| 1. |
- 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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| 2. |
- Prins, A. J., et al.
(författare)
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Visualization of Biomass Pyrolysis and Temperature Imaging in a Heated-Grid Reactor
- 2009
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 23:1, s. 993-1006
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Tidskriftsartikel (refereegranskat)abstract
- The main advantage of a heated-grid reactor for studying pyrolysis kinetics of solid fuel samples is that high heating rates of up to 1000 K/s can be obtained. However, one of the concerns is whether the temperature distribution over the grid material is uniform and whether the presence of a thermocouple welded to the grid causes any measurement errors. Biomass samples were placed on the heated-grid reactor, and the volatiles, emitted in the biomass pyrolysis process as hot gas plumes, were imaged with an infrared camera with a high framing speed. The temporal resolved infrared images indicate that the pyrolysis process does not take place at the same rate everywhere on the grid. Two-dimensional temperature images of a heated grid made of stainless steel were recorded using the method of laser-induced thermometry with thermographic phosphors. As expected from a heat-transfer model, measured temperatures were found to be significantly higher than temperatures indicated by a thermocouple welded to the bottom of the grid. It was also observed that there is a large temperature gradient between the two electrodes on which the grid is connected. It is shown that replacing a wire mesh by a foil as a grid material may lead to more homogeneous temperature distribution. The paper recommends additional research to demonstrate the suitability of the heated-grid reactor for carrying out accurate measurements.
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| 3. |
- Prins, M. J., et al.
(författare)
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Biomass pyrolysis in a heated-grid reactor: Visualization of carbon monoxide and formaldehyde using Laser-Induced Fluorescence
- 2011
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Ingår i: Journal of Analytical and Applied Pyrolysis. - : Elsevier BV. - 1873-250X .- 0165-2370. ; 92:2, s. 280-286
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Tidskriftsartikel (refereegranskat)abstract
- The development of improved biomass pyrolysis models is vital for more accurate modelling and design of biomass conversion equipment. Such improved models must be based on reliable experimental data: biomass should be pyrolyzed at high heating rates and the reaction products should be measured using an on-line, non-intrusive method. Therefore, a heated grid reactor with heating rate of 300-600 K/s was used to study pyrolysis of biomass at temperatures in the range of 500-700 degrees C. The formation of formaldehyde and carbon monoxide from wood at high heating rates was successfully visualized using Laser-Induced Fluorescence (LIF). A thin vertical laser line or sheet was present directly above the biomass lying on the heated grid. Two-photon excitation at 230 nm was applied to induce fluorescence of carbon monoxide present in the volatiles, whereas excitation of formaldehyde was done at 355 nm. Visualization of these compounds shows that the release rises strongly with temperature; this typically happens on a timescale in the order of seconds. In principle, the method described allows for the determination of truly primary products. Future research is recommended, aimed at quantifying the concentrations measured by LIE. Care must be taken to calibrate for quenching of the fluorescence signal. Avoiding secondary reactions taking place in the gas phase is another experimental challenge. (C) 2011 Elsevier B.V. All rights reserved.
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| 4. |
- A. Marques, Ana F., et al.
(författare)
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The Seven Sisters Hydrothermal System : First Record of Shallow Hybrid Mineralization Hosted in Mafic Volcaniclasts on the Arctic Mid-Ocean Ridge
- 2020
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Ingår i: Minerals. - : MDPI AG. - 2075-163X.
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We document the discovery of an active, shallow, seafloor hydrothermal system (known as the Seven Sisters Vent Field) hosted in mafic volcaniclasts at a mid-ocean ridge setting. The vent field is located at the southern part of the Arctic mid-ocean ridge where it lies on top of a flat-topped volcano at ~130 m depth. Up to 200 deg C phase-separating fluids vent from summit depressions in the volcano, and from pinnacle-like edifices on top of large hydrothermal mounds. The hydrothermal mineralization at Seven Sisters manifests as a replacement of mafic volcaniclasts, as direct intraclast precipitation from the hydrothermal fluid, and as elemental sulfur deposition within orifices. Barite is ubiquitous, and is sequentially replaced by pyrite, which is the first sulfide to form, followed by Zn-Cu-Pb-Ag bearing sulfides, sulfosalts, and silica. The mineralized rocks at Seven Sisters contain highly anomalous concentrations of ‘epithermal suite’ elements such as Tl, As, Sb and Hg, with secondary alteration assemblages including silica and dickite. Vent fluids have a pH of ~5 and are Ba and metal depleted. Relatively high dissolved Si (~7.6 mmol/L Si) combined with low (0.2–0.4) Fe/Mn suggest high-temperature reactions at ~150 bar. A delta-13C value of -5.4 permil in CO2 dominated fluids denotes magmatic degassing from a relatively undegassed reservoir. Furthermore, low CH4 and H2 (<0.026 mmol/kg and <0.009 mmol/kg, respectively) and 3He/4He of ~8.3 R/Racorr support a MORB-like, sediment-free fluid signature from an upper mantle source. Sulfide and secondary alteration mineralogy, fluid and gas chemistry, as well as delta-34S and 87Sr/86Sr values in barite and pyrite indicate that mineralization at Seven Sisters is sustained by the input of magmatic fluids with minimal seawater contribution. 226Ra/Ba radiometric dating of the barite suggests that this hydrothermal system has been active for at least 4670 +/- 60 yr.
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| 5. |
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| 6. |
- 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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| 7. |
- Kiefer, J., et al.
(författare)
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Gas diagnostics by laser-induced breakdown spectroscopy employing polarization filtering
- 2010
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Ingår i: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2010. - 2162-2701. - 9781557528803
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Konferensbidrag (refereegranskat)abstract
- In this work we present a setup for laser-induced breakdown spectroscopy (LIBS) employing a polarization filtering approach and use it for gas diagnostics. A one parts-per-million (ppm) detection sensitivity is achieved for hydrogen atoms.
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| 8. |
- Kiefer, J., et al.
