ADVANCES IN COMBUSTION MODELING IN STAR-CD: VALIDATION OF ECFM CLE-H MODEL TO ENGINE ANALYSIS

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1 18 th Intenatonal Multdmensonal Engne Use s Meetng at the SAE ongess 2008,Apl,13,2008 Detot, MI ADVANES IN OMBUSTION MODELING IN STAR-D: VALIDATION O EM LE-H MODEL TO ENGINE ANALSIS D. Abou, M. ellat, S. Duant D-adapco. Ravet Renault, ABSTRAT New engne combuston egmes, lke HI ae n contnuous development and consdeed as potental methods to each the futue emsson and pefomance tagets. Unfotunately, HI combuston can t be used fo all engne opeaton condtons. Theefoe, a mx between conventonal Desel combuston and HI s a vey pomsng soluton. At pesent, the combuston mode of such engnes s not well undestood and D ae now an essental tool n the concepton loop of advanced engnes. EM LE-H s a new appoach developed by ORIA [1][2] to smulate the dffeent phases of Desel combuston; auto-gnton, pemxed and dffuson flame bunng. The ognal poposal was based on two modelng fo the two flame stuctues: pemxed and dffuson flame. atcula emphass was put on mpovng modelng fo the dffuson combuston. The combuston model splt the flame font n thee zones: non-eactve zone, pemxed zone and unpemxed zone. o each zone, a specfc combuston model s attached based on flame stuctue analyss. LE-H stands fo ombuston Lmted by Equlbum Enthalpy; model uses an equlbum fuel mass facton to compute the aveage heat elease ate. Ths equlbum fuel mass facton has been calculated a po fom complex chemsty calculatons fo fuel to lmt bunng ates. A pesumed Beta-shape D s adopted to aveage the equlbum at equlbum. Auto-gnton s modeled fom tabulated fully detaled chemsty. The tabulaton stategy TKI poposed by I [3] s used. Ths model was mplemented n STAR-D and has been the object of a wde ange of academc valdatons on test cases to check that fundamental dynamcs ae well captued. To evaluate the model, esults wee compaed wth extensve data fom DI Engnes n poducton at full and pat load. The esults show that the models gve ealstc Heat Release Hstoy, Indcated owe, as well as NOx emssons. INTRODUTION the njecton tmng. Thus, fo example, n HI combuston, most of fuel s consumed dung the autognton phase. EM LE-H model s based on EM fomula developed by EM2 [5] and EM-3 model developed by I [4] and cuently used at Renault n STAR-D. These modfcatons wee motvated by the mplementaton of a dffuson flame descpton. In the case of classcal combuston, close to TD, most of the enegy flux comes fom the dffuson flame. Ths appoach was developed by ORIA. The mplementaton was done by D-adapco. n STAR-D. A detaled valdaton was caed out on the base of a wde ange of test esults. EM LE-H MODEL DESRITION LAME RONT DESRITION The appoach EM LE-H poposes to substtute the ognal model fo bunt gas developed n EM-3 by two sub-models elaboated on both the descpton of the pemxed flame (EM fomulaton and the dffuson flame (LE-H fomulaton. EM: Extended oheent lame Model LE-H: ombuston lmted by themodynamc equlbum Thus, the flame font n each cell s splt nto thee zones (gue 1: assve mxng zone emxed flame zone Dffuson flame zone A thee-step pocess govens the combuston fom dect njecton, gasolne and desel: gnton, pemxed flame and dffuson flame. The weght of the fuel consumpton by one o anothe flame stuctue depends stongly on

