Validation of some engine combustion and emission parameters of a bioethanol fuelled DI diesel engine using theoretical modelling

ORIGINAL ARTICLE Valida ion o some engine combus ion and emission pa ame e s o a bioe hanol uelled DI diesel engine using heo e ical modelling Mu ugan Si alingam a,b,* , Sub anshu Sekha Mahapa a b , Dula i Hansdah b , Bohumil Ho a ´k a a Depa men o Cybe ne ics and Biomedical Enginee ing, VSB Technical Uni e si y, Os a a, Czech Republic b Depa men o Mechanical Enginee ing, Na ional Ins i u e o Technology, Rou kela, India Recei ed 10 June 2015; e ised 19 Augus 2015; accep ed 1 Sep embe 2015 A ailable online 19 Oc obe 2015 KEYWORDS Comp ession igni ion (CI) engine; Madhuca Indica flowe ; Bioe hanol; Ma hema ical modelling; MATLAB Abs ac Ea lie epo s indica e ha e hanol/bioe hanol can eplace con en ional diesel uel by 15%, when i is emulsified wi h diesel and used as an al e na i e uel in a comp ession igni ion (CI) engine. In his s udy, ini ially BMDE15, a bioe hanol emulsion con aining 15% bioe hanol, 84% diesel and 1% su ac an was cha ac e ised o i s uel p ope ies and compa ed wi h hose o diesel uel p ope ies. The nume ical alue indica es he pe cen age o bioe hanol in he BMDE15 emulsion. Fo he in es iga ion, bioe hanol was ob ained om he Mahua Indica flowe which was collec ed om he Madhuca Indica ee, and i was p oduced om e men a ion p ocess using Sac- cha omyces ce e isiae. Fu he , he BMDE15 emulsion was es ed in a single cylinde , ou s oke, ai cooled, DI diesel engine de eloping a powe o 4.4 kW a a a ed speed o 1500 pm. Two impo - an combus ion pa ame e s: cylinde p essu e and igni ion delay, and wo impo an emission pa ame e s: ni ic oxide (NO) and smoke emissions we e de e mined and compa ed wi h hose o diesel ope a ion a all loads. The expe imen al esul s we e alida ed using ma hema ical modelling, and he analysis o he esul s is p esen ed in his pape . Ó2015 Facul y o Enginee ing, Alexand ia Uni e si y. P oduc ion and hos ing by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). 1. In oduc ion E hanol is conside ed o be a po en ial al e na i e uel o anspo applica ions. I can be de i ed om a a ie y o sou ces. Al hough e hanol has been used in he o m o a blend wi h gasoline, in spa k igni ion (SI) engines in he las h ee dec- ades, he use o e hanol in comp ession igni ion (CI) engines is o mo e in e es because o he wide accep ance o CI engines in many applica ions [1]. E hanol de i ed om biomass ma e ials known as bioe hanol is paid mo e a en ion because i can be de i ed om a a ie y o biomass ma e ials which a e enewable and abundan ly a ailable [2,3]. Nume ous esea ch wo ks ha e been documen ed o use in he o m o blending/emulsion, umiga ion, dual injec ion, su ace igni ion, *Co esponding au ho a : Depa men o Cybe ne ics and Biomed- ical Enginee ing, VSB Technical Uni e si y, Os a a, Czech Republic. Tel.: +420 702959180/+91 661 2462525 E-mail add ess: [email p o ec ed] (M. Si alingam). Pee e iew unde esponsibili y o Facul y o Enginee ing, Alexand ia Uni e si y. Alexand ia Enginee ing Jou nal (2015) 54, 993–1002 HOSTED BY Alexand ia Uni e si y Alexand ia Enginee ing Jou nal www.else ie .com/loca e/aej www.sciencedi ec .com h p://dx.doi.o g/10.1016/j.aej.2015.09.003 1110-0168 Ó2015 Facul y o Enginee ing, Alexand ia Uni e si y. P oduc ion and hos ing by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). e c. in CI engines [4]. In ecen yea s he s udy and con ol o emissions om in e nal combus ion (IC) engines ha e been highly concen a ed. Theo e ical analysis accomplished by ma hema ical mod- elling o nume ical solu ions using compu e p og am o com- pu a ional fluid dynamics (CFD) can gi e mo e ui ul p edic ions on he engine pa ame e s [5]. The simula ion model by MATLAB p og am o nume ical solu ion was used o analyse he engine pa ame e s o a single cylinde 3.5 kW a ed powe diesel engine uelled wi h diesel, Palm Oil Me hyl Es e and POME-diesel blends [6]. The esul s epo ed ha , he sim- ula ed esul s on he b ake he mal e ficiency and in-cylinde p essu e we e close by abou 2–3% o he expe imen al esul s. A single-zone he modynamic model was de eloped o a diesel engine uelled wi h biodiesel om was e [6]. The single zone model coupled wi h a iple-Wiebe unc ion was pe o med o simula e hea elease and cylinde p essu e. I was epo ed ha , he hea elease a e and cylinde p essu e p edic ed we e 2.5% and 2.2% close o he expe imen