Recently, hydrogen has been explored as an aviation energy carrier to support various critical energy challenges for the upcoming decades. Thus, conventional and non-conventional hydrogen production ...methods have been developed worldwide. This paper investigates Steam Methane Reforming (SMR) and Alkaline Electrolysis (AWE) hydrogen production as primary processes from an energy requirement and life cycle perspective. Besides, It also considers hydrogen liquefaction for aviation use. In this context, an attributional, Cradle-to-Gate life cycle assessment was carried out to compare the environmental impact of SMR and AWE hydrogen production processes under four German energy mix scenarios. The assessment method selected was ReCiPe 2016, and the main impact categories were climate change and acidification potential. The results show that greenhouse gas emissions from each production method highly depend on energy sources. The CO2 emissions from SMR and AWE processes in a base case scenario are 12 and 51 kgCO2eq/kgH2, respectively, and these values decrease to 7 (SMR) and 22 kgCO2eq./kgH2 (AWE) in a 2050 renewable energy scenario. Concerning the energy requirements, each process requires different energy amounts to produce 1 kgH2 (functional unit). SMR requires 11.3 kWh, AWE 61.8 kWh, and hydrogen liquefaction 5.1 kWh. In brief, hydrogen is widely promoted as an alternative energy carrier in Germany; however, depending on the production process and technical considerations, further studies are required to support and explore its applications.
Fuel microchannels for regenerative cooling are receiving increasing attention in advanced aviation technologies. Those microchannels allow heat integration between the endothermic cracking of the ...jet fuels and their subsequent combustion. In this work, a detailed elementary-step kinetic model is developed to gain insights into the cracking chemistry of a Jet A surrogate (n-dodecane, isooctane, n-propyl benzene, and 1,3,5-trimethylbenzene), which allows for further optimization of those aviation technologies. A dedicated procedure is described for the automated generation of kinetic models for multi-component mixtures with the open-source Reaction Mechanism Generator (RMG) software. The full kinetic model is validated against experimental measurements in multiple reactor geometries, under various experimental conditions, including both a surrogate mixture and a commercial Jet A. The experimental data include new experimental measurements for the pyrolysis of a Jet A surrogate in a tubular reactor with a detailed product analysis using comprehensive 2D GC. The good performance of the kinetic model for data from a broad range of experimental conditions demonstrates the advantage of a kinetic model with detailed chemistry against empirical kinetic models that are limited in their applicability range. Further analysis of the important chemistry in the kinetic model shows that it is essential to account for cross-reactions between the different surrogate components.
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IJS, KILJ, NUK, PNG, UL, UM
Using Reaction Mechanism Generator (RMG), we have automatically constructed a detailed mechanism for acetylene pyrolysis, which predicts formation of polycyclic aromatic hydrocarbons (PAHs) up to ...pyrene. To improve the data available for formation pathways from naphthalene to pyrene, new high‐pressure limit reaction rate coefficients and species thermochemistry were calculated using a combination of electronic structure data from the literature and new quantum calculations. Pressure‐dependent kinetics for the C4H4 potential energy surface calculated by Zádor et al. were incorporated to ensure accurate pathways for acetylene initiation reactions. After adding these new data into the RMG database, a pressure‐dependent mechanism was generated in a single RMG simulation which captures chemistry from C2 to C16. In general, the RMG‐generated model accurately predicts major species profiles in comparison to plug‐flow reactor data from the literature. The primary shortcoming of the model is that formation of anthracene, phenanthrene, and pyrene are underpredicted, and PAHs beyond pyrene are not captured. Reaction path analysis was performed for the RMG model to identify key pathways. Notable conclusions include the importance of accounting for the acetone impurity in acetylene in accurately predicting formation of odd‐carbon species, the remarkably low contribution of acetylene dimerization to vinylacetylene or diacetylene, and the dominance of the hydrogen ion C2H2 addition (HACA) mechanism in the formation pathways to all PAH species in the model. This work demonstrates the improved ability of RMG to model PAH formation, while highlighting the need for more kinetics data for elementary reaction pathways to larger PAHs.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
•Parallel computing for reaction generation and chemical data computation allows for new opportunities in detailed modeling of diverse real-world processes.•Improved load balancing with distributed ...reaction families for reaction generation.•RMG wall clock time reduces by at least 85% for isolated reaction generation and 95% for isolated chemical data computation.
