| 1. |
- Han, Joonsoo, 1990
(författare)
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Fundamentals of NH3-SCR and SOx chemistry over copper zeolite for the control of NOx and greenhouse gas (N2O) emissions
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The release of N2O over Cu-zeolite was investigated due to the critical contribution it makes to the atmosphere as one of the greenhouse gases (GHGs). An exhaust after-treatment system (EATS) for heavy-duty vehicles that uses Cu/SSZ-13 as the selective catalyst reduction (SCR) catalyst experiences not only a variety of flow, temperature and chemical conditions but is also exposed to various resulting contaminants. Among these, sulfur has been the focus of studies due to its critical deactivation of DeNOx performance, even at low concentration levels. Adsorption/desorption of sulfur species over Cu/SSZ-13 is connected closely to the lifetime of the SCR catalyst. The task of unravelling the synergistic effect of sulfur has on the formation of N2O during the NH3-SCR of NOx, while also reflecting realistic application conditions, is challenging. The ambition here is to gain a comprehensive understanding of the formation of N2O in the presence of sulfur species during the NH3-SCR of NOx at low temperature for NOx emissions control. Model catalysts were prepared to investigate a variety of copper species and ammonium nitrate (AN) within the CHA cage. It was found that the CHA structure promotes surface nitrate species in NO2-rich conditions, and an environment with strong polarity within the CHA cage was proposed as a feasible reason for the largest formation of ammonium nitrate compared to the MFI and BEA structures with medium and large pore/cage sizes. In addition, zeolite acidity was more a viable reason as to why ammonium nitrate is thermally stable in Cu/CHA compared to Cu/MFI and Cu/BEA than the pore-confinement effect, which has been used to explain the thermal stability of AN over Cu/zeolites. The IR signature of the ammonium nitrate was also obtained; it is believed that ammonium nitrate exists mainly by interacting with copper ions to form copper-ammonium nitrate within the CHA cage. Copper species and the adsorption of sulfur oxides (SO2/SO3) were investigated and their synergistic effects on the formation of N2O assessed. The SO3-poisoning effect was highlighted which, from an experimental aspect, is very challenging. We found two different states of sulfur species. SO2 and SO3 interaction with copper-monomers (Z1CuOH and Z2Cu) and copper-dimer (Z2Cu2O2) are possible. Sulfated Cu-dimer is lower in energy compared to its copper-monomers counterparts. SO3 interacts with both Z1CuOH and Z2Cu but SO2 mainly interacts with Z1CuOH. SO3-poisoning only causes (bi)sulfate (Z1HSO4), whereas SO2-poisoning can cause both (bi)sulfite (Z1HSO3) and (bi)sulfate (Z1HSO4). Taken together, out results well demonstrates why the SO3 exposure results in more critical chemical poisoning (irreversible deactivation) compared to the SO2 exposure to Cu/CHA. Finally, synergistical effect of sulfur, copper, and Brønsted sites were found for N2O formation under NO2-rich condition. Consequently, we found that sulfur promotes N2O intermediate formation but increasing Brønsted site density increases N2 selectivity, thereby, reducing N2O formation from Cu/CHA.
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| 2. |
- Hoffmann, Laurie, et al.
(författare)
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The green seaweed Ulva: tomorrow’s “wheat of the sea” in foods, feeds, nutrition, and biomaterials
- 2024
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Ingår i: Critical reviews in food science and nutrition. - 1040-8398.
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Forskningsöversikt (refereegranskat)abstract
- Ulva, a genus of green macroalgae commonly known as sea lettuce, has long been recognized for its nutritional benefits for food and feed. As the demand for sustainable food and feed sources continues to grow, so does the interest in alternative, plant-based protein sources. With its abundance along coastal waters and high protein content, Ulva spp. have emerged as promising candidates. While the use of Ulva in food and feed has its challenges, the utilization of Ulva in other industries, including in biomaterials, biostimulants, and biorefineries, has been growing. This review aims to provide a comprehensive overview of the current status, challenges and opportunities associated with using Ulva in food, feed, and beyond. Drawing on the expertise of leading researchers and industry professionals, it explores the latest knowledge on Ulva’s nutritional value, processing methods, and potential benefits for human nutrition, aquaculture feeds, terrestrial feeds, biomaterials, biostimulants and biorefineries. In addition, it examines the economic feasibility of incorporating Ulva into aquafeed. Through its comprehensive and insightful analysis, including a critical review of the challenges and future research needs, this review will be a valuable resource for anyone interested in sustainable aquaculture and Ulva’s role in food, feed, biomaterials, biostimulants and beyond.
