Effect of n-Butanol Blending with a Blend of Diesel and Biodiesel on

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

Faculty of Technical Education, Batman University, 72100, Batman, Turkey Technology Faculty, Fırat University, 23119, Elazıg, 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 diesel fuel biodiesel blends on the engine performance and exhaust emissions of a single cylinder direct injection compression ignition engine with the engine working at a constant engine speed and at different three engine loads. A blend of biodiesel and diesel fuel known as B20 (20% biodiesel and 80% diesel in volume) was prepared, and then n-butanol was added to B20 at a volume percent of 10% and 20% (denoted as B20Bu10 and B20Bu20, respectively). Fuel consumption; regulated exhaust emissions such as nitrogen oxides, carbon monoxide, and total unburned hydrocarbons; and smoke opacity were measured. The brake specific fuel consumption of fuel blends was found to be higher when compared to that of conventional diesel fuel. On the other hand, the addition of n-butanol to the B20 fuel blend caused a slight increase in the brake specific fuel consumption and brake thermal efficiency in comparison to the B20 fuel blend. For exhaust emissions, carbon monoxide (CO) and hydrocarbon (HCs) emissions decreased, and NOx remained almost unchanged at low engine loads, while it decreased at high engine loads. Fuel blends also resulted in a sharp reduction of smoke opacity in the whole range of engine tests.

1. INTRODUCTION Diesel engines are widely used for transportation, energy production, and agricultural and industrial applications because of their high fuel conversion efficiencies and durability. Petroleum-based fuels are used in diesel engines, which have a wide range of use in many sectors. However, it is well-known that petroleum resources are limited and depleting day by day. In addition, pollutant emissions resulting from diesel combustion have negative effects on both human health and the environment, so it is necessary to reduce these emissions in diesel engines fueled with petroleum diesel fuels. The main regulated pollutants in diesel engines are nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (HC), and smoke, and they have been regulated by the laws in many countries. Therefore, due to the depletion of petroleum resources and increasing environmental concerns, there is great demand for finding alternatives to petroleum-based diesel fuel. Biodiesel and alcohol fuels, clean renewable fuels, have received considerable attention in recent years as alternative fuels in diesel engines. Biodiesel fuels obtained from various sources such as soybean oil, rapeseed oil, sunflower oil, animal fats, etc. have offered a potentially very interesting alternative regarding pollutant emissions and availability. In alcohols, methanol and ethanol are used most often as fuel additives in diesel engines. The major drawback in ethanol diesel blends is that ethanol is immiscible in diesel over a wide range of temperatures,1 and also the addition of ethanol causes a reduction in cetane number and lubricity of diesel fuels. The before-mentioned blending problems can be reduced as a consequence of the progressive incorporation of biodiesel in commercial diesel fuel, because biodiesel fuels improve the stability of r 2011 American Chemical Society

the blends and compensate for the reduction in cetane number and lubricity derived from the addition of ethanol.2 Thus, works on the use of blends containing biodiesel, diesel fuel, and alcohol in diesel engines have been performed, for example, see refs 3 5. The beneficial effects of using various blends containing the mentioned fuels on performance and exhaust emissions and blending stability have been reported in experimental investigations. Shi et al.3 investigated the emission characteristics of BEdiesel on a diesel engine. The results showed a significant reduction in PM emissions and an increase in NOx emissions from BE-diesel. Total hydrocarbon (THC) from BE-diesel was lower than that from diesel fuel under most operating conditions. Ali et al.4 used 12 different blends of methyl tallowate, methyl soyate, ethanol, and diesel fuel in a Cummins N14 410 diesel engine and found that engine performance with these fuel blends did not differ to a great extent from engine performance with diesel fuel. Qi et al.5 conducted an experimental investigation to evaluate the effects of using methanol as an additive to biodiesel diesel blends on the engine performance characteristics of a direct injection diesel engine under variable operating conditions. In that study, it was found that 5% by volume of methanol can be mixed uniformly with a biodiesel diesel blend without using additives, but when the methanol content is more than 5%, it is necessary to add oleic acid as an additive to prevent phase separation of the blended fuel. Although the power and torque Received: February 28, 2011 Accepted: June 22, 2011 Revised: June 21, 2011 Published: June 22, 2011 9425

