Effect of exhaust gas recirculation and intake pre-heating on performance and emission characteristi

J. Cent. South Univ. (2012) 19: 1346-1352包SpringerDOI: 100751710121148-15Effect of exhaust gas recirculation and intake pre-heating onperformance and emission characteristics of dual fuel engines at part loadsA. Paykani', R. Khoshbakhti Saray, M T. Shervani-Tabar, A. Mohammadi-Kousha'1. Department of Automotive Engineering, Iran University of Science and Technology,Narmak, Tehran 1684613114, lran;2. Department of Mechanical Engineering, Sahand University of Technology, Sahand New City, Tabriz, Iran;3. Department of Mechanical Engineering, University of Tabriz, Tabriz, IranC Central South University Press and Springer-Verlag Berlin Heidelberg 2012Abstract: Achieving simultaneous reduction of NO,, CO and unburned hydrocarbon (UHC) emissions without compromising engineperformance at part loads is the current focus of dual fuel engine rescarcb. The present work focuses on an experimental investigationconducted on a dual fuel (diesel-natural gas) engine to examine the simultancous ffect of inlet air pre-heating and exhaust gasrecirculation (EGR) ratio on performance and emission characteristics at part loads. The use of EGR at high levels seems to beunable to improve the engine performance at part loads. However, it is shown that EGR combined with pre-heating of inlet air canslightly increase thermal efficiency, resulting in reduced levels of both unburmed hydrocarbon and NO, emissions. co and UHCemissions are reduced by 24% and 31%, respectively. The NO, emissions decrease by 21% because of the lower combustiontemperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.Key words: dual fuel engine; exhaust gas recirculation (EGR); emision; performnance; venturi EGR systemand igmite the flame of the CNG in the combustion1 Introductionchamber [4].Dual fuel engine is one of the possible short-termThe concept of using alternative gaseous fuel insolutions to reduce emissions from traditional dieseldiesel engines has gained worldwide attention.engines, meanwhile, utilizing an altemnative fuel likeIncreasing fossil fuel prices and the deterioration tonatural gas as primary fuel. It consequently results in notenvironment have led to the scarch for alternative fuelsonly an interesting technology to meet future emissionsince past several years. Natural gas is one such fuelregulations, but also a powerful solution to retrofitavailable in large quantities in many parts of world atexisting engines [5]. In this method, natural gas isattractive prices. It is a clean burming fuel as compared topremixed with fresh air in the intake manifold, whichthe conventional liquid fuels like diesel or gasoline. It .then undergoes a multi-point ignition due to thehas a high octane number and therefore it is suitable forcompression-ignition and combustion of a pilot dieselengincs with relatively high compression ratio [1 -2]. Itsfuel spray. Then, flame propagates through the premixedself ignition temperature is 730 °C and it requires intensenatural gas mixture. Thus, dual fucl operation withsource of energy to enable combustion, i.e. glow plug,natural gas fuel can yield a high thermal efficiencyspark plug or pilot liquid fuel. It mixes rapidly with air toalmost comparable to the same engine operating onform homogenous air fuel mixture forefficientdiesel fuel at higher loads. However, engine performancecombustion inside engine cylinder and substantaland emissions suffer at low loads when operating io dualreduction in harmful emissions [3]. There are twofuel mode [6- -7]. During part load engine operation, themethods for converting diesel engine to utilize naturalfuel gas supply is reduced by means of a gas controlgas as the main fuel. The first method is to utilizevalve. However, a simultaneous reduction of the aircompressed natural gas (CNG) fully in diesel enginesupply decreases the air quantity induced. Hence, th(known as the CNG dedicated conversion). In thiscompression pressure and the mean efective pressure ofmethod, the engine cylinder head should be changed tothe engine decrease. This would finally lead to a drop inimplement an ignition system and a CNG injector. The中国煤化工_this is resulted fromsecond method is the dual-fuel conversion using CNG asoveraEat low loads.the main fuel and pilot diesel fuel to start combustionThe:YHC N M H Gnd burn slowly [8].Received date: 2011 07- -20; Accepted date; 2011-09- -26Corresponding suthor: A. Paykani; PhD Candidate, Tel: +98- 9397905698; E-mail: a.paykani@gmnail.comJ. Cent. South Univ. (2012) 