Amercan Journal of Appled Scences, 2012, 9 (11), 1813-1817 ISS 1546-9239 2012 Scence Publcaton do:10.3844/ajassp.2012.1813.1817 Publshed Onlne 9 (11) 2012 (http://www.thescpub.com/ajas.toc) Gaseous Emssons and Combuston Effcency Analyss of Hydrogen- Desel Dual Fuel Engne under Fuel-Lean Condton 1,2 Prateep Chasermtawan, 1 Sompop Jarungthammachote, 1 Sathaporn Chuepeng and 2 Thanya Katwat 1 Department of Mechancal Engneerng, Faculty of Engneerng at S Racha, Kasetsart Unversty, 199 Sukhumvt Road, Chonbur 20230, Thaland 2 Department of Mechancal Engneerng, Faculty of Engneerng, Kasetsart Unversty, 50 gamwongwan Road, Bangkok 10900, Thaland Receved 2012-07-11, Revsed 2012-08-16; Accepted 2012-09-01 ABSTRACT Exhaust gas emssons from desel combuston usng alternatve fuel may change n ther quanttes that can affect exhaust gas after-treatment devces and envronmental ambent. Ths study presents theoretcal analyss of combuston generated emssons and effcency of hydrogen-desel duel fuel n fuel-lean condton. A chemcal equlbrum method by mnmzng Gbbs free energy s employed to estmate exhaust gas products from desel and hydrogen-desel mode combuston. The combuston products, e.g., unburned hydrocarbons (CH 4 ), hydrogen (H 2 ), carbon doxde (CO 2 ), carbon monoxde (CO) are comparatvely nvestgated, based upon smlar specfc energy nput. Subsequently, the obtaned combustble products (CH 4, H 2 and CO) are used to calculate combuston effcency, based upon chemcal energy left n waste exhaust gases. The man fndngs are assocated wth the reducton n CO 2 correspondng to the ncrease n combuston effcency n hydrogen-desel combuston mode, dependng on relatve ar-to-fuel ratos. Meanwhle, the CH 4, H 2 and CO contents n the flue gas ncrease n the operatng condtons used. Keywords: Equlbrum Analyss, Hydrogen, Dual Fuel, Desel Engne, Emssons, Combuston Effcency 1. ITRODUCTIO In present, desel s are appled n many works such as ndustral, agrculture and transportaton. Some advantages comparng to spark gnton (gasolne) are manly to offer better fuel converson effcency. Moreover, desel exhbts n fuel flexblty under varous operatng condtons, superor durablty, hgher thermal effcency and lower fuel consumpton. However, the desel s also have a few dsadvantages. Frstly, the exhaust gas conssts of hydrogen (H 2 ), carbon monoxde (CO), unburned hydrocarbons (uhcs), excess oxygen (O 2 ) and carbon doxde (CO 2 ). The latter s consdered as a major source of greenhouse effect. Secondly, the lack of fossl fuel makes t expensve n the desel fuel prce. From these reasons, desel vehcles, used n ndustry and transportaton have nvolved envronmental problems and need remedaton. An alternatve energy such as hydrogen s becomng a choce among others due to ts postve effects. It contans no carbon and has hgher energy densty when compared to fossl desel as well as ts global avalablty. Moreover, a trend of ncreasng use of hydrogen s prospectvely observed towards the future. Hydrogen can be found n chemcal compounds, e.g., natural gas, coal, bomass, water, as t does not exst by tself on Earth (Wllams, 1980). owadays, the most hydrogen producton s by reformng natural gas process (Pohl, 1995). In addton, pure hydrogen from water electrolyss s produced by fossl fuel burnng generated electrcty (Marrero-Alfonso et al., 2007), hydroelectrc, wnd energy and solar energy (Khaselev and Turner, 1998). Among such renewable resources, bomass converson s also a technque usually used for hydrogen producton (Cortrght et al., 2002). Padro and Lau (2000) lsted some other advanced technques for hydrogen generaton. A number of research works apply hydrogen for reducng the fossl fuels. Tomta et al. (2001) and Tsolaks et al. (2005) presented ther expermental fndngs on exhaust emsson effects from dual fuel desel operaton usng H 2. Kumar et al. (2003) lsted a Correspondng Author: Prateep Chasermtawan, Department of Mechancal Engneerng, Faculty of Engneerng at S Racha, Kasetsart Unversty, 199 Sukhumvt Road, Chonbur 20230, Thaland 1813