(författare)
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Laser-induced breakdown spectroscopy in gases using ungated detection in combination with polarization filtering and online background correction
- 2010
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Ingår i: Measurement Science & Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 21:6
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative and fast analysis of gas mixtures is an important task in the field of chemical, security and environmental analysis. In this paper we present a diagnostic approach based on laser-induced breakdown spectroscopy (LIBS). A polarization filter in the signal collection system enables sufficient suppression of elastically scattered light which otherwise reduces the dynamic range of the measurement. Running the detector with a doubled repetition rate as compared to the laser online background correction is obtained. Quantitative measurements of molecular air components in synthetic, ambient and expiration air are performed and demonstrate the potential of the method. The detection limits for elemental oxygen and hydrogen are in the order of 15 ppm and 10 ppm, respectively.
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| 9. |
- Kiefer, J., et al.
(författare)
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Laser-induced plasma in methane and dimethyl ether for flame ignition and combustion diagnostics
- 2011
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 103:1, s. 229-236
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report the investigation of the laser-induced breakdown and ignition behaviour of methane/air and dimethyl ether (DME)/air mixtures. Moreover, the optical emission from the induced plasma is utilized for determining the mixture composition quantitatively by means of laser-induced breakdown spectroscopy (LIBS). To the best of the authors' knowledge, LIBS and laser ignition of DME have not been reported in literature before. The technique under investigation is finally employed for combustion diagnostics in laminar as well as turbulent flames. In the laminar premixed and non-premixed flames the LIBS spectra allow spatially resolved measurements of the equivalence ratio and enable studying the mixing of gases provided through the burner with the surrounding room air. In addition, the breakdown threshold of the applied laser pulse energy yields an estimate for the local temperature. In the turbulent cases single-shot LIBS spectra are recorded at fixed position allowing the derivation of local statistical fluctuations of the equivalence ratio in partially premixed jet flames. The results show that laser-induced breakdowns have a strong potential for flame diagnostics and, under suitable conditions, for the ignition of combustible mixtures.
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| 10. |
- Larsson, A., et al.
(författare)
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Skeletal Methane-Air Reaction Mechanism for Large Eddy Simulation of Turbulent Microwave-Assisted Combustion
- 2017
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Ingår i: Energy and Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 31:2, s. 1904-1926
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Tidskriftsartikel (refereegranskat)abstract
- Irradiating a flame via microwave radiation is a plasma-assisted combustion (PAC) technology 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 combustion engines may be able to operate with leaner fuel mixtures and have an improved fuel flexibility capability including biofuels. Furthermore, this technology may assist in reducing thermoacoustic instabilities, which is a phenomenon that may severely damage the engine and increase NOX production. To further understand microwave-assisted combustion, a skeletal kinetic reaction mechanism for methane-air combustion is developed and presented. The mechanism is detailed enough to take into account relevant features, but sufficiently small to be implemented in large eddy simulations (LES) of turbulent combustion. The mechanism consists of a proposed skeletal methane-air reaction mechanism accompanied by subsets for ozone, singlet oxygen, chemionization, and electron impact reactions. The baseline skeletal methane-air mechanism contains 17 species and 42 reactions, and it predicts the ignition delay time, flame temperature, flame speed, major species, and most minor species well, in addition to the extinction strain, compared to the detailed GRI 3.0 reaction mechanism. The amended skeletal reaction mechanism consists of 27 species and 80 reactions and is developed for a reduced electric field E/N below the critical field strength (of ∼125 Td) for the formation of a microwave breakdown plasma. Both laminar and turbulent flame simulation studies are carried out with the proposed skeletal reaction mechanism. The turbulent flame studies consist of propagating planar flames in homogeneous isotropic turbulence in the reaction sheets and the flamelets in eddies regimes, and a turbulent low-swirl flame. A comparison with experimental data is performed for a turbulent low-swirl flame. The results suggest that we can influence both laminar and turbulent flames by nonthermal plasmas, based on microwave irradiation. The laminar flame speed increases more than the turbulent flame speed, but the radical pool created by the microwave irradiation significantly increases the lean blow-out limits of the turbulent flame, thus making it less vulnerable to thermoacoustic combustion oscillations. Apart from the experimental results from low-swirl flame presented here, experimental data for validation of the simulated trends are scarce, and conclusions build largely on simulation results. Analysis of chemical kinetics from simulations of laminar flames and LES on turbulent flames reveal that singlet oxygen molecule is of key importance for the increased reactivity, accompanied by production of radicals such as O and OH.
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| 11. |
- Lee, Eun-Young, et al.
(författare)
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Play, Learn, and Teach Outdoors—Network (PLaTO-Net) : terminology, taxonomy, and ontology
- 2022
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Ingår i: International Journal of Behavioral Nutrition and Physical Activity. - : BioMed Central (BMC). - 1479-5868. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: A recent dialogue in the field of play, learn, and teach outdoors (referred to as “PLaTO” hereafter) demonstrated the need for developing harmonized and consensus-based terminology, taxonomy, and ontology for PLaTO. This is important as the field evolves and diversifies in its approaches, contents, and contexts over time and in different countries, cultures, and settings. Within this paper, we report the systematic and iterative processes undertaken to achieve this objective, which has built on the creation of the global PLaTO-Network (PLaTO-Net). Methods: This project comprised of four major methodological phases. First, a systematic scoping review was conducted to identify common terms and definitions used pertaining to PLaTO. Second, based on the results of the scoping review, a draft set of key terms, taxonomy, and ontology were developed, and shared with PLaTO members, who provided feedback via four rounds of consultation. Third, PLaTO terminology, taxonomy, and ontology were then finalized based on the feedback received from 50 international PLaTO member participants who responded to ≥ 3 rounds of the consultation survey and dialogue. Finally, efforts to share and disseminate project outcomes were made through different online platforms. Results: This paper presents the final definitions and taxonomy of 31 PLaTO terms along with the PLaTO-Net ontology model. The model incorporates other relevant concepts in recognition that all the aspects of the model are interrelated and interconnected. The final terminology, taxonomy, and ontology are intended to be applicable to, and relevant for, all people encompassing various identities (e.g., age, gender, culture, ethnicity, ability). Conclusions: This project contributes to advancing PLaTO-based research and facilitating intersectoral and interdisciplinary collaboration, with the long-term goal of fostering and strengthening PLaTO’s synergistic linkages with healthy living, environmental stewardship, climate action, and planetary health agendas. Notably, PLaTO terminology, taxonomy and ontology will continue to evolve, and PLaTO-Net is committed to advancing and periodically updating harmonized knowledge and understanding in the vast and interrelated areas of PLaTO.
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| 12. |
- Malmqvist, E., et al.
