Energy Fuels 2010, 24, 6172–6178 Published on Web 10/15/2010
: DOI:10.1021/ef100962a
Fuel Spray and Exhaust Emission Characteristics of an Undiluted Soybean Oil Methyl Ester in a Diesel Engine Su Han Park,† Hyung Jun Kim,‡ and Chang Sik Lee*,‡ † Graduate School of Hanyang University Department of Mechanical Engineering, Hanyang University, 17 Haengdang-dong, Sungdong-gu, Seoul, 133-791, Korea, and ‡Department of Mechanical Engineering, Hanyang University 17 Haengdang-dong, Sungdong-gu, Seoul 133-791, Korea
Received July 27, 2010. Revised Manuscript Received October 2, 2010
The aim of this work is to investigate and analyze the spray and exhaust emission characteristics of biodiesel fuel derived from soybean oil in a diesel engine, both experimentally and numerically. The spray characteristics of biodiesel fuel are measured and investigated in a constant volume vessel and analyzed using spray images obtained by a high speed camera. The calculated combustion and exhaust emission characteristics of the biodiesel fuel are compared to experimental results from diesel fuel. The combustion and exhaust emission calculations for the biodiesel fuel are performed in KIVA-3v code. Investigations revealed that biodiesel fuel shows a fast spray development in the initial stage of injection. However, at the end of injection, the biodiesel spray shows a somewhat slow development compared to diesel spray in the same injection quantity conditions. In addition, the biodiesel spray targeted the piston lib due to the piston geometry and the low ambient gas density at an injection timing of BTDC 30°. At this time, the spray and combustion temperature distributions are concentrated within the entire engine cylinder, while they are mainly concentrated in the piston bowl region when injected after BTDC 30°. When compared to diesel fuel at the same injection quantity, biodiesel fuel shows lower NOx and soot emissions, and the CO and HC emissions of biodiesel fuel show similar trends.
direct-injection diesel engine with diesel fuel and neat biodiesel derived from coconut oil and found that the rate of change in the cylinder pressure was the same for both fuels. They also found 3-4% lower peak cylinder pressure, lower ignition delay, lower heat release, slightly higher brake thermal efficiency, and lower exhaust CO, HC, NOx, and smoke emissions with neat biodiesel than with diesel fuel. These results for biodiesel may be attributable to changes in engine type, operating conditions, and the type of vegetable oil used for producing the biodiesel fuel. Kim et al.8 investigated the effect of split injection on exhaust emissions, soot particulate, and engine performance when using biodiesel fuel. They reported that split injection reduced NOx emissions significantly without a significant increase in soot emission. In addition, many experts on the internal combustion engine are investigating the combustion and exhaust emission characteristics of biodiesel fuel as well as its spray and atomization performance.2,9-11 This paper describes the spray, combustion, and exhaust emission characteristics of biodiesel fuel. The overall spray characteristics such as the spray tip penetration and spray cone angle were obtained from the experiment. The combustion and exhaust emissions characteristics were analyzed using experimental and numerical results. In addition, the possibility of using biodiesel fuel in a diesel engine through a comparison of diesel and biodiesel fuels is studied.
