Nadogradnja modela za obradu izmjerenih rezultata u Ottovom motoru s pretkomorom

master's thesis

• Title (english): Upgrade of model for re-calculation of measured results from pre-chamber spark ignited engine
• Author: Sara Ugrinić
• Mentor: Momir Sjerić (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2021-12-17, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; General Mechanical Engineering (Construction)

Abstract

Tema ovog rada je nadogradnja modela za obradu izmjerenih rezultata u Ottovom motoru s pretkomorom. Motori s pretkomorom imaju potencijal smanjiti potrošnju goriva i ispust štetnih plinova u okoliš. Danas, u vrijeme kada su dokazani štetni utjecaji ispušnih plinova na ljudsko zdravlje i okoliš, to je iznimno važno. Povećanjem faktora pretička zraka iznad 1,4 postiže se veća učinkovitost i smanjuje emisija dušikovih oksida NOx. Vrlo siromašne smjese imaju problem s težim paljenjem i nestabilnim izgaranjem uz povećane emisije neizgorjelih ugljikovodika (THC) i ugljikovih monoksida (CO) zbog nemogućnosti rada trokomponentnog katalizatora. Tako je jedno od rješenja problema siromašnih smjesa motor s pretkomorom. U ovom će se radu proračunati izgaranje u Ottovim motorima s pretkomorom. Prostor izgaranja u takvom se motoru sastoji od glavnog prostora izgaranja omeđenog klipom, glavom motora i košuljicom cilindra te pretkomore koja je s glavnim prostorom izgaranja povezana određenim brojem kanala, odnosno provrta. Izgaranje u Ottovim motorima s pretkomorom naziva se Turbulent Jet Ignition - TJI izgaranje gdje se siromašna smjesa u glavnom prostoru izgaranja pali pomoću višestrukih turbulentnih mlazova produkata izgaranja koji struje iz pretkomore.
Matematički model izgaranja razvijen je u programskom paketu MATLAB 7.11.0 (R2010b). Na postojeći programski kod za konvencionalni motor s unutarnjim izgaranjem nadograđene su jednadžbe za izračun fizikalnih veličina zbog utjecaja pretkomore.
Dobivene fizikalne veličine opisuju izmjenu mase između pretkomore i glavnog prostora izgaranja, prijelaz topline (toplinske gubitke) za pretkomoru, dodavanje mase uslijed ubrizgavanja goriva u pretkomoru i brzinu oslobađanja topline (engl. rate of heat release). Pojedine fizikalne veličine (ukupna masa, mase pojedinih komponenti – gorivo, zrak i produkti izgaranja, temperatura, gubici topline, sastav, faktor pretička zraka) definirane su za svaki kut zakreta koljenastog vratila koje opisuju visokotlačni dio procesa (od zatvaranja usisnog do otvaranja ispušnog ventila) u glavnom prostoru izgaranja i pretkomori.
Rezultati iz pregleda literature pokazali su da je primjenom sustava pretkomore moguće upaliti smjese u glavnom prostoru izgaranja s faktorima pretička zraka preko 1,4 te je time moguće smanjiti emisije dušikovih oksida NOx. Obrada rezultata profila tlaka u pretkomori i glavnom prostoru izgaranja za nekoliko različitih radnih točaka provedena je nadograđenim programskim kodom u MATLAB-u. Ostvareni rezultati vrlo dobro se podudaraju s referentnim vrijednostima iz programa AVL Boost.

Abstract (english)

Model for recalculation of measured results in pre-chamber spark ignited engine was developed within this diploma thesis. Internal combustion engine with prechamber spark ignition is a possible solution for reduction of the fuel consumption and reduction of exhaust emissions which is extremely important in the time when all the consequences of pollution are known. By increasing the air to fuel ratio to more than 1.4, higher efficiency and the reduction of nitrogen oxides (NOx) are possible. Very lean mixtures (air to fuel ratio higher than 1,4) encounter unstable burning issues with higher emissions of unburned hydrocarbons (THC) and carbon monoxide (CO) because the three-way catalyst works only with the nearly stoichiometric mixtures. One of the solutions for ignition of very lean mixtures is a pre-chamber spark ignited engine and in this thesis the combustion inside spark ignition (SI) engine with a pre-chamber is modelled and computed. The ignition of a lean mixture in the main combustion chamber is achieved by the penetration of multiple turbulent jets of combustion products from the pre-chamber where the mixture is rich. Pre-chamber and main chamber are connected by nozzles on the prechamber. In SI engines with a pre-chamber, this mode of combustion is most called Turbulent Jet Ignition - TJI where the ignition of a lean mixture in the main combustion chamber is achieved by the penetration of multiple turbulent jets of combustion products from the pre-chamber.
Model for re-calculation of combustion in the SI engine with a pre-chamber is developed in MATLAB version 7.11.0 (R2010b). The existing code for standard SI engine is upgraded to calculate the pre-chamber influence. Physical quantities that are calculated in this thesis are mass exchange through pre-chamber nozzles, heat losses in pre-chamber, added fuel to pre-chamber and rate of heat release (ROHR). Also, all physical quantities of pre- and main chamber during the high-pressure part of the process (between inlet valve closure and outlet valve opening) are defined for every crank angle (mass, individual masses of fuel, air and combustion products, temperature, heat losses, air to fuel ratio, etc.).
Literature results have shown that by implementing pre-chamber in SI engine, ignition of lean mixtures to more than 1,4 is possible and ensures reduction of nitrogen oxides. Furthermore, re-calculation of results from pre-chamber spark ignited engine for few different operating points is made in program code MATLAB. Calculated results match referent results from AVL Boost program.

• Keywords: Ottov motor s pretkomorom; nadogradnja MATLAB modela; obrada izmjerenih podataka; analiza izgaranja
• Keywords (english): Pre-chamber spark-ignited engine; MATLAB model upgrade; relaculation of measured data; combustion analysis
• Language: croatian
• URN:NBN: urn:nbn:hr:235:441818
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2021-12-02 10:37:27