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A one-dimensional premixed ethylene–air flame is investigated regarding the presence of various combustion intermediates and products relevant for the formation of carbonaceous particles for various equivalence ratios and spatial positions using in situ UV–Vis absorption spectroscopy. A laser driven light source in combination with a fast spectrometer allow to record absorption spectra at a high rate required for practical combustion devices. The approach is coupled with a least squares regression procedure using a database of several absorbing species in the flame. To account for the high temperature flame conditions, the absorption spectra are convoluted by a simplified Maxwell–Boltzmann distribution model. While the approach is based on several assumptions and a verification requires future detailed intercomparison with other techniques, a first semi-quantitative evaluation can be obtained. This novel approach opens a potential route to the in situ measurement of the evolution of polycyclic aromatic hydrocarbons (PAHs) in flames.
Florian J. Bauer; Michael U. J. Degenkolb; Franz J. T. Huber; Stefan Will. In situ characterisation of absorbing species in stationary premixed flat flames using UV–Vis absorption spectroscopy. Applied Physics A 2021, 127, 1 -15.
AMA StyleFlorian J. Bauer, Michael U. J. Degenkolb, Franz J. T. Huber, Stefan Will. In situ characterisation of absorbing species in stationary premixed flat flames using UV–Vis absorption spectroscopy. Applied Physics A. 2021; 127 (8):1-15.
Chicago/Turabian StyleFlorian J. Bauer; Michael U. J. Degenkolb; Franz J. T. Huber; Stefan Will. 2021. "In situ characterisation of absorbing species in stationary premixed flat flames using UV–Vis absorption spectroscopy." Applied Physics A 127, no. 8: 1-15.
Pumped Thermal Energy Storages (PTES) are suitable for bridging temporary energy shortages, which may occur due to the utilization of renewable energy sources. A combined heat pump (HP)-Organic Rankine Cycle (ORC) system with suitable thermal storage offers a favorable way to store energy for small to medium sized applications. To address the aspect of flexibility, the part load behavior of a combined HP-ORC system, both having R1233zd(E) (Trans-1-chloro-3,3,3-trifluoropropene) as working fluid and being connected through a water filled sensible thermal energy storage, is investigated using a MATLAB code with integration of the fluid database REFPROP. The influence on the isentropic efficiency of the working machines and therefore the power to power efficiency (P2P) of the complete system is shown by variation of the mass flow and a temperature drop in the thermal storage. Further machine-specific parameters such as volumetric efficiency and internal leakage efficiency are also considered. The results show the performance characteristics of the PTES as a function of the load. While the drop in storage temperature has only slight effects on the P2P efficiency, the reduction in mass flow contributes to the biggest decrease in the efficiency. Furthermore, a simulation for dynamic load analysis of a small energy grid in a settlement is conducted to show the course of energy demand, supplied energy by photovoltaic (PV) systems, as well as the PTES performance indicators throughout an entire year. It is shown that the use of PTES is particularly useful in the period between winter and summer time, when demand and supplied photovoltaic energy are approximately equal.
Bernd Eppinger; Mustafa Muradi; Daniel Scharrer; Lars Zigan; Peter Bazan; Reinhard German; Stefan Will. Simulation of the Part Load Behavior of Combined Heat Pump-Organic Rankine Cycle Systems. Energies 2021, 14, 3870 .
AMA StyleBernd Eppinger, Mustafa Muradi, Daniel Scharrer, Lars Zigan, Peter Bazan, Reinhard German, Stefan Will. Simulation of the Part Load Behavior of Combined Heat Pump-Organic Rankine Cycle Systems. Energies. 2021; 14 (13):3870.
Chicago/Turabian StyleBernd Eppinger; Mustafa Muradi; Daniel Scharrer; Lars Zigan; Peter Bazan; Reinhard German; Stefan Will. 2021. "Simulation of the Part Load Behavior of Combined Heat Pump-Organic Rankine Cycle Systems." Energies 14, no. 13: 3870.
In order to understand the evaporation and particle formation processes of sprays in technical applications such as fuel injectors or drying processes in the food and pharmaceutical industries in detail, single droplet drying experiments, for example, acoustic levitation, are widely used as model experiments. We combined acoustic levitation and tunable diode laser absorption spectroscopy (TDLAS) to measure the absolute H2O concentration in the exhaust gas of a levitation chamber to investigate drying and particle formation processes from single droplets of pure water and protein–water solutions. To that end, we designed and developed a non-invasive, calibration-free TDLAS-based hygrometer to analyze the 1.4 µm overtone band. To increase the detection range of the developed hygrometer and to track the complete drying process of protein solution droplets even after the critical point of drying, the absorption length was extended to a path length of 18 m using an astigmatic multipass cell of the Herriott type. The setup was validated by drying pure water droplets, resulting in a determination of the water mole fraction in a range from 73 ppm to 1314 ppm, with a single scan resolution of 1.7 ppm. For protein solution droplets, the entire drying process, even beyond the critical point of drying, can be tracked and the different phases of the drying process can be characterized at different drying temperatures.