al esul s o he engine. A wo dimensional, mul i-zone model was de eloped o a DI diesel engine un wi h he e hanol– diesel blend [7] and ege able oil, bio-diesel and diesel [8]. The simula ion model was suppo ed by Fo an V language and sol ed nume ically by solu ion ma ching echnique wi h a compu a ional s ep size o 1°c ank angle. The hea ans e o mula ions used in a diesel engine unde di e en ope a ing condi ions we e compu ed using compu a ional fluid dynamics (CFD) codes [9] was e alua ed and compa ed wi h he expe - imen al da a. The model p edic ed mo e accu a ely he hea ans e du ing he comp ession s oke o mo o ed ope a ion and a he same ime he p edic ed peak hea flux was close o he expe imen al esul s. A quasi-dimensional, mul i-zone, di ec injec ion (DI) diesel combus ion model has been de el- oped and implemen ed in a ull cycle simula ion o a u - bocha ged engine. P edic ions o hea elease a e, as well as NO and soo emissions a e compa ed wi h expe imen al da a ob ained om ep esen a i e hea y-du y, u bocha ged diesel engines. I is demons a ed ha he model can p edic he a e o hea elease and engine pe o mance wi h high fideli y. Howe e , addi ional e o is equi ed o enhance he fideli y o NO and soo p edic ions ac oss a wide ange o ope a ing condi ions [10]. A quasi-dimensional, h ee-zone combus ion model o he diesel engine o calcula e pe o mance and emissions using he diesel–e hanol dual uel was de eloped by Jun a akod [11]. A s udy was ca ied ou using mul izone modelling o analyse he sp ay de elopmen o a diesel engine un on ege able oil, and biodiesel diesel blends [12]. I was epo ed ha he p edic ion o esul s om modelling was mo e p oxima e han he expe imen al esul s. The compu a- ional ime equi ed was no a ec ed in he mul i- dimensional modelling. The combus ion model o a diesel engine was de eloped using compu a ional fluid dynamics (CFD) so wa e-AVL Fi e, and he pe o mance and emission cha ac e is ics o second gene a ion biodiesel we e analysed [13]. The simula ed esul s epo ed ha , biodiesel p o ided be e pe o mance and e ficiency, and significan ly educed engine emissions. The quasi-dimensional, mul i-zone (QDMZ) models [14,15] we e o mula ed by he quasi s eady equa ions which desc ibed he indi idual p ocesses ha occu in he engine cylinde such as uel a omisa ion, uel injec ion, ai en e ainmen , ai – uel mixing, combus ion and hea ans e . A combus ion model [16,17] was de eloped o he heo e ical DI diesel engine and pe o mance pa ame e s. I was epo ed ha he de eloped model could be adap ed o an al e na i e uel in a diesel engine and he pe o mance and cylinde p es- su e esul s we e close o he heo e ical. In ecen yea s, he alida ion o he expe imen al esul s om ma hema ical modelling o simula ion h ough ad ance so wa e is essen ial, so ha he andomness o he esul s is minimised. In his s udy, a ma hema ical modelling was de el- oped o alida e he expe imen al esul s ob ained om a single cylinde , ou s oke, ai cooled, DI diesel engine, ha was un on he BMDE15 emulsion. A MATLAB p og am was de el- oped o a wo zone model o he alida ion. One zone con- sis ed o pu e ai called he non-bu ning zone, and he o he consis ed o uel and combus ion p oduc s, called he bu ning zone. In o de o ob ain he cylinde p essu e and empe a u e by ma hema ical modelling, he fi s law o he modynamics and he equa ion o s a e we e used o bo h he zones. The combus ion pa ame e s, such as igni ion delay and hea elease a e he chemical equilib ium composi ion we e calcula ed he- o e ically, using he wo zone model. As he NO and soo emis- sions a e impo an in a CI engine, hey we e calcula ed using a semi-empi ical model. A compa ison o he heo e ical and expe imen al esul s o he BMDE15 emulsion is p esen ed in his pape . A sp ay p ofile o diesel and he BMDE15 emulsion is also ob ained using a MATLAB p og am and is p esen ed. 2. Ma e ials and me hod In his expe imen al in es iga ion, bioe hanol ob ained om he Madhuca Indica flowe and emulsified wi h diesel (BMDE15) was used as an al e na i e uel in a single cylinde , ou s oke, di ec injec ion (DI) diesel engine. Table 2 lis s he impo an p ope ies o diesel and BMDE15. The comple e p ocedu e o p oducing he bioe hanol om he Madhuca Indica flowe has al eady been desc ibed in [18]. The nume ic alue a e BMDE indica es he pe cen age o bioe hanol in he emulsion. The physicochemical p ope ies o he BMDE15 emulsion a e shown in Table 1 in compa ison wi h