Energy Fuels 2010, 24, 2675–2682 Published on Web 03/11/2010
: DOI:10.1021/ef901451n
Effect of Fuel Injection Timing on the Emissions of a Direct-Injection (DI) Diesel Engine Fueled with Canola Oil Methyl Ester-Diesel Fuel Blends Cenk Sayin,† Metin Gumus,† and Mustafa Canakci*,‡,§ †
Department of of Automotive Engineering Technology, Marmara University, Istanbul 34722, Turkey, ‡ Department of Automotive Engineering Technology, Kocaeli University, Izmit 41380, Turkey, and § Alternative Fuels Research and Development Center, Kocaeli University, Izmit 41275, Turkey Received December 1, 2009. Revised Manuscript Received March 1, 2010
Biodiesel is the name of a clean burning monoalkyl-ester-based oxygenated fuel made from natural, renewable sources, such as new/used vegetable oils and animal fats. The injection timing plays an important role in determining engine performance, especially pollutant emissions. In this study, the effects of fuel injection timing on the exhaust emission characteristics of a single-cylinder, direct-injection diesel engine were investigated when it was fueled with canola oil methyl ester-diesel fuel blends. The results showed that the brake-specific fuel consumption and carbon dioxide and nitrogen oxide emissions increased and smoke opacity, hydrocarbon, and carbon monoxide emissions decreased because of the fuel properties and combustion characteristics of canola oil methyl ester. The effect of injection timing on the exhaust emissions of the engine exhibited the similar trends for diesel fuel and canola oil methyl ester-diesel blends. When the results are compared to those of original (ORG) injection timing, at the retarded injection timings, the emissions of nitrogen oxide and carbon dioxide increased and the smoke opacity and the emissions of hydrocarbon and carbon monoxide decreased for all test conditions. On the other hand, with the advanced injection timings, the smoke opacity and the emissions of hydrocarbon and carbon monoxide diminished and the emissions of nitrogen oxide and carbon dioxide boosted for all test conditions. In terms of brake-specific fuel consumption, the best results were obtained from ORG injection timing in all fuel blends.
sources, is sustainable as a result of applicability to diesel engines without any modification.3,4 A lot of researchers have reported that using biodiesel as a fuel in diesel engines causes a diminution in harmful exhaust emissions as well as equivalent engine performance with diesel fuel.5-11 Several studies have found that biodiesel seems to emit far less of the most regulated pollutants than standard diesel fuel. Decreasing
Introduction Increasing air pollution is one of the most important problems of countries. Exhaust emissions from diesel engines have a main role on this pollution. The European Commission published some directives (2005/55/EC for Euro 4/5, etc.) to reduce exhaust emissions from light- and heavy-duty diesel engines. Hence, the vehicle manufacturers and researchers have been directed to produce diesel engines with high performance and low emissions. The vehicle manufacturers can meet the diesel engine emissions within the accepted level using the highest injection pressure, multipoint injection, different catalyst types (oxidation catalyst, nitrogen oxide absorber, etc.), exhaust gas recirculation, particulate traps, and controlling the start of injection timing. Nevertheless, all exhaust emissions from diesel engines are difficult to reduce simultaneously. One approach to solve this problem is to use oxygenated fuels. Therefore, the development in alternative fuel sources is important for diesel engine applications.1,2 Numerous vegetable oil esters have been tried as an alternative to diesel fuel. Biodiesel is made from renewable biological sources, such as vegetable oils and animal fats. Biodiesel, being renewable and widely available from a variety of
(3) Puhan, S.; Vedaraman, N.; Ram, V. B.; Sankarnarayanan, G.; Jeychandran, K. Mahua oil (Madhuca indica seed oil) methyl ester as biodiesel preparation and emission characteristics. Biomass Bioenergy 2005, 28 (1), 87–93. (4) Ramadhas, A. S.; Jayaraj, S.; Muraleedharan, C. Use of vegetable oils as IC engine fuels;A review. Renewable Energy 2004, 29 (5), 727– 742. (5) Graboski, M. S.; McCormick, R. L. Combustion of fat and vegetable oil derived fuels in diesel engines. Prog. Energy Combust. Sci. 1998, 24 (2), 125–164. (6) Altun, S.; Bulut, H.; Oner, C. The comparison of engine performance and exhaust emission characteristics of sesame oil-diesel fuel mixture with diesel fuel in a direct injection diesel engine. Renewable Energy 2008, 33 (8), 1791–1795. (7) Ramadhas, A. S.; Muraleedharan, C.; Jayaraj, S. Performance and emission evaluation of a diesel engine fueled with methyl esters of rubber seed oil. Renewable Energy 2005, 30 (12), 1789–1800. (8) Canakci, M.; Ozsezen, A. N.; Turkcan, A. Combustion analysis of preheated crude sunflower oil in an IDI diesel engine. Biomass Bioenergy 2009, 33 (5), 760–767. (9) Lee, S. W.; Herage, T.; Young, B. Emission reduction potential from the combustion of soy methyl ester fuel blended with petroleum distillate fuel. Fuel 2004, 83 (11-12), 1607–1613. (10) Alptekin, E.; Canakci, M. Determination of the density and the viscosities of biodiesel-diesel fuel blends. Renewable Energy 2008, 33 (12), 2623–2630. (11) Huzayyin, A. S.; Bawady, A. H.; Rady, M. A.; Dawood, A. Experimental evaluation of diesel engine performance and emission using blends of jojoba oil and diesel fuel. Energy Convers. Manage. 2004, 45 (13-14), 2093–2112.
