Modeling of Heat Losses Within Combustion Chamber of Diesel Engines

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1 IUST Iteratoal Joral of Egeerg Scece, Vol 7, No3-4, 006, Page 47-5 Modelg of Heat Losses Wt Combsto Camber of Desel Eges M Nka, M Nagaszadega ad S K Arya Abstract: Te cylder workg fld mea temperatre, rate of eat flxes to combsto camber ad temperatre dstrbto o combsto camber srface wll be calclated ts researc By smlatg termodyamc cycle of ege, temperatre dstrbto of combsto camber wll be calclated by te Crak- Ncolso metod A mplct fte dfferece metod was sed ts code Specal treatmets for psto movemet ad a grd trasformato for descrbg te realstc psto bowl sape were desged ad tlzed Te reslts were compared wt a fte elemet metod ad were verfed to be accrate for smplfed test problems I addto, te metod was appled to realstc problems of eat trasfer a Isz Desel ege, ad gave good agreemet wt avalable expermetal Keywords: Heat loss, Combsto camber, Desel ege, Ege performace Itrodcto It s kow tat eat trasfer effects teral combsto ege performace, effcecy, ad emssos As far as performace s cocered, coolg for te cylder ead, cylder wall, ad psto s desred Ts s becase of problems sc as termal stresses regos of g eat flx, deterorato of te lbrcatg ol flm, ad kock ad pre-gto spark gto eges O te oter ad, a crease of eat trasfer to te combsto camber walls wll lower te gas temperatre ad pressre wt te cylder, wc redces te work per cycle trasferred to te psto Heat trasfer from te workg gas to te coolg system of a covetoal Desel ege accots for p to 30% of te fel eergy Abot 50% of ts eergy s lost trog te psto ad 30% trog te ead [] By smlatg te termodyamc cycle of ege, mea temperatre of cylder workg fld ad eat flxes to combsto camber wll be calclated Followg tat, sg te eat codcto eqatos, by cosderg materal property data ad approprate bodary codtos a temperatre dstrbto s obtaed for calclated eat flxes Te camber wall temperatre Tw s a vtal parameter for determg magtde of eat flx ad ege cycle Paper frst receved Agst, 4, 003 ad revsed: Ag, 30, 006 M Nka s wt te Departmet of Mecacal Egeerg, Islamc Azad Uversty of Takesta, m_ka@otmalcom M Nagaszadega s wt te Departmet of Mecacal Egeerg, Uversty of Gla S K Arya s wt te Departmet of Mecacal Egeerg, Uversty of Uroma smlato I geeral, cylder wall, ead ad psto form te combsto camber of a teral combsto ege, were te temperatre dstrbtos are dfferet for eac srface Typcally, te temperatre of eac srface s assmed to be a costat [] were ts s ot cosstet wt te actal stato occrrg o te srface of te combsto Ege ad Operatg Specfcatos Te ege stded ts work was a Isz Desel ege developed by Isz Ceramcs Researc Isttte (ICRI) It s a ceramc, sgle cylder DI Desel ege Te psto crow, ead, lear, cylder ad valves are made of Slco Ntrde (Kyocera SN35) Ts materal as te followg propertes at room temperatre: 3 desty ρ = 340 kgm ;termal codctvty k=3 Wm - K - ; ad specfc eat cp=680 Jkg - K - Addtoal slato s provded by ar gaps ad slatg rgs betwee te ceramcs ad te metal compoets of te ege Te ege as lmted coolg of te cylder wall ad of te bottom of te metal skrt of te psto Bot of tese regos are cooled by lbrcatg ol Te ege specfcato ad operato codtos are lsted Table Te prmary featre sed te developmet of ts cycle smlato s te frst law of termodyamcs wc s tlzed to derve a expresso for te crak agle (tme) dervatve of te overall gas temperatre terms of ege desg varables, operatg codtos, ad sb-model parameters