Julian Perlitz; Heiko Broß; Stefan Will. Measurement of Water Mole Fraction from Acoustically Levitated Pure Water and Protein Water Solution Droplets via Tunable Diode Laser Absorption Spectroscopy (TDLAS) at 1.37 µm. Applied Sciences 2021, 11, 5036 .
AMA StyleJulian Perlitz, Heiko Broß, Stefan Will. Measurement of Water Mole Fraction from Acoustically Levitated Pure Water and Protein Water Solution Droplets via Tunable Diode Laser Absorption Spectroscopy (TDLAS) at 1.37 µm. Applied Sciences. 2021; 11 (11):5036.
Chicago/Turabian StyleJulian Perlitz; Heiko Broß; Stefan Will. 2021. "Measurement of Water Mole Fraction from Acoustically Levitated Pure Water and Protein Water Solution Droplets via Tunable Diode Laser Absorption Spectroscopy (TDLAS) at 1.37 µm." Applied Sciences 11, no. 11: 5036.
Emissions from diesel engines can be limited and potentially decreased by modifying the fuel chemical composition through additive insertion. One class of additives that have shown to be particularly efficient in the reduction of the particulates from the combustion of diesel fuels are oxygenated compounds. In the present study we investigate the effect of tripropylene glycol methyl ether (TPGME) and two polyoxymethylene dimethyl ethers (POMDME or OMEs) on soot formation in a laminar diesel diffusion flame. From the evaluation of soot volume fraction by laser-induced incandescence (LII) measurements we could observe that OME additives have a substantial capability (higher compared to TPGME) to decrease the particle concentration, which drops by up to 36% with respect to the pure diesel fuel. We also note a reduction in particle aggregate size, determined by wide-angle light scattering (WALS) measurements, which is more pronounced in the case of OME–diesel blends. The effects we observe can be correlated to the higher amount of oxygen content in the OME molecules. Moreover, both additives investigated seem to have almost no impact on the local soot temperature which could in turn play a key role in the production of soot particles.
Natascia Palazzo; Lars Zigan; Franz J. T. Huber; Stefan Will. Impact of Oxygenated Additives on Soot Properties During Diesel Combustion. Energies 2020, 14, 147 .
AMA StyleNatascia Palazzo, Lars Zigan, Franz J. T. Huber, Stefan Will. Impact of Oxygenated Additives on Soot Properties During Diesel Combustion. Energies. 2020; 14 (1):147.
Chicago/Turabian StyleNatascia Palazzo; Lars Zigan; Franz J. T. Huber; Stefan Will. 2020. "Impact of Oxygenated Additives on Soot Properties During Diesel Combustion." Energies 14, no. 1: 147.
In this article, the application of the FRAME (Frequency Recognition Algorithm for Multiple Exposures) technique is presented for multi-species measurements in symmetric and asymmetric ethylene/air diffusion flames. Laminar Bunsen-type and swirled diffusion flames are investigated to gain a better understanding of sooting combustion. For this purpose, simultaneous imaging is conducted in terms of Laser-Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAH) and Laser-Induced Incandescence (LII) of soot particles. Subsequently, the approach is utilized for simultaneous imaging of hydroxyl (OH)-LIF and soot-LII. Here, the modulated LIF- and LII-signals are acquired together as a single sub-image—with a single exposure utilizing the full sensor size of a single camera. By employing the frequency-recognition algorithm on the single image, the LIF- and LII-signals are spectrally isolated—generating two individual LIF- and LII-images. The flame luminosity and out-of-focus light such as reflected surrounding laser light are detected as non-modulated signals in the unprocessed image. These unwanted signals are suppressed using the image post-processing, and, therefore, the image contrast of the two resulting images is improved. It is found that PAHs mainly exist in the inner region near the burner and are surrounded by soot. The majority of the OH is distributed on the outer edges of the flame—representing the reaction zone and soot-oxidation region of the flame.
Yogeshwar Nath Mishra; Prasad Boggavarapu; Devashish Chorey; Lars Zigan; Stefan Will; Devendra Deshmukh; Ravikrishna Rayavarapu. Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera. Sensors 2020, 20, 5534 .
AMA StyleYogeshwar Nath Mishra, Prasad Boggavarapu, Devashish Chorey, Lars Zigan, Stefan Will, Devendra Deshmukh, Ravikrishna Rayavarapu. Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera. Sensors. 2020; 20 (19):5534.
