| 1. |
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| 2. |
- Alsved, Malin, et al.
(författare)
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Droplet, aerosol and SARS-CoV-2 emissions during singing and talking
- 2021
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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.
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| 3. |
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| 4. |
- Alsved, Malin, et al.
(författare)
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Exhaled respiratory particles during singing and talking
- 2020
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Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 1521-7388 .- 0278-6826. ; 54:11, s. 245-1248
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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.
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| 5. |
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| 6. |
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| 7. |
- Falk, John, et al.
(författare)
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Immersion freezing ability of freshly emitted soot with various physico-chemical characteristics
- 2021
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Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 12:9
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Tidskriftsartikel (refereegranskat)abstract
- The immersion freezing ability of soot particles has in previous studies been reported in the range of low/insignificant to very high. The aims of this study were to: (i) perform detailed physico-chemical characterisation of freshly produced soot particles with very different properties, (ii) investigate the immersion freezing ability of the same particles, and (iii) investigate the potential links between physico-chemical particle properties and ice-activity. A miniCAST soot generator was used to produce eight different soot samples representing a wide range of physico-chemical properties. A continuous flow diffusion chamber was used to study each sample online in immersion mode over the temperature (T) range from −41 to −32◦C, at a supersaturation of about 10% with respect to liquid water. All samples exhibited low to no heterogeneous immersion freezing. The most active sample reached ice-activated fractions (AF) of 10−3 and 10−4 at temperatures of 1.7 and 1.9 K, respectively, above the homogeneous freezing temperature. The samples were characterized online with respect to a wide range of physico-chemical properties including effective particle density, optical properties, particle surface oxidation and soot maturity. We did observe indications of increasing immersion freezing ice-activity with increasing effective particle density and increasing particulate PAH fraction . Hence, those properties, or other properties co-varying with those, could potentially enhance the immersion freezing ice-activity of the studied soot particle types. However, we found no significant correlation between the physico-chemical properties and the observed ice-nucleating ability when the particle ensemble was extended to include previously published results including more ice-active biomass combustion soot particles. We conclude that it does not appear possible in general and in any straightforward way to link observed soot particle physico-chemical properties to the ice-nucleating ability using the online instrumentation included in this study. Furthermore, our observations support that freshly produced soot particles with a wide range of physico-chemical properties have low to insignificant immersion freezing ice-nucleating ability.
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| 8. |
- Fooladgar, Ehsan, et al.
(författare)
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CFD modeling of pyrolysis oil combustion using finite rate chemistry
- 2021
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 299
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Tidskriftsartikel (refereegranskat)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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| 9. |
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| 10. |
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| 11. |
- Hosseinnia, Ali, et al.
(författare)
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Simultaneous temporally and spectrally resolved Raman coherences with single-shot fs/ns rotational CARS
- 2020
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Ingår i: Optics Letters. - 0146-9592. ; 45:2, s. 308-311
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Tidskriftsartikel (refereegranskat)abstract
- A novel technique for studies of the dynamics of molecular coherences has been developed. The concept is based on prompt excitation using broadband femtosecond (fs) laser pulses, whereupon a narrowband nanosecond (ns) laser pulse probes the fast dynamics of the coherences. Detection of the spectrally dispersed coherent signal using a streak camera allows simultaneous spectrally and temporally resolved studies of all excited coherences in a single-shot acquisition. Here we demonstrate the high capacity and versatility of this hybrid fs/ns coherent anti-Stokes Raman scattering (CARS) technique through some illustrative examples, all single-shot measurements, namely time-resolved studies of rotational Raman coherences in nitrogen and air, dynamics of Stark effect on rotational lines, and beating phenomena originating from close-lying rotational lines.
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| 12. |
- Hosseinnia, Ali, et al.
