Energy Fuels 2010, 24, 3199–3213 Published on Web 04/09/2010
: DOI:10.1021/ef9014247
Effect of Fuel Injection Timing on the Injection, Combustion, and Performance Characteristics of a Direct-Injection (DI) Diesel Engine Fueled with Canola Oil Methyl Ester-Diesel Fuel Blends Metin Gumus,† Cenk Sayin,† and Mustafa Canakci*,‡,§ †
Department of Automotive Engineering Technology, Marmara University, 34722 Istanbul, Turkey, ‡Department of Automotive Engineering Technology, Kocaeli University, 41380 Izmit, Turkey, and §Alternative Fuels Research and Development Center, Kocaeli University, 41275 Izmit, Turkey Received November 22, 2009. Revised Manuscript Received March 29, 2010
In the last 3 decades, the search for alternative and renewable fuels, which have to be not only sustainable but also friendly with respect to the environment and techno-economically competitive, has gained importance because of the increasing environmental concerns and depletion in petroleum resources. Therefore, in this study, the influence of injection timing on the injection, combustion, and performance characteristics of a single-cylinder, four-stroke, direct-injection, naturally aspirated diesel engine has been experimentally investigated when using canola oil methyl ester (COME) and its blends with diesel fuel. The tests were conducted for three different injection timings [15°, 20°, and 25° crank angle (CA) before top dead center (BTDC] at constant engine speed and different loads. The experimental test results showed that, because of the different properties of COME and diesel, both fuels exhibit different injection, combustion, and performance characteristics for different engine loads and injection timing. Investigation of injection characteristics of the fuels showed that using COME instead of diesel resulted in earlier injection timings. The maximum cylinder pressure, the maximum rate of pressure rise, and the maximum heat release rate are slightly lower, while the ignition timing is higher for COME and its blends for all loads and injection timings. The brake-specific fuel consumption for COME is higher than that of diesel fuel, while the brake thermal efficiency of COME is lower than that of diesel fuel. The original injection timing gave the best results for brake-specific fuel consumption, brake-specific energy consumption, and brake thermal efficiency compared to the advanced and retarded injection timings.
Biodiesel is oxygenated, biodegradable, nontoxic, and environmentally friendly. It consists of alkyl monoesters of fatty acids from triacylglycerols and can be produced from vegetable oils, animal fats, and waste restaurant grease. Additionally, biodiesel is not a unique compound, and therefore, its composition and properties will depend upon the nature of the feedstock used in the production.5 With the expansion of using biodiesel around the world, numerous studies have been carried out to investigate the performance and emission characteristics of CI engines fueled by this alternative fuel.5-11 The differences in physical properties between petroleum-derived diesel fuels and vegetable-oil-based fuels also affect the injection and combustion characteristics.3-5,12-15 Nowadays, environmental
Introduction Compression-ignition (CI) or diesel engines are widely used for transportation, automotive, and agricultural applications and industrial sectors because of their high fuel conversion efficiencies and easy operation.1,2 The existing CI engines operate with conventional diesel fuel derived from crude oil. It is well-known that the world petroleum resources are limited and the production of crude oil is becoming more difficult and expensive. On the other hand, the pollutants including unburned hydrocarbons (UHCs), carbon monoxide (CO), nitrogen oxides (NOx), and smoke opacity emissions have been regulated by laws in many countries. Recently, changing the engine-operating parameters, such as valve timing, injection timing, and atomization ratio, has been carried out in many studies on the CI engines aiming to reduce the emissions. At the same time, depletion of fossil fuels and environmental considerations have led to investigations in alternative fuels.1-4
(5) Ozsezen, A. N.; Canakci, M.; Sayin, C. Energy Fuels 2008, 22, 1297–1305. (6) Puhan, S.; Vedaraman, N.; Ram, V. B.; Sankarnarayanan, G.; Jeychandran, K. Biomass Bioenergy 2005, 28, 87–93. (7) Ramadhas, A. S.; Muraleedharan, C.; Jayaraj, S. Renewable Energy 2005, 30, 1789–1800. (8) Lee, S. W.; Herage, T.; Young, B. Fuel 2004, 83, 1607–1613. (9) Huzayyin, A. S.; Bawady, A. H.; Rady, M. A.; Dawood, A. Energy Convers. Manage. 2004, 45, 2093–2112. (10) Raheman, H.; Phadatare, A. G. Fuel 2004, 27, 393–397. (11) Gumus, M. Renewable Energy 2008, 33, 2448–2457. (12) Graboski, M. S.; McCormick, R. L. Prog. Energy Combust. Sci. 1998, 24, 125–164. (13) Canakci, M.; Ozsezen, A. N.; Turkcan, A. Biomass Bioenergy 2009, 33, 760–767. (14) Canakci, M. Bioresour. Technol. 2007, 98, 1167–1175. (15) Scholl, K. W.; Sorenson, S. C. SAE Tech. Pap. 930934, 1993.
*To whom correspondence should be addressed. Telephone: þ90-262-3032285. Fax: þ90-262-3032203. E-mail: mustafacanakci@ hotmail.com. (1) Sayin, C.; Kilicaslan, I.; Canakci, M.; Ozsezen, N. Appl. Therm. Eng. 2005, 25, 1315–1324. (2) Asfar, K. R.; Hamed, H. Energy Convers. Manage. 1998, 39, 1081– 1093. (3) Chao, M. R.; Lin, C. T.; Chao, H. R.; Chang, F. H.; Chen, C. B. Sci. Total Environ. 2001, 279, 167–179. (4) Yuksel, F.; Yuksel, B. Renewable Energy 2004, 29, 1181–1191. r 2010 American Chemical Society
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an indirect injection diesel engine running with the fuels derived from pure jojoba oil, jojoba methyl ester, and its blends with gas oil. Test parameters were selected as a percentage of jojoba methyl ester in the blend, engine speed, load, injection timing, and engine compression ratio. The results showed that the fuel derived from jojoba is generally comparable and a good replacement to gas oil in a diesel engine at most engine-operating conditions. Sahoo et al.22 compared the combustion characteristics of Jatropha-, Karanja-, and Polanga-oil-based mono esters. The engine combustion parameters, such as peak pressure, time of occurrence of peak pressure, heat release rate, and ID, were analyzed. The IDs were consistently shorter for neat Jatropha biodiesel, varying between 5.9 and 4.2° CA, which was lower than diesel, with the difference increasing with the load. Similarly, IDs were shorter for neat Karanja and Polanga biodiesel when compared to diesel. Radu et al.23 investigated the fuel injection characteristics of a diesel engine that was fueled with biodiesel. The results indicated that the injection characteristics are clearly affected by the blends containing more than 50% biodiesel. The use of a biodiesel blend led to a lower output power and torque. The lower ID and pressure wave propagation time led to changes in the cylinder pressure and heat release traces and led to lower peak combustion pressures. Ozsezen et al.24 discussed the performance and combustion characteristics of a direct-injection (DI) diesel engine fueled with biodiesels, such as waste palm oil methyl ester and canola oil methyl ester (COME). The results indicated that, when the test engine was fueled with waste palm oil methyl ester or COME, the engine performance slightly weakened; the combustion characteristics slightly changed when compared to petroleum-based diesel fuel. The biodiesels caused reductions in CO, HC, and smoke opacity emissions, but they caused an increase in NOx emissions. In another study by Ozsezen et al., the engine performance, injection, and combustion characteristics were investigated for petroleum-based diesel fuel, biodiesel (used frying palm oil methyl esters), and its blends. When the test engine was fueled with biodiesel and its blends, the brake-specific fuel consumption (BSFC) increased slightly relative to diesel fuel because of its fuel properties and combustion characteristics. Biodiesel and its blends also showed a slight drop in the engine power with increased maximum cylinder gas pressure (MGP) and reduced ID when compared to diesel fuel. In all of the test conditions, the premixed combustion phase and the start of injection timing of biodiesel and its blends took place earlier than those of diesel fuel.5 In the other study, the combustion characteristics of a CI engine were analyzed when using biodiesel produced from crude soybean oil. The results showed that biodiesel exhibits similar combustion stages to that of diesel; however, it has an earlier start of combustion. At lower engine loads in biodiesel use, the MGP, the peak rate of pressure rise, and the peak of the heat release rate during the premixed combustion phase were higher than those of diesel. At higher engine loads, the MGP of biodiesel was almost similar to that of diesel, but the peak rate of pressure rise and the peak of the heat release rate were lower for biodiesel.25
