| 1. |
|
|
| 2. |
- Nilsson, Lovisa, et al.
(författare)
-
Relating the single particle soot photometer (SP2) signal response to soot maturity
-
Ingår i: Aerosol Science and Technology. - 1521-7388.
-
Tidskriftsartikel (refereegranskat)abstract
- Light absorbing carbonaceous aerosols produced from combustion span over a range of physicochemical properties. Soot is the most recognized species in this category and its formation process involves gradual maturation from amorphous young soot with a high hydrogen-to-carbon-ratio toward mature soot aggregates. In this work, the optical response of a single particle soot photometer (SP2) to electrical mobility size selected soot of different maturity produced by a mini-CAST soot generator is investigated. The results show that for soot of a specific mobility diameter, the laser-induced incandescence (LII) signal appears earlier and with a higher LII peak height for increasing soot maturity. The experimental observations are supported by simulations using a numerical model for the LII process. Furthermore, the effect of systematically varying the SP2 laser power on the detection of soot of different maturity using LII is explored. This work can be seen as a step toward the aim of using the SP2 instrument to identify soot particles of different maturity in the atmosphere.
|
|
| 3. |
- Bergh, Jonas, et al.
(författare)
-
Tailored fluorouracil, epirubicin, and cyclophosphamide compared with marrow-supported high-dose chemotherapy as adjuvant treatment for high-risk breast cancer : A randomised trial
- 2000
-
Ingår i: The Lancet. - 0140-6736 .- 1474-547X. ; 356:9239, s. 1384-1391
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Chemotherapy drug distribution varies greatly among individual patients. Therefore, we developed an individualised fluorouracil, epirubicin, cyclophosphamide (FEC) regimen to improve outcomes in patients with high-risk early breast cancer. We then did a randomised trial to compare this individually tailored FEC regimen with conventional adjuvant chemotherapy followed by consolidation with high-dose chemotherapy with stem-cell support. Methods: 525 women younger than 60 years of age with high-risk primary breast cancer were randomised after surgery to receive nine cycles of tailored FEC to haematological equitoxicity with granulocyte colony-stimulating factor (G-CSF) support (n=251), or three cycles of FEC at standard doses followed by high-dose chemotherapy with cyclophosphamide, thiotepa, and carboplatin (CTCb), and peripheral-blood stem-cell or bone-marrow support (n=274). Both groups received locoregional radiation therapy and tamoxifen for 5 years. The primary outcome measure was relapse-free survival, and analysis was by intention to treat. Findings: At a median follow-up of 34.3 months, there were 81 breast-cancer relapses in the tailored FEC group versus 113 in the CTCb group (double triangular method p=0.04). 60 deaths occurred in the tailored FEC group and 82 in the CTCb group (log-rank p=0.12). Patients in the CTCb group experienced more grade 3 or 4 acute toxicity compared with the tailored FEC group (p<0.0001). Two treatment-related deaths (0.7%) occurred in the CTCb group. Six patients in the tailored FEC group developed acute myeloid leukaemia and three developed myelodysplastic syndrome. Interpretation: Tailored FEC with G-CSF support resulted in a significantly improved relapse-free survival and fewer grade 3 and 4 toxicities compared with marrow-supported high-dose chemotherapy with CTCb as adjuvant therapy of women with high-risk primary breast cancer.
|
|
| 4. |
|
|
| 5. |
- Bladh, Henrik, et al.
(författare)
-
Influence of Soot Particle Aggregation on Time-Resolved Laser-Induced Incandescence Signals
- 2011
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 104:2, s. 331-341
-
Tidskriftsartikel (refereegranskat)abstract
- Laser-induced incandescence (LII) is a versatile technique for quantitative soot measurements in flames and exhausts. When used for particle sizing, the time-resolved signals are analysed as these will show a decay rate dependent on the soot particle size. Such an analysis has traditionally been based on the assumption of isolated primary particles. However, soot particles in flames and exhausts are usually aggregated, which implies loss of surface area, less heat conduction and hence errors in estimated particle sizes. In this work we present an experimental investigation aiming to quantify this effect. A soot generator, based on a propane diffusion flame, was used to produce a stable soot stream and the soot was characterised by transmission electron microscopy (TEM), a scanning mobility particle sizer (SMPS) and an aerosol particle mass analyzer coupled in series after a differential mobility analyzer (DMA-APM). Despite nearly identical primary particle size distributions for three selected operating conditions, LII measurements resulted in signal decays with significant differences in decay rate. However, the three cases were found to have quite different levels of aggregation as shown both in TEM images and mobility size distributions, and the results agree qualitatively with the expected effect of diminished heat conduction from aggregated particles resulting in longer LII signal decays. In an attempt to explain the differences quantitatively, the LII signal dependence on aggregation was modelled using a heat and mass transfer model for LII given the primary particle and aggregate size distribution data as input. Quantitative agreement was not reached and reasons for this discrepancy are discussed.
|
|
| 6. |
- Bladh, Henrik, et al.
