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Comparative analysis of biodiesel–ethanol–diesel and biodiesel–methanol–diesel blends in a diesel engine
Energy 40 (2012) 210e213
Contents lists available at SciVerse ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Comparative analysis of biodieseleethanolediesel and biodieselemethanolediesel blends in a diesel engine Nadir Yilmaz* Department of Mechanical Engineering, New Mexico Institute of Mining and Technology, Socorro, NM 87801, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 September 2011 Received in revised form 23 January 2012 Accepted 27 January 2012 Available online 3 March 2012
In this work, standard diesel fuel, biodiesel (45%)emethanol (10%)ediesel (45%), biodiesel (40%) emethanol (20%)ediesel (40%), biodiesel (45%)eethanol (10%)ediesel (45%) and biodiesel (40%) eethanol (20%)ediesel (40%) blends are tested in a compression ignited engine under the same operating conditions. Performance and emission characteristics of the engine fueled with biodiesel emethanolediesel (BMD) and biodieseleethanolediesel (BED) are compared to standard diesel fuel as the baseline. Overall, biodieselealcoholediesel blends show a higher brakespecific fuel consumption than diesel. As alcohol concentrations in blends increase, CO and HC emissions increase, while NO emissions are reduced. Also, methanol blends are more effective than ethanol blends for reducing CO and HC emissions, while NO reduction is achieved by ethanol blends. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Biodieselemethanolediesel Biodieseleethanolediesel Engine performance Emissions Combustion
1. Introduction While investigation of ethanolebiodiesel and methanolebiodiesel fuels in compressions ignited engines is limited in the literature, studies on biodieselemethanolediesel (BMD) and biodieseleethanolediesel (BED) are also relatively low and more work needs to be done in order to understand the behavior of compression ignited engines, fueled with combinations of these fuels. Qi et al. [1] investigated performance and combustion characteristics of biodieselemethanolediesel blends in compression ignited engines. 50% biodiesel and 50% diesel fuels (BD50) were prepared as the baseline fuel. Also, methanol was added to BD50 as an additive with volume percent of 5% and 10% (BDM5 and BDM10). Results indicated that BDM5 and BDM10 show a significant decrease of smoke emissions, while CO emissions are slightly lower. NOx and HC emissions were almost similar to those of BD50, at full load. Results also show that BDM5 and BDM10 indicate combustion starts later than when compared to BD50 at low engine load. But, the engine start is almost identical at high engine load. In addition, the power and torque outputs of BDM5 and BDM10 were slightly lower than for those of BD50.
* Tel.: þ1 575 8355304; fax: þ1 575 8355209. E-mail address: [email protected]. 0360-5442/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2012.01.079
There are slightly more studies for the investigation of biodieseleethanolediesel blends as compared to biodieselemethanolediesel in the literature [2e5]. Shi et al. [2] used ethanolebiodieselediesel fuel blends with the blend ratio of 5% ethanole20% methanole75% diesel fuel by volume. Biodieseleethanolediesel showed a significant reduction in particulate matter (PM) emissions and a 2e14% increase of NOx emissions. The change of CO emission depended on operating conditions. The total hydrocarbons (THC) from biodieseleethanolediesel were lower than for diesel fuel under most of the tested conditions. Guarieiro et al. [3] discussed that the combustion efficiencies of diesel fuel can be enhanced by the addition of oxygenate fuels such as ethanol and biodiesel/vegetable oil, resulting in more complete combustion for NOx emission. Based on the various blends of dieseleethanol, dieseleethanolesoybean biodiesel, diesele ethanolecastor biodiesel, dieseleethanoleresidual biodiesel, dieseleethanolesoybean oil and dieseleethanolecastor oil, there was no significant change in CO emissions. Jha et al. [4] studied exhaust gas emissions using biodieseleethanolediesel blends in both new and used engines. Blend ratios were 70e25e5%, 70e20e10% and 70e15e15%. The results showed that biodieseleethanolediesel blends significantly reduce NOx emissions in new engines with increased ethanol concentration, while the old engine showed an increase in NOx emissions. CO emissions increased in both engines by increasing ethanol concentrations in the blends. In another study by Cheenkachorn and Fungtammasan [5],