protection is one of the most frequent problems. The reduction of the environmental pollutants produced by the industrial and automotive transportation sectors is one of the most important targets that are being taken into account in industrialized countries. It is necessary that both sectors adopt future strategies for the reduction of pollutant emissions to the atmosphere.16 Many researchers have reported that, with the use of vegetable oil ester as a fuel in diesel engines, a diminution in harmful exhaust emissions as well as equivalent engine performance with diesel fuel were achieved. The high oxygen content in biodiesel results in the improvement of its burning efficiency and reduction of particulate matter (PM), CO, and UHC, but it produces larger nitrogen oxides (NOx). It is estimated that the burning of neat biodiesel would produce about 10% more NOx than that of petroleum-based diesel fuel. Also, the decrease of carbon dioxide (CO2) using biodiesel contributes to the reduction in the greenhouse effect.17,18 In comparison to petroleum-based diesel fuel, biodiesel has important disadvantages: cold-start problems, lower energy content, and fuel-pumping difficulty. These disadvantages imposed the use of biodiesel-diesel fuel mixtures in CI engines. A 2-5% biodiesel in diesel fuel does not affect the performance of the engine and efficiency and does not involve any changes in the construction of the fueling system of the engine. This type of biodiesel blend can be burned directly in unmodified diesel engines. Many researchers have been devoted to study the influence of biodiesel on the exhaust emissions, engine performance, and combustion characteristics of diesel engines. Yu et al.19 carried out tests to determine engine performance and combustion analysis as well as emissions for both waste cooking oil and diesel. Because of the shorter ignition delay (ID), the premixed combustion phase of waste cooking oil was less intense than that of diesel. However, because of the corresponding smaller combustion volume, the peak pressures were on average 1.5 bar higher and occurred 1.1-3.8° crank angle (CA) earlier than that of diesel. In terms of the emissions of CO, NO, and sulfur dioxide (SO2), the levels were higher for waste cooking oil compared to diesel. Kumar et al.20 experimentally studied various methods of using Jatropha oil and methanol, such as blending, transesterification, and dual-fuel operation. ID was higher with neat Jatropha oil. It increased further with the blend and in dual-fuel operation. It was reduced with the ester use. The peak pressure and rate of pressure rise were higher with all of the methods compared to neat Jatropha oil operation. Jatropha oil and methyl ester showed higher diffusion combustion compared to standard diesel operation. However, dual-fuel operation resulted in higher premixed combustion. On the whole, it was concluded that transesterification of vegetable oils and methanol induction can significantly enhance the performance of a vegetable-oil-fueled diesel engine. An experimental investigation was carried out by Selim et al.21 to examine the performance and combustion noise of (16) Coronado, C. R.; Carvalho, J. A.; Yoshioka, J. T.; Silveira, J. L. Appl. Therm. Eng. 2009, 29, 1887–1892. (17) Haas, J. M.; Scott, K. M.; Alleman, T. L.; McCormick, R. L. Energy Fuels 2001, 15, 1207–1212. (18) Canakci, M.; Van Gerpen, J. H. Trans. ASAE 2003, 46, 945–954. (19) Yu, C. W.; Bari, S.; Ameen, A. Proc. Inst. Mech. Eng., Part D 2002, 216, 237–243. (20) Kumar, M. S.; Ramesh, A.; Nagalingam, B. Biomass Bioenergy 2003, 25, 309–318. (21) Selim, M. Y. E.; Radwan, M. S.; Elfeky, S. M. S. Renewable Energy 2003, 28, 1401–1420.
(22) Sahoo, P. K.; Das, L. M. Fuel 2009, 88, 994–999. (23) Radu, R.; Petru, C.; Edward, R.; Gheorghe, M. Energy Convers. Manage. 2009, 50, 2158–2166. (24) Ozsezen, A. N.; Canakci, M.; Turkcan, A.; Sayin, C. Fuel 2009, 88, 629–636. (25) Qi, D. H.; Geng, L. M.; Chen, H.; Bian, Y. Z. H.; Liu, J.; Ren, X. C. H. Renewable Energy 2009, 34, 2706–2713.
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Gumus et al. Table 1. Technical Specifications of the Test Engine51
For a diesel engine, fuel injection timing is a major parameter that affects the combustion and exhaust emissions. The state of air into which the fuel injected changes as the injection timing is varied and, thus, ID will vary. ID is the most important parameter that affects all of combustion process. If the injection starts earlier, the initial air temperature and pressure are lower; therefore, the ID will increase. If the injection starts later, the temperature and pressure are initially higher and a decrease in ID results. Thus, the variation in injection timing has effects on the engine performance and exhaust emissions, especially on the BSFC, brake thermal efficiency (BTE), and NOx emissions, because of changing the combustion characteristics in the engine cylinder.26-32 Several studies have shown that the injection timing affects the injection and combustion characteristics, engine performance, and exhaust emissions of diesel engines using biodiesel. When the injection timing is advanced, in comparison to the original (ORG) injection timing, UHC and CO emissions decrease while NOx emissions increase for biodiesel and diesel fuel. On the other side, with the retarded injection timings, NOx and CO2 emissions decrease while UHC and CO emissions increase for biodiesel and diesel fuel.19,24,28-30,33,34 Biodiesel and its blends also show a slight drop in the engine power with a decreased MGP and reduced ID when compared to diesel fuel. The start of injection timing and the premixed combustion phase of biodiesel and its blends take place earlier than diesel fuel because of higher bulk modules and shorter ID. The peak rate of pressure rise and the peak of the heat release rate of biodiesel are generally lower than that of diesel fuel. Biodiesel also shows higher diffusion combustion compared to standard diesel fuel operation. With the advanced injection timing, MGP, rate of heat release (ROHR), and combustion efficiency increase, but with the retarded injection timing, MGP, ROHR, and combustion efficiency decrease.5,25,19-22 Moreover, when the test engine is fueled with biodiesel and its blends, the BSFC increases, while output power and torque weaken slightly relative to diesel fuel because of properties and combustion characteristics of biodiesel.5,26,20,29 Sayin et al.33 investigated the influence of injection timing on the exhaust emissions of a DI diesel engine. The tests were performed at five different injection timings. When the injection timing was retarded, NOx and CO2 emissions decreased and UHC and CO emissions increased for all test conditions. On the other hand, with the advanced injection timings, UHC and CO emissions diminished and NOx and CO2 emissions boosted for all test conditions. Canakci et al.34 experimentally investigated the influence of injection timing on the engine performance, exhaust emissions, and combustion characteristics of a diesel engine.
