1. Cavitation erosion modelling on a radial divergent test section using RANSLuka Kevorkijan, Luka Lešnik, Ignacijo Biluš, 2022, original scientific article Abstract: Cavitation is the phenomenon of fluid evaporation in hydraulic systems, which occurs due to a pressure drop below the value of the vapor pressure. For numerical modelling of this generally undesirable phenomenon, which is often associated with material damage (erosion), there are various mathematical vapor transfer models that have been validated in the past. There are different approaches to predicting cavitation erosion, which have mostly been experimental in the past. Recently various numerical models have been developed with the development of numerical simulations. They describe the phenomenon of cavitation erosion based on different theoretical considerations, such as Pressure wave hypothesis, Microjet hypothesis, or a combination of both. In the present paper, an analysis of the Schnerr-Sauer transport cavitation model was used, upgraded with an erosive potential energy model based on pressure wave hypothesis for cavitation erosion prediction. The extended numerical model has been applied to the case of a radial divergent test section in three different mathematical formulations. The results of simulation were compared and validated to experimental work performed by other authors. The study shows that the distribution of surface accumulated energy agrees with the experimental results, although certain differences exist between formulations. The applied method appears to be appropriate for further use, and to be extended to materials response modelling in the future.
Keywords: kavitacija, erozija, erozivna potencialna energija, numerične simulacije, cavitation, erosion, erosive potential energy, numerical simulation
Published in DKUM: 26.03.2025; Views: 0; Downloads: 3
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2. Settling of mesoplastics in an open-channel flowLuka Kevorkijan, Elvis Žic, Luka Lešnik, Ignacijo Biluš, 2022, original scientific article Abstract: Pollution of water by plastic contaminants has received increasing attention, owing to
its negative effects on ecosystems. Small plastic particles propagate in water and can travel long
distances from the source of pollution. In order to research the settling motion of particles in
water flow, a small-scale experiment was conducted, whereby spherical plastic particles of varying
diameters were released in an open-channel flow. Three approaches were investigated to numerically
simulate the motion of particles. The numerical simulation results were compared and validated
with experimental data. The presented methods allow for deeper insight into particle motion in
fluid flow and could be extended to a larger scale to predict the propagation of mesoplastics in
natural environments.
Keywords: dense discrete phase model, discrete element method, diameter, discrete phase model, mesoplastics, particles, settling
Published in DKUM: 20.03.2025; Views: 0; Downloads: 4
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3. Enhancing utilization of municipal solid waste bottom ash by the stabilization of heavy metalsFilip Kokalj, Vesna Alivojvodić, Luka Lešnik, Nela Petronijević, Dragana Radovanović, Niko Samec, 2025, original scientific article Abstract: Waste-to-energy (WtE) is a key part of modern waste management. In the European Union, approximately 500 WtE plants process more than 100 million tons of waste yearly, while globally, more than 2700 plants handle over 500 million tons. Roughly 20% of the waste processed is bottom ash (BA). However, this ash can contain heavy metals in concentrations that may render it hazardous. This paper presents a study focusing on stabilizing municipal solid waste incineration BA using simple and industrially viable treatments. The Slovenian WtE plant operator wishes to install the stabilization process; thus, the samples obtained from the plant were treated (1) with a CO2 gas flow, (2) with water spraying, and (3) with a combination of water spraying and a CO2 gas flow under laboratory conditions. Thermodynamic calculations were applied to define potential reactions during the treatment processes in the temperature range from 0 to 100 ◦C and to define the equilibrium composition of the treated ash with additions of CO2 and water. The standard leaching test EN 12457-4 of treated ash shows a reduction of over 40% in barium concentration and over 30% in lead concentration in leachates.