Detailed modeling of complex chemical processes, like pollutant formation during combustion events, remains challenging and often intractable due to tedious and error-prone manual mechanism generation strategies. Automated mechanism generation methods seek to solve these problems but are held back by prohibitive computational costs associated with generating larger reaction mechanisms. Consequently, automated mechanism generation software such as the Reaction Mechanism Generator (RMG) must find novel ways to explore reaction spaces and thus understand the complex systems that have resisted other analysis techniques. In this contribution, we propose three scalability strategies — code optimization, algorithm heuristics, and parallel computing — that are shown to considerably improve RMG's performance as measured by mechanism generation time for three representative simulations (oxidation, pyrolysis, and combustion). The improvements create new opportunities for the detailed modeling of diverse real-world processes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Experimental investigations assess for the first time the influence of the gradient of the square of the magnetic flux density (∇(B2)) on the soot production in a laminar axisymmetric non-premixed ...flame. The steady non-smoking ethylene flame is established in a coflowing mixture, composed of oxygen and nitrogen, over a Santoro type burner. This burner is located in an electromagnet. The flame experiences different magnitudes of upward ∇(B2), ranging from 0 to 18.2T2/m, as well as different oxygen contents of the coflow, ranging from 21% to 50% in volume. Soot volume fraction is mapped in the flame by Laser Extinction Measurement technique. Increasing the magnitude of the ∇(B2) allows for the modification of soot production in the flame. This modification is enhanced by increasing oxygen content, as oxygen exhibits a relatively high paramagnetic susceptibility. Furthermore, the aforementioned modification is shown to enable the shift among similar soot concentration profiles in the flame, just as the variation of oxygen content can do. Consequently, modification of the inner flame structure by magnetic effects could contribute to the control of oxyfuel combustion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The aeronautical sector faces challenges in meeting its net-zero ambition by 2050. To achieve this target, much effort has been devoted to exploring sustainable aviation fuels (SAF). Accordingly, we ...evaluated the technical performance of potential SAF production in an integrated first- and second-generation sugarcane biorefinery focusing on Brazil. The CO2 equivalent and the renewability exergy indexes were used to assess environmental performance and impact throughout the supply chain. In addition, exergy efficiency (ηB) and average unitary exergy costs (AUEC) were used as complementary metrics to carry out a multi-criteria approach to determine the overall performance of the biorefinery pathways. The production capacity assumed for this analysis covers 10% of the fuel demand in 2020 at the international Brazilian airports of São Paulo and Rio de Janeiro, leading to a base capacity of 210 kt jet fuel/y. The process design includes sugarcane bagasse and straw as the feedstock of the biochemical processes, including diverse pre-treatment methods to convert lignocellulosic resources to biojet fuel, and lignin upgrade alternatives (cogeneration, fast pyrolysis, and gasification Fischer-Tropsch). The environmental analysis for all scenarios shows a GHG reduction potential due to a decrease of up to 30% in the CO2 equivalent exergy base emissions compared to fossil-based jet fuel.
Air-Cored Linear Motor: Design and Operating Behavior Hofmann, Tim; Radeck, Domenik; Jocher, Agnes
2024 IEEE International Magnetic Conference - Short papers (INTERMAG Short papers),
2024-May-5
Conference Proceeding
Long-stator linear synchronous motors have been proven to operate efficiently at high speeds, making them suitable for ground-based high-speed transportation technologies such as Maglev trains or ...Hyperloop. The need for laminated steel along the track makes this type of motor cost-prohibitive which argues in favor of an ironless design. Air-cored synchronous motors are more difficult to control, especially at low speeds at the beginning of acceleration phases. Here, we report the design and low-speed performance of a long-stator air-cored linear synchronous motor. This study is based on a 4.8 m long test track with a rail-bound vehicle. Successfull motor operation with a conventional variable frequency drive system demonstrates sufficient magnetic flux linkage between an optimized multi-turn stator and a permanent magnet excitation system. We infer information from measurements for different driving profiles and air gaps from 5 mm to 25 mm. Depending on whether position and speed feedback are integrated, we observe a major difference in vibrations, leading to different levels of potential passenger comfort.