Chicago/Turabian StyleYogeshwar Nath Mishra; Prasad Boggavarapu; Devashish Chorey; Lars Zigan; Stefan Will; Devendra Deshmukh; Ravikrishna Rayavarapu. 2020. "Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera." Sensors 20, no. 19: 5534.
In polymer laser transmission welding (LTW) the process parameters affect the weld seam crystallinity, which impacts mechanical, optical and chemical properties of the weld seam material. However, correlations between process parameters and these material properties are still under investigation. To improve the necessary understanding, spatially resolved crystallinity measurements by Raman microscopic mapping offer valuable insights. This paper demonstrates an advanced spectroscopic evaluation method capable of resolving crystallinity distributions even within the absorbing joining partner. Besides the description of the utilized self-developed Raman microscope, the main focus is put on the mathematical spectral reconstruction by multiple Voigt functions used to calculate the crystallinity.
Phillipp A.B. Braeuer; Leo A. Bahr; Marie-Louise Röhricht; Michael Schmidt; Stefan Will. Spatially-resolved crystallinity determination of polymer welding seams by Raman-microscopy. Procedia CIRP 2020, 94, 796 -801.
AMA StylePhillipp A.B. Braeuer, Leo A. Bahr, Marie-Louise Röhricht, Michael Schmidt, Stefan Will. Spatially-resolved crystallinity determination of polymer welding seams by Raman-microscopy. Procedia CIRP. 2020; 94 ():796-801.
Chicago/Turabian StylePhillipp A.B. Braeuer; Leo A. Bahr; Marie-Louise Röhricht; Michael Schmidt; Stefan Will. 2020. "Spatially-resolved crystallinity determination of polymer welding seams by Raman-microscopy." Procedia CIRP 94, no. : 796-801.
Combining a heat pump cycle (HP) and an organic Rankine cycle (ORC) in one reversible cycle and adding a thermal storage enables an innovative and reversible energy storage concept. This paper describes preliminary considerations, design methods and the development of a HP-ORC-pilot-plant. The storage temperatures are critical factors, as they determine the storage capacity and influence the power-to-power-efficiency. Methods of multicriteria decision-making, such as Pareto optimization, identify favorable combinations. On this basis a pilot plant is designed for 90°C lower and 120°C upper storage temperature aiming at a power-to-power-efficiency of 59% and an electrical storage capacity of 3,6 kWh/t. The selection of the working fluid has also a strong impact on the reversible process, as apparatus properties alter, in some cases effecting significant increase in costs. In the considered case the refrigerant R1233zd(E) shows the best combination of performance, costs and safety. The realization of the compressor of the heat pump and the expander of the organic Rankine cycle in one single machine is another complex task to be considered. Especially the lubrication system has to fulfill the demands of both modes, thus innovative designs of the oil supply and separation are shown, like parallel and serial layouts.
Daniel Steger; Christoph Regensburger; Bernd Eppinger; Stefan Will; Jürgen Karl; Eberhard Schlücker. Design aspects of a reversible heat pump - Organic rankine cycle pilot plant for energy storage. Energy 2020, 208, 118216 .
AMA StyleDaniel Steger, Christoph Regensburger, Bernd Eppinger, Stefan Will, Jürgen Karl, Eberhard Schlücker. Design aspects of a reversible heat pump - Organic rankine cycle pilot plant for energy storage. Energy. 2020; 208 ():118216.
Chicago/Turabian StyleDaniel Steger; Christoph Regensburger; Bernd Eppinger; Stefan Will; Jürgen Karl; Eberhard Schlücker. 2020. "Design aspects of a reversible heat pump - Organic rankine cycle pilot plant for energy storage." Energy 208, no. : 118216.
The life cycle assessment of components is becoming increasingly important for planning and construction. In this paper, a novel storage technology for excess electricity consisting of a heat pump, a heat storage and an organic rankine cycle is investigated with regards to its environmental impact. Waste heat is exergetically upgraded, stored in a hot water storage unit and afterwards reconverted to electricity when needed. Such a pilot plant on a lab scale is currently built in Germany. The first part of this paper focuses on geothermal energy as a potential heat source for the storage system and its environmental impact. For a large scale application, geothermal hotspots in Germany are further investigated. The second part analyzes the storage technology itself and compares it to the impacts of commonly used battery storage technologies. Especially during the manufacturing process, significantly better global warming potential values are shown compared to lithium-ion and lead batteries. The least environmental impact while operating the system is with wind power, which suggests an implementation of the storage system into the grid in the northern part of Germany.
Daniel Scharrer; Bernd Eppinger; Pascal Schmitt; Johan Zenk; Peter Bazan; Jürgen Karl; Stefan Will; Marco Pruckner; Reinhard German. Life Cycle Assessment of a Reversible Heat Pump – Organic Rankine Cycle – Heat Storage System with Geothermal Heat Supply. Energies 2020, 13, 3253 .
