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Original Article

Proc IMechE Part D:J Automobile Engineering227(2) 261–271� IMechE 2013Reprints and permissions:sagepub.co.uk/journalsPermissions.navDOI: 10.1177/0954407012453231pid.sagepub.com

Experimental study on theperformance of and emissions froma low-speed light-duty diesel enginefueled with n-butanol–diesel andisobutanol–diesel blends

Xiaolei Gu1,2, Guo Li2,3, Xue Jiang1, Zuohua Huang1 and Chia-fon Lee2,4

AbstractThe effects of isobutanol- and n-butanol-enriched diesel fuel on the diesel engine performance and emissions are investi-gated. Neat diesel, 15% isobutanol–85% diesel, 30% isobutanol–70% diesel, 15% n-butanol–85% diesel, and 30% n-buta-nol–70% diesel blends are investigated in this study. The tests were carried out at light and medium loads and a fixedlow engine speed, and by using various combinations of the exhaust gas recirculation rate and the injection timing toinvestigate the effect of the molecular structure difference on soot formation. The results show that n-butanol–dieselblends give a longer ignition delay than isobutanol–diesel blends do. Hence isobutanol has a higher peak cylinder pres-sure and a higher premixed heat release rate than n-butanol does. Adding butanol (isobutanol and/or n-butanol) to dieselfuel is able to decrease the soot emissions substantially, while the change in the nitrogen oxide emissions varies slightly.Soot emissions from n-butanol–diesel blends are lower than those from isobutanol–diesel blends. Introducing exhaustgas recirculation and retarding the injection timing are effective approaches to decrease the nitrogen oxide emissions.However, a high exhaust gas recirculation rate leads to a loss in the fuel efficiency. The combination of a low exhaust gasrecirculation rate, later injection and butanol blends can achieve low-temperature combustion and simultaneouslydecrease the nitrogen oxide and soot emissions.

KeywordsIsobutanol–diesel, n-butanol–diesel, low-temperature combustion, soot

Date received: 13 March 2012; accepted: 7 June 2012

Introduction

To meet the stringent engine-out emission regulations,increasingly advanced engine technologies and strate-gies are adopted, such as exhaust gas after-treatment,multi-injection strategies, and clean alternative fuels.As is well known, the trade-off relationship betweennitrogen oxides (NOx) and particulate matter (PM)restricts the reduction in these emissions simultaneouslyin the conventional diesel engine. The local equivalenceratio f and temperature are the key factors for NOx

and PM formation. To shift outside both the NOx andthe soot ‘islands’ which are favorable for formation ofNOx and soot pollutants, several combustion strategiesare employed, such as mixing control combustion, low-temperature combustion (LTC), and premixed LTC.Introduction of exhaust gas recirculation (EGR) andretardation of injection timing are the most effective

approaches to achieve the LTC mode.1 In this paper,these two strategies are employed to realize LTC.

The large challenge for LTC is to provide as muchpremixed mixture as possible before the start of

1State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an

Jiaotong University, Xi’an, People’s Republic of China2Department of Mechanical Science and Engineering, University of Illinois

at Urbana2Champaign, Urbana, Illinois, USA3Department of Mechanical Science and Engineering, East China

University of Science and Technology, Shanghai, People’s Republic of

China4Center for Combustion Energy and State Key Laboratory of

Automotive Safety and Energy, Tsinghua University, Beijing, People’s

Republic of China

Corresponding author:

Zuohua Huang, State Key Laboratory of Multiphase Flow in Power

Engineering, Xi’an Jiaotong University, Xi’an, People’s Republic of China.