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

Industrial & Engineering Chemistry Research outputs of fuel blends containing methanol were slightly lower than those of the biodiesel diesel blend, fuel blends showed a dramatic reduction in smoke emissions. On the other hand, butanol, which can easily be blended with both gasoline and diesel, has been drawing the attention of researchers. Butanol has properties which make it a suitable ethanol replacement, having a higher energy content in addition to a significant improvement in mixing properties with petroleum diesel fuels. Butanol has a lower autoignition temperature than methanol and ethanol. Therefore, butanol can be ignited easier when burned in diesel engines. Butanol also has a higher cetane number; thus this makes it a more suitable additive than ethanol and methanol for diesel fuel.6 The attraction in butanol as an alternative fuel for diesel engines is due to the fact that it has significant advantages over ethanol and methanol, especially mixing properties. Investigation of butanol usage as diesel engine fuel has been conducted by researchers. It has been used both for blending gasoline and as a diesel fuel for IC engines. For example, the effect of iso-butanol/diesel fuel blends on engine performance and exhaust emissions was investigated by Karabektas) and Hos) € oz.7 They found a trend of reduced engine power, brake thermal efficiency (BTE), and exhaust gas temperature and increased brake specific fuel consumption (BSFC) with an increase in the iso-butanol content in the blends. In that study, the results compared with diesel fuel showed that CO and NOx emissions decreased with the use of blends, while HC emissions increased considerably. However, it was reported that n-butanol/diesel fuel blends increased the BTE and the BSFC and decreased the exhaust gas temperature, with the same trend in exhaust emissions.8,9 A drive cycle analysis in a light-duty turbo-diesel vehicle was carried out with two blends of n-butanol (20% and 40%, by volume) and compared with diesel fuel.10 The results showed that both HC and CO emissions increased for the urban drive cycle, when larger quantities of n-butanol were added to the diesel fuel. In the same study, HC and CO emissions were not significantly impacted, but NOx emissions showed a slight increase for the highway drive cycle, when the n-butanol percentage increased in the fuel blends. In addition, it was reported that a significant drop in smoke density was observed for all n-butanol/diesel fuel blends. Butanol has also been used for blending diesel biodiesel or in vegetable oil blends for IC engines. Mehta et al.11 used butanol/diesel/biodiesel blends in different ratios to determine physical stability and various fuel properties. In that study, engine performance and emission tests were also conducted with these fuel blends. Lebedevas et al.12 showed that the introduction of biobutanol in a three-component mixture (diesel, butanol, and biodiesel) instead of ethanol is more promising due to the better performance and environmental characteristics of the fuel. Lujaji et al.13 evaluated the effects of blends containing croton oil (CRO), 1-butanol (BU), and diesel (D2) on the engine performance, combustion, and emission characteristics. It was reported that the addition of butanol in the blend reduced the brake thermal efficiency and carbon dioxide and smoke emissions in comparison to those of diesel fuel. In the present study, we investigated the effect of using n-butanol (normal butanol) in conventional diesel fuel biodiesel blends on the engine performance and exhaust emissions of a single cylinder direct injection compression ignition engine with the engine working at a constant engine speed (2000 rpm) and at different engine loads.

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

diesel

n-butanol

kinematics viscosity, mm /s (at 40 °C)

2.72

4.34

3.6

42700 825.6

38630 883.9

33100 810

cetane number

47

56a

25

11

21.6

oxygen, % weight

a

biodiesel

lower heating value, kJ/kg density, kg/m3 (at 15 °C)

2

latent heat of evaporation, kJ/kg

250

230

585

boiling point (°C)

365

347

118

Estimated from cetane numbers of individual methyl esters.