Keywords: heavy metals, waste-to-energy, bottom ash, leachate, reuse
Published in DKUM: 10.03.2025; Views: 0; Downloads: 6
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4. Primerjava občutljivosti atmosferskega in tlačno polnjenega motorja z notranjim zgorevanjem na spremembe fizikalnega stanja okoliškega zraka : diplomsko deloPrimož Burg, 2024, undergraduate thesis Abstract: Diplomska naloga vsebuje rezultate simulacij, izvedenih na enodimenzijskem numeričnem modelu atmosferskega in tlačno polnjenega motorja z notranjim zgorevanjem. Rezultati simulacij so moč, navor in izkoristek posameznega motorja, vhodne spremenljivke pa so temperatura, tlak in nadmorska višina. Ugotovili smo, da se moč, navor in efektivni izkoristek povečujejo s padanjem temperature zraka, s padanjem tlaka pa se ti karakteristični parametri znižujejo. Primerjava rezultatov je pokazala, da so spremembe moči, navora in izkoristka pri enakih pogojih večje pri atmosferskem motorju v primerjavi s tlačno polnjenim motorjem.
Keywords: atmosferski motor z notranjim zgorevanjem, tlačno polnjen motor z notranjim zgorevanjem, vpliv stanja okoliškega zraka
Published in DKUM: 06.03.2025; Views: 0; Downloads: 6
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5. Numerična simulacija vbrizgavanja piroliznega olja iz odpadne LDPE plastike v vbrizgalni šobi dizelskega motorja : diplomsko delo univerzitetnega študijskega programa I. stopnjeAndraž Dobaj, 2024, undergraduate thesis Abstract: Proučevan je bil vpliv dodatka piroliznega olja, pridobljenega iz polietilena nizke gostote dizelskemu gorivu na pojavnost kavitacije v vbrizgalni šobi dizelskega motorja. V numerični simulaciji s programsko opremo Ansys Fluent so bile upoštevane lastnosti treh različnih goriv: čistega dizelskega goriva, dizelskega goriva z dodatkom 10% in 20% piroliznega olja (volumski deleži). Analiza rezultatov je pokazala, da dodajanje piroliznega olja dizelskemu gorivu vpliva na pojavnost kavitacije. Najnižja pojavnost kavitacije je bila zabeležena pri sto odstotnem dizelskem gorivu, najvišja pa pri gorivu z dodatkom 20% piroliznega olja. Pirolizno olje, pridobljeno iz polietilena nizke gostote ima nižji vrednosti viskoznosti in gostote kot dizelsko gorivo. Možno je sklepati, da nižji vrednosti viskoznosti in gostote vplivata na večjo pojavnost kavitacije pri gorivu z višjim volumskim deležem piroliznega olja iz polietilena nizke gostote v zmesi.
Keywords: kavitacija, računalniška dinamika tekočin, pirolizno olje, polietilen nizke gostote, vbrizgalna šoba, dizelski motor
Published in DKUM: 08.01.2025; Views: 0; Downloads: 29
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6. Recikliranje odpadnih kompozitnih materialov z vgrajenimi ogljikovimi vlakni s postopkom pirolize : diplomsko deloAndrej Umbreht, 2024, undergraduate thesis Abstract: V tej študiji smo raziskovali recikliranje polimera, ojačenega z ogljikovimi vlakni z uporabo pirolize. Začeli smo z opisom temeljnih lastnosti kompozitnih materialov in specifičnih značilnosti polimernega kompozita ojačenega z ogljikovimi vlakni. Podali smo pregled različnih metod recikliranja s poudarkom na pirolizi kot tehniki za predelavo ogljikovih vlaken. Poleg tega smo izvedli postopek oksidacije, da bi primerjali njegove učinke na material. Za analizo kemičnih sprememb v vlaknih, ki so posledica teh obdelav, je bila uporabljena spektroskopija FTIR. Nazadnje smo naše ugotovitve primerjali še z obstoječo literaturo.
Keywords: ogljikova vlakna, kompozitni materiali, piroliza, recikliranje
Published in DKUM: 03.10.2024; Views: 0; Downloads: 34
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7. Termična piroliza visokokaloričnega goriva iz odpadkov (RDF)Maja Bagari, 2024, master's thesis Abstract: V skladu s cilji Direktive o odpadkih (2008/98/ES) si države članice EU prizadevajo zmanjšati količine odloženih odpadkov, zato jih centri za ravnanje z odpadki predelujejo v uporabno gorivo iz odpadkov, imenovano RDF. Ta ima izjemen energetski potencial, ki ostaja premalo izkoriščen.