hose o diesel. The expe imen al se -up used in his in es iga ion is shown in Fig. 1. A se ies o es s we e ca ied ou on a single cylinde , ai cooled, s a iona y DI diesel engine ha has a bo e diame e o 87.5 mm and a s oke leng h o 110 mm and a displacemen o 662 cm. The engine had a a ed ou pu o 4.4 kW 1500 pm wi h a comp ession a io 17.5:1. The nozzle opening p essu e o he injec o was 200 ba and he injec ion iming was 23 °CA bTDC, se by he manu ac u e . The engine was coupled o an elec ical dynamome e o p o ide he b ake load wi h an elec ic panel. Diesel and Table 1 P ope ies o diesel and BMDE15. Desc ip ion Diesel BMDE15 Chemical o mula C 16 H 34 C 5.471 H 6.039 O Molecula weigh 170 48 Viscosi y a 40 °C, cS 2.4 1.73 Ca bon 86 65.65 Hyd ogen 13.60 10.21 Ni ogen 0.18 0.14 Sul u 0.22 0.01 Oxygen by diffe ence 0 24 994 M. Si alingam e al. BMDE15 emulsion we e s o ed in wo di e en uel anks, espec i ely. A uel con ol al e was loca ed in he uel line be ween diesel ank and al e na i e uel ank, o allow ei he diesel o emulsion uel. The uel consump ion was measu ed wi h he help o a uel senso , which was fixed in he uel line. The emulsion was injec ed by he uel injec o o he sys em. An ai box was p o ided on he suc ion side o he ai . Ai consump ion was measu ed wi h he help o ai senso which is fi ed on he ai box. The exhaus gas empe a u e measu ed by a K ype he mocouple and inpu we e gi en o he da a acquisi ion sys em. The da a collec ed by he da a acquisi ion sys em om all he senso s o he co esponding loads we e displayed on he moni o o he compu e . A wa e cooled piezo-elec ic p essu e ansduce wi h a sensi i i y o 12.5 pC/ba , was moun ed on he cylinde head. A TDC posi ion senso was fixed on he flywheel o he engine. The p essu e ansduce and he TDC posi ion senso ga e he inpu o he da a acquisi ion sys em. Wi h he help o he p es- su e measu ed a e e y c ank angle, p essu e–c ank angle dia- g am was d awn. Fo he emission measu emen s, an exhaus gas analyse was used o measu e he le el o HC, CO 2 , CO, and NO. A diesel smoke me e was used o measu e he smoke in he engine exhaus . Ini ially, he engine was ope a ed wi h diesel o ob aining he e e ence da a. 3. Ma hema ical modelling 3.1. Fuel model 3.1.1. Sp ay o ma ion model In a CI engine, he uel ai mix u e is ob ained inside he com- bus ion chambe o he engine. The injec ed uel abso bs he hea om he su ounding ai and apou ises. Fu he , he uel apou mixes wi h he a ailable ai in he cylinde . The uel injec o plays an impo an ole in he injec ion p ocess, because i a omises he liquid uel in o fine d ople s in he o m o a sp ay. Depending on he sp ay, he uel ai mix u e is ob ained in he cylinde . The be e he uel sp ay, he be e he mix u e o ma ion. The combus ion, pe o mance and emission o he engine a e analysed wi h he help o a sp ay pa e n o he uel. In his sec ion, he wo-dimensional, mul i-zone model o uel sp ays is de eloped, whe e he issuing je is di ided in o disc e e olumes, called zones. The desc ip- ions o he model a e discussed in he ollowing subsec ions. 3.1.2. Fuel injec ion p ocess Du ing he comp ession o fluid in he uel injec ion p ocess, a p essu e wa e is p opaga ed down he connec ing pipe a a sonic speed, o open he needle o he injec o . The speed o sound is gi en by as¼ffiffiffiffiffiffiffiffi Kbm q1 sð1Þ Then, he ime o he p essu e wa e o a el down he connec ing pipe leng h (LpÞi.e. injec ion delay was exp essed by Duinjdel ¼Lp as  6Nð2Þ The p essu e wa e in he injec o nozzle holes has a magni- ude o Dpw¼asq1cpump Fpump=Fnozzle  ð3Þ Table 2 Impo an p ope ies o diesel and BMDE15. P ope ies ASTM s anda d Diesel BMDE15 Densi y a 40 °C (kg/m 3 ) D4052-11/ D4815 860 809 Lowe hea ing alue (MJ/kg) D 4809 43.8 35.34 Kinema ic iscosi y a 40 °C (cS ) D 445 2.58 1.95 Ce ane numbe D613 51 36 Flash poin (°C) D 2500 52 26 1. Engine 6. C ank angle encode 12. P essu e ansduce 2. Ai box 7. Al e na o 13. Da a acquisi ion ca d 3. U- ube Manome e 8. Load cell 14. Pe sonal compu e 4A.Diesel ank 9. Val e 15. AVL437C smoke me e 4B.Emulsion ank 10. Fuel injec o 16. AVL Digas 444 analyse 5. Bu e e 11. Con ol panel 8 4A 4B 5 3 2 1 6 7 10 12 11 13 14 15 16 DAC 9 Figu e 1 Expe imen al se -up. Valida ion o some engine combus ion and emission pa ame e s 995 whe e Fpump and Fnozzle a e he c oss sec ional a eas o he pump ba el and o he o al o he nozzle holes. 