19: 1346-13521347The use of exhaust gas recirculation has been suggestedfuel engines at part loads. In order to meet futureto improve part load performance and emissionemission standards, EGR must be done over wider rangecharacteristics of dual fuel engines. The exhaust gaof engine operation, and larger EGR ratio will be needed.recirculation (EGR) may be used for improving part loadThus, utilizing a specific device to expand EGR area isoperation and reducing the exhaust emissions of NO。.necessary. In this work, the venturi type EGR system wasIntroduction of EGR has combinations of some of theseselected because it is rather effective for expanding theeffects [9]: 1) dilution effect, 2) chemical effect and 3)EGR range up to low engine load conditions.thermal effect.2 Experimentalsolve above mentioned issues [8]. Some researchersinvestigate the effect of hot and cooled EGR onAn experiment was carried out to investigate theperformance and emission characteristics of dual fueeffect of exhaust gas recirculation and pre-heating of theengines at part loads. KUSAKA et al [3, 10] ancinlet air on performance and emission characteristics ofDAISHO et al [11-12] studied experimentally the effectdual fuel engines at part loads. The engine used for theof EGR on combustion and exhaust emissioninvestigation was a single-cylinder, four-stroke, watercharacteristics of dual fuel engines with the objective ofcooled, indirect injection (Lister 8-1) dual fuel engineimproving their drawbacks at part loads. It was shownwhich was coupled to a direct curent (D.C.)that hot EGR with high ratios could improvedynamometer through a torque meter providing bothperformance and emission characteristics of thesetorque and speed measurements. The technicalengines at part loads. ABD ALLA et al [13-15]specifications of the engine are given in Table 1, and theconducted some experiments on a Ricardo E6 dual fuelschematic of the experimental setup is shown in Fig. 1.engine to investigate the effect of pilot fucl quantity andAir flow rate was derived from the measured pressureadmission of high ratio of EGR gases on the performancedrop across an orifice installed on a surge tank. Massand exhaust emissions of dual fuel engines at part loads.flow rates of diesel and natural gas fuels were measuredTbe results showed that both of the methods couldby volumetric flow meters. Temperature of cooling water,improve performance and ermission characteristics exceptlubricating oil, inlet air and exhaust gas were alsofor NO, emission when using larger amounts of pilot fuel.measured to ensure proper engine operating conditions.PIROUZPANAH et al [16] conducted an experimentalThe engine is supplied with natural gas obtained from thestudy to determine performanceand emissionlocal distribution network. The inlet and exhaust aircharacteristics of an automotive direct injectiontemperatures were mcasured by K-type thermocoupledual-fuelled diescl engine. Cooled EGR was used tomade by Testo Co. Also, EGR line and an electric heaterresolve the poor light load performance of the engine.were designed and manufactured to enter differentThe results showed that at part loads, the application ofamountsof EGR to the intake charge. The exhaustEGR could considerably reduce CO and unbumedemissions, HC, CO, CO2 and NOx were measured byhydrocarbon (UHC) emissions. PIROUZPANAH et alAVL 4000 exbaust gas analyzer.[17- 18] investigated theoretically the combustionphenomenon of dual fuel engines at part loads and using2.1 EGR systemhot EGR to improve the mentioned drawbacks. ByThe EGR system used with the test engine was theemploying this technique, it was found that, lower ratiotype that exhaust gas was recirculated back into the inletof EGR considering its thermal and radical effects hadthe positive effect on performance and emissionTable 1 General specifcations of Lister (8-1) dual fucl cngineparameters of dual fuel engines at part loads.ItenSpecificationKHOSHBAKHTI et al [19 -20] investigatedypeFour strokeexperimentallyheemissionandperformanceNumber of eylinderscharacteristics of a dual fuel engine operating on naturalCombustion systemIDIgas with pilot diesel injection. The results of their workBore/mm114.1showed that the ignition delay and combustion durationsshorten sufficiently by increasing EGR ratio and itsStroke/mm139.7temperature to a specified level. Also, Co and UHCSwept volume/L1.43emissions reduce whereas NOx emission increases but中国煤化工17.5:not too much for low ratio of EGR.8/850This work touches upon investigating thMYHCNMHG 9.17simultancous effect of EGR and pre-beating of the inletair on performance and emission characteristics of dualInjection timing20 CA BTDC .1348J. Cent. South Univ. (2012) 19: 1346-1352Air tankOrificelined|[manometer| MhaenNG 2 NG valveExhaustmixerr区CprobeC]EGRExhaust gas .valvegY锦iDiesetanalyzertanktoTest engineDynamometerFig. 