| 1. |
- Fooladgar, Ehsan, et al.
(author)
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CFD modeling of pyrolysis oil combustion using finite rate chemistry
- 2021
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In: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 299
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Journal article (peer-reviewed)abstract
- This paper reports the first Computational Fluid Dynamics (CFD) model developed for biomass pyrolysis oil spray combustion using Finite-Rate Chemistry (FRC) approach. To make the CFD calculations feasible, a reduced mechanism for modeling the combustion of biomass Fast Pyrolysis Oil (FPO) based on the POLIMI 1412 mechanism and a model for eugenol oxidation was developed. The reduced mechanism consisted of 200 reactions and 71 species. This level of complexity was found to be a good tradeoff between predictive power and computational cost such that the reduced model could be used in CFD modeling. The predictive power of the reduced mechanism was demonstrated via 0D (adiabatic, premixed, constant pressure reactor), 1D (laminar counterflow flame) and 3D (CFD of a methane-air flat-flame piloted FPO spray flame) calculations. Results from CFD were compared against experimental data from non-intrusive optical diagnostics. The reduced model was successfully used in CFD calculations—the computational cost was approximately 2 orders of magnitude higher than that of a simplified model. Using the reduced mechanism, the concentration of pollutants, minor combustion products, and flame radicals could be predicted—this is added capability compared to already existing models. The CFD model using the reduced mechanism showed quantitative predictive power for major combustion products, flame temperature, some pollutants and temperature, and qualitative predictive power for flame radicals and soot.
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| 2. |
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| 3. |
- Gunnarsson, Adrian, 1990, et al.
(author)
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Radiative Heat Transfer Modeling and in Situ Diagnostics of Soot in an 80 kWth Propane Flame with Varying Feed-Gas Oxygen Concentration
- 2018
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 57:36, s. 12288-12295
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Journal article (peer-reviewed)abstract
- This work presents experimental measurements of various 80 kWth propane flames, using a swirl burner, and modeling of the radiative heat transfer. The combustion conditions were altered by varying the oxygen concentration in the oxidant within range of 21-32%, while keeping the thermal input and oxygen-to-fuel ratio constant. Temperature, gas composition, and radiative intensity were measured using probes, while the soot volume fraction was quantified using nonintrusive laser-induced incandescence. The radiative intensity and the soot volume fraction increased with an increased oxygen concentration in the flame. When the oxygen concentration exceeded 27% the soot volume fraction was increased more than 14-fold. The results reveal the potential of promoting radiative heat transfer by increasing the oxygen concentration; the total radiative intensity becomes dominated by the soot particle contribution. In addition, laser-induced incandescence was successfully used for instantaneous and spatially resolved soot measurements in this type of furnace being at a technical scale.
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| 4. |
- Gunnarsson, Adrian, 1990, et al.
(author)
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Soot Formation and Radiative Heat Transfer in Oxy-Fuel and Oxygen-Enhanced Propane Flames
- 2018
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Conference paper (other academic/artistic)abstract
- This work aims to determine radiation-related properties of various propane flames, where the measurements were conducted in a down-fired and cylindrical 100 kW furnace equipped with a swirl burner. The combustion conditions were varied by altering the composition of the oxidant. For six cases, oxygen-enhanced air was used, step-wise varying the oxygen concentration in the oxidant from 21% to 32%. Also for six cases, the furnace was operated in oxy-fuel mode, recirculating dry flue gas and varying the oxygen concentration from 25% to 42%. All measurements were conducted at an axial distance of 384 mm from the burner. Temperature, gas composition and radiative intensity were measured (by intrusive instruments) along the furnace diameter using probes while the soot volume fraction was quantified using non-intrusive laser induced incandescence (LII). An Nd:YAG laser at wavelength 1064 nm was used for the LII measurements, and a diode laser at wavelength 808 nm was used for extinction measurements for absolute calibration of the LII-signal. Two-dimensional images of the LII-signal were captured using an intensified CCD-camera and radial profiles of the soot volume fraction were achieved. The soot volume fraction increased with increasing oxygen concentration in the feed gas, and, when the oxygen concentration exceeded 30 and 42% for the oxygen-enriched air and oxy-fuel cases, respectively, the soot formation was substantially enhanced with volume fractions more than 10 times higher than for lower oxygen concentrations. The higher oxygen concentration required for the increased soot production in the oxy-fuel combustion cases is mainly due to the higher heat capacity of carbon dioxide that lowers the flame temperatures. The data collected from the measurements was used to model the radiative intensity using a discrete transfer model. In this model, gas properties are calculated using a statistical narrow-band model and particle properties are calculated using Rayleigh theory. Good agreement was achieved between the modeled and measured radiative intensity for most flames and the use of an LII-system to measure the soot volume fraction in this type of furnace was successful.
