| 1. |
- Leffler, T., et al.
(författare)
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Development of an alkali chloride vapour-generating apparatus for calibration of ultraviolet absorption measurements
- 2017
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 88:2
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Tidskriftsartikel (refereegranskat)abstract
- A novel design of alkali chloride vapour-generating cell has been developed, which can serve as a calibration cell for quantitative ultraviolet absorption concentration measurements and meticulous spectral investigations of alkali compounds. The calibration cell was designed to provide alkali vapour of well-controlled concentrations and temperatures, and consisted of a sealed quartz cell measuring 0.4 m in length with a temperature-controlled reservoir containing solid alkali salt. The cell was placed in a furnace and the alkali vapours generated from the reservoir have direct access to the measuring chamber. Investigations of potassium chloride (KCl) were made on sublimated vapour at temperatures 650, 700, 750, 780, and 800 °C while the reservoir temperature was kept 50 °C lower to avoid condensation. The cell provides stable KCl vapour pressures, and the furnace provides a homogenous temperature profile along the cell. KCl vapour pressures are well characterised and conform the base for determination of the KCl concentration in the cell. The alkali chloride levels matched the concentration range of the absorption setup and indicated a previously employed calibration method to overestimate KCl concentrations. The KCl absorption cross sections for wavelengths λ=197.6 nm and λ=246.2 nm were calculated to be 3.4 × 10−17 and 2.9 × 10−17 cm2/molecule, respectively. The absorption cross section spectra did not show any structural differences with increasing temperature, which could indicate influence of dimers or significant changes of the population in the KCl vibrational states. The KCl absorption cross sections thus did not show any temperature dependence in the temperature region of 700-800 °C. Moreover, the applicability of the calibration cell for measurement of other alkali chlorides and hydroxides is discussed.
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| 2. |
- Leffler, Tomas, et al.
(författare)
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ON-Line alkali measurement for fuel quality control in biomass-Operated boilers
- 2016
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Ingår i: IFRF Combustion Journal. - 1562-479X. ; 2016:1, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Today's power plants are shifting their combustion toward a more complex fuel mix on the grounds of environmental impact, cost, availability and regulations. Certain new types of fuel can be classified into the following groups: herbaceous material (straw and grass), agricultural by-products (pits, shells and hulls), wood, and waste fuels. These fuels contain various amounts of alkali metals, mainly potassium and sodium, as well as chlorine and sulphur, which are easily vaporised in the combustion process and are involved in processes that cause severe slagging, fouling and high-temperature corrosion problems in the furnace and further downstream in the boiler. In this study, combustion of three different biomass fuel mixes was investigated in a circulating fluidized bed boiler. An on-line alkali-chloride monitoring instrument was used to gather valuable information for evaluating the fuel quality in terms of harmful alkali chlorides, measuring the sum of alkali chlorides (potassium chloride and sodium chloride) based on ultraviolet absorption. In addition, two batches of wood biomass fuel were compared during combustion in a full-scale powder fuel boiler. In all cases the impact of changes in fuel composition on alkali-chloride formation levels were monitored quantitatively with a time resolution in the order of seconds, allowing for analysis and countermeasures. The study concluded that the employment of an on-line alkali monitoring device to prevent alkali-chloride problems is a cost-efficient, sustainable solution that extends the operational time of the boiler and reduces its maintenance costs.
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| 3. |
- Malmqvist, E., et al.
(författare)
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CW-laser radar for combustion diagnostics
- 2016
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Ingår i: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2016. - 2162-2701. - 9781943580156 ; Part F10-LACSEA 2016
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Konferensbidrag (refereegranskat)abstract
- A CW-laser radar system developed for combustion diagnostics is described. It is based on triangulation to attain range information. Some initial results from measurements in sooting flames are shown and some future perspectives are discussed.
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| 4. |
- Wang, Sheng, et al.
(författare)
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De Novo Sequence and Copy Number Variants Are Strongly Associated with Tourette Disorder and Implicate Cell Polarity in Pathogenesis
- 2018
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Ingår i: Cell Reports. - : CELL PRESS. - 2211-1247. ; 24:13, s. 3441-
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Tidskriftsartikel (refereegranskat)abstract
- We previously established the contribution of de novo damaging sequence variants to Tourette disorder (TD) through whole-exome sequencing of 511 trios. Here, we sequence an additional 291 TD trios and analyze the combined set of 802 trios. We observe an overrepresentation of de novo damaging variants in simplex, but not multiplex, families; we identify a high-confidence TD risk gene, CELSR3 (cadherin EGF LAG seven-pass G-type receptor 3); we find that the genes mutated in TD patients are enriched for those related to cell polarity, suggesting a common pathway underlying pathobiology; and we confirm a statistically significant excess of de novo copy number variants in TD. Finally, we identify significant overlap of de novo sequence variants between TD and obsessive-compulsive disorder and de novo copy number variants between TD and autism spectrum disorder, consistent with shared genetic risk.
