Recent enhancement to SI-ICE combustion models: Application to - - PowerPoint PPT Presentation

• G. Desoutt

utter er, A. Despor

• rtes

es, J. Hira, D. Ab Abou

• uri

ri, , K.Ober berhum humer er, M. . Zellat* t*

Recent enhancement to SI-ICE combustion models: Application to stratified combustion under large EGR rate and lean burn

Intr troduct

• duction

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

• dels

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

• n and

d persp spec ecti tives es

TOPICS PICS

Introducti

• duction
• n : Schemat

matic c of Premixed d Regimes

Fla lame me brush ush is is thic icke kened ed Fla lame me structur ructure e chan anges

• High EGR
• Lean Mixture

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

 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

• lve

e So So sub sub-gri grid d modelling ling needed ed

Kolm lmogo

• gorov

rov scale ale

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

• n (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

• n

Consum umption ption to flame me propagat pagation ion Change ge due to gas compr pres ession/ex

• n/expansi

pansion

• n

Change ge due to flame e expansion pansion  Initiation ation due to ignit ition ion (spark rk or knoc

• ck)

* Though gh an exact ct tran anspo sport equat ation ion for

• r the

e FSD can n be derived ved from

• m the

e Navie

vier-Sto toke kes equat

ation ions, s, the e above ve ter erms s are e modelled. delled.

• Tempe

mperature ture = 800 K ; Press ressur ure = 10 bar :

Laminar flame speed

Metgha ghalch lchi with ithout ut extension ension Metgha ghalch lchi with ith exten ensio sion Table ble from

• m detailed

ailed chem emistry istry Laminar minar fla lame speed eed decrea creases ses arou

• und

nd stoic

• ichiometry

hiometry

The he la laminar r fla lame speed eed : EGR R effect ect

Th The data a above e is are stoic

• ichio

hiometr etric ic mixtur ure e : Is this is linearity arity cons nserve rved d for lean or rich h mixtur ture e ??

Laminar minar Fla lame e Speed ed EGR Leve vel Experimental perimental data a : lin linear r effect ct of EG EGR Leve vel l on Laminar minar Fla lame e speed eed

Laminar flame speed (LFS) : EGR Effect Comparison between Linear correction and detailed chemistry

Ratio io factor

• r using

ing lin linear ar cor

• rrection

ection LFS (EGR) R) ver ersus sus LFS(EGR= (EGR=0) 0) Mix ixture ure Equiva valence lence Ratio io Results sults from

• m detaile

ailed d chemistry hemistry ( freely eely prop

• paga

agating ing fla lame e using ing detailed ailed mechanism chanism ) Around

• und 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

• ve

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’ Equiva uivalence lence ratio tio

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

Stoic ichiome hiometry ry

Brea eakdo kdown wn Volta tage

Breakdo eakdown wn volta ltage ge for diff ifferent rent mix ixture ure

• Taken

n int into account nt

• Equiva

ivalen lence ce ratio tio mixt ixture ure

• Re

Residu idual l gases composi

• sitio

tion and concent ntratio ration

Spa park rk forma rmati tion

• n and

d burnt t ga gas de depo posit it

Breakdown

spk bd

V V 

a spark is formed (lspk) The Energy of the spark is transferred to the gas (Eign)

ign crit

If E E 

Ignition is successful Impose burnt gas mass at the spark plug

( )

in bg spk

m l

Initialize progress variable profile

,

ign ign

c 

Growth of flame kernel in the

modified -equation

Ignition Initialization

) (t vie

Breakdown phase Spark phase Glow phase

! Breakdown

(Inter-electrode voltage) Ignition Ele lectri rical al Cir ircui uit

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

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

• n by Ex

Exhaust aust Valve e phasing ing change nge

Si Side injector ctor Ai Air and Wall guided ed Op Operating ating condition dition : 1300 rpm – Low L w Load

Incr creasing easing EGR (tra rapp pped ed Res esidual idual Burn n Gase ses) s)

40% 40% 20% 20% 10% 0%

Resi sidual ual Burn n Gases es and Equivalenc ivalence e Ratio io contour ur around d Spark k tim imin ing

Equivalence Ratio – Low EGR Equivalence Ratio – Medium EGR Equivalence Ratio – High EGR Residual Burnt Gas (%) – Medium EGR Residual Burnt Gas (%) – Low EGR Residual Burnt Gas (%) – High EGR

Volta tage ge at spark: k: Energy ergy trans ansfer erred red to the gas.

~0.070 0.070 Joule ules s avail ilab able le in in the e secon

• nda

dary y cir ircui cuit

Spark k tim iming ing Ignition tion succeed eed

Volt ltag age e at spar ark Energ ergy trans ransferr rred ed to the he gas as

In In-cylind ylinder er pressure essure hist stor

• ry 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

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

• r 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)

SUMMAR MARY