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| 5. |
- Mannazhi, Manu, et al.
(author)
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Influence of potassium chloride on PAH concentration during soot formation studied using laser-induced fluorescence
- 2022
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In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 235
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Journal article (peer-reviewed)abstract
- Previous studies have shown that addition of potassium chloride (KCl) reduces soot concentration and primary particle size. To improve the understanding of this phenomenon, this work focuses on investigating the influence of KCl addition on formation of polycyclic aromatic hydrocarbons (PAHs), assumed to be precursors of soot. The method used is laser-induced fluorescence (LIF), for which different size classes of PAHs can be probed using selected combinations of excitation and detection wavelengths. KCl solutions of different concentrations were aspirated into premixed ethylene-air flames, and spectral and 2D imaging PAH-LIF measurements were performed using laser excitation at 266 nm and 532 nm. PAH-LIF spectra using 266 nm excitation showed a peak in the UV region at around 350 nm and a peak at around 550 nm in visible region, where the latter peak intensity increased strongly with flame height. The normalised PAH-LIF spectra obtained using 532 nm excitation showed no spectral change with flame height. The main results from this study showed that KCl addition, firstly, had negligible influence on the formation of smaller PAHs (measured using excitation at 266 nm and detection at ∼ 320 nm), and secondly, decreased the formation of larger PAHs at increasing flame heights (measured using excitation at 532 nm and detection in the visible region).
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| 6. |
- Mannazhi, MANU
(author)
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Laser-based diagnostics for investigating soot formation in combustion processes
- 2021
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Doctoral thesis (other academic/artistic)abstract
- In this work, laser-based diagnostic techniques were developed and applied to investigate soot formation in small-scale laboratory burners as well as in practical combustion devices. Quantitative 2D laser-induced incandescence (LII) measurements often use a cylindrical lens to shape the beam and illuminate the planar region of interest. The varying laser fluence and sheet width in the imaged flame region created due to this focusing was found to introduce significant bias in the 2D LII signal distributions, especially for short focal length lenses combined with long imaged regions. Experimental data were recorded with variations in laser fluence and detector gate, which were reproduced through numerical simulations using a heat-and-mass-transfer-based LII model. It was shown that adequate choices of experimental parameters could minimize bias in the 2D LII signal distribution. Combined measurements using LII and extinction as well as laser-induced fluorescence of polycylic aromatic hydrocarbons (PAH-LIF) were applied to characterize soot formation in methane-air diffusion flames at elevated pressures. A special focus was on the evaluation of optical properties of soot at various spatial locations in the flames through the analysis of LII fluence curves. The absorption function E(m) was found to increase strongly with increase in pressure at the position of maximum soot volume fraction (fv), and also along the centreline of the flame until the position of maximum fv. It was demonstrated that an assumption of constant E(m) in 2D LII measurements in sooting diffusion flames leads to large uncertainties in evaluated soot volume fractions.Previous studies have shown that addition of potassium chloride (KCl) reduces soot concentration and primary particle size. As PAHs are precursors of soot, this work focused on the influence of potassium and sodium salt additives on PAH formation, and measurements were primarily made using PAH-LIF and elastic light scattering (ELS). Using different combinations of excitation and fluorescence wavelengths, the detected fluorescence could be classified to originate from two groups: small PAHs (~ 2-3 rings) and large PAHs (≳ 4 rings). Addition of potassium and sodium salts were found to have no observable influence on the formation of smaller PAHs. However, the concentration of larger PAHs decreased in the sooting flame region with the addition of these salts, where the largest effect was seen for potassium salts. Additionally, different salts of potassium (or sodium) showed similar fluorescence and scattering response, thus showing that it is the metal ion which is primarily responsible for the influence on PAH concentrations observed in this study. Laser diagnostic techniques have also been applied in an optical diesel engine to study the effects of injector aging and oxygenated fuel additive tripropylene glycol monomethyl ether (TPGME) on spray and soot formation as well as soot oxidation. Studies in the literature have shown that aging of injectors adversely affects diesel engine combustion. TPGME has also been found to lower soot emissions. The spray and soot formation were investigated using high-speed imaging measurements of Mie scattering and natural luminosity, whereas late cycle soot oxidation was studied using semi-quantitative 2D LII and extinction measurements. Aged injector showed higher fuel injection rates resulting in higher soot formation and faster soot oxidation, predominantly at low load conditions. The fuel with added TPGME produced lesser soot in the cycle and showed faster soot oxidation rates.