vable technology n hydrogen usage. Recently, Jarungthammachote et al. (2012) studed on thermodynamcs of hydrogen addton effects on desel operaton, some combuston characterstcs and ntrogen oxdes emssons, usng fnte dfference method. From the aforementoned reasons, there are yet some aspects of usng hydrogen as dual fuel wth fossl desel n terms of theoretcal analyss. Therefore, the man am of ths study s to analyze the combuston generated exhaust gas emssons and effcency of hydrogen-desel duel fuel mode. 2. MATERIALS AD METHODS The combuston of hydrogen-desel dual fuel was studed through the chemcal equlbrum method. The concept of mnmzaton of Gbbs free energy combned wth the energy balance was used. The amount of added hydrogen was vared to study ts effect on the combuston process. Moreover, the result of changng relatve ar/fuel rato was also observed. In every case, the compostons of exhaust gas, whch are CO 2, CO, H 2 O, H 2, 2, O 2 and HC represented by CH 4 and the combuston temperature were found. Then, the combuston effcency was evaluated. However, the calculatons n all cases were carred out based on smlar total energy nput. 2.1. Combuston Reacton of Hydrocarbon Fuel For desel fuel wth the emprcal formula CH y, the composton of the unburned and burned gas fractons can be theoretcally calculated usng a stochometrc combuston equaton, showng n Equaton 1: y C H y + 1 + (O 2 + 3.7 7 3 2 ) 4 y y = C O + H O + 3.7 73 1 + 2 4 2 2 2 (1) In such crcumstances the combuston can also be n fuel-rch or fuel-lean condton. Therefore, the relatve ar/fuel rato (λ) defned n Equaton 2 are used: λ (A/F) (A/F) actual = (2) stochometrc where, (A/F) actual s ar-to-fuel rato on mass bass used n real combuston and (A/F) stochometrc s chemcally correct or theoretcal proporton of ar and fuel on mass bass (Chuepeng and Komntarachat, 2010). 2.2. Chemcal Equlbrum Analyss The desel-hydrogen combuston equaton s shown n Equaton 3: C H + H + 22.5 λ (O + 3.773 ) = 15 27 2 2 2 15CO + 14.5H O + 2 2 (22.5λ 22.25)O + (22.5 3.773 λ) 2 2 (3) where, λ s relatve ar/fuel rato. From Equaton 1, t can be observed that, for lean fuel combuston, the major gas speces n exhaust gas are CO 2, H 2 O, excess O 2 and 2. The amount of each gas speces can be obtaned by usng mole balance concept. However, n the real combuston process, CO and H 2 can also be found n sgnfcant amount n the exhaust gas. Consderng CO, H 2 and ncomplete cracked hydrocarbon represented by CH 4, the smple mole balance method cannot fnd the number of mole of each gas speces. To evaluate the fnal product n complex chemcal reacton, lke combuston process, the chemcal equlbrum method s often used. Ths method s based on the concept that at equlbrum state, the total Gbbs free energy of the system has mnmum value. For the mult-reacton, sngle phase system, the total Gbbs free energy (G t ) can be expressed as Equaton 4: G t = n g (4) = 1 where, g and n are the chemcal potental and the number of mole of spece, respectvely. The problem s to fnd the set of whch mnmzes the total Gbbs free energy of system. In combuston system, the deal gas assumpton can be appled because of hgh temperature. Thus, the total Gbbs free energy for deal gas system can be calculated by Equaton 5: t o n G = n G f, + nrt ln = 1 = 1 n tot (5) o where, G f, s the standard Gbbs free of formaton of speces and R s the unversal gas constant. To fnd the mnmum value of G t, an