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1.
Obtaining the synthetic fuels from waste plastic and their effect on cavitation formation in a common-rail diesel injector
Luka Kevorkijan, Amalia Palomar-Torres, Eloisa Torres Jiménez, Carmen Mata, Ignacijo Biluš, Luka Lešnik, 2023, izvirni znanstveni članek

Opis: 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.
Ključne besede: plastic waste, synthetic fuels, pyrolytic oils, common-rail, cavitation, erosion, transient simulation
Objavljeno v DKUM: 18.03.2024; Ogledov: 73; Prenosov: 5
.pdf Celotno besedilo (4,55 MB)
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2.
Hop (Humulus lupulus L.) essential oils and xanthohumol derived from extraction process using solvents of different polarity
Katja Bizaj, Mojca Škerget, Iztok Jože Košir, Željko Knez, 2022, izvirni znanstveni članek

Opis: This study evaluates the content of essential oils (EOs) and prenylated flavonoid Xanthohumol (XN) in extracts of Slovenian hops, cultivar Aurora, obtained by using fluids of different polarity. It is a continuation of our previous work, investigating the extraction of bitter acids from hops. Extraction was conducted semi-continuously, using sub- and supercritical fluids of different polarity, i.e., carbon dioxide (CO2) and propane as non-polar and dimethyl ether (DME) as the polar solvent. The experiments explored a temperature range between 20 °C and 80 °C and pressures ranging from 50 bar to 150 bar. The content of XN in extracts was analysed using high-performance liquid chromatography and experiments demonstrated the largest concentration of XN was obtained using DME. In order to analyse the EO components in extracts, connected with a distinct odour, the steam distillation of extracts was performed and GC analysis was employed. Hop oil derived from CO2 extracts at specific conditions, had the highest relative concentration of linalool, β-caryophyllene and α-humulene, and oil derived from propane extracts had the highest content of all other five selected components (myrcene, geraniol, farnesene, α-selinene and δ-cadinene). The relative content of the investigated EO components in DME extracts was similar to that in propane extracts.
Ključne besede: hop extract, hop essential oils, flavonoids, carbon dioxide, propane, dimethyl ether
Objavljeno v DKUM: 17.08.2023; Ogledov: 206; Prenosov: 29
.pdf Celotno besedilo (2,30 MB)
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3.
Evaluation of LNPs as an emulsion stabilizer in Pickering emulsions for cosmetic applications : master's thesis
Nicole Blažević, 2022, magistrsko delo

Opis: The growing concern about the environmental impact and human health risk related to the excessive use of synthetic ingredients in cosmetics and topical formulations calls for the exploration of safe and sustainable natural alternatives. Kraft lignin is a polyphenolic compound generated as a by-product from the kraft pulping process in large quantities annually worldwide. In addition to its commercial availability, its structural features and diverse functional properties make it worth to be considered as a bio‐active ingredient for cosmetic and personal care products. The intrinsic limitations of its native form for the development of high-performance products can be overcome by morphology control through particle size reduction to nanoscale. Therefore, in this research lignin nanoparticles were evaluated for the stabilization of Pickering emulsions. First, a screening of conditions and ingredients was carried out to assess the most suitable parameters for the synthesis of emulsions. The synthesis of final Pickering emulsions was performed using a rotor-stator homogenizer followed by ultrasound. The quality of emulsions stabilized with LNPs were assessed in relation to the emulsification process parameters and ingredients used in the formulation. In generenal, higher concentration of LNPs and volume of oil favoured the emulsion stability. Sun protection factor test showed promising values for application of LNPs in the sunscreen field. We compared the SPF of emulsions prepared with orange, coconut, and paraffin oil. The results showed that emulsion with orange oil had the highest SPF at 16.5, with coconut oil it was 8.8, and the lowest for emulsion with paraffin oil which was 1.7.
Ključne besede: lignin, LNPs, oils, Pickering emulsions
Objavljeno v DKUM: 05.09.2022; Ogledov: 809; Prenosov: 0
.pdf Celotno besedilo (6,36 MB)

4.
On-line condition monitoring and evaluation of remaining useful lifetimes for mineral hydraulic and turbine oils
Vito Tič, Darko Lovrec, 2017, znanstvena monografija

Opis: Condition monitoring of hydraulic and turbine oils, and especially their remaining useful life, is becoming an important strategic business advantage for plant owners, which benefits in environment protection and cost reduction. This monograph discusses the problem of condition monitoring of hydraulic fluids throughout their life-cycles. Particular emphasis is placed on assessing mineral-based oils’ conditions and their remaining useful lifetimes quantitatively. Practicality and usefulness are vital when developing and deploying various methods for condition monitoring systems within industrial environments. Therefore, it is important to know the oil degradation mechanisms and influencing factors, commonly used laboratory methods and oil ageing tests, as well as, for on-line condition monitoring system design, the available sensors with all their characteristics and restrictions. The proposed approach is based on a novel method for testing the durability and oxidation stability of different hydraulic and turbine oils. The developed mathematical model is based on data from previously conducted oil-ageing tests for the assessment of an oil's condition and its remaining useful lifetime. The method can also be used for comparison of different oils and selection of a more adequate oil with high oxidation stability and long service-lifetime.
Ključne besede: Hydraulic and turbine oils, degradation mechanisms, on-line condition monitoring, test methods, remaining useful lifetime
Objavljeno v DKUM: 22.12.2017; Ogledov: 1578; Prenosov: 406
.pdf Celotno besedilo (7,75 MB)
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5.
Phenols, proanthocyanidins, flavones and flavonols in some plant materials and their antioxidant activities
Mojca Škerget, Petra Kotnik, Majda Hadolin Kolar, Andreja Rižner Hraš, Marjana Simonič, Željko Knez, 2005, izvirni znanstveni članek

Opis: Methanol extracts prepared from five plant materials native to the Mediterranean area, namely olive tree (Olea europaea) leaf, St. John's wort (Hypericum perforatum), hawthorn (Crataegus laevigata), oregano (Origanum vulgare) and laurel leaf (Lauris nobilis), were examined for their phenolic components. Total phenolic content was determined by the Folin-Ciocalteu method. The content of proanthocyanidins in acid-hydrolysed extracts was determined spectrophotometrically. The contents of free flavones (apigenin andluteolin) and flavonols (kaempferol, myricetin and quercetin) were determined by HPLC analysis. The time of hydrolysis of flavones, flavonols andproanthocyanidins was optimised. Antioxidant activities of apigenin, luteolin, kaempferol, myricetin, quercetin and of plant extracts were examined. Antioxidative activities were studied in sunflower oil at 98 °C, by measuring peroxide value, and in an aqueous emulsion system of -carotene and linoleic acid by measuring the absorbance of the sample. Among flavones and flavonols investigated, only myricetin inhibited oxidation of sunflower oil. All other flavones and flavonols showed pro-oxidative activity. Oppositely, in the emulsion system, only apigenin showed pro-oxidative activity while otherflavones and flavonols and plant extracts inhibited oxidation of -carotene.
Ključne besede: chemical processing, extraction, plant material, fenolic content, hidrolysis, antioxidants, flavones, flavonols, proanthocyanidines, oils, emulsions
Objavljeno v DKUM: 01.06.2012; Ogledov: 2548; Prenosov: 122
URL Povezava na celotno besedilo

6.
Concentration of free fatty acids in rapeseed oil
Petra Kotnik, Mojca Škerget, Željko Knez, 2012, objavljeni znanstveni prispevek na konferenci

Ključne besede: materials, methods, vegetable oils
Objavljeno v DKUM: 01.06.2012; Ogledov: 2000; Prenosov: 30
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