N. Yilmaz / Energy 40 (2012) 210e213
a diesel (84%)ehydrous ethanol (0.25%)eanhydrous ethanol (4.75%)ebiodiesel (11%) blend was tested in a light-duty truck and compared to diesel fuel. It was found that the two fuels showed no significant difference on CO2 and NOx emissions. But, dieseleethanolebiodiesel blends reduced particulate matter (PM) and CO emissions as compared to diesel. In addition, there was no significant difference in the fuel consumption of the two fuels. In summary of the literature review based on biodiesele ethanolediesel blends, PM emissions are reduced, while there are mixed results for CO and NOx emissions. While some studies show no significant change in CO emissions, some research show an increase or decrease in CO emissions. Likewise, contradictory results occur regarding NOx emissions. While some research show an increase in NOx emissions, one research investigation showed reduction of NOx emissions in the case of using a new engine rather than an old engine. In this paper, biodieseleethanolediesel and biodiesele methanolediesel blends were tested in the same engine and under the same conditions, where results are compared to standard diesel fuel. Biodieselealcoholediesel fuels were prepared with 45:10:45 and 40:20:40 ratios (B45M10D45, B40M20D40, B45E10D45, B40E20D40). Brake specific fuel consumption, exhaust gas temperature, CO, NO and HC emissions were compared based on the fuel type, mixing ratio and operating conditions. Overall, alcohol blended fuels show a higher brake specific fuel consumption than diesel. Also, exhaust gas emissions indicate that biodieseleethanolediesel blends, as compared to standard diesel, reduce NO emissions and increase CO and HC emissions, while biodieselemethanolediesel blends show the opposite effects. It is discussed that cooling effect of alcohols has an important role in CO, NO and HC emissions [1,6].
211
Data Acquisition System
Thermocouple Gas Analyzer Fuel Mixture
Fuel
Diesel Engine Generator
Exhaust Gas
Scale
Fig. 1. A representation of the experimental setup.
Standard diesel, biodiesel (45%)emethanol (10%)ebiodiesel (45%), biodiesel (40%)emethanol (20%)ebiodiesel (40%), biodiesel (45%)eethanol (10%)ebiodiesel (45%) and biodiesel (40%)eethanol (20%)ebiodiesel (40%) blends were prepared for engine testing. Biodiesel was made of used cooking oil using the standard transesterification method. The process followed ASTM D6751 guidelines and the fuel met the standard specification. Table 2 shows the basic properties of fuels used in this study. 3. Engine performance and emissions Biodieselemethanolebiodiesel [1] and biodieseleethanole biodiesel [2e5] blends were previously studied. Since there are more investigations on biodieseleethanolebiodiesel, their findings are compared and contradictory results are discussed for emissions such as CO and NOx in the following section. Also, both biodieseleethanolediesel and biodieselemethanolediesel blends are compared under the same operating conditions and results are compared to baseline diesel fuel as a function of load and mixing ratios.
2. Experimental procedure and specifications Experiments were carried out using a two-cylinder, 4-cycle, direct injected, liquid-cooled Kubota GL-7000 diesel engine generator. Specifications of the engine are shown in Table 1. Loads were applied to the engine using two Holmes 1000/1500 watt electric heaters and one Dayton 2500/5000 watt heater. A Sun Diognostics DGA1000 5-gas analyzer was used to measure exhaust gas emissions of CO, NO and HC. The analyzer was calibrated using BAR 97 low and BAR 97 high calibration gases, and the calibration was routinely checked throughout the emission measurement process. Exhaust temperature was determined by using a type-K thermocouple which was connected to an Enerac combustion analyzer. Both combustion analyzer and thermocouple were connected to a data acquisition system to collect data. Fig. 1 shows a representation of the experimental setup. The engine was run between no load and full load conditions. 