3.1.3. Fuel je b eak-up poin and ini ial angle To ob ain he loca ion o he sp ay ip as a unc ion o ime, based on he ele an expe imen al da a and u bulen je heo y, a co ela ion de eloped by A ai e al. [19] is inco po a ed in he modelling. O he co ela ions [20,21] a e also used o ob ain he uel b eak-up poin , swi ling mo ion o he ai and sp ay pene a ion con aining he swi l a io. The mean je eloci y om each nozzle hole is gi en by  uinj ¼Cdffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2Dpinj=q1 qð4Þ The Cd alue was aken as 0.39. The mean uel injec ion a e pe je (kg/°CA) is gi en as   m inj ¼pD2 n=4  q uinj=6Nð5Þ Fo he gi en global ai o uel a io, he o al uel mass o be injec ed in he cycle m o is fixed, i he o al ai mass apped in he cylinde ma o is known. Then, he alue o he o al du a ion o he uel injec ion is gi en in deg ees o he c ank angle, Duinj ¼m o =Z  =  m inj ð6Þ The sp ay de elopmen will con inue un il he pene a ion o each sp ay eaches a alue o ðD=2þpD=zÞ, o un il i en ains he maximum quan i y o ai equal o ma o =z. The b eak-up ime b was ob ained by equa ing he wo sp ay pene a ion co ela ions be o e and a e b , co espond- ing o he b eak-up leng h S¼Sb S¼0:39 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2Dpinj=q1 q o 0 < 6 b ð7Þ S¼2:95 Dpinj=qa  0:25 ffiffiffiffiffiffiffiffiffiffiffi Dn p o P b ð8Þ Then b is gi en by b ¼28:61q1Dnffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi qaDpinj q ð9Þ whe e qais he densi y o ai inside he cylinde jus be o e he beginning o he combus ion o uel. The b eak-up leng h is gi en as Sb ¼ uinj  b ð10Þ The b eak-up leng h wi h he swi l a io can be w i en as Sb s ¼Sb 1þpRsNSb =30  uinj  1ð11Þ The co esponding b eak-up ime is gi en by b s ¼Sb s= uinj ¼Sb s=Sb ðÞ b ð12Þ The ini ial sp ay angle ( ad) is [22] h¼2 a c an 1  A4pffiffiffiffiffi qa q1 ffiffiffi 3 p 6 ! ð13Þ whe e  Ais cons an and gi en by he empi ical ela ions,  A¼3þ0:28 Ln=Dn ðÞ ð14Þ 3.1.4. Fuel sp ay de elopmen The ollowing s eps a e used o he sp ay de elopmen o each zone, (a) Fo axial zones, he zones a e aken as imax ¼Duinj=Du, and o adial zones, hey a e di ided in o jmax ¼imax=2 o imax. The ins an aneous uel injec ion eloci y and injec- ion a e in each sp ay, using ins an aneous alues o Dpinj ¼Dpwa e gi en as uinj i ðÞ¼Cdffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2DpinjðiÞ=q1 qð15Þ And  m injðiÞ¼ pD2 n=4  quinjðiÞ=6Nð16Þ Then he cumula i e uel injec ed in each sp ay is, m inj iðÞ¼Zu 0  minj iðÞduð17Þ (b) The uel is dis ibu ed equally in o he adial zones jmax a each c ank angle in s eps o ‘‘i”, which is gi en by he ol- lowing equa ion, m inj iðÞ¼ minj iðÞdu=jmax ð18Þ (c) The Sau e mean diame e (DSM ) is calcula ed o each s ep. (d) The mid zone is selec ed as jmid ¼jmax=2þ1ð19Þ (e) The mid-zone pene a ion in he adial dis ance om he cylinde axis is calcula ed as mid iðÞ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi x2i;jmid ðÞþy2i;jmid ðÞ pð20Þ ( ) The mid-zone eloci y in each c ank angle s ep iðÞis calcu- la ed as umid iðÞ¼2:95bDpinjðiÞ=qa  0:25 ffiffiffiffiffiffi Dn p1 1bð21Þ (g) The cen e line angle o each zone is gi en as hzi;jðÞ¼ h 2þj1 jmax hþh 2jmax ð22Þ (h) The eloci y dis ibu ion o a lowe axis pene a ion loca ed a he je pe iphe y o each zone is calcula ed as uzi;jðÞ¼umid iðÞexp ah2 zði;jÞ  ð23Þ whe e a¼4:52 (i) The swi l coe ficien be o e he wall impingemen is calcu- la ed by he ollowing equa ion, Cswz i;jðÞ¼1þpRnNffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi x2i;jmid ðÞþy2i;jmid ðÞ p30uzði;jÞð24Þ 996 M. Si alingam e al. while Cswz i;jðÞis 1 a e he wall impingemen . The coo - dina es o xand ya e calcula ed om he p e ious s ep. (j) Also he d op o he Sau e mean diame e om he cen e line o he sp ay wi h inc easing dis ance is conside ed as DSM i;jðÞ¼11 w  DSMMðiÞþ 2 w  DSMMðiÞðj1Þ=ðjmid 1Þ ð25Þ whe e wis in he ange o 5–10. (k) The numbe o d ople s in each zone is also calcula ed wi h he ollowing ma hema ical ela ion: Nd op i;jðÞ¼m z iðÞ=p=6ðÞ½DSM i;jðÞ 3q1ð26Þ (l) The zone eloci y wi h swi l is calcula ed as uzs i;jðÞ¼uzi;jðÞ=Cswz i;jðÞ ð27Þ (m)The mass o ai in each zone is calcula ed as maz i;jðÞ¼m z iðÞuinj iðÞuzs i;jðÞcos hzi;jðÞ uzs i;jðÞcos hzi;jðÞ ð28Þ (n) The uel ai equi alence a io o he zone is, £zi;j ðÞ ¼m z iðÞ=maz i;jðÞ 1 AFs  ð29Þ (o) The e ec o swi l o each zone on he angle is conside ed as (i) Fo j<jmid , hzs i;jðÞ¼hzi;jðÞCswzði;jÞ2ð30Þ (ii) Fo j¼jmid , hzs i;jmid ðÞ¼ 1 2hzs i;jmid ðÞþ 1 2hzs i;jmid 1ðÞ ð31Þ (iii) Fo j>jmid , hzs i;jðÞ¼hzi;jðÞþhzs i;jmid ðÞ ð32Þ (p) The