Effect of n-Butanol Blending with a Blend of Diesel and Biodiesel on Performance and Exhaust Emissions of a Diesel Engine

Published: June 22, 2011

r 2011 American Chemical Society 9425 dx.doi.org/10.1021/ie201023f | Ind. Eng. Chem. Res. 2011, 50, 9425–9430

ARTICLE

pubs.acs.org/IECR

Effect of n-Butanol Blending with a Blend of Diesel and Biodiesel onPerformance and Exhaust Emissions of a Diesel EngineS) ehmus Altun,*,† Cengiz €Oner,‡ Fevzi Yas) ar,§ and Hamit Adin||

†Faculty of Technical Education, Batman University, 72100, Batman, Turkey‡Technology Faculty, Fırat University, 23119, Elazı�g, Turkey§Dept. Refinery and Petro-Chemistry, Batman University, 72100, Batman, Turkey

)Dept. Mechanical Engineering, Batman University, Batman 72100, Turkey

ABSTRACT: Experimental work was conducted to evaluate the effect of using n-butanol (normal butanol) in conventional dieselfuel�biodiesel blends on the engine performance and exhaust emissions of a single cylinder direct injection compression ignitionengine with the engine working at a constant engine speed and at different three engine loads. A blend of biodiesel and diesel fuelknown as B20 (20% biodiesel and 80% diesel in volume) was prepared, and then n-butanol was added to B20 at a volume percent of10% and 20% (denoted as B20Bu10 and B20Bu20, respectively). Fuel consumption; regulated exhaust emissions such as nitrogenoxides, carbon monoxide, and total unburned hydrocarbons; and smoke opacity were measured. The brake specific fuelconsumption of fuel blends was found to be higher when compared to that of conventional diesel fuel. On the other hand, theaddition of n-butanol to the B20 fuel blend caused a slight increase in the brake specific fuel consumption and brake thermalefficiency in comparison to the B20 fuel blend. For exhaust emissions, carbon monoxide (CO) and hydrocarbon (HCs) emissionsdecreased, and NOx remained almost unchanged at low engine loads, while it decreased at high engine loads. Fuel blends alsoresulted in a sharp reduction of smoke opacity in the whole range of engine tests.

1. INTRODUCTION

Diesel engines are widely used for transportation, energyproduction, and agricultural and industrial applications becauseof their high fuel conversion efficiencies and durability. Petro-leum-based fuels are used in diesel engines, which have a widerange of use in many sectors. However, it is well-known thatpetroleum resources are limited and depleting day by day. Inaddition, pollutant emissions resulting from diesel combustionhave negative effects on both human health and the environment,so it is necessary to reduce these emissions in diesel enginesfueled with petroleum diesel fuels. The main regulated pollutantsin diesel engines are nitrogen oxides (NOx), carbon monoxide(CO), unburned hydrocarbons (HC), and smoke, and they havebeen regulated by the laws in many countries. Therefore, due tothe depletion of petroleum resources and increasing environ-mental concerns, there is great demand for finding alternatives topetroleum-based diesel fuel. Biodiesel and alcohol fuels, cleanrenewable fuels, have received considerable attention in recentyears as alternative fuels in diesel engines. Biodiesel fuelsobtained from various sources such as soybean oil, rapeseedoil, sunflower oil, animal fats, etc. have offered a potentially veryinteresting alternative regarding pollutant emissions and avail-ability. In alcohols, methanol and ethanol are used most often asfuel additives in diesel engines. The major drawback in ethanol�diesel blends is that ethanol is immiscible in diesel over a widerange of temperatures,1 and also the addition of ethanol causes areduction in cetane number and lubricity of diesel fuels. Thebefore-mentioned blending problems can be reduced as a con-sequence of the progressive incorporation of biodiesel in com-mercial diesel fuel, because biodiesel fuels improve the stability of

