| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Pulit, S. L., et al.
(författare)
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Atrial fibrillation genetic risk differentiates cardioembolic stroke from other stroke subtypes
- 2018
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Ingår i: Neurology-Genetics. - : Ovid Technologies (Wolters Kluwer Health). - 2376-7839. ; 4:6
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Tidskriftsartikel (refereegranskat)abstract
- Objective We sought to assess whether genetic risk factors for atrial fibrillation (AF) can explain cardioembolic stroke risk. We evaluated genetic correlations between a previous genetic study of AF and AF in the presence of cardioembolic stroke using genome-wide genotypes from the Stroke Genetics Network (N = 3,190 AF cases, 3,000 cardioembolic stroke cases, and 28,026 referents). We tested whether a previously validated AF polygenic risk score (PRS) associated with cardioembolic and other stroke subtypes after accounting for AF clinical risk factors. We observed a strong correlation between previously reported genetic risk for AF, AF in the presence of stroke, and cardioembolic stroke (Pearson r = 0.77 and 0.76, respectively, across SNPs with p < 4.4 x 10(-4) in the previous AF meta-analysis). An AF PRS, adjusted for clinical AF risk factors, was associated with cardioembolic stroke (odds ratio [OR] per SD = 1.40, p = 1.45 x 10(-48)), explaining similar to 20% of the heritable component of cardioembolic stroke risk. The AF PRS was also associated with stroke of undetermined cause (OR per SD = 1.07,p = 0.004), but no other primary stroke subtypes (all p > 0.1). Genetic risk of AF is associated with cardioembolic stroke, independent of clinical risk factors. Studies are warranted to determine whether AF genetic risk can serve as a biomarker for strokes caused by AF.
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| 3. |
- Huang, Yuting, et al.
(författare)
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Host-Guest Strategy Enabling Nonhalogenated Solvent Processing for High-Performance All-Polymer Hosted Solar Cells
- 2023
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Ingår i: Chinese journal of chemistry. - : WILEY-V C H VERLAG GMBH. - 1001-604X .- 1614-7065. ; 41:9, s. 1066-1074
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Tidskriftsartikel (refereegranskat)abstract
- The power conversion efficiencies (PCEs) of all-polymer solar cells (all-PSCs), usually processed from low-boiling-point and toxic solvents, have reached high values of 18%. However, poor miscibility and uncontrollable crystallinity in polymer blends lead to a notable drop in the PCEs when using green solvents, limiting the practical development of all-PSCs. Herein, a third component (guest) BTO was employed to optimize the miscibility and enhance the crystallinity of PM6/PY2Se-F host film processed from green solvent toluene (TL), which can effectively suppress the excessive aggregation of PY2Se-F and facilitate a nano-scale interpenetrating network morphology for exciton dissociation and charge transport. As a result, TL-processed all-polymer hosted solar cells (all-PHSCs) exhibited an impressive PCE of 17.01%. Moreover, the strong molecular interaction between the host and guest molecules also enhances the thermal stability of the devices. Our host-guest strategy provides a unique approach to developing high-efficiency and stable all-PHSCs processed from green solvents, paving the way for the industrial development of all-PHSCs.
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| 4. |
- Liu, Y., et al.
(författare)
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Amorphous and nanocrystalline Al82Ni10Y8 alloy powder prepared by gas atomization
- 2005
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Ingår i: Intermetallics. - : Elsevier BV. - 0966-9795. ; 13:3-4, s. 393-398
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Tidskriftsartikel (refereegranskat)abstract
- An Al-10Ni-8Y (at.%) alloy was atomized by Ar gas and the morphology, microstructure, thermal stability, phase composition and microhardness of the as-atomized powder were investigated. Most of the powders are spherical in shape, but the surface morphology was different for powder of different size. The cross-section microstructure of powder with size below 15 Pro in diameter showed no detailed feature, indicating existence of amorphous phase or nanocrystalline structure. The as-atomized powder showed four distinct exothermic peaks when heated at 296, 340, 366 and 456 degrees C. The glass transition temperature T-g, crystallization temperature T-x, and the temperature interval of the supercooled liquid region Delta T-x(=T-x-T-g) were detected to be about 266, 288 and 22 degrees C. The Al82Ni10Y8 alloy powder exhibits a high Vickers hardness of 230.6, and shows great potential for structural application. (c) 2004 Elsevier Ltd. All rights reserved.
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| 5. |
- Liu, Y., et al.
(författare)
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Microstructural evolution of Al-Ni-Y powders an with different sizes
- 2005
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Ingår i: Zeitschrift fuer Metallkunde/Materials Research and Advanced Techniques. - 0044-3093. ; 96:1, s. 83-88
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Tidskriftsartikel (refereegranskat)abstract
- An Al-10Ni-8Y (at.%) alloy was atomized by Ar gas atomization in a close-coupled nozzle atomizer. The microstructure, phase composition, and thermal stability of the as-atomized powder were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis and differential scanning calorimetry. Activation energies for different crystallization reactions were calculated using both Kissinger and Ozawa methods. The supercooled liquid region DeltaT(x) (= T(x) - T(g), where T(x) and T(g) are crystallization onset temperature and glass transition temperature, respectively) was detected to be in the range of 14-24 K. Also presented were attempts to determine the critical particle size for amorphous structure.
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| 6. |
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| 7. |
- Wang, Fang, et al.