(författare)
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Lidar thermometry using two-line atomic fluorescence
- 2019
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Ingår i: Applied Optics. - 1559-128X. ; 58:4, s. 1128-1133
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, Scheimpflug lidar has been combined with the thermometric technique two-line atomic fluorescence, to carry out stand-off, spatially resolved temperature measurements. Indium atoms were seeded into a modified Perkin-Elmer-burner and two tunable single-mode diode lasers with their wavelengths tuned to 410.17 and 451.12 nm were used to excite the seeded atoms. The fluorescence signal was collected using both a line-scan detector and a two-dimensional intensified CCD camera. One-dimensional flame temperature profiles were measured at different heights above a porous-plug burner, located at a distance of 1.5 m from the lidar system. The technique was also used to demonstrate two-dimensional temperature measurements in the same flame. The accuracy of the measured temperature was found to be limited mainly by uncertainty in the spectral overlap between the laser emission and the indium atom absorption spectrum as well as uncertainty in laser power measurements. With the constraint that indium can be introduced into the measurement volume, it is anticipated that the developed measurement concept could constitute a valuable tool, allowing in situ spatially resolved thermometry in intractable industrial applications, sufferings from limited optical access, thus requiring remote single-optical-port sensing.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
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| 17. |
- Zetterberg, Johan, et al.
(författare)
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Laser diagnostics for the study of heterogeneous catalysis
- 2016
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Ingår i: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2016. - 9781943580156 ; Part F10-LACSEA 2016
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Konferensbidrag (refereegranskat)abstract
- In heterogeneous catalysis the reactions occur on the surface of a catalyst. To understand the reaction pathways, a detailed understanding on an atomic level is critical. However, the gas atmosphere surrounding the surface dictates the interaction between the surface and the gas. At low pressures this is often neglected, but as the community turns to higher pressures it becomes important to consider gas related effects. We have used laser diagnostics to characterize the gas distributions during catalysis and thereby been able to deduce information that would otherwise lay hidden. Several of our recent results are summarized and highlighted and simultaneous measurements of the surface structure using synchrotron based methods and the gas phase using laser diagnostics is discussed.
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| 18. |
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| 19. |
- Bood, J., et al.
(författare)
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Temperature and concentration measurements in acetylene-nitrogen mixtures in the range 300-600 K using dual-broadband rotational CARS
- 2000
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Ingår i: Applied Physics B. - 0946-2171. ; 70:4, s. 607-620
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Tidskriftsartikel (refereegranskat)abstract
- Pure rotational coherent anti-Stokes Raman scattering (CARS) experiments have been performed in acetylene for temperatures ranging from 294 to 582 K, and in mixtures of acetylene and nitrogen in the mole fraction range of 0.06-0.32 for acetylene at room temperature. The experimental spectra are evaluated by a least-square fitting to libraries of theoretically calculated spectra using two different Raman linewidth models, one with and one without dependence on the rotational quantum number J. It is found that a J-dependent model is favourable, both regarding temperature measurements in pure acetylene, and simultaneous acetylene concentration and temperature measurements in different mixtures of acetylene and nitrogen. For the temperature measurements performed in pure acetylene the temperature inaccuracy is generally less than 2% when the J-dependent model for the Raman linewidths is used. It is found that fitting the value of the non-resonant susceptibility significantly improves the quality of the spectral fits and is a requirement for high temperature accuracy with the present model. The evaluated concentrations show a maximum error of 13% on a relative scale. Potential sources of systematical errors both regarding measured temperatures and acetylene concentrations are discussed.
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| 20. |
- Brackmann, Christian, et al.
(författare)
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Formation of NO and NH in NH3-doped CH4 + N2 + O2 flame : Experiments and modelling
- 2018
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 194, s. 278-284
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Tidskriftsartikel (refereegranskat)abstract
- Co-combustion of 5200 ppm NH3 with a stoichiometric, atmospheric pressure, CH4 + N2 + O2 flame has been investigated with experiments and kinetic modelling. Profiles of the amidogen (NH) radical and nitric oxide (NO) have been measured using laser-induced fluorescence, the latter being quantitatively determined. Temperature profiles were measured using Rayleigh scattering and thermocouple, the nonintrusive measurements were considered more reliable and were used for evaluation of LIF data as well as input for flame modelling. Experimental results are compared with predictions of a chemical mechanism developed by Mendiara and Glarborg (2009), with simulations based on solution of energy equation as well as on experimental temperature profiles as input. Compared with a neat flame, the NH3-doped flame shows a shift in position ∼0.7 mm downstream, as established from the measurements of the NH profile. Modelling prediction of post-flame NO concentrations in the NH3-doped flame, around 1160 ppm, was within the evaluated uncertainty with experimental data (1460 ppm). Reaction path analysis indicated NH2 as a key species in the formation of NO and N2 from the nitrogen added to the flame by NH3. Altogether, the mechanism predicts concentration levels rather well but fails to predict the shift in flame position obtained with addition of NH3 to the rather slowly burning hydrocarbon flame.
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| 21. |
- Bruebach, J., et al.
(författare)
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Determination of surface normal temperature gradients using thermographic phosphors and filtered Rayleigh scattering
- 2006
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 84:3, s. 537-541
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Tidskriftsartikel (refereegranskat)abstract
- Wall temperature as well as the temperature distribution within or close-by the boundary layer of an electrically heated axisymmetric jet impinging on a flat plate were monitored to deduce wall-normal temperature gradients. The radial surface temperature profile of the plate was determined by coating it with thermographic phosphors (TPs), materials whose phosphorescence decay time is dependent on their temperature. The TP was excited electronically by a frequency-tripled Nd:YAG laser (355 nm) and the temporal decay of the phosphorescence intensity was measured zero-dimensionally by a photomultiplier tube. In this case the 659-nm emission line of Mg3F2GeO4:Mn was monitored. The non-intrusive measurement of gas temperatures near the surface was performed two-dimensionally by filtered Rayleigh scattering (FRS). A tunable frequency-tripled single-longitudinal-mode alexandrite laser beam at 254 nm was formed into a light sheet pointing parallel to the surface. The scattered light was imaged through a very narrow linewidth atomic mercury filter onto an intensified charged coupled device (ICCD). The elastic stray light from surfaces was strongly suppressed, whereas Doppler-broadened light was detected. Thermographic phosphors proved to be reliable for the measurement of surface temperatures. Dependent on the specific experimental conditions, problems appeared with signals interfering with the FRS radiation close-by the surface. Results and challenges of this approach are discussed.
