1. 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: 105; Downloads: 7
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2. 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: 271; Downloads: 14
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3. Experimental analysis of cavitation erosion in a particle-laden flowFilip Jovanovski, 2023, undergraduate thesis Abstract: Cavitation erosion is a problem that presents a challenge for the engineers in different industries, as it erodes the machinery which leads to lower efficiency and higher maintanance costs. An experimental investigation has been conducted to evaluate cavitation and cavitation erosion with and without the presence of solid particles in a Venturi channel. The methodology is based on observing and analysing the evolution of the vapour structures and occurence of cavitation erosion on the sample surface in the Venturi channel. To conduct experiments the cavitation tunnel was used, with the central component being a transparent test section with a Venturi-like channel (constructed from Plexiglass walls and a metal insert) to monitor the process of cavitation. To detect the damage caused by cavitation erosion and abrasion, the most effective solution was found to be an indicator in the form of black acrylic paint thinned with water (at a ratio of 1:2). On the sample surface, a self-adhesive aluminium tape was applied to protect the aluminium base from erosive characteristics from cavitation Furthermore, a comparison between cavitation with and without solid particles was made to determine the effects of solid particles on both cavitation and abrasion of the sample surface. The observation revealed that no matter the solid particles, damage from cavitation erosion appears at the separation point and in proximity to the location of the detached cloud collapse. The spherical glass particles with diameters between 40 µm and 70 µm added an abrasive effect on the sample surface only in the presence of cavitation structures. It was determined, that the intensity of cavitation erosion and abrasion increases when the cavitation number decreases and volumetric flow rate increases. Also, an economic analysis was conducted, to determine which is the more cost beneficial solution between replacement of the metal insert and application of protective coatings over the metal insert.
Keywords: cavitation erosion, solid particles, abrasion, experiment
Published in DKUM: 28.02.2024; Views: 226; Downloads: 25
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4. Cavitation erosion modelling : comparison of different driving pressure approachesLuka Kevorkijan, Marko Pezdevšek, Ignacijo Biluš, Gorazd Hren, 2023, original scientific article Abstract: In this paper we compared different driving pressure approaches to calculate the cavitation potential energy from a source, which is transferred to a surface. The first approach used the reference pressure, the second approach used the pressure calculated at each timestep with no averaging, the third approach used the averaged pressure values from all timesteps included in one shedding cycle, and the last approach used pressure values from the steady state simulations results. The results show that for all formulations the averaged pressure values and steady state pressure values give similar results in terms of mean potential power distribution on the hydrofoil surface as in absolute values. The reference pressure approach gave similar results for the derivative and divergence formulation while for the source term the mean potential power distribution on the hydrofoil surface differs and the maximums were near the leading edge. The approach where we used no pressure averaging gave adequate results in terms of mean potential power distribution but differs from other approaches in absolute values which were considerably lower for all potential power formulations.
Keywords: cavitation, erosion potentional, driving pressure, numerical simulations
Published in DKUM: 21.02.2024; Views: 387; Downloads: 13
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5. Development of an experimental Dead-End microfiltration layout and process repeatability analysisGorazd Bombek, Luka Kevorkijan, Grega Hrovat, Drago Kuzman, Aleks Kapun, Jure Ravnik, Matjaž Hriberšek, Aleš Hribernik, 2024, original scientific article Abstract: Microfiltration is an important process in the pharmaceutical industry. Filter selection and validation is a time-consuming and expensive process. Quality by design approach is important for product safety. The article covers the instrumentalization and process control of a laboratory-scale dead-end microfiltration layout. The layout is a downscale model of the actual production line, and the goal is filter validation and analysis of process parameters, which may influence filter operation. Filter size, fluid pressure, valve plunger speed, and timing issues were considered. The focus is on the identification of the most influential process parameters and their influence on the repeatability of pressure oscillations caused by valve opening. The goal was to find the worst-case scenario regarding pressure oscillations and, consequently, filter energy intake. The layout was designed as compact as possible to reduce pressure losses between the filter and valve. Valve-induced pressure oscillations proved to be prevailing over the water hammer effect. Several filters in sizes between 3.5 cm2 and 6900 cm2 were tested, and some recommendations were suggested for the reduction of energy intake of the filter and to improve the repeatability of the process.
Keywords: filtration, pressure oscillations, repeatability, processes, parameters
Published in DKUM: 01.02.2024; Views: 410; Downloads: 18
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6. Prediction of cavitation and particle erosion in a radial divergent test sectionLuka Kevorkijan, Luka Lešnik, Ignacijo Biluš, 2022, original scientific article Abstract: The 3D unsteady, cavitating, particle-laden flow through a radial divergent test section was simulated with the homogeneous mixture model and Discrete Phase Model (DPM) within the commercial CFD code ANSYS Fluent. For turbulence, a RANS approach was adopted with the Reboud’s correction of turbulent viscosity in the k-ω SST model. Cavitation erosion was predicted with the Schenke-Melissaris-Terwisga (SMT) model, while particle erosion was predicted with the Det Norske Veritas (DNV) model. Two distinct erosion zones were identified, one for pure cavitation erosion and one for pure particle erosion. The occurrence of the pure particle erosion zone downstream of the cavitation erosion zone was analysed. By observing the streamlines downstream of the cavitation structures, it was found that vortices form in the flow and redirect the particles towards the wall, causing a pure particle erosion zone on the wall. Particles under consideration in this study were not found to alter the flow to the extent that the cavitation erosion zone would be significantly altered compared with the results without solid particles which are reported in the literature.
Keywords: cavitation, Particles ANSYS Fluent, erosion, CFD, modelling, DPM
Published in DKUM: 30.10.2023; Views: 279; Downloads: 8
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8. Numerična simulacija prenosa toplote pri toplotni obdelavi aluminjastih vzorcev : diplomsko deloLuka Kevorkijan, 2018, undergraduate thesis Abstract: Opravljena je numerična simulacija segrevanja in ohlajanja aluminijastih vzorcev med raztopnim žarjenjem in gašenjem. Simulacija je pripravljena z uporabo toplotne prehodnosti izračunane iz meritev temperature, kjer so vzorci obravnavani kot telesa idealne toplotne prevodnosti. Ugotovljeno je, da takšen pristop omogoča hitre in zadovoljive rezultate v primeru segrevanja dimenzijsko podobnih vzorcev med raztopnim žarjenjem. Pri ohlajanju med gašenjem z vodo ob predpostavki telesa idealne toplotne prevodnosti je napaka večja. Prikazane so meritve mehanskih lastnosti, ki pokažejo vpliv odstopanja izvedbe toplotne obdelave na končne lastnosti. Predstavljen je predlog oblikovanja velikostnih razredov vzorcev z namenom zmanjšanja razlik časov raztopnega žarjenja.
Keywords: numerična simulacija, prenos toplote, telo idealne toplotne prevodnosti, aluminij, raztopno žarjenje, gašenje, merjenje temperature, mehanske lastnosti
Published in DKUM: 07.09.2018; Views: 1826; Downloads: 150
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