6 kW (rated output) which corresponds to 90% of maximum output of the engine was achieved as the maximum engine load. Table 1 Specifications for Kubota diesel engine generators. Generator Type Maximum output (kW) Rated output (kW) Engine cooling No of cycles Model Rated output (kW/rpm) Displacement (cm3) No. of cylinders Combustion system Compression ratio
Kubota diesel generator GL-7000 6.5 6 Horizontal liquid-cooled 4-cycle Z482 8.95/3000 479 2 Direct injection 23.5:1
3.1. Brake-specific fuel consumption Biodieselemethanolediesel blends show a higher brake specific fuel consumption than do biodieseleethanolediesel blends, as shown in Fig. 2. As the methanol or ethanol concentration increases, brake specific fuel consumption increases as well. Overall, standard diesel fuel results in the lowest consumption. It means that methanol blended fuels consume more fuel per energy extracted as load decreases. As a result, more fuel carry-over or unburned fuel would be expected from methanol-blended fuels. This problem could be fixed, to some extent, with better vaporization of fuel mixtures if the engine were run at full load or high loads, and/or intake air is preheated. 3.2. Exhaust gas temperature Fig. 3 shows the variation of exhaust gas temperature for standard diesel and biodieselealcoholsediesel mixtures. For all of the cases, exhaust gas temperature increases as a function of load, as expected. Although there is not a significant difference between results, biodieseleethanolediesel blends show slightly higher
Table 2 Properties of biodiesel, diesel, ethanol and methanol. Fuels
Biodiesel
Diesel
Ethanol
Methanol
Heating value (MJ kg1) Density @20 C (kg m3) Flash Point ( C) Viscosity @ 40 C (mPa s) Cetane number
40.5 855 126 4.57 52
44.8 815 70 2.95 52
28.6 790 13 1.1 6
19.8 792 11 0.59 <5
N. Yilmaz / Energy 40 (2012) 210e213
3000
B40-M20-D40 B45-M10-D45 B40-E20-D40 B45-E10-D45 Diesel
BSFC (g/kW-hr)
2500 2000 1500
0.20
B40-M20-D40 B45-M10-D45 B40-E20-D40 B45-E10-D45 Diesel
0.18 0.16 0.14
CO (%)
212
1000
0.12 0.10 0.08 0.06 0.04
500
0.02 0.00
0 0%
20%
40%
60%
80%
100%
0%
20%
40%
Load
60%
80%
100%
Load
Fig. 2. Brake specific fuel consumption for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/ diesel (45%), biodiesel (40%)/ethanol (20%)/diesel (%40), biodiesel (45%)/ethanol (10%)/ diesel (45%).
temperatures than the other fuels, which might be because of the shortened combustion duration of alcohol-blended fuels. 3.3. CO emissions Fig. 4 shows CO emissions as a function of load for standard diesel and the other four blends. It is clearly seen from the figure that CO emissions increase by increasing ethanol and methanol concentrations. This is perhaps due to lower cetane numbers of alcohol fuels, which increase the ignition delay, leading to incomplete combustion, which increases CO emission. Another observation indicates that biodieseleethanolediesel blends result in higher CO emissions than biodieselemethanolediesel. As compared to diesel fuel, ethanol blended fuels produce higher CO emissions and methanol blended fuels show lower CO emissions. However, it is expected that if methanol concentration in biodiesele methanolediesel is higher than 20%, biodieselemethanolediesel blends might result in higher CO emission than diesel. This would be because adding a small amount of methanol improves oxygen content of blends, which leads to better combustion and lower CO. But, as the methanol concentration increases, the cooling effects of methanol reduce the gas temperature and leads to higher CO emission. Thus, fuel blend ratio and operating conditions play important roles in the change of CO emissions.
Fig. 4. CO emissions for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/diesel (45%), biodiesel (40%)/ethanol (20%)/diesel (40%), biodiesel (45%)/ethanol (10%)/diesel (45%).