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| 22. |
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| 23. |
- Ehn, Andreas, et al.
(författare)
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Plasma assisted combustion: Effects of O3 on large scale turbulent combustion studied with laser diagnostics and Large Eddy Simulations
- 2015
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35:3, s. 3487-3495
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Abstract In plasma-assisted combustion, electric energy is added to the flame where the electric energy will be transferred to kinetic energy of the free electrons that, in turn, will modify the combustion chemical kinetics. In order to increase the understanding of this complex process, the influence of one of the products of the altered chemical kinetics, ozone (O3), has been isolated and studied. This paper reports on studies using a low-swirl methane (CH4) air flame at lean conditions with different concentrations of O3 enrichment. The experimental flame diagnostics include Planar Laser Induced Fluorescence (PLIF) imaging of hydroxyl (OH) and formaldehyde (CH2O). The experiments are also modeled using Large Eddy Simulations (LES) with a reaction model based on a skeletal CH4-air reaction mechanism combined with an O3 sub-mechanism to include the presence of O3 in the flame. This reaction mechanism is based on fundamental considerations including reactions between O3 and all other species involved. The experiments reveal an increase in CH2O in the low-swirl flame as small amounts of O3 is supplied to the CH4-air stream upstream of the flame. This increase is well predicted by the LES computations and the relative radical concentration shift is in good agreement with experimental data. Simulations also reveal that the O3 enrichment increase the laminar flame speed, su, with ∼10% and the extinction strain-rate, Ïext, with ∼20%, for 0.57% (by volume) O3. The increase in Ïext enables the O3 seeded flame to burn under more turbulent conditions than would be possible without O3 enrichment. Sensitivity analysis indicates that the increase in Ïext due to O3 enrichment is primarily due to the accelerated chain-branching reactions H 2 + O â OH + H , H 2 O + O â OH + OH and H + O 2 â OH + O . Furthermore, the increase in CH2O observed in both experiments and simulations suggest a significant acceleration of the chain-propagation reaction CH 3 + O â CH 2 O + H .
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| 24. |
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| 25. |
- Hosseini, Seyed Mohammad, et al.
(författare)
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Study of Flame Dynamics and Flashback Mechanism in a Gas Turbine Combustor Using Simultaneous OH-PLIF and PIV
- 2010
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Ingår i: AIAA 2010-6668. - Reston, Virigina : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- The present study aims to investigate the effects of burner geometry on flame characteristics, stabilization, and the occurrence of flashback using the Triple Annular Research Swirler (TARS). A premixing tube is placed at the exit of the burner. Simultaneous Planar Laser Induced Fluorescence (PLIF) of OH radicals indicating the reacting zone and Particle Image Velocimetry (PIV) for flow field mapping, were applied to study the flow- and flame-dynamics during transition from flame stabilized in the combustion chamber to flame flashback in the mixing tube. Particular attention was placed on the flame behavior/dynamics near the lean blow out (LBO). The flow field featured a central recirculation zone (CRZ), and an annular swirling jet with internal and external shears layers. The movement of the flame front relative to the upstream stagnation point of the vortex breakdown at different conditions was studied. Simultaneous planar measurements using laser diagnostics, namely, Planar Laser Induced Fluorescence (PLIF) of OH radicals and Particle Image Velocimetry (PIV), have been carried out. With mixing tube and at lean cases, vortex breakdown and the flame holding occurred close to the tube exit. As the equivalence ratio was increased, the flame entered intermittently into the premixing tube. Increasing further the equivalence ratio, the flame was stabilized inside the premixing tube. Different statistical evaluations were performed on the data to obtain better understanding of the flame stabilization mechanism. They included PDF of the axial velocity, mean velocity field and mean intensity of the OH radical, two-dimensional correlation between PIV and LIF data, POD analysis of the velocity vectors, distribution of OH radical intensity and binary images of density distribution of the seeding particles.
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| 26. |
- Hsu, Li-Jen, et al.
(författare)
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Sodium and Potassium Released from Burning Particles of Brown Coal and Pine Wood in a Laminar Premixed Methane Flame Using Quantitative Laser-Induced Breakdown Spectroscopy
- 2011
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 65:6, s. 684-691
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Tidskriftsartikel (refereegranskat)abstract
- A quantitative point measurement of total sodium ([Na](total)) and potassium ([K](total)) in the plume of a burning particle of Australian Loy Yang brown coal (23 +/- 3 mg) and of pine wood pellets (63 +/- 3 mg) was performed using laser-induced breakdown spectroscopy (LIBS) in a laminar premixed methane flame at equivalence ratios (Phi) of 1.149 and 1.336. Calibration was performed using atomic sodium or potassium generated by evaporation of droplets of sodium sulfite (Na2SO3) or potassium sulfate (K2SO4) solutions seeded into the flame. The calibration compensated for the absorption by atomic alkalis in the seeded flame, which is significant at high concentrations of solution. This allowed quantitative measurements of sodium (Na) and potassium (K) released into the flame during the three phases of combustion, namely devolatilization, char, and ash cooking. The [Na](total) in the plume released from the combustion of pine wood pellets during the devolatilization was found to reach up to 13 ppm. The maximum concentration of total sodium ([Na](total)(max)) and potassium ([K](total)(max)) released during the char phase of burning coal particles for Phi = 1.149 was found to be 9.27 and 5.90 ppm, respectively. The [Na](total)(max) and [K](total)(max) released during the char phase of burning wood particles for Phi = 1.149 was found to be 15.1 and 45.3 ppm, respectively. For the case of Phi = 1.336, the [Na](total)(max) and [K](total)(max) were found to be 13.9 and 6.67 ppm during the char phase from burning coal particles, respectively, and 21.1 and 39.7 ppm, respectively, from burning wood particles. The concentration of alkali species was higher during the ash phase. The limit of detection (LOD) of sodium and potassium with LIBS in the present arrangement was estimated to be 29 and 72 ppb, respectively.
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| 27. |
- 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
-
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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| 28. |
- Iudiciani, Piero, et al.
