In chemical kinetics research, kinetic models containing hundreds of species and tens of thousands of elementary reactions are commonly used to understand and predict the behavior of reactive ...chemical systems. Reaction Mechanism Generator (RMG) is a software suite developed to automatically generate such models by incorporating and extrapolating from a database of known thermochemical and kinetic parameters. Here, we present the recent version 3 release of RMG and highlight improvements since the previously published description of RMG v1.0. Most notably, RMG can now generate heterogeneous catalysis models in addition to the previously available gas- and liquid-phase capabilities. For model analysis, new methods for local and global uncertainty analysis have been implemented to supplement first-order sensitivity analysis. The RMG database of thermochemical and kinetic parameters has been significantly expanded to cover more types of chemistry. The present release includes parallelization for faster model generation and a new molecule isomorphism approach to improve computational performance. RMG has also been updated to use Python 3, ensuring compatibility with the latest cheminformatics and machine learning packages. Overall, RMG v3.0 includes many changes which improve the accuracy of the generated chemical mechanisms and allow for exploration of a wider range of chemical systems.
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IJS, KILJ, NUK, PNG, UL, UM
Based on commercial passenger-carrying airships like LZ129 or R100, a hypothetical electric rigid framed airship including a solar cell covered surface and a lithium-ion battery is designed. The size ...of the battery and the coverage with solar cells are selected such that long-haul flights are possible. To simulate flight times, weather data from 2019 and time-dependent solar irradiation are used. Travel route and battery use are optimised in order to reduce flight times. For a mid-range and long-haul use case for passenger or freight transport, travel times have been calculated. Building on these results, analysis of CO
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emissions, land-use, and operating costs are carried out to reveal that depending on the use case, CO
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emissions of solar-powered airships could be as low as 1% to 5% of the emissions of a conventional aircraft at an estimated energy consumption in USD per km of 0.5% to 2.5%.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The hyperloop concept envisions a low pressure tube and capsules, called pods, traveling at the speed of commercial aircraft as a sustainable, future-proof mass transportation system between cities. ...However, in contrast to the use case of such a system, the detailed technical concept is still under development. One challenging difference in comparison to other modes of transportation lies in the technical concept of the infrastructure, which is hard to change in the long term and therefore allows a few iterations only. This study’s key contribution is to showcase the conceptual design decisions of the 24 m full-scale Hyperloop Demonstrator at the Technical University of Munich (TUM) for the propulsion and suspension system, featuring the design decision tree (DDT) method as a framework to visualize and explain the technical design decisions and dependencies of complex hardware systems. The construction of the full-scale demonstrator not only proved the feasibility of the concept but also provided valuable concept-level experiences, which are shared within this work. Compared to existing maglev and hyperloop concepts, the presented concept features a separated air-cored long stator propulsion system and a homopolar electromagnetic suspension at the bottom with the track wrapping around the vehicle, revealing promising advantages like the structural simplification of the infrastructure and the independence of the guideway and tube.
Advancing permanent magnet arrays for linear electric machines is a compelling endeavor with the potential to further improve efficiencies in the fields of power generation or passenger and cargo ...transportation. Permanent magnets offer an unparalleled advantage by providing a consistent and efficient source of magnetic flux density without the need for external power input. This remarkable property allows for the development of smaller, lighter, and more energy-efficient electric machines, making them ideal for applications in several industries. Here, we present the design of an optimal linear Halbach array with a sinusoidal distribution of the magnetic flux density component Bz perpendicular to the surface of the array. A large scale and easy scalable six-segmented Halbach array has been built without the use of a steel backplate enabling a lightweight and compact design. Numerical results of the magnetic flux density distributions are calculated by relying on finite element methods and are compared with experimental measurements of the magnetic flux density, showing good agreement. The demonstration revealed that, with an optimal magnet configuration, the absence of a backplate does not result in any diminishment of magnetic flux density strength.