AMA StyleDaniel Scharrer, Bernd Eppinger, Pascal Schmitt, Johan Zenk, Peter Bazan, Jürgen Karl, Stefan Will, Marco Pruckner, Reinhard German. Life Cycle Assessment of a Reversible Heat Pump – Organic Rankine Cycle – Heat Storage System with Geothermal Heat Supply. Energies. 2020; 13 (12):3253.
Chicago/Turabian StyleDaniel Scharrer; Bernd Eppinger; Pascal Schmitt; Johan Zenk; Peter Bazan; Jürgen Karl; Stefan Will; Marco Pruckner; Reinhard German. 2020. "Life Cycle Assessment of a Reversible Heat Pump – Organic Rankine Cycle – Heat Storage System with Geothermal Heat Supply." Energies 13, no. 12: 3253.
Laser-induced phosphorescence based on luminescent particles is a suitable technique for remote temperature sensing. The luminescence characteristics of the phosphor (Sr,Ca)SiAlN3:Eu2+ (”SCASN”) were investigated regarding the suitability of the material for phosphor thermometry. The phosphor has a high quantum efficiency, a very broad excitation band, an emission peak centered at about 620 nm and a short lifetime of less than 1μs, which makes it promising for thermometry measurements. After excitation at 532 nm, the luminescence emission reveals a blue shift with increasing temperature, which can be used for temperature calibration based on the two-color intensity ratio method. The excitation and emission characteristics are favorable for measurements in environments containing fuels and oils, which tend to fluorescence after UV-excitation. The phosphor allows for measurements up to 800 K, with a quenching temperature of 530 K. Spectral characteristics are presented for both bulk powder and a surface coating. For the former, a significant shift in the position of the emission peak is observed, which is most probably due to distinct re-absorption. A change in excitation laser fluence slightly affected the luminescence emission spectrum of both bulk material and coating and thus requires consideration in temperature determination.
Ellen Hertle; Jonas Bollmann; Simon Aßmann; Violetta Kalancha; Andres Osvet; Miroslaw Batentschuk; Stefan Will; Lars Zigan. Characterization of the phosphor (Sr,Ca)SiAlN3: Eu2+ for temperature sensing. Journal of Luminescence 2020, 226, 117487 .
AMA StyleEllen Hertle, Jonas Bollmann, Simon Aßmann, Violetta Kalancha, Andres Osvet, Miroslaw Batentschuk, Stefan Will, Lars Zigan. Characterization of the phosphor (Sr,Ca)SiAlN3: Eu2+ for temperature sensing. Journal of Luminescence. 2020; 226 ():117487.
Chicago/Turabian StyleEllen Hertle; Jonas Bollmann; Simon Aßmann; Violetta Kalancha; Andres Osvet; Miroslaw Batentschuk; Stefan Will; Lars Zigan. 2020. "Characterization of the phosphor (Sr,Ca)SiAlN3: Eu2+ for temperature sensing." Journal of Luminescence 226, no. : 117487.
Stefan Will; Klaus Peter Geigle. Laser-induced incandescence. Applied Physics A 2020, 126, 1 .
AMA StyleStefan Will, Klaus Peter Geigle. Laser-induced incandescence. Applied Physics A. 2020; 126 (6):1.
Chicago/Turabian StyleStefan Will; Klaus Peter Geigle. 2020. "Laser-induced incandescence." Applied Physics A 126, no. 6: 1.
1-methylnaphthalene (1-MN) is a widely used laser-induced fluorescence (LIF) tracer for planar imaging of mixture formation and temperature distributions in internal combustion (IC) engines. As the LIF measurement results can be biased by partial tracer oxidation, the conversion of 1-MN and the base fuel isooctane is analyzed in a calibration cell. First, measurements using supercontinuum laser absorption spectroscopy (SCLAS) are presented in order to quantify the conversion by detection of the produced H2O mole fraction. A single mode fiber (SMF) coupled setup is presented, with the fiber core acting as entrance slit of a Czerny-Turner spectrometer. Dependencies on residence time and global air-fuel ratio are presented at pressures up to 1.5 MPa and temperatures up to 900 K, at which distinct tracer and fuel consumption is observed. Signal loss due to intense beam steering was partially compensated using a self-stabilizing double-pass setup with a retroreflector.
Peter Fendt; Ulrich Retzer; Hannah Ulrich; Stefan Will; Lars Zigan. Stability Analysis of the Fluorescent Tracer 1-Methylnaphthalene for IC Engine Applications by Supercontinuum Laser Absorption Spectroscopy. Sensors 2020, 20, 2871 .
AMA StylePeter Fendt, Ulrich Retzer, Hannah Ulrich, Stefan Will, Lars Zigan. Stability Analysis of the Fluorescent Tracer 1-Methylnaphthalene for IC Engine Applications by Supercontinuum Laser Absorption Spectroscopy. Sensors. 2020; 20 (10):2871.