1. Introduction To solve environmental problems and guarantee a new energy source, the best current alternative fuel for the compression ignition diesel engine is biodiesel fuel. Biodiesel fuel is made through a process called trans-esterification,1 a procedure that consists of a catalyzed reaction between a triglyceride (vegetable oil) and alcohol. During the process, byproducts are produced, including methyl esters and glycerin.2 The advantages of biodiesel as a diesel fuel are its portability, ready availability, renewability, higher combustion efficiency, lower sulfur and aromatic content, higher cetane number, and higher biodegradability compared to those of normal diesel fuel.3-5 Scholl and Sorenson6 observed similar instantaneous and cumulative heat release with neat biodiesel fuel (soybean based) and normal diesel fuel, along with a higher peak cylinder pressure, higher rate of pressure rise, comparable NOx, and lower CO and HC emissions for biodiesel. However, Shaheed and Swain7 performed experiments in a single cylinder naturally aspirated *To whom correspondence should be addressed. Telephone: þ82-22220-0427. Fax: þ82-2-2281-5286. E-mail:
[email protected]. (1) Fukuda, H.; Kondo, A.; Noda, H. J. Biosci. Bioeng. 2001, 92 (5), 405–416. (2) Desentes, J. M.; Payri, R.; Salvador, F. J.; Manin, J. SAE Technical Paper 2009-01-0851, 2009. (3) Demirbas, A. Biodiesel - A Realistic Fuel Alternative for Diesel Engines; Springer: London, 2008. (4) Knothe, G.; Sharp, C. A.; Ryan, T. W. Energy Fuels 2006, 20, 403– 408. (5) Zhang, Y.; Dub, M. A.; McLean, D. D.; Kates, M. Bioresour. Technol. 2003, 90, 229–240. (6) Scholl, K. W.; Sorenson, S. C. SAE Technical Paper SAE930934, 1993. (7) Shaheed, A.; Swain, E. Proc. Inst. Mech. Eng. Part A: J. Power Energy 1999, 213, 417–425. r 2010 American Chemical Society
(8) Kim, M. Y.; Yoon, S. H.; Lee, C. S. Energy Fuels 2008, 22, 1260– 1265. (9) Park, S. H.; Kim, H. J.; Suh, H. K.; Lee, C. S. Int. J. Heat Fluid Flow 2009, 30, 108–116. (10) Anand, K.; Sharma, R. P.; Mehta, P. S. Proc. Inst. Mech. Eng., Part D: J. Automobile Eng. 2010, 224, 661–679. (11) Park, S.; Kim, H.; Choi, B. J. Mech. Sci. Technol. 2009, 23, 2555– 2564.
6172
pubs.acs.org/EF
Energy Fuels 2010, 24, 6172–6178
: DOI:10.1021/ef100962a
Park et al.
2. Numerical Model Formulation Generally, biodiesel fuel derived from soybean oil consists of various components.12 This fuel has long chain methyl esters, and mechanisms with large chemical reactions are needed for the analysis of the fuel oxidation processes. To predict the combustion and emission characteristics of biodiesel fuel, the Lawrence Livermore National Laboratory (LLNL) recently developed a detailed kinetic reaction mechanism13 for methyl butanoate (MB) including 264 species and 1219 reactions for use as a substitute for biodiesel fuel. However, methyl butanoate shows significant different characteristics and differences in reactions for lower level carbon species compared to sobean-based biodiesel typically used. Therefore, a reduced mechanism with 41 species and 150 reactions was suggested by Brakora et al.14 for biodiesel fuel derived from soybean. The reduced mechanism was validated against the detailed mechanism using ignition sensitivity analysis and modification of the reaction rate constants. In addition, it is assumed that 1 mol of biodiesel fuel is composed of 1 mol of methyl butanoate (C5H10O2) and 2 mol of normal heptane (C7H16) to maintain the oxygen amount at 11% by mass. Also, the ratio of carbon to oxygen of the hypothetical fuel shows good agreement in comparison with the average chemical formula of biodiesel with the five main biodiesel components.15 This fuel composition has a similar molecular weight and a lower heat value compared to those of soybean based biodiesel fuel. This reduced mechanism was recently used by other researchers.16-18 Besides the chemical properties, the fuel library in the KIVA code was expanded to include the physical properties for biodiesel fuel such as density, viscosity, latent heat, and vapor pressure. In addition, methyl oleate as a major component of biodiesel fuel was used, and the CHEMKIN code was modified to calculate the chemistry of two fuel components.21 The KIVA-3 V release 219 coupled with the CHEMKIN II chemistry solver20 was used to predict the combustion and emission characteristics of biodiesel fuel. The physical properties of the fuel21 were added to the fuel library in the KIVA code. To analyze the fuel spray and atomization characteristics when injected by a high pressure diesel injector, the Kelvin-Helmholtz & Rayleigh-Taylor (KH-RT) hybrid breakup model22 was used. To study the ignition and combustion of the biodiesel fuel, the reduced oxidation mechanism for biodiesel fuel was applied as calculated from the CHEMKIN chemistry solver integrated into the KIVA code. In addition, a hydrocarbon (HC) and carbon monoxide (CO) emissions were predicted according to the biodiesel fuel oxidation
Figure 1. Schematic of the experimental setup for the analysis of biodiesel fuel.
