| 1. |
- Ehn, Andreas, et al.
(författare)
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Development of a temporal filtering technique for suppression of interferences in applied laser-induced fluorescence diagnostics.
- 2009
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Ingår i: Applied Optics. - 2155-3165. ; 48:12, s. 2373-2387
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Tidskriftsartikel (refereegranskat)abstract
- A temporal filtering technique, complementary to spectral filtering, has been developed for laser-induced fluorescence measurements. The filter is applicable in cases where the laser-induced interfering signals and the signal of interest have different temporal characteristics. For the interfering-signal discrimination a picosecond laser system along with a fast time-gated intensified CCD camera were used. In order to demonstrate and evaluate the temporal filtering concept two measurement situations were investigated; one where toluene fluorescence was discriminated from interfering luminescence of an aluminum surface, and in the other one Mie scattering signals from a water aerosol were filtered out from acetone fluorescence images. A mathematical model was developed to simulate and evaluate the temporal filter for a general measurement situation based on pulsed-laser excitation together with time-gated detection. Using system parameters measured with a streak camera, the model was validated for LIF imaging of acetone vapor inside a water aerosol. The results show that the temporal filter is capable of efficient suppression of interfering signal contributions. The photophysical properties of several species commonly studied by LIF in combustion research have been listed and discussed to provide guidelines for optimum use of the technique.
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| 2. |
- Kaldvee, Billy
(författare)
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Development and Application of Single-Ended Picosecond Laser Diagnostics
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Light detection and ranging (lidar), a method for nonintrusive, single-ended, and range resolved measurements, has been developed and applied for combustion related diagnostics. Employing picosecond laser pulse durations and detectors providing temporal resolution on the order of picoseconds, lidar has been applied successfully for both quantitative temperature- and species concentration measurements, obtaining an ultimate range resolution of 0.46 cm. The use of a streak camera as detector allows two-dimensional imaging in a radar-like fashion, or the possibility to extract time resolved spectral information. The experimental setup, permitting lidar measurements in the near field (<10 m), has been developed and characterized, yielding detailed knowledge of picosecond lidar (ps-lidar) and its feasibility in combustion studies. Rayleigh scattering thermometry has been conducted in a tube furnace, various flames, and a large scale room fire experiment. The accuracy, under ambient conditions, was within 5% and the measurements were less prone to scattering off dust in the air than traditional perpendicular detection schemes. In premixed ethylene/air flames, the lidar temperatures agree very well with reference data from coherent anti-Stokes Raman Spectroscopy (CARS) measurements up to an equivalence ratio of 1.3. A filtering routine has been developed to be used for applications in which interfering scattering from particles is expected. The filtering routine was applied in the room fire measurements, which resulted in temperature images of two dimensional planes. The temperatures achieved in experiments with a methanol pool fire located in the room agree well with thermocouple measurements and computational fluid dynamics (CFD) simulations, while the signals recorded with a methane gas diffusion flame in the room are dominated by particle scattering, preventing Rayleigh thermometry, but allowing qualitative particle mapping instead. Tunable optical parametric picosecond lasers were used for differential absorption lidar (DIAL), yielding species concentrations of acetone, ammonia, hydroxyl radical (OH), and potassium chloride (KCl). With a range resolution of 15 cm, a fractional absorption of ~5%, for example corresponding to an ammonia concentration of 40 ppm at ambient condition employing the wavelengths 212.2 and 214.5 nm, sets the detection limit. Processes based on non-elastic light-matter interaction have been investigated for use with ps-lidar. Raman scattering from liquid samples was used for demonstration of range resolved species determination of nitromethane and hydrogen peroxide. Laser-induced fluorescence (LIF) was used in a demonstration of hydroxyl radical (OH) detection and mapping in a slot burner flame. A model for evaluation of laser-induced incandescence (LII) signals acquired with ps-lidar has been developed and demonstrated. Measurements of spatial soot volume fraction distributions yielded results that are in excellent agreement with reference measurements carried out with regular right-angle LII. The following major conclusions can be drawn: ps-lidar is suitable for diagnostics in large scale combustion related devices, particularly devices limited to only one optical access, and, hence, it permits measurements that are currently not possible to realize in any other way, making it a very valuable asset for today’s as well as future challenges within energy science.
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| 3. |
- Kaldvee, Billy, et al.
(författare)
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Development of a picosecond lidar system for large-scale combustion diagnostics.
- 2009
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Ingår i: Applied Optics. - 2155-3165. ; 48:4, s. 65-72
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, a picosecond lidar system aiming at single-ended combustion diagnostics in full-scale combustion devices with limited optical access, such as power plants, is described. The highest overall range resolution of the system was found to be <0.5 cm. A demonstration has been made in a nonsooty and sooty Bunsen burner flame. A well-characterized ethylene flame on a McKenna burner was evaluated for different equivalence ratios using Rayleigh thermometry. The results indicate both that picosecond lidar might be applicable for single-shot Rayleigh thermometry, even two-dimensional, and that there is a possibility to qualitatively map soot occurrence. Furthermore, differential absorption lidar has been investigated in acetone vapor jets for fuel visualization purposes.
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| 4. |
- Kaldvee, Billy, et al.