Chicago/Turabian StylePeter Fendt; Ulrich Retzer; Hannah Ulrich; Stefan Will; Lars Zigan. 2020. "Stability Analysis of the Fluorescent Tracer 1-Methylnaphthalene for IC Engine Applications by Supercontinuum Laser Absorption Spectroscopy." Sensors 20, no. 10: 2871.
The morphological parameters of polydisperse aerosolized soot can be found by regressing modeled angularly-resolved elastic light scattering to experimental measurements, but this is an ill-posed problem in the presence of measurement noise or model error. Rayleigh-Debye-Gans Fractal Aggregate (RDG-FA) theory provides a closed-form solution for the light scattering kernel in the measurement model but can be subject to 30% model error (or more) compared to the exact solution, which is amplified by the ill-posedness of the inference problem into significant errors in the recovered morphological parameters. More precise approaches, e.g. the multi-sphere T-matrix method (MSTM), are too expensive for inference problems, which require repeated evaluation of the forward model; this is particularly true when computing posterior probability densities and credibility intervals. In this work, a computationally-efficient artificial feed-forward multi-layered neural network (ANN) is trained using MSTM scattering simulations on randomly-generated soot aggregates sampled from plausible morphological parameters. A fixed value is specified for the refractive index, while the monodisperse primary particle diameters are specified, and sintering, overlap or necking phenomena are ignored for the MSTM simulations. The ANN is then used to approximate the light scattering kernel in the measurement model, which is incorporated into the Bayesian inference procedure. The Bayesian/ANN approach is shown to be more accurate compared to a Bayesian approximation error technique. The Bayesian/ANN is then applied to in-flame measurements of soot and results are compared with transmission electron microscopy results from the literature. Parameters derived from electron micrographs of extracted soot are not contained within 90% credibility intervals; this is likely due to some of the simplifying assumptions in the scattering model, which points the way towards future work.
S. Talebi-Moghaddam; F.J. Bauer; F.J.T. Huber; S. Will; K.J. Daun. Inferring soot morphology through multi-angle light scattering using an artificial neural network. Journal of Quantitative Spectroscopy and Radiative Transfer 2020, 251, 106957 .
AMA StyleS. Talebi-Moghaddam, F.J. Bauer, F.J.T. Huber, S. Will, K.J. Daun. Inferring soot morphology through multi-angle light scattering using an artificial neural network. Journal of Quantitative Spectroscopy and Radiative Transfer. 2020; 251 ():106957.
Chicago/Turabian StyleS. Talebi-Moghaddam; F.J. Bauer; F.J.T. Huber; S. Will; K.J. Daun. 2020. "Inferring soot morphology through multi-angle light scattering using an artificial neural network." Journal of Quantitative Spectroscopy and Radiative Transfer 251, no. : 106957.
In spray flame synthesis the processes of spray formation and evaporation of the single droplets greatly affect the morphology and size of particles formed. An in situ measurement of these parameters is thus essential for process control and development. In this work, wide-angle light scattering (WALS) is applied to measure droplet sizes in a spray flame. The scattering data of the spherical droplets are evaluated by applying Mie-theory. For droplet sizing, the number of characteristic maxima in the scattering pattern and the measured scattering intensities are evaluated. Droplet size distributions and their parameters were determined by repetitive exposures in various heights above the nozzle outlet for two solvents: pure ethanol and a mixture of ethanol and 2-ethylhexanoic acid at a volume ratio of 35/65. While for ethanol the median droplet size decreases with increasing height, it decreases less for the mixture, which in general exhibits increased droplet sizes for all heights compared to pure ethanol. Furthermore, we could show that using air instead of nitrogen as a co-flow barely affects droplet evaporation in the flame.
Simon Aßmann; Bettina Münsterjohann; Franz J. T. Huber; Stefan Will. Droplet sizing in spray flame synthesis using wide-angle light scattering (WALS). Applied Physics A 2020, 126, 1 -13.
AMA StyleSimon Aßmann, Bettina Münsterjohann, Franz J. T. Huber, Stefan Will. Droplet sizing in spray flame synthesis using wide-angle light scattering (WALS). Applied Physics A. 2020; 126 (5):1-13.
Chicago/Turabian StyleSimon Aßmann; Bettina Münsterjohann; Franz J. T. Huber; Stefan Will. 2020. "Droplet sizing in spray flame synthesis using wide-angle light scattering (WALS)." Applied Physics A 126, no. 5: 1-13.