(författare)
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Single-shot fs/ns rotational CARS for temporally and spectrally resolved gas-phase diagnostics
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:1, s. 1843-1850
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Tidskriftsartikel (refereegranskat)abstract
- We report thermometry and new Raman linewidth data using a novel method for time-domain rotational coherent anti-Stokes Raman spectroscopy (RCARS) on single-shot basis. The coherences are generated by two fs pulses and probed by a ns pulse. The resulting signal is detected using a combined spectrograph/streak camera setup with high spectral and temporal resolution. Rotational CARS spectrograms of nitrogen (N2), ethylene (C2H4), ethane (C2H6), and argon (Ar) are demonstrated at ambient condition. Self-broadened N2–N2 S-branch Raman linewidths were measured on single-shot basis and show excellent agreement with literature values. Furthermore, Raman linewidths of N2 S-branch perturbed by C2H4 and C2H6 were measured for the first time. The time-resolved approach was also utilized to separate complex spectra from a mixture of species through their difference in coherence lifetimes. Since the Raman coherences decay much faster for both ethane and ethylene than for nitrogen, pure nitrogen spectra could be obtained by analyzing only the temporal tail of the signal. Moreover, a model for time-resolved RCARS of N2 was developed, which employs the single-shot measured Raman linewidths to calculate the corresponding spectro-temporally resolved spectrograms at different temperatures. The model was used to evaluate the temperature from single-shot data of an N2/C2H6 mixture, showing very high accuracy. The demonstrated method constitutes an essential improvement for single-shot thermometry as it does not require pre-knowledge about collider species concentrations and their impact on linewidths.
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| 13. |
- Kadefors, Anna, Professor, 1962-, et al.
(författare)
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Samverkan Hög inom väg- och järnvägsunderhåll : Uppföljning av tidiga skeden i tre pilotkontrakt
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- BakgrundAffärsformerna för drifts- och underhållskontrakt har varit föremål för diskussion av flera olika anledningar de senaste åren. Dels har entreprenörerna påtalat att osäkerheten i uppdragens innehåll är för stor för att de traditionella mängdkontrakten, upphandlade på lägsta pris, ska fungera bra. Man menar att sådana kontrakt medför stora risker för företagen och även påverkar arbetsmiljön och förutsättningarna att rekrytera personal till branschen negativt. Entreprenörerna har därför efterlyst kontrakt med mindre risk och bättre samverkan. En annan aspekt är att Trafikverkets egna kontraktsanalyser och Riksrevisionens granskningar har pekat på att taktiserad prissättning (obalanserad budgivning) i traditionella driftkontrakt medför att Trafikverket har bristande kunskap om kostnadsbilden och även kan leda till ineffektiv användning av statliga resurser.Trafikverket har sedan några år börjat testa samverkansinriktade upphandlingsstrategier (Samverkan Hög) i större investeringsprojekt inom verksamhetsområdena Stora projekt och Investering. Utifrån dessa erfarenheter och kritiken mot de traditionella kontrakten beslöt Trafikverket att även utveckla en kontraktsmodell för Samverkan Hög för baskontrakt för väg- och järnvägsunderhåll. Den nya kontraktsmodellen innebär att entreprenören upphandlas i ett tidigt skede, baserat på kvalitetsparametrar samt entreprenörarvodet. Kontraktet delas in i två faser, där Fas 1 utgörs av en process där entreprenören och beställaren gemensamt tar fram genomförandeplan, produktionskalkyl, detaljerad tidplan och riktkostnad. I Fas 2, som är en option, ingår sedan etablering (Fas 2a) och utförande av basunderhåll (Fas 2b). Våren 2020 upphandlade Trafikverket tre pilotkontrakt med kontraktsmodellen Samverkan Hög inom drift och underhåll: två vägkontrakt och ett järnvägskontrakt.Under hösten 2021 initierades ett nytt forskningsprojekt i samarbete mellan Trafikverket och forskare knutna till det nationella forskarnätverket ProcSIBE ((Procurement for Sustainable Innovation in the Built Environment[1]) för att följa upp och utvärdera kontraktsmodellen Samverkan Hög inom basunderhåll för väg och järnväg. Hela forskningsprojektet omfattar tre delstudier av anbudsskedet, Fas 1 samt Fas 2. Den här rapporten behandlar Fas 1 i de tre pilotkontrakten. De två vägkontrakten har följts upp genom intervjuer med Trafikverket och entreprenörerna. Forskningsprojektet kommer att fortsätta med att följa upp utvecklingen under Fas 2 och även jämföra med två traditionellt upphandlade kontrakt. Järnvägskontraktet avbröts efter Fas 1 och