engine type cylinder number bore (mm) stroke (mm) total cylinder volume (cm3) injector opening pressure (MPa) number of nozzle holes 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
The experimental test results showed that, at the retarded injection timing, MGP, ROHR, combustion efficiency, and NOx and CO2 emissions decreased while the smoke number and UHC and CO emissions increased at all test conditions. On the other side, with the advanced injection timing, the smoke number and UHC and CO emissions diminished and MGP, ROHR, combustion efficiency, and NOx and CO2 emissions were boosted at all test conditions. Leung et al.35 studied the effect of injection timing on the emissions and combustion characteristics of a diesel engine fueled with biodiesel. The tests were conducted at two different injection timings. The results indicated that the peak cylinder pressure and NOx emissions decreased with retarded injection timing, while PM showed the reverse trend. Combustion, performancem and emission characteristics of a CI engine were investigated for various fuel delivery advance timings by some researchers.36,37 The results showed that the ID, the rapid burning duration, and the total combustion duration (CD) increase with the advanced fuel injection for different fuels. The center of the heat release curve moves close to the top dead center (TDC). The MGP, the maximum rate of pressure rise, and the maximum ROHR increase with the advanced fuel injection timing. From the literature review, the influence of injection timing, such as retarded or advanced injection timing, on the injection, combustion, and performance characteristics of a DI diesel engine has not been clearly studied when using COME and its blends with diesel. Therefore, these topics need to be investigated to make up for the deficiency in the literature. In the present study, the effects of both injection timing and biodiesel-blended diesel fuel on the injection, combustion, and performance characteristics of a DI diesel engine were experimentally investigated. Experimental Apparatus and Procedure The experiments were performed on a Lombardini 6 LD 400, single-cylinder, naturally aspirated, air-cooled, DI diesel engine. Details of the engine specification are given 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 with a strain gauge load sensor, electrical tachometer, and switches for load remote control measurement instruments, was used in the experiments. The dynamometer is a direct current (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
(26) Canakci, M. Fuel 2008, 87, 1503–1514. (27) Sayin, C.; Uslu, K. Int. J. Energy Res. 2008, 32, 1006–1015. (28) Bari, S.; Yu, C. W.; Lim, T. H. Proc. Inst. Mech. Eng., Part D 2003, 218, 160–172. (29) Aktas, A.; Sekmen, Y. J. Fac. Pharm. Gazi Univ. 2008, 23, 199– 207 (in Turkish). (30) Nwafor, O. M. I.; Rice, G.; Ogbonna, A. I. Renewable Energy 2000, 21, 433–444. (31) Ma, Z.; Huang, Z.; Li, C.; Wang, X.; Miao, H. Energy Fuels 2007, 21, 1504–1510. (32) Sayin, C.; Ilhan, M.; Canakci, M.; Gumus, M. Renewable Energy 2009, 34, 1261–1269. (33) Sayin, C.; Uslu, K.; Canakci, M. Renewable Energy 2008, 33, 1314–1323. (34) Canakci, M.; Sayin, C.; Gumus, M. Energy Fuels 2008, 22, 3709– 3723.
(35) Leung, D. Y. C.; Luo, Y.; Chan, T. L. Energy Fuels 2006, 20, 1015–1023. (36) Huang, Z. H.; Lu, H. B.; Jiang, D .M.; Zeng, K.; Liu, B.; Zhang, J. Q.; Wang, X. B. Energy Fuels 2005, 19, 403–410. (37) Huang, Z. H.; Lu, H. B.; Jiang, D. M.; Zeng, K.; Liu, B.; Zhang, J. Q.; Wang, X. B. Bioresour. Technol. 2004, 95, 331–341.
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Figure 1. Experimental setup.
or adding an advance shim. 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 dynamic fuel injection timing. In this study, the start of fuel injection (dynamic injection timing) was determined from the pressure data, which is taken from the fuel line. All tests were conducted at a constant speed [2200 revolutions per minute (rpm)] and four different loads (5, 10, 15, and 20 N m). The values of engine oil temperature, mass flow rate of air, engine speed, torque, exhaust temperature, and combustion parameters, such as cylinder pressure, rate of pressure rise, start of combustion, ID, ROHR, heat release, and end of combustion, were recorded during the experiments. Before each experiment, the engine was regulated according to the catalogue values. All data were collected after the engine stabilized. The engine was sufficiently warmed up for each test, and the engine oil temperature was maintained around 85-90 °C. The tests were carried out under steady-state conditions. The test procedure is repeated 3 times. The values given in this study are the average of these three results. During the tests, the engine did not show any starting difficulties when fueled with COME and its blends, and the engine ran satisfactorily throughout the entire test.
Table 2. Accuracies of the Measurements and Uncertainties in the Calculated Results measurements
accuracy
load (N) speed (rpm) time (%) temperatures (°C)
(2 (10 (0.5 (1
calculated results
uncertainty (%)
power BSFC BSEC BTE
(2.55 (2.60 (2.60 (2.60
manometer (error (3%). Different digital thermocouples (error (1%) monitored the temperatures of intake air, engine oil, 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%. The pressure time history of cylinder was measured by a Kistler model 6052B air-cooled piezo-quartz pressure sensor, which was mounted on the cylinder head. The cylinder signals were then passed onto a Kistler model 5644A charge amplifier. A Kistler model 4067 A2000 piezo-resistive pressure sensor with a charge amplifier was mounted on the fuel line to measure the fuel line pressure. The crankshaft position was obtained using a crankshaft angle sensor to determine cylinder pressure as a function of the CA. The CA signal was obtained from an angle-generating device mounted on the main shaft. The signal of the cylinder pressure was acquired for every 0.75° CA, and the acquisition process covered 100 completed cycles. The accuracies of the measurements and the uncertainties in the calculated results are given in Table 2. In the tests, the ordinary diesel fuel was obtained from the T€ urkiye Petrol Rafinerileri A.S-. (TUPRAS) Petroleum Corporation. COME was purchased from a commercial supplier. Some properties of both fuels are given in Table 3. The nomenclature BX represents a blend including X% COME; i.e., B5 indicates a blend including 5% COME, and B100 represents pure COME. Static injection timing or, in other words, fuel delivery advance timing is the timing when fuel starts to fuel in the pump. The original static injection timing of the test engine is 20° CA before top dead center (BTDC). The thickness of the advance shim, located in the connection place between the engine and fuel pump, is 0.25 mm, and adding one shim advances the injection timing 5° CA. Experiments were carried out in three different static injection timings (15°, 20°, and 25° CA BTDC) by removing
Calculation Methods Heat release analysis can yield valuable information about the effect of engine design changes, the fuel injection system, fuel type, and engine operating conditions on the combustion process and engine performance.38 In this study, engine cylinder pressure data were used to evaluate the ROHR, which is a simplified thermodynamic model. The ROHR was calculated using the first law analysis of thermodynamics. The ROHR at each CA was determined by the following formula: Q ¼
γ 1 ðPdVÞ þ ðVdPÞ þ Qw γ-1 γ-1
ð1Þ
where Q is the apparent heat release rate (J), γ is the ratio of specific heats, which is calculated according to an empirical equation,39 P is the cylinder pressure (Pa), V is the instantaneous volume of the cylinder (m3), and Qw is heat-transfer (38) Ghojel, J.; Honnery, D. Appl. Therm. Eng. 2005, 25, 2072–2085. (39) Brunt, M. F. J.; Rai, H.; Emtage, A. L. SAE Tech. Pap. 981052, 1998.
