Numerical modelling of multiphase flow in combustion of liquid fuel

doctoral thesis

• Title (croatian): Numeričko modeliranje višefaznog strujanja pri izgaranju tekućeg goriva
• Author: Milan Vujanović
• Mentor: Neven Duić (mentor)
• Committee member: Željko Bogdan (predsjednik povjerenstva)
• Committee member: Neven Duić (član povjerenstva)
• Committee member: Zdravko Virag (član povjerenstva)
• Committee member: Daniel Rolph Schneider (član povjerenstva)
• Committee member: Reinhard Tatschl (član povjerenstva); strani drzavljanin: Nije dostupno
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2010-05-20, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; Process Energy Engineering
• Universal decimal classification (UDC): 51 - Mathematics

Abstract

The focus of this work is on an integrated simulation approach, which can be applied in numerical simulations of turbulent multiphase droplet flow in practical combustion systems, adopting methods for simulation of dense and dispersed spray in conjunction with combustion and nitrogen emission formation. The first objective was to establish the validated Eulerian multiphase spray modelling approach, which can be applied with confidence in high pressure diesel spray simulations, particularly in dense spray regions. The Eulerian multiphase spray modelling concept, using an approach with fixed droplet size classes, was applied in liquid spray simulations. Several simulations of high pressure diesel injections, combined with different chamber pressures, were carried out and compared with the experimental data. The suitable validated Eulerian multiphase spray method was then coupled with the classic the Lagrangian Discrete Droplet Model (DDM), in conjunction with the classic combustion model and the validated nitrogen oxides (NOx) chemical reaction mechanisms. The NOx reaction mechanisms were investigated and implemented into the CFD code FIRE. The nitrogen scheme was limited to sufficiently few homogeneous reactions to allow effective coupling with the turbulent mixing process. The effects of the turbulent fluctuations on the reaction rates when predicting NOx concentrations were modelled by using the presumed Probability Density Function (PDF) approach. The model was applied to the turbulent non-premixed jet diffusion flame (Sandia flame D) and the nitrogen predictions were compared to the results obtained by the Steady Laminar Flamelet Model (SLFM) and to the experimental data. Furthermore, to demonstrate the capability of the coupling concept, an integrated simulation approach was applied for calculation of the real internal combustion engine, which is particularly challenging for such modelling. Two different CFD simulations, the Eulerian multiphase spray simulation and the single-phase engine simulation (DDM spray in conjunction with the combustion and nitrogen emission models), were coupled and performed simultaneously to take advantage of the capabilities inherent in both simulations.

Abstract (croatian)

U ovome radu prikazane su integrirane simulacijske metode koje objedinjuju opis ponašanja gustog i razrijeđenog spreja tekućeg goriva u sprezi s izgaranjem i stvaranjem emisija dušičnih polutanata, te se kao takve mogu koristiti za numeričke simulacije turbulentnih višefaznih strujanja u sustavima izgaranja u praksi. Primarni cilj rada je bio uspostaviti validiran Eulerov pristup za modeliranje višefaznog strujanja tekućeg goriva koji se može pouzdano primijeniti u simulacijama visokotlačnog ubrizgavanja i raspršivanja tekućeg goriva, posebice u područjima gustog spreja. Eulerov višefazni model spreja s unaprijed određenim klasama veličina kapljica primijenjen je za simulacije spreja goriva. Provedene su numeričke simulacije visokotlačnog ubrizgavanja dizela za različite tlakove ubrizgavanja u kombinaciji s različitim tlakovima komore. Rezultati simulacija su uspoređeni su s eksperimentalnim podacima. Odgovarajuća validirana Eulerova metoda višefaznog spreja povezana je i s klasičnim Lagrange modelom diskretnih kapljica (MDK), te spregnuta s klasičnim modelom izgaranja i validiranim reakcijskim mehanizmima stvaranja dušičnih oksida (NOx). Kemijski kinetički mehanizmi nastajanja NOx-a istraživani su i implementirani u FIRE kod. Pritom su korišteni reducirani kemijski mehanizmi nastajanja dušičnih polutanata da bi se omogućilo efikasno povezivanje s procesima turbulentnog miješanja u numeričkim simulacijama. Utjecaj turbulentnih fluktuacija kod nastajanja NOx modeliran je primjenom funkcije gustoće vjerojatnosti. Razvijeni model je primijenjen u proračunu izgaranja na pilotiranom metanovom slobodnom plamenu (Sandia plamen D). Rezultati simulacije uspoređeni su s rezultatima mjerenja te s rezultatima simulacije koja koristi standardni laminarni flamelet model. Nadalje, da bi se demonstrirale mogućnosti istovremenog izvođenja povezanih simulacija, primijenjen je integrirani simulacijski pristup u proračunima stvarne konfiguracije motora s unutrašnjim izgaranjem. Dvije različite simulacije, višefazna Eulerova simulacija spreja i jednofazna simulacija motora (Lagrangeovo računanje spreja u sprezi s procesom izgaranja i procesom stvaranja dušičnih polutanata), povezane su i računate istovremeno. Primjenom ovakvog integriranog pristupa omogućeno je da se ove dvije simulacije međusobno nadopunjavaju, odnosno da se iskoriste prednosti inherentne svakoj od simulacija.

• Keywords: computational fluid dynamics; multiphase flow; nitrogen oxides; Eulerian multiphase model; discrete droplet model; diesel spray
• Keywords (croatian): računalna dinamika fluida; višefazno strujanje; dušični oksidi; Eulerov višefazni model; model diskretnih kapljica; dizel sprej
• Language: english
• URN:NBN: urn:nbn:hr:235:036060
• Study programme: Title: Mechanical Engineering and Naval Architecture; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje tehničkih znanosti (doktor/doktorica znanosti, područje tehničkih znanosti)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Access restricted to students and staff of home institution
• Created on: 2020-06-30 12:18:37