uppföljningen av detta baseras på medverkan i tre workshops som organiserades av Trafikverket efter avbrottet.ResultatIntervjuerna visar på ett stort stöd bland de intervjuade, även på järnvägssidan, för att arbeta mer samverkansinriktat. De fördelar som framhålls har att göra med ökad resurseffektivitet och innovation, bättre arbetsmiljö som ökar branschens attraktivitet, samt att lägre risk gör det lättare för nya aktörer att etablera sig på marknaden. Sammanfattningsvis visar erfarenheterna på en betydande potential i den modell som har testats, men det är också tydligt att det behövs ytterligare utveckling och justeringar, liksom kompetensutveckling och ett mer långsiktigt utvecklingsarbete.Några centrala resultat och rekommendationer sammanfattas nedan[2]:· För att lyckas i ett samverkanskontrakt är det avgörande att ledande personer på båda sidor är erfarna i sina roller, tror på samverkan, har skaffat sig en förståelse av både kontrakt och etablerade principer för samverkan, och inte underskattar uppgiftens komplexitet. Båda kontraktsparterna behöver därför ha funktioner som kan förbereda personalen, följa upp samverkan och flytta personer som inte fungerar. Detta är en organisatorisk kompetens som även kan bedömas vid utvärdering av anbud.· För Trafikverket har insynen i entreprenörernas kostnadskalkyler inneburit en ökad förståelse av hur förfrågningsunderlagen för driftkontrakt ska vara konstruerade för att vara lätta för entreprenörerna att prissätta och minska onödiga riskpåslag. Man har också kunnat konstatera att Trafikverkets egenkalkyler stämmer relativt bra. Arbetet med att ta fram självkostnader för olika poster tog dock betydligt mer tid och kraft än vad man hade förväntat sig. Utifrån den kunskap man nu har fått skulle Trafikverket och entreprenörsidan kunna gå vidare och gemensamt identifiera principer för prissättning och områden där det kan vara bättre att använda schabloner. Kostnadsindexering, viten och bonusar behöver också ses över på basis av de erfarenheter som gjorts i pilotkontrakten.· Det finns goda möjligheter för utveckling och innovation i Samverkan Högkontrakten. En viktig lärdom är att förutsättningarna för att driva utvecklingsarbete i driftkontrakt snarast är bättre i Fas 2, då hela organisationen och alla underentreprenörer är på plats. Detta är en skillnad mot investeringsprojekt, där Fas 1 uppfattas vara mest central. Medarbetarna på projektnivån upplever dock att Trafikverkets ambitioner har varit otydliga, framför allt när det gäller vilken frihet pilotkontrakten haft att utmana regelverken. Inför Fas 2 och kommande kontrakt behöver Trafikverket förtydliga vilka frihetsgrader som finns, samt aktivt stödja nytänkande även under Fas 2.· De flesta av de intervjuade ser betydande fördelar med samverkan med Samverkan Hög och menar att kommande projekt kan ha stor nytta av de lärdomar som gjorts. Trafikverksrepresentanterna upplever dock att det interna stödet för pilotkontrakten har minskat över tid och att syftet att driva utveckling har ersatts av ett ensidigt fokus på kostnadsutvecklingen på kort sikt. Man ser ingen tydlig plan för hur erfarenheterna ska föras vidare och upplever att rutiner och funktioner för att stödja sådant lärande till stor del saknas.· För att investera i ny kunskap och anpassa sina strategier behöver entreprenörerna se en tydlig riktning, men även de intervjuade entreprenörrepresentanterna uppfattar Trafikverkets långsiktiga målsättningar för Samverkan Hög och andra samverkansmodeller inom driftverksamheten som oklara. Flera intervjuade från både Trafikverket och entreprenörerna lyfter risken att förlora tid och missa chansen att vara på erfarenheterna från de tre kontrakten.· En slutsats är att Trafikverket bör överväga att snarast starta ytterligare några pilotkontrakt där konceptet utvecklas baserat på lärdomarna från pilotkontrakten. Det är också viktigt att ta fram en plan för fortsättningen baserat på de resultat som kommer fram. ProcSIBEs tidigare studier har visat att Trafikverket har svårt att uppnå tillräcklig uthållighet och systematik det förändringsarbete man driver kopplat till kontraktsmodeller. För att stärka kan Trafikverket kommunicera strategier och planer brett samt involvera andra beställare, branschrepresentanter och forskning i utveckling och uppföljning. Detta skulle öka trycket på Trafikverket att hålla fast vid intentioner och överenskommelser, bygga förtroende samt tillföra fler kunskaper och perspektiv. [1] ProcSIBE (på svenska: Upphandling för ett hållbart och innovativt samhällsbyggande) har under flera år studerat och utvärderat ett flertal modeller som Trafikverket har tillämpat för upphandling av olika typer av uppdrag. Se www.procsibe.se för mer information och rapporter från tidigare studier. [2] Fler slutsatser och rekommendationer återfinns i kapitel 8 i rapporten.