(författare)
-
Optical soot characterization using two-color laser-induced incandescence (2C-LII) in the soot growth region of a premixed flat flame
- 2011
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 33, s. 641-648
-
Tidskriftsartikel (refereegranskat)abstract
- The soot growth region of a premixed one-dimensional ethylene/air flame has been investigated using two-color laser-induced incandescence (2C-LII) with focus on optical soot properties. From the 2C-LII technique, primary soot particle sizes were deduced together with the temperature from pyrometry of the laser-heated particles, while the gas temperatures were obtained from pure rotational CARS nitrogen thermometry. Soot particle sizes were also measured from thermophoretically sampled soot particles analyzed by transmission electron microscopy (TEM), and the results showed growing isolated primary soot particles up to a height of 10 mm, after which strong soot aggregation occurred and the increase in soot primary particle size ceased. The measured data was used in the evaluation of the soot absorption function, E(m), and a strong increase by a factor of two was observed from the lowest heights to the highest for assumed constant values of soot density and specific heat at all heights. By comparing the 2C-LII particle sizes with the sizes obtained from TEM, differences were observed. Part of the explanation is that the 2C-LII evaluation did not take aggregation into account, but it is additionally speculated that the thermal accommodation coefficient decreases with height above burner. These results are interesting in view of morphological and composition changes of the soot during the growth process and have implications for the use of 2C-LII as a soot diagnostic technique. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
|
|
| 7. |
- Bladh, Henrik, et al.
(författare)
-
Probing the smallest soot particles in low-sooting premixed flames using laser-induced incandescence
- 2015
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35, s. 1843-1850
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we investigate nascent soot particles by analyzing laser-induced incandescence (LII) signals obtained in low-sooting premixed flames. The analysis covers two data sets obtained in separate experimental campaigns. The first data set was obtained in a previous work (Mouton et al., 2013) in methane/oxygen/nitrogen flames (equivalence ratio range 1.95 < Phi < 2.32) at 26.7 kPa, whereas the second was performed in atmospheric ethylene/air flames (1.77 < Phi < 2.00). Both studies show similar trends, i.e. a gradual change of the fluence curves (evolution of the LII signal as function of the laser fluence) from the well-known S-shaped curve for mature soot found at high heights above the burner (HAB) and high equivalence ratio, to a nearly linear behavior for nascent soot found at low HAB and reduced equivalence ratio. With this change comes a decrease in the LII decay time (and hence inferred particle size). Also, this decay time appears to be almost constant with HAB in flames having the lowest equivalence ratio at which the incandescence signal could be detected. In these flames, so-called nucleation flames, the stability of the particle size with HAB suggests that recently nucleated particles have undergone marginal surface growth and coagulation. Existence of such nucleation flames is of great interest for improving the theoretical description of the nucleation step. Experimental results are analyzed by using a theoretical model for LII to determine the particle size evolution throughout the flame at various experimental conditions. We highlight the size difference from nascent soot particles up to mature soot, giving insight into the particle nucleation and the surface growth processes as a function of reaction time and flame conditions. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
|
|
| 8. |
|
|
| 9. |
- Gallo, Yann, et al.
(författare)
-
Investigation of Late-Cycle Soot Oxidation Using Laser Extinction and In-Cylinder Gas Sampling at Varying Inlet Oxygen Concentrations in Diesel Engines
- 2017
-
Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 193, s. 308-314
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the relative importance of O2 and OH as oxidizers of soot during the late cycle in diesel engines, where the soot oxidation is characterized in an optically accessible engine using laser extinction measurements. These are combined with in cylinder gas sampling data from a single cylinder engine fitted with a fast gas sampling valve. Both measurements confirm that the in-cylinder soot oxidation slows down when the inlet concentration of O2 is reduced. A 38% decrease in intake O2 concentration reduces the soot oxidation rate by 83%, a non-linearity suggesting that O2 in itself is not the main soot oxidizing species. Chemical kinetics simulations of OH concentrations in the oxidation zone and estimates of the OH soot oxidation rates point towards OH being the dominant oxidizer.
|
|
| 10. |
- Johansson, Nils, et al.
(författare)
-
Möjlighet till utrymning vid brand
- 2012
-
Ingår i: Brandskyddshandboken - En handbok för projektering av brandskydd i byggnader. - 1402-3504. ; , s. 75-116
-
Bokkapitel (refereegranskat)
|
|
| 11. |
- Johnsson, Jonathan, et al.
(författare)
-
Influence of soot aggregate structure on particle sizing using laser-induced incandescence: importance of bridging between primary particles
- 2013
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 112:3, s. 321-332
-
Tidskriftsartikel (refereegranskat)abstract
- Soot aggregates formed in combustion processes are often described as clusters of carbonaceous particles in random fractal structures. For theoretical studies of the physical properties of such aggregates, they have often been modelled as spherical primary particles in point contact. However, transmission electron microscopy (TEM) images show that the primary particles are more connected than in a single point; there is a certain amount of bridging between the primary particles. Particle sizing using the diagnostic technique laser-induced incandescence (LII) is crucially dependent on the heat conduction rate from the aggregate to the ambient gas, which depends on the amount of bridging. In this work, aggregates with bridging are modelled using overlapping spheres, and it is shown how such aggregates can be built to fulfil specific fractal parameters. Aggregates with and without bridging are constructed numerically, and it is investigated how the bridging influences the heat conduction rate in the free-molecular regime. The calculated heat conduction rates are then used in an LII model to show how LII particle sizing is influenced by different amounts of bridging. For realistic amounts of bridging (), the primary particle diameters were overestimated by up to 9 % if bridging was not taken into account.
|
|
| 12. |
- Lind, Ted, et al.