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| 7. |
- Mannazhi, Manu, et al.
(author)
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Laser-induced fluorescence for studying the influence of potassium and sodium salts on PAH formation in sooting premixed flames
- 2022
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In: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 128:4
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Journal article (peer-reviewed)abstract
- Previous studies have shown that alkali salts influence combustion processes and soot formation, although the effects seem to vary across systems. Moreover, fundamental studies on the effect of potassium and sodium salts on formation of polycyclic aromatic hydrocarbons (PAH), which are precursors in soot formation, are scarce. Here, we report a study in which the effects on PAH formation due to the addition of alkali metal salts (KCl, KOH, K2CO3, NaCl and NaOH) to premixed ethylene–air flames were investigated. Different size classes of PAHs were probed using both spectral and 2D measurements of laser-induced fluorescence (PAH-LIF) using the excitation wavelengths 266 nm and 532 nm, while detecting the fluorescence emission at selected wavelength ranges. Elastic light scattering (ELS) measurements were also used to complement the fluorescence data. It was found that potassium and sodium salts do not significantly influence the formation of small PAHs (2–3 rings), while decreasing the concentration of larger PAHs at higher heights above burner (HAB). Another important result was that the anion in the salt (Cl−, OH−, CO32−) negligibly influences the PAH and soot formation processes after dissociation of the salts.
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| 8. |
- Mannazhi, Manu, et al.
(author)
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Soot maturity studies in methane-air diffusion flames at elevated pressures using laser-induced incandescence
- 2021
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In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:1, s. 1217-1224
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Journal article (peer-reviewed)abstract
- Two-dimensional laser-induced incandescence (LII) measurements were used for quantitative soot volume fraction ( fv) measurements in methane-air diffusion flames at pressures ranging from 0.1 to 0.5 MPa. Additionally, laser-induced fluorescence (LIF) was used for visualization of polycyclic aromatic hydrocar-bons (PAHs) considered as important soot precursors. A heat and mass transfer-based LII model was used for the analysis of experimental LII fluence curves to evaluate soot absorption functions, E(m), at various spatial positions in the flames. Based on previous work, variations in the evaluated E(m) was assumed to be related to soot maturity. Generally, the most mature soot was found at the spatial position of maximum fv along the central axis and at the flame edges. Also, the soot maturity at the position of maximum fv at each pressure was found to increase from the flame at 0.1 MPa to 0.5 MPa. A critical examination of the assumptions and uncertainties in the E(m) analysis was made. The present study emphasizes the limitation of assigning soot a constant E(m) in the overall flame for temperature and soot concentration evaluation using the optical methods spectral soot emission (SSE) and line-of-sight attenuation (LOSA), which are commonly used non-intrusive optical diagnostic techniques in sooting high-pressure flames. The study also demonstrates the critical choice of fluence in quantitative imaging LII measurements of fv when the E(m) of soot spans over large range ofvalues.