2 48 Modelg of Heat Losses Wt Combsto Camber of Desel Eges Table Specfcatos of Isz ceramc Desel ege Bore of cylder 84 mm Stroke 9 mm Sqs 3 mm Compresso rato 6 Coectg rod 93 mm legt Psto crow sallow ds Ege speed 500 rev/m Pressre (kpa) θ =7 BTDC Termodyamc Cycle Smlato Te frst law of termodyamcs for te oe-zoe formlato for ts system s [3]: de dq = dw m m ot ot () were E s te al eergy, Q s te al et eat pt, W s te et work doe by te system, m& s te mass flow rate to or ot of te system, ad s te specfc etalpy eter to or ot of te system Te oly sgfcat eergy of te system s teral eergy (), te oly sgfcat work term s de to te psto moto (system bodary moto) So eqato () becomes: d(m) = Q p V m m ot ot () were m s te mass te cylder, p s te cylder pressre, ad V & s te cylder volme tme rate of cage To obta a dervatve of te pressre, wc s depedet of te gas temperatre, a expresso for te dervatve of te pressre, p& s eeded Ts may be obtaed from te dervatve of deal gas eqato of state: p & = (mrt& mrt & mrt & pv) & / V (3) Combg eqatos (), (3) ad assmg tat te composto ad termodyamc propertes are costat terefore: ad T& = (Q& pv& m& CpT m& otc ptot m) & (4) mc v ( γ ) γ p = Q & pv& m& CpT m& otcptot V γ & (5) Solvg tese dfferetal eqatos ad assmg a costat wall temperatre te cylder workg fld mea temperatre, pressre ad magtde of eat flxes to combsto camber wll be obtaed Fgres () ad () sow te pressre ad gas temperatre of cylder workg fld agast crak agle (tme) Crake agle (Deg) Fg Cylder Pressre Agast Crak Agle for Isz Ege θ =7 BTDC 0 00 Crak agle(deg) Fg Cylder Temperatre Agast Crak Agle for Isz Ege 4 Models ad Nmercal Metods Te approac to determe te combsto camber temperatre dstrbto s dedced from te eergy coservato law For smplcty t s assmed tat te ege geometry s axsymmetrc I two dmesoal cyldrcal coordate te eat codcto eqato s: r T T kr k r r r z = ρc p T t (6) were r ad z are te coordates te radal ad axal drectos, respectvely; T s te wall temperatre; k s te termal codctvty ; c p s te specfc eat ad t s tme As te bodary codto, te temperatres o te oter srface of te cylder wall ler, ead ad psto were treated as costat srface temperatre codtos, wc te temperatre eqals eter te measred coolat temperatre or te ol temperatre te craksaft case Ts s reasoable becase te varato of te temperatre o tese srfaces s mc smaller ta tat o te er srfaces of te combsto camber Te bodary codto o te er gas-sde srface of te combsto camber was a specfed eat flx, wc was obtaed trog te cycle smlato process

M Nka, M Nagaszadega ad S K Arya 49 Te mercal metod sed ere s te Crak-Ncolso metod wc s a mplct ad accrate metod For te costat coeffcet eat codcto eqato, ( T = α(t T ) ) te Crak-Ncolso metod s [4]: t

3 M Nka, M Nagaszadega ad S K Arya 49 Te mercal metod sed ere s te Crak-Ncolso metod wc s a mplct ad accrate metod For te costat coeffcet eat codcto eqato, ( T = α(t T ) ) te Crak-Ncolso metod s [4]: t xx yy t, = α ( x),, ( x), (7), t,, = α ( y),, ( y) (8) Psto movemet s a complcated featre tat caracterzes ege operato wc s mportat te eat codcto problem Assmg tat te coectg rod legt s l, crak rads s rad crak agle s θ, te accordg to Fg 3(a) [5]: s = r( cos θ) l (l r s θ) (9) z p = r cosθ (l r s θ) b (0) cos θ v p = πrns θ () (l r s θ) Were s c s te sqs egt; s s te psto posto; z p s te dstace betwee te crak axs ad te psto top srface; v p s te stataeos psto velocty; N s te rotatoal speed of te craksaft ad b s te dstace betwee te psto top srface ad te psto p axs I ts researc a specal tecqe was developed to solve te movg bodary problem of ege pstos Te grds were formed a cyldrcally symmetrc doma were te left sde represet te ceterle of te ege cylder Nodes represetg bodares or er pots of te cylder wall, ead ad psto were determed Tese odes partcpate te comptato ad are termed compted odes, bt oters otsde te bodares are o-compted odes I Fg 3 (b) te odes te wte regos are te compted odes ad te odes sadowed regos are te o-compted odes Fg 3 Scematc Dagrams Sowg; (a) geometrcal relato-sps of psto movemet (b) grd dstrbto a ege cylder Te compted odes represetg te psto ad te gap betwee te psto ad cylder wall [rego ABCD Fg 3 (b)] are separated from oter compted odes We te ege s rg, te psto posto s s determed sg eq (9) If ss c s moved to z te ext tme step [Fg s p 3(b)], te odes st above te psto top bodary AB are coverted to te odes of a ew top bodary ad te odes o te former bottom bodary CD are caged to o-compted odes Meawle, temperatres at eac ode at te former psto posto are moved to te correspodg ode at te ew psto posto I ts way te pward psto movemet s realzed te fte dfferece aalyss Dowward psto movemet s treated wt a aalogos metod Istead of a flat-topped psto sc as tat typcally sed spark-gto eges, Desel eges sally ave a psto wt bowl I medm-to-small sze drect-ecto Desel eges, se of a bowl--psto combsto camber reslts sbstatal swrl amplfcato at te ed of te compresso process Te effect of ar swrl o te performace ad emssos caracterstc of ts type of ege s very mportat I order to descrbe te cofgrato of a bowl-saped psto te fte dfferece represetato, tablar formato abot te psto otle s sed [e te coordates r ad z Fgre 4 Fg 4 Sloette of Psto Bowl