(författare)
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Emerging contaminants: A One Health perspective
- 2024
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Ingår i: Innovation. - 2666-6758. ; 5
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Forskningsöversikt (refereegranskat)abstract
- Environmental pollution is escalating due to rapid global development that often prioritizes human needs over planetary health. Despite global efforts to mitigate legacy pollutants, the continuous introduction of new substances remains a major threat to both people and the planet. In response, global initiatives are focusing on risk assessment and regulation of emerging contaminants, as demonstrated by the ongoing efforts to establish the UN's Intergovernmental Science-Policy Panel on Chemicals, Waste, and Pollution Prevention. This review identifies the sources and impacts of emerging contaminants on planetary health, emphasizing the importance of adopting a One Health approach. Strategies for monitoring and addressing these pollutants are discussed, underscoring the need for robust and socially equitable environmental policies at both regional and international levels. Urgent actions are needed to transition toward sustainable pollution management practices to safeguard our planet for future generations.
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| 8. |
- Zhang, Bin, et al.
(författare)
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Band structure of wurtzite GaBiAs nanowires
- 2019
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19, s. 6454-6460
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first successful growth of wurtzite (WZ) GaBiAs nanowires (NWs) and reveal the effects of Bi incorporation on the electronic band structure by using polarization-resolved optical spectroscopies performed on individual NWs. Experimental evidence of a decrease in the band-gap energy and an upward shift of the topmost three valence subbands upon the incorporation of Bi atoms is provided, whereas the symmetry and ordering of the valence band states remain unchanged, that is, Γ9, Γ7, and Γ7 within the current range of Bi compositions. The extraordinary valence band structure of WZ GaBiAs NWs is explained by anisotropic hybridization and anticrossing between p-like Bi states and the extended valence band states of host WZ GaAs. Moreover, the incorporation of Bi into GaAs is found to significantly reduce the temperature sensitivity of the band-gap energy in WZ GaBiAs NWs. Our work therefore demonstrates that utilizing dilute bismide alloys provides new avenues for band-gap engineering and thus photonic engineering with NWs.
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| 9. |
- Chen, W., et al.
(författare)
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Revealing the Position Effect of an Alkylthio Side Chain in Phenyl-Substituted Benzodithiophene-Based Donor Polymers on the Photovoltaic Performance of Non-Fullerene Organic Solar Cells
- 2019
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 11:36, s. 33173-33178
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Tidskriftsartikel (refereegranskat)abstract
- In this work, position effects of an alkylthio side chain were investigated by designing and synthesizing two copolymers based on a phenyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTP) and difluorobenzotriazole (FTAZ). The polymer based on the meta-position-alkylthiolated BDTP, named m-PBDTPS-FTAZ, showed a relatively broader bandgap (2.00 vs 1.96 eV) and lower highest occupied molecular orbital (HOMO) energy level (-5.40 vs-5.32 eV) than its para-positioned structural isomeric analogue polymer (named p-PBDTPS-FTAZ), that is, m- A nd p-PBDTPS-FTAZ with the side chain structured as ethylhexyl-in the phenyl unit and hexyldecyl-in the FTAZ moiety. When blended with ITIC, m-PBDTPS-FTAZ showed a comparable crystallinity but more uniform morphology compared to that of p-PBDTPS-FTAZ. A high power conversion efficiency of 13.16% was achieved for m-PBDTPS-FTAZ:ITIC devices with a high open circuit voltage (VOC) of 0.95 V, which is higher than that of p-PBDTPS-FTAZ:ITIC devices (10.86%) with a VOC of 0.89 V. Therefore, m-BDTPS could be an effective donor unit to construct high-efficiency polymers due to its effectively decreased HOMO energy level of polymers while still maintaining good molecular stacking.
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| 10. |
- Hu, Q., et al.
(författare)
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Anomalous thermal expansion in the deep super-cooled liquid region of a ZrCuAlAg bulk metallic glass
- 2018
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Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 6:2, s. 121-129
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Tidskriftsartikel (refereegranskat)abstract
- Bulk metallic glasses (BMGs), like other glasses, soften in the super-cooled liquid region (SCLR). Here in this work, surprisingly, a large expansion is reported occurring in the deep SCLR of a Zr 47 Cu 37 Al 8 Ag 8 BMG. Nano-crystals (NCs) are found precipitated during the anomalous expansion of Zr 47 Cu 37 Al 8 Ag 8 , but also in the SCLR of Zr 43 Cu 41 Al 8 Ag 8 that exhibits a conventional softening. It is found that there is a steep composition and density change at the NCs/amorphous matrix transition region in the former alloy, and this transition region exerts a thermal stress of about 0.15 MPa to the surrounding super-cooled liquid (SCL) and drives the soft SCL to expand severely. (Figure presented) IMPACT STATEMENT An anomalous expansion, and particularly a large expansion instead of softening, is reported occurring in the deep SCLR of a Zr-based bulk metallic glass for the first time.
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| 11. |
- Huang, Chen, 1981, et al.
(författare)
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A Chemical Model of Gasoline/Ethanol Blends
- 2009
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Ingår i: The First Joint Meeting of the Scandinavian-Nordic and French Sections of the Combustion Institute, Copenhagen, November 9-10, 2009. ; , s. 2-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 12. |
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| 13. |
- Huang, Chen, 1981, et al.