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Table 3. Some Properties of 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 EN 14124 limits
U.S.A. ASTM D 6751 limits
g/mol % mass kg/m3 (at 15 °C)
maximum at 0.02 860-900
maximum at 0.02
°C % mass kJ/kg
minimum at 120 maximum at 0.30
minimum at 130
minimum at 51 3.5-5.0 maximum at 0.50 minimum at 6.0
minimum at 41 1.9-6.0 maximum at 0.80
mm2/s (at 40 °C) mg of KOH/g 1 h (at 110 °C) °C °C
maximum at 360
COME52
diesel53
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 2. Fuel line pressure versus CA at ORG injection timing for (a) 10 and (b) 20 N m loads.
rate (J) from the wall calculated on the basis of the Hohenberg correlation,40 and the wall temperature was assumed to be 723 K. For this calculation, the contents of the cylinder were
assumed to behave as an ideal gas (air), with the specific heat being dependent upon the temperature, and leakage through the piston rings was neglected.41 (41) Hayes, T. K.; Savage, L. D.; Sorenson, S. C. SAE Tech. Pap. 860029, 1986.
(40) Hohenberg, G. H. SAE Tech. Pap. 790825, 1979.
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Figure 3. Fuel line pressure versus CA at different injection timing for (a) 10 and (b) 20 N m loads.
are shown in Figures 4-9. The important parameters of combustion are also given in Table 5. The significant features related to engine performance are summarized in Table 6.
Results and Discussion The injection timing has a significant effect on the combustion characteristics and performance of a CI engine. Therefore, in this study, the influence of injection timing on the injection, combustion characteristics, and engine performance of a single-cylinder diesel engine has been experimentally investigated when using COME and its blends with diesel fuel. The experimental conditions were selected as follows: four engine loads (5, 10, 15, and 20 N m), 2200 rpm constant speed, and three injection timings (15°, 20°, and 25° CA BTDC). The fuels were B0, B5, B20, B50, and B100, indicating the content of COME in different volume ratios (e.g., B5 contains 5% canola oil methyl esters and 95% diesel fuel in volume). The fuel line pressure versus CA at different loads and injection timings for diesel, COME, and their blends are shown in Figures 2 and 3. The important parameters of fuel injection, such as start of injection timing and maximum fuel line pressure, are also given in Table 4. The cylinder gas pressure, ROHR, and cumulative heat release rate versus CA at different loads and injection timings for all test fuels
Fuel Injection Characteristics The effect of biodiesel on the fuel injection characteristics has been comprehensively investigated in numerous studies. When biodiesel is used as an alternative fuel, the earlier fuel injection timings have occurred in the engines with mechanical injection systems. When B100 is used instead of diesel fuel, advances in fuel injection are lesser than 2° CA.14,42,43 These earlier injection timings obtained with biodiesel have been attributed to differences in the physical properties between biodiesel and diesel fuels. A critical difference between the diesel and biodiesel fuel properties was the compressibility (bulk modulus). The compressibility of biodiesel and its (42) Chang, D. Y.; Van Gerpen, J. H. SAE Tech. Pap. 971684, 1997. (43) Szybist, J. P.; Song, J.; Alam, M.; Boehman, A. L. Fuel Process. Technol. 2007, 88, 679–691.
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Table 4. Fuel Injection Characteristics for Different Static Injection Timings 10 N m
15° CA BTDC 20° CA BTDC (ORG) 25° CA BTDC
dynamic injection timing (deg CA BTDC) maximum fuel line pressure (MPa) maximum fuel line pressure (deg CA BTDC) dynamic injection timing (deg CA BTDC) maximum fuel line pressure (MPa) maximum fuel line pressure (deg CA BTDC) dynamic injection timing (deg CA BTDC) maximum fuel line pressure (MPa) maximum fuel line pressure (deg CA BTDC)
20 N m
B0
B5
B20
B50
B100
B0
B5
B20
B50
B100
15.31 23.59 12.72 19.14 25.12 16.65 23.89 24.91 21.92
15.31 24.16 12.80 19.27 25.00 16.69 24.29 25.81 22.04
15.97 24.76 14.02 19.54 24.88 16.76 24.82 24.61 23.25
16.37 24.93 14.12 19.80 25.31 18.08 25.08 25.63 23.36
16.76 25.74 14.22 19.93 25.94 16.86 25.48 26.17 23.67
13.73 24.88 3.47 19.54 21.95 8.84 25.21 23.48 14.05
13.86 25.12 3.56 20.20 23.28 8.86 25.61 27.29 14.12
15.05 25.20 4.76 20.59 23.79 8.98 26.53 26.09 15.32
15.18 25.70 4.88 20.99 25.35 10.02 27.19 27.19 15.44
16.10 26.41 4.89 22.04 26.88 10.16 27.06 27.72 15.53
Figure 4. Cylinder gas pressure versus CA at ORG injection timing for (a) 10 and (b) 20 N m loads.
blends is lower than that of diesel fuel. When biodiesel is injected, the liquid fuel pressure rise produced by the pump is faster as a consequence of its lower compressibility (higher bulk modulus) and also the pressure waves can propagate quicker toward the injectors (higher sound velocity). Thus, for all fuels, using the same fuel pump at the same speed, the injection characteristics of biodiesel and its blends are not the same as each other. The difference in this physical property
has provided that the injection timing of biodiesel and its blends is effectively advanced relative to that of diesel fuel. Another physical property having an effect on the injection timing is density. The biodiesel has a slightly higher density, which affects the fuel compression process in the volumetric injection pump. The higher density of biodiesel causes advancement in the injection timing. Also, this case causes a different quantity of fuel to be injected per stroke for the same 3205
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Figure 5. Cylinder gas pressure versus CA at different injection timing for (a) 10 and (b) 20 N m loads.
volume of CA. In addition, its higher viscosity reduces pump leakages, leading to an increase in the injection line pressure, a faster evolution of pressure, and thus, advanced injection timing. Furthermore, lower vapor content in a high-pressure injection system could also be the reason for the advanced injection timing. When the vapor volume is decreased, the injection delay decreases, which results in advanced injection timing.5,44-46 In this study, the start of fuel injection (opening time of the needle) was determined from fuel injection line pressure data. The start of injection is defined as the CA of rising fuel injection pressure to the opened pressure of the injector (20 MPa). Fuel line pressures versus CA at ORG injection timing for 10 and 20 N m loads are shown in Figure 2. Fuel line pressures versus CA at various injection timings and different loads for COME, diesel, and their blends are also shown in Figure 3.