mechanism. To study the nitric oxide (NOx) emissions, the reduced Gas Research Institute (GRI) NO mechanism,23 including four species (N, NO, N2O, and NO2) and nine reactions, was used. This mechanism in combination with the biodiesel oxidation mechanism was calculated using the CHEMKIN chemistry solver. A two-step phenomenological soot model,23 along with the Hiroyasu model24 and the Nagle-Strickland-Constable model,25,26 was employed to analyze the soot formation and oxidation processes, respectively. A three-dimensional computational grid of a 60° sector was created to reduce calculation time, and the number of holes in the injector was considered to be the same size as that in the experimental piston head. The calculation was conducted from the intake valve closing timing (BTDC 128°) to exhaust valve opening timing (ATDC 172°). In addition, the initial conditions such as the intake air temperature and pressure were set up be the same as those in the experiment. 3. Experimental Setup and Procedure
(12) Basha, S. A.; Gopal, K. R.; Jebaraj, S. Renewable Sustianable Energy Rev. 2009, 13, 1628–1634. (13) Fisher, E. M.; Pitz, W. J.; Curran, H. J.; Westbrook, C. K. P. Combust. Inst. 2000, 28, 1579–86. (14) Brakora, J. L.; Ra, Y.; Reitz, R. D.; McFarlane, J.; Daw, C. S. SAE Technical Paper 2008-01-1378, 2008. (15) Brakora, J. L.; Reitz, R. D. SAE Technical Paper 2010-01-0577, 2010. (16) Ren, Y.; Li, X.; Abu-Ramadan, E. SAE Technical Paper 201001-1259, 2010. (17) Um, S.; Park, S. W. Fuel 2010, 89, 1415–1421. (18) Um, S.; Park, S. W. Energy Fuels 2010, 24, 916–927. (19) Amsden, A. A. KIVA-3V release 2. Improvement to KIVA-3V, Los Alamos National Laboratory, LA-UR-99-915, 1999. (20) Kee, R. J.; Rupley, F. M.; Miller, J. A. Sandia Report SAND 898009, 1989, . (21) Brakora. J. L. Development and Validation of a Reduced Reaction Mechanism for Biodiesel-fueled Engine Simulations. M.S. Thesis, University of Wisconsin-Madison, Madison, WI, 2007. (22) Beale, J. C.; Reitz, R. D. Atomization Sprays 1999, 9, 623–650.
3.1. Spray Visualization System. A nozzle injector with six holes, a 0.126 mm orifice diameter, and a 156° spray angle were utilized to study macroscopic spray characteristics such as the spray tip penetration and spray cone angle. To compare the spray characteristics of ULSD and SME at the same injection condition (Pinj = 130 MPa, Pamb = 2 MPa, mfuel = 10 mg), a spray visualization system was installed as shown in Figure 1a. (23) Kong, S. C.; Sun, Y.; Reitz, R. D. J. Eng. Gas Turbines Power 2007, 129, 252–260. (24) Hiroyasu, H.; Katota, T. SAE Technical Paper 760129, 1976. (25) Nagle, J. S.; Strickland-Constable, R. F. Oxidation of carbon between 1000-2000 °C. In Proceedings of the Fifth Carbon Conference, Vol. 1; Pergamon: Oxford, 1962; pp 154-164. (26) Han, Z.; Uludogan, A.; Hampson, G. J.; Reitz, R. D. SAE Technical Paper 960633, 1996.
6173
Energy Fuels 2010, 24, 6172–6178
: DOI:10.1021/ef100962a
Park et al.
Table 1. Specifications of the Test Engine with a Single Cylinder item engine type bore stroke (mm mm) displacement volume (cm3) compression ratio combustion chamber type number of valve fuel injection system number of nozzle holes nozzle hole diameter (mm) spray angle (deg)
description direct injection diesel engine (NA) with single cylinder 75.0 84.5 373.3 17.8 re-entrant 2-intake, 2-exhaust Bosch common rail type 6 0.128 156
Spray images from the bottom view type were obtained with a high-speed camera (Photron, Fastcam-APX RS), using two metal-halide lamps (Photron, HVC-SL) as the light source. To synchronize the fuel injection and camera shutter signals, a multichannel digital delay/pulse generator (Berkeley Nucleonics Corp, model 555) was used. The spray images were stored in a computer with an image grabber. The operation of the test injector was controlled by an injector driver (TEMS, TDA3200H). 3.2. Single Cylinder Diesel Engine and Emission Analyzers. As illustrated in Figure 1b, a naturally aspirated single-cylinder diesel engine with common-rail direct injection and a displacement volume of 373.3 cm3 was used to examine the combustion and exhaust emission characteristics of the biodiesel fuel. The compression ratio of the test engine was 17.8 to 1. The valve train was a double overhead cam type, and the valve mechanism had two intake valves and two exhaust valves. Detailed engine specifications are listed in Table 1. The single cylinder test engine was controlled by a dc dynamometer (55 kW), and the combustion pressure was measured using a piezoelectric pressure transducer (6057A80, Kistler) coupled to a charge amplifier (5018A, Kistler). In addition, the fuel pressure of the common rail, the injection timing, and the fuel injection mass were controlled by an injection pressure controller (TDA-1100, TEMS) and an injector driver (TDA-3300, TEMS) with a crank angle sensor. The exhaust emissions were analyzed using a NOx analyzer (BCL-511, Yanaco), a soot analyzer (AVL-407, AVL), and an HC-CO analyzer (MEXA-554K, Horiba). The injected fuel mass in this study was set to 10 mg per injection. For each combustion test, the combustion pressure was sampled over 1 000 cycles at intervals of 0.1° crank angle, and then the incylinder pressure was averaged and calculated for each case.