Email: [email protected]

combustion.2–4 Introduction of EGR can significantlyreduce the engine-out NOx emissions and can increasethe ignition delay time; both of these are beneficial toLTC. However, a large amount of EGR will reduce thein-cylinder oxygen content, will cause combustion todeteriorate and will increase the soot, carbon monoxide(CO), and unburned hydrocarbon emissions. To avoida high EGR rate, a fuel with a lower cetane numberand a higher volatility is necesssary. A fuel with a lowcetane number gives a longer ignition delay time forsufficient mixing and evaporation, and a high volatilityincreases the mixing rate. Gasoline, as the commonfuel, is the most widely used. Recently, the performanceand emissions of the diesel–gasoline blend called ‘diese-line’ were investigated in a partially premixed compres-sion ignition engine.5 However, with the increasingenergy demands and the limits of petroleum reserves,more attention is being paid to renewable alternativefuels such as alcohol fuels.5–11 Furthermore, alcoholfuels have a low cetane number and a high volatility,making them good candidates to meet futurerequirements.

Many studies have been conducted on the perfor-mance of and emissions from engines fueled withdiesel–alcohol blends,5,12 and most of these investiga-tions have concentrated on methanol and ethanol.Compared with ethanol and methanol, butanol hasmany advantages. First, it has a higher energy densitythan those of ethanol and methanol.13 Second, butanolcan be produced by fermentation of biomass, such ascorn, algae, and other celluloses. Third, butanol has ahigh cetane number which makes it more suitable as anadditive to diesel fuel.14 Also, n-butanol is much lesshygroscopic than ethanol and methanol are, preventingit from water contamination. Fourth, butanol is lesscorrosive to the materials in the fuel delivery and injec-tion system, which allows it to be used in the existingpipeline.

Extensive studies have been focused on the n-buta-nol–diesel blends. Rakopoulos et al.15 studied the per-formance, emissions, and combustion noise radiationcharacteristics of an engine fueled with biodiesel and/or

n-butanol–diesel blends. They reported a decrease inthe smoke and PM emissions with a moderate increasein NOx emissions. However, few studies have reportedresults from using isobutanol–diesel blends in dieselengines.16,17 Isobutanol is used as a chemical compoundin the food industry and can be produced from non-petroleum resources,18 e.g. agriculture crops; therefore,it is classified as a renewable fuel. Blending isobutanolwith diesel can maintain good stability for a long timewithout phase separation. Moreover, it has a lowerheating value that is higher than that of ethanol, whichis favorable for improving the engine performance anddecreasing the fuel consumption.

The injection timing plays an important role in com-pression ignition engines with different fuel blends.Paryri et al.19 used one-dimensional modeling to ana-lyze the influence of the use of biodiesels on thedynamic behavior of solenoid-operated injectors incommon-rail systems. Desantes et al.20 presented anexperimental comparison of three biodiesel blends in adirect-diesel-injection process using a standard injectionsystem. Yao et al.21 studied the effects of an n-butanoladditive and multi-injection on the performance of andemissions from a heavy-duty diesel engine. Their resultsshowed that the n-butanol additive could significantlyreduce the soot and CO emissions without largeincrease in the brake specific fuel consumption (BSFC)and the NOx emissions. The properties of the fuelsstudied are summarized in Table 1.

There are several motivations for the present study.First, isobutanol and n-butanol are butanol isomers.They have the same molecular formula, but differentmolecule structures. n-butanol is a straight-chain typeand isobutanol is a branched-chain type. Some studieshave shown that the soot precursor benzene increasedin the presence of the branched structure of butanol iso-mers.10,24 However, few studies have been made on die-sel engines. Second, both isobutanol and n-butanol areregarded as promising renewable biofuels; therefore,the effects of the addition of isobutanol or n-butanol todiesel fuel on the engine performance and emissions areworth studying. Third, the combustion characteristics

Table 1. Properties of fuels.22,23

Property (units) Value for the following

Diesel Ethanol Isobutanol n-butanol

Molecular structure C12–C25 C2H5OH CH3CH(CH3)CH2OH CH3(CH2)2CH2OHCetane number ’50 8 — 25Specific gravity at 20 �C (kg/m3) 809.6 794 802 810Viscosity at 40 �C (mm2/s) 1.9–4.1 1.08 . 2.63 2.63Solubility in water at 20 �C (wt %) Negligible Miscible 8.7 7.7Self-ignition temperature (�C) ’300 434 415.6 385Boiling temperature (�C) 182–288 78 107.9 117.7Lower heating value (MJ/L) ’42.5 21.4 26.6 26.9Saturation pressure at 38 �C (kPa) 0.13–1.3 16 3.3 2.2Latent heating at 25 �C (kJ/kg) \ 300 919.6 686.4 707.9Oxygen content (wt %) — 34.8 21.6 21.6

262 Proc IMechE Part D: J Automobile Engineering 227(2)

are also analyzed under LTC coupled with a low-cetane-number fuel.