(författare)
-
Characterization of a multi-swirler fuel injector using simultaneous laser based planar measurements of reaction zone, flow field and fuel distribution
- 2009
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Ingår i: Proceedings Of The Asme Turbo Expo 2009, Vol 2. - 9780791848838 ; 2, s. 1041-1052
-
Konferensbidrag (refereegranskat)abstract
- Modern gas turbine spray combustors feature multiple swirlers with distributed fuel injection system for rapid fuel/air mixing and flame stabilization ensuring low NOx operations. In the present paper, we investigate the effects of different swirler designs on flame characteristics, stabilization, and behavior at lean blow out using a Triple Annular Research Swirler (TARS) burner. Simultaneous planar measurements using laser diagnostics, namely, Planar Laser Induced Fluorescence (LW) of OH radicals indicating the reacting zone, LW Acetone indicating unburnt fuel distribution and Particle Image Velocimetry (PIV) for flow field mapping, were applied to study the flow dynamics, fuel distribution and flame dynamics for different swirler geometries, air flow rates, and equivalence ratios. Both axial and nearly perpendicular to axis cross-sectional planes were investigated. The three swirler configurations allowed getting stable and repeatable flames over a wide range of different flow and fuel equivalence ratio conditions, confirming the good flexibility and operability of the TARS burner. Averaged fields are presented to compare the effect of different flow conditions using the same swirler configuration, and the effect of different swirler configurations at the same flow conditions. LIF and PIV instantaneous samples are also shown, both in axial and cross sectional planes, with structures captured in detail. Perfect matching is found between unburnt and burnt field, as well as agreement between axial and cross-sectional measurements. Particular attention has been placed on unstable flames and a highly unsteady flame near the lean blow out (LBO) is shown. Local extinctions are occasionally seen on instantaneous snapshots. Unsteadiness of such flame is suitable to exemplify the use of Proper Orthogonal Decomposition (POD) analysis that identifies the most "energetic" large scale structures or modes of the flame. In particular, rotational and helical modes are observed which can contribute to the swirling flame instability. The results show the effect of the strength and rotation direction of the swirlers can lead to strong flame stratification or to a more homogenous flames. Analysis of the flame dynamics, indicates that the flame can be stabilized dynamically without the presence of a Central Recirculation Zone (CRZ) through flame quenching and flame propagation.
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| 29. |
- Iudiciani, Piero, et al.
(författare)
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Proper Orthogonal Decomposition for experimental investigation of swirling flame instabilities
- 2010
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Ingår i: Paper AIAA 2010-584. - Reston, Virigina : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- An experimental investigation of both confined and unconfined flames on a Triple Annular Research Swirler (TARS) is presented. The paper focuses on post-processing techniques aiming at extracting information on the dynamics that are lost through classical statistics approach. POD together with a derived a-posteriori phase averaging procedure successfully reconstructed the dynamics of flames under thermo-acoustic instabilities in the confined case. For unconfined flames, an analysis of the azimuthal modes is performed.
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| 30. |
- Jonsson, M., et al.
(författare)
-
Imaging of hydrogen peroxide in an HCCI engine using photofragmentation laser-induced fluorescence
- 2012
-
Ingår i: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2012. - Washington, D.C. : OSA. - 9781557529336
-
Konferensbidrag (refereegranskat)abstract
- Hydrogen peroxide (H2O2) is for the first time measured and imaged in two-dimensions in an HCCI engine using photofragmentation laser-induced fluorescence (PF-LIF). Qualitatively, the experimental data agree with simulations.
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| 31. |
- Kiefer, J., et al.
(författare)
-
Investigation of local flame structures and statistics in partially premixed turbulent jet flames using simultaneous single-shot CH and OH planar laser-induced fluorescence imaging
- 2008
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 154:4, s. 802-818
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the application of simultaneous single-shot imaging of CH and OH radicals using planar laser-induced fluorescence (PLIF) to investigate partially permixed turbulent jet flames. Various flames have been stabilized on a coaxial jet flame burner consisting of an outer and an inner tube of diameter 22 and 2.2 mm, respectively. From the outer tube a rich methane/air mixture was supplied at a relatively low flow velocity, while a jet of pure air was introduced from the inner one, resulting in a turbulent jet flame on top of a laminar pilot flame. The turbulence intensity was controlled by varying the inner jet flow speed from 0 up to 120 m/s, corresponding to a maximal Reynolds number of the inner jet airflow of 13,200. The CH/OH PLIF imaging clearly revealed the local structure of the studied flames. In the proximity of the burner, a two-layer reaction zone structure was identified where an inner zone characterized by strong CH signals has a typical structure of rich premixed flames. An outer reaction zone characterized by strong OH signals has a typical structure of a diffusion flame that oxidizes the intermediate fuels formed in the inner rich premixed flame. In the moderate-turbulence flow, the CH layers were very thin closed surfaces in the entire flame, whereas the OH layers were much thicker. In the high-intensity-turbulence flame, the CH layer remained thin until it vanished in the upper part of the flame, showing local extinction and reignition behavior of the flame. The single-shot PLIF images have been utilized to determine the flame surface density (FSD). In low and moderate turbulence intensity cases the FSDs determined from CH and OH agreed with each other, while in the highly turbulent case a locally broken CH layer was observed, leading to a significant difference in the FSD results determined via the OH and CH radicals. Furthermore, the means and the standard deviations of CH and OH radicals were obtained to provide statistical information about the flames that may be used for validation of numerical calculations. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 32. |
- Kiefer, J., et al.
(författare)
-
OH-thermometry using laser polarization spectroscopy and laser-induced fluorescence spectroscopy in the OH A-X (1,0) band
- 2009
-
Ingår i: Journal Of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 40:7, s. 828-835
-
Konferensbidrag (refereegranskat)abstract
- Laser-induced fluorescence (LIF) and polarization spectroscopy (PS) is used for OH-thermometry utilizing the off-diagonal A-X (1,0) band. Both techniques are used simultaneously in order to allow a comparison of the results. For deriving temperature information from the spectra, three methods are employed: (1) a contour fit method comparing experimental and calculated spectra, (2) spectral fitting of a single highly resolved spectral line and (3) a two-line intensity ratio approach. In general, both spectroscopic techniques gave similar results. The high-resolution approach (2) did not deliver reasonable results in our experiments. The most accurate but also most time consuming method was the contour fit (1). For future two-dimensional temperature measurements, the 2-line-method (3) was identified to be the method of choice. The present study contains, to the best of our knowledge, the first polarization spectroscopic study in the A-X (1,0) band of OH. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 33. |
- Kiefer, J, et al.