3.4. NO emissions As seen in Fig. 5, NO emissions are reduced by increasing ethanol and methanol concentrations in biodieselealcoholediesel blends. Also, it is shown that ethanol-blended fuels show lower emissions than methanol blended fuels. As compared to standard diesel, ethanol-blended fuels reduce NO emissions while methanol-blended fuels increase NO emissions if methanol concentration is equal to or less than 20%. This might be due to that a low concentration of methanol increases the oxygen content of the fuel mixture, which leads to better combustion and a higher combustion temperature. As methanol concentration increases, the cooling effect of methanol becomes more dominant, leading to a lower combustion temperature and a reduction of NO emission. Ethanol blends are expected to show higher NO emission due to an increase in oxygen content and better combustion for much lower values of ethanol concentration. 3.5. Unburned HC emissions Fig. 6 shows that unburned HC emissions decrease with respect to load. And, at full load, there is no significant difference between emissions. Below 50% load, although methanol-blended fuels do not indicate any change in HC emissions as compared to diesel, ethanol-blended fuels show a significant increase in HC emissions. This figure also indicates that increasing ethanol concentration in
450 250
B40-M20-D40 B45-M10-D45 B40-E20-D40 B45-E10-D45 Diesel
400 350
200 150
B40-M20-D40 B45-M10-D45 B40-E20-D40 B45-E10-D45 Diesel
100 50 0 0%
20%
40%
60%
80%
100%
Load
NO (ppm)
Exhaust Gas Temperature (C)
300
300 250 200 150 100 50 0 0%
20%
40%
60%
80%
100%
Load Fig. 3. Exhaust gas temperature for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/diesel (45%), biodiesel (40%)/ethanol (20%)/diesel (40%), biodiesel (45%)/ethanol (10%)/diesel (45%).
Fig. 5. NO emissions for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/diesel (45%), biodiesel (40%)/ethanol (20%)/diesel (40%), biodiesel (45%)/ethanol (10%)/diesel (45%).
N. Yilmaz / Energy 40 (2012) 210e213
140
B40-M20-D40 B45-M10-D45 B40-E20-D40 B45-E10-D45 Diesel
120
HC (ppm)
100 80 60 40 20 0 0%
20%
40%
60%
80%
100%
Load Fig. 6. Unburned HC emissions for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/diesel (45%), biodiesel (40%)/ethanol (20%)/ diesel (40%), biodiesel (45%)/ethanol (10%)/diesel (45%).
biodieseleethanolediesel blend increases HC emissions. HC emission is a product of incomplete combustion. Perhaps methanol concentrations up to 20% increase oxygen content of the mixture, which leads to better combustion and lower HC emissions. On the other hand, more methanol addition is expected to show a cooling effect, which causes incomplete combustion and higher HC. The results show that ethanol concentration should be much lower than 10% in order to have the positive effect of higher oxygen content rather than the cooling effect of ethanol. 4. Conclusions Biodiesel (45%)emethanol (10%)ebiodiesel (45%), biodiesel (40%)emethanol (20%)ebiodiesel (40%), biodiesel (45%)eethanol (10%)ebiodiesel (45%) and biodiesel (40%)eethanol (20%)e
213
biodiesel (40%) blends were run in a diesel engine under the same operating conditions and compared to a baseline diesel fuel. Overall, brake specific fuel consumption of alcohol blends is higher than for diesel, while ethanol-blended fuels show lower BSFC than methanol-blended fuels. There is no significant different in exhaust gas temperature. Increasing alcohol concentration reduces NO emissions, while increasing CO and HC emissions. Biodieseleethanolediesel blends, as compared to standard diesel, increase CO and HC emissions while reducing NO emissions. Interestingly, biodieselemethanolediesel blends have opposite effects on the emissions. Methanol blends would be the choice if CO and HC emissions are the aim. Ethanol blends would be the right choice for reducing NO emissions for the concentrations investigated in this work. Overall, emissions strongly depend on engine operating conditions and alcohol blend ratios, which could have positive and negative effects overall, due to oxygen content and cooling effects. References [1] Qi DH, Chen H, Geng LM, Bian YZH, Ren XCH. Performance and combustion characteristics of biodiesel-diesel-methanol blend fuelled engine. Applied Energy 2010;87:1679e86. [2] Shi X, Pang X, Mu Y, He H, Shuai S, Wang J, et al. Emission reduction potential of using ethanol-biodiesel-diesel fuel blend on a heavy-duty diesel engine. Atmospheric Environment 2006;40:2567e74. [3] Guarieiro LLN, de Souza AF, Torres EA, de Andrade JB. Emission profile of 18 carbonyl compounds, CO, CO2, and NOx emitted by a diesel engine fuelled with diesel and ternary blends containing diesel, ethanol and biodiesel or vegetable oils. Atmospheric Environment 2009;43:2754e61. [4] Jha SK, Fernando S, Columbus E, Willcutt H. A comparative study of exhaust emissions using diesel-biodiesel-ethanol blends in new and used engines. Transactions of the ASABE 2009;52:375e81. [5] Cheenkachorn K, Fungtammasan B. An investigation of diesel-ethanol-biodiesel blends for diesel engine: Part 2 e Emission and engine performance of a lightduty truck. Energy Sources, Part A: Recovery, Utilization and Environmental Effects 2010;32:894e900. [6] Abu-Audais M, Haddad O, Qudaisat M. The effect of alcohol fumigation on diesel engine performance and emissions. Energy Conversion & Management 2000;41:389e99.