Figure 2. Comparison between the experimental and the calculated results for the model validation (Pinj = 130 MPa, mfuel = 10 mg, SOE = BTDC 10°).
4. Model Validation for the Combustion Analysis of Biodiesel Fuel Figure 2 shows a comparison of the experimental and numerical results for the combustion pressure and rate of heat release (ROHR) of biodiesel fuel in order to validate the numerical model used in this study. The validation conditions were 130 MPa of injection pressure, 10 mg of injection quantity, and BTDC 10° for the injection timing. Also, the numerical results for the combustion characteristics of biodiesel fuel are compared to those of diesel fuel. As shown in Figure 2, the trends of the combustion pressure and ROHR of biodiesel fuel in the numerical results agree reasonably with those in the experimental results. When diesel and biodiesel fuels are compared at the same injection quantity conditions, the biodiesel fuel shows earlier ignition timing, a lower peak combustion pressure, and a lower peak ROHR than dose diesel fuel because the biodiesel fuel has a higher cetane number and low lower heating value (LHV). These characteristics indicate that the numerical method and model used in the present study are sufficient for investigating the combustion and emission characteristics of biodiesel fuel.
Figure 3. Spray behavior characteristics of biodiesel fuel in a constant volume chamber (Pinj = 130 MPa, Pamb = 2 MPa, mfuel = 10 mg).
5. Results and Discussion The spray tip penetration and spray cone angle characteristics of diesel and biodiesel fuels are presented in Figure 3. These characteristics were analyzed using the spray images obtained using the spray visualization system. The injection pressure and ambient pressure were 130 MPa and 2 MPa, respectively, and the injection quantity was fixed at 10 mg. In the initial stage of the injection, the spray development of the biodiesel fuel was slightly faster than that of diesel fuel because of biodiesel’s high fuel density. However, the spray tip 6174
Energy Fuels 2010, 24, 6172–6178
: DOI:10.1021/ef100962a
Park et al.
Figure 4. Spray development and behavior characteristics of biodiesel fuel at two injection timings (Pinj = 130 MPa, mfuel = 10 mg).
penetration of biodiesel fuel was shorter than that of diesel fuel in the later stages of the injection because the biodiesel fuel has a shorter energizing duration for the same injection quantity and the biodiesel ends earlier. After the end of injection, spray tip penetration is mainly affected by the aerodynamic resistance of the surrounding air.27 Therefore, the spray tip penetration of the biodiesel fuel was influenced by the resistance of the surrounding air. On the other hand, biodiesel fuel showed a narrower spray cone angle compared to that of diesel fuel. The biodiesel fuel has a fast injection velocity due to its high spray momentum and fuel density. In addition, the biodiesel fuel had a bad atomization performance, so the droplet breakup did not occur easily. Because of this, the mass and momentum of a single droplet were large, and the dispersion characteristics were inferior. These characteristics influenced the narrow spray cone angle observed with biodiesel fuel.28,29 Figure 4 shows the calculated spray development and behavior characteristics of biodiesel fuel in the combustion cylinder. The test conditions were 130 MPa of the injection pressure and 10 mg of the injection quantity. The injection timings were TDC and BTDC 30°, and then the figures illustrated the moment after 6° from injection. In TDC injection, the injected spray progressed toward the upper side of the piston bowl. Then, it is thought that the most of the injected spray and droplets were distributed in the piston bowl region. In BTDC 30° injection, the injected spray already targeted the piston lib, which is the border between the squish region and the piston bowl. Because of the low ambient gas density at BTDC 30° compared to that at TDC, the injected spray developed rapidly. After targeting the piston lib, the spray progressed in two directions, toward the squish region and toward the piston bowl. Also, the droplet breakup in the spray injected at BTDC 30° was more active than that at TDC, and the atomized droplets were easily mixed with the ambient gas. This was confirmed by comparing the fuel distributions at TDC and BTDC 30°.