Experimental set-up and procedures

Engine set-up

A naturally aspirated common-rail direct-injectionFord Lion V6 diesel engine with a water-cooled EGRsystem was used to conduct the study. The specifica-tions of the engine are shown in Table 2.

The engine was connected to an eddy-currentdynamometer. For monitoring and measuring the rele-vant properties of the intake air, fuel, oil, and coolingwater, various data acquisition devices such as thermo-couples and pressure transducers were installed. Anin-cylinder pressure transducer was installed in thecylinder in place of its glow plug to record the in-cylinder pressure history during combustion. Mean-while, a shaft encoder was mounted on to the crankshaft to determine the crank angle and location of thetop dead center. The signal of the cylinder pressure wasrecorded for every 0.25� crank angle. To eliminatecycle-by-cycle variations, the average value of 30 cycleswas used to calculate the heat release rate (HRR)from25

dqndu

=g

g � 1pdV

du+

1

g � 1Vdp

duð1Þ

Here dqn/du is the HRR, which is the differencebetween the chemical energy rate and the heat transferrate. g is the ratio of the specific heat at constant pres-sure to the specific heat at constant volume. p and Vare the cylinder pressure and the cylinder volumerespectively.

A LabVIEW program was developed to monitorthese data acquisition devices and to control the enginepedal signal. A programmable electronic control mod-ule (ECM) was applied, through which a variety ofengine operating parameters, such as the injection tim-ing and the EGR valve position can be monitored andadjusted using the software ETAS INCA coupled withthe engine’s ECM. The EGR rate is calculated from

EGRrate=½CO2�manifold

½CO2�exhaustð2Þ

By default, the ECM operates according to the origi-nal specifications of the engine. After connection isestablished between INCA and the ECM, the calibra-tions can be modified. In this study, the injection tim-ing and EGR are varied. EGR is achieved byinstalling a connection between the exhaust systemand the intake system and by providing a pressuredifferential to drive the flow. A restricting valve wasinstalled in the exhaust pipe, allowing the flow to berestricted and sufficient back pressure to be created todrive the EGR flow. Adjustment of EGR was accom-plished as follows. Under certain operating condi-tions, the positions of the EGR valves on the enginewere set manually through the INCA software. Theexhaust-flow-restricting valve and the EGR valvewere adjusted as needed to achieve the desiredamount of EGR. The schematic diagram of theexperimental set-up is shown in Figure 1.

Figure 1. Schematic diagram of the experimental set-up.EGR: exhaust gas recirculation.

Table 2. Engine specifications.

Engine type V-type, four-stroke dieselNumber of cylinders 6Bore (mm) 81Stroke (mm) 88Displacement volume (L) 2.7Displacement per cylinder (cm3) 453.46Clearance volume (cm3) 27.82Compression ratio 17.3:1Combustion system Direct injectionInjection system Common railInjector type Six nozzles, piezoelectricExhaust gas recirculation Water cooled

Gu et al. 263

Fuel tested

Three different fuels were used in this study. They areultra-low sulfur diesel 2 supplied by Illini FS, analysis-grade n-butanol, and isobutanol (99.7% purity). Twofractions of isobutanol–diesel blends and two fractionsof n-butanol–diesel blends are used, which are denotedas IB15, IB30, NB15, and NB30, corresponding to 15%isobutanol, 30% isobutanol, 15% n-butanol, and 30%n-butanol fractions respectively in the blends. Pure die-sel fuel was tested as the baseline fuel, which is labeledB0.

