| Abstract | Svrha motora s unutarnjim izgaranjem je proizvodnja mehaničke snage iz kemijske energije goriva. Ključnu ulogu u radu i kontroli motora s unutarnjim izgaranjem imaju ventili. Ta komponenta omogućuje protok zraka i smjese goriva u komoru za izgaranje. Također, omogućuje istjecanje ispušnih plinova izvan nje. Najčešći tip ventila u današnjim motorima je tanjurasti ventil. Po funkcionalnosti se dijeli na dvije vrste: usisni i ispušni.
Povijesnim razvojem motora pokušavalo se pronaći rješenje za mnoge izazove iz domena učinkovitosti, performansi, ekologije i pristupačnosti. Obzirom na značajnu funkciju ventila u radu motora s unutarnjim izgaranjem, oni su imali ključnu ulogu u njihovom razvoju. Dizajn usisnog kanala i ventila najviše je zadužen za dostatan protok zraka u cilindru. Naime, povećanjem količine zraka koja se dovode u komoru za izgaranje povećava se stupanj punjenja. Time se povećava snaga motora, bez promjene radnog volumena i frekvencije odvijanja procesa. Potreba za povećanjem protoka zraka u cilindru dovela je do postepenog povećanja broja ventila u cilindru. Konvencionalni tanjurasti ventil ima kružni poprečni presjek, odnosno osnosimetričan je. Iako to ima svoje prednosti, kao želja za povećanjem razvodnog presjeka ventila, a samim time i protoka zraka, javlja se ideja o nekonvencionalnom obliku ventila. Glavna ideja ovog rada je predstaviti ventil nekonvencionalne geometrije te analizirati promjene u strujanju zraka. Ključne veličine koje opisuju strujanje zraka u cilindru su: površina razvodnog presjeka, maseni protok zraka, koeficijent protoka i koeficijent pražnjenja.
Najprije se izrađuje 3D CAD model, kako konvencionalnog, tako i nekonvencionalnog usisnog kanala i ventila. Izrađeni CAD modeli potrebni su za izradu simulacije u programskom paketu Ansys Student. Primjenom računalne dinamike fluida (CFD) računaju se veličine potrebne za određivanje glavnih razlika u strujanju. Također, analizira se i utjecaj strukture mreže konačnih volumena na rezultat. Za konvencioanlni i nekonvencionalni ventil detaljno se uspoređuju veličine kao što su razvodni presjeci, maseni protoci te koeficijenti protoka. Navedene veličine u oba slučaju određuju se za zamrznute položaje ventila pri 25%, 50%, 75% i 100 ukupnog podizaja ventila.
U konačnici, predstavljene su glavne prednosti i nedostatci nekonvencionalnog ventila. |
| Abstract (english) | The purpose of the internal combustion engine is to produce mechanical power from the chemical energy of the fuel. Valves play a key role in the operation and control of internal combustion engines. This component allows the flow of air and fuel mixture into the combustion chamber. Also, it allows exhaust gases to flow out. The most common type of valve in today's engines is the poppet valve. By functionality, it is divided into two types: intake and exhaust.
The historical development of the engine tried to find a solution to many challenges in the domain of efficiency, performance, ecology and affordability. Considering the significant function of valves in the operation of internal combustion engines, they played a key role in their development. The design of the intake port and valve is mainly responsible for sufficient air flow in the cylinder. Namely, by increasing the amount of air supplied to the combustion chamber, the degree of filling increases. This increases the power of the engine, without changing the engine capacity and frequency of the process. The need to increase the air flow in the cylinder led to a gradual increase in the number of valves in the cylinder. A conventional poppet valve has a circular cross-section, that is, it is axisymmetric. Although this has its advantages, as a desire to increase curtain valve area, and thus the air flow, the idea of an unconventional valve shape appears. The main idea of this paper is to present a valve with an unconventional geometry and to analyze the changes in air flow. The key quantities that describe the air flow in the cylinder are: curtain valve area, mass air flow, flow coefficient and discharge coefficient.
First, a 3D CAD model is created, both of the conventional and unconventional intake port and valve. The created CAD models are needed to create a simulation in the Ansys Student software package. Using computational fluid dynamics (CFD), the quantities necessary to determine the main differences in the flow are calculated. Also, the influence of the finite volume network structure on the result is analyzed. For conventional and non-conventional valves, parameters such as curtain valve area, mass flows and flow coefficients are compared in detail. The specified sizes in both cases are determined for fixed valve positions at 25%, 50%, 75% and 100% of the total valve lift.
Finally, the main advantages and disadvantages of the unconventional valve are presented. |
| Study programme | Title: Mechanical Engineering; specializations in: Design, Process and Energy Engineering, Production Engineering, Engineering Modelling and Computer Simulation, Marine Engineering, Industrial Engineering and Management, Materials Engineering, Mechanics and Robotics, Autonomous Systems, Mechatronics and Robotics
Course: Design
Study programme type: university
Study level: graduate
Academic / professional title: sveučilišni/a magistar/magistra inženjer/inženjerka strojarstva (sveučilišni/a magistar/magistra inženjer/inženjerka strojarstva) |