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| 9. |
- Mannazhi, Manu, et al.
(author)
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Soot Oxidation Studies in an Optical Diesel Engine Using Laser-Induced Incandescence and Extinction : The Effects of Injector Aging and Fuel Additive
- 2021
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In: SAE International Journal of Engines. - : SAE International. - 1946-3936 .- 1946-3944. ; 14:5, s. 749-761
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Journal article (peer-reviewed)abstract
- Previous studies have shown that injector aging adversely affects the diesel engine spray formation and combustion. It has also been shown that the oxygenated fuel additive tripropylene glycol monomethyl ether (TPGME) can lower soot emissions. In this study, the effects of injector aging and TPGME on the late cycle oxidation of soot were investigated using laser diagnostic techniques in a light-duty optical diesel engine at two load conditions. The engine was equipped with a quartz piston with the same complex piston geometry as a production engine. Planar laser-induced incandescence (LII) was used to obtain semiquantitative in-cylinder two-dimensional (2D) soot volume fraction (fv) distributions using extinction measurements. The soot oxidation rate was estimated from the decay rate of the in-cylinder soot concentration for differently aged injectors and for cases with and without TPGME in the fuel. The aged injector produced higher soot concentrations than the new injector at both load conditions. The aged injector also showed higher soot oxidation rates than the new injector at the low load condition. TPGME resulted in lower soot concentrations at both load conditions and faster oxidation rates, especially at mid load conditions.
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| 10. |
- Mannazhi, Manu, et al.
(author)
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Strongly reduced optical absorption efficiency of soot with addition of potassium chloride in sooting premixed flames
- 2023
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In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 39:1, s. 867-876
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Journal article (peer-reviewed)abstract
- Optical properties of soot have been investigated with and without potassium chloride (KCl) salt added to the soot formation process in a premixed ethylene/air flame. A strong decrease in optical absorption efficiency of the soot was observed with increasing amounts of KCl added to the fuel based on the method of fluence curve analysis using laser-induced incandescence (LII). To understand the reason for this major change in absorption efficiency, probe sampling and subsequent structural analysis were performed using Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). Raman spectra indicated no significant difference between the nanostructure of soot from the two main cases; a reference case without addition of salt, and a case with addition of -600 ppm K. In the case of K addition, HRTEM showed slightly less compact nanostructure signified by somewhat shorter interlayer spacing, and significantly different polar ordering of carbon lamellae indicating smaller primary particles, thereby supporting previous TEM studies on soot sampled from the same flames showing smaller soot particle sizes with KCl addition. The impact on soot absorption properties from the observed differences is discussed. It is speculated that the main cause for the lower absorption with K addition is a quantum confinement effect due to reduction in soot particle size.
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| 11. |
- Mannazhi, Manu, et al.
(author)
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Two-dimensional laser-induced incandescence for soot volume fraction measurements : issues in quantification due to laser beam focusing
- 2020
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In: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 126:12
-
Journal article (peer-reviewed)abstract
- Two-dimensional laser-induced incandescence (LII) measurements usually involve the use of a cylindrical lens to illuminate the planar region of interest. This creates a varying laser fluence and sheet width in the imaged flame region which could lead to large uncertainties in the quantification of the 2D LII signals into soot volume fraction distributions. To investigate these effects, 2D LII measurements using a wide range of laser pulse energies were performed on a premixed flat ethylene–air flame while employing a cylindrical lens to focus the laser sheet. Using shorter focal length of the focusing lens resulted in larger variation of the LII signal profiles across the flame. A heat – and – mass – transfer - based LII model was also used to simulate the measurements and good agreement was found. The ratio between focal length (FL) and image length (IL) was introduced as a useful parameter for estimating the bias in estimated soot volume fractions across the flame. The general recommendation is to maximize this FL/IL ratio in an experiment, which in practice means the use of a long focal length lens. Furthermore, the best choices of laser fluence and detection gate width are discussed based on results from these simulations.
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| 12. |
- Palazzo, Natascia, et al.