the blends and compensate for the reduction in cetane numberand lubricity derived from the addition of ethanol.2 Thus, workson the use of blends containing biodiesel, diesel fuel, and alcoholin diesel engines have been performed, for example, see refs 3�5.The beneficial effects of using various blends containing thementioned fuels on performance and exhaust emissions andblending stability have been reported in experimental investiga-tions. Shi et al.3 investigated the emission characteristics of BE-diesel on a diesel engine. The results showed a significantreduction in PM emissions and an increase in NOx emissionsfrom BE-diesel. Total hydrocarbon (THC) from BE-diesel waslower than that from diesel fuel under most operating conditions.Ali et al.4 used 12 different blends of methyl tallowate, methylsoyate, ethanol, and diesel fuel in a Cummins N14�410 dieselengine and found that engine performance with these fuel blendsdid not differ to a great extent from engine performance withdiesel fuel. Qi et al.5 conducted an experimental investigation toevaluate the effects of using methanol as an additive to biodie-sel�diesel blends on the engine performance characteristics of adirect injection diesel engine under variable operating condi-tions. In that study, it was found that 5% by volume of methanolcan be mixed uniformly with a biodiesel�diesel blend withoutusing additives, but when the methanol content is more than 5%,it is necessary to add oleic acid as an additive to prevent phaseseparation of the blended fuel. Although the power and torque

Received: February 28, 2011Accepted: June 22, 2011Revised: June 21, 2011

9426 dx.doi.org/10.1021/ie201023f |Ind. Eng. Chem. Res. 2011, 50, 9425–9430

Industrial & Engineering Chemistry Research ARTICLE

outputs of fuel blends containing methanol were slightly lowerthan those of the biodiesel�diesel blend, fuel blends showed adramatic reduction in smoke emissions.

On the other hand, butanol, which can easily be blended withboth gasoline and diesel, has been drawing the attention ofresearchers. Butanol has properties which make it a suitableethanol replacement, having a higher energy content in additionto a significant improvement in mixing properties with petro-leum diesel fuels. Butanol has a lower autoignition temperaturethan methanol and ethanol. Therefore, butanol can be ignitedeasier when burned in diesel engines. Butanol also has a highercetane number; thus this makes it a more suitable additive thanethanol and methanol for diesel fuel.6 The attraction in butanolas an alternative fuel for diesel engines is due to the fact that ithas significant advantages over ethanol and methanol, espe-cially mixing properties. Investigation of butanol usage as dieselengine fuel has been conducted by researchers. It has been usedboth for blending gasoline and as a diesel fuel for IC engines.For example, the effect of iso-butanol/diesel fuel blends onengine performance and exhaust emissions was investigated byKarabektas) and Hos)€oz.7 They found a trend of reduced enginepower, brake thermal efficiency (BTE), and exhaust gas tem-perature and increased brake specific fuel consumption (BSFC)with an increase in the iso-butanol content in the blends. In thatstudy, the results compared with diesel fuel showed that COand NOx emissions decreased with the use of blends, while HCemissions increased considerably. However, it was reportedthat n-butanol/diesel fuel blends increased the BTE and theBSFC and decreased the exhaust gas temperature, with thesame trend in exhaust emissions.8,9 A drive cycle analysis in alight-duty turbo-diesel vehicle was carried out with two blendsof n-butanol (20% and 40%, by volume) and compared withdiesel fuel.10 The results showed that both HC and COemissions increased for the urban drive cycle, when largerquantities of n-butanol were added to the diesel fuel. In thesame study, HC and CO emissions were not significantlyimpacted, but NOx emissions showed a slight increase for thehighway drive cycle, when the n-butanol percentage increasedin the fuel blends. In addition, it was reported that a significantdrop in smoke density was observed for all n-butanol/diesel fuelblends. Butanol has also been used for blending die-sel�biodiesel or in vegetable oil blends for IC engines. Mehtaet al.11 used butanol/diesel/biodiesel blends in different ratiosto determine physical stability and various fuel properties. Inthat study, engine performance and emission tests were alsoconducted with these fuel blends. Lebedevas et al.12 showedthat the introduction of biobutanol in a three-componentmixture (diesel, butanol, and biodiesel) instead of ethanol ismore promising due to the better performance and environ-mental characteristics of the fuel. Lujaji et al.13 evaluated theeffects of blends containing croton oil (CRO), 1-butanol (BU),and diesel (D2) on the engine performance, combustion, andemission characteristics. It was reported that the addition ofbutanol in the blend reduced the brake thermal efficiency andcarbon dioxide and smoke emissions in comparison to those ofdiesel fuel.

In the present study, we investigated the effect of usingn-butanol (normal butanol) in conventional diesel fuel�biodiesel blends on the engine performance and exhaust emis-sions of a single cylinder direct injection compression ignitionengine with the engine working at a constant engine speed(2000 rpm) and at different engine loads.

