| 1. |
- Borggren, Jesper, et al.
(författare)
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Diode laser-based thermometry using two-line atomic fluorescence of indium and gallium
- 2017
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Ingår i: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 123:12
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Tidskriftsartikel (refereegranskat)abstract
- A robust and relatively compact calibration-free thermometric technique using diode lasers two-line atomic fluorescence (TLAF) for reactive flows at atmospheric pressures is investigated. TLAF temperature measurements were conducted using indium and, for the first time, gallium atoms as temperature markers. The temperature was measured in a multi-jet burner running methane/air flames providing variable temperatures ranging from 1600 to 2000 K. Indium and gallium were found to provide a similar accuracy of ~ 2.7% and precision of ~ 1% over the measured temperature range. The reliability of the TLAF thermometry was further tested by performing simultaneous rotational CARS measurements in the same experiments.
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| 2. |
- Borggren, Jesper, et al.
(författare)
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Spatially Resolved Temperature Measurements Above a Burning Wood Pellet Using Diode Laser-Based Two-Line Atomic Fluorescence
- 2018
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 72:6, s. 964-970
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Tidskriftsartikel (refereegranskat)abstract
- Diode laser-based two-line atomic fluorescence (TLAF) thermometry applied to flames of combusting wood pellets is demonstrated. The temperature above burning wood pellets placed in the hot product gas of gallium seeded laminar flames is measured. The calibration-free technique provides spatially resolved temperatures in one dimension with sufficient temporal resolution to resolve all combustion stages of a pellet, even in highly sooting flames. The temperature above a burning pellet was found to decrease due to the release of volatile gases and the accuracy and precision of the technique is assessed at flame temperatures.
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| 3. |
- Borggren, Jesper, et al.
(författare)
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Temperature imaging in low-pressure flames using diode laser two-line atomic fluorescence employing a novel indium seeding technique
- 2016
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 122:3
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Tidskriftsartikel (refereegranskat)abstract
- The use of diode lasers for spatially resolved temperature imaging is demonstrated in low-pressure premixed methane–air flames using two-line atomic fluorescence of seeded indium atoms. This work features the advantages of using compact diode lasers as the excitation sources with the benefits of two-dimensional planar imaging, which is normally only performed with high-power pulsed lasers. A versatile and reliable seeding technique with minimal impact on flame properties is used to introduce indium atoms into the combustion environment for a wide range of flame equivalence ratios. A spatial resolution of around 210 µm for this calibration-free thermometry technique is achieved for three equivalence ratios at a pressure of 50 mbar in a laminar flat flame.
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| 4. |
- Borggren, Jesper, et al.
(författare)
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Temperature imaging in low-pressure flames using diode lasers
- 2014
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Ingår i: Imaging and Applied Optics - Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2014. - Washington, D.C. : OSA. - 2162-2701. - 9781557523082 - 9781557523082
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Konferensbidrag (refereegranskat)abstract
- We present a calibration free technique for spatially resolved imaging of flame temperature. Its application is demonstrated in a low pressure premixed methane flame seeded with indium. Temperature measurements over a range of equivalence ratios are investigated.
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| 5. |
- Borggren, Jesper
(författare)
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Two-Line Atomic Fluorescence for Thermometry in Reactive Flows
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Advances in the field of laser-based combustion diagnostics over the past decades have allowed for detailed characterisation, modelling and increased understanding of the complex combustion process. However; many combustion phenomena are still unexplained and there is a continued need for development and application of diagnostic tools to further the understanding of the combustion process. One of the governing physical properties in the combustion process is the temperature due to its exponential effect on the chemical reaction rates. Hence, the work reported throughout this thesis deals with the development and extension of a thermometric technique for reactive flows called two-line atomic fluorescence (TLAF). In TLAF an atomic species with a suitable electronic structure, that of a three-level lambda-system, is seeded to the flame and the two lower levels are consecutively probed with light. The ratio of the emitted laser-induced fluorescence intensities is governed by the temperature-dependent Boltzmann distribution and used to infer the temperature of the system. TLAF offers several beneficial features such as being independent on the gas composition, strong fluorescence signals and insensitivity to elastic scattering.The thesis reports on the application of the thermometric technique in a wide range of combustion environments, from low-pressure flat flames, atmospheric jet flames to sooty and particulate laden flames of burning biomass pellets. Two variations of the TLAF technique were performed with external-cavity diode lasers (ECDL): 1) Line shape resolved TLAF where the absorption profile of the two excited levels are recorded as the lasers are tuned and 2) fixed wavelength TLAF where the lasers are stabilized to the peak of the absorption profile. The accuracy and precision, being figures of merit for any quantitative technique, have been measured and estimated for all the applied cases. An accuracy in the order of 2-3% at flame temperatures around 1800 K is typical for the TLAF technique and the precision is for many cases below 1% for averaged measurements. Even with low-power ECDLs imaging and temporally resolved temperature measurements have been demonstrated. A versatile seeding system being able to seed a wide range of burners with an adjustable and constant concentration of the necessary atomic species is also presented.