loca ion o he co-o dina es o each zone is calcula ed wi h he ollowing equa ion: (i) Be o e he wall impingemen , xi;jðÞ¼x0i;jðÞþuzs i;jðÞcos hzs i;jðÞ Du 6Nð33Þ yi;j ðÞ ¼y0i;j ðÞ þuzs i;j ðÞ sin hzs i;j ðÞ Du 6Nð34Þ (ii) A e he wall impingemen , xi;jðÞ¼ zimp i;jðÞcos hzs i;jðÞ ð35Þ yi;jðÞ¼ zimp i;jðÞsin hzs i;jðÞ ð36Þ 3.1.5. Fuel d ople e apo a ion The uel e apo a ion in each zone is conside ed wi h he calcula ion o he Sau e mean diame e , which is gi en by he ollowing ela ions: DSM;1¼0:38Re0:25 inj We0:32 inj 1= a ðÞ 0:37 q1 qa  0:47 Dnð37Þ DSM;2¼4:12Re0:12 inj We0:75 inj 1= a ðÞ 0:45 q1 qa  0:18 Dnð38Þ Also, he equi alence a io o each zone is calcula ed using he e apo a ion model, £z ap i;jðÞ¼ m z ap iðÞ=maz i;jðÞ 1 AFs  ð39Þ 3.1.6. Calcula ion o Whi ehouse–Way uel p epa a ion a e cons an A e he uel is injec ed in o he cylinde chambe , i will unde go physical and chemical p ocesses o bu ning inside he chambe . In he physical p ocess, he uel ge s a omised, hea ed, e apo a ed and mixed wi h su ficien ai o o m he cha ge mix u e. Then, he chemical kine ic eac ions occu , o bu n he mix u e in he chemical p ocess. The Whi ehouse and Way model [23] was used o he compa ison o he esul s ob ained om he uel e apo a ion model. So, he pene a ion a e p oposed by he Whi ehouse–Way model was gi en as dmp du¼Kp m1x inj mx uppm ox ð40Þ whe e m inj ¼Zu 0 dm inj duduð41Þ m up ¼m inj Zu 0 dm inj duduð42Þ 3.2. Gene al desc ip ion o he model In his in es iga ion, a single cylinde , ou s oke, ai cooled, di ec injec ion (DI) diesel engine is used. The combus ion chambe is a bowl in pis on ype and he uel injec o has a h ee hole nozzle. The model used in his s udy is a wo zone he modynamic model. I is assumed ha he cylinde con ains a nonbu ning zone o ai , and ano he bu ning zone in which he uel is con inuously injec ed du ing injec ion and bu n wi h he a ailable ai om he ai zone. The model conside s only hose p ocesses which occu du ing he possession o comp ession and expansion s oke. I is assumed ha he inle and exhaus al es a e ully closed du ing he s oke. The com- p ession p ocess in p ac ically all engines is a poly opic one, which begins om he momen he inle al e, closes and ends when he injec ion p ocess s a s. The main calcula ion is based on he in eg a ion o he fi s law o he modynamics and he ideal gas equa ion. The ollowing assump ions a e made o he analysis: (a) The cylinde con ains he non-bu ning zone and bu ning zone. (b) The p essu e and empe a u e in each zone a e uni o m and a y wi h he c ank angle. The con en o each zone ollows he pe ec gas laws. Valida ion o some engine combus ion and emission pa ame e s 997 3.2.1. Ene gy equa ions Du ing he comp ession s oke, only one zone (o pu e ai ) exis s. Then, he fi s law o he modynamics o a closed sys- em is applied, oge he wi h he pe ec gas s a e equa ion. The change in in e nal ene gy is exp essed [21] as ollows: dðmuÞ dh¼dQ dhdQh dhdW dhð43Þ By eplacing he wo k ans e e m dW/dhwi h PdV/dho by he ideal gas law PV =mRT, he abo e Eq. (43) can be ea - anged as mdu dh¼dQ dhhA dT dhRT dV dhð44Þ whe e Vis he ins an aneous cylinde olume wi h espec o he c ank angle, which is gi en by V¼Vcl þpD2=4  1þk1cosuk2sin2u  1=2 hi ð45Þ In he abo e equa ions, he e m dQ is gi en as he ou h o de polynomial exp ession o he absolu e empe a u e T, including he en halpy o o ma ion a absolu e ze o. The in e nal ene gy calcula ion as a unc ion o empe a- u e is as ollows: hi RmolT¼ai1þai2=2Tþai3=3T2þai4=4T3þai5=5T4þai6=3T5 ð46Þ ui ¼hi RT ð47Þ Fo he su ounding ai zone, which only loses he mass (ai ) o he bu ning zone, he fi s law o he modynamics o he unbu ned zone is w i en as dE ¼dQ pdV hadmað48Þ The bu ning zone no only ecei es he mass om he ai zone, bu also he e is an en halpy flow om he uel, which is eady o be bu ned in he ime s ep. So, he fi s law o he - modynamics o he bu ning zone becomes dE ¼dQ pdV þhadmaþh dm ð49Þ The fi s law o he modynamics o he combus ion in ime s ep d is ðEÞ¼EðT2ÞEðT1ÞdQ þdW þdm Q s ¼0ð50Þ I (E) is g ea e han he accu acy, he equi ed new alue o T 2 is calcula ed using he New on–Raphson nume ical me hod. The unbu ned zone empe a u e is calcula ed using he equa ion, Tu¼Tsoc P Psoc  c1=c ð51Þ 3.2.2. Hea ans e model The hea ans e be ween he cylinde apped mass and he su ounding walls is calcula ed, using he o mula o Annand [23]. The Annand o mula o calcula e he hea loss om he cylinde , is dQ=d ¼akg DReðÞ bTwTg  þcT4 wT4 