*To whom correspondence should be addressed. Telephone: þ90262-3032285. Fax: þ90-262-3032203. E-mail: mustafacanakci@ hotmail.com. (1) Ozsezen, A. N.; Canakci, M.; Sayin, C. Effects of biodiesel from used frying palm oil on the exhaust emissions of an indirect injection (IDI) diesel engine. Energy Fuels 2008, 22 (4), 2796–2804. (2) Ozsezen, A. N. Investigation of the effects of biodiesel produced from waste palm oil on the engine performance and emission characteristics. Ph.D. Dissertation, Kocaeli University, Izmit, Turkey, 2007; pp 4-7 (in Turkish). r 2010 American Chemical Society
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carbon dioxide (CO2) using biodiesel contributes to a reduce greenhouse effect. In another sense, diminishing carbon monoxide (CO), hydrocarbons (HCs), and smoke opacity improves air quality.12-17 In efforts to achieve the reduction of engine emissions and fuel consumption while keeping other engine performances at an acceptable level, the fuel injection plays an important role. The most important injection characteristics are injection timing, injection duration, and injection pressure. Fuel injection timing affects the combustion and exhaust emissions. The state of air into which the fuel is injected changes as the injection timing is varied, and thus, ignition delay varies. If the injection starts earlier, the initial air temperature and pressure in the cylinder are low; therefore, the ignition delay will increase. If the injection starts later, which means the piston is closer to top dead center (TDC), the temperature and pressure will be high and a decrease in ignition delay will occur. Thus, variation in the start of injection timing has effects on the engine performance and exhaust emissions, especially on the brake-specific fuel consumption (BSFC), brake thermal efficiency (BTE), and nitrogen oxide (NOx) emissions, because of the changing of the maximum pressure and temperature in the engine cylinder.18,19 Several studies have shown that the injection timing affects the level of exhaust emissions of diesel engines when using biodiesel. Bari et al.20 examined the influence of advanced injection timing on the CO and NOx emissions of a directinjection (DI) diesel engine using waste cooking oil (WCO) and diesel fuel. The original (ORG) start of injection timing of the test engine was 15° crank angle (CA) before top dead center (BTDC). The tests were carried out at the engine speed of 3600 revolutions per minute (rpm) and repeated for the injection timings of 16.3 and 19° CA BTDC. With the injection timing advanced by 4°, the CO emission reduced by 9.9% for WCO and 44.9% for diesel but the NOx emission was increased by 77.6% for WCO and 91.4% for diesel. Aktas and Sekmen21 investigated the effect of advanced injection timing on the CO, NOx, and HC emissions of a diesel engine fueled with biodiesel. The ORG injection timing of the engine was 24.9° CA BTDC. The tests were conducted at three
engine type cylinder number bore (mm) stroke (mm) total cylinder volume (cm3) injector opening pressure (MPa) number of nozzle holes start of injection timing (deg CA BTDC) compression ratio maximum torque (N m at 2200 rpm) maximum power (kW at 3600 rpm)
Lombardini 6 LD 400 1 86 68 395 20 4 20 18:1 21 8
different injection timings (24.9, 26.6, and 28.5° CA BTDC) for 20 N m constant load and six different engine speeds (1400-3400 rpm) with 400 rpm intervals for each injection timing. When the injection timing was advanced to 26.6° CA BTDC, CO and HC emissions decreased, while NOx emissions increased by 4-11%, when the engine was run with biodiesel. Nwafor et al.22 researched the effects of advanced injection timing on the HC emissions of a diesel engine using rapeseed oil. The ORG injection timing of the engine was 30° CA BTDC. When the injection timing was advanced by 5° CA BTDC (35° CA BTDC), HC emissions decreased by 12.2%. From the literature review, it seems that the effects of retarded and advanced injection timings on the exhaust emissions of a diesel engine have not been clearly studied when using canola oil