There was a clear advancement in fuel delivery for B100 compared to B0 at the different injection timings and all loads, which suggests that there was an advancement in the injection timing, as shown in Figures 2 and 3. As seen in the figures, when the test engine was fueled with COME, the start of the nozzle needle is carried out at earlier CAs than that of diesel fuel. At the ORG injection timing, the start of injection timing for B100 is 0.79° and 2.5° CA earlier than that of diesel fuel at 10 and 20 N m loads, respectively. Table 4 shows the CA of the start of injection, the maximum fuel line pressure, and the CA of the maximum fuel line pressure at different engine loads and injection timings for all test fuels. Combustion Characteristics The cylinder gas pressure and heat release were investigated as combustion characteristics. The analysis of heat release was performed on the basis of the cylinder gas pressure data. Figures 4 and 5 show the cylinder gas pressure; Figures 6 and 7 demonstrate the ROHR; and Figures 8 and 9 illustrate the cumulative heat release (CHR) at different injection timings
(44) Benjumea, P.; Agudelo, J.; Agudelo, A. Fuel 2009, 88, 725–731. (45) Kegl, B.; Hribernik, A. Energy Fuels 2006, 20, 2239–2248. (46) Lapuerta, M.; Armas, O.; Rodrı´ guez-Fernandez, J. Prog. Energy Combust. Sci. 2008, 34, 198–223.
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Figure 6. ROHR versus CA at ORG injection timing for (a) 10 and (b) 20 N m loads.
and engine loads for all fuels. Combustion parameters, such as the start of combustion, ID, maximum cylinder pressure, maximum rate of pressure rise, maximum ROHR, CHR, end of combustion, and CD, were determined by investigation of the cylinder gas pressure and heat release. Combustion parameters of each fuel for different injection timings and engine loads are shown in Table 5. Analysis of the Cylinder Gas Pressure. Pressure data of 100 engine cycles were averaged to analyze the cylinder gas pressure, and the resolution of the pressure data is 0.26° CA. Figures 4 and 5 show the changes in cylinder gas pressures with respect to CA at various engine loads and injection timings. The variation of the cylinder gas pressure during the combustion indicates engine knock or noise. As seen in the figures, all fuels had no trace of knock and the cylinder gas pressure smoothly varied with respect to CA. During the experimental study, it was detected that the engine noise was qualitatively less than that of diesel fuel when the engine was running with B100. ID, rate of pressure rise, and MGP were determined with respect to the analysis of the cylinder gas pressure.
ID. ID is an important parameter in combustion phenomenon. The ID is the time between the start of fuel injection and the start of combustion.47,48 Many parameters, such as fuel type, fuel quality, air/fuel ratio, compression ratio, engine speed, cylinder gas pressure, the intake-air temperature, and the quality of fuel atomization, influence the ID. The fuel type is the one important parameter that affects ID.24 Biodiesel and its blends showed shorter IDs compared to diesel because of the higher cetane number of biodiesel. A high cetane number makes autoignition easy and gives a short ID. Therefore, the primary reason for the decrease in ID is the cetane number of the biodiesel, which is higher than that of diesel fuel, as seen in Table 3. The decrease in the ID would make less fuel to burn in the premixed burning phase. Because of this, the rate of pressure rise decreases and the peak cylinder gas pressure diminishes.19,49 (47) Owen, K.; Coley, T. Automotive Fuels Reference Book; Society of Automotive Engineers, Warrendale, PA, 1995; p 375. (48) Challen, B.; Baranescu, R. Diesel Engine Reference Book; Butterworth-Heinemann: Woburn, MA, 1999; p 97. (49) Heywood, J. B. Internal Combustion Engine Fundamentals; McGraw-Hill: New York, 1988; pp 491-497.
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Figure 7. ROHR versus CA at different injection timing for (a) 10 and (b) 20 N m loads.
Table 5 shows the IDs of the tested fuels for different engine loads and injection timings. In the 10 N m load and ORG ignition timing, the ID for B100 is 13.04° CA, while the ID in the case of B0 is 14.89° CA. In the 20 N m load, the ID for B100 is 9.08° CA, while the ID in the case of B0 is 10.93° CA. The IDs for B5, B20, and B50 at 10 and 20 N m loads are shown in Table 5. For example, the ID was obtained as 18.9°, 14.89°, and 12.33° CA for advanced, ORG, and retarded injection timings, respectively, for the 10 N m load and diesel fuel operation. However, the ID for COME operation at the same load condition was obtained as 18.57°, 13.04°, and 11.54° CA for advanced, ORG, and retarded injection timings, respectively. It can also be observed that generally the ID for the all test fuels decreased with the increase of the engine load and retarded injection timing. MGP. As seen in Figure 4, no significant differences in the in-cylinder pressure were registered during most of the compression and expansion strokes. However, the MGP for diesel fuel was higher at all tests. This result can be related to the differences in the heat release pattern shown in
Figure 6. A given amount of heat released before TDC will cause a higher maximum cylinder pressure than the same amount of heat released at the same angle after TDC. The MGP mainly depends upon the combustion rate in the initial stages, which is influenced by the fuel taking part in the uncontrolled heat release phase.45 The high viscosity and low volatility of the biodiesel lead to poor atomization and mixture preparation with air during the ID period. The MGP of biodiesel and its blends are lower because of the deterioration in the preparation of the air-fuel mixture as a result of high fuel viscosity.32 Therefore, normal diesel operation showed the highest peak pressure and maximum rate of pressure rise. Figure 4 shows the cylinder gas pressure with respect to CA for ORG injection timing at 10 and 20 N m loads, respectively. As seen in the figures, MGP slightly decreases with the addition of the COME content in the blend. While the MGP at 10 N m load occurred between 6.74 and 7.19 MPa, the MGP at 20 N m load occurred between 7.54 and 7.96 MPa at ORG injection timing for all of the test fuels. The MGP occurred within the range of 2.21-7.49° CA after top dead 3208
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Figure 8. CHR rate versus CA at ORG injection timing for (a) 10 and (b) 20 N m loads.
center (ATDC) for all test fuels. When COME or its blends were used, the MGP slightly goes away from TDC because of the poor atomization mixture preparation and combustion process. In the 10 N m load and ORG injection timing, the MGP for B100 was 6.74 MPa occurring at 5.84° CA ATDC, while the MGP in the case of B0 was 7.19 MPa occurring at 4.85° CA ATDC. In the 20 N m load, the MGP for B100 was 7.54 MPa occurring at 4.52° CA ATDC, while the MGP in the case of B0 was 7.96 MPa occurring at 3.2° CA ATDC. The values and positions of the MGP at 10 and 20 N m loads for B5, B20, and B50 are shown in Table 5. As seen in the comparison of panels a and b of Figure 4, the cylinder gas pressure increased with the increasing engine load. Experimental results show that fuel consumption per unit time increases with the increasing engine load; this behavior provided an increase in the MGP. The increase in the cylinder pressure was approximately 5.4% for B100 when the engine load was increased from 10 to 20 N m. The locations of MGP are close to TDC at 20 N m engine load because starting the fuel injection occurred earlier than that of 10 N m.