Optical, non-invasive techniques for temperature and mole fraction measurements in flames and other reactive flows are often limited to applications under well-defined laboratory environments. These limitations mainly arise from various prerequisites of the techniques e.g. regarding the optical accessibility of the systems under investigation, its environmental conditions such as vibrations and temperature or the need of tracers inside the flow. In order to weaken these constrains, we present a robust, fiber-based sensor system, utilizing tracer-free spontaneous rotational Raman spectroscopy with tunable near-infrared (NIR) continuous-wave laser-excitation capable of a simultaneous point-wise determination of gas temperature and mole fractions in laminar spatially uniform non-sooting reactive flows. Benefits and limits of this method are evaluated investigating a laminar premixed methane/air flat-flame of a McKenna-type burner. In that case, the main rotational Raman-active and, therefore, detectable compounds are nitrogen, oxygen and carbon dioxide. For the subtraction of flame luminosity two different techniques were used: simple background subtraction (BGS) and shifted-excitation Raman difference spectroscopy (SERDS). For both methods, the corrected spectra are matched to simulated spectra via a least-square fit algorithm in order to extract the quantities of interest. Hereby, Bayesian inference enables the determination of the uncertainties of the results. The consideration of the covariance within the multi-variate analysis allows for the combination of the BGS and SERDS method to establish a more advanced analysis routine.
Leo A. Bahr; Franz J.T. Huber; Stefan Will; Andreas S. Braeuer. Shifted-excitation rotational Raman spectroscopy and Bayesian inference for in situ temperature and composition determination in laminar flames. Journal of Quantitative Spectroscopy and Radiative Transfer 2020, 249, 106996 .
AMA StyleLeo A. Bahr, Franz J.T. Huber, Stefan Will, Andreas S. Braeuer. Shifted-excitation rotational Raman spectroscopy and Bayesian inference for in situ temperature and composition determination in laminar flames. Journal of Quantitative Spectroscopy and Radiative Transfer. 2020; 249 ():106996.
Chicago/Turabian StyleLeo A. Bahr; Franz J.T. Huber; Stefan Will; Andreas S. Braeuer. 2020. "Shifted-excitation rotational Raman spectroscopy and Bayesian inference for in situ temperature and composition determination in laminar flames." Journal of Quantitative Spectroscopy and Radiative Transfer 249, no. : 106996.
In this work, the UV absorption cross sections of the fluorescence tracer 1-methylnaphthalene are determined in the range of 230–330 nm. The experiments are performed in a continuously scavenged gas flow cell, which allows for defined homogeneous conditions regarding temperature, pressure, and tracer/fuel composition. A LSDS (laser driven light source) is used for irradiation, which enables high spectral emission intensities in the UV range studied. For detection, a spectrograph in combination with an intensified camera is applied. Absorption cross sections at temperatures up to 850 K are determined and compared to sparsely available published data. Possible uncertainties caused by the optical setup and the flow cell, respectively, are considered.
Ulrich Retzer; Hannah Ulrich; Florian J. Bauer; Stefan Will; Lars Zigan. UV absorption cross sections of vaporized 1-methylnaphthalene at elevated temperatures. Applied Physics A 2020, 126, 1 -6.
AMA StyleUlrich Retzer, Hannah Ulrich, Florian J. Bauer, Stefan Will, Lars Zigan. UV absorption cross sections of vaporized 1-methylnaphthalene at elevated temperatures. Applied Physics A. 2020; 126 (3):1-6.
Chicago/Turabian StyleUlrich Retzer; Hannah Ulrich; Florian J. Bauer; Stefan Will; Lars Zigan. 2020. "UV absorption cross sections of vaporized 1-methylnaphthalene at elevated temperatures." Applied Physics A 126, no. 3: 1-6.
In charged spark-ignition engines, additional water injection allows for the reduction of temperature under stoichiometric mixture conditions. However, a higher complexity of the injection and combustion processes is introduced when a mixture of fuel and water ("emulsion") is injected directly into the combustion chamber using the same injector. For this purpose, the mixture must be homogenized before injection so that a reproducible composition can be adjusted. In principle, gasoline and water are not miscible, and may form an unstable macro-emulsion during mixing. However, the addition of ethanol, which is a biofuel component that is admixed to gasoline, can improve the mixing and may lead to a stable micro-emulsion. For the assessment of the distribution of the water and fuel phases in the mixture, a novel imaging concept based on laser-induced fluorescence (LIF) is proposed. In a first spectroscopic study, a fluorescence dye for imaging of the water phase is selected and evaluated. The fluorescence spectra of the dye dissolved in pure water are investigated under varied conditions using a simplified pressure cell equipped with a stirrer. The study comprises effects of temperature, dye concentration, and photo-dissociation on fluorescence signals. In a second step, fuel is mixed with water (5 vol. % to 10 vol. %) containing the dye, and the water dispersion in the fuel is investigated in an imaging study. Additionally, the miscibility of fuel and water is studied for varying ethanol content, and the homogeneity of the mixture is determined. These first investigations are also essential for the assessment of the potential of the LIF technique for studying the distribution of the water phase in internal combustion engine injection systems and sprays.
