Recent enhancement to SI-ICE combustion models: Application to stratified combustion under large EGR rate and lean burn G. Desoutt utter er, A. Despor ortes es, J. Hira, D. Ab Abou ouri ri, , K.Ober berhum humer er, M. . Zellat* t*
TOPICS PICS Intr troduct oduction ion Challen lengi ging ng for r stratif tified ied combustion mbustion – under large EGR rate – Lean burn Point nt out ut some me weakne eakness sses es Present sent state e of STAR-CD CD mode odels s predict dictions ions and d measures asures to imp mprove e them em. . Ap Application ation and validat ation ion to SI-GDI DI Conc nclusi sion on and d persp spec ecti tives es
Introducti oduction on : Schemat matic c of Premixed d Regimes High EGR Lean Mixture Fla lame me brush ush is is thic icke kened ed Fla lame me structur ructure e chan anges
To what t exten ent t does s turbul ulent nt flame me ret etain n laminar inar flame me structure: cture: The Turbule ulent nt Energy ergy Spectr trum um as a functi tion n of Wavelength length Kolm lmogo ogorov rov scale ale Corrugated & Wrinkled Flamelets - Flame still retains laminar flame structure - Wrinkled or corrugated by turbulent eddies Broken Reaction Zones - Kolmogorov is now smaller than reaction sheet thickness - Flame now lacks local structure (extinguishes) would d require ire very ry fine e mesh h to resolv olve e So sub So sub-gri grid d modelling ling needed ed
EC ECFM-CL CLEH EH MODEL EL : FLA FLAME ME SURFACE CE DEN ENSI SITY (FSD)* FSD)* Ensem emble ble averaged raged flamlet let Abili lity ty of small ll turbulent lent eddies ies to inter erac act t with the flame front ITNFS S functi tion on (Interm rmit ittent tent Turbulent ulent Net Flame e Stretc tch) h) Intermit mittent tent stretc tch h function tion due to strain in and curvatur ature Flame e wall intera racti tion on Consum umption ption to flame me propagat pagation ion Change ge due to gas compr pres ession/ex on/expansi pansion on Change ge due to flame e expansion pansion Initiation ation due to ignit ition ion (spark rk or knoc ock) e Navie vier-Sto toke kes equat * Though gh an exact ct tran anspo sport equat ation ion for or the e FSD can n be derived ved from om the ation ions, s, the e above ve ter erms s are e modelled. delled.
Laminar flame speed Metgha ghalch lchi with ithout ut extension ension Tempe mperature ture = 800 K ; Press ressur ure = 10 bar : Metgha ghalch lchi with ith exten ensio sion Table ble from om detailed ailed chem emistry istry Laminar minar fla lame speed eed decrea creases ses arou ound nd stoic oichiometry hiometry
The he la laminar r fla lame speed eed : EGR R effect ect Experimental perimental data a : lin linear r effect ct of EG EGR Leve vel l on Laminar minar Fla lame e speed eed Laminar minar Fla lame e Speed ed EGR Leve vel Th The data a above e is are stoic oichio hiometr etric ic mixtur ure e : Is this is linearity arity cons nserve rved d for lean or rich h mixtur ture e ??
Laminar flame speed (LFS) : EGR Effect Comparison between Linear correction and detailed chemistry Ratio io factor or using ing lin linear ar cor orrection ection LFS (EGR) R) ver ersus sus LFS(EGR= (EGR=0) 0) Results sults from om detaile ailed d chemistry hemistry ( freely eely prop opaga agating ing fla lame e using ing detailed ailed mechanism chanism ) Mix ixture ure Equiva valence lence Ratio io Around ound Stoic ichiome hiometry ry : Lin inear ear correlat rrelation ion fit it with ith detaile ailed d chem emistry istry BUT NOT belo low w and d above ove
Li Libraries braries Generation eneration us using ing DA DARS RS
Minimum um ener ergy gy for Ignition ition at SPARK RK Spark energy for ignition ‘ mJ mJ ’ Laminar ar flame e speed ed decre reas ase Laminar ar flame e thickne kness incre reas ase Requir ire e more energy gy for Ignition ition Equiva uivalence lence ratio tio Stoic ichiome hiometry ry
Brea eakdo kdown wn Volta tage Breakdo eakdown wn volta ltage ge for diff ifferent rent mix ixture ure o Taken n int into account nt o Equiva ivalen lence ce ratio tio mixt ixture ure o Re Residu idual l gases composi ositio tion and concent ntratio ration
Ignition Spa park rk forma rmati tion on and d burnt t ga gas de depo posit it Initialization v ie ( t ) Breakdown ! Ignition (Inter-electrode voltage) Breakdown phase Spark phase Glow phase Compu mpute e the current urrent in in th the secondar econdary cir ircu cuit it Compu mpute e the in inter-elec electro trode de volta ltage Breakdown The Energy of the a spark is formed Ele lectri rical al Cir ircui uit spark is transferred to V V (l spk ) spk bd the gas (E ign ) Initialize progress If E E Impose burnt gas mass ign crit variable profile at the spark plug Ignition is in c , m ( l ) successful ign ign bg spk Growth of flame kernel in the modified -equation
Applicat licatio ion n I : High h EGR GR ra rate Spark k Ignit ited ed Di Dire rect t Inject ctio ion EG EGR variati tion on by Ex Exhaust aust Valve e phasing ing change nge 40% 40% 20% 20% 10% 0% Si Side injector ctor Ai Air and Wall guided ed Incr creasing easing EGR (tra rapp pped ed Res esidual idual Burn n Gase ses) s) Op Operating ating condition dition : 1300 rpm – Low L w Load
Resi sidual ual Burn n Gases es and Equivalenc ivalence e Ratio io contour ur around d Spark k tim imin ing Residual Burnt Gas (%) – High EGR Residual Burnt Gas (%) – Low EGR Residual Burnt Gas (%) – Medium EGR Equivalence Ratio – High EGR Equivalence Ratio – Low EGR Equivalence Ratio – Medium EGR
Volta tage ge at spark: k: Energy ergy trans ansfer erred red to the gas. Energ ergy trans ransferr rred ed to the he gas as Volt ltag age e at spar ark ~0.070 0.070 Joule ules s avail ilab able le in in the e secon onda dary y cir ircui cuit Spark k tim iming ing Ignition tion succeed eed
In In-cylind ylinder er pressure essure hist stor ory and apparen rent t rate e of heat release lease Dash shed d lin lines :meas asurem rement nt Cont ntinuous inuous lin lines s : pred edict iction ion
BURN N MASS S FRACTION CTION HIS ISTOR ORY Early stage of combustion: 0-10% Duration
SUMMAR MARY Stra rati tifi fied ed combustio ustion n under r high gh EGR level have been investi estigat gated ed Ho Homogeneous eous LEAN BURN combust stion n have been investi estigated ed Lamina nar r Flame speed d is a k key fa factor or for these se extre reme me condi diti tions ns Ad Adva vanc nced ed spark k model : Breakd kdown n voltage e reviewed ed and enhance nced Applica cati tion n and va valida dati tion n to SI-GDI DI (homoge gene neous us ) an and PFI engines nes – Good match for global thermodynamic quantities – Good match for combustion history – Good match for combustion history (0-5% and 10% burn) – NOx prediction match well (not presented here) – Work in progress for emissions (CO and UHC)
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