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| 5. |
- Weuve, Jennifer, et al.
(författare)
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Guidelines for reporting methodological challenges and evaluating potential bias in dementia research.
- 2015
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Ingår i: Alzheimer's & dementia : the journal of the Alzheimer's Association. - : Wiley. - 1552-5279. ; 11:9, s. 1098-109
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Tidskriftsartikel (refereegranskat)abstract
- Clinical and population research on dementia and related neurologic conditions, including Alzheimer's disease, faces several unique methodological challenges. Progress to identify preventive and therapeutic strategies rests on valid and rigorous analytic approaches, but the research literature reflects little consensus on "best practices." We present findings from a large scientific working group on research methods for clinical and population studies of dementia, which identified five categories of methodological challenges as follows: (1) attrition/sample selection, including selective survival; (2) measurement, including uncertainty in diagnostic criteria, measurement error in neuropsychological assessments, and practice or retest effects; (3) specification of longitudinal models when participants are followed for months, years, or even decades; (4) time-varying measurements; and (5) high-dimensional data. We explain why each challenge is important in dementia research and how it could compromise the translation of research findings into effective prevention or care strategies. We advance a checklist of potential sources of bias that should be routinely addressed when reporting dementia research.
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| 6. |
- Brackmann, C., et al.
(författare)
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Strategies for Quantitative Planar Laser-Induced Fluorescence of NH Radicals in Flames
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 188:4-5, s. 529-541
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced fluorescence imaging of the NH radical using excitation in the (0-0) and (1-0) vibrational bands of the A3Π-X3Σ– electronic transition is characterized in premixed NH3-air flames. Filtered detection for excitation of the (1-0) band is found to be beneficial for measurement conditions with a challenging background and/or interferences. Concentration evaluation for excitation in the (0-0) and (1-0) bands is feasible by means of fully or partially saturated fluorescence, respectively. Detection limits of a few tens of ppm for averaged data and 100 ppm on a single-shot basis was achieved for 3-cm imaging size using both excitation alternatives. Thinning and broadening of the NH layer in a turbulent flame indicate turbulence/flame chemistry coupling, which occurred at lower turbulence levels compared with hydrocarbon combustion. Fluorescence imaging of the NH flame-front marker in such flames thus provide an experimental configuration for detailed studies of turbulence/flame chemistry interactions.
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| 7. |
- Ehn, A., et al.
(författare)
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Investigations of microwave stimulation of a turbulent low-swirl flame
- 2017
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 36:3, s. 4121-4128
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Tidskriftsartikel (refereegranskat)abstract
- Irradiating a flame by microwave radiation is one of several plasma-assisted combustion (PAC) technologies that can be used to modify the combustion chemical kinetics in order to improve flame-stability and to delay lean blow-out. One practical implication is that engines may be able to operate with leaner fuel mixtures and have an improved fuel flexibility capability including biofuels. In addition, this technology may assist in reducing thermoacoustic instabilities that may severely damage the engine and increase emission production. To examine microwave-assisted combustion a combined experimental and computational study of microwave-assisted combustion is performed for a lean, turbulent, swirl-stabilized, stratified flame at atmospheric conditions. The objectives are to demonstrate that the technology increases both the laminar and turbulent flame speeds, and modifies the chemical kinetics, enhancing the flame-stability at lean mixtures. The study combines experimental investigations using hydroxyl (OH) and formaldehyde (CH2O) Planar Laser-Induced Fluorescence (PLIF) and numerical simulations using finite rate chemistry Large Eddy Simulations (LES). The reaction mechanism is based on a methane (CH4)-air skeletal mechanism expanded with sub-mechanisms for ozone, singlet oxygen, chemionization, electron impact dissociation, ionization and attachment. The experimental and computational results show similar trends, and are used to demonstrate and explain some significant aspects of microwave-enhanced combustion. Both simulation and experimental studies are performed close to lean blow off conditions. In the simulations, the flame is gradually subjected to increasing reduced electric field strengths, resulting in a wider flame that stabilizes nearer to the burner nozzle. Experiments are performed at two equivalence ratios, where the leaner case absorbs up to more than 5% of the total flame power. Data from experiments reveal trends similar to simulated results with increased microwave absorption.