(författare)
-
Planar laser-induced fluorescence of HCO for instantaneous flame front imaging in hydrocarbon flames
- 2009
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 32, s. 921-928
-
Tidskriftsartikel (refereegranskat)abstract
- The detection of the formyl radical (HCO) is of great interest in the field of combustion research since it can provide information about the local heat release (HR) rate which is a key parameter in the understanding of combustion processes. Unfortunately, due to the low signal level, HCO planar laser-induced fluorescence (PLTF) has so far not been applicable for single-shot imaging, which is necessary in particular for studying turbulent flames. In the present paper for the first time, to the best of our knowledge, single-shot PLIF imaging of HCO in flames is demonstrated by employing-a multimode frequency-tripled alexandrite laser. Oil the basis of long pulse duration along with a spectrally broad bandwidth enabling multi-line excitation a sufficient signal-to-noise ratio is achieved. In detail, excitation in the B-X system around 258.69 nm is applied and subsequent fluorescence detection in the spectral range 300-400 nm is performed. A series of experiments concerning spectral interferences, saturation behavior and the influence of flame stoichiometry (in the range phi = 0.6-2) have been conducted. Two typical fuels have been employed: methane (CH4) as conventional hydrocarbon as well as dimethyl ether (DME) as modern bio fuel. Single-shot HCO imaging is finally demonstrated in a laminar DME/air Bunsen flame and in a slightly turbulent methane/oxygen welding torch flame. The results indicate that the developed HCO PLIF technique offers a strong potential for improved flame Studies particularly in turbulent flames, In general, the approach to employ laser sources with reasonably broader bandwidth and longer pulse duration compared to conventional Nd:YAG pumped systems for PLIF will open up new possibilities in the field of Combustion diagnostics. (c) 2009 The Combustion Institute. Published by Elsevier file. All rights reserved.
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| 34. |
- Kiefer, J., et al.
(författare)
-
Spectral interferences from formaldehyde in CH PLIF flame front imaging with broadband B-X excitation
- 2011
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 158:3, s. 583-585
-
Tidskriftsartikel (refereegranskat)abstract
- In this letter we show that the use of slightly broadband laser sources like multimode alexandrite lasers for CH PLIF bears the danger of interferences from formaldehyde. Such interferences occur when the laser frequency is not carefully tuned to the B-X (0,0) R-branch band head at around 387.2 nm and manifest either in the appearance of an additional layer in the PLIF image or in a slight broadening of the actual CH layer. With careful frequency selection the formaldehyde signals were not observed. Suppression of the interferences is feasible by employing appropriate spectral filters. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 35. |
- Kristensson, Elias, et al.
(författare)
-
Analysis of multiple scattering suppression using structured laser illumination planar imaging in scattering and fluorescing media
- 2011
-
Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:14, s. 13647-13663
-
Tidskriftsartikel (refereegranskat)abstract
- The accuracy, precision and limitations of the imaging technique named Structured Laser Illumination Planar Imaging (SLIPI) have been investigated. SLIPI, which allows multiply scattered light to be diminished, has previously demonstrated improvements in image quality and contrast for spray imaging. In the current study the method is applied to a controlled confined environment consisting of a mixture of water and monodisperse polystyrene microspheres. Elastic scattering and fluorescence are studied and the results obtained when probing different particle concentrations and diameters conclusively show the advantages of SLIPI for imaging within moderately turbid media. Although the technique presents both good repeatability and agreement with the Beer-Lambert law, discrepancies in its performance were, however, discovered. Photons undergoing scattering without changing their incident trajectory cannot be discriminated and, owing to differences in scattering phase functions, probing larger particles reduces the suppression of multiply scattered light. However, in terms of visibility such behavior is beneficial as it allows denser media to be probed. It is further demonstrated that the suppression of diffuse light performs equally well regardless of whether photons propagate along the incident direction or towards the camera. In addition, this filtering process acts independently on the spatial distribution of the multiply scattered light but is limited by the finite dynamic range and unavoidable signal noise of the camera.
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| 36. |
- Kröll, Stefan, et al.
(författare)
-
Noise characteristics of single shot broadband Raman-resonant CARS with single- and multimode lasers
- 1987
-
Ingår i: Applied Optics. - 2155-3165. ; 26:6, s. 1068-1073
-
Tidskriftsartikel (refereegranskat)abstract
- A simple model is presented as an aid in understanding, first, the relative noise performance and, second, the noise reduction achievable by referencing, in different experimental approaches to single shot broadband coherent anti-Stokes Raman scattering (CARS). Qualitative agreement is obtained with previous experimental investigations of CARS noise. The broadband dye laser radiation is described as the sum of independent modes with random phases. The dye laser contribution to the CARS noise is then approximately inversely proportional to the square root of the number of dye laser modes generating the detected signal. A fundamental idea is that in Raman resonant spectra only the number of Stokes modes actually participating in driving the Raman resonance should be counted. This means, e.g., that for narrow Raman resonances, as in an atmospheric flame, the noise generated by the dye laser will be higher for a single-mode pump laser than for a multimode pump laser with the experimental CARS configuration normally employed. The implications of the model for the dual broadband type CARS techniques are also discussed.
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| 37. |
- Lantz, Andreas, et al.
(författare)
-
Investigation of ozone stimulated combustion in the SGT-800 burner at atmospheric conditions
- 2016
-
Ingår i: Combustion, Fuels and Emissions. - 9780791849750 ; 4A-2016
-
Konferensbidrag (refereegranskat)abstract
- The effect of ozone (O3) in a turbulent, swirl-stabilized natural gas/air flame was experimentally investigated at atmospheric pressure conditions using planar laser-induced fluorescence imaging of formaldehyde (CH2O PLIF) and dynamic pressure monitoring. The experiment was performed using a dry low emission (DLE) gas turbine burner used in both SGT-700 and SGT-800 industrial gas turbines from Siemens. The burner was mounted in an atmospheric combustion test rig at Siemens with optical access in the flame region. CH2O PLIF imaging was carried out for four different seeding gas compositions and seeding injection channel configurations. Two seeding injection-channels were located around the burner tip while the other two were located along the center axis of the burner at different distances upstream the burner outlet. Four different seeding gas compositions were used: nitrogen (N2), oxygen (O2) and two ozone/oxygen (O3/O2) mixtures with different O3 concentration. The results show that the O3 clearly affects the combustion chemistry. The natural gas/air mixture is preheated before combustion which is shown to kick-start the cold combustion chemistry where O3 is highly involved. The CH2O PLIF signal increases with O3 seeded into the flame which indicates that the pre-combustion activity increases and that the cold chemistry starts to develop further upstream. The small increase of the pressure drop over the burner shows that the flame moves upstream when O3 is seeded into the flame, which confirms the increase in pre-combustion activity.