Figure 5 shows a comparison of the changes in the cylinder gas pressures with respect to CA obtained for B0 and B100 at different injection timings and loads. In the 10 N m load and COME operation, the MGP was obtained at 7.55 MPa (at 3.20° CA ATDC), 6.74 MPa (at 5.84° CA ATDC) and 6.10 MPa (at 7.49° CA ATDC) for advanced, ORG, and retarded injection timings, respectively. In the 20 N m load, the MGP was obtained at 9.03 MPa (at 1.62° CA ATDC), 7.54 MPa (at 4.52° CA ATDC) and 6.43 MPa (at 5.84° CA ATDC) for advanced, ORG, and retarded injection timings, respectively. When the injection started earlier, peak pressures became higher for all fuel blends. Also, the peak pressures occurred earlier with the advanced injection timings. Maximum Cylinder Gas Pressure Rise Rate (MPR). The MPR and location of MPR at different injection timings and engine loads for COME, diesel, and their blends are shown in Table 5. In the 20 N m load and ORG injection timing, the MPR for B100 was 4.64 MPa/deg occurring at 10.92° CA BTDC, while the MPR in the case of B0 was 5.04 MPa/deg occurring at 9.08° CA BTDC. The MPR decreases with the increase of the COME amount in the fuel blend. This lower 3209
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Figure 9. CHR rate versus CA at different injection timing for (a) 10 and (b) 20 N m loads.
MPR obtained with COME and its blends can be explained as a consequence of less ID and premixed combustible mixture. The reasons for the less premixed combustible mixture are the higher viscosity and lower volatility of COME compared to diesel fuel. The MPR increases with the rise in load with all of the test fuels because of the increase in the quantity of fuel injected. In the 20 N m load and COME operation, the MPR was obtained at 6.28 MPa/deg (at 11.39° CA BTDC), 4.64 MPa/deg (at 10.92° CA BTDC), and 3.79 MPa/deg (at 6.77° CA BTDC) for advanced, ORG, and retarded injection timings, respectively. It may be noticed from Table 5 that advancing the injection timing generally increases the MPR. This may be postulated to the fact that the air pressure and temperature at the point of injection drop, resulting in a longer ID and, thereby, producing a higher pressure rise rate. A higher pressure rise rate means a greater proportion of the injected fuel being burned in the premixed combustion phase.21 Analysis of the Heat Release. Heat release calculations are an attempt to learn something about the combustion process in an engine. Several combustion parameters, such as ROHR,
premixed combustible mixture, CHR, CD, can be determined by the analysis of heat release. ROHR and CHR. As illustrated in Figure 6, ROHR decreases with the increase of the COME amount in the fuel blend. The maximum ROHR was obtained at 25.33 kJ/deg (at 5.18° CA BTDC), 24.65 kJ/deg (at 5.51° CA BTDC), 24.05 kJ/deg (at 5.58° CA BTDC), 22.73 kJ/deg (at 5.67° CA BTDC), and 20.21 kJ/deg (at 7.16° CA BTDC) for B0, B5, B20, B50, and B100 at 10 N m load and ORG injection timing, respectively. In the 20 N m load, the maximum ROHR was obtained at 31.58 kJ/deg (at 9.47° CA BTDC), 30.68 kJ/deg (at 9.80° CA BTDC), 30.21 kJ/deg (at 10.13° CA BTDC), 27.78 kJ/deg (at 10.79° CA BTDC), and 28.13 kJ/ deg (at 10.86° CA BTDC) for B0, B5, B20, B50, and B100 at ORG injection timing, respectively. It is clear that the premixed heat release phase of COME was shorter than diesel fuel. The premixed combustion phase for diesel fuel was longer and more pronounced, owing to a longer ID of the diesel fuel. The diffusion burning phase (mixing-controlled combustion phase) indicated that the second stage is greater for COME. At the time of ignition, 3210
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Table 5. Combustion Characteristics of the Fuels for Different Injection Timings 10 N m B0
B5
B20
20 N m B50
B100
B0
B5
B20
B50
B100
maximum cylinder pressure (MPa) 6.58 6.56 6.48 6.34 6.10 6.94 6.89 6.81 6.65 6.43 maximum cylinder pressure (deg CA ATDC) 6.17 6.50 6.83 7.16 7.49 4.17 4.19 4.52 5.74 5.84 maximum rate of pressure rise (MPa/deg) 0.35 0.35 0.34 0.32 0.29 0.44 0.44 0.43 0.42 0.38 start of combustion (deg CA BTDC) 2.67 2.48 2.49 3.00 3.47 5.97 6.52 6.63 6.71 6.77 ignition delay (deg) 12.33 12.53 12.51 12.00 11.54 9.03 8.48 8.37 8.29 8.24 15° CA BTDC maximum rate of heat release (kJ/deg) 23.23 22.89 21.89 20.27 16.77 27.06 26.81 25.84 24.89 20.78 maximum rate of heat release (deg CA BTDC) 2.28 2.32 2.54 2.65 3.20 5.84 6.48 6.57 6.50 7.16 maximum heat release (kJ) 461.51 461.42 454.51 445.10 433.15 554.31 551.31 548.63 545.35 540.21 end of combustion (deg CA ATDC) 36.66 36.80 36.86 36.93 37.06 37.19 39.83 39.96 39.90 40.16 maximum cylinder pressure (MPa) 7.19 7.15 7.09 6.94 6.74 7.96 7.94 7.90 7.71 7.54 maximum cylinder pressure (deg CA ATDC) 4.85 4.90 5.18 5.21 5.84 3.20 2.87 3.79 3.86 4.52 maximum rate of pressure rise (MPa/deg) 0.42 0.42 0.41 0.40 0.37 0.50 0.50 0.49 0.47 0.46 start of combustion (deg CA BTDC) 5.12 5.45 5.97 5.78 6.96 9.08 9.60 9.93 10.07 10.92 20° CA BTDC 14.89 14.56 14.03 14.23 13.04 10.93 10.40 10.07 9.94 9.08 (ORG injection ignition delay (deg) maximum rate of heat release (kJ/deg) 25.33 24.65 24.05 22.73 20.21 31.58 30.68 30.21 27.78 28.13 timing) maximum rate of heat release (deg CA BTDC) 5.18 5.51 5.58 5.67 7.16 9.47 9.80 10.13 10.79 10.86 maximum heat release (kJ) 474.55 477.64 477.71 461.63 453.47 615.48 611.22 606.77 597.79 588.34 end of combustion (deg CA ATDC) 36.66 36.67 36.86 39.96 39.77 40.16 40.26 31.05 40.23 40.29 maximum cylinder pressure (MPa) 7.86 7.82 7.75 7.63 7.55 9.34 9.32 9.26 9.17 9.03 maximum cylinder pressure (deg CA ATDC) 2.54 2.87 2.97 3.20 3.20 2.21 1.12 1.15 1.55 1.62 maximum rate of pressure rise (MPa/deg) 0.55 0.54 0.53 0.51 0.48 0.69 0.69 0.68 0.68 0.63 start of combustion (deg CA BTDC) 6.11 6.21 6.32 6.63 6.44 10.25 11.25 11.03 11.06 11.39 ignition delay (deg) 18.90 18.79 18.68 18.37 18.57 14.75 13.75 13.98 13.95 13.62 25° CA BTDC maximum rate of heat release (kJ/deg) 33.98 33.44 32.90 30.74 28.56 46.99 47.84 46.80 46.40 40.94 maximum rate of heat release (deg CA BTDC) 6.44 6.49 6.50 6.56 6.60 11.19 11.27 11.12 11.45 11.85 maximum heat release (kJ) 520.68 525.59 526.25 504.92 489.13 709.39 695.30 681.98 659.81 648.97 end of combustion (deg CA ATDC) 36.73 36.00 34.16 36.80 36.86 40.82 39.63 37.06 37.59 37.06
