| 1. |
- Hot, Dina
(författare)
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Infrared Laser-Induced Grating Techniques for Diagnostics in Reactive Flows
- 2020. - 1
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- AbstractThe work presented in this thesis is mainly focused on the development andapplication of infrared laser-induced grating techniques in order to measure the gasphase temperature and species concentrations in reactive flows. The two techniquesused for this purpose are laser-induced grating spectroscopy (LIGS) and degeneratefour-wave mixing (DFWM). Their coherent nature allows to perform laser-baseddiagnostics in the infrared spectral region where fundamental ro-vibrationaltransitions of several combustion-related molecular species can be utilized.Gas phase temperature measurements has been performed with laser-inducedthermal grating spectroscopy, known as LITGS. The single-shot precision andaccuracy of mid-infrared LITGS was investigated in premixed CH4/H2/air flames atatmospheric pressure by probing the hot water absorption lines around 3.1 μm,resulting in a single-shot precision better than 1 % and an accuracy of 2.5 %.Furthermore, the technique has been applied in sooty premixed atmosphericC2H4/air flames. Besides the application of mid-IR LITGS, the alignment of thetechnique in terms of grating spacing, number of resolved oscillation peaks in theLITGS signal and its time characteristics has been investigated as well asmisalignment effects. Attention has also been paid to select absorption lines whichresults in thermalization and hence are present in a LITGS excitation spectrum. Inaddition to LITGS, laser-induced electrostrictive grating spectroscopy (LIEGS) wasinvestigated for possible application in harsh environments at temperatures up to700 K. This study was carried out in the spectral band of oxygen at 760 nm and fortwo different geometrical alignments of LIEGS/LITGS.Ammonia (NH3) and hydrogen cyanide (HCN) are two molecular species ofparticular interest in the thermochemical conversion of biomass, which havefundamental or combinational vibrational bands in the mid-IR. Hence, speciesconcentration measurements were carried out using mid-IR DFWM. A feasibilitystudy has been performed for application of DFWM for ammonia detection around2.3 μm. Moreover, DFWM was applied for HCN detection during thethermochemical conversion of straw pellets, where the HCN release history duringthe devolatilization stage was quantified at different flue gas temperatures.
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| 2. |
- Hot, Dina, et al.
(författare)
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Investigation of laser-induced grating spectroscopy of O2 for accurate temperature measurements towards applications in harsh environments
- 2021
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 52:9, s. 1569-1581
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Tidskriftsartikel (refereegranskat)abstract
- We present an in-depth investigation of laser-induced grating spectroscopy (LIGS) for temperature measurements in practical applications using a narrow-band dye laser with 760 nm wavelength and a pulse duration of 8 ns as the source for the pump beams creating the laser-induced grating. The pump laser wavelength was set to be either resonant with the (Formula presented.) transition from the (Formula presented.) band of O2 for generation of thermal LIGS or nonresonant for generation of purely electrostrictive LIGS. Signals were generated in ambient air as well as in high-pressure or high-temperature dry air mixtures. Pump laser irradiances up to 11 GW/cm2 were used, which resulted in strong electrostrictive contribution to the overall LIGS signals at atmospheric pressure, with a low thermal contribution due to the weak absorption by the singlet O2 (Formula presented.). The advantage and disadvantage of thermal or electrostrictive LIGS for temperature measurements are discussed, as well as potential applications in high-pressure environments. Furthermore, the precision of the temperature measurement is discussed by comparing different analysis methods.
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| 3. |
- Hot, Dina, et al.
(författare)
-
Mid-infrared laser-induced thermal grating spectroscopy of hot water lines for flame thermometry
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:1, s. 1885-1893
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report the impact of using mid-infrared laser-induced thermal grating spectroscopy (IRLITGS) for temperature measurements in flames by probing hot water lines. The measurements have been performed in the product zone of laminar atmospheric CH 4 /H 2 /air flat flames with equivalence ratio ranging between 0.6 and 1.05. LITGS is a technique based on thermalization through collisions of the excited molecules for generation of a laser-induced grating, which then decays through thermal diffusion. As such, it tends to have limited application in atmospheric flames compared to flame measurements at elevated pressures due to the faster decay at low gas densities. However, by using mid-IR pump laser beams, it enables the generation of laser-induced gratings with large grating spacing, resulting in strong signal intensities and long signal durations. Single-shot IR-LITGS signals were recorded in the different CH 4 /H 2 /air flames that covered a temperature range between 1500 and 1800 K. To test the accuracy, the IR-LITGS flame temperature measurements were compared with laser Rayleigh scattering measurements and the result were in good agreement with each other. The IR-LITGS flame temperature measurements show a repetitive single-shot temperature precision better than 1% and an accuracy of 2.5% of the flame temperature. An IR-LITGS excitation scan of water in the flame shows that some ro-vibrational transitions exhibit no IR-LITGS signal, probably due to less efficient collisional energy transfer mechanism. This is important when deciding the wavelength to use for IR-LITGS flame temperature measurements using water absorption.
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| 4. |
- Hot, Dina, et al.