Matthias Koegl; Christopher Mull; Yogeshwar Nath Mishra; Stefan Will; Lars Zigan. Characterization of fuel/water mixtures and emulsions with ethanol using laser-induced fluorescence. Applied Optics 2020, 59, 1136 -1144.
AMA StyleMatthias Koegl, Christopher Mull, Yogeshwar Nath Mishra, Stefan Will, Lars Zigan. Characterization of fuel/water mixtures and emulsions with ethanol using laser-induced fluorescence. Applied Optics. 2020; 59 (4):1136-1144.
Chicago/Turabian StyleMatthias Koegl; Christopher Mull; Yogeshwar Nath Mishra; Stefan Will; Lars Zigan. 2020. "Characterization of fuel/water mixtures and emulsions with ethanol using laser-induced fluorescence." Applied Optics 59, no. 4: 1136-1144.
In this work, the possibility of using planar droplet sizing (PDS) based on laser-induced fluorescence (LIF) and Mie scattering was investigated within the framework of measuring the droplet Sauter mean diameter (SMD) of direct-injection spark-ignition (DISI) spray systems. For this purpose, LIF and Mie signals of monodisperse fuel droplets produced by a droplet generator were studied at engine relevant diameters (20–50 µm). The surrogate gasoline fuel Toliso (consisting of 65 vol. % isooctane, 35 vol. % toluene) and the biofuel blend E20 (consisting of 80 vol. % Toliso, 20 vol. % ethanol) were used and which were doped with the fluorescence dye “nile red”. The effects of ethanol admixture, dye concentration, laser power, and temperature variation on the LIF/Mie ratio were studied simultaneously at both macroscopic and microscopic scale. The deduced calibration curves of the LIF and Mie signals of both fuels showed volumetric and surface dependent behaviors, respectively, in accordance with the assumptions in the literature. The existence of glare points and morphology-dependent resonances (MDRs) lead to slightly higher LIF and Mie exponents of E20 in comparison to Toliso. In principle, these calibration curves enable the determination of the SMD from LIF/Mie ratio images of transient fuel sprays.
Matthias Koegl; Kevin Baderschneider; Florian J. Bauer; Bernhard Hofbeck; Edouard Berrocal; Stefan Will; Lars Zigan. Analysis of the LIF/Mie Ratio from Individual Droplets for Planar Droplet Sizing: Application to Gasoline Fuels and Their Mixtures with Ethanol. Applied Sciences 2019, 9, 4900 .
AMA StyleMatthias Koegl, Kevin Baderschneider, Florian J. Bauer, Bernhard Hofbeck, Edouard Berrocal, Stefan Will, Lars Zigan. Analysis of the LIF/Mie Ratio from Individual Droplets for Planar Droplet Sizing: Application to Gasoline Fuels and Their Mixtures with Ethanol. Applied Sciences. 2019; 9 (22):4900.
Chicago/Turabian StyleMatthias Koegl; Kevin Baderschneider; Florian J. Bauer; Bernhard Hofbeck; Edouard Berrocal; Stefan Will; Lars Zigan. 2019. "Analysis of the LIF/Mie Ratio from Individual Droplets for Planar Droplet Sizing: Application to Gasoline Fuels and Their Mixtures with Ethanol." Applied Sciences 9, no. 22: 4900.
For a comprehensive understanding of nanoparticle formation in gas phase processes, such as soot formation, morphological parameters of fractal-like particle aggregates, like the radius of gyration, the fractal dimension and the primary particle size, have to be determined. Often transmission electron microscopy (TEM) is employed for the investigation of particle characteristics as it not only allows to investigate ensemble averages but single particle aggregates and thus also to determine statistical properties, such as the size distribution within a sample. Many different evaluation methods can be found in the literature. We investigated different approaches for the determination of morphological parameters from TEM images of soot and compared the results to derive an optimized evaluation strategy for TEM nanoparticle characterization. We compared four methods for the determination of the radius of gyration – three length- and one pixel-based methods – showing good agreement within 9% deviation for the median of the recovered lognormal size distribution. Furthermore, the fractal dimension was determined via a sample-based and various box counting methods with different limiting box sizes. Here, we could show that the upper and lower bounds (aggregate size in terms of radius of gyration and primary particle size in terms of its radius, respectively) of self-similarity of fractal-like aggregates should be accounted for by choosing corresponding upper and lower box sizes. Using box counting, we could show that for small aggregates the fractal dimension as well as its span are increased, yet with increasing aggregate size the fractal dimension converges towards 1.6. Furthermore, we could show the potential of semi-automatic aggregate detection through Trainable Weka Segmentation. However, image noise resulting in erroneous aggregate splitting often leads to smaller aggregate sizes by automatic detection compared to manual segmentation. Generalized Hough Transformation for the semi-automatic determination of primary particle sizes performs well for large soot particle aggregates as those often show spherical primary particles. For leaner combustion conditions, the primary particles of the formed clumpy soot aggregates cannot be detected well via semi-automatic detection. TEM images were taken on soot samples from premixed laminar flat flames (burner type: McKenna) under various conditions to provide comprehensive reference data.