g  ð52Þ In his equa ion ‘T w ’ is he cylinde wall empe a u e which is assumed as 450 K, and a,b, and ca e cons an s. The cons an alues a e aken as a= 0.2626, b= 0.6, c= 5.67 *10 8 W/ m 2 /K. 3.2.3. Igni ion delay The ime delay be ween he s a o injec ion and he s a o combus ion is defined as he igni ion delay pe iod [24]. The de e mina ion o he s a o combus ion (SOC) by selec ing he p ope me hod is a key issue in igni ion delay s udies. In he combus ion model, he igni ion delay is also aken in o accoun . The igni ion delay pe iod is calcula ed by in eg a ing Wol e ’s ela ion, using he apezoidal ule [25]. Z ign inj d ðp;TÞ¼1 K inj Z ign inj d p ðÞðÞ qexp E RT ðÞ  ¼1ð53Þ The alues o a ious cons an s co esponding o a DI diesel engine a e K= 2272; q=1.19; E/R= 4650. Whe e K= he mal conduc i i y, q= hea losses and E/R= ac i a ion ene gy/uni e sal gas cons an . 3.2.4. Wiebe’s combus ion model The Wiebe unc ion is used o p edic he mass ac ion bu n and he bu n a e in IC engines, ope a ing wi h di e en com- bus ion sys ems and uels. Wiebe linked he chain chemical eac ions wi h he uel eac ion a e in IC engines and his app oach is based on he p emise ha a simple one-s ep a e equa ion would no be adequa e o desc ibe he complex eac - ing sys ems, such as hose occu ing in an IC engine. The Wiebe unc ions [26] o he non-dimensional bu n ac ion x as a unc ion o he deg ees o c ank angle can be w i en as x¼1exp 6:908 hho Dh  mþ1 "# ð54Þ The hea elease a e calcula ed wi h he help o he Wiebe unc ion is, dQc dh¼6:908ðmþ1ÞQa Dh  hho Dh  m exp 6:908 hho Dh  mþ1 "# ð55Þ whe e xis he mass ac ion bu ned, hois he s a o combus- ion and Dhis he combus ion du a ion. The pa ame e m ep esen s he a e o combus ion. Q a is he hea eleased pe cycle. The alue o m o bo h he uels is aken as 3.0. When calcula ing he hea elease, p io knowledge o he ac ual o e all equi alence a io is necessa y. The e m equi a- lence a io is defined as he a io o he ac ual ai – uel a io o he s oichiome ic ai – uel a io. This helps in fixing he mass o uel o be admi ed. 3.2.5. Chemis y o combus ion In a combus ion p ocess, he uel and he oxidise eac o p o- duce p oduc s o di e en composi ions. The heo y o com- bus ion is a complex one, and has been he opic o in ensi e esea ch o many yea s. Le us ep esen he chemical o mula o a uel as CaHbOcNd. In he p esen case, i was conside ed ha 10 species we e p esen in he combus ion p oduc , and he combus ion equa ion is gi en by: 998 M. Si alingam e al. euCaHbOcNdþ0:21O2þ0:79N2 !m1CO2þm2H2Oþm3N2þm4O2þm5CO þm6H2 þm7H þm8O þm9OH þm10NO ð56Þ F om he a omic balance o each species CAHAOAN he ol- lowing 4 equa ions, a e ob ained: Ceua¼ðy1þy5ÞN1 ð57Þ Heub¼ð2y1þ2y6þy7þy9ÞN1 ð58Þ Oeucþ0:42 ¼ð2y1þy2þ2y4þy5þy8þy9þy10ÞN1 ð59Þ Neudþ1:58 ¼ð2y3þy10ÞN1 ð60Þ The chemical eac ions conside ed in equilib ium, a e as ollows: 0:5H2!Hð61Þ 0:5O2!Oð62Þ 0:5H2þ0:5O2!OH ð63Þ 0:5O2þ0:5N2!NO ð64Þ H2þ0:5O2!H2Oð65Þ CO þ0:5O2!CO2ð66Þ The use o he equilib ium cons an is iden ical o maximis- ing he en opy o he gas. This me hod is simila , when con- side ing a es ic ed species lis such as he p esen case [27]. Once he composi ion is known, he he modynamic p ope ies o in e es such as en halpy, en opy, specific olume and in e - nal ene gy, can be compu ed. 3.2.6. Ni ic oxide (NO) o ma ion model The cu en app oach o model he NO x emissions om diesel engines is, o use he ex ended Zeldo ich he mal NO mecha- nism, by neglec ing o he sou ces o NOx o ma ion. The ex ended Zeldo ich mechanism consis s o he ollowing eac ions: OþN2!NO þNð67Þ NþO2!NO þOð68Þ NþOH!NO þHð69Þ This mechanism can be w i en as an explici exp ession o he a e o change o he concen a ion o NO. The change o NO concen a ion is exp essed as ollows: ðdðNOÞÞ=d ¼2ð1a2ÞR1=ð1þaR1=ðR2þR3ÞÞ ð70Þ whe e R i is he one-way equilib ium a e o he eac ion i, defined as R1¼k1 ðNÞeðNOÞe;R2¼k2 ðNÞeðO2Þe;ð71Þ R3¼k3 ðNÞeðOHÞe;a¼ðNOÞ=ðNOÞeð72Þ 3.2.7. The ne soo o ma ion model The exhaus o he CI engine con ains solid ca bon soo pa icles ha a e gene a ed in he uel ich egions inside he cylinde du ing combus ion. Soo pa icles a e clus e s o solid ca bon sphe es, wi h he HC and aces o o he componen s abso bed on he su ace. They a e gene a ed in he combus ion chambe in he uel ich zones, whe e he e is no enough oxygen o con e all he ca bon o CO 2 . Subsequen ly, as he u bulence mo ion con inues o mix he componen s, mos o hese ca bon pa icles find su ficien oxygen o eac and o m CO 2 . Thus, soo pa icles a e o med and consumed simul aneously in he combus ion chambe . The ne soo o ma ion a e was calcula ed by using he semi-empi ical model p oposed by Hi oyasu e al. [28]. Acco ding o his model, he soo o ma ion a e (index s ) and soo oxida ion a e (index sc) we e gi en by dms d ¼As m e m bu  0:8p0:5exp Es =RmolT ð73Þ dms d ¼Ascmsn po2=pðÞp1:8exp Esc=RmolTðÞ ð74Þ whe e, he p essu es a e exp essed in ba and d m is he unbu ned uel mass in kg o be bu ned in ime s ep d . The e o e, he ne soo o ma ion a e is exp essed as dmsn d ¼dms d dmsc d ð75Þ A compu e p og am using MATLAB was gene a ed, wi h all he abo emen ioned equa ions and conside ing all he alues o he cons an s, in o de o p edic he combus ion a ibu es, such as he in-cylinde p essu e, c ank angle, hea elease a e, hea losses and he NO emissions. 4. Resul s and discussion 4.1. Sp ay p o ile o diesel and BMDE15 In a CI engine, once he uel is injec ed in o he comp essed ai s eam in he cylinde , he uel je disin eg a es in o a co e o uel su ounded by he sp ay en elope o ai and uel pa icles. The sp ay en elope is c ea ed bo h by he a omisa ion and by he apou isa ion o he uel. The u bulence o ai in he com- bus ion chambe passing ac oss he je ea s he uel pa icles om he co e. A mix u e o ai and uel is ound a some loca- ion in he sp ay en elope and he oxida ion s a s. Thus, he s udy o o ma ion o sp ay is impo an o any diesel uel, when i is used in a diesel engine. In his s udy, he uel sp ay pa e ns o diesel and he BMDE15 emulsion a e ob ained using he MATLAB p og am. Fig. 2(a) and (b) shows he sp ay p ofile o diesel and BMDE15 espec i ely a ull load. I can be obse ed om bo h he figu es, ha nea he noz- zle exi he sp ay is na ow and u he downs eam a he egion o he sp ay body he sp ay widens, because o he d o- ple b eakup and collision phenomena and he in e ac ion wi h he induced gas flow field. Chemical p ope ies such as densi y, iscosi y and su ace ension will a ec he sp ay angle. Diesel has highe densi y and iscosi y in compa ison wi h he BMDE15 emulsion. Howe e , when su ace ension is low, sp ay d ople is p one o quickly b eak-up and wide dispe - sion and cause a ela i ely la ge sp ay d ople . I is appa en om Fig. 2(a) and (b) ha BMDE15 has a smalle cone angle wi h high pene a ion which may be due o he combined e ec s o densi y, iscosi y and su ace ension. Valida ion o some engine combus ion and emission pa ame e s 999 4.2. Combus ion pa ame e s 4.2.1. Cylinde p essu e Fig. 3 depic s he expe imen al and simula ed esul s o he die- sel engines uelled wi h diesel and BMDE15, a ull load. The simula ed esul s o bo h he es uels ga e highe al- ues compa ed o he expe imen al esul s. The lowe cylinde p essu e o he expe imen al esul s may be due o he ins u- men s’ e o , and physical condi ion du ing he expe imen s and he unce ain y o he da a. I is appa en om he figu e ha he igni ion o diesel is he ea lies o he simula ed esul s ollowed by i s expe imen al esul s, he BMDE15 simula ed esul s, and finally, he BMDE15 expe imen al esul s. The peak cylinde p essu e o a CI is p edominan ly influenced by he igni ion delay, he amoun o uel bu n in he ini ial s age o uel combus ion and he mix u e o ma ion in he delay pe iod. The peak cylinde p essu e o he BMDE15 is ound o be he highes , ollowed by he BMDE15 expe imen- al esul s, diesel simula ed and expe imen al esul s. The di - e ence in he peak cylinde p essu e o BMDE15 be ween he simula ed and expe imen al esul s is abou 3%. The peak p essu e is shi ed away om he op dead cen e by abou 5–7 °CA. In he case o diesel, he peak cylinde p essu e o he simula ed and expe imen al esul s is abou 75–70.6 ba which is a ained close o he TDC. The peak cylinde p essu es o BMDE15 ope a ion, bo h in he simula ed and expe imen al esul s, a e highe han hose o diesel ope a ion, due o longe igni ion delay and be e uel mix u e o ma ion, ha esul s in mo e comple e combus ion. The de ia ion be ween he simula ed and he expe imen al esul s o diesel and BMDE15 is abou 2–4 °CA espec i ely. 4.2.2. Igni ion delay Fig. 4 illus a es he a ia ion o igni ion delay a di e en loads o diesel and BMDE15 ope a ions. Igni ion delay is he ime di e ence measu ed in c ank angle be ween he s a o injec ion and s a o combus ion [25]. I is e iden om he figu e, ha he simula ed and he expe imen al esul s o he igni ion delay o he diesel and BMDE15 ope a ions ollow a simila end. The igni ion delay inc eases wi h