(författare)
-
Simultaneous PLIF Imaging of OH and PLII Imaging of Soot for Studying the Late-Cycle Soot Oxidation in an Optical Heavy-Duty Diesel Engine
- 2016
-
Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3936 .- 1946-3944. ; 9:2, s. 849-858
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of injection pressure and swirl ratio on the in-cylinder soot oxidation are studied using simultaneous PLIF imaging of OH and LII imaging of soot in an optical diesel engine. Images are acquired after the end of injection in the recirculation zone between two adjacent diesel jets. Scalars are extracted from the images and compared with trends in engine-out soot emissions. The soot emissions decrease monotonically with increasing injection pressure but show a non-linear dependence on swirl ratio. The total amount of OH in the images is negatively correlated with the soot emissions, as is the spatial proximity between the OH and soot regions. This indicates that OH is an important soot oxidizer and that it needs to be located close to the soot to perform this function. The total amount of soot in the images shows no apparent correlation with the soot emissions, indicating that the amount of soot formed is a poor predictor of the emission trends.
|
|
| 13. |
- Nordström, Emil, et al.
(författare)
-
Local gas heating in sooting flames by heat transfer from laser-heated particles investigated using rotational CARS and LII
- 2015
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35, s. 3707-3713
-
Tidskriftsartikel (refereegranskat)abstract
- Soot particles strongly absorb radiation in the visible and infrared spectral regions, and the soot interaction with laser light during laser diagnostic interrogation leads to particle heating and often to subsequent sublimation. Consequently, laser-heated particles transfer heat to the ambient gas leading to local gas heating, a process that has received minor attention so far in the diagnostic community. In the present work, this specific local gas heating is measured in a pump-probe-type experiment. A 1064-nm laser beam heated the soot particles in an ethylene/ air diffusion flame (on a Gulder-burner) with known soot volume fraction, and a two-beam rotational coherent anti-Stokes Raman spectroscopy (CARS) setup was used to probe the local gas temperature on time scales from nanoseconds to milliseconds. The temperature of the heated particles was simultaneously probed using a two-color laser-induced incandescence (2C-LII) detection system. The results show that laser heating of soot particles from flame temperatures to sublimation temperatures leads to local gas heating of similar to 100 K at a soot volume fraction of 4 ppm, in good agreement with theoretical predictions. The implication of these results to the application of laser diagnostic techniques is briefly discussed. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
|
|
| 14. |
- Oliveira, M. H. de Andrade, et al.
(författare)
-
Soot, PAH and OH measurements in vaporized liquid fuel flames
- 2013
-
Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 112, s. 145-152
-
Tidskriftsartikel (refereegranskat)abstract
- Qualitative measurements of both OH and polycyclic aromatic hydrocarbons (PAH) as well as quantitative data of soot volume fraction f(v) have been obtained in vaporized liquid fuels, with the main goal of providing experimental data for combustion models and numerical mechanism validation. Measurements were carried out in a laminar coflow burner which was designed, built and integrated with an evaporation system, enabling the combustion of vaporized liquid fuels at pressures of up to 3.0 MPa to be studied. The fuels n-heptane and n-decane, referred to in the literature as being important surrogate fuels, were selected for measurements at atmospheric pressure that were carried out in the experimental setup described, making use of a combination of the Laser Induced Fluorescence (LIF) and Laser Induced Incandescence (LII) techniques. Partially premixed flames of n-heptane and n-decane showed similar combustion characteristics in the range of 1.9 < phi < 3.7. For both of the fuels the threshold for soot formation was found to be at about phi similar to 3.3. Comparison of the LIF and LII measurements for the n-heptane flames within the range of 3.7 <= phi <= 8.5 indicated the maximum PAH LIF signal to be a good predictor of f(vmax) obtained from LII. Excitation at 266 nm using delayed detection was found to result in the signals obtained showing a close linear correlation with the soot volume fraction obtained from LII when prompt detection at 1064 nm excitation was used. Neither the effects of any additional photo-chemical processes making use of high laser power at 266 nm nor the effects of particle size on the delayed gate times appeared to be of any significance for the flame conditions studied here. (C) 2013 Elsevier Ltd. All rights reserved.
|
|
| 15. |
- Olofsson, Nils-Erik, et al.
(författare)
-
Are Sooting Premixed Porous-Plug Burner Flames One-Dimensional? A Laser-Based Experimental Investigation
- 2013
-
Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 185:2, s. 293-309
-
Tidskriftsartikel (refereegranskat)abstract
- The one-dimensional character of sooting premixed porous-plug (McKenna) burner flames has been examined, motivated by recent investigations where the one-dimensionality has been questioned. The examination employs laser diagnostic techniques to measure different characteristics: temperature using rotational coherent anti-Stokes Raman spectroscopy (CARS) and soot properties using laser-induced incandescence and elastic light scattering. Special attention has been paid to the influence of an outer shroud gas flow of either nitrogen or air. The nitrogen shroud gas leads to flame cooling at the outer edge, whereas the air shroud results in heating through the oxidation of CO/H-2/soot. This generally results in a more inhomogeneous spatial particle size profile for the nitrogen shroud flame, with smaller particle sizes at the flame edge. The present results emphasize the need to characterize burner and operating conditions accurately, and also, regarding parameters that at first glance seem less relevant, such as the shroud gas, to provide useful data for comparison between laboratories.
|
|
| 16. |
- Olofsson, Nils-Erik, et al.