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| 6. |
- Dominguez, Armand, et al.
(författare)
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A compact Scheimpflug lidar imaging instrument for industrial diagnostics of flames
- 2023
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Ingår i: Measurement science and technology. - : Institute of Physics. - 0957-0233 .- 1361-6501. ; 34:7
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Tidskriftsartikel (refereegranskat)abstract
- Scheimpflug lidar is a compact alternative to traditional lidar setups. With Scheimpflug lidar it is possible to make continuous range-resolved measurements. In this study we investigate the feasibility of a Scheimpflug lidar instrument for remote sensing in pool flames, which are characterized by strong particle scattering, large temperature gradients, and substantial fluctuations in particle distribution due to turbulence. An extinction coefficient can be extracted using the information about the transmitted laser power and the spatial extent of the flame. The transmitted laser power is manifested by the intensity of the ‘echo’ from a hard-target termination of the beam located behind the flame, while the information of the spatial extent of the flame along the laser beam is provided by the range-resolved scattering signal. Measurements were performed in heptane and diesel flames, respectively. © 2023 The Author(s).
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| 7. |
- Jonsson, Malin, et al.
(författare)
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Investigation of photochemical effects in flame diagnostics with picosecond photofragmentation laser-induced fluorescence
- 2016
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 171, s. 59-68
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation laser-induced fluorescence (PFLIF) is for the first time performed based on picosecond laser pulses for detection of hydroperoxyl radicals (HO2) in a stoichiometric laminar methane/air flame. Photofragmentation is performed with a pump laser pulse of 80 ps duration and a wavelength of 266 nm, whereupon the produced OH photofragments are detected by a second picosecond probe laser pulse, inducing fluorescence via excitation in the A2Σ+(v = 1) ← X2Π(v = 0) band of OH near 283 nm. Excitation spectra of the OH photofragments formed in the reaction zone were recorded for pump-probe delays ranging from 0 to 5 ns. The spectra suggest that the population distribution of the nascent OH fragments is rotationally cold and that it takes on the order of 5 ns for the nascent non-equilibrium rotational distribution to relax into a thermal distribution. The radial OH-fragment distribution was extracted from spectral images (radial position versus emission wavelength) recorded at six different pump-probe delays. Photochemical OH production was observed both in the reaction zone and the product zone. Comparison with a kinetic model for OH production suggests that more than 20% of the oxygen fragments produced by photolysis in the reaction zone are formed in the excited 1D state, explaining a very rapid initial signal growth. The OH-production model was also compared with previous reaction-zone data, acquired with nanosecond laser pulses in the same flame, indicating that no O(1D), but only O(3P), is formed. A plausible explanation of the discrepancy between the two results is that the picosecond pulses, having more than two-orders of magnitude higher irradiance than the nanosecond pulses used in the previous study, might cause 2-photon photodissociation, allowing production of O(1D). In terms of flame diagnostics with PFLIF, it is concluded that a setup based on nanosecond laser pulses, rather than picosecond pulses, appears preferable since photochemical OH production in the reaction zone can be avoided while for short delay times the ratio between the photofragment signal and the photochemical interference in the product zone, stemming from CO2 photolysis, is sufficiently large to clearly visualize the photofragments.
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| 8. |
- Jonsson, Malin, et al.