2. MATERIALS AND METHODS 2.1. Properties of Experimental Fuels. The biodiesel employed in this study was produced from cottonseed oil via a alkalicatalyzed transesterification process with methyl alcohol in the presence of KOH as a catalyst. Cottonseed oil from Turkish commercial sources was used to obtain cottonseed oil methyl ester (CSOME). The cottonseed oil was selected for biodiesel production, as cottonseed is a major product of Turkey. Detailed information about the CSOME used in the experiments can be found in ref 14. Reidel-Haen brand n-butanol with a purity of >99% (Sigma-Aldrich), provided from the Refinery and PetroChemistry Laboratory of Batman University, Batman, Turkey, was used to prepare blends. The conventional diesel fuel employed in the tests was obtained locally. Density, kinematic viscosity, heating value, and flash points of the fuels were determined using an Anton Paar densitometer model DMA 5000, a Herzog kinematic viscosity meter model HVM 472, an IKA C2000 Basic Calorimeter, and a Herzog HFP360 closed-cup Pensky Martens apparatus, respectively. These tests were performed in accordance with ASTM standards. The fuel-related properties of biodiesel, diesel fuel, and n-butanol are presented in Table 1. It can be seen that the latent heat of evaporation of n-butanol is 585 kJ/kg, which is higher than that of other fuels. The heating value of biodiesel is approximately 9.5% lower and that of n-butanol is 22.5% lower than that of diesel fuel. The viscosity of biodiesel is evidently higher than that of n-butanol and diesel fuel. The oxygen content of n-butanol is 21.6% and higher than that of biodiesel. Furthermore, CSOME has higher distillation temperatures than that of diesel fuel. Contrary to the initial distillation temperature, the final distillation temperature for 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 Automotive Department of Technical Education Faculty at the University of Batman. The schematic diagram of the experimental setup is shown in Figure 1. A Rainbow-186, single-cylinder, four-stroke, air-cooled, naturally aspired direct injection diesel engine was used for engine tests. The basic specifications of the engine are shown in Table 2. Engine tests were conducted on a BT-140 model hydraulic dynamometer. The required engine load was obtained through the dynamometer control. A CAPELEC CAP 3200 brand exhaust gas analyzer was used to measure emissions of the test fuels. An exhaust gas measuring device determines the emissions of CO and HC by means of infrared measurement (nondispersive infrared) and NOx by means of electrochemical sensors. An infrared temperature measurement device was used to specify the exhaust temperature. The exhaust temperature was 9426

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

Industrial & Engineering Chemistry Research

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Figure 1. A schematic diagram of the engine setup.

Table 2. Technical Specifications of the Test Engine rainbow 186 four stroke, air cooled, type of engine volume

single cylinder DI diesel engine 406 cm3

compression ratio maximum engine speed

18/1 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 BTDC

intake valve close

50° crank angle ATDC

exhaust valve open

54° crank angle BBDC

exhaust valve close

10° crank angle ABDC

measured from the external surface of the exhaust manifold using an infrared temperature measurement device. The fuel consumption was measured with burettes with 50 and 100 mL volumes and a stopwatch. The accuracy of the measurements and the results of uncertainty analysis of the calculated results are shown in Table 3. Four fuels were prepared: conventional diesel fuel as a baseline 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 conducted using each of the fuel blends and diesel fuel, with the engine working 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 to reduce experimental uncertainties, and the results of the three repetitions were averaged. For every fuel change, the fuel tank and lines were cleaned. Before running the engine to a new fuel, it was allowed to run for some time to consume the remaining fuel from the previous experiment. In each test, brake torque, engine

speed, fuel flow rate, exhaust temperature, and exhaust emissions were measured. Significant engine performance parameters such as brake specific fuel consumption (BSFC) and brake thermal efficiency (BTE) for each fuel tested were calculated.

3. RESULTS AND DISCUSSION 3.1. Engine Performance. Figure 2 shows the results of brake specific 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 an engine speed of 2000 rpm. The BSFC was found to decrease with an increase in load for all tested fuels, as can be seen in Figure 2. From the results, it is observed that the brake specific fuel consumption for all of the fuel mixtures is slightly higher than that of diesel under the whole range of engine loads, with the increase being higher the higher the percentage of the n-butanol in the blend. An increase in fuel consumption is the expected result since the loss of heating value of fuel mixtures must be compensated with a higher fuel consumption to maintain the same torque output. As shown in Table 1, the maximum LHV belongs to diesel fuel, followed by biodiesel, and the lowest one belongs to n-butanol. Therefore, when using fuel mixtures, a larger amount of fuel is required for supplying the same amount of energy in the cylinder because of their lower heating values. Figure 2 also shows an increase in the efficiency with an increase in the engine load. For all fuel mixtures, brake thermal efficiency was slightly lower than that of diesel fuel. The brake thermal efficiency is the inverse of the product of the brake specific fuel consumption and the lower heating value of the fuels. Therefore, BTE values calculated for diesel fuel are higher than those of fuel mixtures. Furthermore, for fuels containing n-butanol, BTE was higher than that of B20. This could be attributed to the presence of an increased amount of oxygen in fuels containing n-butanol, 9427



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Table 3. Accuracy of the Measurements and Uncertainties in the Calculated Results parameter

measuring range

accuracy

load

250 N m max.

(2 N m

speed time

7500 rpm max.