2. MATERIALS AND METHODS

2.1. Properties of Experimental Fuels. The biodiesel em-ployed in this study was produced from cottonseed oil via a alkali-catalyzed transesterification process with methyl alcohol in thepresence of KOH as a catalyst. Cottonseed oil from Turkishcommercial sources was used to obtain cottonseed oil methylester (CSOME). The cottonseed oil was selected for biodieselproduction, as cottonseed is a major product of Turkey. Detailedinformation about the CSOME used in the experiments can befound in ref 14. Reidel-Haen brand n-butanol with a purity of>99% (Sigma-Aldrich), provided from the Refinery and Petro-Chemistry Laboratory of Batman University, Batman, Turkey,was used to prepare blends. The conventional diesel fuelemployed in the tests was obtained locally. Density, kinematicviscosity, heating value, and flash points of the fuels weredetermined using an Anton Paar densitometer model DMA5000, a Herzog kinematic viscosity meter model HVM 472, anIKAC2000 Basic Calorimeter, and aHerzog HFP360 closed-cupPensky Martens apparatus, respectively. These tests were per-formed in accordance with ASTM standards. The fuel-relatedproperties of biodiesel, diesel fuel, and n-butanol are presented inTable 1. It can be seen that the latent heat of evaporation ofn-butanol is 585 kJ/kg, which is higher than that of other fuels.The heating value of biodiesel is approximately 9.5% lower andthat of n-butanol is 22.5% lower than that of diesel fuel. Theviscosity of biodiesel is evidently higher than that of n-butanoland diesel fuel. The oxygen content of n-butanol is 21.6% andhigher than that of biodiesel. Furthermore, CSOME has higherdistillation temperatures than that of diesel fuel. Contrary to theinitial distillation temperature, the final distillation temperaturefor CSOME was lower than that of diesel fuel.2.2. Engine Test Setup and Procedure. Experiments were

carried out in the Engine Test Laboratory of the AutomotiveDepartment of Technical Education Faculty at the University ofBatman. The schematic diagram of the experimental setup isshown in Figure 1. A Rainbow-186, single-cylinder, four-stroke,air-cooled, naturally aspired direct injection diesel engine wasused for engine tests. The basic specifications of the engine areshown in Table 2. Engine tests were conducted on a BT-140model hydraulic dynamometer. The required engine load wasobtained through the dynamometer control. A CAPELEC CAP3200 brand exhaust gas analyzer was used to measure emissionsof the test fuels. An exhaust gas measuring device determines theemissions of CO and HC by means of infrared measurement(nondispersive infrared) and NOx by means of electrochemicalsensors. An infrared temperature measurement device was usedto specify the exhaust temperature. The exhaust temperature was

Table 1. Fuel Properties of Biodiesel, n-Butanol, and DieselFuel

parameters diesel biodiesel n-butanol

kinematics viscosity, mm2/s (at 40 �C) 2.72 4.34 3.6

lower heating value, kJ/kg 42700 38630 33100

density, kg/m3 (at 15 �C) 825.6 883.9 810

cetane number 47 56a 25

oxygen, % weight � 11 21.6

latent heat of evaporation, kJ/kg 250 230 585

boiling point (�C) 365 347 118a Estimated from cetane numbers of individual methyl esters.



measured from the external surface of the exhaust manifold usingan infrared temperature measurement device. The fuel consump-tion was measured with burettes with 50 and 100 mL volumesand a stopwatch. The accuracy of the measurements and theresults of uncertainty analysis of the calculated results are shownin Table 3. Four fuels were prepared: conventional diesel fuel as abaseline fuel, a 20 vol% cottonseed oil methyl ester and 80%diesel fuel blend known as B20, B20Bu10 (a blend of 10%n-butanol and B20 in volume), and B20Bu20 (a blend of 20%n-butanol and B20 in volume). A series of tests was conductedusing each of the fuel blends and diesel fuel, with the engineworking at a speed of 2000 rpm at three engine loads of 6.5 N m,11.6 N m, and 17.8 N m. Each test was repeated three times toreduce experimental uncertainties, and the results of the threerepetitions were averaged. For every fuel change, the fuel tankand lines were cleaned. Before running the engine to a new fuel, itwas allowed to run for some time to consume the remaining fuelfrom the previous experiment. In each test, brake torque, engine

speed, fuel flow rate, exhaust temperature, and exhaust emissionswere measured. Significant engine performance parameters suchas brake specific fuel consumption (BSFC) and brake thermalefficiency (BTE) for each fuel tested were calculated.