methyl ester (COME) blended diesel fuel. Therefore, in the present study, the effects of both injection timing and COME-blended diesel fuel on the exhaust emissions of a DI diesel engine were experimentally investigated. Experimental Section The experiments were performed on a Lombardini 6 LD 400, single-cylinder, naturally aspirated, air-cooled DI diesel engine. The basic specifications of the engine are shown in Table 1. A schematic layout of the experimental setup is depicted in Figure 1. A Cussons-P8160-type single-cylinder test bed, which is equipped with an instrument cabinet (column mounted), fitted the torque gauge, electrical tachometer, and switches for load remote control, measurement instruments was used in the experiments. The dynamometer is a DC machine rated at 380 V and 10 kW. An inductive pickup speed sensor was also used to measure the engine speed. Air consumption was measured using a sharp-edged orifice plate [ISO 5167(1980)] and inclined manometer (error (3%). Different digital thermocouples (error (1%) monitored the temperatures of intake air, engine oil, coolant inlet and outlet, and exhaust. Fuel consumption was determined using a calibrated buret with an accuracy of 0.1% and a stopwatch with an accuracy of 0.5%. A Bilsa 2100 model exhaust gas analyzer was used to measure the concentration of emissions, such as HC, CO, and CO2. A Sun 1500-type smoke meter was employed to measure the smoke opacity of the exhaust gas emitted from the diesel engine. A KaneMay Quintox exhaust gas analyzer was used to measure the NOx emissions. These analyzers were calibrated before the experiments. Table 2 shows the accuracies of the measurements and the uncertainties in the calculated results. The ordinary diesel fuel was obtained from the T€ upras- Petroleum Corporation. COME was purchased from EKO Biodiesel, a commercial supplier. Some properties of the both fuels are shown in Table 3. The nomenclature BX represents a blend including X% COME; i.e., B5 indicates a blend including 5% COME, and B100 represent pure COME.
(12) Zhang, Y.; Van Gerpen, J. H. Combustion analysis of esters of soybean oil in a diesel engine. SAE Tech. Pap. 960765, 1996. (13) Raheman, H.; Phadatare, A. G. Diesel engine emissions and performance from blends of karanja methyl ester and diesel. Fuel 2004, 27 (4), 393–397. (14) Canakci, M. Combustion characteristics of a turbocharged DI compression ignition engine fueled with petroleum diesel fuels and biodiesel. Bioresour. Technol. 2007, 98 (6), 1167–1175. (15) Canakci, M. The potential of restaurant waste lipids as biodiesel feedstocks. Bioresour. Technol. 2007, 98 (1), 183–190. (16) Ozsezen, A. N.; Canakci, M.; Turkcan, A.; Sayin, C. Performance and combustion characteristics of a DI engine fueled with waste palme oil and canola oil methyl esters. Fuel 2009, 88 (4), 629–636. (17) Baldassarri, L. T.; Battistelli, C. L.; Conti, L.; Crebelli, R.; Berardis, B. D.; Iamiceli, A. L. Emission comparison of urban bus engine fueled with diesel oil and biodiesel blend. Sci. Total Environ. 2004, 327 (1-3), 147–162. (18) Sayin, C.; Uslu, K. Influence of advanced injection timing on the performance and emissions of CI engine fueled with ethanol-blended diesel fuel. Int. J. Energy Res. 2008, 32 (11), 1006–1015. (19) Sayin, C.; Uslu, K.; Canakci, M. Influence of injection timing on the exhaust emissions of a dual-fuel CI engine. Renewable Energy 2008, 33 (6), 1314–1323. (20) Bari, S.; Yu, C. W.; Lim, T. H. Effect of fuel injection timing with waste cooking oil as a fuel in a direct injection diesel engine. J. Automob. Eng. 2003, 218 (1), 160–172. (21) Aktas, A.; Sekmen, Y. The effects of advance fuel injection on engine performance and exhaust emissions of a diesel engine fuelled with biodiesel. J. Fac. Eng. Archit. Gazi Univ. 2008, 23 (1), 199–207 (in Turkish).
(22) Nwafor, O. M. I.; Rice, G.; Ogbonna, A. I. Effect of advanced injection timing on the performance of rapeseed oil in diesel engines. Renewable Energy 2000, 21 (3-4), 433–444.
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Figure 1. Experimental layout.
