Combustion Modeling of Diesel Engine Using Bio-Diesel as Secondary Fuel

Transcription

1 Iteratioal Coferece o Mechaical ad Robotics Egieerig (ICMRE'0) May 67, 0 huket Combustio Modelig of Diesel Egie Usig BioDiesel as Secodary Fuel Vivek Kumar Gaba, reraa Nashie ad Shubhakar.Bhowmick Abstract The preset work aims to develop a combustio model for a diesel compressio igitio (CI) egie for costat pressure combustio process. The work aalytically examies the performace of a CI egie with the miimum use of diesel fuel as pilot fuel, ad biodiesel as secodary fuel. The combustio model has bee developed for a ideal diesel egie usig bleds of biodiesel ragig from 0% to 00%. Usig the first law of thermodyamics ad equatio of state i each process, the cycle has bee critically aalyzed. The specificatio of a stadard CI egie has bee used for umerical calculatios. The variatio of temperature with differet equivalece ratio is studied ad reported. The thermal efficiecy of a pure diesel egie is observed to decrease expoetially from 67% to 47% as the equivalece ratio icreases from 0.7 to.3. It is also observed that B 0 ad B40 formed a good mixture amog all other bleds ad the efficiecy of pure biodiesel is comparatively less tha diesel as well as for other bleds. Keywords Biodiesel, equivalece ratio, models have bee compared with D model for average mixture temperature, the temperatures of the bured ad ubured gases ad the flame surface area ad idicate that the oedimesioal model predictios are very sesitive to the eddy diffusivity ad reactio rate data where as the twozoe thermodyamic model predicts, first, a mootoically icreasig flame surface area with time ad, the, a mootoically decreasig surface area. I aother study [], the fuel evolutio is modeled by studyig the spray atomizatio, peetratio, air etraimet, ad evaporatio; the air motio; the igitio delay; ad the combustio. The model cosists of aalytical ad semi empirical sub models for each of the above metioed pheomea, with a special emphasis o the spray behavior durig the atomizatio process ad after the impigemet agaist the walls. The problems associated with the coversio of a directijectio diesel egie to dualfuel operatio have bee reported i [3]. The effects of chages i various operatig parameters such as itake TABLE I: NOMENCLATURE M I. INTRODUCTION & LITERATURE REVIEW ODELING of mixture formatio ad combustio processes is a very useful tool to aalyze ad predict the performace of reciprocatig iteral combustio egies. I case of compressioigitio egies (CE), it is ecessary to characterize ad model each of the processes relevat to the fuel ijectio ad combustio iside the combustio chamber. Compressio igitio (CI) egies, commoly kow as diesel egies, are importat compoets of the trasportatio ad eergy sectors of the world. Millios of uits are used o a daily basis ad therefore the emissio of CI egies is a importat aspect of pollutio cotrol. CI egies are desiged to operate o less refied petroleum distillate tha gasolie which cotais less eergy cotet. Yet CI egies are more efficiet at covertig fuel eergy cotet ito output tha the spark igitio egie. CI egies also have fewer overall emissios tha spark igitio egies ad are preferred for emissios reductios. However, depletig fuel reserves have forced researchers to look for alterative/reewable eergy sources for operatig these egies. The work i a oedimesioal combustio model [], employig costat eddy diffusivity ad a oestep chemical reactio has bee developed ad applied to study the flame propagatio i a Spark Igitio (SI) egie at 600 ad 400 rpm uder fuel rich coditios usig oe ad two zoe thermodyamic models. The thermodyamic * Correspodig author V.K. Gaba* is Assistat rofessor, NIT Raipur(CG)4900 Idia hoe: ; vgaba.mech@itrr.ac.i rera Nashie is i GET Departmet Egieerig Desig ad Research Cetre, L&T Dr. S. Bhowmick is Assistat rofessor, NIT Raipur(CG)4900 Idia shubh.ju@gmail.com Symbol α β st β act ɸ m air D m f L M N R T U V X Q U W dm f du dv CV diesel m fb Quatity ercetage of bled Stoichiometric airfuel ratio Actual airfuel ratio Equivalece ratio Mass of air Bore diameter of cylider Mass of fuel Stroke Legth Number of gram mole Nth umber of divisio ressure Uiversal Gas Costat Temperature Absolute Iteral Eergy Volume Fractio of diesel coverted i each divisio Heat trasfer Chage i iteral eergy Work trasfer Gram mole of diesel supplied i each divisio durig combustio Chage i iteral eergy i each divisio Chage i volume i each divisio Lower Calorific value of diesel Total gmmole of Biodiesel supplied durig combustio ressure after th divisio ressure before th divisio 89