(författare)
-
Evolution of properties for aging soot in premixed flat flames studied by laser-induced incandescence and elastic light scattering
- 2015
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 119:4, s. 669-683
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed study has been made of soot growth in two premixed flat ethylene/air flames, at I broken vertical bar = 2.1 and I broken vertical bar = 2.3, where focus has been on following the change in optical properties from nascent to more mature soot, and the importance of these properties for laser-induced incandescence (LII). A combination of two-color LII (2C-LII) and elastic light scattering was utilized for studies of soot absorption and sublimation for a range of laser fluences in a pump-probe experiment, and the experimental results were compared with LII model predictions. Both flames show similar trends, indicating that the soot becomes less transparent during the growth process until some level of maturity is reached at higher flame heights, where the measured properties reach almost constant values. A sublimation fluence threshold of similar to 0.14 J/cm(2) (at 1064 nm for a flame temperature around 1700 K) was evaluated for mature soot, corresponding to a sublimation temperature of similar to 3400 K. Soot peak temperatures from 2C-LII were evaluated both using a constant E(m) and a wavelength dependence for E(m) extracted from extinction measurements, leading to a discussion on how the sublimation temperature relates to the maturity of soot.
|
|
| 17. |
- Olofsson, Nils-Erik, et al.
(författare)
-
Soot sublimation studies in a premixed flat flame using laser-induced incandescence (LII) and elastic light scattering (ELS)
- 2013
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 112:3, s. 333-342
-
Tidskriftsartikel (refereegranskat)abstract
- Laser-induced incandescence (LII) as a diagnostic technique is based on rapid heating of soot particles to temperatures of several thousand Kelvin and subsequent detection of the thermal radiation from the laser-heated particles. At such high temperatures, soot sublimation effects must be considered when estimating uncertainties in LII measurements. In this work we have investigated the use of various laser fluences in LII using a Nd:YAG laser at 1,064 nm. Using another Nd:YAG laser at 532 nm, the elastic light scattering (ELS) signal from soot particles heated by the 1,064-nm laser was monitored. This approach makes it possible to determine at which fluence of the LII laser soot sublimation starts to become visible as a decrease in the ELS signal. By performing the measurements at various heights in a premixed sooting flat ethylene/air flame, the fluence threshold above which the ELS signal decreased was found to be higher at the lower flame heights corresponding to younger, smaller and less aggregated particles. The results from this work indicate that the different fluence thresholds for sublimation may be explained by a lower absorption function E(m) for the younger soot particles.
|
|
| 18. |
- Robert, Etienne, et al.
(författare)
-
Soot Formation in Unstrained Diffusion Flames
- 2015
-
Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 187:4, s. 577-593
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of soot particles has been investigated in CH4/O-2 diffusion flames using a unique burner design, which allows the creation of a nearly unstrained planar reaction sheet. Spatially resolved soot volume fractions were obtained using laser-induced incandescence. These soot measurements and the sooting limits were obtained as a function of bulk flow across the flame and mixture strength. Samples were collected using thermophoretic sampling and analyzed using electron microscopy, revealing a broad range of microstructures including particles with unusually large primary diameters and carbon nanotubes. A theoretical model is presented, which confirms that under certain conditions the 1D nature of the flow field of the burner and the strong adverse temperature gradient on the fuel side of the flame result in the soot particles being held in place by thermophoretic forces and allowed to grow for very long time periods. Some of these so-called super aggregates reached sizes of tens of microns and became visible to the naked eye in the soot layer.
|
|
| 19. |
- Simonsson, Johan, et al.
(författare)
-
Influence of potassium and iron chloride on the early stages of soot formation studied using imaging LII/ELS and TEM techniques
- 2017
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 36:1, s. 853-860
-
Tidskriftsartikel (refereegranskat)abstract
- Laser-induced incandescence (LII), elastic light scattering (ELS) and extinction were used to investigate the early stages of soot formation when seeding metal salts at various concentrations into a premixed ethylene/air flame on a PerkinElmer burner. The investigation contained seven salts, where we in this work mainly focus on two of these salts, potassium chloride (KCl) and iron chloride (FeCl3), as these for mature soot resulted in the largest reduction and highest increase in soot concentration, respectively. The optical measurements show that the potassium chloride significantly reduces the build-up of larger soot precursors and also decreases the sizes of the primary soot particles both at the nucleation stage as well as for more mature soot later in the formation process. This is also confirmed by analysis of transmission electron microscopy (TEM) images, which clearly show smaller primary soot particles for the potassium chloride-seeded flame. The iron chloride-seeded flames were found to have marginal influence on the primary particle sizes based on the optical data, although somewhat more irregular shapes could be observed in TEM images.
|
|
| 20. |
- Simonsson, Johan, et al.