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| 8. |
- Fureby, C., et al.
(författare)
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Investigations of microwave stimulation of turbulent flames with implications to gas turbine combustors
- 2017
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Ingår i: AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624104473
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Konferensbidrag (refereegranskat)abstract
- Efficient and clean production of electrical energy and mechanical (shaft) energy for use in industrial and domestic applications, surface- and ground transportation and aero-propulsion is currently of significant general concern. Fossil fuels are mainly used for transportation and aero-propulsion, but also for power generation. Combustion of fossil fuels typically give rise to undesired emissions such as unburned hydrocarbons, carbon dioxide, carbon monoxide, soot and nitrogen oxides. The most widespread approach to minimize these is to apply various lean-burn technologies, and sometimes also dilute the fuel with hydrogen. Although efficient in reducing emissions, lean-burn often results in combustion instabilities and igniteon issues, and thus become challenging itself. Another desired aspect of today’s engines is to increase the fuel flexibility. One possible technique that may be useful for circumventing these issues is plasma-assisted combustion, i.e. to supply a small amount of electric energy to the flame to stimulate the chemical kinetics. Although not new, this approach has not yet been fully explored, partly because of it’s complexity, and partly because of apparent sufficiency. Recently, however, several research studies of this area have emerged. This paper attempts to provide a brief summary of microwave-assisted combustion, in which microwaves are utilized to supply the electrical energy to the flame, and to demonstrate that this method is useful to enhance flame stabilization, delay lean blow-off, and to increase combustion efficiency. The main effect of microwaves (or electrical energy) is to enhance the chemical kinetics, resulting in increased reactivity and laminar and turbulent flame speeds. Here we will demonstrate that this will improve the performance of gas turbine combustors.
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| 9. |
- Hesameddin, Fatehi, et al.
(författare)
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Modeling of alkali metal release during biomass pyrolysis
- 2017
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 36:2, s. 2243-2251
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Tidskriftsartikel (refereegranskat)abstract
- The release of alkali metals (Na and K) during biomass pyrolysis was numerically and experimentally investigated using Laser-Induced Breakdown Spectroscopy technique that could extend the measurements of alkali metal concentration to the sooty pyrolysis stage. Two distinct peaks of metal concentrations were observed at the pyrolysis stage and at the gasification stage. Since during the pyrolysis stage a large temperature gradient exists inside the particle numerical simulations were performed to elucidate the experimental measurements and extract the kinetic data. For Na and K release the activation energies were in the range of 218 to 248 kJ/mole and 168 and 198 kJ/mole respectively. Equilibrium calculations were performed to identify the stable Na and K compounds and their phases during the pyrolysis stage of the particle.
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| 10. |
- Hu, S., et al.
(författare)
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Assessment of uncertainties of laminar flame speed of premixed flames as determined using a Bunsen burner at varying pressures
- 2018
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619. ; 227, s. 149-158
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Tidskriftsartikel (refereegranskat)abstract
- Laminar methane/air premixed flames at different pressures in a newly developed high-pressure Bunsen flame rig are studied using detailed numerical simulations and laser diagnostics. In the numerical simulations, one-dimensional and two-dimensional axisymmetric configurations were considered employing detailed transport properties and chemical kinetic mechanisms. In the measurements, OH PLIF was employed. The aims are to improved the understanding of the structures of the flames at varying pressures, to measure the laminar flame speed at different pressures, and to quantify the accuracy of the Bunsen flame method for measurement of laminar flame speed at different pressures. The stoichiometric and fuel-rich flames were found to exhibit a two-reaction-zone structure: an inner premixed flame in which the fuel was converted to CO and H2, and an outer diffusion flame in which CO and H2 were oxidized further to form combustion products. With increasing pressure, the inner premixed flame becomes thinner and the flame as a whole has the tendency to become unstable. Using the numerical and the experimental data, the methods of flame-cone-angle and flame-area were used to extract the laminar flame speed for different equivalence ratios and pressures. The flame-cone-angle method showed slightly better accuracy than the flame-area method did. The accuracy of both methods became lower under high pressure conditions. The inlet velocity of the burner was shown to affect the accuracy of the extracted laminar flame speed. For a stoichiometric atmospheric flame it was found that the most suitable inlet velocity for the fuel/air mixture was about 6 times the laminar flame speed, yielding a flame length about 7 times the radius of the burner. With appropriate flame length, the mid-height of the flame showed a rather low flame stretch rate, the laminar flame speed being in close agreement with the unstretched laminar flame speed, the error being less than 6% for the flames that were studied.
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