combustion chamber design, atomization rate, start of injection timing, engine load, and speed. The most important among these parameters is the equivalence ratio.1,23 The variation of CO with engine load for the fuels is presented in Figure 2. While the fuels produced a low amount of CO emission at high-load levels, those resulted in more emissions at light loading conditions. The CO emissions were found to decrease with the increasing load. This is a typical result for internal combustion engines because the combustion temperature increases with the engine load, as shown in Figure 8. Therefore, CO emissions start to decrease.7 The results obtained in this study confirmed this statement. At ORG injection timing, while the CO emission was measured to be 0.22% with B20 at 20 N m load, it was 0.43% at 5 N m. Figure 2 shows that the CO emission level decreased with the increasing COME percentage in the fuel blend. COME contains about 11% oxygen. This helps for the complete combustion.24,25 For all engine loads, CO emissions for B100, B50, B20, and B5 decreased by 40.11, 25.82, 15.18, and 3.73% compared to those of B0, respectively. The effect of fuel injection timing on the CO emissions is shown in Figure 3. CO emissions increased with retarded fuel injection timing. Retarding the fuel injection timing decreases the amount of fuel burned in the premixed combustion phase and increases the amount of fuel burned in the subsequent diffusive combustion phase. The latter phase always takes place in a rich mixture environment and easily produces the incomplete burning product CO.26 Retarding the injection timing by 5° (from 20° to 15° CA BTDC) caused the CO emission, which increased by 31.25% for B50 at 20 N m
Table 2. Accuracies of the Measurements and the Uncertainties in the Calculated Results measurements
accuracy
load (N m) speed (rpm) time (%) temperatures (°C)
(2 (10 (0.5 (1
calculated results
uncertainty
power (%) BSFC (%)
(2.55 (2.60
Dynamic fuel injection timing is adjusted on the basis of the opening time of the needle. Fuel properties, such as bulk modulus and density, affect the dynamic fuel injection timing. Static injection timing, in other words fuel delivery advance timing, is the timing when fuel starts to pressurize in the injection pump. In this study, static injection timing was taken into account. The ORG injection timing of the test engine is 20° CA BTDC. Injection timing adjustment is accomplished by adding or removing the shims in the injection pump. The addition or removal of 0.25 mm of shim changes the injection timing approximately 5° CA. The experiments were carried out at three different injection timings (15, 20, and 25° CA BTDC). For each injection timing, the engine was run at constant engine speed (2200 rpm) and four different loads (5, 10, 15, and 20 N m). The values of the engine oil temperature, exhaust gas temperature, and emissions, such as smoke opacity, CO, HC, NOx, and CO2, were recorded during the experiments. Each test was repeated 3 times. The values given in this study are the average of these three results. All data were collected after the engine stabilized. The engine was sufficiently warmed up at each test, and the engine oil temperature was maintained around 85-90 °C. During the experimental study, all fuels had no trace of knock at different injection timing and it was detected that the engine noise was qualitatively less than that of petroleum-based diesel fuel (PBDF) when the engine was running with B100.
(23) Heywood, J. B. Internal Combustion Engines; McGraw-Hill: New York, 1988, pp 491-499, 297, 571. (24) Gumus, M. Evaluation of hazelnut kernel oil of Turkish origin as alternative fuel in diesel engines. Renewable Energy 2008, 33 (11), 2448–2457. (25) Huang, Z. H.; Lu, H. B.; Jiang, D. M.; Zeng, K.; Liu, B.; Zhang, J. Q.; Wang., X. B. Combustion behaviors of a compression ignition engine fuelled with diesel/methanol blends under various fuel delivery advance angles. Bioresour. Technol. 2004, 95 (3), 331–341. (26) Ma, Z.; Huang, Z. H.; Li, C.; Wang, X. B.; Miao, H. Effects of fuel injection timing on combustion and emission characteristics of a diesel engine fueled with diesel-propane blends. Energy Fuels 2007, 21 (3), 1504–1510.
Results and Discussion CO Emissions. The CO emissions in the exhaust represent lost chemical energy that is not fully used in the engine. Generally, the CO emission is affected by the equivalence ratio, fuel type, 2677
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Table 3. Some Properties of the Fuels Used in the Experiments units typical formula molecular weight sulfated ash content density carbon/hydrogen ratio flash point carbon residue heating value cetane number kinematic viscosity acid value oxidation stability distillation initial boiling point 90% recovered
EU limits (EN 14214)
U.S.A. limits (ASTM D 6751)
g/mol mass % kg/m3 (at 15 °C)
maximum of 0.02 860-900
maximum of 0.02
°C mass % kJ/kg
minimum of 120 maximum of 0.30
minimum of 130
minimum of 51 3.5-5.0 maximum of 0.50 minimum of 6.0
minimum of 41 1.9-6.0 maximum of 0.80
mm2/s (at 40 °C) mg of KOH/g 1 h (at 110 °C) °C °C
maximum of 360
Figure 2. CO emissions versus engine load for the fuels at ORG injection timing.
COME45
diesel46
C18.08H34.86O2 284.17 0.0004 885 1:1.93 74.1 0.0004 38730 60.4 4.39 0.15 10.1
C14.16H25.21 195.50 0.0015 840.3 1:1.78 61.5 0.067 42930 56.5 3.18
331 348
164.7 351.1
Figure 4. HC emissions versus engine load for the fuels at ORG injection timing.