(författare)
-
Influence of potassium chloride and other metal salts on soot formation studied using imaging LII and ELS, and TEM techniques
- 2018
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 190, s. 188-200
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation has been performed where the influence of metal salts on soot formation has been studied. By combining two-dimensional laser-induced incandescence (LII) and elastic light scattering (ELS), two-dimensional information could be obtained on soot properties in the flames. For these studies, seven metal salts (NaCl, MgCl2, AlCl3, KCl, CaCl2, FeCl3 and ZnCl2) were dissolved in water and aspirated into a premixed ethylene/air flame. At lower flame heights, in the soot inception region, the LII signal (representing soot volume fraction) was marginally affected by all additives, whereas the ELS signal strongly decreased with increasing additive concentration for the alkali salts. At higher heights, in the soot growth region, the soot volume fractions were lowered for the addition of potassium, calcium and sodium chloride, in order of significance. Some of the salts (MgCl2, AlCl3 and FeCl3) resulted in negligible influence on LII signals and slightly higher ELS signals throughout the flames, and we relate the increased ELS signals to salt particles propagating through the flame. Main focus in our study was on the addition of potassium chloride for which several parameters were investigated. For example, soot primary particle sizes were evaluated using combined LII and ELS, showing decreasing particle sizes for increasing concentrations of potassium, in reasonable agreement with particle sizes evaluated using transmission electron microscopy. Also, CARS thermometry showed slightly higher flame temperature, ∼30 K, for the potassium-seeded flame compared to the reference flame.
|
|
| 21. |
- Simonsson, Johan, et al.
(författare)
-
Wavelength dependence of extinction in sooting flat premixed flames in the visible and near-infrared regimes
- 2015
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 119:4, s. 657-667
-
Tidskriftsartikel (refereegranskat)abstract
- A diode-laser-based setup was used for extinction measurements at various heights in two flat premixed sooting ethylene/air flames in order to investigate the wavelength dependence of the extinction. Twelve laser wavelengths were used in the interval 405-1064 nm, and with this setup, a sensitivity of similar to 10(-4) was achieved for the extinction. Soot volume fractions inferred from the extinction measurements were always higher in the visible spectral region than in the infrared, an effect associated with additional absorption by large hydrocarbons, such as polycyclic aromatic hydrocarbons. For wavelengths greater than around 700 nm and at high heights above burner (HAB), the extinction shows an inverse dependence with wavelength, in concurrence with wavelength-independent optical properties of soot. In the same spectral region at lower HAB, the wavelength dependence is observed to be stronger, indicating that the soot optical properties show variation with wavelength. Furthermore, a continuous change in the wavelength dependence of the absorption function E(m) is shown from nascent soot at lower heights to more mature soot at higher heights. The presented results are of importance for soot diagnostics relying on the efficiency of light absorption by soot such as laser-induced incandescence (LII).
|
|
| 22. |
- Afzelius, Mikael, et al.
(författare)
-
Development of multipoint vibrational coherent anti-Stokes Raman spectroscopy for flame applications
- 2006
-
Ingår i: Applied Optics. - 2155-3165. ; 45:6, s. 1177-1186
-
Tidskriftsartikel (refereegranskat)abstract
- A novel technique for coherent anti-Stokes Raman spectroscopy (CARS) measurements in multiple points is presented. In a multipass cavity the pump and Stokes laser beams are multiply reflected and refocused into a measurement volume with an adjustable number of separated points along a line. This optical arrangement was used in a vibrational CARS setup with planar BOXCARS phase-matching configuration. The CARS spectra from spatially separated points were recorded at different heights on a CCD camera. Measurements of temperature profiles were carried out in the burned gas zone of a premixed one-dimensional flame to demonstrate the applicability of this method for temperature measurements in high-temperature regions. The ability to measure in flames with strong density gradients was demonstrated by simultaneous measurements of Q-branch spectra of N-2 and CO in a Wolfhard-Parker burner flame. Interference phenomena found in multipoint spectra are discussed, and possible solutions are proposed. Merits and limitations of the technique are discussed. (c) 2006 Optical Society of America.
|
|
| 23. |
- Afzelius, Mikael, et al.
(författare)
-
Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. I. Inter-branch interference effect
- 2002
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 763-769
-
Tidskriftsartikel (refereegranskat)abstract
- An improved model for pure rotational coherent anti-Stokes Raman scattering (CARS) has been developed or the dual-broadband approach. This model takes into account the fact that coherent anti-Stokes as well as Stokes radiation are generated simultaneously, and these two branches overlap and interact at high pressures giving rise to an inter-branch interference effect. In combustion studies, the anti-Stokes branch is used to determine temperature and concentrations of key species, of which nitrogen is the most widely used, and we have found that the interference effect on the anti-Stokes side is of such magnitude that it clearly needs to be taken into account at pressures of a few MPa. The necessary modifications to the total third-order susceptibility are presented and a derivation of the convolution integral for a finite-bandwidth pump source is given.
|
|
| 24. |
- Afzelius, Mikael, et al.
(författare)
-
Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. II. Rotational Raman line widths
- 2002
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 771-778
-
Tidskriftsartikel (refereegranskat)abstract
- Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures an atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5-9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S-1-branch Raman line widths measured at 295 K, with a temperature dependence extracted from semi-classical calculations following the Robert-Bonamy formalism. It is shown that these two modifications significantly improve the theoretical model, since both the spectral fits and the accuracy of the evaluated temperatures are considerably improved.
|
|
| 25. |
- Afzelius, Mikael, et al.