2 ORMALISM OR THE UNMIXED ONE The unmxed zone descbes the mxng pogess befoe the auto-gnton. It s pesented by the followng set of equatons: gue 1: lame font modellng stuctue The couple (, govens each zone. A tanspot equaton s used to detemne the value of the couple. The fomalsm efes to ave mean value fo the mxng vaable and efes to the mean value fo the assocated eactve scala. KINETI SHEME Knetc scheme may be pesented as the followng genec fom: ( + s sβd + s( Ox + β D 1 + (1 Wth: efeed to the fuel, Ox, to the oxdze, D to the dlute and to the poduct. s efes to the mass stoechometc value and β to the ato between the y M O2 dlute and the oxdze n pue a: s x 4 + M x H y Thus, the mass facton fo speces s defned as followng: spece mass mxng mass By selected the couple of vaables (, deduce the followng elatons: Ox D 1 ( 1 EGR s( 1+ β ( 1+ s( β ( 1 1+ β EGR, we can The mxng composton s dawn fom the couple (,. onsequently, each zone of the flame font may be descbed wth two equatons showng the evoluton of these two vaables educed to these zones. (2 ρ gad ( ρ +Η( cˆ c S T S s the souce tem fom the doplet vapozaton. Η ( Heavesde functon, c pogess vaable fo the pemxed flame and ĉ, a model constant. ( R et T ρ tem of tansfe to the ( R et pemxed zone and, a chaactestc fequency of the tubulent spectum detemned by the tubulent Reynolds numbe. ORMALISM OR THE REMIXED ONE The pemxed zone s descbed by the followng set of equatons: ρ ρ gad gad ( ρ ( ρ + T T ω ( R + T T et T ρη( c cˆ c tem of tansfe to the dffuson zone ( R et T ρη( c cˆ c tem of tansfe to the dffuson zone ω s the eactve tem gven ethe by the autognton model [3], o by the spak gnton model [4], o by the popagated flame font model: ω ρs Σ [5], S l s the lamna l ( flame speed, Σ s the flame suface densty and eq s the equlbum fuel mass facton fo the eq (3 (4

3 pemxed flame. Thus, the pemxed flame pogess vaable s gven by the followng expesson: c + (5 eq ORMALISM OR THE DIUSION ONE The dffuson zone s gven by the followng set of equatons: ρ ρ DI DI gad gad DI ( ρ + T +Η( c ˆ DI DI ( ρ + T +Η( c cˆ S ω DI DI ( Re t ( c S ω ρ α s the DI DI eq DI eactve tem fo the dffuson flame and DI DI α s the pogess vaable fo the DI eq dffuson flame [1,2]. DI (6 The equlbum functons wee deduced fom the ntegaton of the df on mxng scala. 1 eq 0 Wth: eq (, θ (, T d dθ ( θ δ ( ( θ (9, fo the pemxed flame, whee δ s the Dac functon and s a beta functon ( δ ( θ θ ( fo the DI dffuson flame. gue 3 gves an example of eq functons n the phase space. MIXING OMOSITION The mxng composton s gven by the followng elatons: DI DI EQUILIBRI UNTION OMUTATION The equlbum functon eq and eq (7 DI ae defned as the fuel lmted value such as the fnal tempeatue fom the combuston defned by the one step elaton, may be equal to the equlbum tempeatue computed fom a detaled knetc scheme fo fuel oxdaton. Equlbum functons ae computed fom the followng elatons: Teq T ( Teq T eq eq dt Oxeq Ox Deq D eq dt (8 gue 2: Equlbum functon S s the segegaton vaable defned as: 2 ' S ( 1 The heat elease coesponds to the mass of fuel consumed between the mxng lne and the equlbum functon, multpled by the of the fuel. MIXING TEMERATURE OMUTATION The mxng tempeatue s computed wth the followng elaton: T T ef β β ( 1 EGR 1 T dt + dt T Ox 1 + β ef (10 T T ( 1 [ ] EGR dt H Tef Tef The mxng enthalpy H follows the classcal tanspot equaton: The ght membe s computed fom a detaled knetc mechansm, T coesponds to the mxng tempeatue.

4 ρh gad ( ρh H D + S + x ρ x ρ ρ p (11 wth S and ae the enthalpy souce tems fo the fuel vapozaton and wall losses espectvely DI ENGINE: MODEL VERIATION MDEL VALIDATION ull load valdaton was done n dffeent engne confguatons, not communcable. ombuston evoluton though A vaables and IME value wee compaed wth the measuements. We have used two dffeent engnes qute dffeent n tem of bowl desgn, ntal swl as well as njecto nozzle damete. The combuston n DI engne and especally unde full load condtons exhbts the thee mode of combuston: Auto-gnton, popagaton and dffuson. Theefoe, the emssons hstoy wll stongly depend on the combuston mode dependng on the dffeent pogess of the combuston. THE ENGINE ONIGURATION The computed confguaton s a typcal 2 ltes DI Engne-4 cylndes, unde poducton. The symmety of the geomety, the elatve poston f the njecto nto the combuston chambe and the natue of the swlng flow at Intake Valve losng make the choce of a secto mesh good enough fo ths evaluaton. The geomety and the mesh ae shown n fgue 5. gue 4: edcted and measued essue hstoy fo ENGINE A (Nomalzed quanttes gue 3: Typcal mesh used fo combuston gue 5: edcted and measued Appaent Heat Release hstoy fo ENGINE A (Nomalzed quanttes