1 Schematic diagram of experimental setupmanifold where it mixes with air and natural gas and getsdrawn in:diluted with the intake charge which in turm acts as a=(14.532mp+16.684mNc)ms(2)diluents and reduces the peak combustion temperatureinside the combustion chamber. It includes a controlThe gas equivalence ratio, 中g，is defned as thevalve, pipes and venture, as shown in Fig. 1. To measureratio of the mass of the stoichiometric amount of airthe amount of EGR, the EGR ratio [16] was considered:required for the combu-tion of the gaseous fuel to themass of the actual amount of air drawn in:q:(CO2)(1)9o(CO2)qa-=(16.684mxc)ma(3where qn(CO2) and φo(CO2) are the volume fraction ofwhere ms, mp and mNG are the mass flow rates of air, pilotinlet CO2 and outlet CO2, respectively.and natural gas fuels, respectively.2.2 Test conditions examined3 Estimation of uncertaintyAfter starting the engine on diesel mode, differentperformance and emission tests were conducted on theAny experimental measurement possesses a certainengine at diesel mode to gain the base diesel engineamount of uncertainty. The uncertainty in anyperformance and emission characteristics at differentmeasurement may be due to either fixed or random errors.loads. Later, the diesel was reduced and the rest of inputAs the fixed errors are repeat nle in nature, they can beenergy was supplied by a venturi type mixer installed oneasily accounted for to get the true value of measurement.the intake manifold which can introduce suficientHowever, random errors have to be estimated onlyamount of natural gas fuel to operate engine in dual fuelanalytically. In this work, we repeated each measurementmode in various load conditions. During engine tests atfive times. These repetitions have been used for the errorpart loads, the amount of EGR which introduced to theanalysis of some of the parameters which wereengine increased progressively until the performance andintroduced in Table 2 as follows:ermission parameters were deteriorated. It is necessary to1) Outier excluding the unacceptable measuredmention that the amounts of pilot and natural gas fuclsvalues;were kept constant at each set of experiments to evaluate2) Standard deviation besides of the average valuesthe effect of EGR on the combustion, performance andto report each parameters error;emissionTotal equivalence ratio,中is defined as the ratio of中国煤化工y of the parametrsthe mass of the stoichiometric amount of air required for(powneasured pararnetersthe combustion of both of the gascous and the pilotusingrH.CNMHGfor cnhotmhediesel fuels to the mass of the actual amount of airmeasured values.1 Cent. South Univ. (2012) 19: 1346-13521349Table 2 Average uncertainties of some measured and calculatedthe mixture, widen its flammability limits and sustainsparametersflame propagation within relatively leaner mixtures [16].NoParameterUncertainty/%The chemical effect is associated with the participationof active free radicals present in exhaust gas to enhance1Speed1.1combustion by taking part in pre-ignition reactions.Temperature.8However, this effect causes an increase in thernalMass 0ow rate of air.7efficiency. With more EGR substitution, the thermalMass flow rate of diesel3.5efficiency falls. This is due to the dilution effect of theMass flow rate of natural gas4.1EGR used, as it depleted the oxygen present in thecombustion chamber {21].Oxides of nitogen2.2Unbumed hydrocarbons.90.22Cartbon monoxide.3一RecR=18 5%9EGR ratio0.20一. REGR- 13.5%4 Results and discussion昌0.18Io order to study the effects of EGR combined with美0.16intake preheating on performance and exhaust gasemissions of a dual fuel engine at part loads, according to0.14Table 3, the experiments were conducted at a constantengine speed of 730 r/min.0.1236038400Intake mixture temperatureKTable 3 Engine tests conditions for intake heating combinedwith EGR (Engine speed: 730 r/min, load: 1/5 full load, NGFg.2 Variation of brake themnal efficiency with intake mixiuretemperature at constant EGR flow rates (Load: 1/5, NG fraction.fnaction: 75%)75%)Intake mixtureCaseEGR ratio/%temperature/KFigure 3 represents the variation of oxides 037nitrogen with intake mixture temperature at constan:13.5EGR flow rates. It can be abserved that the NO403ermissions decrease as the EGR ratio increases. AConstant