(författare)
-
Precision of single-shot dual-broadband rotational CARS thermometry with single-mode and multi-mode Nd : YAG lasers
- 2003
-
Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 34:12, s. 940-945
-
Konferensbidrag (refereegranskat)abstract
- The precision of single-shot coherent anti-Stokes Raman spectroscopy (CARS) thermometry is an important characteristic for the application of CARS in various combustion devices such as internal combustion engines. It is generally assumed that the precision of CARS is directly related to the spectral noise of the interacting laser fields, and previous studies have presented a theoretical model describing the behaviour of the noise as a function of various experimental parameters. In this work, the aim was to test the results predicted by the previously developed model for dual-broadband rotational CARS. We studied the precision of evaluated temperatures in pure nitrogen under different experimental conditions, namely the dependence of precision on the gas pressure and on the linewidth of the narrowband laser (the Nd: YAG laser). It was demonstrated that our experiments reproduce the main features of the model, and that a single-mode Nd: YAG laser leads to better precision than a multi-mode Nd: YAG laser for dual-broadband rotational CARS thermometry. Copyright (C) 2003 John Wiley Sons, Ltd.
|
|
| 26. |
- Afzelius, Mikael, et al.
(författare)
-
Pure rotational coherent anti-Stokes Raman spectroscopy in mixtures of CO and N-2
- 2004
-
Ingår i: Applied Optics. - 2155-3165. ; 43:36, s. 6664-6672
-
Tidskriftsartikel (refereegranskat)abstract
- We present a model for quantitative measurements in binary mixtures of nitrogen and carbon monoxide by the use of dual-broadband rotational coherent anti-Stokes Raman spectroscopy. The model has been compared with experimental rotational coherent anti-Stokes Raman scattering spectra recorded within the temperature range of 294-702 K. Temperatures and concentrations were evaluated by spectral fits using libraries of theoretically calculated spectra. The relative error of the temperature measurements was 1-2%, and the absolute error of the CO concentration measurements was <0.5% for temperatures less than or equal to600 K. For higher temperatures, the gas composition was not chemically stable, and we observed a conversion of CO to CO2. The influence of important spectroscopic parameters such as the anisotropic polarizability and Raman line-broadening coefficients are discussed in terms of concentration measurements. In particular, it is shown that the CO concentration measurement was more accurate if N-2-CO and CO-N-2 line-broadening coefficients were included in the calculation. The applicability of the model for quantitative flame measurements is demonstrated by measuring CO concentrations in ethylene/air flames. (C) 2004 Optical Society of America.
|
|
| 27. |
- Afzelius, Mikael, et al.
(författare)
-
Semiclassical calculations of collision line broadening in Raman spectra of N-2 and CO mixtures
- 2004
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:18, s. 8616-8623
-
Tidskriftsartikel (refereegranskat)abstract
- We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N-2 and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N-2, the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N-2 and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N-2. The central results of this work are the Q-branch linewidths of N-2-CO and CO-N-2, which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules. (C) 2004 American Institute of Physics.
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
|
|
| 31. |
|
|
| 32. |
|
|
| 33. |
- Almgren, Erik, et al.
(författare)
-
Brandförlopp
- 2012
-
Ingår i: Brandskyddshandboken - En handbok för projektering av brandskydd i byggnader. - 1402-3504. ; , s. 211-228
-
Bokkapitel (refereegranskat)
|
|
| 34. |
- Alsved, Malin, et al.
(författare)
-
Droplet, aerosol and SARS-CoV-2 emissions during singing and talking
- 2021
-
Konferensbidrag (refereegranskat)abstract
- IntroductionAs the pandemic continues to spread, more knowledge is needed about the viral transmission routes. Several super spreading events during the Covid-19 pandemic have been linked to singing in choirs and talking loud. However, in the beginning of the pandemic there was only one study about emitted aerosols and droplets from singing, published in 1968, and only a handful on emissions from talking. Therefore, we conducted a study to measure the aerosol and droplet emissions from talking and singing. We also evaluated the emissions from singing when wearing a face mask.We have further developed our setup so that we collect the aerosol particles from Covid-19 infected patients that are talking and singing, and analyze our samples for SARS-CoV-2, the virus causing Covid-19.MethodTwelve healthy singers (7 professionals, 5 amateurs) were included in the first study part on quantifying the amount of emitted aerosols and droplets. The singers were singing or talking a short consonant rich text repeatedly at a constant pitch with their face in the opening of a funnel. The aerosol particle size and concentration was measured from the other end of the funnel using an aerodynamic particle sizer (APS, 3321, TSI Inc). In addition, the amount of un-evaporated droplets were captured with a high-speed camera and quantified using image analysis.During February and March 2021 we will collect aerosol particles from patients with confirmed Covid-19 that are singing and talking into a funnel. We will use a growth tube condensation collector, a BioSpot (Aerosol Devices), operating at 8 L min-1, and a NIOSH BC-251 cyclone sampler operating at 3.5 L min-1 (TISCH Environmental). The BioSpot collects the whole range of exhaled aerosol particles with high (95%) efficiency into liquid, and the NIOSH cyclone sampler collects particles into three size fractions: <1 µm (filter), 1-4 µm (liquid), >4 µm (liquid). The APS is again used to measure size and concentration of the emitted aerosol particles, so that emissions from infected test subjects can be compared with those of the healthy test subjects. Air samples will be analyzed for detection of SARS-CoV-2 genes, and if possible, SARS-CoV-2 infectivity in cell cultures.ResultsAerosol particle emissions from healthy test subjects were significantly higher during normal singing (median 690, range [320–2870] particles/s) than during normal talking (270 [120–1380] particles/s) (Wilcoxon’s signed rank test, p=0.002). Loud singing produced even more aerosol particles (980 [390–2870] particles/s) than normal singing (p=0.002). The amount of non-evaporated droplets detected by the high-speed camera setup showed similar results: more droplets during loud singing or talking. For both aerosol particle concentrations and droplet numbers, the levels were reduced by on average 70-80% when wearing a surgical face mask.ConclusionsSinging and talking give rise to high aerosol and droplet emissions from the respiratory tract. This is likely an important transmission route for Covid-19. In our upcoming part of the study we hope to determine how much SARS-CoV-2 that is emitted during these social activities.
|
|
| 35. |
|
|
| 36. |
- Alsved, Malin, et al.