3. RESULTS AND DISCUSSION

3.1. Engine Performance. Figure 2 shows the results of brakespecific fuel consumptions (BSFCs) and thermal efficiency(BTE) of the direct injection diesel engine fueled with diesel,B20, B20Bu10, and B20Bu20 with respect to engine load at anengine speed of 2000 rpm. The BSFCwas found to decrease withan increase in load for all tested fuels, as can be seen in Figure 2.From the results, it is observed that the brake specific fuelconsumption for all of the fuel mixtures is slightly higher thanthat of diesel under the whole range of engine loads, with theincrease being higher the higher the percentage of the n-butanolin the blend. An increase in fuel consumption is the expectedresult since the loss of heating value of fuel mixtures must becompensated with a higher fuel consumption to maintain thesame torque output. As shown in Table 1, the maximum LHVbelongs to diesel fuel, followed by biodiesel, and the lowest onebelongs to n-butanol. Therefore, when using fuel mixtures, alarger amount of fuel is required for supplying the same amountof energy in the cylinder because of their lower heating values.Figure 2 also shows an increase in the efficiency with an increasein the engine load. For all fuel mixtures, brake thermal efficiencywas slightly lower than that of diesel fuel. The brake thermalefficiency is the inverse of the product of the brake specific fuelconsumption and the lower heating value of the fuels. Therefore,BTE values calculated for diesel fuel are higher than those of fuelmixtures. Furthermore, for fuels containing n-butanol, BTE washigher than that of B20. This could be attributed to the presenceof an increased amount of oxygen in fuels containing n-butanol,

Figure 1. A schematic diagram of the engine setup.

Table 2. Technical Specifications of the Test Engine

type of engine

rainbow�186 four stroke, air cooled,

single cylinder DI diesel enginevolume 406 cm3

compression ratio 18/1

maximum engine speed 3600 ( 20 rpm

cooling system air cooling

injection pressure 19.6 ( 0.49 MPa

medium piston speed 7.0 m/s (at 3000 rpm)

intake valve open 14� crank angle BTDCintake valve close 50� crank angle ATDCexhaust valve open 54� crank angle BBDCexhaust valve close 10� crank angle ABDC



which might have resulted in its improved combustion ascompared to diesel and B20.3.2. NOx Emissions. Figure 3 shows results of NOx emissions

of the direct injection diesel engine fueled with diesel, B20,B20Bu10, and B20Bu20 with respect to engine load at an enginespeed of 2000 rpm. From the results, it can be seen that the NOx

emissions increased with an increase of the engine load for alltested fuels. This may be due to a higher combustion temperatureinside the cylinder at a higher load, as a greater amount of fuel isburned at higher loads. One can also observe that the NOx

emitted by fuel mixtures is slightly lower than that of diesel fuel,with the reduction being higher the higher the percentage ofn-butanol in the blend. This may be attributed to the enginerunning “leaner” overall and the temperature lowering effect ofthe butanol (due to its lower calorific value and its higher heat ofevaporation) having a dominant influence, against the opposingeffect of the lower cetane number (and thus longer ignitiondelay) of the butanol, leading possibly to higher temperaturesduring the premixed part of combustion.9 Furthermore, at highloads, the reduction in NOx emissions was higher than that ofunder low load conditions.

3.3. Exhaust Temperature. Figure 4 shows a comparison ofexhaust temperatures of the direct injection diesel engine fueledwith diesel, B20, B20Bu10, and B20Bu20 with respect to engineload at an engine speed of 2000 rpm. It is observed from this figurethat the exhaust temperatures for all fuel mixtures are slightly lowerthan that of diesel fuel. One can also observe from this figure thatfuels containing n-butanol tend to produce a little higher exhausttemperature values than that of B20, with this increase being higherthe higher the percentage of n-butanol in the blend as well as thehigher the engine load. The reason may be that the premixedburning heat release is higher for fuels containing n-butanol owingto the better volatility of n-butanol, which promotes the formationof more of the air�fuel mixture in the premixed burning phase.Normally, an increase in the premixed fraction results in moreenergy being released over a short time scale close to top deadcenter with a nearly constant combustion chamber volume, result-ing in higher pressure gradients and in-cylinder gas temperatures.3.4. HC Emissions. Figure 5 shows the results of unburnt HC

emissions from the engine tests fueled with the four differentfuels. It can be seen in Figure 5 that there is a slight decrease in theHC emissions with fuel mixtures as compared to diesel fuel

Table 3. Accuracy of the Measurements and Uncertainties inthe Calculated Results

parameter measuring range accuracy

load 250 N m max. (2 N m

speed 7500 rpm max. (25 rpm

time (0.1s

temperatures �32 to +545 �C (1%

HC 0�20 000 ppm (1 ppm

CO2 0�20% (0.1%

CO 0�15% (0.001%

O2 0�21.7% (0.01%

NOx 0�5000 ppm (1 ppm

smoke 0�100% (0.1%

calculated results uncertainty

BSFC (2.5% max.