(författare)
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A Numerical Study on Stratified Turbulent Combustion in a Direct-Injection Spark-Ignition Gasoline Engine Using an Open-Source Code
- 2014
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 1
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, a free, open source CFD software package called OpenFOAM has been attracting increasing amounts of attention as a promising, inexpensive, and efficient CFD tool for the numerical simulation of processes such as fuel injection and evaporation, turbulent mixing and burning. Here, we describe the further development of OpenFOAM to enable its use in simulating stratified turbulent combustion in DI SI engines. Advanced models of various phenomena relevant to partially premixed turbulent flames were implemented into the code, and the effects of these implementations were investigated by performing unsteady 3D RANS simulations of stratified turbulent burning in a DI SI engine. First, the Flame Speed Closure (FSC) model of premixed turbulent combustion was implemented. Second, a method for evaluating the mean density in premixed turbulent flames that is available in the standard OpenFOAM library was improved. Third, a semi-detailed chemical mechanism was introduced to describe the influence of the equivalence ratio, pressure, and temperature of the unburned gas on the burning rate and flame temperature. The flame temperature and laminar flame speed are computed, approximated and further implemented into the OpenFOAM library. Fourth, to address the influence of turbulent fluctuations in mixture composition on mean variables, a presumed Favre beta-PDF for the mixture fraction was implemented. Fifth, the implementation of the balance equation for mixture fraction variance was improved with the consideration for the evaporation source term. Finally, the mean burning rates computed with and without the aforementioned models were compared to assess the importance of the studied effects.
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| 14. |
- Huang, Chen, 1981, et al.
(författare)
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A Semi-Detailed Chemical Mechanism of Combustion of Gasoline-Ethanol Blends
- 2010
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Ingår i: 33nd International Symposium on Combustion, Tsinghua University, Beijing, China, August 1-6, 2010. Abstracts of Work-in-Progress Poster Presentations. The Combustion Institute, Pittsburgh, 2010. File W4P014.pdf on Flash Disk..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 15. |
- Huang, Chen, 1981, et al.
(författare)
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A Study of Two Basic Issues Relevant to RANS Simulations of Stratified Turbulent Combustion in a Spray-Guided Direct-Injection Spark-Ignition Engine
- 2014
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2014-October
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Tidskriftsartikel (refereegranskat)abstract
- A Spray-Guided (SG) Direct-Injection (DI) Spark-Ignition (SI) engine is widely recognized to be a promising technology capable for substantially reducing fuel consumption and carbon dioxide emissions. Accordingly, there is a strong need for developing models of some effects specific to stratified turbulent burning under conditions of elevated and rapidly varying pressure. Two such effects were addressed in the present work by performing unsteady three-dimensional URANS simulations of stratified turbulent combustion in a SG DISI engine. First, a simple method of evaluation equilibrium combustion temperature, implemented into the CFD code OpenFOAM ® , was improved in order to take into account the dissociation of the combustion products. Second, stratified turbulent combustion is affected by fluctuations in mixture composition. A widely used approach to modeling this effect consists of invoking a presumed Probability Density Function (PDF) for mixture fraction f . Because parameters of this PDF are determined using the first and second Favre moments of the mixture fraction field, the PDF is density-weighted. However, the canonical PDF P f is required to average certain important combustion characteristics that are straightforwardly relevant to local burning rate e.g. the laminar flame speed or the product density. In the present work, the relation between the Favre and canonical PDFs was investigated under conditions associated with burning in a SG DISI engine. Finally, the stratified turbulent combustion model which invo
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| 16. |
- Huang, Chen, 1981, et al.
(författare)
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Application of Flame Speed Closure Model to RANS Simulations of Stratified Turbulent Combustion in a Gasoline Direct-Injection Spark-Ignition Engine
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 188:1, s. 98-131
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Taylor & Francis. The present work aims at development and validation of a tool for numerically modeling stratified turbulent combustion in a gasoline direct injection (GDI) engine. For this purpose, an open source code called OpenFOAM ® , which has been attracting growing interests from both industries and academies due to an opportunity to access the source code and to test new models without paying license fees, is further developed by implementing advanced models relevant to stratified turbulent burning. In particular, first, the Flame Speed Closure model of premixed turbulent combustion is implemented in order to simulate flame propagation through inhomogeneously premixed reactants. Second, a newly calculated approximation of the laminar flame speed of gasoline-air mixtures as a function of the equivalence ratio, pressure, and temperature is implemented in order to simulate dependence of burning rate on the local mixture composition. Third, a newly calculated approximation of the combustion temperature of gasoline-air mixtures as a function of the equivalence ratio, pressure, and product enthalpy is implemented in order to allow for dissociation of combustion products and heat losses. Fourth, a presumed mixture-fraction probability density function (PDF) approach is implemented in order to simulate the influence of turbulent fluctuations in the mixture fraction on the local burning rate. In addition to commonly used mass-weighted mixture-fraction PDF, a more consistent model that deals also with the canonical mixture-fraction PDF is developed and the two approaches are compared. Numerical results that show the influence of the aforementioned implementations on computed global characteristics of stratified combustion in a research GDI engine are discussed. The developed numerical tool is quantitatively validated by comparing computed pressure traces in the GDI engine with experimental data obtained in three different cases associated with two different loads, late injection timings, and short time intervals between the injection and spark ignition.
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| 17. |
- Huang, Chen, 1981, et al.
(författare)
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Chemical model of gasoline-ethanol blends for internal combustion engine applications
- 2010
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- A semi-detailed chemical mechanism for combustion of gasoline-ethanol blends, which is based on sub-mechanisms of gasoline surrogate and for ethanol is developed and validated aiming at CFD engine modeling. The gasoline surrogate is composed of iso-octane, toluene, and n-heptane in volumetric proportions of 55%:35%:10%, respectively. In this way, the hydrogen-carbon atomic ratio H/C, which is around 1.87 for real gasoline, is accurately reproduced as well as a mixture equivalence ratio that is important for Gasoline Direct Injection engine applications. The integrated mechanism for gasoline-ethanol blends includes 120 species participating in 677 reactions. The mechanism is tested against experimental data on ignition delay times and laminar flame speeds, obtained for various n-heptane/iso-octane/toluene/ethanol-air mixtures under various equivalence ratios, initial temperatures, and pressures. Chemical, thermodynamic and transport properties used in the calculations are discussed.