Test conditions

The engine was operated at a low speed of 1000 rev/minat two loads (0.3 MPa and 0.5 MPa brake mean effec-tive pressures). For each load, the EGR rate is changedfrom zero to the EGR rate when combustion deterio-rates (evaluated by high CO emissions). The injectiontiming is also varied. Variations in the injection timingsuse the following strategy. One pilot injection and onemain injection are used, and the interval between themis fixed. In other words, the pilot injection timing andthe main injection timing will be advanced or retardedsimultaneously. The ECM default injection timing atthe operating speed and load is used as the reference.The injection timing is advanced or retarded as far as 6�crank angle earlier or later than the default timing,using a 2� crank angle step. The ECM default injectiontimings are denoted as 0, while the advanced timingsand the retarded timings are labeled as 2 and +respectively.

Emission analyzer

All the emissions measured are the raw exhaust gasesbefore the after-treatment device. A MEXA-554JUexhaust gas analyzer was used to measure the concen-trations of oxygen, carbon dioxide, CO, and hydrocar-bons in the exhaust gases or the manifold mixture. Icebaths were installed in the sampling line to condensethe water vapor. A Horiba MEXA-720 NOx gas analy-zer was used to measure the NOx concentration with630ppm accuracy for the 0–1000ppm range, whilesoot measurement was performed using a standard fil-ter paper method. A clean filter paper was placed in thesmoke meter, and smoke was collected on the paper.The dark filter paper was then transferred to a digitalimage processor.

Results and discussion

Combustion characteristics

Figure 2 gives the in-cylinder pressure trace and HRRversus the crank angle for the three fuels without EGRat different values of the start of injection (SOI). Theresults show the bimodal distribution of the HRRs andthe pressure history for the two-stage fuel injection. The

combined effects of the low cetane numbers of the IB30and NB30 fuels, which give longer ignition delays thanthat of diesel fuel, and the high volatilities contribute tobetter fuel vaporization and fuel–air mixing. IB30 andNB30 fuels give higher peak HRRs than pure dieselfuel does, and this is due to the increase in the fuelburned in the premixed combustion mode for IB30and NB30 fuels. Moreover, IB30 gives a longer igni-tion delay than NB30 does, and this resulted from thelower cetane number for isobutanol.26 Advancing andretarding the SOI show that retarding the SOI resultsin a lower second peak of the in-cylinder pressure,suggesting an overall lower combustion temperature.It should be noted that the peak HRR due to the pilotinjection is high for a retarded injection timing as themain injection is retarded, and the pilot injection ispostponed as well, causing the fuel to be injected intoa hotter environment during the pilot injection as thepiston moves closer to the top dead center. However,the peak of the main HRR is almost the same in theabsence of EGR, regardless of the SOI. The peak ofthe main HRR increases rapidly when the injectiontiming is retarded for diesel fuel under the mediumload. The time difference between the end of the pilotheat release and the start of the main heat release islonger for diesel than for the isobutanol–diesel blendand the n-butanol–diesel blend. This increases theignition delay, which enhances mixing prior tosecond-stage combustion. Moreover, retarding theinjection timing results in a hotter environment, whichreduces the ignition delay for all the fuels. However,the isobutanol–diesel blend, n-butanol–diesel blend,and pure diesel have different ignition delay sensitiv-ities to this high temperature; compared with thehigher viscosity of isobutanol, n-butanol is more likelyto be volatile, resulting in a shorter ignition delay.The above-mentioned factors give the results shownin Figure 2.