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| 14. |
- Karlsson, Anders, et al.
(författare)
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Numerical scattering simulations for estimating soot aggregate morphology from nephelometer scattering measurements
- 2022
-
Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 159
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Tidskriftsartikel (refereegranskat)abstract
- Nephelometers are regularly used for air quality monitoring through scattering measurements of aerosols in the atmosphere. Less attention has been paid to the potential of estimating soot morphological parameters from nephelometer measurements in combination with scattering theory. In this work, we perform a fundamental laboratory study where an Ecotech Aurora 3000 nephelometer is used for measuring the scattering properties of soot with different characteristics. The nephelometer monitors the forward and backward scattering at three wavelengths (450 nm, 525 nm, and 635 nm) to retrieve information on the ratio of forward and backward scattering intensities, as well as the scattering wavelength dependence. An inverse scattering method, based on the Rayleigh–Debye–Gans theory, for determination of the equivalent fractal dimension (Df) and radius of gyration (Rg) of soot particles from the experimental scattering data was developed. It is shown that the inverse method can estimate Rg and Df when Rg<185nm and from the wavelength dependence, information on the relative amount of organic soot could be obtained. For validation, estimated parameters are compared with the morphological parameters of soot sampled from the mini-CAST soot generator and evaluated using transmission electron microscopy (TEM). Uncertainties and limitations of the procedure are discussed.
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| 15. |
- Le, Kim Cuong, et al.
(författare)
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Polarization effects in Raman spectroscopy of light-absorbing carbon
- 2021
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 52:6, s. 1115-1122
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Tidskriftsartikel (refereegranskat)abstract
- Raman spectroscopy is widely used for characterization of carbon-based mate- rials including light-absorbing carbonaceous (LAC) matter. However, informa- tion on polarization properties of these materials are generally lacking, and often the polarization characteristics of experiments are not presented in the literature thereby giving uncertainty to presented data. In this work, the polari- zation properties of various LACs are studied using Raman spectroscopy. The Raman spectra have been compared while varying the relative polarization, particularly the relative direction of the electric field between the incident light and the detected scattered light. Specifically, the intensity ratio between the D1 and G peaks (ID1/IG) was analyzed in parallel and perpendicular polarization configurations for samples taken from a sooting flame, in the exhaust of a soot generator and carbon blacks. In this work, the parallel and perpendicular polarization configurations mean that the polarization of the detected scattered light is parallel and orthogonal, respectively, to the linearly polarized incident light. It was found that the (ID1/IG) ratio decreased in the more ordered carbo- naceous structures when changing the polarization configuration from parallel to perpendicular. Additionally, based on the depolarization ratios (Dp < 0.75), the prominent Raman peaks of LAC were found to originate from totally sym- metric vibrations. For the G peak, the depolarization ratio was measured to be in the range 0.46–0.56 for all LAC materials.
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| 16. |
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| 17. |
- Le, Thi Kim Cuong, et al.
(författare)
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Observation of Structural Changes during Oxidation of Black and Brown Soot Using Raman Spectroscopy
- 2024
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Ingår i: C: Journal of Carbon Research. - 2311-5629. ; 10:38
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Raman spectroscopy has been used to evaluate the evolution of the structural modification of soot during oxidation processes at various preset temperatures up to 700 °C. Two types of well-characterized mini-CAST soot, representing black soot and brown soot, were examined. The major difference between the signals from the two types of soot was the higher photoluminescence (PL) signal for brown soot compared with black soot, in addition to some variations in the first-order Raman signatures such as oxygenated groups and their evolutions during thermal oxidation treatment. An interesting observation was the increase in the PL signal for brown soot at increasing temperatures up to 150 °C probably due to the formation of small oxidized polycyclic aromatic hydrocarbon and defects, followed by a decrease in the PL signal until the soot was fully oxidized. We also demonstrated that brown soot is prone to oxidation in ex situ measurements, a factor that should be considered in the Raman analysis of soot.