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| 18. |
- Huang, Chen, 1981
(författare)
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Combustion Modelling
- 2011
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- The development and introduction of new engine technologies are primarily motivated by the need to comply with increasingly stringent emissions legislation and to reduce fuel consumption. One of the most important of these new engine technologies is Gasoline Direct Injection (GDI), which is considered to be an important and cost-effective measure to meet both targets. Computational Fluid Dynamics (CFD) simulations and optical methods are important tools in the development of direct injection gasoline engines. The aim of this work was to develop models, methods, and a numerical platform for simulating the behavior of GDI engines using a variety of fuels, including gasoline-ethanol blends. One of the most important goals of this work was to devise improvements to OpenFOAM (a free, open source CFD package) that would increase its utility as a tool for studying GDI engines, as there is strong industrial demand for inexpensive software. This book addressed two important problems relevant to modelling combustion in a GDI engine, including combustion chemistry and spray modelling.
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| 19. |
- Huang, Chen, 1981, et al.
(författare)
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Comparison of presumed PDF models of turbulent flames
- 2012
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Ingår i: Journal of Combustion. - : Hindawi Limited. - 2090-1976 .- 2090-1968. ; 2012:564621, s. 15-
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Tidskriftsartikel (refereegranskat)abstract
- Over the past years, the use of a presumed probability density function (PDF) for combustion progress variable or/and mixture fraction has been becoming more and more popular approach to average reaction rates in premixed and partially premixed turbulent flames. Commonly invoked for this purpose is a beta-function PDF or a combination of Dirac delta functions, with the parameters of the two PDFs being determined based on the values of their first and second moments computed by integrating proper balance equations. Because the choice of any of the above PDFs appears to be totally arbitrary as far as underlying physics of turbulent combustion is concerned, the use of such PDFs implies weak sensitivity of the key averaged quantities to the PDF shape. The present work is aimed at testing this implicit assumption by comparing mean heat release rates, burning velocities, and so forth, averaged by invoking the aforementioned PDFs, with all other things being equal. Results calculated in the premixed case show substantial sensitivity of the mean heat release rate to the shape of presumed combustion-progress-variable PDF, thus, putting the approach into question. To the contrary, the use of a presumed mixture-fraction PDF appears to be a sufficiently reasonable simplification for modeling the influence of fluctuations in the mixture fraction on the mean burning velocity provided that the mixture composition varies within flammability limits.
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| 20. |
- Huang, Chen, 1981, et al.
(författare)
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Gasoline Direct Injection - Simulations and Experiments
- 2011
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Ingår i: ILASS2011. The 24th European Conference on Liquid Atomization and Spray Systems, Estoril, Portugal, September, 5-7, 2011. ; , s. 4 pagews-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 21. |
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| 22. |
- Huang, Chen, 1981, et al.
(författare)
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Modelling of Gasoline and Ethanol Hollow-Cone Sprays Using OpenFOAM
- 2011
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Ingår i: 2011 JSAE/SAE International Powertrains, Fuels & Lubricants, Aug. 30 - Sep. 2, 2011, Kyoto, Japan. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Konferensbidrag (refereegranskat)abstract
- Over the past few years, an open-source code calledOpenFOAM has been becoming a promising CFD toolfor multi-dimensional numerical simulations of internalcombustion engines. The primary goal of the presentstudy is to assess the feasibility of the code forcomputations of hollow-cone sprays discharged by anoutward-opening pintle-type injector by simulating theexperiments performed recently by Hemdal et al.(SAE 2009-01-1496) with gasoline and ethanolsprays under the following conditions: air temperatureTair=295 or 350 K, air pressure pair=6 bar, fueltemperature Tfuel=243, or 295, or 320 K, and fuelinjection pressure pinj=50, or 125, or 200 bar. Tosimulate the experiments, a pintle injector model andthe physical properties of gasoline were implementedin OpenFOAM. The flow field calculated using thepintle injector model is more realistic than that yieldedby the default unit injector model normally used inOpenFOAM. Moreover, a number of modificationswere made to the standard implementation of severalspray models in OpenFOAM, with modifications in theimplementation of the KHRT model having noticeableeffects on the accuracy of the simulated liquidpenetration and Sauter mean diameter (SMD).Results of numerous simulations performed byrunning OpenFOAM and activating various spraymodels indicate that (i) a combination of theRosin-Rammler distribution with Reitz-Diwakarsecondary breakup model and (ii) the KHRT modelyield the best agreement between the measured andcomputed spray penetration length, with the lattermodel showing the best performance as far as theSMD obtained from high-pressure (200 bar) sprays isconcerned.
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| 23. |
- Huang, Chen, 1981, et al.
(författare)
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Numerical and Experimental Study of Stratified Turbulent Combustion in a Spray-Guided Gasoline Direct Injection Engine
- 2015
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Ingår i: Lecture Notes in Mobility. - Cham : Springer International Publishing. - 2196-5544 .- 2196-5552. - 9783319179988 ; , s. 77-84
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Direct Injection (DI) of gasoline into cylinder of a Spark Ignition (SI) engine is widely recognized to be a promising technology capable for significantly reducing fuel consumption and carbon dioxide emissions as compared to a port-fuel injection SI engine. In particular, spray-guided (SG) GDI combustion systems allow for further improvement in fuel efficiency. Moreover, efficient CFD tools fornumerical simulations of spray and combustion processes have been becoming increasingly important in engine development. In previous papers, a so-called FlameSpeed Closure (FSC) model was implemented into an open source code OpenFOAM® with the capability of addressing important phenomena in SG GDI engines, e.g. fluctuations in mixture composition and the proper evaluation of combustion temperature for the products. In this paper, the aforementioned FSC model is applied to investigate the stratified turbulent combustion in a SG GDI enginein the frame work of unsteady 3D Reynolds-Averaged Navier–Stokes (RANS) simulations. The computed results are compared with the measured pressure traces obtained in the same research group for both low and medium load conditions.Further on, the calculated Reynolds-averaged progress variable is compared to the experimentally observed images.
