Primerjalna analiza rekacijskih mehanizmov za modeliranje distribuiranih konceptov zgorevanja

Zuljan, Vid (author), Seljak, Tine (mentor)

V magistrski nalogi je z modelskega vidika obravnavan brezplamenski koncept zgorevanja, ki je svoje ime dobil po odsotnosti vidnega plamena. Zanj so se uveljavila različna poimenovanja (FLOX, MILD, CDC in HiTAC), ki pa sicer opisujejo fundamentalno enak proces z manjšimi razlikami glede na termodinamske pogoje doseganja. V analizi trenutnega stanja smo identificirali glavne izzive, ki so prisotni pri modeliranju brezplamenskega zgorevanja. Zaradi intenzivne prepletenosti časovnih in kemijskih skal posamezne predpostavke zgorevalnih modelov in kemijskih reakcijskih mehanizmov za uporabo pri konvencionalnem zgorevanju niso primerne za modeliranje brezplamenskega zgorevanja. V nalogi smo analizirali ustreznost različnih modelov zgorevanja ter različnih mehanizmov kemijske kinetike, ter odstopanja, ki se pojavijo pri uporabi privzetih parametrov, ki temeljijo na konvencionalnem zgorevanju. V nalogi je izvedenih več simulacij z EDC modelom ter dvema reakcijskima mehanizma, in sicer dvo-koračnim globalnim in uveljavljenim detajlnim mehanizmom GRI Mech 3.0 ter z in brez uporabe sevalnega prenosa toplote. Simulacije potekajo v zgorevalni komori z osnovnimi funkcionalnostmi, prehod v brezplamensko zgorevanje pa je modeliran postopno, z zmanjševanjem vsebnosti kisika od 23 % do 6 % masnega deleža v zraku. Rezultati so pokazali, da je EDC model z uporabo detajlnega mehanizma sposoben predvideti brezplamensko zgorevanje, in sicer se prehod zgodi pri 9 % O2. Obratno globalni mehanizem ni sposoben popisati brezplamenskih pogojev. Obenem ima sevalni model največji vpliv pri 9 % koncentraciji O2.

• Language: Slovenian
• Keywords: brezplamensko zgorevanje, modeliranje, zgorevalni model, kemijski mehanizem, redčenje, sevanje
• Work type: Master's thesis/paper
• Organization: FS - Faculty of Mechanical Engineering
• Year: 2023
• PID: 20.500.12556/RUL-147056
• Publication date in RUL: 22.06.2023

Secondary language

• Language: English
• Title: Comparative analysis of reaction mechanisms for modeling of distributed combustion concepts

Abstract

In this master thesis, flameless combustion is assessed from a modelling standpoint. Flameless combustion received its name from the absence of a visible flame. Through the years, several different acronyms have been introduced, such as FLOX, MILD, CDC and HiTAC, which all cover the same process with slightly different definitions regarding the thermodynamic conditions. In the analysis of the current state of the art, we identified the main challenges arising in modelling of flameless combustion. Because of the intensive interaction between the chemical and mixing time scales, some of the assumptions in currently used combustion models and chemical kinetic mechanisms for conventional combustion are not appropriate for flameless combustion modelling. In this study, we analyzed different combustion models and chemical kinetic mechanisms currently in use for conventional combustion modelling. Several simulations were run with the EDC combustion model and two chemical kinetic mechanisms, namely a two-step global mechanism and a widely known detailed mechanism GRI Mech 3.0, with and without the use of a radiation model. Simulations were performed in a basic combustion chamber geometry, where a transition to flameless combustion was modelled step by step, by lowering oxygen mass fraction in air from 23 % to 6 %. From all of the models, the EDC with the use of the detailed mechanism, showed the best capabilities of reproducing flameless conditions. On the other hand, global mechanism was not able to reproduce flameless conditions. Meanwhile, the use of the radiation model had the biggest effect on the results at 9 % O2 mass fraction.

• Keywords: flameless combustion, modelling, combustion model, chemical mechanism, dilution, radiation