The in-cylinder pressures and HRRs for B0, IB30,and NB30 at different EGR rates and SOIs are shownin Figure 3. Introduction of EGR increases the ignitiondelay for all fuels when the injection timing is fixed.The presence of EGR in the cylinder increases the spe-cific heat capacity of the intake mixture, leading toslow increases in the pressure and temperature in thecompression stroke. The ignition delays of IB30 andNB30 are more sensitive than that of B0. Introductionof EGR gives a higher peak of the main HRR at thedefault SOI condition. However, the combination ofEGR and the retarded injection timing gives a differentbehavior (IB30 and NB30 have lower peaks of the mainHRR than diesel fuel does), as shown in Figure 3(c).The ignition delays for B0, IB30, and NB30 give uniquebehaviors at the main heat release stage. NB30 gives ashorter ignition delay than those of both IB30 and B0,and IB30 gives a longer ignition delay than those of theother two fuels. The reasons for this are as follows. Onthe one hand, n-butanol and isobutanol with high vola-tilities have better evaporation than diesel does, which


Figure 3. Cylinder pressure and HRR versus crank angle for different fuels with different EGR rates and SOIs.SOI: start of injection; EGR: exhaust gas recirculation; BMEP: brake mean effective pressure; B0: pure diesel fuel; IB30: 30% isobutanol–70% diesel;

NB30: 30% n-butanol–70% diesel; ATDC: after top dead center.

Figure 2. Cylinder pressure and HRR versus crank angle for different fuels without EGR at different SOI timings and loads.SOI: start of injection; EGR: exhaust gas recirculation; BMEP: brake mean effective pressure; B0: pure diesel fuel; IB30: 30% isobutanol–70% diesel;

NB30: 30% n-butanol–70% diesel; ATDC: after top dead center.

Gu et al. 265

is favorable for mixing and formation of a combustiblemixture. On the other hand, n-butanol and isobutanolhave lower cetane numbers than that of diesel, whichincreases the ignition delay time. The result is the com-petition of these two factors, as shown in Figure 3(c).The LTC regime is achieved for IB30 and NB30 blendsat an EGR rate of 28% and retarded SOI, resulting insimultaneous reductions in the soot emissions and theNOx emissions.

Engine performance

The BSFCs at two loads for neat diesel and butanolblends versus the EGR rate are plotted in Figure 4.The BSFC increases monotonically with increasingamount of EGR introduced in all cases, as shown inFigure 4. However, at low EGR rates (below 20%), theBSFC is slightly higher than without EGR. Neat dieselfuel gives the lowest BSFC while IB30 gives the highestBSFC. This is reasonable since diesel has a lower heat-ing value that is the highest and isobutanol has a lowerheating value that is the lowest, as shown in Table 1.Advancing the injection timing relative to the default

SOI slightly decreases the BSFC. Retarding the injec-tion timing relative to the default SOI results in a rapidincrease in the BSFC, as shown in Figure 5. A similartrend is observed at the medium load. The exhaust tem-perature is given in Figure 6. It can be seen that n-buta-nol has a higher exhaust gas temperature than that ofisobutanol because to its lower heating value is higher.

Exhaust emissions

CO emissions. Figure 7(a) and (b) gives the relationshipbetween the CO emissions and the EGR rates andbetween the CO emissions and the SOIs respectivelyfor different fuels. It can be seen that the CO emissionsincrease slightly with n-butanol–diesel blends in com-parison with those for pure diesel fuel. The n-butanol–diesel blends produce lower CO emissions than theisobutanol–diesel blends do under different operatingconditions. This is probably because n-butanol has ahigh combustion temperature (Figure 6) throughoutthe cycle, which results in a high oxidation rate of COemissions.

Figure 5. BSFC versus SOI for different fuels.BSFC: brake specific fuel consumption; EGR: exhaust gas recirculation;

BMEP: brake mean effective pressure; SOI: start of injection; B0: pure

diesel fuel; IB15: 15% isobutanol–85% diesel; IB30: 30% isobutanol–70%

diesel; NB15: 15% n-butanol–85% diesel; NB30: 30% n-butanol–70%

diesel.

Figure 4. BSFC versus EGR rate for different fuels.BSFC: brake specific fuel consumption; SOI: start of injection; BMEP:

brake mean effective pressure; B0: pure diesel fuel; IB15: 15%

isobutanol–85% diesel; IB30: 30% isobutanol–70% diesel; NB15: 15% n-

butanol–85% diesel; NB30: 30% n-butanol–70% diesel; EGR: exhaust gas

recirculation.