2 Iteratioal Coferece o Mechaical ad Robotics Egieerig (ICMRE'0) May 67, 0 huket temperature ad the quatity ad quality of the pilot liquid fuel, while usig various primary gaseous fuels (propae, methae ad hydroge) ad their bleds o the kockfree performace limits is studied. The fidigs supported the view that the kock observed i a typical dualfuel egie is maily caused by the auto igitio of the gaseous fuelair mixture i the eighborhood of the igitio ceters origiatig from the small pilot liquid fuel sprays. The volumetric efficiecy represets a measure of the effectiveess of a air pumpig system, ad is oe of the most commoly used parameters i the characterizatio ad cotrol of fourstroke iteral combustio egies [4]. The problem cosidered here is viewed as a realistic bechmark for differet estimatio techiques. I [5] the results from multidimesioal umerical simulatios ad cycle simulatios are preseted i a effort to optimize the performace of a fuelleabur, homogeeous charge, atural gas sparkigitio iteral combustio (IC) egie. I aother work [6], the desig ad operatioal variables of ilet ad exhaust system are studied ad are reported to be decisive i determiig overall egie performace. The best egie overall performace ca be obtaied by proper desig of the egie ilet ad exhaust systems ad by matchig the correct turbocharger to the egie. I [7], a attempt to develop a complete cycle model has bee implemeted ad a computer code for determiig complete cycle has bee developed for calculatig performace characteristics, ad exhaust emissios of diesel egies. The combustio model is based o a multizoe combustio modelig cocept by cosiderig details of fuel spray formatio, fuel air mixig, swirl ad heat trasfer. A emissio model based o the chemical equilibrium ad kietics of NO has bee developed to calculate the pollutat cocetratios withi each zoe ad the whole of the cylider. Icylider pressure is a importat parameter that is used to study the combustio process i iteral combustio (IC) egies ad has bee ivestigate[8] based o a thermodyamic model of IC egie combustio. A heat release fuctio ad a empirical coversio efficiecy factor are itroduced to solve the model. The work i area of reduced chemical kietic mechaisms for the oxidatio of represetative surrogate compoets of a typical multicompoet automotive fuel have bee developed ad applied to model iteral combustio egies [9]. The results show that the multicompoet combustio model gives reliable performace for combustio predictios, as well as computatioal efficiecy improvemets through the use of reduced mechaism for multidimesioal CFD simulatios. The performace aalysis [0] shows that i a dieselproducer gas CI egie the thermal efficiecy icreases as the percetage of diesel supplied durig costat volume combustio process icreases but there is o sigificat effect o work output. It further reports that there is o sigificat chage i thermal efficiecy if the quatity of producer gas bured i the costat volume combustio process is icreased keepig the quatity of diesel fixed. Hydroge additio icreases the work output rapidly but decreases the thermal efficiecy slightly. I aother work [], the combustio of Rapeseed Methyl Ester (RME), has bee studied. The chemical model, developed is a modificatio of the approach. The existig detailed mechaism of methyl butaoate (MB) ester oxidatio was supplemeted by submechaisms for supposed fuel costituet compoets, C 7 H 6 ad C 7 H 8 O to represet combustio of RME, C 9 H 34 O or C 9 H 36 O whe MB ad C 3 H 4 were selected. Biodiesel autoigitio properties were validated usig costat volume ad shock tube data at diesel egie coditios. For spray combustio applicatios, the detailed mechaism has bee reduced to 88 species participatig i 363 reactios. This mechaism has bee used to ivestigate combustio ad emissios (NOx ad soot) formatio/oxidatio i the research diesel egie (Volvo DC). The compariso was made with egie performace ad the emissio formatios for covetioal diesel oil. The 3D egie simulatios have bee carried out usig KIVA3V egie combustio code modified for detailed chemistry applicatios. Fig. IDEAL DIESEL CYCLE II. ANALYSIS AND METHODOLOGY The preset work deals with the combustio modelig of diesel egie. The problem is solved i three steps usig first law of thermodyamics, ad