperature diagnostics},

author = {Johannes Lill and Andreas Dreizler and Dirk Geyer},

doi = {10.1016/j.jqsrt.2025.109449},

issn = {00224073},

year  = {2025},

date = {2025-01-01},

journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},

volume = {340},

pages = {109449},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Koschnick.2024,

title = {Dual-track spectrometer design for 1D gas-phase Raman spectroscopy},

author = {Konrad Koschnick and Alison M. Ferris and Johannes Lill and Marcel Stark and Nico Winkler and Andreas Weinmann and Andreas Dreizler and Dirk Geyer},

doi = {10.1364/OE.523437},

year  = {2024},

date = {2024-01-01},

journal = {Optics Express},

volume = {32},

number = {14},

pages = {24384},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dubal.2024,

title = {Chemical reactor network modeling in the context of solid fuel combustion under oxy-fuel atmospheres},

author = {Sören Dübal and Leon L. Berkel and Paulo Debiagi and Hendrik Nicolai and Tiziano Faravelli and Christian Hasse and Sandra Hartl},

doi = {10.1016/j.fuel.2024.131096},

issn = {00162361},

year  = {2024},

date = {2024-01-01},

journal = {Fuel},

volume = {364},

pages = {131096},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lill.2024,

title = {Towards non-intrusive, quantitative N2O Raman measurements in ammonia flames},

author = {Johannes Lill and Marcel Stark and Robin Schultheis and Andreas Weinmann and Andreas Dreizler and Dirk Geyer},

doi = {10.1016/j.proci.2024.105458},

issn = {15407489},

year  = {2024},

date = {2024-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {40},

number = {1-4},

pages = {105458},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Schultheis.2024,

title = {Quantitative measurements of thermo-chemical states in turbulent lean and rich premixed NH3/H2/N2-air jet flames},

author = {Robin Schultheis and Tao Li and Shuguo Shi and Robert S. Barlow and Bo Zhou and Dirk Geyer and Andreas Dreizler},

url = {https://www.sciencedirect.com/science/article/pii/S1540748924003791},

doi = {10.1016/j.proci.2024.105571},

issn = {15407489},

year  = {2024},

date = {2024-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {40},

number = {1-4},

pages = {105571},

abstract = {Premixed piloted jet flames are an ideal generic configuration to examine the impact of turbulence on thermo-chemical states for staged-combustion systems, like rich-quench-lean technologies, which have been proposed for ammonia combustion to minimize emissions. The current study aims to gain fundamental insights on the internal scalar structure of such premixed and rich-lean stratified ammonia-hydrogen flames. Turbulent premixed NH3/H2/N2-air jet flames, stabilized by a large, lean pilot flame (ϕ<math><mi is=textquotedbltruetextquotedbl>ϕ</mi></math> ~=~0.57), were investigated over a range of lean to rich global equivalence ratios (ϕglobal<math><msub is=textquotedbltruetextquotedbl><mrow is=textquotedbltruetextquotedbl><mi is=textquotedbltruetextquotedbl>ϕ</mi></mrow><mrow is=textquotedbltruetextquotedbl><mi mathvariant=textquotedblnormaltextquotedbl is=textquotedbltruetextquotedbl>global</mi></mrow></msub></math> ~=~0.8, 1.2, and 1.6), employing simultaneous 1D Raman/Rayleigh spectroscopy with a novel calibration approach for NH3. The quantitative scalar data of instantaneous flame structures and thermo-chemical states are analyzed with emphasis on the NH3–H2 interaction and its effects on differential diffusion. In the transition from lean to rich jet flames, the spatial flame structures reveal the presence of residual H2 in the products, while a significant minimization of the NH3 slip is observed. The remaining H2 undergoes turbulent mixing with the hot exhaust gas causing additional heat release and elevated temperatures compared to 1D adiabatic flame simulations. The local oxygen concentration is found to be a determining factor in the interaction between thermal cracking and oxidation of NH3. Due to the formation of H2 as a result of NH3 cracking on the one hand and the oxidation reactions and diffusion of H2 on the other hand, a relatively high H2 concentration is still observed at relatively high temperatures despite the presence of O2. This interplay between in situ cracking, diffusion, turbulent mixing, and oxidation reactions leads to a zone of stratified combustion, so that overall a two-stage combustion characteristic is observed, showing premixed combustion primarily within the jet flow and stratified combustion in the mixing zone with the pilot exhaust gas.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}