Figure 4. Typically, HC emissions are a serious problem at light loads for diesel engines. At light loads, the fuel is less to impinge on surfaces, but because of poor fuel distribution, large amounts of excess air, and low cylinder temperature, lean fuel-air mixture regions may survive to escape into exhaust.28 The results acquired in this study supported this explanation. At the ORG injection timing, while the HC emission was measured to be 23 particulates per million (ppm) with B0 at 15 N m load, it was 28 ppm at 5 N m. As shown in the Figure 4, the HC emission was steadily decreased when the amount of COME increased in the blend. This is also due to the oxygenated nature of COME, where more oxygen is available for burning and reducing HC emissions in the exhaust.29 On average, HC emissions for all engine loads for B100, B50, B20, and B5 decreased by 65.25, 48.1, 39.82, and 12.47% compared to those of B0, respectively. Figure 5 shows the effect of fuel injection timing on HC emissions. When combustion was retarded, which happens with the retarded start of injection, the maximum gas temperatures were lower, as shown in Figure 9. While the volume increases during the expansion stroke, HC emissions increased drastically.30 Retarding the injection timing by
Figure 3. CO emissions versus injection timing at 20 N m engine load.
load. However, the CO emission decreased with the advanced injection timing. The advanced injection timing produces a higher cylinder temperature, as seen in Figure 9, and increases the oxidation process between carbon and oxygen molecules. This causes a reduction in CO emission. Advancing the injection timing by 5° (from 20° to 25° CA BTDC) caused a lower CO emission, which decreased by 18.75% for B50 at 20 N m load. HC Emissions. HC emissions from DI diesel engines are mainly caused by the fuel injected and mixed beyond the lean combustion limit during the ignition delay and fuel effusing from the nozzle sac at low pressure.27 The variation of HC with engine load for different fuels tested is shown in
(28) Sayin, C.; Ilhan, M.; Canakci, M.; Gumus, M. Effect of injection timing on the exhaust emissions of a diesel engine using diesel-methanol blends. Renewable Energy 2009, 34 (5), 1261–1269. (29) Agarwal, A. K. Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines. Prog. Energy Combust. Sci. 2007, 33 (3), 233–271. (30) Payri, F.; Benajes, J.; Arregle, J.; Riesco, J. M. Combustion and exhaust emissions in a heavy-duty diesel engine with increased premixed combustion phase by means of injection retarding. Oil Gas Sci. Technol. 2006, 61 (2), 247–258.
(27) Lakshminarayanan, P. A.; Nayak, N.; Dingare, S. V.; Dani, A. D. Predicting hydrocarbon emissions from direct injection diesel engines. J. Eng. Gas Turbines Power 2002, 124 (3), 708–807.
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Figure 6. NOx emissions versus engine load for the fuels at ORG injection timing.
Figure 5. HC emissions versus injection timing for the fuels at 20 N m engine load.
5° (from 20° to 15° CA BTDC) caused the emission to augment by 9.1% for B5 at 20 N m load. On the other hand, the advanced injection timing caused an earlier start of combustion relative to the TDC. Because of this, the cylinder charge, being compressed as the piston moved to the TDC, had relatively higher temperatures and thus lowered the HC emissions. Advancing the injection timing by 5° (from 20° to 25° CA BTDC) caused lower HC emissions, which reduced by 36.34% for B5 at 20 N m load. NOx Emissions. The conversion of nitrogen and oxygen to NOx is generated by the high combustion temperatures occurring within the burning fuel sprays and is controlled by local conditions. NOx is a collective term used to refer to nitric oxide (NO) and nitrogen dioxide (NO2). NOx emissions form in the high-temperature burned gas region, which is non-uniform, and the formation rates are highest at the regions close to stoichiometry.31 The variation of NOx with the engine load for different fuel blends is presented in Figure 6. NOx emissions increased with the increasing engine load because of the increasing combustion temperature, as shown in Figure 8. At the ORG injection timing, while the NOx emission was determined to be 133 ppm with B50 at 20 N m load, it was 19 ppm at 5 N m. As seen in Figure 6, the NOx emissions generally increased with the increasing fraction of COME in the fuel blend. It is obvious that the increased NOx with the use of COME and its blends is a result of increasing oxidation. The oxygen content of COME is an important factor in the high NOx formation levels, because the oxygen content of COME provides high local peak temperatures and a corresponding excess of air.32-34 As indicated in Figure 8, the combustion temperature increased with the increasing amount of COME in the fuel blend. For all engine loads, NOx emissions for B100, B50, B20, and B5 increased by 65.25, 48.1, 39.82, and 12.47% compared to those of B0, respectively.
Figure 7. NOx emissions versus injection timing for the fuels at 20 N m engine load.