(författare)
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Time-resolved spectroscopic study of photofragment fluorescence in methane/air mixtures and its diagnostic implications
- 2015
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 120:4, s. 587-599
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Tidskriftsartikel (refereegranskat)abstract
- In this work 80-picosecond laser pulses of 266-nm wavelength with intensities up to (2.0 +/- A 0.5) x 10(11) W/cm(2) were used for fragmentation of methane/air gas mixtures at ambient pressure and temperature. Emission spectra are, for the first time, studied with ultrahigh temporal resolution using a streak camera. Fluorescence spectra from CH(A(2)Delta-(XI)-I-2 , (BI)-I-2 (-)-(XI)-I-2 pound , (CI)-I-2 (+)-(XI)-I-2 pound ), CN((BI)-I-2 (+)-(XI)-I-2 pound (+) pound, Delta v = 0 and Delta v = +/- 1), NH(A(3)I (-)-(XI)-I-3 (-)) pound, OH(A(2)I (+)-(XI)-I-2 pound ) and N-2 (+)((BI)-I-2 pound (u) (+) -(XI)-I-2 pound (g) (+) ) were recorded and analyzed. By fitting simulated spectra to high-resolution experimental spectra, rotational and vibrational temperatures are estimated, showing that CH(C), CN(B), NH(A), and OH(A) are formed in highly excited vibrational and rotational states. The fluorescence signal dependencies on laser intensity and CH4/air equivalence ratio were investigated as well as the fluorescence lifetimes. All fragments observed are formed within 200 ps after the arrival of the laser pulse and their fluorescence lifetimes are shorter than 1 ns, except for CN(B-X) Delta v = 0 whose lifetime is 2.0 ns. The CN(B-X) Delta v = 0 fluorescence was studied temporally under high spectral resolution, and it was found that the vibrational levels are not populated simultaneously, but with a rate that decreases with increasing vibrational quantum number. This observation indicates that the rate of the chemical reaction that forms the CN(B) fragments is decreasing with increasing vibrational state of the product. The results provide vital information for the application of laser diagnostic techniques based on strong UV excitation, as they show that such methods might not be entirely non-intrusive and suffering from spectral interferences, unless the laser intensity is kept sufficiently low. Finally, equivalence ratios were determined from "unknown" spectra using multivariate analysis, showing a good agreement with theoretical compositions with an error of 4 %. The method is expected to be a useful diagnostic tool for measurements of local equivalence ratios in for example combustion environments.
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| 9. |
- Larsson, Kajsa, et al.
(författare)
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Single-shot photofragment imaging by structured illumination
- 2015
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Ingår i: Optics Letters. - 0146-9592. ; 40:21, s. 5019-5022
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Tidskriftsartikel (refereegranskat)abstract
- A laser method to suppress background interferences in pump - probe measurements is presented and demonstrated. The method is based on structured illumination, where the intensity profile of the pump beam is spatially modulated to make its induced photofragment signal distinguishable from that created solely by the probe beam. A spatial lock-in algorithm is then applied on the acquired data, extracting only those image components that are characterized by the encoded structure. The concept is demonstrated for imaging of OH photofragments in a laminar methane/air flame, where the signal from the OH photofragments produced by the pump beam is spatially overlapping with that from the naturally present OH radicals. The purpose was to perform for the first time, to the best of our knowledge, single-shot imaging of HO2 in a flame. These results show an increase in signal-to-interference ratio of about 20 for single-shot data. (C) 2015 Optical Society of America
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| 10. |
- Li, Zheming, et al.
(författare)
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Simultaneous multispectral imaging of flame species using Frequency Recognition Algorithm for Multiple Exposures (FRAME)
- 2018
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 192, s. 160-169
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Tidskriftsartikel (refereegranskat)abstract
- Imaging the interaction between different combustion species under turbulent flame conditions requires methods that both are extremely fast and provide means to spectrally separate different signals. Current experimental solutions to achieve this often rely on using several cameras that are time-gated and/or equipped with different spectral filters. In this work we explore a technique called Frequency Recognition Algorithm for Multiple Exposures (FRAME) as an alternative solution for instantaneous multispectral imaging of flame species. The method is based on exciting different species with different spatial “codes” and to separate each signal component using a spatial frequency-sensitive lock-in algorithm. This methodology permits the signal from several different species to be recorded at the exact same time with a single camera. Furthermore, since the signals are recognized based on the superimposed spatial codes, there is no need for spectral separation prior to detection. The entire fluorescence envelope from each species can thus, in principle, be detected. In the current work, we present simultaneous planar laser-induced fluorescence imaging of OH and CH2O in a turbulent dimethyl ether (DME)/air flame.