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| 18. |
- Li, Zhongshan, et al.
(författare)
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Laser diagnostics in combustion and beyond dedicated to Prof. Marcus Aldén on his 70th birthday
- 2024
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Ingår i: Combustion and Flame. - 0010-2180. ; 263
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Forskningsöversikt (refereegranskat)abstract
- Laser diagnostics has been one of the most powerful tools in advancing state-of-the-art combustion research over the last five decades. Prof. Marcus Aldén, one of the most well-known pioneers in this field, has contributed many influential original publications over more than 40 years of his research career. In this paper, we will review some selected contributions, with emphasis on optical techniques developed and applied by Marcus and the group in Lund under his leadership, which are expected to play important roles in facing the challenge of the transition to a carbon-neutral energy system. A brief biography of Marcus is presented in the introduction section, including a summary of his academic services and achievements. The following sections are organized into chapters on different well-recognized techniques, i.e., laser-induced fluorescence, Raman and Rayleigh scattering, thermographic phosphors, coherent anti-Stokes Raman spectroscopy, resonant four-wave mixing, and additional novel technical developments and approaches. The description often follows different categories, including technique development, activities using relatively mature techniques for studies of combustion phenomena, and applications of the most mature techniques in practical devices. The last part of the paper includes a short interview with Marcus for his comments, suggestions, and thoughts on the future challenges and opportunities in this field. This article, on the one hand, is an acknowledgment of the outstanding contribution of Marcus to the field of combustion research and, on the other hand, intends to provide a valuable review of laser diagnostics in combustion research.
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| 19. |
- Malmborg, Vilhelm, et al.
(författare)
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Characteristics of BrC and BC emissions from controlled diffusion flame and diesel engine combustion
- 2021
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Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 55:7, s. 769-784
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Tidskriftsartikel (refereegranskat)abstract
- Constraining the climate impact of particulate brown carbon (BrC) will require identification of formation mechanisms and isolation of its different components to allow for source apportionment. For fresh combustion aerosols, the light absorption characteristics and the Absorption Ångstrom Exponent (AAE) are principally controlled by the combustion conditions in which the particles formed and evolved. We investigated the influence of combustion temperatures on the BrC or black carbon (BC) emission characteristics for a miniCAST soot generator (propane fuel) and a modern heavy-duty diesel engine (petroleum diesel and two renewable diesel fuels). Changes in the AAE, mass spectral signatures, and thermal-optical characteristics were studied. We show that changing operating parameters to gradually reduce the combustion temperatures in these two fundamentally different combustion devices result in a regression from BC dominated to BrC dominated particle emissions. The regression toward BrC was associated with: (1) an increasing mass fraction of particulate non-refractory polycyclic aromatic hydrocarbons (PAHs), (2) an increasing fraction of refractory organic carbon, (3) more curved soot nanostructures and shorter fringe lengths, and (4) increased signal from (refractory) large carbon fragments in IR laser-vaporization aerosol mass spectra. Based on these results we argue that fresh BrC dominated combustion aerosols are attributed to primary emissions from low temperature combustion, highlighting the influence of refractory constituents and soot nanostructure. Higher temperatures favor the growth of conjugated polyaromatic structures in the soot, a progression hypothesized to control the evolution from BrC to BC character of the emitted aerosols.
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| 20. |
- Mannazhi, Manu, et al.
(författare)
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Influence of potassium chloride on PAH concentration during soot formation studied using laser-induced fluorescence
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 235
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Tidskriftsartikel (refereegranskat)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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| 21. |
- Mannazhi, Manu, et al.
(författare)
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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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Ingår i: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 128:4
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Tidskriftsartikel (refereegranskat)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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| 22. |
- Mannazhi, Manu, et al.
(författare)
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Soot maturity studies in methane-air diffusion flames at elevated pressures using laser-induced incandescence
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:1, s. 1217-1224
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Tidskriftsartikel (refereegranskat)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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| 23. |
- Mannazhi, Manu, et al.