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| 3. |
- Hosseini, Seyedehsan, 1994, et al.
(författare)
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Alkyl ketene dimer modification of thermomechanical pulp promotes processability with polypropylene
- 2024
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Ingår i: Polymer Composites. - 1548-0569 .- 0272-8397. ; 45:1, s. 825-835
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Tidskriftsartikel (refereegranskat)abstract
- Alkyl ketene dimers (AKDs) are known to efficiently react with cellulose with a dual polarity in their structure: a polar component and a nonpolar component. AKD of three different carbon chain lengths, 4, 10, and 16 carbons have been synthesized, and thermomechanical pulp (TMP) fibers were modified by them. The modification of TMP fibers with AKD resulted in an increased water contact angle, showing the presence of the AKDs on the TMP fibers and a new carbonyl peak in the IR spectra, suggesting modification of the TMP fibers with AKD groups. Calculating the Hansen solubility parameters of AKD and AKD conjugated to TMP in polypropylene (PP) indicates improved compatibility, especially of longer chain AKD and TMP AKD. The rheological studies of the composites showed that the AKD with the longest carbon chain decreases the melt viscosity of the PP-TMP-AKD composite, which combined with the shape and the color of the extruded composite filaments indicates improved flow properties and reduced stress build up during processing. The research findings demonstrate the ability of AKD to enhance the dispersibility and compatibility of natural fibers with PP.
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| 4. |
- Maniewski, Pawel, et al.
(författare)
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Advances in laser‐based manufacturing techniques for specialty optical fiber
- 2024
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916.
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Tidskriftsartikel (refereegranskat)abstract
- As demand for customized specialty fibers grows, standardized production methods face challenges. This article reviews industry standards and discusses potentially disruptive techniques that enable rapid prototyping and fabrication of optical fiber devices. Furthermore, we showcase laser powder deposition's (LPD) potential for additive manufacturing (AM) of customized glass structures. In the case of, for example, fiber preforms, although the feasible size is smaller than the industry standard, utilizing laser-based manufacturing techniques for a small batch production presents an attractive avenue for rapid prototyping and expedites material and design optimization. In the realm of AM of glass, LPD offers numerous benefits, including minimal shrinkage, high densification, and the ability to tailor glass composition to achieve desired optical properties. The article reviews the latest achievements and highlights future directions in this technology.
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| 5. |
- Peprah, Godwin, 1990, et al.
(författare)
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Control-Oriented 2D Thermal Modelling of Cylindrical Battery Cells for Optimal Tab and Surface Cooling
- 2024
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Ingår i: Proceedings of the American Control Conference. - 0743-1619.
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Konferensbidrag (refereegranskat)abstract
- Minimising cell thermal gradients and the average temperature rise requires an optimal combination of tab and surface cooling methods to leverage their unique advantages. This work presents a computationally efficient two-dimensional (2D) thermal model for cylindrical lithium-ion battery cells that is developed based on the Chebyshev Spectral-Galerkin method and allows the independent control of tab and surface cooling channels for effective thermal performance optimisa- tion. This obtained model is validated against a high-fidelity finite element model under the worldwide harmonised light vehicle test procedure (WLTP). Results show that the reduced-order model with as few as two states can predict the spatially resolved temperature distribution throughout the cell and that in aggressive cooling scenarios, a model order of nine states can improve accuracy by about 84%. It is also shown that even though cooling all sides of the cylindrical cell achieves the lowest average temperature rise, cooling only the top and bottom sides provides minimum radial thermal gradients.
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| 6. |
- Cheung, Hon Lam, et al.
(författare)
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A multi-fidelity data-driven model for highly accurate and computationally efficient modeling of short fiber composites
- 2024
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Ingår i: Composites Science and Technology. - 0266-3538. ; 246
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Tidskriftsartikel (refereegranskat)abstract
- To develop physics-based models and establish a structure–property relationship for short fiber composites, there are a wide range of micro-structural properties to be considered. To achieve a high accuracy, high-fidelity full-field simulations are required. These simulations are computationally very expensive, and any single analysis could potentially take days to finish. A solution for this issue is to develop surrogate models using artificial neural networks. However, generating a high-fidelity data set requires a huge amount of time. To solve this problem, we used transfer learning technique, a limited amount of high-fidelity full-field simulations, together with a previously developed recurrent neural network model trained on low-fidelity mean-field data. The new RNN model has a very high accuracy (in comparison with full-field simulations) and is remarkably efficient. This model can be used not only for highly efficient modeling purposes, but also for designing new short fiber composites.