Table 6. BSFC (g/kWh), Brake-Specific Energy Consumption (BSEC) (MJ/kWh), and BTE (%) of the Engine BSFC (g/kWh)
15° CA BTDC
20° CA BTDC (ORG injection timing)
25° CA BTDC
B0 B5 B20 B50 B100 B0 B5 B20 B50 B100 B0 B5 B20 B50 B100
BSEC (MJ/kWh)
BTE (%)
5Nm
10 N m
15 N m
20 N m
5Nm
10 N m
15 N m
20 N m
5Nm
10 N m
15 N m
20 N m
477.70 489.60 504.90 513.40 533.80 440.30 448.80 462.40 474.30 503.20 452.20 464.10 476.00 491.30 525.30
321.16 332.01 390.60 414.47 438.34 286.44 301.63 358.05 377.58 394.94 301.63 314.65 371.07 397.11 414.47
328.90 335.80 384.10 411.70 434.70 292.10 294.40 345.00 372.60 368.00 312.80 315.10 363.40 393.30 407.10
352.16 366.36 386.24 394.76 420.32 309.56 315.24 326.60 346.48 366.36 329.44 337.96 346.48 355.00 383.40
20.51 20.92 21.25 20.96 20.67 18.90 19.17 19.46 19.37 19.49 19.41 19.83 20.03 20.06 20.34
13.79 14.18 16.44 16.92 16.98 12.30 12.89 15.07 15.42 15.30 12.95 13.44 15.62 16.21 16.05
14.12 14.35 16.17 16.81 16.84 12.54 12.58 14.52 15.21 14.25 13.43 13.46 15.30 16.06 15.77
15.12 15.65 16.26 16.12 16.28 13.29 13.47 13.75 14.15 14.19 14.14 14.44 14.58 14.49 14.85
17.55 17.21 16.94 17.17 17.41 19.05 18.78 18.50 18.59 18.47 18.54 18.16 17.97 17.95 17.69
26.11 25.38 21.90 21.27 21.21 29.28 27.94 23.89 23.35 23.54 27.80 26.78 23.05 22.20 22.43
25.50 25.10 22.27 21.42 21.38 28.71 28.62 24.79 23.66 25.26 26.81 26.74 23.54 22.42 22.83
23.81 23.00 22.14 22.34 22.11 27.09 26.73 26.19 25.45 25.37 25.45 24.93 24.69 24.84 24.24
a less fuel-air mixture is prepared for combustion with COME. Therefore, more burning occurs in the diffusion phase compared to diesel fuel.20 COME and its blends completed the premixed combustion phase earlier than diesel fuel because of their earlier start of combustion and having a less premixed combustible mixture. The reason for the earlier start of combustion is the earlier start of injection and lower ID of COME compared to diesel fuel. The reasons for the less premixed combustible mixture are the higher viscosity and lower volatility of COME compared to diesel fuel. Also, the lower heating value (LHV) of COME reduces ROHR. As seen in the comparison of panels a and b of Figure 6, ROHR increased with the rise in the engine load because of the increase in the quantity of fuel injected. Figure 7 demonstrates the changes in the ROHR with respect to CA obtained for B0 and B100 at different injection timings and loads. In the 10 N m load and COME operation, the maximum ROHR was obtained at 28.56 kJ/deg (at 6.60° CA BTDC), 20.21 kJ/deg (at 7.16° CA BTDC), and
16.77 kJ/deg (at 3.20° CA BTDC) for advanced, ORG, and retarded injection timings, respectively. In the 20 N m load and COME operation, the maximum ROHR was obtained at 40.94 kJ/deg (at 11.85° CA BTDC), 28.13 kJ/deg (at 10.86° CA BTDC), and 20.78 kJ/deg (at 7.16° CA BTDC) for advanced, ORG, and retarded injection timings, respectively. As seen in Table 5, the ID was increased with advanced injection timing for all fuels because the fuel injected earlier in the combustion chamber. This leads to a greater accumulation of the fuel in the ID period and an increase of the premixed heat release. This is the reason for increasing ROHR. Retarded injection timing leads to a lower accumulation of fuel and poor combustion. The CHR was also calculated for each fuel and illustrated in Figures 8 and 9. The results show that the CHR decreases with the increase of the COME amount in the fuel blend. The CHR was obtained at 554.31, 551.31, 548.63, 545.35, and 540.21 kJ for B0, B5, B20, B50, and B100 at 20 N m load and ORG injection timing, respectively. 3211
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CD. CD is defined as the angular interval occurring between the maximum pressure rise rate and the maximum CHR. The CD increased with the increase of the COME amount in the fuel blend. A longer CD obtained with COME and its blends can be explained as a consequence of constituents having higher viscosity and boiling points than that of diesel fuel. Those constituents with higher viscosity and boiling points were not adequately evaporated from the biodiesel during the main combustion phase, and the biodiesel continued to burn in the late combustion phase. In the 10 N m load and ORG ignition timing, the CD for B100 was 59.77° CA, while the CD in the case of B0 was 56.66° CA. In the 20 N m load, the CD for B100 was 60.29° CA, while the CD in the case of B0 was 60.16° CA. The CD increases with the rise in the load with all of the fuels because of the increase in the quantity of fuel injected. A higher CD was observed with COME than diesel fuel. The increase in CD is mainly due to the slow combustion of the injected fuel. The CD became longer as the injection started earlier for all fuels and loads. In the 10 N m load and COME operation, the CD was obtained at 61.73°, 56.66°, and 51.66° CA for advanced, ORG, and retarded injection timings, respectively. In the 20 N m load, the CD was obtained at 65.82°, 60.16°, and 52.19° CA for advanced, ORG, and retarded injection timings, respectively.