(författare)
-
Exhaled respiratory particles during singing and talking
- 2020
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 1521-7388 .- 0278-6826. ; 54:11, s. 245-1248
-
Tidskriftsartikel (refereegranskat)abstract
- Choir singing has been suspended in many countriesduring the Covid-19 pandemic due to incidental reportsof disease transmission. The mode of transmission has been attributed to exhaled droplets, but with the exception of a study on tuberculosis from1968, there is presently almost no scientific evidence ofincreased particle emissions from singing. A substantial number of studies have,however, investigated aerosols emitted from breathing,talking, coughing and sneezing. It has also been shown that justnormal breathing over time can generate more viablevirus aerosol than coughing, since the latter is a less fre-quent activity.Compared to talking, singing often involves continu-ous voicing, higher sound pressure, higher frequencies,deeper breaths, higher peak airflows and more articu-lated consonants. All these factors are likely to increaseexhaled emissions.The aim of this study was to investigate aerosol anddroplet emissions during singing, as compared to talking and breathing. We also examined the presence of SARS-CoV-2 in the air from breathing, talking and singing,and the efficacy of face masks to reduce emissions. In this study we defined aerosol particles as having a drysize in the range 0.5–10mm. Although debatable from anaerosol physics point of view, a cutoff diameter between5 and 10mm is normally used in medicine for classifica-tion of aerosol versus droplet route of transmission. Droplets are here defined as exhaled particles, frommicron size with no upper size limit, and measured dir-ectly at the mouth before complete evaporation, thuspartly in liquid phase.
|
|
| 37. |
|
|
| 38. |
|
|
| 39. |
- Axelsson, Boman, et al.
(författare)
-
Laser-induced incandescence for soot particle size and volume fraction measurements using on-line extinction calibration
- 2001
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 72:3, s. 367-372
-
Tidskriftsartikel (refereegranskat)abstract
- A novel technique for two-dimensional measurements of soot volume fraction and particle size has been developed. It is based on a combined measurement of extinction and laser-induced incandescence using Nd:YAG laser wavelengths of 532 nm and 1064 nm. A low-energy laser pulse at 532 nm was used for extinction measurements and was followed by a more intense pulse at 1064 nm, delayed by 15 ns, for LII measurements. The 532-nm beam was split into a signal beam passing the flame and a reference beam, both of which were directed to a dye cell. The resulting fluorescence signals, from which the extinction was deduced, together with the LII signal, were registered on a single CCD detector. Thus the two-dimensional LII image could be converted to a soot volume fraction map through a calibration procedure during the same laser shot. The soot particle sizes were evaluated from the ratio of the temporal LII signals at two gate time positions. The uncertainty in the particle sizing arose mainly from the low signal for small particles at long gate times and the uncertainty in the flame temperature. The technique was applied to a well-characterized premixed flat flame, the soot properties of which had been previously thoroughly investigated.
|
|
| 40. |
- Axelsson, Boman, et al.
(författare)
-
Laser-Induced Incandescence for Soot Particle Size Measurements in Premixed Flat Flames
- 2000
-
Ingår i: Applied Optics. - 2155-3165. ; 39:21, s. 3683-3690
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of soot properties by means of laser-induced incandescence (LII) and combined scattering–extinction were performed in well-characterized premixed ethylene–air flames. In particular, the possibility of using LII as a tool for quantitative particle sizing was investigated. Particle sizes were evaluated from the temporal decay of the LII signal combined with heat balance modeling of laser-heated particles, and these sizes were compared with the particle sizes deduced from scattering–extinction measurements based on isotropic sphere theory. The correspondence was good early in the soot-formation process but less good at later stages, possibly because aggregation to clusters began to occur. A critical analysis has been made of how uncertainties in different parameters, both experimental and in the model, affect the evaluated particle sizes for LII. A sensitivity analysis of the LII model identified the ambient-flame temperature as a major source of uncertainty in the evaluated particle size, a conclusion that was supported by an analysis based on temporal LII profiles.
|
|
| 41. |
|
|
| 42. |
|
|
| 43. |
- Bengtsson, Per Erik, et al.
(författare)
-
C2 Production and Excitation in Sooting Flames using Visible Laser Radiation : Implications for Diagnostics in Sooting Flames
- 1991
-
Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 77:4-6, s. 307-318
-
Tidskriftsartikel (refereegranskat)abstract
- Swan band emission of C2. which had been produced and excited (d3∏x←a 3∏u, Δ v = 0) by focused, tunable, visible laser radiation, was studied in sooting ethylene flames. The C2signal from the sooting regions of the flames was found to be proportional to the measured volume fractions of soot, indicating laser-vaporized soot to be the source of the signal, and as such it can be used as a diagnostic tool for point measurements of the volume fraction of soot. C2emission was detected for all incident wavelengths between 485 and 540 nm, with a C2signal 1–2 orders of magnitude higher when the wavelength was tuned to a C2 resonance than when tuned to a wavelength between the Swan bands. High concentrations of laser-produced C2 and emission from C2Swan bands can, through interference effects, limit the applicability of laser diagnostic techniques to sooting flames.
|
|
| 44. |
- Bengtsson, Per Erik, et al.