Figure 7 illustrates the effect of fuel injection timing on NOx emissions. Retarding the fuel injection timing caused a decrease in the ignition delay and cylinder gas temperature. Consequently, the NOx concentration tended to be less.35 The exhaust gas temperatures obtained in the experiments are shown in Figure 9, which confirmed this statement. Retarding the injection timing by 5° (from 20° to 15° CA BTDC) caused the NOx emission to reduce by 28.11% for B20 at 20 N m load. However, advancing the fuel injection timing increased the peak cylinder pressure because of the longer ignition delay. Higher peak cylinder pressures resulted in higher peak temperatures. As a consequence, the NOx concentration started to rise. Advancing the injection timing by 5° (from 20° to 25° CA BTDC) caused the NOx emission to increase by 8.59% for B20 at 20 N m load. Smoke Opacities. Because of the heterogeneous nature of diesel combustion, there is a wide distribution of fuel/air ratios within the cylinder. Smoke emissions are attributed to either fuel-air mixtures that are too lean to auto-ignite or support a propagating flame or fuel-air mixtures that are too rich to ignite. The soot formation mainly takes place in the fuel-rich zone at high temperatures and pressures, especially within the core region of each fuel spray, and is caused by high-temperature decomposition.36 The variation of smoke with the engine load for different fuel blends is depicted in Figure 10. The formation of smoke strongly depends upon the engine load. When the load is increased,
(31) Ilkilic, C. Emission characteristics of a diesel engine fueled with by 25% sunflower oil methyl ester and 75% diesel fuel blend. Energy Sources 2009, 31 (6), 480–491. (32) Beatrice, C.; Bertoli, C.; D’Alessio, J.; Del Giacomo, N.; Lazzaro, M.; Massoli, P. Experimental characterization of combustion behavior of new diesel fuels for low emission engines. Combust. Sci. Technol. 1996, 120 (1-6), 335–355. (33) Theodoros, C. Z.; Dimitrios, T. H. DI diesel engine performance and emissions from the oxygen enrichment of fuels with various aromatic content. Energy Fuels 2004, 18 (3), 659–666. (34) Ren, Y.; Huang, Z. H.; Jiang, D. M; Liu, L. X.; Zeng, K.; Liu, B.; Wang, X. B. Combustion characteristics of a compression-ignition engine fuelled with diesel-dimethoxy methane blends under various fuel injection angles. Appl. Therm. Eng. 2006, 26 (4), 327–337.
(35) Scholl, K. W.; Sorenson, S. C. Combustion of soybean oil methyl ester in a direct injection diesel engine. SAE Tech. Pap. 930934, 1993. (36) Yoshiyuki, K.; Changlin, Y.; Kei, M. Effects of fuel properties on combustion and emission characteristics of a direct injection diesel engine. SAE Tech. Pap. 2000-01-1831, 2000.
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Figure 8. Exhaust temperatures versus engine loads for the fuels at ORG injection timing.
Figure 10. Smoke opacity versus engine load for the fuels at ORG injection timing.
Figure 9. Exhaust temperatures versus injection timing for the fuels at 20 N m engine load.
Figure 11. Smoke opacity versus injection timing for the fuels at 20 N m engine load.
more fuel is injected into the combustion chamber, and this causes an increase in smoke formation.34 The results obtained in this study supported this statement. At the ORG injection timing, while smoke opacity was measured to be 94% with B5 at 20 N m load, it was found as 65% at 5 N m. As seen in Figure 10, smoke opacity has a tendency to decrease with the increasing fraction of COME in the fuel blend. The oxygen content of the COME, which enables more complete combustion even in the regions of the combustion chamber with fuel-rich diffusion flames, promotes the oxidation of the already formed soot.37,38 For all engine loads, smoke opacity for B100, B50, B20, and B5 diminished by 21.26, 12.43, 4.87, and 3.63% compared to those of B0, respectively. The effect of injection timing on smoke opacity can be seen in Figure 11. Retarding the fuel injection timing increased the smoke opacity. This is due to increasing the fraction of diffusive combustion while retarding the fuel injection timing.39,40 Retarding the injection timing by 5° (from 20° to 15° CA BTDC) caused the smoke emission to increase by 3.22%