Contents lists available at SciVerse ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Comparative analysis of biodieseleethanolediesel and biodieselemethanolediesel blends in a diesel engine Nadir Yilmaz* Department of Mechanical Engineering, New Mexico Institute of Mining and Technology, Socorro, NM 87801, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 September 2011 Received in revised form 23 January 2012 Accepted 27 January 2012 Available online 3 March 2012
In this work, standard diesel fuel, biodiesel (45%)emethanol (10%)ediesel (45%), biodiesel (40%) emethanol (20%)ediesel (40%), biodiesel (45%)eethanol (10%)ediesel (45%) and biodiesel (40%) eethanol (20%)ediesel (40%) blends are tested in a compression ignited engine under the same operating conditions. Performance and emission characteristics of the engine fueled with biodiesel emethanolediesel (BMD) and biodieseleethanolediesel (BED) are compared to standard diesel fuel as the baseline. Overall, biodieselealcoholediesel blends show a higher brakespecific fuel consumption than diesel. As alcohol concentrations in blends increase, CO and HC emissions increase, while NO emissions are reduced. Also, methanol blends are more effective than ethanol blends for reducing CO and HC emissions, while NO reduction is achieved by ethanol blends. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Biodieselemethanolediesel Biodieseleethanolediesel Engine performance Emissions Combustion
1. Introduction While investigation of ethanolebiodiesel and methanolebiodiesel fuels in compressions ignited engines is limited in the literature, studies on biodieselemethanolediesel (BMD) and biodieseleethanolediesel (BED) are also relatively low and more work needs to be done in order to understand the behavior of compression ignited engines, fueled with combinations of these fuels. Qi et al. [1] investigated performance and combustion characteristics of biodieselemethanolediesel blends in compression ignited engines. 50% biodiesel and 50% diesel fuels (BD50) were prepared as the baseline fuel. Also, methanol was added to BD50 as an additive with volume percent of 5% and 10% (BDM5 and BDM10). Results indicated that BDM5 and BDM10 show a significant decrease of smoke emissions, while CO emissions are slightly lower. NOx and HC emissions were almost similar to those of BD50, at full load. Results also show that BDM5 and BDM10 indicate combustion starts later than when compared to BD50 at low engine load. But, the engine start is almost identical at high engine load. In addition, the power and torque outputs of BDM5 and BDM10 were slightly lower than for those of BD50.
* Tel.: þ1 575 8355304; fax: þ1 575 8355209. E-mail address: [email protected]. 0360-5442/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2012.01.079
There are slightly more studies for the investigation of biodieseleethanolediesel blends as compared to biodieselemethanolediesel in the literature [2e5]. Shi et al. [2] used ethanolebiodieselediesel fuel blends with the blend ratio of 5% ethanole20% methanole75% diesel fuel by volume. Biodieseleethanolediesel showed a significant reduction in particulate matter (PM) emissions and a 2e14% increase of NOx emissions. The change of CO emission depended on operating conditions. The total hydrocarbons (THC) from biodieseleethanolediesel were lower than for diesel fuel under most of the tested conditions. Guarieiro et al. [3] discussed that the combustion efficiencies of diesel fuel can be enhanced by the addition of oxygenate fuels such as ethanol and biodiesel/vegetable oil, resulting in more complete combustion for NOx emission. Based on the various blends of dieseleethanol, dieseleethanolesoybean biodiesel, diesele ethanolecastor