NOx emissions. The NOx emissions versus EGR ratesfor different fuels are given in Figure 8. As shown inFigure 8, introducing EGR decreases the NOx emis-sions for all fuels. As the EGR rate is increased, thefresh air is diluted, and the combustion temperaturewill decrease, resulting in a decrease in the NOx emis-sions. The effectiveness of the reduction in the NOx

emissions is demonstrated within a certain range ofEGR rates. As the EGR rate increases up to a certainvalue, the NOx emissions remain at a very low leveland the decreasing rate will be small. For neat dieseland butanol–diesel blends, blending butanol with dieselgives different effects on the NOx emissions. On theone hand, butanol blends provide an oxygen-enrichedcombustion environment, which is favorable to NOx

formation because of the high concentration of oxygenradicals in the thermal NOx mechanism. On the otherhand, addition of butanol leads to better spay atomiza-tion and faster fuel evaporation, but the increase in theignition delay due to the low cetane number will in turnfurther promote fuel–air mixing. The final result is thecombined effects of these influences.

As indicated in Figure 9, retarding the SOI decreasesthe NOx emissions for all fuels. Advancing the injection

Figure 7. CO emissions versus (a) EGR rate and (b) SOI fordifferent fuels.CO: carbon monoxide: SOI: start of injection; BMEP: brake mean

effective pressure; B0: pure diesel fuel; IB30: 30% isobutanol–70% diesel;

NB30: 30% n-butanol–70% diesel; EGR: exhaust gas recirculation.

Figure 8. NOx versus EGR rate for different fuels.NOx: nitrogen oxides; SOI: start of injection; BMEP: brake mean


IB30: 30% isobutanol–70% diesel; NB15: 15% n-butanol–85% diesel;


Figure 6. Exhaust gas temperature versus SOI for differentfuels.EGR: exhaust gas recirculation; BMEP: brake mean effective pressure;

SOI: start of injection; B0: pure diesel fuel; IB30: 30% isobutanol–70%

diesel; NB30: 30% n-butanol–70% diesel.

Gu et al. 267

timing relative to the default SOI produces lower NOx

emissions from diesel than from butanol–diesel blends.However, retarding the injection timing produceshigher NOx emissions from diesel than from butanol–diesel blends. Retarding the injection timing relative tothe default SOI gives a longer ignition delay forbutanol–diesel blends than for diesel fuel. The NOx

emissions at the light load is more sensitive than at themedium load, especially to the variation in the SOI.

Soot emissions. As shown in Figure 10, introduction ofEGR increases the soot emissions. Within a certainrange of EGR rates, the soot emissions increase slightly.As more EGR is introduced into the intake manifold,the oxygen concentration is decreased and the localequivalence ratio is increased, promoting soot forma-tion in the early stage of combustion. Meanwhile, low-ering the combustion temperature in the presence ofEGR is unfavorable to soot post-flame oxidation. Acombined effect of these factors results in an increase inthe soot emissions at an increasing EGR rate. Blendingbutanol with diesel decreases the soot emissions

compared with those obtained with neat diesel fuel.Increasing the butanol fraction causes a further reduc-tion in the soot emissions. The n-butanol–diesel blendsproduce lower soot emissions than do the isobutanol–diesel blends. Isobutanol has a branched structure,which is favorable to soot precursor (benzene) forma-tion. This is consistent with previous research studies.27

Furthermore, n-butanol has a higher latent heat ofvaporization than that of isobutanol, which also facili-tates suppression of soot formation. As shown inFigure 11, the soot emissions produced by butanol–diesel blends are less sensitive than those produced byneat diesel fuel.