50 Modelg of Heat Losses Wt Combsto Camber of Desel Eges Te fte dfferece eqatos are most effcetly solved a rectaglar doma Ts, t s coveet to trasform te orectaglar pyscal doma to a rectaglar

4 50 Modelg of Heat Losses Wt Combsto Camber of Desel Eges Te fte dfferece eqatos are most effcetly solved a rectaglar doma Ts, t s coveet to trasform te orectaglar pyscal doma to a rectaglar comptatoal doma From te geometry caracterstcs, te relatosp betwee te pyscal ad te comptatoal doma ca be defed as ξ = ξ( r, z) = r () z η = η( r, z) = z r ( r < r < r ) z r (r r ) z (3) Were ξ = ξ(r, z) ad η = η(r, z) are mappg fctos 5 Reslts ad Dscsso Accordg to te ege specfcatos, a fte dfferece model of ts ege was set p Fgre 5 sows te grds ad bodary codtos of te model for te fe grd opto Te grd mber te r- drecto s 34 for te fe grd opto, wc cldes for grds wt te psto-ler ar gap Te grd sze te r-drecto depeds o te psto sloette ad te dstrbto of ts otle pots (t s 0 mm wt te ar gap, ad 005, 0 or mm wt creasg dept below te cylder wall) Te grd mber te z-drecto, owever, s mc more ta tat te r-drecto ad t s 6 for te fe opto Te grd sze z-drecto s mm wt te cylder wall ad 005, 0, 0 or mm wt creasg dept below te ead srface Te gasket betwee te ead ler ad cylder s made of a metal compressed materal were ts termal resstace was eglected ts model Psto rgs ad te gas betwee tem occpy te gap betwee te psto ad te cylder wall I order to clde te effects of psto rgs o eat codcto, te psto rg propertes for gap grds from te bottom of te psto to te fft mes pot were gve Te temperatres above te ead ler ad otsde te cylder wall were desgated as T 0 = 36K ad T 0 = 36K, e te same as te coolat temperatre; were te temperatres o te bottom srface of te psto ad o te er srface of te cylder wall below te psto were specfed as T ol = 375K ad T ol = 368 K For te fred case te correspodg temperatres are T ol = 368K, respectvely T 0 = 645K, T 0 = 40K, T ol = 675K, Te stataeos temperatre at a pot located o te ead ler srface as bee measred for bot motored ad fred ege operato cases [6] Based o te stataeos srface temperatre, te eat flx at ts pot was calclated sg te traset eat codcto eqato For te motored case, te calclato tme step s s (e 05 crak agle degrees) ad for te 5 fred case, te calclato tme step s 76 0 s Fgres 6 ad 7 compare te compted ad measred temperatre at te motorg pot for te motored ad fred cases Note tat, ts case te fte dfferece code was r for 500 ege cycles (startg from te form wall temperatre tal codto of T = 355K ) tl a psedo-steady state was reaced (e for te warmed p ege) Te compted temperatre te measremet posto s good agreemet wt te measred temperatre for bot te motored ad fred cases Tese reslts strogly verfy tat te preset code developed ts stdy s stable for modelg te temperatre dstrbto of te combsto camber srfaces eges Fg 5 Nmercal Mes of Isz Ceramc Desel Ege at 90 o ATDC Measred Compted Crak agle (deg) Fg 6 Srface Temperatre Ccomparso o te Cylder Head for Motored Case Measred Compted Crak agle (deg) Fg 7 Srface Temperatre Comparso o te Cylder Head for Fred Ege case