BTE (2.5% max.

Figure 2. Comparison of brake specific fuel consumption and brakethermal efficiency when the diesel engine is fueled with fuel mixtures anddiesel fuel.

Figure 3. Concentration of nitrogen oxides (NOx) in exhaust gaseswhen the diesel engine is fueled with fuel mixtures and diesel fuel.

Figure 4. Comparison of exhaust gas temperature when the dieselengine is fueled with fuel mixtures and diesel fuel.



operation. At high loads, the reduction in HC emissions from thecombustion of the fuel mixtures was lower than that of under lowload conditions. On average, the HC emissions of B20, B20Bu10,and B20Bu20 compared to those of diesel fuel decreased by 7.4%,15.8%, and 22.3%, respectively. Biofuels provide more oxygen inthe fuel, which enhances the combustion of fuel mixtures, andhence HC emissions reduce. Besides, the final distillation tem-perature of diesel fuel is higher than that of biodiesel andn-butanol. Therefore, a higher final distillation temperature ofdiesel fuel might increase HC emissions.3.5. CO Emission. Figure 6 shows the carbon monoxide (CO)

emissions for diesel fuel and blended fuels. It can be seen that COemissions produced by fuel mixtures are lower than that of dieselfuel, with the reduction being higher than the percentage ofbiofuel in the fuel blends. In contrast to airborne oxygen, the fuel-based oxygen accelerates the combustion process fromwithin thefuel-rich spray patterns themselves. A more complete combus-tion caused by the increased oxygen content in the flame comingfrom the biofuel molecules can be pointed out as the main reasonfor the reduction of CO emissions. As can be seen in Figure 6, theminimumCOemission values were obtained for B20Bu20 due to

a higher oxygen content than in the other fuels. It is agreed thatthe fuel-borne oxygen is more effective than the external oxygensupplied with the air for reducing CO emissions since theaspirated air mass remains the same.3.6. SmokeOpacity. Smoke curves of the four fuels are shown

in Figure 7. From the results, it can be seen that the smokeemissions for all fuel mixtures are significantly lower than that ofdiesel fuel in the whole range of the engine tests. The smokeemissions for B20, B20Bu10, and B20Bu20 were lower than thatof diesel by 20.5%, 27.9%, and 35.2%, respectively, on average.From these results, it is agreed that the more oxygenated fueladded in, the greater the reductions of smoke emissions were.

4. CONCLUSIONS

The following conclusions can be drawn from the experi-mental results:

For all of the fuel mixtures, the brake specific fuel consumptionshowed an increase, whereas brake thermal efficiency showed adecrease as compared to conventional diesel fuel for the sametorque output. Besides, the addition of n-butanol in the B20 fuelblend resulted in improved brake thermal efficiency. Fuel mix-tures resulted in significant reductions in considered emissions.Nitrogen oxide (NOx) emissions also decreased with the use ofall fuel mixtures, with this effect being more appreciable underhigh loads. Also, fuel mixtures resulted in a sharp reduction ofsmoke opacity in the whole range of the engine tests. Theaddition of n-butanol in the B20 fuel blend performed better interms of performance and exhaust emissions than the biodiesel�diesel blend. Taking these facts into account, biodiesel, conven-tional diesel fuel, and n-butanol mixtures can be considered to bepromising alternative fuels for diesel engines.

’AUTHOR INFORMATION

Corresponding Author*Tel./Fax: +90488-217-3675/+90488-215-7201. E-mail: [email protected].

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Figure 5. Concentration of hydrocarbons (HCs) in exhaust gases whenthe diesel engine is fueled with fuel mixtures and diesel fuel.

Figure 6. Concentration of carbon monoxide emissions (CO) inexhaust gases when the diesel engine is fueled with fuel mixtures anddiesel fuel.

Figure 7. Change in smoke when the diesel engine is fueled with fuelmixtures and diesel fuel.



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Documents

Effect of n-Butanol Blending with a Blend of Diesel and Biodiesel on Performance and Exhaust Emissions of a Diesel Engine