optmzaton method, called Lagrange multplers, s used. The mass balance of each chemcal element s carred out and t s set as the constrant of ths problem. The obtaned fnal equaton s as Equaton 6: o n G f, + RT ln + Π a = 0 n k k tot k (6) where, a k s the number of atom of the k th element n a mole of the th speces. The values of k represent the Lagrange multplers. The desred soluton can be acheved be solvng equaton 6 wth constrant equatons. In ths problem, the mass balance equatons of chemcal elements found n reactants were appled as constrant equatons. To predct the combuston temperature, the energy balance equaton s formed as Equaton 7: n H (T ) = n H (T ) (7) r r r p p p r = react p= prod 1814
Fg. 1. Combuston temperature determnng dagram Fg. 2. The alteraton n combuston temperature from hydrogen dual fuel In Equaton 7, the energy loss from combuston system s assumed as zero. Hr and H p represent the enthalpes of reactants and products, respectvely. The combuston temperature, T p s mplctly obtaned from the enthalpy of product mxture. The step of calculaton can be shown as n Fg. 1. 2.3. Combuston Effcency Generally, there are stll combustble speces left n exhaust gas.e., CO, H 2 and unburned hydrocarbon. The hgher amounts of these speces reflect combuston neffcency. The combuston effcency (η c ) can be calculated usng Equaton 8: x Q η c = mɺ f Q HV m a + m ɺ ɺ f HV 1 100 (8) where, x are the mass fractons of CO, H 2 and CH 4 (obtaned from chemcal equlbrum analyss), Q HV are the lower heatng values of each speces and the subscrpts a and f denote ar and fuel, respectvely. 3. RESULTS 3.1. Combuston Temperature The temperature varaton of the desel-h 2 duel fuel combuston under fuel lean condtons s shown n Fg. 2. It has seen that the temperatures tend to reduce wth relatve ar-to-fuel ratos. However, there s only a subtle ncrease n the temperature when hydrogen s added to the combuston at constant relatve ar-to-fuel rato. 3.2. Exhaust Gas Emssons The combuston generated exhaust gas varatons,.e., H 2, CO, unburned hydrocarbon (CH 4 ) and CO 2 are shown n Fg. 3-6, respectvely. When hydrogen added to the ncreases, the amounts of H 2, CO and CH 4 n the exhaust gas are ncreased, dependng on relatve ar-to-fuel ratos. Meanwhle, the CO 2 composton n the exhaust gas s reduced when the ncreasng hydrogen s added to the. 1815
Fg. 3. The alteraton of H 2 emsson from hydrogen dual fuel Fg. 6. The alteraton of CO 2 emsson from hydrogen dual fuel Fg. 4. The alteraton of CO emsson from hydrogen dual fuel Fg. 7. The alteraton of combuston effcency from hydrogen dual fuel 3.3. Combuston Effcency The combuston effcences on the bass of energy left n unburned combustble products were calculated and are compared n Fg. 7. It has seen that almost all the effcences of the combuston are subtle ncreased when hydrogen s added, dependng on the relatve arto-fuel ratos. 4. DISCUSSIO Fg. 5. The alteraton of CH 4 emsson from hydrogen dual fuel In Fg. 2 the combuston temperature strongly depends on the fuel composton n the mxture to be combusted. As the relatve ar-to-fuel ratos ncrease, more ar s nduced n to the combuston chamber, resultng n lesser fuel proporton for burnng and thus, the reduced combuston temperature. Even the calculaton was accomplshed on the equvalent energy bass, the hydrogen added up to 10 molar percentage as a dual fuel 1816