(författare)
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Spatially and temporally resolved IR-DFWM measurement of HCN released from gasification of biomass pellets
- 2019
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:2, s. 1337-1344
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, to the best of the authors' knowledge, nonintrusive quantitative measurement of hydrogen cyanide (HCN) released during the devolatilization phase of straw pellets gasification is demonstrated with high spatial and temporal resolution. Mid-infrared degenerate four-wave mixing (IR-DFWM) measurements of HCN were performed by probing the interference-free P(20) line in the v 1 vibrational band at around 3 μm and the IR-DFWM signal was detected with an upconversion-based detector, providing discrimination of thermal noise and increased sensitivity. A novel single-pellet setup consisting of a multi-jet burner was used to provide hot flue gas environments with an even and well-defined temperature distribution, for single straw pellet gasification at atmospheric pressure. The environments had temperatures of 1380 K, 1540 K and 1630 K with a constant oxygen concentration of 0.5 vol%. In order to quantify the amount of HCN released during the devolatilization of straw pellets, calibration measurements were performed in well-defined HCN gas flows. Selected hot water lines were probed with IR-DFWM in the interrogated volume to obtain the instantaneous temperature, which were used to correct the temperature effect. HCN concentrations up to 1500 ppm were detected during the devolatilization stage, and the results indicate a strong temperature dependence of the HCN release.
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| 5. |
- Kiefer, Johannes, et al.
(författare)
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Gas-Phase and Combustion Diagnostics by Infrared Laser-Induced Grating Spectroscopy
- 2016
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Ingår i: Optics and Photonics for Energy and the Environment, E2 2016. - 9781557528209
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Konferensbidrag (refereegranskat)abstract
- Infrared laser-induced grating spectroscopy (IR-LIGS) is a powerful method for the detection of molecules in atmospheric and combustion chemistry by exploiting their strong and species-specific fundamental vibrations. This work discusses potentials and limitations of the method.
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| 6. |
- Kiefer, Johannes, et al.
(författare)
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Misalignment Effects in Laser-Induced Grating Experiments
- 2016
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 70:12, s. 2025-2028
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced grating spectroscopy (LIGS) is an experimental method in which two pulsed laser beams and a continuous-wave laser beam have to be superimposed under well-defined angles to generate a coherent signal beam. In this Note, the possible effects of different forms of misalignment are examined. This includes the overlap of the pump lasers as well as the influence of the probe laser alignment on the temporal profile of the signal.
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| 7. |
- Larsson, Kajsa, et al.
(författare)
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Instantaneous imaging of ozone in a gliding arc discharge using photofragmentation laser-induced fluorescence
- 2018
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 51:13
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Tidskriftsartikel (refereegranskat)abstract
- Ozone vapor, O3, is here visualized in a gliding arc discharge using photofragmentation laser-induced fluorescence. Ozone is imaged by first photodissociating the O3 molecule into an O radical and a vibrationally hot O2 fragment by a pump photon. Thereafter, the vibrationally excited O2 molecule absorbs a second (probe) photon that further transits the O2-molecule to an excited electronic state, and hence, fluorescence from the deexcitation process in the molecule can be detected. Both the photodissociation and excitation processes are achieved within one 248 nm KrF excimer laser pulse that is formed into a laser sheet and the fluorescence is imaged using an intensified CCD camera. The laser-induced signal in the vicinity of the plasma column formed by the gliding arc is confirmed to stem from O3 rather than plasma produced vibrationally hot O2. While both these products can be produced in plasmas a second laser pulse at 266 nm was utilized to separate the pump- from the probe-processes. Such arrangement allowed lifetime studies of vibrationally hot O2, which under these conditions were several orders of magnitude shorter than the lifetime of plasma-produced ozone.
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| 8. |
- Larsson, Kajsa, et al.
(författare)
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Quantitative Imaging of Ozone Vapor Using Photofragmentation Laser-Induced Fluorescence (LIF)
- 2017
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 71:7, s. 1578-1585
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, the spectral properties of gaseous ozone (O3) have been investigated aiming to perform quantitative concentration imaging of ozone by using a single laser pulse at 248 nm from a KrF excimer laser. The O3 molecule is first photodissociated by the laser pulse into two fragments, O and O2. Then the same laser pulse electronically excites the O2 fragment, which is vibrationally hot, whereupon fluorescence is emitted. The fluorescence intensity is found to be proportional to the concentration of ozone. Both emission and absorption characteristics have been investigated, as well as how the laser fluence affects the fluorescence signal. Quantitative ozone imaging data have been achieved based on calibration measurements in known mixtures of O3. In addition, a simultaneous study of the emission intensity captured by an intensified charge-coupled device (ICCD) camera and a spectrograph has been performed. The results show that any signal contribution not stemming from ozone is negligible compared to the strong fluorescence induced by the O2 fragment, thus proving interference-free ozone imaging. The single-shot detection limit has been estimated to ∼400 ppm. The authors believe that the presented technique offers a valuable tool applicable in various research fields, such as plasma sterilization, water and soil remediation, and plasma-assisted combustion.
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| 9. |
- Pedersen, Rasmus L., et al.
(författare)
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Comparison of an InSb Detector and Upconversion Detector for Infrared Polarization Spectroscopy
- 2018
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 72:5, s. 793-797
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Tidskriftsartikel (refereegranskat)abstract
- This paper compares the signal-to-noise ratio obtained using an InSb photodiode for infrared (IR) polarization spectroscopy to that obtained using an upconversion detector, and shows a factor 64 improvement by the change. Upconversion detection is based on using sum frequency generation to move the IR optical signal to near-visible wavelengths to improve the sensitivity.
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| 10. |
- Pedersen, Rasmus L., et al.
(författare)
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Saturation Dependence of Flame Thermometry by Mid-IR Degenerate Four Wave Mixing
- 2021
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 75:1, s. 107-114
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Tidskriftsartikel (refereegranskat)abstract
- It has previously been demonstrated that the ratio of the degenerate four wave mixing signal from two hot water line groups near 3231 cm–1 can be used for seedless flame temperature measurements. This paper presents an investigation of the impact of saturation effects on the measured signal intensity from each line group, as well as an estimation of the accuracy of the method. The saturation effects observed here would result in a large systematic error if they are not taken into account when using the degenerate four-wave mixing intensity of these water line groups to calculate the flame temperature.
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