5 gue 6: edcted and measued Appaent Heat Release hstoy fo ENGINE B (Nomalzed quanttes gue 7: edcted and measued essue hstoy fo ENGINE B (Nomalzed quanttes The computed and measued n-cylnde pessues and coespondng ate of heat elease ae epesented on fgues 4,5,6 and 7 fo two engnes opeatng at full load The oveall ageement s athe good ncludng the combuston hstoy ndcatng that the model s vey well captung the pemx phase and the dffuson phase. ART LOAD AND OTHER OERATIG ONDITION A sees of anothe dffeent opeatng condtons ncludng EGR vaaton fom 0% to 50% was executed fo a patal load valdaton. As a esult, the IME measuements have been compaed to the calculated ones. Ths s shown n fgue 8 n whch almost all pedcted values ae wthn the ange of 2% of eo. e d c t e d s u ull load at load Measuements Accuacy 2 % gue 8: IME: Measued and edcted values NO EMISSIONS: The majo development n EM-LEH s elated to efned descpton of the smultaneous pemxed and dffuson combuston. Two dffeent pogess vaables ae deved fo each mode of combuston. These vaables ae c fo the pemxed combuston and alpha fo the dffuson. Theefoe, all speces and especally the emssons wll contan two dffeent souces tems. omally, the equaton below s an example fo NO fomaton. & ω c & ω + cα & ω NO NO NO DI edcted gue 8: IME: (ppm Measued and edcted values Accuacy 20% Measued gue 9:NOx : Measued and edcted values

6 NOx esults fom calculaton fo the two engnes and fo all opeatng condton nvestgated n the wok ae summazed n fgue 9. The values epoted n fgue 9 ae ppm and the pedcted values ae dectly compaed to the measued ones. One can seed n fgue 9 the excellent tends obtaned, the maxmum eo s about 20% ONLUSION New appoach fo combuston n dffuson flames n ca engnes was valdated on Desel applcatons. Ths new appoach was based on a calculaton of the pogess vaable ncludng equlbum nfomaton. The dstbuton n the dffuson flame was smulated by df, functon beta appoach. nally, ths appoach was coupled to pemxed flame smulaton base on EM model. ompasons on IME level and the dffeent combuston chaactestc angles show a good ageement wth expemental data. A sgnfcant beakthough was eached n tem of u savng. The usng of look-up tables fo all chemsty descpton, ncludng pollutants, mpoved the numecal stablty sgnfcantly and made the ncease of the tme step possble. utue woks wll be devoted to couple all pollutants fomaton ate wth ths new appoach and test t on gasolne dect njecton confguatons. REERENES 1. G. Subamanan, L. Vevsch,. Ravet, New Developments n Tubulent ombuston Modelng fo Engne Desgn: EM-LEH ombuston Submodel ance, SAE pape , Ravet,. and Vevsch, L., modelng non-pemxed tubulent combuston n aeonautcal engnes usng D-geneato, AIAA pape , 36th AIAA Aeospace Scences Meetng and Exhbt, Reno NV, Januay 12-15, oln, O., es Da uz, A. and Jay S., detaled chemsty based on auto-gnton model ncludng low tempeatue phenomena appled to 3D engne calculatons, 30th ntenatonal symposum on combuston, ttsbugh, The ombuston Insttute, Duclos, J.M. and oln, O Ac and Kenel Tackng Ignton Model fo 3D Spak-Ignton engne calculatons, The fth Intenatonal Symposum on Dagnostcs and Modelng of ombuston n Intenal ombuston Engnes (OMODIA 2001, 1-4 July Duclos, J.M, Veynante, D. And onsot T. (1993. A compason of flaet models fo pemxed tubulent combuston. ombuston and flame, 95, pages