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| 11. |
- Reifarth, Simon, 1980-, et al.
(författare)
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Analysis of EGR/Air Mixing by 1-D Simulation, 3-D Simulation and Experiments
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The use of EGR for NOX reduction is today a standard technology for diesel engines. The mixing of air and EGR is an important issue, especially for high-pressure EGR systems. Anuneven distribution of EGR between the cylinders can lead tohigher overall engine emissions when some cylinders producemore soot, others more NOX than they would with a perfectlyeven distribution.It is therefore important to understand the processes thatcontrol the mixing between air and EGR. The mixing isinfluenced by both the geometry of the mixing area and thepulsating nature of the flow.The aim of this work is to point out the high importance of thepulses present in the EGR-flow. By simulation in 1-D and 3-Das well as by a fast measurement method, it is shown that theEGR is transported in the air flow in packets. This implies thatthe timing between intake valve opening and the positioning ofthe EGR packets has a high influence of the distribution ofEGR between the cylinders.The ability of 1-D and 3-D simulation to predict the behavior isevaluated. It is shown how standard 1-D simulations fail topredict the pulsation effects. Furthermore, it is shown how 1-Dmodels can be modified to give results reasonably close to the3-D simulation results.
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| 12. |
- Weng, Wubin, et al.
(författare)
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A novel multi-jet burner for hot flue gases of wide range of temperatures and compositions for optical diagnostics of solid fuels gasification/combustion
- 2017
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 88:4
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Tidskriftsartikel (refereegranskat)abstract
- A novel multi-jet burner was built to provide one-dimensional laminar flat flames with a wide range of variable parameters for multipurpose quantitative optical measurements. The burner is characterized by two independent plenum chambers, one supporting a matrix of 181 laminar jet flames and the other supporting a co-flow from a perforated plate with small holes evenly distributed among the jets. A uniform rectangular burned gas region of 70 mm × 40 mm can be generated, with a wide range of temperatures and equivalence ratios by controlling independently the gas supplies to the two plenum chambers. The temperature of the hot gas can be adjusted from 1000 K to 2000 K with different flame conditions. The burner is designed to seed additives in gas or liquid phase to study homogeneous reactions. The large uniform region can be used to burn solid fuels and study heterogeneous reactions. The temperature was measured using two-line atomic fluorescence thermometry and the temperature profile at a given height above the burner was found to be flat. Different types of optical diagnostic techniques, such as line of sight absorption or laser-induced fluorescence, can be easily applied in the burner, and as examples, two typical measurements concerning biomass combustion are demonstrated.
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| 13. |
- Whiddon, Ronald, et al.
(författare)
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Vapor phase tri-methyl-indium seeding system suitable for high temperature spectroscopy and thermometry.
- 2015
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 86:9
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Tidskriftsartikel (refereegranskat)abstract
- Tri-methyl-indium (TMI) is used as an indium transport molecule to introduce indium atoms to reactive hot gas flows/combustion environments for spectroscopic diagnostics. A seeding system was constructed to allow the addition of an inert TMI laden carrier gas into an air/fuel mixture burning consequently on a burner. The amount of the seeded TMI in the carrier gas can be readily varied by controlling the vapor pressure through the temperature of the container. The seeding process was calibrated using the fluorescent emission intensity from the indium 6(2)S1/2 → 5(2)P1/2 and 6(2)S1/2 → 5(2)P3/2 transitions as a function of the calculated TMI seeding concentration over a range of 2-45 ppm. The response was found to be linear over the range 3-22.5 ppm; at concentrations above 25 ppm there is a loss of linearity attributable to self-absorption or loss of saturation of TMI vapor pressure in the carrier gas flow. When TMI was introduced into a post-combustion environment via an inert carrier gas, molecular transition from InH and InOH radicals were observed in the flame emission spectrum. Combined laser-induced fluorescence and absorption spectroscopy were applied to detect indium atoms in the TMI seeded flame and the measured atomic indium concentration was found to be at the ppm level. This method of seeding organometallic vapor like TMI to a reactive gas flow demonstrates the feasibility for quantitative spectroscopic investigations that may be applicable in various fields, e.g., chemical vapor deposition applications or temperature measurement in flames with two-line atomic fluorescence.
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