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•Design and construction of optimal linear Halbach arrays without magnetic backplate.•Automated assembly machine to produce linear magnet arrays from single magnets.•Numerical and experimental analysis of magnetic flux density distributions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Oscillating jet flames in a coflow mimic certain features of turbulent flows in a simplified and controllable way. Our study aims to identify the potential of the HMOM soot model, which is validated ...in steady laboratory flames to be applied in practical, mostly turbulent flames. The model is found to accurately predict all the measurement parameters in a steady laminar sooting jet flame of ethylene/nitrogen mixture. When applied to an oscillating flame with the same fuel mixture, it was found that, while velocity, temperature, and OH fields are well predicted, the peak soot volume fraction is over predicted and occurs away from the experimentally measured location. The potential for soot model improvement is analysed by correlating the transient gas-phase species, polycyclic aromatic hydrocarbon, and soot formation or destruction behaviour. A need for improved soot nucleation, condensation, and oxidation formulations is identified. It is further found that the soot number density distribution in mixture fraction space is comparable to the transitional turbulent flame regime dominated by Kelvin-Helmholtz rollers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This present study explores possible stabilization mechanisms in flickering, sooting, ethylene flames burning in varying density coflow and exposed to different levels of an upward gradient of the ...square of the magnetic flux density (∇(B2)). In normal gravity, flame flickering defines a natural large scale and low frequency flame oscillation that is induced by a so called modified Kelvin–Helmholtz type instability. To assess the potential of the magnetically induced stabilization process, a range of coflow mixtures with varying N2, O2, and CO2 contents in volume is studied. As a result, a domain of controllable flame stability is identified. Its extension depends on the maximum magnitude of ∇(B2), i.e., 18.2 T2/m for the present experimental setup. Spectral emission rate, spectral absorption coefficient, soot volume fraction, and soot temperature fields are measured in the flame by the Modulated Absorption/Emission technique (MAE). In agreement with former studies, the soot content is shown to play a key role in the stabilization process. Due to the magnetic force that is mainly acting on paramagnetic oxygen molecules, opposing gravity, and generated by ∇(B2), the residence time of soot particles in the flame presumably increases with ∇(B2). With growing soot volume fraction, radiative heat losses are enhanced leading to flame cooling. Therefore, flames exposed to the magnetic field exhibit both lower density gradients through the flame sheet and a weaker field of buoyant acceleration in the hot exhaust gas stream. Both mechanisms then reduce the flame vulnerability to the onset of oscillations due to modified Kelvin–Helmholtz type instabilities. The findings may be relevant for designing strategies to control the stability of oxyfuel combustion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The present interdisciplinary study combines electromagnetics and combustion to unveil an original and basic experiment displaying a spontaneous flame instability that is mitigated as the ...non-premixed sooting flame experiences a magnetic perturbation. This magnetic instability mitigation is reproduced by direct numerical simulations to be further elucidated by a flow stability analysis. A key role in the stabilization process is attributed to the momentum and thermochemistry coupling that the magnetic force, acting mainly on paramagnetic oxygen, contributes to sustain. The spatial local stability analysis based on the numerical simulations shows that the magnetic field tends to reduce the growth rates of small flame perturbations.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
This combined numerical and experimental study assesses the transient coupling of soot formation, flame chemistry and fluid transport in ethylene-air coflow flames at acoustic forcing frequencies of ...20 and 40 Hz. The measurements report soot volume fraction and flow velocity. For the computational analysis, the numerical code’s capability in modeling soot formation is first demonstrated in a steady coflow flame. Soot volume fraction and temperature measurements from different laboratories and optical techniques are used for validation. Then, acoustic forcing is applied to investigate the transient behavior of this multi-dimensional combustion problem. Forcing at different frequencies and amplitudes provokes very distinct transient soot, temperature, and flow conditions. The discussed steady ethylene-air flame is excited with 20 and 40 Hz, corresponding to Strouhal numbers of 0.23 and 0.46. For both frequencies, forcing amplitudes of 20, 50, and 60% are studied numerically and validated against measurements at 50%. With a start-up transient analysis, the computation time to reach a periodic state is evaluated and soot volume fraction predictions are then compared with the measurements. A reduction in maximum soot volume fraction for the increased forcing frequency is observed experimentally and numerically. The decrease in maximum soot volume fraction is explained by a residence time analysis revealing shorter maximum fluid parcel residence times for the 40 Hz than for the 20 Hz case. It is also found that at 40 Hz the transient evolution of maximum soot production and forced fuel velocity is almost synchronized, while for the 20 Hz case, a time lag of 32.5 ms is observed, corresponding to 65% of a full period.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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