Cette thèse consiste en l'étude expérimentale et numérique des processus de formation des particules de suie au sein des flammes laminaires non-pré-mélangées et partiellement prémélangées sous ...l'influence d'un champ magnétique ou d'une stimulation acoustique. Dans une premiére étape, la capacité du code CIAO à prédire la fraction volumique de suie dans une flamme axisymétrique est étudiée. Par la suite, deux flammes subissant une stimulation acoustique ont été étudiées. Les résultats peuvent être utilisés pour améliorer les modèles de suie futurs, en particulier concernant les différentes échelles temporelles de la chimie en phase gazeuse, et la formation d'hydrocarbures polyaromatiques (PAH) et de suie couplée avec des flux transitoires. Pour étudier la formation des particules de suie sous l'influence de gradients de champ magnétique, un brûleur de type Santoro est utilisé. Les techniques de mesure utilisées dans le cadre de cette thèse sont l'imagerie directe à haute cadence, la technique Background Oriented Schlieren (BOS) et la méthode d'Absorption/Emission Modulée (MAE). Une augmentation de la fraction volumique de suie intégrée a été mise en évidence lorsque le gradient de champ magnétique est ascendant. Une analyse de stabilité linéaire locale appliquée à l'écoulement non-visqueux est présentée pour une flamme sous l'influence de la perturbation magnétique envisagée. Le gradient de champ magnétique provoque alors une réduction du taux d'amplification. De fait, l'étude est complété par l'identification d'un domaine où les flammes qui oscillent naturellement peuvent être stabilisées et contrôlées par des gradients de champ magnétique.
In this thesis light is shed on the soot formation processes in laminar coflow flames influenced by magnetic field gradients and acoustic forcing. Both influences have been assessed experimentally and numerically. First, the CIAO in-house code's ability to predict soot volume fraction fields in a steady coflow flame is studied. Then, two acoustically forced cases were studied. These findings are used to improve future soot models, especially, concerning the different time scales of gas phase chemistry and the formation of polycyclic aromatic hydrocarbons (PAH) and soot coupled with unsteady flows. To investigate soot formation under magnetic field gradients, a Santoro type burner is used. The measurement techniques applied in the course of this thesis are high-speed luminosity measurements, Background Oriented Schlieren (BOS) and one- and two-color Modulated Absorption/Emission (MAE) techniques. The magnetic field impact on soot formation was first studied experimentally in steady laminar flames. A scaling of soot production similar to the increased integrated soot volume fraction with increased oxygen content in the coflow was documented. A local inviscid stability analysis is presented for an ethylene coflow flame to investigate the flame's response to small perturbations of the mean velocity, temperature, fuel, and oxygen massfraction under magnetic field exposure. The magnetic field is found to reduce the perturbations' growth rate. The magnetic field study is completed by identifying a domain where naturally oscillating flames can be stabilized and controlled by magnetic field gradients.
Soluble RANKL and Risk of Nontraumatic Fracture Schett, Georg; Kiechl, Stefan; Redlich, Kurt ...
JAMA : the journal of the American Medical Association,
03/2004, Volume:
291, Issue:
9
Journal Article
Peer reviewed
Open access
CONTEXT The receptor activator of nuclear factor κB ligand (RANKL) is
essential for osteoclast and, possibly, osteoblast activation and may represent
a key link between bone formation and resorption. ...OBJECTIVE To determine the relationship between serum level of RANKL and the risk
of nontraumatic fracture. DESIGN, SETTING, AND PARTICIPANTS As part of a prospective population-based study conducted in Bruneck,
Italy, we recorded all fractures that occurred between 1990 and 2000 in 906
participants and classified them as traumatic (n = 115) or nontraumatic (n
= 31). Serum levels of RANKL and osteoprotegerin and characteristics of bone
metabolism and lifestyle were assessed in 1990 and at follow-up in 1995 and
2000. MAIN OUTCOME MEASURE Incident nontraumatic fracture by levels of RANKL. RESULTS Levels of RANKL did not differ between sexes and were not related to
age, menopausal status, lifestyle characteristics, or data from bone ultrasound
at the heel. However, RANKL emerged as a significant predictor of nontraumatic
fracture. In pooled logistic regression analysis, the relative risks of nontraumatic
fracture in the lowest and middle vs highest tertile for RANKL were 10.0 (95%
confidence interval CI, 2.3-43.1) and 3.9 (95% CI, 0.8-19.0) (P<.001 for trend), respectively. Patients in the highest-tertile
group had a low risk of fracture even in the presence of other predisposing
factors, whereas women aged 60 years or older in the lowest tertile had a
5-year rate of nontraumatic fracture greater than 7%. CONCLUSIONS A low level of RANKL is an independent predictor of nontraumatic fracture.
This finding is consistent with the hypothesis of an important role of RANKL
in human bone turnover and if confirmed in future investigations may gain
relevance for assessment of fracture risk.
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