5 M Nka, M Nagaszadega ad S K Arya 5 Te compted tme-averaged temperatre dstrbtos o eac srface of te combsto camber are sow Fg 8 to 0 Te temperatre dstrbtos for te cylder ead was sow Fg 8 wc s 50-0 K lower ta te orgal (assmed) costat temperatre, ad ave ter maxmm vale at te edge of te bowl Te maxmm tme-averaged temperatre dfferece at pots o te srface s abot 70 K Fal Reslt Orgal Ipt r (mm) Fg 8 Predcted Tme-Averaged Temperatre Dstrbtos o te Cylder Head Ssrface Temperatre dstrbtos for te psto was gve Fg 9 wc s also lower ta te orgal gess, wc formed a g temperatre rego o te bowl-sde srface ad a low temperatre rego o te bowl-valley srface Fal Reslt Orgal Ipt of volmetrc effcecy as te wall temperatre creases [7] Vol Effc Fal Reslt Orgal Ipt z (mm) Fg 0 Predcted tme-averaged Temperatre Dstrbtos o te Cylder Ler Wall Mea Wall TEmperatre Fg Dfferece of Volmetrc Effcecy Verss Max Temp (K) Fg Dfferece of maxmm temperatre verss mea wall temperatre S (mm) Fg 9 Predcted Tme-Averaged Temperatre Dstrbtos o te Psto Srface Fgre 0 sows tat te temperatre dstrbtos o te cylder wall srface s te same as te ol temperatre adacet to te wall for te maorty of locatos o te srface, bt tere s a 30 K cremet temperatre te rego ear te cylder ead Ts proves tat combsto ad eat trasfer wt te cylder do ot ave mc flece o te temperatre dstrbto of te wall srface, except for a arrow rego te rg reversal rego ear te cylder ead A detaled presetato of te effect of combsto camber mea wall temperatre o ege performace, as calclated from te termodyamc cycle smlato model, s gve fgres to 5 As expected, a cosderable crease te maxmm gas temperatre s observed, accompaed by a correspodg decrease Max Press (bar) Fg 3 Dfferece of Maxmm Pressre Verss Mea flx (kw/m ) Fg 4 Dfferece of Average eat Flx Verss Mea Wall Temperatre

6 5 Modelg of Heat Losses Wt Combsto Camber of Desel Eges Max flx (kw/m ) Ts code was sed to calclate eat codcto processes occrrg te combsto cambers of a Isz ceramc ege Te preset code provdes a accrate ad cosstet metod for obtag te temperatre dstrbtos wt ege compoets ad tese reslts wold also be sefl for strctral aalyss Fg 5 Dfferece of Maxmm Heat Flx Verss Mea Wwall temperatre Refereces [] Borma, GL ad Nswak K, "Iteral combsto ege eat trasfer" Progress Eergy Combsto Scece, 987, 3, -46 Te average amot of eat flx to te wall preset a sgfcat decrease as te wall temperatre creases, wereas te correspodg peak eat flx creases Ts s maly de to te fact tat te creased cylder srface temperatre cases a respectve crease te peak vale of covectve eat trasfer coeffcet, ad so te expected ga from te redcto of eat losses (de to te elevated wall srface temperatres) almost vases or s eve reversed over a certa part of te ege cycle 6 Coclso Te cylder workg fld mea temperatre, rate of eat flxes to combsto camber ad temperatre dstrbto o combsto camber srface were sccessflly developed ts stdy Te mercal metod sed s Crak-Ncolso fte dfferece metod Ts metod s caracterzed by ts mplct atre, codtoal mercal stablty ad good accracy Specal treatmets for te ead gasket ad te pstoler ar gap, ad a grd trasformato for descrbg te realstc psto bowl sape were desged ad tlzed te preset stdy Te accomplsmet of modelg psto movemet wt te preset fte dfferece formlato makes ts code a compter program wt te capablty of realstc ege smlato [] Amsde, AA, O'Rorke, PJ, ad Btler, TD, KIVA-II: "A Compter Program for Cemcally Reactve Flows wt Sprays" Los Alamos Natoal Labs, LA-560-MS, 989 [3] Fergso, Col R, "Iteral Combsto Eges- Appled Termosceces", Jo Wley & Sos, New York, 986 [4] Hoffma, Klas A, Cag, Steve T, "Comptatoal fld dyamcs for egeers", McGraw-Hll, New York, 995 [5] Heywood, JB, "Iteral Combsto Ege Fdametals" McGraw-Hll, New York, 989 [6] Smesc, S, "Heat flx measremets of te combsto camber ead srface of a slco trde DI Desel ege" PD tess, Uversty of Wscos-Madso, 997 [7] Rakopolos, CD, Adrtsaks, EC, ad Hotalas, D T, Te flece of te exast system steady gas flow ad slato o te performace of a mltcylder trbocarged desel ege, Heal Recovery Systems & CHP5, 5-7, 995

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