(25 rpm (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 3. Concentration of nitrogen oxides (NOx) in exhaust gases when the diesel engine is fueled with fuel mixtures and diesel fuel.

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

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

which might have resulted in its improved combustion as compared 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 engine speed of 2000 rpm. From the results, it can be seen that the NOx emissions increased with an increase of the engine load for all tested fuels. This may be due to a higher combustion temperature inside the cylinder at a higher load, as a greater amount of fuel is burned 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 of n-butanol in the blend. This may be attributed to the engine running “leaner” overall and the temperature lowering effect of the butanol (due to its lower calorific value and its higher heat of evaporation) having a dominant influence, against the opposing effect of the lower cetane number (and thus longer ignition delay) of the butanol, leading possibly to higher temperatures during the premixed part of combustion.9 Furthermore, at high loads, the reduction in NOx emissions was higher than that of under low load conditions.

3.3. Exhaust Temperature. Figure 4 shows a comparison of exhaust temperatures of the direct injection diesel engine fueled with diesel, B20, B20Bu10, and B20Bu20 with respect to engine load at an engine speed of 2000 rpm. It is observed from this figure that the exhaust temperatures for all fuel mixtures are slightly lower than that of diesel fuel. One can also observe from this figure that fuels containing n-butanol tend to produce a little higher exhaust temperature values than that of B20, with this increase being higher the higher the percentage of n-butanol in the blend as well as the higher the engine load. The reason may be that the premixed burning heat release is higher for fuels containing n-butanol owing to the better volatility of n-butanol, which promotes the formation of more of the air fuel mixture in the premixed burning phase. Normally, an increase in the premixed fraction results in more energy being released over a short time scale close to top dead center with a nearly constant combustion chamber volume, resulting 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 different fuels. It can be seen in Figure 5 that there is a slight decrease in the HC emissions with fuel mixtures as compared to diesel fuel 9428



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

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

a higher oxygen content than in the other fuels. It is agreed that the fuel-borne oxygen is more effective than the external oxygen supplied with the air for reducing CO emissions since the aspirated air mass remains the same. 3.6. Smoke Opacity. Smoke curves of the four fuels are shown in Figure 7. From the results, it can be seen that the smoke emissions for all fuel mixtures are significantly lower than that of diesel fuel in the whole range of the engine tests. The smoke emissions for B20, B20Bu10, and B20Bu20 were lower than that of diesel by 20.5%, 27.9%, and 35.2%, respectively, on average. From these results, it is agreed that the more oxygenated fuel added in, the greater the reductions of smoke emissions were.

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

operation. At high loads, the reduction in HC emissions from the combustion of the fuel mixtures was lower than that of under low load 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 in the fuel, which enhances the combustion of fuel mixtures, and hence HC emissions reduce. Besides, the final distillation temperature of diesel fuel is higher than that of biodiesel and n-butanol. Therefore, a higher final distillation temperature of diesel 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 CO emissions produced by fuel mixtures are lower than that of diesel fuel, with the reduction being higher than the percentage of biofuel in the fuel blends. In contrast to airborne oxygen, the fuelbased oxygen accelerates the combustion process from within the fuel-rich spray patterns themselves. A more complete combustion caused by the increased oxygen content in the flame coming from the biofuel molecules can be pointed out as the main reason for the reduction of CO emissions. As can be seen in Figure 6, the minimum CO emission values were obtained for B20Bu20 due to