V okviru magistrske naloge se je izvedla raziskava potencialne uporabnosti treh različnih RDF frakcij kot surovin v postopku pirolize. Rezultati analiz goriv so potrdili visoke kurilne vrednosti in raznolik materialni spekter.
Po izvedbi pirolize so bila okarakterizirana tudi pirolizna olja. Rezultati so nakazali na podobnost s konvencionalnim dizelskim gorivom in na možnost potencialnega energetskega izkoriščanja. Kljub temu trenutna struktura olj še ne omogoča njihove neposredne uporabe kot tekočega goriva, kar nakazuje nujnost nadaljnjih prilagoditev procesa pirolize in ustreznih predhodnih obdelav vhodnih surovin.
Keywords: gorivo iz odpadkov, RDF, piroliza
Published in DKUM: 27.09.2024; Views: 0; Downloads: 0
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8. Analiza tekočih in trdnih produktov procesa torefikacije odpadne biomase : diplomsko delo visokošolskega strokovnega študijskega programa I. stopnjeAnteja Garmut, 2024, undergraduate thesis Abstract: Cilj diplomske naloge je obravnava procesa torefikacije odpadne biomase in karakterizacija nastalih produktov. Za predstavnike odpadne biomase so bili izbrani tri različni vzroci, in sicer miskantus, mešan les ter hmelj. Cilj naloge je proizvesti trdno biogorivo z višjo kurilno vrednostjo v primerjavi s surovo biomaso. Proces torefikacije je potekal eno uro pri treh različnih temperaturah, 250 °C, 350 °C in 450 °C. Produkte smo nato kemijsko karakterizirali. Karakterizacijo smo izvedli na trdnih in tekočih produktih torefikacije ter tudi na surovih vzorcih posameznih biomas. Ovrednotili smo masne izgube, masne izkoristke, energijsko učinkovitost, doprinos energije glede na maso, kurilne vrednosti, vsebnost hlapnih snovi, vlage in pepela. S Fourierjevo transformacijo (FTIR) je bila določena struktura vzorcev, s termogravimetrično analizo (TGA) pa termična razgradnja surove in toreficirane biomase.
Z naraščanjem temperature torefikacije se kurilne vrednosti trdnih produktov višajo, nižje pa so vrednosti masnih izkoristkov, energetske učinkovitosti ter delež hlapnih komponent. FTIR analiza prikazuje razgradnjo celuloze, ki jo zaznamo z zmanjšanimi vrhovi, z eliminacijo manjših vrhov pa opazimo delno ragradnjo hemiceluloze in lignina. Zvišanje temperature je povzročilo zmanjšanje moči karboksilnih in -OH skupin. V surovi biomasi zaznamo prisotnost aromatskih spojin, simetrične alifatske skupine ter CO-C funkcionalne skupine, ki jih v primerjavi s toreficirano biomaso več ne zaznamo. TGA analiza je bila izvedena v kisikovi atmosferi pri konstantni hitrosti segrevanja v temperaturnem območju 30-900 °C. Ob višjih temperaturah je pokazala oksidacijo fiksnega ogljika, izhlapevanje težko hlapnih snovi ter razgradnjo anorganskih materialov. Glede na rezultate analiz je razvidno, da so trdni produkti primerni za uporabo kot biogorivo, medtem ko je v tekočih produktih delež vode previsok.