(författare)
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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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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3936 .- 1946-3944. ; 14:5, s. 749-761
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Tidskriftsartikel (refereegranskat)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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| 24. |
- Mannazhi, Manu, et al.
(författare)
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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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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 39:1, s. 867-876
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Tidskriftsartikel (refereegranskat)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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| 25. |
- Mannazhi, Manu, et al.
(författare)
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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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Ingår i: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 126:12
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Tidskriftsartikel (refereegranskat)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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| 26. |
- Michelsen, Hope A., et al.
(författare)
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A Review of Terminology Used to Describe Soot Formation and Evolution under Combustion and Pyrolytic Conditions
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 14:10, s. 12470-12490
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Tidskriftsartikel (refereegranskat)abstract
- This review presents a glossary and review of terminology used to describe the chemical and physical processes involved in soot formation and evolution and is intended to aid in communication within the field and across disciplines. There are large gaps in our understanding of soot formation and evolution and inconsistencies in the language used to describe the associated mechanisms. These inconsistencies lead to confusion within the field and hinder progress in addressing the gaps in our understanding. This review provides a list of definitions of terms and presents a description of their historical usage. It also addresses the inconsistencies in the use of terminology in order to dispel confusion and facilitate the advancement of our understanding of soot chemistry and particle characteristics. The intended audience includes senior and junior members of the soot, black carbon, brown carbon, and carbon black scientific communities, researchers new to the field, and scientists and engineers in associated fields with an interest in carbonaceous material production via high-temperature hydrocarbon chemistry.
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| 27. |
- Rosander, Lilly
(författare)
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Adhocracy in the Bureaucracy : Practices of implementing collaborative contracting in infrastructure client organizations
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The building of infrastructure is a capital and resource-demanding activity, generally carried out in large interorganizational projects. Most infrastructure clients are public entities, implying that contracting processes are governed by public procurement regulations. Many infrastructure projects have high requirements for sustainability, both regarding impact on the local environment and the climate footprint. In addition to this, the construction often takes place in urban areas. To manage this complexity and uncertainty it has, over the past decades, become more common for public clients to apply procurement strategies that aim at fostering a good collaboration and integrate processes between client and contractor. Despite examples of advantages with such collaborative contracting the results vary and the institutionalization of collaborative contracting practices has proven difficult. Additionally, concepts and models vary between contexts and are hard to compare. How clients develop their procurement strategies and project practices, therefore, merits close attention. When the public sector uses procurement as tools to achieve their strategic goals, it is reasonable to analyze such decisions and processes as cases of policy implementation. Still, however, a large part of existing research on procurement of collaborative contracting focuses on a single project. By directing focus toward the organization as a whole, and on the implementation process of procurement strategies in several projects over time, the thesis aims to increase the understanding of how new organizational practices develop at different levels in public project-based organizations.The empirical foundation of the thesis is a longitudinal case study that follows the implementation of a new procurement strategy in the Swedish Transport Administration over seven years. The material includes data from seven projects that all used a two-stage Early Contractor Involvement model (called High collaboration). The case also includes material from the permanent organization, mainly in the Purchasing department. The five papers in the thesis analyze the implementation process from several perspectives, with specific attention to the characteristics of the organization as both public and project-based and how these features influence routines, legitimacy, learning and collaboration at different levels. The study adopts a practice perspective where interviews and observations focus on the actions and experiences of the individuals in the study. The result shows that there is a strong project autonomy, which is reinforced both by the project-based structure and by the public character of the client organization. Subsequently, there are few overarching structures at the central level to develop routines and procurement strategies in collaboration with the projects and suppliers. Thus, project managers have had a great influence on the finalization of project-specific procurement models and experiences has principally been shared between individuals, resulting in large variations between projects and limited organizational learning. Nonetheless, decisions in the permanent organization still influence the conditions at the operational project level, by dedicating resources and focusing attention on the topmanagement priorities. At the central level, collaborative contracting, as a concept has had varying legitimacy over time, and the initial problems in some of the seven projects gained considerable strategic importance by reinforcing such pendulum movements. Legitimacy seeking at higher organizational levels has also contributed to a variation in concepts and models, further complicating structured learning in the field of collaborative contracting.The thesis contributes to the construction management literature by providing deeper insights into why procurement models and collaborative practices vary between projects. Furthermore, the results contribute to project studies by expanding the understanding of how the specific character of public project-based client organizations impacts on learning processes for collaborative contracting. Finally, the thesis is relevant for public procurement research, as well as for practitioners in infrastructure and public procurement, since it provides novel insights into how the project-based nature of anorganization affects implementation and procurement processes.