(author)
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Investigation of soot formation in a novel diesel fuel burner
- 2019
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In: Energies. - : MDPI AG. - 1996-1073. ; 12:10
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Journal article (peer-reviewed)abstract
- In the present work, a novel burner capable of complete pre-vaporization and stationary combustion of diesel fuel in a laminar diffusion flame has been developed to investigate the effect of the chemical composition of diesel fuel on soot formation. For the characterization of soot formation during diesel combustion we performed a comprehensive morphological characterization of the soot and determined its concentration by coupling elastic light scattering (ELS) and laser-induced incandescence (LII) measurements. With ELS, radii of gyration of aggregates were measured within a point-wise measurement volume, LII was employed in an imaging approach for a 2D-analysis of the soot volume fraction. We carried out LII and ELS measurements at different positions in the flame for two different fuel types, revealing the effects of small modifications of the fuel composition on soot emission during diesel combustion.
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| 13. |
- Toth, Pal, et al.
(author)
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Experimental and numerical study of biomass fast pyrolysis oil spray combustion : Advanced laser diagnostics and emission spectrometry
- 2019
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In: Fuel. - : Elsevier Ltd. - 0016-2361 .- 1873-7153. ; 252, s. 125-134
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Journal article (peer-reviewed)abstract
- The objective of this work was to move towards developing a comprehensible Computational Fluid Dynamics (CFD) model to facilitate the predictive modeling of Fast Pyrolysis Oil (FPO) spray combustion. A CFD model was implemented from the literature and results were compared to 2D data from non-intrusive optical diagnostics involving Planar Laser Induced Fluorescence of the OH radical, Mie scattering imaging and two-color pyrometry using a laboratory-scale, CH 4 /air flat-flame with an air-assist atomizer. Furthermore, flame radiation and contributions from graybody sources, chemiluminescence and soot were studied experimentally using emission spectroscopy and Laser Induced Incandescence (LII). Reasonable qualitative agreement was found between experimental and model results in terms of flame structure and temperature. Emission spectroscopy and LII results revealed and confirmed earlier observations regarding the low soot concentration of FPO spray flames; furthermore, it was shown that a significant portion of flame radiation originated from graybody char radiation and chemiluminescence from the Na-content of the FPO. These suggest that the treatment of soot formation might not be important in future computational models; however, the description of char formation and Na chemiluminescence will be important for accurately predicting temperature and radiation profiles, important from the point of e.g., large-scale power applications. Confirmed low soot concentrations are promising from an environmental point of view.
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| 14. |
- Török, Sandra, et al.
(author)
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Influence of rapid laser heating on differently matured soot with double-pulse laser-induced incandescence
- 2022
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In: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 56:6, s. 488-501
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Journal article (peer-reviewed)abstract
- For accurate laser-induced incandescence (LII) measurements of soot properties it is of great importance to understand the nature of the physical processes involved during rapid laser heating. In this work, we investigate how well-characterized differently matured fresh soot from a soot generator responds to rapid laser heating. For this purpose, a double-pulse LII setup is used with 10 μs time separation between the pulses using various combinations of two common LII wavelengths (532 and 1064 nm). Detection is performed at two wavelength bands for fluorescence analysis, and additionally elastic light scattering is used for mass loss analysis during heating. We investigate how the LII signal changes with pre-heating laser energy, specifically by fluence curve analysis to estimate the influence of thermal annealing, sublimation and laser-induced fluorescence interference. It is shown that extensive absorption enhancement occurs for all types of soot as the soot is thermally annealed, which is manifested through decreasing dispersion coefficient ξ and an increasing absorption coefficient E(m,λ). When comparing young and mature soot, a much larger impact of sublimation can be observed in the fluence curves of the mature soot. Also, we observe an enhanced contribution of laser-induced fluorescence for the young soot when performing LII measurements using 532 nm, which is suggested to originate from vaporized carbon fragments with an aromatic structure. This work further shows the potential of utilizing double-pulse arrangements for increasing the detectability of poorly absorbing soot, but also it highlights the impact of laser heating on soot, which may be important to avoid interferences when performing soot diagnostics.
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| 15. |
- Török, Sandra, et al.