EGR ratio and425possible reason is the reduction of oxygen available forvariations of intakecombustion, and reduction of peak combustionmixture temperaturetemperature due to high specific heat capacity. On the38318.5other hand, the NO, emissions reduce with increase in420intake mixture temperature, so, the optimum intake440temperature in which the minimum NO, can be achievedis 410 K approximately. This can be explained by the17.5355fact that the inert gas included in the recirculated exhaustConstant intake mixturegas decreases the combustion temperature in spite of19temperature andintake pre -heating. However, NO, emissions tend tovariations of13.6increase at high intake mixture temperatures. Th16.5430presence of radicals can help to initiate the combustion19.5process, epecially with the increase of intake mixturetemperature due to mixing with exhaust gases. .4.1 Constant EGR percentage and variations ofhe diluents try to stop the reactions, the combinedintake mixture temperatureffects of radicals and intake temperature are dominant.Figure 2 shows the effects of pre-heating inlet airHence, the NO, increases with increasing intake mixturecombined with EGR at 75% natural gas fraction and 15%temperature.of full load. It is clear that remarkable improvements inzcarbons with intakethermal efficiency are obtained in this case. This is duem中国煤化工3GR flow rates isto the increased intake temperature. The increase of;[YHC N M H Garc considerable forintake temperatures will aceleratc the reaction rates ofhigh EGiR ratios. It can De seen unat increasing the intake1350J. Cent. South Univ. (2012) 19: 1346-13520.7r00 r一RecR-18.5%- - REcn=18.5%2 0.一REcR-13.5%一REGR=13.5%80 |.5.4 t60会0.320.2L40L36038044040020emixtuteateIntake mixture temperature/KFig.3 Variation of NO, emission with intake mixtureFig.5 Variation of carbon monoxide with intake mixturetemperature at constant EGR flow rates (Load: 1/5, NG fraction:75%)280It is well known that duel fuel operation remarkablyproduces lttle smoke emission. Moreover, combustion of260NG produces no particulates, so, the main source is pilot240injection of diesel. Since pilot injection of diesel is smallat low loads, less smoke is produced in this case. With220-EGR substiution, there is trade-off of NO, and smokeemission. With increasing EGR ratio, smoke opacity200increases. This is because of the decrease in the amount80 tof oxygen present in the combustion chamber with thesubstinution of EGR. Therefore, the smoke is not taken160into account in the present work.420.2 Constant intake mixture temperature andFig. 4 Variation of unburmed bydrocarbon with intake mixturevariations of EGR percentagetemperature at constant EGR flow rates (Load: 1/5, NG ftaction:Figure 6 shows the variation of brake thermalefficiency with different EGR flow rates at constantintake mixture temperatures. The brake thermalmixture temperature has a beneficial effect in reducingefficiency decreases slightly with increasing EGR flowunburned hydrocarbon emissions. One reason for this israte at both constant intake temperatures. The reductionthat a portion of the unburmed gases in the exhaust from18.0the previous cycle is recirculated and burmed in the一Intake mixture temperature: 355 Ksucceeding cycle. On the other hand, increasing intake--- Intake mixture temperature: 430 Kmixture temperature decreases ignition delay and results17.5in improvements in combustion process. At low loads,the flame cannot propagate successfully, which leads tothe increase in the UHC emissions.The variation of carbon monoxide with intake后16.5-mixture temperature at constant EGR flow rates is shownin Fig. 5. The CO variation follows a close trend with16.0increase in intake mixture temperature resulting indecrease in CO emission. The main reason for this trend15.5is perhaps due to overcoming the positive efects of EGR中国煤化工’25(ie. thermnal and radical effects) on is negative effects(i.e. chemical efect) [22]. Also, the high EGR ratiosFig.YHC N M H G&y with dferent EGRcreate a hotter environment, which makes theflow rares ar consant intakc mixlure temperatures (Load: 1/5,combustion to improve.NG fraction; 75%)」Cent. South Univ. (2012) 19: 1346-13521351in thernal efficiency is due to the EGR that results in400deficiency in oxygen concentration in combustionIntake mixture temperature: 430 Kprocess at part loads and larger replacement of air by一Intake mixture temperature: 355 K50 tEGR. The higher specific heat capacity of both CO2 andH2O and high flow rates of EGR reduce the average300 Icombustion temperature in the combustion chamber,resulting in the brake thermal efficiency to reduce.250Figure 7 depicts variation of oxides of nitrogen withdifferent EGR flow rates at constant intake mixture200temperatures. The NO, emissions reduce with increase inEGR ratio at constant intake mixture temperatures. The150 tcombustion temperature and local oxygen concentrationare dominant parameters for NO, formation. The1005015202presence of inert gases in the combustion chamberRecR/%reduces the peak combustion temperature, and also itFig. 