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| 38. |
- Larsson, K., et al.
(författare)
-
Quantitative NO2 measurements in an industrial sterilization rig using laser induced fluorescence
- 2016
-
Ingår i: Digital Holography and Three-Dimensional Imaging, DH 2016. - 2162-2701. - 9781943580156 ; Part F8-DH 2016
-
Konferensbidrag (refereegranskat)abstract
- NO2 concentration measurements have been performed in an industrial test rig using laser-induced fluorescence. The goal is to improve the understanding of the electron-induced chemical species in the plasma, thus improving the neutralization scheme.
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| 39. |
- Li, Zhongshan, et al.
(författare)
-
Development of improved PLIF CH detection using an Alexandrite laser for single-shot investigation of turbulent and lean flames
- 2007
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489 .- 1873-2704. ; 31 I, s. 727-735
-
Konferensbidrag (refereegranskat)abstract
- We report on the development of planar laser-induced fluorescence (PLIF) for CH imaging with improved detection sensitivity for single-shot investigations of turbulent, lean, premixed flames. A ringcavity, pulsed Alexandrite laser was frequency-doubled to excite the lines in the R-branch band-head of the B-X (0,0) band and broadband fluorescence from the B-X (0,1), A-X (1,1) and (0,0) bands, overlapping in the spectral range around 431 nm, was collected. The employed Alexandrite laser, which is characterized by its long pulse duration (150 ns), gives a tunable laser beam around 775 nm with a pulse energy for the second harmonic at the CH absorption wavelength of about 70 mJ. Moreover, the laser has the possibility to be operated in narrow bandwidth (100 MHz) or broad bandwidth (8 cm-1). An introductory high resolution excitation scan over the R-branch band-head was performed and, in addition, saturated excitation with the broadband option of the laser was investigated. By simultaneous excitation of several rotational transitions and to bring these transitions close to saturation, high signal-to-noise ratios were reached over a wide range of equivalence ratios. A sharp and thin CH layer was observed in single-shot PLIF images from laminar premixed methane/air flames from Φ = 0.6 to Φ = 1.5. Finally, the impact of the developed CH PLIF technique is demonstrated in a highly turbulent, lean, partially premixed methane/air flame established on a co-axial jet flame burner. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 40. |
- Li, Zhongshan, et al.
(författare)
-
Mid-infrared polarization spectroscopy of C2H2: Non-intrusive spatial-resolved measurements of polyatomic hydrocarbon molecules for combustion diagnostics
- 2007
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489 .- 1873-2704. ; 31 I, s. 817-824
-
Konferensbidrag (refereegranskat)abstract
- Polarization spectroscopy in the mid-infrared (IRPS) has been applied to the detection of acetylene molecules making use of the asymmetric C-H stretching vibration at around 3 μm. The infrared laser pulses were produced through difference frequency generation in a LiNbO3 crystal pumped by a Nd:YAG and dye laser system. By directly probing the ro-vibrational transitions with IRPS, sensitive detection of molecules with otherwise inaccessible electronic states was realized with high temporal and spatial resolution by using a pulsed laser and a cross-beam geometry. Detection sensitivities of 2 × 1013 molecules/cm3 (10 ppm in 70 mbar gas mixture) of C2H2 were achieved using the P(11) line of the (010(11)0)-(0000000) band. The dependence of the IRPS signal on the pump laser fluence, acetylene mole fraction, and buffer gas pressure of Ar, N2, H2, and CO2 has been studied experimentally. The investigation demonstrates the quantitative nature of IRPS for sensitive detection of polyatomic IR active molecules. In order to fully demonstrate the technique for combustion applications, nascent acetylene molecules were measured in a low pressure methane/oxygen flame. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 41. |
- Li, Z. S., et al.
(författare)
-
Mid-infrared PS and LIF detection of CH4 and C2H6 in cold flows and flames at atmospheric pressure
- 2004
-
Ingår i: ; , s. 10-11
-
Konferensbidrag (refereegranskat)abstract
- Mid-IR polarization spectroscopy (IRPS) and laser-induced fluorescence were applied for detection of CH4 and ethane in 1 atm cold flows and flames. The dependence of IRPS and IRLIF signal of CH4 on different buffer gases, including He, Ar, N2, and CO2 were studied. Simultaneous measurements of IRPS and IRLIF signals allowed a direct comparison of the two techniques. IRPS was superior in detection sensitivity and background discrimination. IRPS excitation scans of a CH4 and ethane mixture diluted in argon were also carried out in a jet at ambient pressure and temperature. Lines in the spectrum belonging to CH4 and ethane were fully recognized and assigned. From the ethane lines in the IRPS excitation spectrum, a detection limit of 50 ppm was conservatively estimated, indicating that IRPS is a promising sensitive technique for hydrocarbon identification and detection. CH4 IRPS detection in a CH4/H2/air premixed flat flame was demonstrated, with spatially resolved IRPS CH4 measurements along different heights in the flame. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).
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| 42. |
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| 43. |
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| 44. |
- Malmqvist, E., et al.
(författare)
-
CW-laser radar for combustion diagnostics
- 2016
-
Ingår i: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2016. - 2162-2701. - 9781943580156 ; Part F10-LACSEA 2016
-
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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| 45. |
- Nogenmyr, Karl-Johan, et al.