(författare)
-
Dual-broadband rotational cars measurements in an IC engine
- 1994
-
Ingår i: Symposium (International) on Combustion. - 0082-0784. ; 25:1, s. 1735-1742
-
Tidskriftsartikel (refereegranskat)abstract
- This is the first report of pure rotational coherent anti-Stokes Raman spectroscopy (CARS) measurementsin an internal combustion (IC) engine. Single-shot, dual-broadband rotational CARS (DB-RCARS) spectra were recorded both prior to ignition and in the postcombustion gases. From these spectra, both temperature and relative oxygen concentrations were evaluated. The pressure was registered simultaneously with the CARS measurements in the spark-ignition engine burning natural gas and air. Prior to ignition, normally at temperatures below 1000 K and pressures below 2 MPa, a rotational CARS spectrum is very temperature sensitive, and the technique can be used for temperature measurements with high accuracy. Evaluated temperatures show a negligible dependence on uncertainties in parameters such as the nonresonant susceptibility of the gas and the slit width. Moreover, no collisional narrowing of the lines has to be taken into account. The relative standard deviation of evaluated temperatures and of relative oxygen concentrations from single-shot measurements were as low as 1, and 1.4-1.9%, respectively. In the postcombustion gases at temperatures above 2000 K and pressures above 1.5 MPa, the nonresonant CARS background gave a large contribution to the total spectrum. In this temperature and pressure range, the evaluated values of temperature and nonresonant susceptibility are not independent, and the nonresonant susceptibility had to be fixed at a precalculated value to get a reliable temperature evaluation. The avantages and disadvantages of rotational CARS in comparison with vibrational CARS for IC engine measurements are discussed.
|
|
| 45. |
|
|
| 46. |
- Bengtsson, Per Erik, et al.
(författare)
-
Rotational cars thermometry in sooting flames
- 1992
-
Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 81:1-3, s. 129-140
-
Tidskriftsartikel (refereegranskat)abstract
- Coherent anti-Stokes Raman scattering of pure rotational transitions, rotational CARS, is demonstrated as an efficient method for temperature determination in sooting flames. The dual broadband CARS approach was used to measure temperature profiles in premixed, sooting ethylene flames at atmospheric pressure by probing the nitrogen gas. The recorded spectra were of equally high quality in non-sooting and sooting flames with volume fractions of soot of up to 7 x 10 7 cm3 soot/cm3The advantages of rotational CARS in comparison with several other techniques for the measurement of temperatures in sooting flames, and the general applicability of the technique to different combustion conditions, are discussed. Potential limitations in the application of rotational CARS to sooting flames that are more heavily sooting than the ones investigated in this study, are outlined.
|
|
| 47. |
- Bengtsson, Per Erik
(författare)
-
Simultaneous two-dimensional visualization of soot and OH in flames using laser-induced fluorescence
- 1996
-
Ingår i: Applied Spectroscopy. - 0003-7028. ; 50:9, s. 1182-1186
-
Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional visualization of soot has been realized in flames with the use of laser-induced fluorescence in C2 from laser-vaporized soot [LIF(C2)LVS]. Soot particles are heated to vaporization temperatures by the absorption of laser radiation. C2 radicals produced by this process are excited at wavelengths around 563 nm through the transition ν′ = 0 d3∏g←ν″ = 1 a3∏u, and the subsequent fluorescence at approximately 516 nm is detected. By frequency-doubling of the laser radiation, wavelengths around 281.5 nm are achieved, which can excite OH radicals to the ν′ = 1 A2Σ+ state from ν″ = 0 X2∏, with subsequent fluorescence at approximately 310 nm. With the use of both these excitation wavelengths, and a Cassegrainian split-mirror telescope as the imaging detection system in front of the charge-coupled device (CCD) camera, simultaneous two-dimensional single-shot images of soot and OH were obtained on a single CCD chip, thus enabling both sooting regions and reaction zones in flames to be monitored.
|
|
| 48. |
|
|
| 49. |
|
|
| 50. |
- Bengtsson, Per-Erik, et al.
(författare)
-
Vibrational CARS thermometry in sooty flames: Quantitative evaluation of C2 absorption interference
- 1990
-
Ingår i: Combustion and Flame. - 0010-2180. ; 82:2
-
Tidskriftsartikel (refereegranskat)abstract
- The application of nitrogen vibrational CARS thermometry to sooty, premixed, atmospheric pressure flames has been investigated using a Nd:YAG laser based system. It was found that laser-produced C2 radicals strongly absorb part of the fundamental band peak in the CARS spectrum. This was the most severe interference to the CARS signal. A quantitative investigation of temperature errors caused by the C2 absorption effect is presented. The correlation between the absorption interference and the soot volume fraction was examined for different flame conditions. Also, the increase of the nonresonant susceptibility in sooty flame regions is clearly illustrated and its effect on thev evaluated temperature is quantitatively determined. The single-shot temperature standard deviation has also been investigated in flames with different soot loadings. Finally, other interference effects to the CARS signals in sooty flames are described and discussed.
|
|