Figure 5. Combustion characteristics of biodiesel fuel (SME) for the injection timing (Pinj = 130 MPa, mfuel = 10 mg, engine speed = 1400 rpm).
Combustion characteristics, such as the combustion pressure, ROHR, and the indicated mean effective pressure (IMEP) of biodiesel fuel, are illustrated in Figure 5 for various injection timings. As shown in Figure 5a representing the experimental combustion pressure and ROHR, advancing the injection timing caused an increase in the peak combustion pressure from TDC to BTDC 20°. At these injection timings, the ignition delay and the peak value of ROHR were about 8° and 90 J/deg, respectively. The increase in the peak combustion pressure with advanced injection timing is explained by the spray development and fuel distribution as shown in Figure 4. The advance of the injection timing induced a decrease in the ambient gas density and then caused fast spray development and improved atomization performance during the same lapse of time.30 This allowed for the formation of a good-quality mixture of injected spray and ambient air and activated the combustion reaction. On the other hand, when the fuel injected at BTDC 30°, the peak combustion pressure and the peak ROHR suddenly decreased. Also, the ignition delay at BTDC 30° was remarkably increased. It is thought that the very low ambient pressure and temperature affected the deterioration of the combustion. In addition, the divided sprays targeting the piston lib influenced the formation of the lean combustion conditions in the piston bowl. Figure 5b shows a comparison of the experimental and numerical IMEP of biodiesel fuel, an important index that represents engine performance. As shown in Figure 5b, the IMEP gradually decreased as the injection timing advanced in both the experiment and the calculation. This is why the advanced injection timing caused
(27) Lefebvre, A. H. Atomization and Sprays; Taylor & Francis: NewYork, 1989. (28) Wang, X.; Huang, Z.; Kuti, O. A.; Zhang, W.; Nishida, K. Int. J. Heat Fluid Flow 2010, 31 (4), 659–666. (29) Genzale, C. L.; Pickett, L. M.; Kook, S. SAE Technical Paper 2010-01-0610, 2010.
(30) Kim, H. J.; Park, S. H.; Lee, C. S. Fuel Process. Technol. 2010, 91 (3), 354–363.
6175
Energy Fuels 2010, 24, 6172–6178
: DOI:10.1021/ef100962a
Park et al.
Figure 7. Exhaust emissions distribution in the combustion cylinder (start of injection, BTDC 30° and TDC).
the distribution near the injector nozzle position was due to residual fuel in the sac volume of the injector with a very low injection velocity. Also, CO and HC from injection at the BTDC 30° showed a high distribution in the crevice region because of the inflow of injected fuel into the squish and crevice regions. Combustion in these regions was incomplete due to a lack of oxygen amount. In Figure 8, the NOx and soot emissions from biodiesel fuel are compared experimentally and numerically. Also, the NOx and soot emissions of biodiesel fuel are compared to those of diesel fuel. In Figure 8a,b, there are some differences between the numerical and the experimental results. Because of the different molecular structure and chemical composition of the actual used biodiesel and the surrogate fuel, it is very difficult to reproduce the actual combustion phenomena of biodiesel fuel by using the oxidation mechanism of the hypothetical fuel mixture of 1 mol of methyl butanoate and 2 mol of n-heptane. However, the numerical analysis for biodiesel fuel is possible for the prediction of the pattern of the exhaust emissions, although it cannot predict the accurate value for the exhaust emission amounts. The pattern of the calculated NOx and soot emissions follows the experimental results. According to the advance of the injection timing to BTDC 20°, NOx emissions increased and the soot emissions slightly decreased. These emissions characteristics are related to the results of the peak combustion pressure as shown in Figure 5a. Because the increase in combustion pressure indicates an active combustion reaction in the cylinder, an increase in the combustion temperature caused an increase in NOx emissions. However, at BTDC 30°, the NOx emissions dramatically decreased and soot emissions increased due to spray targeting. As mentioned above, a divided spray causes a low combustion temperature. Also, the inflow of the injected spray to the squish region may have caused incomplete combustion or combustion with lean conditions. These characteristics induced a decrease in NOx and an increase in soot emissions. On the other hand, the biodiesel fuel showed low level emissions of NOx and soot compared to those of diesel fuel at the same injection quantity conditions. As shown in Figure 8, at the same test conditions (the same injection quantity and the variation in injection
Figure 6. Combustion temperature distribution in the combustion cylinder at two injection timings (start of injection, BTDC 30° and TDC).