mixture. Thus, the engine needs more fuel consumption to maintain the same amount of output power.50 The BSEC reduces with increasing engine loads because of noticeably diminishing BSFC for all of the fuel blends and injection timings. The BSEC reduces by 7.82% as the engine load increases from 10 to 20 N m load for B100 at ORG injection timing. When the injection timing was changed from ORG injection timing, BSEC values increased because of the increase in the energy requirement to sustain the same amount of output power at ORG injection timing. The increments for the advanced and retarded injection timings were 6.40 and 13.77% for B0 at 20 N m, respectively. BTE. The BTE is defined as the ratio of the brake power to fuel consumption and LHV. BTE indicates the ability of the combustion system and provides comparable means of assessing how efficient the energy in the fuel was converted to mechanical output. Therefore, the BTE increased as the COME content decreased in the blended fuel for all injection timings.22 As demonstrated in Table 6, BTE was 27.09, 26.73, 26.19, 25.45, and 25.37 for B0, B5, B20, B50, and B100, respectively, at 20 N m load and ORG injection timing. Increasing engine load causes an increase in BTE values because of the noticeable decline in BSFC for all fuel blends and injection timings. The BTE increased by 7.77% as the engine load augments from 10 to 20 N m load for B100 at ORG injection timing. The best results in terms of BTE were obtained at ORG injection timing. Retarded or advanced injection timings diminished BTE values by the reason for increasing BSFC. When the injection timing was advanced and retarded in comparison to ORG injection timing, BTE decreased by 4.45 and 12.85% for B100 at 20 N m load, respectively. As seen in Table 6, the differences occurred in the BTE especially at partial loads. The cause of these differences may be different fuel properties and injection characteristics.
Engine Performance In this study, BSFC, BSEC, and BTE were investigated as the engine performance. Table 6 shows the BSFC, BSEC, and BTE values for COME and its blends with diesel fuel at different engine loads and injection timings. BSFC. BSFC is defined as the ratio of the fuel consumption to the brake power. As shown in Table 6, the BSFC slightly increased with an increasing COME amount in the fuel blend because of the LHV and higher viscosity of COME. Therefore, the amount of fuel introduced to the cylinder for a desired energy input has to be greater with COME. The BSFC was 309.56, 315.24, 326.60, 346.48, and 366.36 g/kWh for B0, B5, B20, B50, and B100, respectively, at 20 N m and ORG injection timing. The BSFC of COME is also higher than that of diesel fuel for all loads. In comparison to B0, on average, BSFC for B100, B50, B20, and B5 was boosted by 22.89, 18.26, 12.32, and 2.38%, respectively, for all engine loads. The variation of BSFC for different loads is presented in Table 6. For all fuels tested, BSFC decreased with an increase in the load. At ORG injection timing, while BSFC was measured to be 346.48 g/kWh with B50 at 20 N m load, it was found as 474.30 g/kWh at 5 N m. As seen in Table 6, the minimum BSFC values were obtained at ORG injection timing for all of the fuel blends. When the injection timing was retarded and advanced 5° CA BTDC compared to ORG injection timing, BSFC increased by 10.07 and 4.32%, respectively, for B5 at 10 N m. BSEC. The BSEC is described as a multiplication of BSFC and LHV. As shown in Table 6, the BSEC increases with the COME content in the blends. The BSEC was acquired at 13.29, 13.47, 13.75, 14.15, and 14.19 MJ/kWh for B0, B5, B20, B50, and B100, respectively, at 20 N m load and ORG injection timing. It is well-known that the LHV of the fuel affects the engine power. The lower heat content of the COME-diesel blend causes some reductions in the engine power. For these reasons, the effective power should decrease with the increase of the COME amount in the fuel
Conclusions In this study, the influence of injection timing on the engine performance, injection, and combustion characteristics of a single-cylinder, four-stroke, DI, naturally aspirated diesel engine has been experimentally investigated using COME and its blends with diesel fuel. From the experimental results, the following conclusions were made: The fuel properties of COME are slightly different from those of diesel. The LHV of COME is approximately 9.78% lower than that of diesel fuel. The cetane number of COME is approximately 6.9% higher than that of diesel fuel. The viscosity of COME is obviously higher than that of diesel fuel. The density and flash point of COME are higher than those of diesel fuel. COME has a narrow boiling range, which is boiled off between 331 and 348 °C. Injection characteristics of COME and its blends with diesel fuel, as compared to that of diesel fuel, resulted in the earlier injection timings, owing to differences in the physical properties between COME and diesel fuel. (50) Rakopolous, C. D.; Kyristis, D. C. Energy 2001, 26, 705–722. (51) Lombardini. Engine technical specification. Turkey, 2000 (in Turkish). (52) EKO Biodiesel. Product specification. Istanbul, Turkey, 2009 (in Turkish). (53) T€ urkiye Petrol Rafinerileri A.S-. (TUPRAS). Product specification. Izmit, Turkey, 2009 (in Turkish).
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Because of the different properties of COME and diesel fuel, both fuels exhibited different combustion characteristics with the variation of engine load and injection timing. Combustion for COME started earlier, owing to a shorter ID at all engine loads and injection timings. The MGP and MPR of biodiesel and its blends were lower than that of petroleum diesel because of the deterioration in the preparation of the air-fuel mixture during the ID period and less premixed combustible mixture as a result of the higher viscosity and lower volatility of COME compared to petroleum diesel. The maximum ROHR was also lower for COME and its blends with diesel fuel because the premixed heat release phase of COME was shorter than petroleum diesel. The CHR decreased slightly with the increase of the COME amount in the fuel blend. The CD increased with the increase of the COME amount in the fuel blend because biodiesel did not evaporate adequately during the main combustion phase and the biodiesel continued to burn in the late combustion phase, owing to the high viscosity and boiling point. The BSFC and BSEC for COME were higher than those for diesel fuel, while BTE for COME was lower than that for diesel fuel. This is probably a result of the LHV of COME, which is distinctly lower than that of the diesel fuel. The ORG injection timing gave the best results for BSFC, BSEC, and BTE compared to the other injection timings. When the injection timing is advanced, the ID will be longer, and this leads to a reduction in the engine output power. Thus, fuel consumption per output power will increase. Also, advanced injection timing boosted MGP and ROHR because of the increase in ID and premixed combustible mixture. On the other hand, retarded injection timing reduced the MGP and
ROHR, owing to the decrease in ID and premixed combustible mixture, and this result increased fuel consumption per output power. Acknowledgment. This study was supported by the Scientific Research Project Commission of Marmara University under Grant BSE-075/131102.
Nomenclature ATDC = after top dead center BTDC = before top dead center BTE = brake thermal efficiency (%) BSEC = brake-specific energy consumption (MJ/kWh) BSFC = brake-specific fuel consumption (g/kWh) CA = crank angle CD = combustion duration CHR = cumulative heat release CI = compression ignition CO = carbon monoxide COME = canola oil methyl ester CO2 = carbon dioxide ID = ignition delay LHV = lower heating value MGP = maximum cylinder gas pressure MPR = maximum cylinder gas pressure rise rate NOx = nitrogen oxides rpm = revolutions per minute ROHR = rate of heat release TDC = top dead center UHC = unburned hydrocarbon
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