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| 24. |
- Huang, Chen, 1981
(författare)
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Numerical Modelling of Fuel Injection and Stratified Turbulent Combustion in a Direct-Injection Spark-Ignition Engine Using an Open Source Code
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stringent regulations on the emission of pollutants, especially carbon dioxide (CO2), necessitate the development of advanced combustion technologies. Gasoline direct injection (GDI) into the combustion chamber of a Spark Ignition (SI) engine is a combustion strategy that is widely recognized as having the potential to improve fuel efficiency of internal combustion engines for passenger cars. In particular, the CO2 emissions of GDI engines could be 20-26% lower than those of equivalent port-fuel injected (PFI) SI engines. Unfortunately, the development of combustion systems for GDI engines is very challenging because the creation of an appropriate combustion system is a major challenge because they require very precise formation of an ignitable fuel-air mixture with a steep stratification gradient right between the ignition electrodes to permit efficient operation under a wide range of operating conditions.CFD simulations are widely used to increase the efficiency of engine R&D. This thesis aimed at development of a tool for numerically modelling of working process in a GDI engine. The work had two main objectives. First, an available CFD code should be applied to multidimensional GDI engine simulations. Second, the code should be developed by implementing advanced models of stratified turbulent combustion, followed by validation against experimental data.As far as a code is concerned, although there are several mature commercial CFD packages on the market, there is also a need for less expensive software. Consequently, there is growing interests from both industry and academia in the OpenFOAM open source CFD code, whose source code is freely available so that users can implement and test new models without paying licence fees. However, it had not been used to simulate combustion in a GDI engine when the work reported herein was begun. This thesis presents an assessment of OpenFOAM as a tool for the numerically modelling of fuel injection, spray breakup, evaporation, mixture formation, and stratified turbulent burning in the combustion chamber of a GDI engine.OpenFOAM was used to simulate hollow-cone sprays of gasoline and ethanol discharged by a piezo-controlled pintle-type injector. The liquid properties of gasoline were implemented in the code to enable the simulation of gasoline sprays. In addition, the implementations of various spray breakup models such as LISA, TAB, Reitz-Diwakar, and KHRT into the standard OpenFOAM package were checked and modified in order to more closely reflect their descriptions in the original papers. Liquid penetration and SMD calculated by simulations using the revised model implementations were compared to experimental data provided by my colleagues. These comparisons showed that the best agreement between the experimental data and simulations was achieved when using a combination of the uniform droplet size and KHRT models. This model was therefore used in all subsequent engine simulations.As far as modelling is concerned, the code’s modelling capabilities were enhanced by implementing and developing models relevant to the turbulent burning of stratified gasoline-air mixtures at the elevated temperatures and pressures associated with combustion in a GDI engine. More specifically, two relevant issues were addressed.First, a semi-detailed chemical mechanism for the combustion of a gasoline surrogate in air was developed and validated. The gasoline surrogate consisted of iso-octane, toluene, and n-heptane in volumetric proportions of 55%:35%:10%, respectively. The mechanism includes 120 species participating in 677 reactions. It was validated against experimental data on the ignition delay times and laminar flame speeds of different mixtures at a range of pressures and temperatures. The mechanism was then used to compute laminar flame speeds for gasoline-air mixtures at equivalence ratios of 0.2≤ϕ≤2.0, unburned gas temperatures of 298≤T_u≤800K, and pressures of 1≤P≤30 atm. The results of these calculations were approximated and the approximations were implemented into OpenFOAM for subsequent CFD modelling of stratified turbulent combustion in a GDI engine.In order to study stratified burning in a GDI engine, the Flame Speed Closure (FSC) model of premixed turbulent combustion was combined with a so-called presumed Probability Density Function (PDF) method that made it possible to account for the influence of turbulent fluctuations in local mixture composition on the local burning rate. The combined model based on the FSC and presumed PDF approach was implemented into OpenFOAM and the roles played by its various submodels were investigated in a step-wise fashion. Finally, the so-extended code was used to simulate a GDI engine burning a globally lean mixture. Good agreement between results computed by me and experimental data provided by my colleagues was obtained. In addition, the model’s sensitivity was investigated.