biodiesel, dieseleethanoleresidual biodiesel, dieseleethanolesoybean oil and dieseleethanolecastor oil, there was no significant change in CO emissions. Jha et al. [4] studied exhaust gas emissions using biodieseleethanolediesel blends in both new and used engines. Blend ratios were 70e25e5%, 70e20e10% and 70e15e15%. The results showed that biodieseleethanolediesel blends significantly reduce NOx emissions in new engines with increased ethanol concentration, while the old engine showed an increase in NOx emissions. CO emissions increased in both engines by increasing ethanol concentrations in the blends. In another study by Cheenkachorn and Fungtammasan [5],
N. Yilmaz / Energy 40 (2012) 210e213
a diesel (84%)ehydrous ethanol (0.25%)eanhydrous ethanol (4.75%)ebiodiesel (11%) blend was tested in a light-duty truck and compared to diesel fuel. It was found that the two fuels showed no significant difference on CO2 and NOx emissions. But, dieseleethanolebiodiesel blends reduced particulate matter (PM) and CO emissions as compared to diesel. In addition, there was no significant difference in the fuel consumption of the two fuels. In summary of the literature review based on biodiesele ethanolediesel blends, PM emissions are reduced, while there are mixed results for CO and NOx emissions. While some studies show no significant change in CO emissions, some research show an increase or decrease in CO emissions. Likewise, contradictory results occur regarding NOx emissions. While some research show an increase in NOx emissions, one research investigation showed reduction of NOx emissions in the case of using a new engine rather than an old engine. In this paper, biodieseleethanolediesel and biodiesele methanolediesel blends were tested in the same engine and under the same conditions, where results are compared to standard diesel fuel. Biodieselealcoholediesel fuels were prepared with 45:10:45 and 40:20:40 ratios (B45M10D45, B40M20D40, B45E10D45, B40E20D40). Brake specific fuel consumption, exhaust gas temperature, CO, NO and HC emissions were compared based on the fuel type, mixing ratio and operating conditions. Overall, alcohol blended fuels show a higher brake specific fuel consumption than diesel. Also, exhaust gas emissions indicate that biodieseleethanolediesel blends, as compared to standard diesel, reduce NO emissions and increase CO and HC emissions, while biodieselemethanolediesel blends show the opposite effects. It is discussed that cooling effect of alcohols has an important role in CO, NO and HC emissions [1,6].
211
Data Acquisition System
Thermocouple Gas Analyzer Fuel Mixture
Fuel
Diesel Engine Generator
Exhaust Gas
Scale
Fig. 1. A representation of the experimental setup.
Standard diesel, biodiesel (45%)emethanol (10%)ebiodiesel (45%), biodiesel (40%)emethanol (20%)ebiodiesel (40%), biodiesel (45%)eethanol (10%)ebiodiesel (45%) and biodiesel (40%)eethanol (20%)ebiodiesel (40%) blends were prepared for engine testing. Biodiesel was made of used cooking oil using the standard transesterification method. The process followed ASTM D6751 guidelines and the fuel met the standard specification. Table 2 shows the basic properties of fuels used in this study. 3. Engine performance and emissions Biodieselemethanolebiodiesel [1] and biodieseleethanole biodiesel [2e5] blends were previously studied. Since there are more investigations on biodieseleethanolebiodiesel, their findings are compared and contradictory results are discussed for emissions such as CO and NOx in the following section. Also, both biodieseleethanolediesel and biodieselemethanolediesel blends are compared under the same operating conditions and results are compared to baseline diesel fuel as a function of load and mixing ratios.