(författare)
-
Numerical computations and optical diagnostics of unsteady partially premixed methane/air flames
- 2010
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 157:5, s. 915-924
-
Tidskriftsartikel (refereegranskat)abstract
- The structures and dynamics of unsteady laminar partially premixed methane/air Bunsen flames are studied by means of numerical simulations, OH and CH PLIF imaging, and high speed chemiluminescence imaging employing a high framing speed intensified charge coupled device camera. The Bunsen burner has a diameter of 22 mm. Rich methane/air mixtures with an equivalence ratio of 1.5 are injected from the burner into atmosphere at different flow speeds ranging from 0.77 to 1.7 m/s, with Reynolds numbers based on the nozzle flow ranging from I 100 to 2500. The numerical simulations are based on a two-scalar flamelet manifold tabulation approach. Detailed chemistry is used to generate the flamelet manifold tabulation which relates the species concentrations, reaction rates, temperature and density to a distance function G and mixture fraction Z. Two distinct reaction zones are identified using CH and OH PLIF imaging and numerical simulations; one inner reaction zone corresponds to premixed flames on the rich side of the mixture and one outer reaction zone corresponds to mixing controlled diffusion flames on the lean side of the mixture. Under normal gravity conditions both the inner premixed flames and the outer diffusion flames are unsteady. The outer diffusion flames oscillate with a flickering frequency of about 15 Hz, which slightly increases with the burner exit velocity. The inner premixed flames are more random with much more small-scale wrinkling structures. Under zero gravity conditions the outer diffusion flames are stable whereas the inner premixed flames are unstable and highly wrinkled. It appears that the outer diffusion flames are governed by the Rayleigh-Taylor instability whereas the inner premixed flames are dictated by Landau-Darrieus instability. The two-scalar flamelet approach is shown to capture the basic structures and dynamics of the investigated unsteady partially premixed flames. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 46. |
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| 47. |
- Sun, Zhiwei, et al.
(författare)
-
Four-wave mixing with non-resonant pump and resonant probe for OH detection in flames
- 2008
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 92:2, s. 287-293
-
Tidskriftsartikel (refereegranskat)abstract
- A new type of two-color four-wave mixing spectroscopy is theoretically and experimentally demonstrated. By employing a non-resonant pumping and resonant probing scheme, OH radicals are detected in a laminar, atmospheric pressure methane/air flame as a proof-of-principle experiment. Two 532 nm laser beams from a multi-mode Nd:YAG laser are utilized to create an electrostrictive grating in the flame. A probe beam in resonance with the Q(1)( 5) rotational line belonging to the A(2)Sigma-X-2 Pi(1,0) band at 283 nm is employed to achieve species selective detection of OH radicals. In detail, in the present paper the coherence effects of the pump beams are investigated by changing the temporal delay between the two pump beams. A signal enhanced by a factor of 3 is obtained in the coherence range. Furthermore, the dependence of the signal intensity on the laser pulse energy of the pump and probe beams is studied in detail. At high pulse energies even for the pumping process a certain saturation behavior is observed. In general, the demonstrated four-wave mixing scheme is estimated to be superior in terms of the saturation limitation in comparison to the widely applied degenerate four-wave mixing, but still providing a high sensitivity and species selectivity due to the strong resonant signal enhancement.
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| 48. |
- Tham, Wilhelm, 1951-, et al.
(författare)
-
A listeriosis patient infected with two different Listeria monocytogenes strains
- 2002
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Ingår i: Epidemiology and Infection. - 0950-2688 .- 1469-4409. ; 128:1, s. 105-106
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Tidskriftsartikel (refereegranskat)abstract
- Normally, only one isolate of Listeria monocytogenes from a case of listeriosis is subjected to characterization. Here we show that two isolates from different sites of the body were not the same strain. Such a phenomenon may not have any clinical relevance, although it may confuse the epidemiologist trying to match infection source with infection target.
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| 49. |
- Verhoeven, L. M., et al.
(författare)
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A numerical and experimental study of Polycyclic Aromatic Hydrocarbons in a laminar diffusion flame
- 2013
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 34, s. 1819-1826
-
Tidskriftsartikel (refereegranskat)abstract
- During the process of biomass gasification tars are formed which exit the gasifier in vapor phase. Tar condensation creates problems like fouling and plugging of after-treatment, conversion and end-use equipment. Gasification tars consist mainly of Polycyclic Aromatic Hydrocarbons (PAHs). Former research has shown the possibilities and difficulties of tar conversion by partial combustion. Basic studies to investigate the oxidation of tars in non-premixed combustion processes are expected to give more insight in this problem. In this paper the ability of the flamelet-generated manifold (FGM) approach to numerically model multi-dimensional, laminar, non-premixed flames with the inclusion of PAH chemistry is investigated. Modeling detailed PAH chemistry requires the employment of large reaction mechanisms which lead to expensive numerical calculations. The application of a reduction technique like FGM leads to a considerable decrease (up to two orders) in the required computation time. A 1D numerical validation shows that the improvements achieved by implementing a varying Lewis number for the progress variable Y are significant for PAH species with a large Lewis number, such as C10H8. Considerable improvements are found near the flame front and on the fuel side of the flame. A comparison has been made of FGM results with qualitative Planar Laser Induced Fluorescence (PLIF) measurements. A laminar CH4/N-2-air co-flow flame has been doped with two dopants, benzene and toluene, at three different concentrations. A set of filters was used in order to qualitatively distinguish the small (1-2 rings) and large (3 or more rings) aromatic species. The results show that the model is able to capture the major flame characteristics typical for PAH formation in multi-dimensional laminar non-premixed flames. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 50. |
- Wang, Z., et al.
(författare)
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Hydroxyl radical dynamics in a gliding arc discharge using high-speed PLIF imaging
- 2022
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Ingår i: Plasma Research Express. - : IOP Publishing. - 2516-1067. ; 4:2
-
Tidskriftsartikel (refereegranskat)abstract
- Plasma discharges can be transient and randomly distributed where a few investigations have been carried out using laser-induced fluorescence to capture snapshots of plasma-produced radicals in the near vicinity of the discharge. Radical distribution dynamics, however, are challenging to study in situ with high spatial and temporal resolution to fully capture the interactions between the discharge and the gas. We here demonstrate a planar laser-induced fluorescence method that can capture molecular distributions of ground state hydroxyl radicals in a discharge plasma and follow how the distribution develops in time with a repetition rate of 27 kHz. The technique is demonstrated by monitoring, in real-time, how the tube-like distribution of ground state OH radicals, surrounding a gliding arc plasma, is affected by flow dynamics and how it develops as the high voltage is turned off at atmospheric pressure. The method presented here is an essential tool for capturing radical-distribution dynamics in situ of chemically active environments which is the active region of the plasma induced chemistry.
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