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| 25. |
- Huang, Chen, 1981
(författare)
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Simulation of Combustion and Mixture Formation for Gasoline Direct Injection Engine Application
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development and introduction of new engine technologies are primarily motivated by the need to comply with increasingly stringent emissions legislation and to reduce fuel consumption. One of the most important of these new engine technologies is direct gasoline injection, which is considered to be an important and cost-effective measure to meet both targets. Computational Fluid Dynamics (CFD) simulations and optical methods are important tools in the development of direct injection gasoline engines. The aim of the work described in this thesis was to develop models, methods, and a numerical platform for simulating the behavior of Direct Injection Spark Ignition (DISI) engines using a variety of fuels, including gasoline-ethanol blends. One of the most important goals of this work was to devise improvements to OpenFOAM (a free, open source CFD package) that would increase its utility as a tool for studying SIDI engines, as there is strong industrial demand for inexpensive software. The work described in this thesis addressed two important problems relevant to modeling combustion in a DISI engine. First, to facilitate the simulation of turbulent burning and pollutant formation, a chemical mechanism for the combustion of gasoline-ethanol blends was refined and thoroughly validated under various conditions (equivalence ratios Φ, initial temperatures Tu, and pressures p). The gasoline surrogate used in this project was composed of iso-octane, toluene, and n-heptane in volumetric ratios of 55%:35%:10%, respectively. The hydrogen to carbon ratio (the H/C ratio) of this blend is similar to that of gasoline, which is around 1.87, as is its equivalence ratio; this is particularly important when studying DISI engines. The integrated mechanism for gasoline-ethanol blends features 120 species participating in 677 reactions and is suitable for use in CFD engine modeling. The mechanism was tested against experimental data on ignition delay times and laminar flame speeds, obtained for various n-heptane/iso-octane/toluene/ethanol-air mixtures under various equivalence ratios, initial temperatures, and pressures. Second, the gasoline and ethanol hollow cone sprays released by an outward-opening pintle-type piezo-controlled injector commonly associated with GDI engines were studied numerically, since accurate simulation of fuel-air mixing and the flow field is critical for subsequent combustion modeling. A pintle injector model was implemented into OpenFOAM in order to simulate the spray discharged by an outward-opening piezo injector. The flow field calculated using the pintle injector model is more realistic than that predicted by the default unit injector model normally used in OpenFOAM. A number of modifications were made to the standard spray submodels in OpenFOAM, including the LISA, TAB and Reitz-KHRT breakup models and the O'Rourke and Trajectory collision models. For instance, three different modified Reitz-KHRT models were implemented into OpenFOAM; these modifications were found to have noticeable effects on the accuracy of the simulated liquid penetration and SMD. Extensive sensitivity studies were carried out on the hollow cone sprays, focusing on the effects of varying the initial and boundary conditions, spray model constants, and other parameters. Validation studies showed that several combinations of spray submodels yield acceptable results in liquid penetration and SMD, including the combination of the Rosin-Rammler + Reitz-Diwakar models and that of the uniform droplet size + Reitz-KHRT models; the latter combination offered the best performance under the studied conditions.
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| 26. |
- Huang, Chen, 1981, et al.
(författare)
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Vented dust explosions: comparing experiments, simulations and standards
- 2022
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Ingår i: 10th International Seminar on Fire and Explosion Hazards. - 9788272067211 ; , s. 1-9
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Konferensbidrag (refereegranskat)abstract
- A vented corn starch dust explosion in an 11.5 m3 vessel is studied by comparing experiments, simulations and the standards. The reduced explosion overpressure inside the vessel is recorded using two pressure sensors installed on the inner wall of the vessel. 3D Unsteady Reynolds-Averaged Navier-Stokes simulations of the experiment are performed using the Flame Speed Closure (FSC) model and its extended version. The FSC model predicts the influence of turbulence on premixed combustion, and the extended version allows for self-acceleration of a large-scale flame kernel, which is associated with the combustion-induced thermal expansion effect. Such an extension is highly relevant to large-scale industrial application. The explosion overpressure-time trace computed using the extended FSC model agrees reasonably well with the experimental data. Furthermore, the effect of vent size and ignition location on the explosion overpressure is studied by comparing the simulation results and the standards. The developed numerical tool and model is especially useful for scenarios, which are not addressed in the standards, and it deserves further study in simulations of other large-scales dust or gaseous explosions together with comparison with experiments.
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| 27. |
- Kanyolo, Godwill Mbiti, et al.
(författare)
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Honeycomb layered oxides: Structure, energy storage, transport, topology and relevant insights
- 2021
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Ingår i: Chemical Society Reviews. - : Royal Society of Chemistry (RSC). - 1460-4744 .- 0306-0012. ; 50:6, s. 3990-4030
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Forskningsöversikt (refereegranskat)abstract
- The advent of nanotechnology has hurtled the discovery and development of nanostructured materials with stellar chemical and physical functionalities in a bid to address issues in energy, environment, telecommunications and healthcare. In this quest, a class of two-dimensional layered materials consisting of alkali or coinage metal atoms sandwiched between slabs exclusively made of transition metal and chalcogen (or pnictogen) atoms arranged in a honeycomb fashion have emerged as materials exhibiting fascinatingly rich crystal chemistry, high-voltage electrochemistry, fast cation diffusion besides playing host to varied exotic electromagnetic and topological phenomena. Currently, with a niche application in energy storage as high-voltage materials, this class of honeycomb layered oxides serves as ideal pedagogical exemplars of the innumerable capabilities of nanomaterials drawing immense interest in multiple fields ranging from materials science, solid-state chemistry, electrochemistry and condensed matter physics. In this review, we delineate the relevant chemistry and physics of honeycomb layered oxides, and discuss their functionalities for tunable electrochemistry, superfast ionic conduction, electromagnetism and topology. Moreover, we elucidate the unexplored albeit vastly promising crystal chemistry space whilst outlining effective ways to identify regions within this compositional space, particularly where interesting electromagnetic and topological properties could be lurking within the aforementioned alkali and coinage-metal honeycomb layered oxide structures. We conclude by pointing towards possible future research directions, particularly the prospective realisation of Kitaev-Heisenberg-Dzyaloshinskii-Moriya interactions with single crystals and Floquet theory in closely-related honeycomb layered oxide materials. This journal is
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| 28. |
- Liang, Rong-Hao, et al.