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| 7. |
- Wiberg, Viktor, 1988-, et al.
(författare)
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Sim-to-real transfer of active suspension control using deep reinforcement learning
- 2024
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Ingår i: Robotics and Autonomous Systems. - : Elsevier. - 0921-8890 .- 1872-793X. ; 179
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Tidskriftsartikel (refereegranskat)abstract
- We explore sim-to-real transfer of deep reinforcement learning controllers for a heavy vehicle with active suspensions designed for traversing rough terrain. While related research primarily focuses on lightweight robots with electric motors and fast actuation, this study uses a forestry vehicle with a complex hydraulic driveline and slow actuation. We simulate the vehicle using multibody dynamics and apply system identification to find an appropriate set of simulation parameters. We then train policies in simulation using various techniques to mitigate the sim-to-real gap, including domain randomization, action delays, and a reward penalty to encourage smooth control. In reality, the policies trained with action delays and a penalty for erratic actions perform nearly at the same level as in simulation. In experiments on level ground, the motion trajectories closely overlap when turning to either side, as well as in a route tracking scenario. When faced with a ramp that requires active use of the suspensions, the simulated and real motions are in close alignment. This shows that the actuator model together with system identification yields a sufficiently accurate model of the actuators. We observe that policies trained without the additional action penalty exhibit fast switching or bang–bang control. These present smooth motions and high performance in simulation but transfer poorly to reality. We find that policies make marginal use of the local height map for perception, showing no indications of predictive planning. However, the strong transfer capabilities entail that further development concerning perception and performance can be largely confined to simulation.
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| 8. |
- Alijan Farzad Lahiji, Faezeh, et al.
(författare)
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Unusual tilted growth and epitaxial relationship of NaCl B1-structured NiO and CrN on r-plane Al2O3
- 2024
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Ingår i: Journal of Applied Physics. - : American Institute of Physics Inc.. - 0021-8979 .- 1089-7550. ; 135:6
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial NiO and CrN thin films were deposited on a single-crystal Al2O3(11¯02) (r-plane sapphire) using magnetron sputtering. The two materials were intentionally deposited into two different deposition chamber designs and under different conditions (temperature, pressure, gases, and energy of sputtered particles). Despite the differences in the deposition condition and material system, both materials had the same feature with uncommon tilted epitaxial growth. Through an in-depth x-ray diffraction analysis of the NaCl (B1)-structured materials on r-plane sapphire, the full twin domain epitaxial relations were determined and can be described as (110)NaCl(B1)∥(44¯03)Al2O3 and [11¯2]NaCl(B1)∥[1¯1¯20]Al2O3. This relationship differs from the previously observed orientation of (100)NaCl(B1)∥(11¯02)Al2O3 and [100]NaCl(B1)∥[101¯0]Al2O3. These results are of general relevance for the growth of the extended NaCl (B1)-structured cubic material family onto a r-plane sapphire substrate where similar epitaxial growth can be expected.