4. CONCLUSIONS The following conclusions can be drawn from the experimental results: For all of the fuel mixtures, the brake specific fuel consumption showed an increase, whereas brake thermal efficiency showed a decrease as compared to conventional diesel fuel for the same torque output. Besides, the addition of n-butanol in the B20 fuel blend resulted in improved brake thermal efficiency. Fuel mixtures resulted in significant reductions in considered emissions. Nitrogen oxide (NOx) emissions also decreased with the use of all fuel mixtures, with this effect being more appreciable under high loads. Also, fuel mixtures resulted in a sharp reduction of smoke opacity in the whole range of the engine tests. The addition of n-butanol in the B20 fuel blend performed better in terms of performance and exhaust emissions than the biodiesel diesel blend. Taking these facts into account, biodiesel, conventional diesel fuel, and n-butanol mixtures can be considered to be promising alternative fuels for diesel engines. ’ AUTHOR INFORMATION Corresponding Author

*Tel./Fax: +90488-217-3675/+90488-215-7201. E-mail: saltun72@ yahoo.com.

’ REFERENCES (1) Fernando, S.; Hanna, M. Development of a Novel Biofuel Blend Using Ethanol-Biodiesel-Diesel Microemulsions: EB-Diesel. Energy Fuels 2004, 18, 1695–1703. 9429



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(2) Lapuerta, M.; Armas, O.; Garcia-Contreras, R. Effect of Ethanol on Blending Stability and Diesel Engine Emissions. Energy Fuels 2009, 23, 4343–4354. (3) Shi, X.; Yu, Y.; He, H.; Shuai, S.; Wang, J.; Li, R. Emission characteristics using methyl soyate-ethanol diesel fuel blends on a diesel engine. Fuel 2005, 84, 1543–1549. (4) Ali, Y.; Eskridge, K. M.; Hanna, M. A. Testing of alternative diesel fuel from tallow and soybean oil in Cummins N14 410 diesel engine. Bioresour. Technol. 1995, 53, 243–254. (5) Qi, D. H.; Chen, H.; Geng, L. M.; Bian, Y. Z. H.; Ren, X. C. H. Performance and Combustion Characteristics of Biodiesel Diesel Methanol Blend Fuelled Engine. Appl. Energy 2010, 87, 1679–1686. (6) Szwaja, S.; Naber, J. D. Combustion of n-butanol in a sparkignition IC engine. Fuel 2010, 89, 1573–1582. (7) Karabektas) , M.; Hos) €oz, M. Performance and emission characteristics of a diesel engine using isobutanol diesel fuel blends. Renew. Energy 2009, 34, 1554–1559. (8) Dogan, O. The influence of n-butanol/diesel fuel blends utilization on a small diesel engine performance and emissions. Fuel 2011, 90, 2467–2472. (9) Rakopoulos, D. C.; Rakopoulos, C. D.; Giakoumis, E. G.; Dimaratos, A. M.; Kyritsis, D. C. Effects of butanol diesel fuel blends on the performance and emissions of a high-speed DI diesel engine. Energy Convers. Manage. 2010, 51, 1989–97. (10) Miers S. A.; McConnell, S.; Wallner, T.; Ng H. K.; Carlson, R. W.; LeFeber, J. Drive cycle analysis of butanol/diesel blends in a lightduty vehicle. SAE paper no.: 2008-01-2381; SAE: Warrendale, PA, 2008. (11) Mehta, R. N.; Chakraborty, M.; Mahanta, P.; Parikh, P. A. Evaluation of Fuel Properties of Butanol-Biodiesel-Diesel Blends and Their Impact on Engine Performance and Emissions. Ind. Eng. Chem. Res. 2010, 49, 7660–7665. (12) Lebedevas, S.; Lebedeva, G.; Sendzikiene, E.; Makareviciene, V. Investigation of the Performance and Emission Characteristics of Biodiesel Fuel Containing Butanol under the Conditions of Diesel Engine Operation. Energy Fuels 2010, 24, 4503–4509. (13) Lujaji, F.; Bereczky, A.; Mbaraw, M. Performance Evaluation of Fuel Blends Containing Croton Oil, Butanol, and Diesel in a Compression Ignition Engine. Energy Fuels 2010, 24, 4490–4496. € (14) Altun, S) .; Yasar, F.; Oner, C. Biodiesel Production from Raw Cottonseed Oil and its Characterization. Energy Educ. Sci. Technol. Part A 2011, 27 (2), 375–382.

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Effect of n-Butanol Blending with a Blend of Diesel and Biodiesel on

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