operaton can generate the ncrease n temperature wthn 5 K as seen n the magnfed secton n Fg. 2. In Fg. 3-5, at a constant relatve ar-to-fuel rato, the hydrogen addton to the results n CO, H 2 and CH 4 left n the exhaust gas due to ncomplete combuston even n global fuel lean condton. At lower relatve ar-to-fuel ratos n Fg. 3, the lesser amount of the ar s nduced to the whle hydrogen s also added to the. Ths results n greater proporton of H 2 n the exhaust gas composton. Ths effect s also appled to Fg. 4 and 5 for the CO and CH 4, respectvely. Fgure 6 shows, at a constant relatve ar-to-fuel rato that the reducton of CO 2 when ncreasng n H 2 addton s as a result of lesser amount of desel that was substtuted by hydrogen s combusted. At lower relatve ar-to-fuel ratos, the lesser amount of the ar s nduced to the durng hydrogen addton. Ths results n greater reducton proporton of CO 2 n the exhaust gas composton. It s to note n Fg. 7 that the combuston effcency change s apparently at lower relatve ar-to-fuel ratos whle showng only subtle amount wthn 0.03% over the relatve ar-to-fuel ratos nvestgated. 5. COCLUSIO The combuston of hydrogen-desel dual fuel s analyzed usng a chemcal equlbrum model of Gbbs free energy mnmzaton and energy balance to frst determne combuston temperatures. The subsequent combuston temperatures and chemcal elements are nput to the solver to obtan gas-phase speces.e., CO 2, CO, H 2 O, H 2, 2, O 2 and CH 4. Combustble speces (CO, H 2 and CH 4 ) n the exhaust gases are combuston neffcency. It s found that CO 2 was reduced whle CO, H 2 and CH 4 ncreased. H 2 addton ncreases combuston effcency n majorty whle mantanng the effcency n very fuel-lean condtons. 6. ACKOWLEDGMET The present study was conducted at Kasetsart Unversty Sracha Campus. The authors would lke to thank the Kasetsart Unversty Research and Development Insttute (KURDI) for the provson of the research grant to ths project under the contract number V-T(D)173.53. The Kasetsart Unversty Center for Advanced Studes n Industral Technology under the atonal Research Unversty (RU) project s also acknowledged for the support to ths study. 7. REFERECES Chuepeng, S. and C. Komntarachat, 2010. Thermodynamc propertes of gas generated by rapeseed methyl ester-ar combuston under fuellean condtons. Kasetsart J. at. Sc., 44: 308-317. Cortrght, R.D., R.R. Davda and J.A. Dumesc, 2002. Hydrogen from catalytc reformng of bomassderved hydrocarbons n lqud water. ature, 418: 964-967. DOI: 10.1038/nature01009 Jarungthammachote, S., S. Chuepeng and P. Chasermtawan, 2012. Effect of hydrogen addton on desel operaton and O x emsson: A thermodynamc study. Am. J. Appled Sc., 9: 1472-1478. DOI: 10.3844/ajassp.2012.1472.1478 Khaselev, O. and J.A. Turner, 1998. A monolthc photovoltac-photo electrochemcal devce for hydrogen producton va water splttng. Scence, 280: 425-427. DOI: 10.1126/scence.280.5362.425 Kumar, M.S., A. Ramesh and B. agalngam, 2003. Use of hydrogen to enhance the performance of a vegetable ol fuelled compresson gnton. Int. J. Hydrogen Energy, 28: 1143-1154. DOI: 10.1016/S0360-3199(02)00234-3 Marrero-Alfonso, E.Y., J.R. Gray, T.A. Davs and M.A. Matthews, 2007. Hydrolyss of sodum borohydrde wth steam. Int. J. Hydrogen Energy, 32: 4717-4722. DOI: 10.1016/j.jhydene.2007.07.066 Padro, C.E.G. and F. Lau, 2000. Advances n Hydrogen Energy. 1st Edn., Sprnger, ISB-10: 0306464292, pp: 204. Pohl, H.W., 1995. Hydrogen and other Alternatve Fuels for Ar and Ground Transportaton. 1st Edn., J. Wley and Sons, Chchester, ISB-10: 0471953369, pp: 206. Tomta, E.,. Kawahara, Z. Pao, S. Fujta and Y. Hamamoto, 2001. Hydrogen combuston and exhaust emssons gnted wth desel ol n a dual fuel. SAE Int. DOI: 10.4271/2001-01-3503 Tsolaks, A., J.J. Hernandez, A. Megarts and M. Crampton, 2005. Dual fuel desel operaton usng H2 effect on partculate emssons. Energy Fuels, 19: 418-425. DOI: 10.1021/ef0400520 Wllams, L.O., 1980. Hydrogen Power: An Introducton to Hydrogen Energy and ts Applcaton. 1st Edn., Pergamon Press, Oxford, ISB-10: 0080254225, pp: 158. 1817