(author)
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Investigation of the absorption Ångström exponent and its relation to physicochemical properties for mini-CAST soot
- 2018
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In: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 52:7, s. 757-767
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Journal article (peer-reviewed)abstract
- In this work, a mini-CAST soot generator was used to produce soot with different optical and physicochemical characteristics. Absorption Ångström exponents (AAE) expressing the absorption wavelength dependence were assessed by multiwavelength in-situ and filter-based (aethalometer) laser extinction. The two optical techniques showed good agreement. For the chosen mini-CAST operating conditions, AAEs between 1 and 3.5 were found. Soot with high mass-fractions of organic carbon (OC) and pyrolytic carbon (PC) determined with thermal optical analysis were associated with AAEs significantly higher than 1. Heating to 250 and 500°C removed the majority of polycyclic aromatic hydrocarbons. However, the thermal-optical analysis revealed that OC and PC were abundant in the soot with AAE > 2 also after heating the aerosol. Analysis of mass absorption cross section ratios for elemental carbon and OC indicated that elevated AAEs also after heating to 500°C could be related to persistent OC and PC components and/or the refractory soot. By comparing the mini-CAST soot optical properties with soot properties derived from in-situ extinction measurements in a premixed flame, mini-CAST soot with a higher AAE could be identified as less mature soot.
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| 16. |
- Török, Sandra, et al.
(author)
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Laser-induced incandescence (2λ and 2C) for estimating absorption efficiency of differently matured soot
- 2021
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In: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 127:7
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Journal article (peer-reviewed)abstract
- Two-wavelength and two-color laser-induced incandescence (2λ–2C-LII) was used to study the absorption properties of three types of cold soot of different maturity from a mini-CAST soot generator. LII fluence curve analysis allowed for estimating absorption wavelength dependence in terms of dispersion coefficients ξ by the use of two excitation wavelengths (532 and 1064 nm). The estimated ξ (based on E(m, λ) ∝ λ1−ξ) spanned from ~ 1.2 for the mature soot, up to 2.3 for the young soot. The results for the mature soot showed good agreement with previous measurement using multi-wavelength extinction. For the young soot, however, some discrepancy was observed suggesting a weaker wavelength dependence (lower ξ) from the LII fluence analysis. Furthermore, an estimation of the E(m, λ) for the different types of soot was done from the experimental fluence curves with temperature analysis in the low-fluence regime and simulations using an LII model. Additionally, uncertainties and limitations were discussed. Finally, it should be pointed out that caution has to be taken when interpreting 2λ-LII results to obtain quantitative absorption properties of less mature soot, which may be influenced by thermal annealing during the laser pulse and by absorption from non-refractory species externally/internally mixed with the soot.
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| 17. |
- Zhu, Xinda, et al.
(author)
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High-Speed Imaging of Spray Formation and Combustion in an Optical Engine : Effects of Injector Aging and TPGME as a Fuel Additive
- 2020
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In: Energies. - : MDPI AG. - 1996-1073. ; 13:12
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Journal article (peer-reviewed)abstract
- High-speed imaging of fuel sprays and combustion is conducted on a light-duty optical engine to investigate the effects of injector aging, with a focus on soot. The spray behaviors of one new and one aged injector are compared using Mie-scattering. In addition to this, the combustion process of a baseline diesel fuel and a blend with TPGME (tripropylene glycol monomethyl ether) are compared using natural luminosity (NL) imaging. TPGME is an oxygenated additive which can be used to reduce soot emissions. X-ray tomography of the two injectors demonstrates that the aging does not lead to significant geometry differences, nor to formation of dense internal nozzle deposits. Both injectors show similar liquid penetration and spreading angle. However, the aged injector shows a prolonged injection and more fuel dribbling after the injection events, leading to a higher injection quantity. The fuel quantity difference shows a larger impact on the NL at low load than the TPGME additive, indicating that the in-cylinder temperature is more important for soot oxidation than oxygen concentration under these conditions. At medium load, the NL is much less sensitive to small temperature variations, while the TPGME is more effective for soot reduction.
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