for B20 at 20 N m load. Advancing the injection timing leads to higher temperatures during the expansion stroke and more time in which oxidation of the soot particles occurs. Advancing the injection timing by 5° (from 20° to 25° CA BTDC) caused the smoke emission to decrease by 6.51% for B20 at 20 N m load. CO2 Emissions. The CO2 emission is produced by complete combustion of fuel. Ideally, combustion of a HC fuel should produce only CO2 and water (H2O). The concentrations have an opposite behavior when compared to the CO concentrations and because of the improvement in the combustion process.41 The variation of CO2 with the engine load for different fuel blends is shown in Figure 12. As expected, the CO2 emission increased with the increasing load. The main reason of increasing CO2 with an increasing load is more fuel injected into the engine. The other reasons are the increasing combustion temperature and oxidization rates.11 At the ORG injection timing, while CO2 emission was measured to be 13.32% with B20 at 20 N m load, it was found as 11.61% at 5 N m. As seen in Figure 12, the CO2 emission increased with the increasing fraction of COME in the fuel blend. For all engine loads, CO2 emissions increased by 9.25, 4.12, and 1.13% for B100, B50, and B20 and decreased by 1.32% for B5 compared to those of B0, respectively. The figure shows that most of the carbon converts to CO2 under all engine load conditions, except 5 N m. While the test engine was running with
(37) Lapuerta, M.; Armas, O.; Rodriguez-Fernandez, J. Effect of biodiesel fuels on diesel engine emissions. Prog. Energy Combust. Sci. 2008, 34 (2), 198–223. (38) Huang, Z. H.; Lu, H. B.; Jiang, D. M.; Zeng, K.; Liu, B.; Zhang, J. Q.; Wang, X. B. Performance and emissions of a compression ignition engine fueled with diesel/oxygenate blends for various fuel delivery advance angles. Energy Fuels 2005, 19 (2), 403–410. (39) Shuai, S.; Abani, N.; Yoshikawa, T.; Reitz, R. D.; Park, S. V. Evaluation of the effects of injection timing and rate-shape on diesel low temperature combustion using advanced CFD modeling. Fuel 2009, 88 (7), 1235–1244. (40) Buyukkaya, E.; Cerit, M. Experimental study of NOx emissions and injection timing of a low heat rejection diesel engine. Int. J. Therm. Sci. 2008, 56 (2), 97–103.
(41) Sayin, C.; Kilicaslan, I.; Canakci, M.; Ozsezen, A. N. An experimental study of the effect of octane number higher than engine requirement on the engine performance and emissions. Appl. Therm. Eng. 2005, 25 (8-9), 1315–1324.
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Figure 12. CO2 emissions versus engine load for the fuels at ORG injection timing.
Figure 13. CO2 emissions versus injection timing for the fuels at 20 N m engine load.
COME, the air/fuel equivalence ratio was lower than that of diesel fuel at all engine loads. Probably, at 5 N m, a higher BSFC amount, viscosity, and density of COME, which led to poor injection characteristics relative to diesel fuel, affected the complete combustion reaction of COME. The CO2 emission of the COME and its blends was measured lower for 5 N m but higher for 10, 15, and 20 N m than those of diesel fuel. The shorter ignition delay and higher boiling point of COME increased the combustion duration. This behavior became more obvious at the high engine loads. Additionally, the CO2 formation depends upon the carbon-hydrogen ratio of the fuel. Stoichiometrically, combustion of a HC fuel should produce only CO2 and water (H2O), as mentioned above. The relative proportion of these two depends upon the carbon/hydrogen ratio in the fuel. In this study, these ratios are about 1:1.78 for diesel fuel and 1:1.93 for COME (see Table 3). As seen in the eqs 1 and 2, if the complete combustion reactions are established, diesel fuel releases 3.18 kg of CO2/kg of fuel and COME releases 2.79 kg of CO2/kg of fuel. Thus, CO2 emissions from an engine can be reduced by reducing the carbon content of the fuel per unit energy. The complete combustion reaction for COME is C18:08 H34:86 O2 þ 25:79ðO2 þ 3:79N2 Þ f 18:08CO2 þ 17:43H2 O þ 96:97N2
Figure 14. BSFC versus engine load for the fuels at ORG injection timing.
blends, BSFC decreased with the increase in the engine load. One possible explanation for this reduction could be the higher percentage increase in the brake power with load as compared to the fuel consumption. At the ORG injection timing, while BSFC was measured to be 346 g kW-1 h-1 with B50 at 20 N m load, it was found to be 474 g kW-1 h-1 at 5 N m. As seen in the Figure 14, the BSFC was slightly increased with the increased COME percentage in the fuel blend. It should be noted that the lower heating value (LHV) of COME is 14% lower than that of diesel fuel. With the increase in the COME percentage in the fuel blends, the LHV of the fuel blend decreased. The BSFC increased when the COME percentage was increased in the fuel blend compared to that of diesel fuel. On the other hand, COME is an oxygenated fuel and leads to more complete combustion; hence, BSFC may reduce. It is clear from the figure that the LHV is more effective than the oxygen content with regard to increasing BSFC.43 On average, BSFC for all engine loads for B100, B50, B20, and B5 boosted by 23.75, 18.27, 13.27, and 2.25% compared to those of B0, respectively. The effect of fuel injection timing on BSFC is depicted in Figure 15. When the injection timing was retarded and advanced 5° CA BTDC compared to ORG injection timing, BSFC increased by 16.19 and 6.47% for B5, respectively.