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| 28. |
- Ruchkina, Maria, et al.
(författare)
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Laser-induced thermal grating spectroscopy based on femtosecond laser multi-photon absorption
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced grating spectroscopy (LIGS) is for the first time explored in a configuration based on the crossing of two focused femtosecond (fs) laser pulses (800-nm wavelength) and a focused continuous-wave (cw) laser beam (532-nm wavelength). A thermal grating was formed by multi-photon absorption of the fs-laser pulses by N 2 with a pulse energy around 700 μ J (∼ 45 TW/cm 2). The feasibility of this LIGS configuration was investigated for thermometry in heated nitrogen gas flows. The temperature was varied from room temperature up to 750 K, producing strong single-shot LIGS signals. A model based on the solution of the linearized hydrodynamic equations was used to extract temperature information from single-shot experimental data, and the results show excellent agreement with the thermocouple measurements. Furthermore, the fluorescence produced by the fs-laser pulses was investigated. This study indicates an 8-photon absorption pathway for N 2 in order to reach the B 3Π g state from the ground state, and 8 + 5 photon excitation to reach the B2Σu+ state of the N2+ ion. At pulse energies higher than 1 mJ, the LIGS signal was disturbed due to the generation of plasma. Additionally, measurements in argon gas and air were performed, where the LIGS signal for argon shows lower intensity compared to air and N 2.
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| 29. |
- Sandberg, Christer, 1962-
(författare)
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Process intensification in mechanical pulping : Reduced process complexity and improved energy efficiency
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work shows that, for newsprint quality grades, the production processes for mechanical pulp can be simplified, and the specific electrical energy demand can be reduced with around 600 kWh/ton (30%). The purpose of the work is to demonstrate how the production cost for mechanical pulps can be decreased through increased energy efficiency and reduced number of unit operations. The idea was to improve the main line refining conditions so that no additional fibre development or shive reduction is needed and thereby, the normal screening and rejects treatment system could be omitted.Mechanical pulp is used to produce a variety of products, where the two largest categories are printing papers and paperboard for packaging. The pulp is mainly produced by the breakdown of wood chips between rotating metal discs in machines called refiners with the product and process generally referred to as thermomechanical pulp(ing) (TMP). The refiner process requires high specific electrical energy to separate and develop the fibres to a pulp intended for the production of printing papers. Today, many processes need over 2000 kWh/ton of refining energy plus 200-300 kWh/ton of auxiliary energy (to drive pumps, agitators, screw conveyors, screens, presses, etc.).During the last two decades of the 20th century, the chemical processing industry underwent a transformation. The process development changed from being unit operation focused to function focused. The result is more compact processes with less equipment, higher yield and lower energy demand. When the development is made in an innovative way with such large effects on process performance, it is referred to as process intensification. My work is inspired by the concepts of process intensification, especially the striving for more compact processes with higher efficiency. This work is focused on mechanical pulp, intended for the manufacture of printing paper, produced in refiners with Norway spruce (Picea abies) as raw material. However, this approach could also be applied to mechanical pulp production in integrated paperboard mills and also using other raw materials e.g., pines or hardwoods. The investigated pulps and processes in this work are mainly intended for uncoated paper grades (newsprint, improved newsprint and book paper) printed by the offset printing process. In all studies, the pulps have been produced with full scale mill equipment and evaluated using laboratory measurements. However, in two studies, the produced pulps were evaluated on paper machines and at printing houses.A large number of process concepts have been evaluated in which different approaches have been used to reduce the specific energy and, in some cases, improve pulp quality. The approaches include:1. Impressafiner chip pretreatment 2. Primary high consistency (HC) refiner type (DD, RTS, CD, SD)3. Addition of low doses of sodium sulphite 4. Increased refining temperature (housing pressure)5. Refiner segments and centre plate design6. Increased production rate7. Low consistency (LC) refining in different process positions and in combination with different HC refiner typesThe separate effects of all these techniques have not been evaluated systematically neither have potential synergistic effects of all possible combinations been investigated. Even though a large number of combinations of unit operations have been studied, the emphasis has been on trying to do as much fibre