Figure 12 gives the relationship between the sootemissions and the NOx emissions for the B0, IB30, andNB30 fuels. At small and medium loads, the soot emis-sions and the NOx emissions for butanol–diesel blendsare low, indicating an obvious decrease in soot forma-tion over the entire range of test conditions when buta-nol is added. On the other hand, the combination ofhigh EGR, retarded injection timing, and lower cetanenumber fuel (n-butanol or isobutanol) can reduce thesoot emissions and the NOx emissions simultaneously

Figure 9. NOx versus SOI for different fuels.NOx: nitrogen oxides; SOI: start of injection; B0: pure diesel fuel; IB15:

15% isobutanol–85% diesel; IB30: 30% isobutanol–70% diesel; NB15:

15% n-butanol–85% diesel; NB30: 30% n-butanol–70% diesel; EGR:

exhaust gas recirculation; BMEP: brake mean effective pressure.

Figure 10. Soot versus EGR rate for different fuels.FSN: filter smoke number; SOI: start of injection; BMEP: brake mean


IB30: 30% isobutanol–70% diesel; NB15: 15% n-butanol–85% diesel;



at a low load. Soot and NOx can both be maintained atconsiderably low levels at high EGR rates and with aretarded injection, indicating realization of LTC.However, the BSFC is increased from the zero-EGRand default-injection-timing case. To obtain a accepta-ble fuel economy while maintaining low soot and NOx

emissions at a low load, the combination of a low EGRrate (20–23%) and appropriate retarded injection (laterthan the default timing) is necessary.

Conclusions

The effects of adding butanol (isobutanol or n-buta-nol) to diesel fuel on the engine performance andemissions are studied. The main conclusions are asfollows.

1. An engine fueled with an isobutanol–diesel blendhas a longer ignition delay, a longer premixed com-bustion duration, a higher peak cylinder pressure,and a higher premixed HRR than an engine fueledwith an n-butanol–diesel blend.

2. Butanol (isobutanol or n-butanol) addition caneffectively decrease the soot emissions with littlevariation in the NOx emissions. n-butanol produceslower soot emissions than isobutanol does.

3. A low EGR rate (less than 25%) can substantiallydecrease the NOx emissions while maintaining alittle increase in the soot emissions without areduction in the fuel economy. Retarding the injec-tion timing can decrease the NOx and soot emis-sions with a small decrease in the fuel economy.Blending butanol (isobutanol or n-butanol) withdiesel increases the ignition delay time and reducesthe soot emissions. Combination of EGR, retardedinjection timing, and blending butanol with dieselcan achieve LTC and simultaneously decrease theNOx emissions and the soot emissions with a smallreduction in the fuel economy.

Funding

This work is supported in part by the US Departmentof Energy (grant no. DE-FC26-05NT42634), and bythe US Department of Energy Graduate Automotive

Figure 11. Soot versus SOI for different fuels.FSN: filter smoke number; EGR: exhaust gas recirculation; BMEP: brake

mean effective pressure; SOI: start of injection; B0: pure diesel fuel; IB15:

15% isobutanol–85% diesel; IB30: 30% isobutanol–70% diesel; NB15:

15% n-butanol–85% diesel; NB30: 30% n-butanol–70% diesel.

Figure 12. Soot versus NOx for different fuels.FSN: filter smoke number; BMEP: brake mean effective pressure; EGR:

exhaust gas recirculation; B0: pure diesel fuel; IB30: 30% isobutanol–70%

diesel; NB30: 30% n-butanol–70% diesel; NOx: nitrogen oxides.

Gu et al. 269

Technology Education Centers of Excellence (grant no.DEFG26-05NT42622). This work is also supported bythe National Natural Science Foundation of China(grant nos 51136005 and 51121092).

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Appendix

Notation

dqn/du heat release rate per crank anglep cylinder pressureV cylinder volume

g ratio of the specific heatsf equivalence ratio

Abbreviations

BSFC brake specific fuel consumptionB0 pure diesel fuelCO carbon monoxideECM electronic control moduleEGR exhaust gas recirculationHRR heat release rateIB15 15% isobutanol–85% diesel


IB30 30% isobutanol–70% dieselLTC low-temperature combustionNB15 15% n-butanol–85% diesel

NB30 30% n-butanol–70% dieselNOx nitrogen oxidesPM particulate matterSOI start of injection

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