ð1Þ
The complete combustion reaction for diesel fuel is C14:16 H25:21 þ 20:46ðO2 þ 3:76N2 Þ f 14:16CO2 þ 12:60H2 O þ 76:92N2
ð2Þ
The effect of injection timing on CO2 emissions is shown in Figure 13. Retarding the fuel injection timing caused a lower combustion temperature, as depicted in Figure 9, and this reduced the chemical speed. Thus, a decrease in the CO2 emissions occurred.42 Retarding the injection timing by 5° (from 20° to 15° CA BTDC) caused the CO2 emission to reduce by 3.12% for B100 at 20 N m load. CO2 emissions increased with advancing the injection timing for all fuel blends. Advancing the injection timing by 5° (from 20° to 25° CA BTDC) caused the CO2 emission to increase by 2.13% for B100 at 20 N m load. BSFC. BSFC is defined as the ratio of the fuel consumption to the brake power. The variation of BSFC with the load for different fuels is presented in Figure 14. For all fuel
(43) Ozsezen, A. N.; Canakci, M.; Sayin, C. Effects of biodiesel from used frying palm oil on the performance, injection, and combustion characteristics of an indirect injection diesel engine. Energy Fuels 2008, 22 (2), 1297–1305. (44) Lombardini. Engine technical specification; Turkey, 2000 (in Turkish). (45) EKO Biodiesel. Product specification; Turkey, 2009 (in Turkish). (46) T€ upras-. Product specification; Turkey, 2009 (in Turkish).
(42) Sayin, C.; Canakci, M. Effects of injection timing on the engine performance and exhaust emissions of a dual-fuel diesel engine. Energy Convers. Manage. 2009, 50 (1), 203–213.
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: DOI:10.1021/ef901451n
Sayin et al.
injection timing caused an earlier start of combustion relative to the TDC. Because of this, HC emissions decreased and NOx emissions increased. Advancing the injection timing gave the best results for the smoke opacity and the emissions of CO and HC for B100. On the other hand, retarding the injection timing presented the minimum results of NOx and CO2 emissions for B0 and B100, respectively. (3) Increasing the COME ratio in the fuel blend led to an increase in BSFC. This is probably the result of the LHV of the COME, which is lower than that of the diesel fuel. The ORG injection timing gave the best results for BSFC compared to the retarded and advanced injection timings. When the injection timing is advanced, the ignition delay will be longer and the speed of the flame will be shorter. These two lead to the reduction in the maximum cylinder pressure and engine power output. Thus, fuel consumption per power output will augment. On the other hand, retarded injection timing means later combustion, and therefore, cylinder pressure increases only when the cylinder volume becomes higher rapidly and results in a reduced effective pressure to do work.
Figure 15. BSFC versus injection timing for the fuels at 20 N m engine load.
Minimum BSFC was obtained at ORG injection timing for all fuel blends. The fuel consumption at ORG injection timing was the lowest, and it increased at advanced and retarded injection timings. Advancing the injection timing causes the maximum pressure to increase and occurs before TDC in the compression stroke. This reduces the maximum pressure occurring during the expansion stroke and torque output. On the other hand, with retarding the injection timing, the combustion will delay and result in a reduced effective pressure to do work during the expansion stroke. Thus, for both cases, fuel consumption per power output increased.19
Acknowledgment. This study was supported by the Scientific Research Project Commission of Marmara University under Grant BSE-075/131102.
Nomenclature B0 = 100% diesel B5 = 5% COME plus 95% PBDF (volumetric) B20 = 20% COME plus 80% PBDF (volumetric) B50 = 50% COME plus 50% PBDF (volumetric) B100 = 100% COME BSFC = brake-specific fuel consumption (g kW-1 h-1) BTDC = before top dead center BTE = brake thermal efficiency CA = crank angle CI = compression ignition CO = carbon monoxide COME = canola oil methyl ester CO2 = carbon dioxide DI = direct injection LHV = lower heating value (kJ/kg) NOx = nitrogen oxide ORG = original TDC = top dead center HC = hydrocarbon WCO = waste cooking oil ppm = particulates per million rpm = revolutions per minute
Conclusion In this study, the effects of fuel injection timing on the exhaust emission characteristics of a diesel engine have been investigated when the engine was fueled with COME-diesel blends. From the present paper, the following conclusions are summarized: (1) COME is an oxygenated fuel and leads to more complete combustion. It has a high cetane number and low aromatic content when compared to diesel fuel. When the test engine was fueled with COME or its blends, the amount of smoke, HC, and CO emissions reduced. However, the combustion temperature increased with the increasing amount of COME in the fuel blend. This led to a higher quantity of NOx formation. (2) In terms of injection timing, the test results demonstrated that, with the advanced injection timing, the smoke opacity and the emissions of CO and HC decreased, while NOx and CO2 emissions increased. When the injection timing was advanced, the CO emission decreased because of the improved reaction between the fuel and oxygen. This caused an increase in the CO2 emissions. Advancing the
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