Michael Altenhoff; Simon Aßmann; Christian Teige; Franz J.T. Huber; Stefan Will. An optimized evaluation strategy for a comprehensive morphological soot nanoparticle aggregate characterization by electron microscopy. Journal of Aerosol Science 2019, 139, 105470 .
AMA StyleMichael Altenhoff, Simon Aßmann, Christian Teige, Franz J.T. Huber, Stefan Will. An optimized evaluation strategy for a comprehensive morphological soot nanoparticle aggregate characterization by electron microscopy. Journal of Aerosol Science. 2019; 139 ():105470.
Chicago/Turabian StyleMichael Altenhoff; Simon Aßmann; Christian Teige; Franz J.T. Huber; Stefan Will. 2019. "An optimized evaluation strategy for a comprehensive morphological soot nanoparticle aggregate characterization by electron microscopy." Journal of Aerosol Science 139, no. : 105470.
Determination of catalase activity using supercontinuum attenuation spectroscopy and PLSA.
Hanna Koch; Kristina Eisen; Thomas Werblinski; Julian Perlitz; Felix Prihoda; Geoffrey Lee; Stefan Will. High-speed, inline measurement of protein activity and inactivation processes by supercontinuum attenuation spectroscopy. The Analyst 2019, 144, 7041 -7048.
AMA StyleHanna Koch, Kristina Eisen, Thomas Werblinski, Julian Perlitz, Felix Prihoda, Geoffrey Lee, Stefan Will. High-speed, inline measurement of protein activity and inactivation processes by supercontinuum attenuation spectroscopy. The Analyst. 2019; 144 (23):7041-7048.
Chicago/Turabian StyleHanna Koch; Kristina Eisen; Thomas Werblinski; Julian Perlitz; Felix Prihoda; Geoffrey Lee; Stefan Will. 2019. "High-speed, inline measurement of protein activity and inactivation processes by supercontinuum attenuation spectroscopy." The Analyst 144, no. 23: 7041-7048.
The spatial distribution of soot aggregate size and morphology within a premixed flat flame (McKenna-type burner and ethyne–air mixture at an equivalence ratio of Φ = 2.7) is characterized by two-dimensional multi-angle light scattering (2D-MALS). A profound investigation of such an extended, radially symmetrical sooting flame with 2D-MALS requires a sophisticated camera calibration to correct for non-linear image scaling and a careful evaluation of the scattering data. Sharp scattering images were acquired in the angular range from 20° to 155° using a rotatable camera system and an automated Scheimpflug adapter. To correct for non-linear variations in horizontal and vertical image magnification occurring at scattering angles differing from perpendicular view, a polynomial-based image transformation algorithm was developed to convert all scattering images into a common coordinate system. Effective radii of gyration and fractal dimensions of soot aggregates were then derived from scattering data by two different approaches. Due to limited amount of angular positions, the classical method based on Guinier and power law analysis shows limitations, as it yields discontinuous results, predominantly in axial direction of the burner. Bayesian analysis was then used for a data fit of the complete structure factor conducting a least square minimization leading to more consistent results. The use of prior knowledge in the Bayesian evaluation allows for improved data fitting and reduced uncertainties in radius of gyration and fractal dimension even for small aggregate sizes.
Michael Altenhoff; Simon Aßmann; Julian F. A. Perlitz; Franz J. T. Huber; Stefan Will. Soot aggregate sizing in an extended premixed flame by high-resolution two-dimensional multi-angle light scattering (2D-MALS). Applied Physics A Solids and Surfaces 2019, 125, 176 .
AMA StyleMichael Altenhoff, Simon Aßmann, Julian F. A. Perlitz, Franz J. T. Huber, Stefan Will. Soot aggregate sizing in an extended premixed flame by high-resolution two-dimensional multi-angle light scattering (2D-MALS). Applied Physics A Solids and Surfaces. 2019; 125 (9):176.
Chicago/Turabian StyleMichael Altenhoff; Simon Aßmann; Julian F. A. Perlitz; Franz J. T. Huber; Stefan Will. 2019. "Soot aggregate sizing in an extended premixed flame by high-resolution two-dimensional multi-angle light scattering (2D-MALS)." Applied Physics A Solids and Surfaces 125, no. 9: 176.