equatio of state. Step Developmet of relatioship betwee temperature ad absolute iteral eergy. Step Modelig of ideal diesel cycle. Step3 Modelig of diesel cycle usig biodiesel fuel ad diesel as pilot fuel. A real sigle cylider dual fuel egie specificatio has bee used for all calculatios. TABLE II: SECIFICATION OF ENGINE Egie Type 4 Stroke diesel fuel egie Stroke 5mm Bore 05mm Number of cyliders Combustio system direct ijectio Compressio ratio 7.5 RM 500 A. Assumptios i Combustio Modelig: A ideal diesel cycle is cosidered for the aalysis. Thermodyamic properties are assumed uiform throughout the combustio chamber volume. The gaseous mixture behaves as a ideal gas. The combustio process results i complete combustio. To simplify the combustio process, the itermediate steps of chemical kietics are ot cosidered. The combustio products are limited to water vapour, carbo dioxide ad iert itroge gas. 90

3 Iteratioal Coferece o Mechaical ad Robotics Egieerig (ICMRE'0) May 67, 0 huket TABLE III: CORRELATIONS OF INTERNAL ENERGY FOR DIFFERENT COMONENTS Compoets Specific absolute iteral eergy i terms of temperature Air U Air = 9e T T T 0.04 T T CO U(CO) =.e T 6.e T +.e T T T.7e 4 3 CH 4 U(CH ) = 6e T.9e T 8.4e T T +.9 T.6e H 6 3 U(H ).4e = T + 7.5e T.4e T T T CO U(CO ) =.e T + 6.e T.4e T T + T 9.4e H O U(H O) =.3e T 7.3e T +.5e T.5e T T 5.7e N U(N ) =.3e T 7.5e T +.5e T T + 5 T +.8 O U(O ) = 5e T.3e T +.9e T T T + 5. III. GOVERNING EQUATIONS The goverig equatios for the cycle 34 (fig) are aalyzed separately oe by oe as give below. () For Isetropic Compressio(process ) A charge of pure air is compressed isetropically from state to state ad after compressio the pressure ad temperature icreases ad which are calculated by applyig first law of thermodyamics. The whole compressio process is assumed to be divided ito N umber of small steps where, dv = V V () ( varies from to N) From first law of thermodyamics du=δq δw du is the chage i iteral eergy after very small chage i volume durig the process. δq is the heat trasfer which is zero durig isetropic compressio process. δw=pdv, i this case it is the work doe by the system durig th iterval + ( V V ) () Hece equatio () yields, U( T) U( 0) U ( T) U( 0) (3) + = (V V ) For iterative solutio techique, the above equatio assumes the form as give below f( U) = éut U0 ù éut ( ) U0 ù ë û ë û (4) + + ( V V ) where,, V, T are the pressure, volume, ad temperature before th iterval ad are kow apriori;, V, T are the pressure, volume ad temperature after the th iterval durig the compressio stroke. From equatio of state V T = V T (5) The solutio of equatio (4) is obtaied umerically assumig the value of T so that f(u)=0. By repeatig the same process the pressure ad temperature at the ed of compressio ca also be calculated. () For costat ressure combustio(process 3): The iteral eergy values at differet temperatures for these gaseous compoets preset i air ad alterative fuel were obtaied from stadard data []. A empirical relatioship betwee temperature ad absolute iteral eergy for differet gaseous compoets that are preset i air ad biodiesel is obtaied from plottig absolute iteral eergy values at differet temperatures by fittig 5 th degree polyomial curve usig curve fittig algorithm i MATLAB ad the correlatios are obtaied as show i TableIII. Geeral combustio equatio for bled of Biodiesel ad Diesel is give i equatio (6), i which mfd ad m fb are the total umber of moles of diesel & biodiesel respectively. m fd C H 6 + m fb C 9 H 38 O + m air [ 0.79 N + 0. O ] (6) = B CO + B H O m air N Total umber of moles of fuel, mf = mfd + mfb (7) Now, if the percetage bled is represeted by α, the m fb = α m f (8) m fd = (α) m f (9) So, total umber of moles of air required for complete combustio is give by æ4.mf ö 3.4mf + ç 0.mf çè ø mair = (0) 0. Similarly, equivalece ratio, φ is give by b f = st () b act bst ca be calculated by takig the value of molecular weight of air ad effective molecular weight of the bled. Usig (6), the moles for differet compositio of gaseous mixture preset before ad after each small step ca be foud out at differet percetage bled (i.e α ). As a sample calculatio, for α = 0., the moles for differet compositios of gases ca be evaluated from the TABLE IV, for th step. (3) For Isetropic Expasio (rocess 34): The process 34 of isetropic expasio is simulated i a similar maer as process. The proposed umerical model usig (), is simulated usig MATLAB codes. The result obtaied are plotted Fig., 3 ad 4. For each process the umber of divisio take is 00. A sigle cylider 4stroke direct ijectio diesel egie is used for all calculatios. It is observed from the variatio of efficiecy with equivalece ratio plotted i Fig. that the efficiecy decreases as φ icreases ad is maximum for B0 ad B40. This is due to rich mixture available for combustio. 9