(författare)
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Demo Hour
- 2014
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Ingår i: interactions. - : ACM. - 1072-5520 .- 1558-3449. ; 21:5, s. 6-9
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Tidskriftsartikel (refereegranskat)abstract
- Interactivity is a unique forum of the ACM CHI Conference that showcases hands-on demonstrations, novel interactive technologies, and artistic installations. At CHI 2014, we aimed to create a "one of a CHInd" Interactivity experience with more than 60 interactive exhibits to highlight the diverse group of computer scientists, sociologists, designers, psychologists, artists, and many more that make up the CHI community. Julie Rico Williamson and Steven Benford, CHI Interactivity Chairs
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| 29. |
- Lipatnikov, Andrei, 1961, et al.
(författare)
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A Semi-Detailed Chemical Mechanism for Gasoline: Further Validation Against Experimental Data on Laminar flame Speeds of Gasoline/O2/N2 and n-Heptane/iso-Octane/Air Mixtures
- 2012
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Ingår i: 34th International Symposium on Combustion, Warsawe University of Technology, Warsaw, Poland, 29 Jule - 3 August 2012. Abstracts of Work-in-Progress Poster Presentations. The Combustion Institute, Pittsburgh, 2012. File W5P079.pdf on Flash Disk. ; , s. 1-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 30. |
- Lipatnikov, Andrei, 1961, et al.
(författare)
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A Simple Test of Presumed PDF Approach to Modeling Premixed Turbulent Flames
- 2012
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Ingår i: 34th International Symposium on Combustion, Warsawe University of Technology, Warsaw, Poland, 29 Jule - 3 August 2012. Abstracts of Work-in-Progress Poster Presentations. The Combustion Institute, Pittsburgh, 2012. File W4P082.pdf on Flash Disk..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 31. |
- Lipatnikov, Andrei, 1961, et al.
(författare)
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Modelling of the influence of mixture fraction fluctuations on burning rate in partially premixed turbulent flames
- 2015
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 187:4, s. 594-626
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Tidskriftsartikel (refereegranskat)abstract
- A common approach to modeling the influence of turbulent fluctuations in the mixture fraction f on the burning rate in a partially premixed flame consists of invoking a presumed Favre (mass-weighted) probability density function (PDF) . In the present work, two issues relevant to such an approach are addressed. First, averaging of a dependence q(f), where q is an arbitrary quantity, e.g., the laminar flame speed SL, requires modeling of the canonical PDF P(f) if q is not proportional to the density . Second, because the shape of is not known a priori in a typical case, the presumed PDF approach can be a predictive tool only if the mean quantities are weakly sensitive to the PDF shape. To study the two issues, dependencies of and , computed for gasoline surrogate-air mixtures under elevated temperatures and pressures, associated with the conditions in a gasoline direct injection spark ignition engine, are averaged invoking either beta function or double-Dirac delta function Favre or canonical PDFs. Moreover, a simpler approach is proposed to evaluate . The approach consists of expanding in Taylor series with respect to , followed by averaging. The mean quantities and obtained for various Favre first and second moments using the aforementioned alternative methods are compared with each other and with and , respectively. The following conclusions are drawn. First, when averaging under conditions of the present study, the difference between the Favre and canonical beta-function PDFs may be disregarded for simplicity. Second, is sensitive to the shape of presumed PDF if the magnitude of turbulent fluctuations in the mixture fraction is sufficiently large. Third, if the magnitude of turbulent fluctuations in the mixture fraction is sufficiently low in order for the mean laminar flame speeds obtained invoking the beta-function and double-Dirac delta-function PDFs to be approximately equal to one another, then, can also be evaluated using the Taylor-expansion approach.
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| 32. |
- Ouyang, D. L., et al.
(författare)
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Influence of casting temperature on the castability and glass-forming ability of Zr-based bulk metallic glasses
- 2023
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093. ; 603
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Tidskriftsartikel (refereegranskat)abstract
- Both castability and glass-forming ability (GFA) are crucial for die-casting of Zr-based bulk metallic glass (BMG) components. In this work, a simple method is used to quantify the castability required for casting two SIM card slots with different designs, and to quantify the castability at different casting temperatures. It is found that the Zr55Cu30Ni5Al10 (Zr55) BMG has a wider optimal casting temperature region (in which glassy rods with a diameter of at least 5 mm can be formed) than that of Zr52.5Cu25Ni9.5Al7Ti6 (Zr52.5), which is consistent of the better GFA of the Zr55. In the optimal casting temperature region, however, the castability of Zr52.5 is significantly better than that of Zr55, because Zr52.5 has a lower melting point, a poorer wettability to the copper mold, and a higher optimal casting temperature. These results are helpful to guide the production of Zr-based BMG components.
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| 33. |
- Parmar, Priyanka, et al.
(författare)
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Association of maternal prenatal smoking GFI1-locus and cardiometabolic phenotypes in 18,212 adults
- 2018
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Ingår i: EBioMedicine. - : Elsevier BV. - 2352-3964. ; 38, s. 206-216
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Tidskriftsartikel (refereegranskat)abstract
- Background: DNA methylation at the GFI1-locus has been repeatedly associated with exposure to smoking from the foetal period onwards. We explored whether DNA methylation may be a mechanism that links exposure to maternal prenatal smoking with offspring's adult cardio-metabolic health. Methods: We meta-analysed the association between DNA methylation at GFI1-locus with maternal prenatal smoking, adult own smoking, and cardio-metabolic phenotypes in 22 population-based studies from Europe, Australia, and USA (n= 18,212). DNA methylation at the GFI1-locus was measured in whole-blood. Multivariable regression models were fitted to examine its association with exposure to prenatal and own adult smoking. DNA methylation levels were analysed in relation to body mass index (BMI), waist circumference (WC), fasting glucose (FG), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), diastolic, and systolic blood pressure (BP). Findings: Lower DNA methylation at three out of eight GFI1-CpGs was associated with exposure to maternal prenatal smoking, whereas, all eight CpGs were associated with adult own smoking. Lower DNA methylation at cg14179389, the strongest maternal prenatal smoking locus, was associated with increased WC and BP when adjusted for sex, age, and adult smoking with Bonferroni-corrected P < 0.012. In contrast, lower DNA methylation at cg09935388, the strongest adult own smoking locus, was associated with decreased BMI, WC, and BP (adjusted 1 x 10(-7) < P < 0.01). Similarly, lower DNA methylation at cg12876356, cg18316974, cg09662411, and cg18146737 was associated with decreased BMI and WC (5 x 10(-8) < P < 0.001). Lower DNA methylation at all the CpGs was consistently associated with higher TG levels. Interpretation: Epigenetic changes at the GFI1 were linked to smoking exposure in-utero/in-adulthood and robustly associated with cardio-metabolic risk factors. Fund: European Union's Horizon 2020 research and innovation programme under grant agreement no. 633595 DynaHEALTH.