8 Variation of unburmned hydrocarbon with dfferent EGRreplaces the oxygen in the combustion chamber. As aflow rates at constant intake mixture temperatures (Load: 1/5,result of reduction in both parameters, the NO, decreasesNG fraction: 75%)with EGR. However, at high EGR ratio, NO, emissionstend to increase. It can be due to the negative eects of20 r一Tntake mixture temperature: 430 KEGR that may overcome its positive effects.一- Intake mixture temperature: 355 K-Intake mixture temperature: 355 K1.4一Intake mixture temperature: 430 K8060，0.6-4010REGR/%Fig. 9 Variation of carbon monoxide with different EGR flow25rates at constant intake mixture tenperatures (Load: 1/5, NGReEGR/%fraction: 75%)Fig.7 Variation of oxides of nitrogen with diferent EGR flowrates at constant intake mixture temperatures (Load: 1/5, NGcombined with high intake mixture temperatures create ahotter environment, which accelerates the reaction ratesof mixture and as a result, makes the combustionThe variation of unburned hydrocarbon withimproved. However, CO emission tends to increase athigh EGR ratios. Also, this may be due to the partialtemperatures is shown in Fig.8. It can be seen that, UHCreplacement of oxygen in inlet air by inert gas, whichemissions are lower at high intake mixture temperatures,results in deficiency in oxygen concentration.whereas increasing EGR ratio causes a drop in unburnedbydrocarbon emissions. One reason for this is that the5 Conclusionspresence of radicals in the recirculated exhaust gases canhelp to initiate the combustion process, especially with1) Constant EGR ratios combined with variation ofthe increase of intake charge tenperature due to mixingintake mixture temperature can favorably increase brakewith exhaust gases.thermal efficiency; however, it can be observed that, byThe variation of carbon monoxide with differentemploying high ratio of EGR at a constant temperature,EGR flow rates at constant intake mixture temperaturesis depicted in Fig. 9. It is obvious that Co emission is中国煤化工。along with intakelower at high intake mixture temperatures, whilepre-heYHC N M H Grearbons as well asincreasing EGR flow rate results in a decrease in carbon carbon monoxlde emussions ana reauces nitrogen oxidesmonoxide emissions. This is due to the fact that the EGRdue to the presence of higher levels of diluted gases.1352」. Cent. South Univ. (2012) 19. 1346-13523) Constant intake mixture temperatures combinedH. Combsion and exhaut gas emisios cancersics of a diesedwith variation of EGR ratio result in large reductions inengine dual-fueled with natural gas [C] The 4thintermationalthermal fficiency and engine enmissions.symposium COMODIA. Kyolo, Japan, 1998: 555 660.4) By employing low ratio of EGR in comparison[川] DAISHO Y. TAKAHASHI K, IWASHIROSAITO T. Contolling combustion and exhaust emissions in a .with high ratio of EGR at a constant temperature,diect-injcction diesel engine dual fucled wih natural gas凹SAEthermal and radical effects of EGR may overcome itsPaper, 1995, 952436.dilution fects and vice versa.[12] DAISHO Y YAEO T. KOSEKI T, SAITO T. KIAHARA R.5) From the above point of view, EGR combinedCombustion and cxhaust emissions in a dirt ijgection Dieseeslenginewith pre-heating of inlet air reduces NO, unburneddul-fuele wih nanunl gs 0 SAE Paper, 195. 950465.hydrocarbon and CO emissions without deteriorating[13] ABDALLAGH, SOLIMAN HA, BADR OA, ABD RABBOOME.^ Compurational ivsigtion of the efe of exhaust gesengine thermal eficiency.recirculation on the petformance ofa dual fuel engine [0 SAE Paper,2000. 20001-2040.Acknowledgement[14] ABD ALLAG H, SOLIMAN HA BADRO A, ABD RABBOOME.This research is financially supported by Tabriz OilEfect of diluents adnissis and intake air temperature inexhaust gs recirculation on the emissions of an indirect ijcionRefinery Company, lran.dul fuel engine 4 Energy Coversion ad Mangemea, 2001, 42:1033- 1045.References[15] ABD ALLA G H, Using exhauet gas reirculrton in ineralcombustion engines川Enengy Conversion and Mangement, 2002,凹BAHR o. KARIM 0 A, Lu B. 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