he inc ease in he load as a esul o he inc ease in he cylinde gas empe a u e. The igni ion delay is ound o be longe o he simula ed and expe imen al esul s o he BMDE15 ope a ion han hose o diesel ope a ion. I can be obse ed om he figu e, ha he e is abou 5–10 °CA de ia ion in he igni ion Figu e 2 (a) Diesel sp ay and (b) BMDE15 emulsion sp ay. -30 0 30 60 20 40 60 80 P essu e in ba C ank Angle diesel exp . diesel simula ed BMDE15 exp . BMDE15 Simula ed Figu e 3 Cylinde p essu e wi h c ank angle o diesel and BMDE15. Figu e 4 Va ia ion o igni ion delay wi h load. 1000 M. Si alingam e al. delay pe iod o expe imen al and heo e ical esul s o bo h he uels. The igni ion delay depends upon he p essu e, em- pe a u e, uel and ai mix u e, equi alence a io, flame speed, e c. Du ing he engine ope a ing condi ion, he cylinde wall empe a u e may inc ease he uel empe a u e. So, he chem- ical eac ion pe iod may be accele a ed; hence, he delay pe iod is sho ened compa ed o he heo e ical esul . Also, he igni- ion delay pe iod may dec ease in he lean and ich mix u e zones. The calcula ed alues o he igni ion delay in he BMDE15 ope a ion a e highe han hose o diesel alues, which is due o he influence o he empe a u e, p essu e and he ime o injec ion. The longe igni ion delay o he BMDE15 ope a ion han ha o diesel ope a ion h oughou he load spec um, is due o he lowe ce ane numbe o BMDE15. 4.3. Emission pa ame e s 4.3.1. NO emission In a CI engine, he NO x emission is one o he majo pollu an s and is p edominan ly influenced by he amoun o oxygen a ailable, and he in-cylinde empe a u e [26]. The NO x emis- sion is composed o NO, NO 2 ,N 2 O, N 2 O 5 ,NO 3 . Ni ic oxide is he majo cons i uen and NO 2 is a mino cons i uen , while he o he s a e negligible. A ele a ed empe a u es (i.e.) abo e 1500 °C, N 2 can eac wi h O 2 as e and may esul in mo e NO x emission. As CI engines ha e a highe comp ession a io and a e lean bu n engines, he peak empe a u e is well abo e 1500 °C; hence, he e is a highe NO x o ma ion. The compa - ison be ween he simula ed and expe imen al esul s o NO emission om diesel and BMDE15 ope a ions is shown in Fig. 5. The b ake specific NO emissions a e ob ained om he simula ion and expe imen s o bo h diesel and BMDE15, show a declining end as he load inc eases. This is because o he inc ease in he load which is a denomina o o he calcu- la ion o NO. The NO emission alues ob ained om he sim- ula ion and expe imen s a e ound o be lowe han hose o diesel ope a ion, because o he high la en hea o he apou i- sa ion o BMDE15. An o e all ma ginal de ia ion o 2–1% is no iced be ween he simula ion and expe imen al esul s o he NO emission alues in diesel ope a ion om no load o ull load, while he de ia ion is 2–1% om no load o ull load in he BMDE15 ope a ion. 4.3.2. Smoke The a ia ion o he simula ed and expe imen al esul s o smoke emission o diesel and BMDE15 is shown in Fig. 6. The simula ed esul s o diesel o smoke emission a e ound o be high compa ed o he expe imen al esul s o diesel and he simula ed and expe imen al esul s o BMDE15. The smoke emission is a esul o he oxygen una ailabili y in he di usion combus ion phase, use o high molecula weigh uel and he a oma ic con en o uel [29]. Diesel has a high ca bon o hyd ogen a io, high molecula weigh , less oxygen and high a oma ic con en [30]. Hence, highe smoke emission is obse ed wi h he diesel ope a ion compa ed o ha o BMDE15 ope a ion. The de ia ion be ween he simula ed and expe imen al al- ues o diesel and BMDE15 is abou 3% and 4% espec i ely, a ull load. 5. Conclusion A comp ehensi e wo zone model was de eloped o alida e he expe imen al esul s ha we e ob ained om a single cylin- de , ou s oke, ai cooled, DI diesel engine un on wo di e - en uels, iz., diesel and BMDE15. The ollowing is he summa y o he esul s: The sp ay pa e n o BMDE15 is ound o be be e com- pa ed o ha o diesel. The be e a omisa ion and apou i- sa ion o uel is achie ed wi h BMDE15 due o i s lowe densi y. The expe imen al and simula ed esul s show ha he peak cylinde p essu e o he BMDE15 is ound o be ma ginally highe han ha o diesel a ull load. The de ia ion be ween he simula ed and he expe imen al esul s o he diesel ope a ion a ull load is abou 5%. In he case o he BMDE15 ope a ion, he de ia ion is abou 3% a ull load. Figu e 5 Va ia ion o BSNO emission wi h load. Figu e 6 Va ia ion o smoke wi h load. Valida ion o some engine combus ion and emission pa ame e s 1001