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| 34. |
- Wu, Ping-Hsun, 1982-, et al.
(författare)
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The relationship of indoxyl sulfate and p-cresyl sulfate with target cardiovascular proteins in hemodialysis patients
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Protein-bound uremic toxins (Indoxyl sulfate [IS] and p-cresyl sulfate [PCS]) are both associated with cardiovascular (CV) and all-cause mortality in subjects with chronic kidney disease (CKD). Possible mechanisms have not been elucidated. In hemodialysis patients, we investigated the relationship between the free form of IS and PCS and 181 CV-related proteins. First, IS or PCS concentrations were checked, and high levels were associated with an increased risk of acute coronary syndrome (ACS) in 333 stable HD patients. CV proteins were further quantified by a proximity extension assay. We examined associations between the free form protein-bound uremic toxins and the quantified proteins with correction for multiple testing in the discovery process. In the second step, the independent association was evaluated by multivariable-adjusted models. We rank the CV proteins related to protein-bound uremic toxins by bootstrapped confidence intervals and ascending p-value. Six proteins (signaling lymphocytic activation molecule family member 5, complement component C1q receptor, C-C motif chemokine 15 [CCL15], bleomycin hydrolase, perlecan, and cluster of differentiation 166 antigen) were negatively associated with IS. Fibroblast growth factor 23 [FGF23] was the only CV protein positively associated with IS. Three proteins (complement component C1q receptor, CCL15, and interleukin-1 receptor-like 2) were negatively associated with PCS. Similar findings were obtained after adjusting for classical CV risk factors. However, only higher levels of FGF23 was related to increased risk of ACS. In conclusion, IS and PCS were associated with several CV-related proteins involved in endothelial barrier function, complement system, cell adhesion, phosphate homeostasis, and inflammation. Multiplex proteomics seems to be a promising way to discover novel pathophysiology of the uremic toxin.
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| 35. |
- Xue, Lei, 1992, et al.
(författare)
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SOA pattern effect mitigation by neural network based pre-equalizer for 50G PON
- 2021
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 29:16, s. 24714-24722
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor optical amplifier (SOA) is widely used for power amplification in O-band, particularly for passive optical networks (PONs) which can greatly benefit its advantages of simple structure, low power consumption and integrability with photonics circuits. However, the annoying nonlinear pattern effect degrades system performance when the SOA is needed as a pre-amplifier in PONs. Conventional solutions for pattern effect mitigation are either based on optical filtering or gain clamping. They are not simple or sufficiently flexible for practical deployment. Neural network (NN) has been demonstrated for impairment compensation in optical communications thanks to its powerful nonlinear fitting ability. In this paper, for the first time, NN-based equalizer is proposed to mitigate the SOA pattern effect for 50G PON with intensity modulation and direct detection. The experimental results confirm that the NN-based equalizer can effectively mitigate the SOA nonlinear pattern effect and significantly improve the dynamic range of receiver, achieving 29-dB power budget with the FEC limit at 1e-2. Moreover, the well-trained NN model in the receiver side can be directly placed at the transmitter in the optical line terminal to pre-equalize the signal for transmission so as to simplify digital signal processing in the optical network unit.
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| 36. |
- Zhang, Xin, et al.
(författare)
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High-Performance All-Small-Molecule Organic Solar Cells Enabled by Regio-Isomerization of Noncovalently Conformational Locks
- 2022
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 32:19
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Tidskriftsartikel (refereegranskat)abstract
- The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have surpassed 19% thanks to the innovation of polymer donors and molecular acceptors. However, the batch-to-batch variations in polymer materials are detrimental to the reproducibility of the device performance. In comparison, small-molecule donors (SMDs) possess some unique advantages, such as well-defined molecular weights, easy purification, and excellent batch-to-batch repeatability. Herein, a pair of regioisomeric SMDs (BT-O1 and BT-O2) has been synthesized with alkoxy groups as S center dot center dot center dot O noncovalently conformational locks (NoCLs) at the inner and outer position, respectively. Theoretical and experimental results reveal that the regioisomeric effect has a significant influence on the light-harvest ability, energy levels, molecular geometries, internal reorganization energy, and packing behaviors for the two SMDs. As a result, BT-O2-based binary device shows an impressive PCE of 13.99%, much higher than that of BT-O1 based one (4.07%), due to the better-aligned energy level, more balanced charge transport, less charge recombination, lower energy loss, and more favorable phase separation. Furthermore, the fullerene derivative PC71BM is introduced into BT-O2:H3 as the third component to achieve a notable PCE of 15.34% (certified 14.6%). Overall, this work reveals that NoCLs is a promising strategy to achieve high-performance SMDs for all-small-molecule OSCs.
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