2. Experimental procedure and specifications Experiments were carried out using a two-cylinder, 4-cycle, direct injected, liquid-cooled Kubota GL-7000 diesel engine generator. Specifications of the engine are shown in Table 1. Loads were applied to the engine using two Holmes 1000/1500 watt electric heaters and one Dayton 2500/5000 watt heater. A Sun Diognostics DGA1000 5-gas analyzer was used to measure exhaust gas emissions of CO, NO and HC. The analyzer was calibrated using BAR 97 low and BAR 97 high calibration gases, and the calibration was routinely checked throughout the emission measurement process. Exhaust temperature was determined by using a type-K thermocouple which was connected to an Enerac combustion analyzer. Both combustion analyzer and thermocouple were connected to a data acquisition system to collect data. Fig. 1 shows a representation of the experimental setup. The engine was run between no load and full load conditions. 6 kW (rated output) which corresponds to 90% of maximum output of the engine was achieved as the maximum engine load. Table 1 Specifications for Kubota diesel engine generators. Generator Type Maximum output (kW) Rated output (kW) Engine cooling No of cycles Model Rated output (kW/rpm) Displacement (cm3) No. of cylinders Combustion system Compression ratio
Kubota diesel generator GL-7000 6.5 6 Horizontal liquid-cooled 4-cycle Z482 8.95/3000 479 2 Direct injection 23.5:1
3.1. Brake-specific fuel consumption Biodieselemethanolediesel blends show a higher brake specific fuel consumption than do biodieseleethanolediesel blends, as shown in Fig. 2. As the methanol or ethanol concentration increases, brake specific fuel consumption increases as well. Overall, standard diesel fuel results in the lowest consumption. It means that methanol blended fuels consume more fuel per energy extracted as load decreases. As a result, more fuel carry-over or unburned fuel would be expected from methanol-blended fuels. This problem could be fixed, to some extent, with better vaporization of fuel mixtures if the engine were run at full load or high loads, and/or intake air is preheated. 3.2. Exhaust gas temperature Fig. 3 shows the variation of exhaust gas temperature for standard diesel and biodieselealcoholsediesel mixtures. For all of the cases, exhaust gas temperature increases as a function of load, as expected. Although there is not a significant difference between results, biodieseleethanolediesel blends show slightly higher
Table 2 Properties of biodiesel, diesel, ethanol and methanol. Fuels
Biodiesel
Diesel
Ethanol
Methanol
Heating value (MJ kg1) Density @20 C (kg m3) Flash Point ( C) Viscosity @ 40 C (mPa s) Cetane number
40.5 855 126 4.57 52
44.8 815 70 2.95 52
28.6 790 13 1.1 6
19.8 792 11 0.59 <5
N. Yilmaz / Energy 40 (2012) 210e213
3000
B40-M20-D40 B45-M10-D45 B40-E20-D40 B45-E10-D45 Diesel
BSFC (g/kW-hr)
2500 2000 1500
0.20
B40-M20-D40 B45-M10-D45 B40-E20-D40 B45-E10-D45 Diesel
0.18 0.16 0.14
CO (%)
212
1000
0.12 0.10 0.08 0.06 0.04
500
0.02 0.00
0 0%
20%
40%
60%
80%
100%
0%
20%
40%
Load
60%
80%
100%
Load
Fig. 2. Brake specific fuel consumption for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/ diesel (45%), biodiesel (40%)/ethanol (20%)/diesel (%40), biodiesel (45%)/ethanol (10%)/ diesel (45%).
temperatures than the other fuels, which might be because of the shortened combustion duration of alcohol-blended fuels. 3.3. CO emissions Fig. 4 shows CO emissions as a function of load for standard diesel and the other four blends. It is clearly seen from the figure that CO emissions increase by increasing ethanol and methanol concentrations. This is perhaps due to lower cetane numbers of alcohol fuels, which increase the ignition delay, leading to incomplete combustion, which increases CO emission. Another observation indicates that biodieseleethanolediesel blends result in higher CO emissions than biodieselemethanolediesel. As compared to diesel fuel, ethanol blended fuels produce higher CO emissions and methanol blended fuels show lower CO emissions. However, it is expected that if methanol concentration in biodiesele methanolediesel is higher than 20%, biodieselemethanolediesel blends might result in higher CO emission than diesel. This would be because adding a small amount of methanol improves oxygen content of blends, which leads to better combustion and lower CO. But, as the methanol concentration increases, the cooling effects of methanol reduce the gas temperature and leads to higher CO emission. Thus, fuel blend ratio and operating conditions play important roles in the change of CO emissions.
Fig. 4. CO emissions for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/diesel (45%), biodiesel (40%)/ethanol (20%)/diesel (40%), biodiesel (45%)/ethanol (10%)/diesel (45%).