(författare)
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Highly range-resolved ammonia detection using near-field picosecond differential absorption lidar
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:18, s. 20688-20697
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Tidskriftsartikel (refereegranskat)abstract
- Ammonia detection is highly relevant for combustion in boilers and furnaces since NH3 is able to suppress nitric oxide levels by catalytic as well as non-catalytic reduction. The mixing of ammonia with flue gases is an important parameter to obtain efficient non-catalytic reduction. In this paper picosecond DIAL was used for range-resolved, single ended, NH3 detection, utilizing a tunable picosecond laser source. The absorption spectrum of the A(v(2) = 1)-> X(v(2) = 0) band was recorded and 212.2 and 214.5 nm was selected as the on-and off-resonance wavelength, respectively. One-dimensional concentration profiles with various NH3 concentration distributions are presented. The detection limit was found to be 40 ppm with a spatial resolution of 16 cm. (C) 2012 Optical Society of America
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| 5. |
- Kaldvee, Billy, et al.
(författare)
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LII-lidar: range-resolved backward picosecond laser-induced incandescence
- 2014
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 115:1, s. 111-121
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Tidskriftsartikel (refereegranskat)abstract
- A novel concept for remote in situ detection of soot emissions by a combination of laser-induced incandescence (LII) and light detection and ranging (lidar) is presented. A lidar setup based on a picosecond Nd:YAG laser and time-resolved signal detection in the backward direction was used for LII measurements in sooty premixed ethylene-air flames. Measurements of LII-lidar signal versus laser fluence and flame equivalence ratio showed good qualitative agreement with data reported in literature. The LII-lidar signal showed a decay consisting of two components, with lifetimes of typically 20 and 70 ns, attributed to soot sublimation and conductive cooling, respectively. Theoretical considerations and analysis of the LII-lidar signal showed that the derivative was proportional to the maximum value, which is an established measure of soot volume fraction. Utilizing this, differentiation of LII-lidar data gave profiles representing soot volume fraction with a range resolution of similar to 16 cm along the laser beam propagation axis. The accuracy of the evaluated LII-profiles was confirmed by comparison with LII-data measured simultaneously employing conventional right-angle detection. Thus, LII-lidar provides range-resolved single-ended detection, resourceful when optical access is restricted, extending the LII technique and opening up new possibilities for laser-based diagnostics of soot and other carbonaceous particles.
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| 6. |
- Kaldvee, Billy, et al.
(författare)
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Picosecond-lidar thermometry in a measurement volume surrounded by highly scattering media
- 2011
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Ingår i: Measurement Science & Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 22:12
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a picosecond-lidar system, using a Nd:YAG picosecond laser, a Newtonian telescope and a streak camera, was used for single-ended furnace diagnostics. The optical access of the furnace was obstructed by a sooty diffusion ethylene flame. It was demonstrated that, with proper optical arrangement, the elastic scattering of the flame can be mapped in one dimension simultaneously as temperatures, up to 1200 K, are measured in the furnace using Rayleigh thermometry. Accumulated point temperature measurements as well as one-and two-dimensional measurements were conducted. A discussion about noise influence on accuracy and precision shows that measurements allowing a resolution of similar to 6 cm are possible with a single-pixel temperature standard deviation of 91 K, while mapping soot scattering from the flame within the dynamic range of the streak camera, using 30 mJ pulse energy.
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| 7. |
- Kaldvee, Billy, et al.
(författare)
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Room-Fire Characterization Using Highly Range-Resolved Picosecond Lidar Diagnostics and CFD Simulations
- 2013
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 185:5, s. 749-765
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Tidskriftsartikel (refereegranskat)abstract
- In fire safety engineering, the use of computational fluid dynamics (CFD) allows for detailed multidimensional calculations of important parameters, for example, temperature. However, increasing use of CFD models puts requirements on experimental validation, a challenge for many measurement techniques under harsh fire conditions. In this work, laser-based picosecond light detection and ranging (ps-lidar) was used for remote measurements in a 1/2-scale ISO 9705 room containing either a methanol pool fire or a methane diffusion flame. Spatially resolved Rayleigh thermometry was conducted in the vertical door plane and in a horizontal plane inside the room. Temperatures obtained by ps-lidar are compared with values from thermocouples located in the doorway as well as results from CFD simulations. The technique allows for quantitative thermometry provided that minimal particle scattering interferences are present. Measurements of detailed distributions of temperature and particulates clearly demonstrate the potential of ps-lidar for diagnostics in large-scale combustion.
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| 8. |
- Leffler, Tomas, et al.
(författare)
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Range-resolved detection of potassium chloride using picosecond differential absorption light detection and ranging
- 2015
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Ingår i: Applied Optics. - 2155-3165. ; 54:5, s. 1058-1064
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Tidskriftsartikel (refereegranskat)abstract
- A laser diagnostic concept for measurement of potassium chloride (KCl) and potentially other alkali compounds in large-scale boilers and furnaces of limited optical access is presented. Single-ended, range-resolved, quantitative detection of KCl is achieved by differential absorption light detection and ranging (DIAL) based on picosecond laser pulses. Picosecond DIAL results have been compared experimentally with line-of-sight measurements using a commercial instrument, the in situ alkali chloride monitor (IACM), utilizing differential optical absorption spectroscopy. For centimeter-scale range resolution and a collection distance of 2.5 m, picosecond DIAL allowed for measurement of KCl concentrations around 130 ppm at 1200 K, in good agreement with values obtained by IACM. The DIAL data indicate a KCl detection limit of around 30 ppm for the present experimental conditions. In addition, a double-pulse DIAL setup has been developed and demonstrated for measurements under dynamic conditions with strong Mie scattering. The picosecond DIAL results are discussed and related to possible implementations of the method for measurements in industrial environments. (C) 2015 Optical Society of America
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