Keywords: obnovljivi viri energije, odpadna biomasa, hmelj, torefikacija, kurilna vrednost, termogravimetrična analiza, miskantus, les
Published in DKUM: 09.09.2024; Views: 38; Downloads: 28
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9. The ǂeffect of fuel quality on cavitation phenomena in common-rail diesel injector—a numerical studyLuka Kevorkijan, Ignacijo Biluš, Eloisa Torres Jiménez, Luka Lešnik, 2024, original scientific article Abstract: Plastic is one of the most widely used materials worldwide. The problem with plastic
arises when it becomes waste, which needs to be treated. One option is to transform plastic waste
into synthetic fuels, which can be used as replacements or additives for conventional fossil fuels
and can contribute to more sustainable plastic waste treatment compared with landfilling and other
traditional waste management processes. Thermal and catalytic pyrolysis are common processes
in which synthetic fuels can be produced from plastic waste. The properties of pyrolytic oil are
similar to those of fossil fuels, but different additives and plastic stabilizers can affect the quality
of these synthetic fuels. The quality of fuels and the permissible particle sizes and number density
are regulated by fuel standards. Particle size in fuels is also regulated by fuel filters in vehicles,
which are usually designed to capture particles larger than 4 µm. Problems can arise with the
number density (quantity) of particles in synthetic fuels compared to that in fossil fuels. The present
work is a numerical study of how particle size and number density (quantity) influence cavitation
phenomena and cavitation erosion (abrasion) in common-rail diesel injectors. The results provide
more information on whether pyrolysis oil (synthetic fuel) from plastic waste can be used as a
substitute for fossil fuels and whether their use can contribute to more sustainable plastic waste
treatments. The results indicate that the particle size and number density slightly influence cavitation
phenomena in diesel injectors and significantly influence abrasion.
Keywords: plastic waste, synthetic fuels, pyrolytic oil, common rail, cavitation, erosion, particles
Published in DKUM: 05.07.2024; Views: 131; Downloads: 14
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10. Obtaining the synthetic fuels from waste plastic and their effect on cavitation formation in a common-rail diesel injectorLuka Kevorkijan, Amalia Palomar-Torres, Eloisa Torres Jiménez, Carmen Mata, Ignacijo Biluš, Luka Lešnik, 2023, original scientific article Abstract: The presented paper addresses two significant issues of the present time. In general, the studies of the effect of synthetic fuels on cavitation formation and cavitation erosion prediction in the nozzle tip of common-rail diesel injectors were addressed. The first problem is plastic waste, which can have a significant negative environmental impact if not treated properly. Most plastic waste has high energy value, so it represents valuable material that can be used in resource recovery to produce various materials. One possible product is synthetic fuel, which can be produced using thermal and catalytic pyrolysis processes. The first issue addressed in the presented paper is the determination of fuel properties since they highly influence the fuel injection process, spray development, combustion, etc. The second is the prediction of cavitation development and cavitation erosion in a common-rail diesel injector when using pyrolytic oils from waste plastic. At first, pyrolytic oils from waste high- and low-density polyethylene were obtained using thermal and catalytic pyrolysis processes. Then, the obtained oils were further characterised. Finally, the properties of the obtained oils were implemented in the ANSYS FLUENT computational program and used in the study of the cavitation phenomena inside an injection nozzle hole. The cavitating flow in FLUENT was calculated using the Mixture Model and Zwart-Gerber-Belamri cavitation model. For the modelling of turbulence, a realisable k–ε model with Enhanced Wall Treatment was used, and an erosion risk indicator was chosen to compare predicted locations of cavitation erosion. The results indicate that the properties of the obtained pyrolytic oils have slightly lower density, surface tension and kinematic viscosity compared to conventional diesel fuel, but these minor differences influence the cavitation phenomenon inside the injection hole. The occurrence of cavitation is advanced when pyrolytic oils are used, and the length of cavitation structures is greater. This further influences the shift of the area of cavitation erosion prediction closer to the nozzle exit and increases its magnitude up to 26% compared to diesel fuel. All these differences have the potential to further influence the spray break-up process, combustion process and emission formation inside the combustion chamber.
Keywords: plastic waste, synthetic fuels, pyrolytic oils, common-rail, cavitation, erosion, transient simulation
Published in DKUM: 18.03.2024; Views: 299; Downloads: 36
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