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| 9. |
- Chanda Nagarajan, Pratheeba, 1978
(författare)
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Reduced Order Models For Exhaust AfterTreatment Systems - Coupling Modeling, Simulations and Chemometrics
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of hydrocarbon based fuels and the high temperatures generated during combustion processes are major sources of gaseous pollutants that are detrimental to human health and the environment. Emission legislation is increasingly becoming stringent to mitigate the harmful effects of emissions. Exhaust Aftertreatment systems are a group of catalytic devices that convert these harmful emissions into products like carbon dioxide and nitrogen. Space limitation in the exhaust line creates nonuniform flow in terms of flow through bends and dead volumes. This limits the performance of the EATS. The flow from the engine does not proceed uniformly to the EATS, creating a flow maldistribution at the inlet of the EATS. Consequently, velocity, temperature, and concentrations at the exit are influenced by the flow distribution at the inlet. Accurate models that capture the spatial and temporal variations of the flow distribution in EATS, specifically during cold start conditions and real driving emissions (RDE) tests, are essential to comply with stringent emission standards. 1D and 3D-computational fluid dynamics (3D-CFD) models are used to predict the conversion of species at the exit of EATS. While 1D models are robust, they lack accuracy, whereas, 3D-CFD models offer higher accuracy, but require significant computational resources. This study addresses these challenges primarily through Computational Fluid Dynamics (CFD) simulations and proposes a methodology for developing reduced-order models. Firstly, characterizing and quantifying flow distribution in EATS under transient conditions with realistic geometry is performed using non-reactive simulations. Flow uniformity index is used to characterize the extent of variation of the flow parameters in any catalyst plane. In addition to the uniformity index, contours and histograms are employed to demonstrate the non-uniform flow field. The effect of inlet pulsations on the mixed cup conversion at exit of catalyst is studied using transient reactive simulations. Four transient inlet profiles, viz., constant flowrate, sinusoidal, rectangular, and triangular pulse profiles, are chosen to describe the inlet pulsations. The results show that the fluctuations and pulsations in the incoming flow to a monolithic reactor in an aftertreatment system, affect both the transient response of the reactor as well as its time-averaged performance. The method of specifying the inlet boundary conditions also influences the solutions. A methodology for developing a reduced-order model by combining physics-based CFD solutions with multivariate data analysis methods is proposed. This method is demonstrated by combining CFD solutions of transient reactive simulations on a diesel oxidation catalyst with chemometric techniques. Performance evaluations validate the efficacy of the multi-channel model over single-channel models. Computational efforts for creating the multichannel model are comparable to single-channel models, when utilizing available CFD data and coupling chemometrics analysis. This enables rigorous control applications with improved accuracy. The methodology can be extended to real-world emissions aftertreatment systems with complex geometries. Further, predictions of species conversions in systems with flow maldistribution are made by performing steady state reactive 3D-CFD simulations and mapping the same with 1D-SCM. A pseudo-channel is envisaged that provides the same species conversion as the 3D-CFD, by formulating an objective function, which is the difference of species conversions of 3D-CFD and 1D-SCM. The error of the objective function is minimized by iteratively varying the velocity that will provide the same conversion in a 1D-SCM. The pseudo-channel model outputs agree closely with the CFD results in various steady-state and transient test cases. Detached eddy simulations were carried out under nonreactive conditions on the geometry with bends to confirm the validity of RANS simulations, as RANS simulations are computationally more effective than DES. Flow uniformity indices were of the same order in both cases, however, DES showed fluctuations. This thesis aims at developing reduced order models combining CFD simulations and regression and chemometric techniques. It also highlights the limitations of a single channel model in a realistic geometry case. The thesis also attempts to predict species conversion of transient reactive simulations, from the solution of steady state reactive simulations, as the former is computationally more expensive than the latter. The developed pseudo-channel model and multi-channel model can be used for realtime monitoring and control applications. These two methodologies require a computational load comparable to that of 1D models. Validation of these models using EATS experiments under transient conditions is recommended for future research.
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| 10. |
- Wallbaum, Holger, 1967, et al.
(författare)
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Lessons learnt from a regional workshop to develop a transformational plan for the built and urban environment to meet the UNSDGs in 2030
- 2024
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Ingår i: IOP Conference Series: Earth and Environmental Science. - 1755-1307 .- 1755-1315. ; 1363:1
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Konferensbidrag (refereegranskat)abstract
- Urgent transformational change and action within the built environment is needed as it accounts for a large proportion of CO2 emissions and is rapidly growing. A partnership with UN Habitat and Mistra, the Swedish foundation for strategic environmental research, was established to lead a high-level expert workshop for Northwest Europe to develop transformative roadmaps to lead us from current practice to a built and urban environment scenario where the 2030 UNSDGs are achieved. The workshop, aiming to act as a pilot for similar workshops to be held in other parts of the world, was organized around four worksheet sessions that guided the participants through a co-creative process to share and draw on their expertise generating and iteratively narrowing down ideas to actions. The workshop was held over 2 days with 30 participants from various countries and disciplines engaged in the built environment. A wide range of topics was identified to be focused on for action, however, 6 key themes were agreed upon as priorities: Renovation and adaptive reuse, Process and methods, Social sustainability, Nature and biodiversity, Infrastructure, and Sustainable livelihoods. The work towards realizing sustainable cities and buildings is ongoing and the pilot workshop is one step towards building collaborative capacity and facilitating regional, context-based action towards a sustainable transformation of the built environment
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