4 Iteratioal Coferece o Mechaical ad Robotics Egieerig (ICMRE'0) May 67, 0 huket The variatio i work output with φ is plotted i Fig. 3 ad is foud to be maximum for B0 ad B40 i all rage of φ. It shows that B0 ad B40 formed good mixture amogst other bleds. I fig 4, it is further observed that 00% biodiesel bled is havig maximum temperature of the cycle is miimum amogst other bleds, which costraits the formatio of NO x. iv. It has also bee observed that efficiecy of pure biodiesel is comparatively lesser tha all other bleds, but the maximum cycle temperature for this bled is least. This idicates that NOx emissio is ot preset i case of pure diesel; hece pure biodiesel ca be used resultig i less pollutio despite of less efficiecy & work output. Fig. LOT OF EFFICIENCY WITH EQUIVALENCE RATIO Fig. 3 LOT OF WORK DONE WITH EQUIVALENCE RATIO IV. CONCLUSION From the results ad discussios preseted i the precedig sectio followig importat coclusios are draw. i. The thermal efficiecy of a pure diesel egie decreases expoetially from 67% to 47% as the equivalece ratio icreases from 0.7 to.3. The decreasig tred is obvious also sice icrease i equivalece ratio implies rich mixture. ii. B0 ad B40 have obtaied the maximum cycle temperature amogst all the other bleds. So it ca be cocluded that B0 ad B40 forms a good mixture amogst all other bleds ad yield good efficiecy compared to the other bled, The maximum temperature of the cycle approaches to NOx formatio temperature. iii. A sharp icrease i work output is observed as the equivalece ratio icreases due to more fuel ijectio. Fig. 4 LOT OF MAXIMUM TEMERATURE WITH EQUIVALENCE RATIO V. REFERENCES [] J. I. Ramos, Comparisos betwee thermodyamic ad oe dimesioal combustio models of sparkigitio egies, Departmet of Mechaical Egieerig, CaregieMelto Uiversity. ittsburgh, esylvaia, 53, USA, 986. [] F. ayri ad J. Beajes, A pheomeological combustio model for direct ijectio, compressio igitio Egies, Departmet of Thermal Egies, olytechic Uiversity of Valecia Apdo, 0, 4607, Valecia, Spai, 986. [3] Z. Liu ad G. A. Karim, Kock characteristics of DualFuel egies Fuelled with Hydroge Fuel, J. Hydroge Eergy, Vol. 0, pp. 9994, 995. [4] G. De Nicolao, R. Scattolii ad C. Siviero, Modellg the Volumetric efficiecy of IC Egies: arametric, No arametric ad Neural techiques, II: S (96)00505, Vol. 4, No. 0, pp , avia, 996. [5] D. Zhag ad S. Ii. Frakel, A Numerical Study of atural gas combustio i a lea bur egie, II: SOOl636(98)0@0489 Fuel Vol. 77, No., pp , Thermal Sciece ad ropulsio Ceter, School of Mechaical Egieerig, urdue Uiversity, 998. [6] U. Kesgi, Study o the desig of ilet ad exhaust system of a statioary iteral combustio egie, Departmet of Naval Architecture, Yildiz Techical Uiversity, TR , Besiktas, Istabul, Turkey, 58 87, 005. [7] Z. Sahi, O. Durgu, Multizoe combustio modelig for the predictio of diesel egie cycles ad egie performace parameters, Karadeiz Techical Uiversity, Trabzo, Turkey, 45 56, 008. [8] Y. She, J. Bedford, I. S. Wichma, Thermodyamic modelig of direct ijectio methaol fueled egies, Applied Thermal Egieerig, 9, , Michiga State Uiversity, USA, 008. [9] Y. Ra, R. D. Reitz, A combustio model for IC egie combustio simulatios with multicompoet fuels, Egie Research Ceter, Uiversity of WiscosiMadiso, 00. [0] D. Ghosh, Combustio modelig of Hydroge aided Dieselroducer gas dual fuel compressio igitio egie, Birla Istitute of Techology, Mesra8355, Rachi, 008. [] V. I. Golovitchev ad J. Yag, The costructio of the combustio models for RME Biodiesel fuel for ICE applicatio, Departmet of Applied Mechaics, Chalmers Uiversity of Techology, S4 96, Göteborg, Swede, 009. [] 9

5 Iteratioal Coferece o Mechaical ad Robotics Egieerig (ICMRE'0) May 67, 0 huket TABLE IV: NUMBER OF MOLES FOR DIFFERENT COMONENTS Compoets th iterval before combustio th iterval after combustio Diesel ( x) dm ( x) f { ( x) dm } x f CO ( x) ( ( x ) ) ( x) ( ( x ) ) 3.4 ( ) 3.4 N 0.79 m air 0.79 m air H O O ( x) ( x ) 4. ( ) ( x) ( ( x ) ) ( ) dmf x ( x) ( x ) 4. ( x) ( x ) dmf x 93