development as possible in a single HC refining stage.The mill trials with spruce as raw material have shown that a low shive content and appropriate fibre development can be attained in a process without separate treatment of long fibres. High intensity primary stage refining (RTS and DD) was necessary to reach a low shive content at a low specific refining energy (SRE), with DD refiners appearing to be the most suitable for simplified processes. DD and RTS refining produced pulps with fibres exhibiting a higher degree of external fibrillation and share of split fibres than SD refining. DD refining produced fibres with lower cell wall thickness and higher light scattering at given fibre length than RTS refining. The lowest specific refining energy was attained for one of the trials using the process, denoted as S:HT:DD-LC-LC, consisting of DD refining at increased production rate, 18 adt/h, increased housing pressure, 6.6 bar(g), and with 5 kg/adt sodium sulphite added to the chips immediately before the refiner. After DD refining the pulp was refined in two LC refining stages. This process required only 1280 kWh/adt SRE to reach a tensile index of 52 Nm/g (Rapid-Köthen). This is 900 kWh/adt lower than the final pulp for newsprint based on SD HC refining, and over 500 kWh/adt lower than Scandinavian BAT processes (2014). Additionally, the auxiliary energy was around 150 kWh/adt lower for the processes without a conventional rejects treatment system. At 52 Nm/g tensile index, the light scattering coefficient was 2-3 m2/kg higher, and the length-weighted average fibre length was around 0.1 mm lower for this process than for SD TMP final pulp. The fibre bonding, indicated by density, tensile index and Z-strength of fibre fraction handsheets, was similar or higher for the S:HT:DD-LC-LC process than the reference SD TMP process with a rejects treatment system. Other interesting process configurations, with somewhat lower efficiencies, included:1. Impressafiner pretreatment of the chips with sodium sulphite before DD refining, with or without subsequent LC refining. Chip pretreatment with the Impressafiner enabled operating the DD refiner at higher intensity (feeding segments and increased production rate) without significant loss of quality and LC refining enabled increased production rate which increased the overall efficiency.2. RTS-SD refining with sodium sulphite added before the second stage SD refiner referred to as RTS-S:SD. The pulp from the RTS-S:SD process had similar fibre length as the S:HT:DD-LC-LC process but lower light scattering coefficient.3. A single-stage DD refiner operating at 15.5 adt/h and 4 bar(g) housing pressure (no sodium sulphite addition), which produced pulp with lower fibre length but higher light scattering coefficient than the S:HT:DD-LC-LC process. Two simplified processes were evaluated on paper machines and in printing houses. The first, denoted DD-LC-F, involved a combination of DD primary refining followed by LC refining and fractionation (screening). The screen rejects were mixed with the main line DD pulp before the LC refiner. The second process was the CPT:S-DD-LC process (№1 above). Good runnability was attained both on the paper machines and in the offset printing presses and the paper quality was similar to the reference paper.For printing paper applications, the proportion of fibre development in LC refining should preferably be relatively low, since it was shown that LC refiners have limited capacity to reduce fibre wall thickness and thereby develop light scattering and fibre fraction Z-strength.Explicit effects on the number of unit operations and production cost have not been evaluated in this work, but clearly both investment and variable costs as well as fixed costs can be reduced with a simplified process.
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| 30. |
- Török, Sandra, et al.
(författare)
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Influence of rapid laser heating on differently matured soot with double-pulse laser-induced incandescence
- 2022
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Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 56:6, s. 488-501
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Tidskriftsartikel (refereegranskat)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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| 31. |
- Török, Sandra, et al.
(författare)
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Laser-induced incandescence (2λ and 2C) for estimating absorption efficiency of differently matured soot
- 2021
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Ingår i: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 127:7
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Tidskriftsartikel (refereegranskat)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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| 32. |
- Zhu, Xinda, et al.
(författare)
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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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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 13:12
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Tidskriftsartikel (refereegranskat)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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