3.4. NO emissions As seen in Fig. 5, NO emissions are reduced by increasing ethanol and methanol concentrations in biodieselealcoholediesel blends. Also, it is shown that ethanol-blended fuels show lower emissions than methanol blended fuels. As compared to standard diesel, ethanol-blended fuels reduce NO emissions while methanol-blended fuels increase NO emissions if methanol concentration is equal to or less than 20%. This might be due to that a low concentration of methanol increases the oxygen content of the fuel mixture, which leads to better combustion and a higher combustion temperature. As methanol concentration increases, the cooling effect of methanol becomes more dominant, leading to a lower combustion temperature and a reduction of NO emission. Ethanol blends are expected to show higher NO emission due to an increase in oxygen content and better combustion for much lower values of ethanol concentration. 3.5. Unburned HC emissions Fig. 6 shows that unburned HC emissions decrease with respect to load. And, at full load, there is no significant difference between emissions. Below 50% load, although methanol-blended fuels do not indicate any change in HC emissions as compared to diesel, ethanol-blended fuels show a significant increase in HC emissions. This figure also indicates that increasing ethanol concentration in
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Fig. 5. NO emissions for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/diesel (45%), biodiesel (40%)/ethanol (20%)/diesel (40%), biodiesel (45%)/ethanol (10%)/diesel (45%).
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Load Fig. 6. Unburned HC emissions for Kubota diesel engine running on blended fuels of biodiesel (40%)/methanol (20%)/diesel (40%), biodiesel (45%)/methanol (10%)/diesel (45%), biodiesel (40%)/ethanol (20%)/ diesel (40%), biodiesel (45%)/ethanol (10%)/diesel (45%).
biodieseleethanolediesel blend increases HC emissions. HC emission is a product of incomplete combustion. Perhaps methanol concentrations up to 20% increase oxygen content of the mixture, which leads to better combustion and lower HC emissions. On the other hand, more methanol addition is expected to show a cooling effect, which causes incomplete combustion and higher HC. The results show that ethanol concentration should be much lower than 10% in order to have the positive effect of higher oxygen content rather than the cooling effect of ethanol. 4. Conclusions Biodiesel (45%)emethanol (10%)ebiodiesel (45%), biodiesel (40%)emethanol (20%)ebiodiesel (40%), biodiesel (45%)eethanol (10%)ebiodiesel (45%) and biodiesel (40%)eethanol (20%)e
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biodiesel (40%) blends were run in a diesel engine under the same operating conditions and compared to a baseline diesel fuel. Overall, brake specific fuel consumption of alcohol blends is higher than for diesel, while ethanol-blended fuels show lower BSFC than methanol-blended fuels. There is no significant different in exhaust gas temperature. Increasing alcohol concentration reduces NO emissions, while increasing CO and HC emissions. Biodieseleethanolediesel blends, as compared to standard diesel, increase CO and HC emissions while reducing NO emissions. Interestingly, biodieselemethanolediesel blends have opposite effects on the emissions. Methanol blends would be the choice if CO and HC emissions are the aim. Ethanol blends would be the right choice for reducing NO emissions for the concentrations investigated in this work. Overall, emissions strongly depend on engine operating conditions and alcohol blend ratios, which could have positive and negative effects overall, due to oxygen content and cooling effects. References [1] Qi DH, Chen H, Geng LM, Bian YZH, Ren XCH. Performance and combustion characteristics of biodiesel-diesel-methanol blend fuelled engine. Applied Energy 2010;87:1679e86. [2] Shi X, Pang X, Mu Y, He H, Shuai S, Wang J, et al. Emission reduction potential of using ethanol-biodiesel-diesel fuel blend on a heavy-duty diesel engine. Atmospheric Environment 2006;40:2567e74. [3] Guarieiro LLN, de Souza AF, Torres EA, de Andrade JB. Emission profile of 18 carbonyl compounds, CO, CO2, and NOx emitted by a diesel engine fuelled with diesel and ternary blends containing diesel, ethanol and biodiesel or vegetable oils. Atmospheric Environment 2009;43:2754e61. [4] Jha SK, Fernando S, Columbus E, Willcutt H. A comparative study of exhaust emissions using diesel-biodiesel-ethanol blends in new and used engines. Transactions of the ASABE 2009;52:375e81. [5] Cheenkachorn K, Fungtammasan B. An investigation of diesel-ethanol-biodiesel blends for diesel engine: Part 2 e Emission and engine performance of a lightduty truck. Energy Sources, Part A: Recovery, Utilization and Environmental Effects 2010;32:894e900. [6] Abu-Audais M, Haddad O, Qudaisat M. The effect of alcohol fumigation on diesel engine performance and emissions. Energy Conversion & Management 2000;41:389e99.