the start of the combustion reaction before TDC. The engine work performed by the combustion before TDC was the negative work. On the other hand, the calculation results follow the patterns of the experimental results showing slightly higher value due to the difference in heat loss. Figure 6 shows the combustion temperature distribution in the combustion cylinder at two injection timings. The analysis of the combustion temperature distribution makes a prediction of the possible degree of combustion. The upper images indicate the combustion temperature distribution for the crank angle BTDC 9° and ATDC 1° at the injection timing of BTDC 30°. As shown in Figure 6, the targeted spray at the piston lib progressed in two directions, toward the squish region and the piston bowl. Then, the combustion reaction occurred in the entire combustion cylinder due to the well distributed spray. However, most of the spray injected at TDC was concentrated in the piston bowl, and the combustion reaction mainly occurred in the piston bowl. Consequently, the TDC injection case shows a high combustion temperature near the rich-fuel region compared to that at BTDC 30°. In addition, the injection at BTDC 30° allowed for combustion in the squish region because of the spray targeting characteristics in the combustion cylinder. These temperature distributions in the combustion cylinder influenced the formation of exhaust emissions. The concentration distribution of exhaust emissions such as NOx, CO, and HC which are related to the combustion temperature, are illustrated in Figure 7. With dependence on the combustion temperature distribution in the combustion cylinder, the NOx emissions from injection at TDC were concentrated in the piston bowl because NOx formation is highly dependent on the combustion temperature above 2 000 K. On the other hand, injected at BTDC 30° at a relatively low combustion temperature showed a very low concentration of NOx emissions. In the CO and HC emission distributions in Figure 7, 6176
Energy Fuels 2010, 24, 6172–6178
: DOI:10.1021/ef100962a
Park et al.
Figure 9. Comparison between the experimental and calculated results on CO and HC emissions characteristics of biodiesel fuel (Pinj = 130 MPa, mfuel = 10 mg).
Figure 8. Comparison between the experimental and calculated results on NOx and soot emissions characteristics of biodiesel fuel (Pinj = 130 MPa, mfuel = 10 mg).
timing from BTDC 30° to TDC), the low LHV and oxygenated content of the biodiesel fuel had an influence on the simultaneous reductions of NOx and soot emissions. Figure 9 shows the comparison between the experimental and numerical results for CO and HC emission characteristics of biodiesel fuel. The calculated CO and HC emissions followed the experimental patterns and the increase in the HC emission at BTDC 30°; it was observed that part of the injected spray entered the squish region, where the lean oxygen concentration caused incomplete combustion. In the comparison of diesel and biodiesel fuels, biodiesel fuel showed the lowest level of CO emissions, while showing similar or slightly higher HC emission levels. The oxygen content in the biodiesel fuel affected the reduction of CO emission, and the high viscosity of biodiesel affected the increase in HC emissions. Oxygen can improve the combustion reaction, and a high viscosity causes adsorption of biodiesel fuel to the piston wall, which interrupted the active combustion and was directly exhausted as a type of HC emission.
injection quantity conditions, biodiesel fuel showed a fast spray development in the initial stage of the injection. However, at the end of injection, the biodiesel spray showed a slightly slower development compared to that of diesel spray. (2) At the injection timing of BTDC 30°, the biodiesel spray targeted the piston lib due to the piston geometry (re-entrant type) and the low ambient gas density. This spray behavior characteristic in the engine cylinder affected the combustion and exhaust emissions characteristics as well as the spray distribution and combustion temperature distribution. (3) An advance in the injection timing causes an increase in the peak combustion pressure and a decrease in the IMEP. However, the peak combustion pressure dramatically decreased at the injection timing of BTDC 30° with the spay targeting the piston lib. In addition, for injection at BTDC 30°, the spray and combustion temperature distributions were represented in the whole engine cylinder (piston bowl, squish area, and crevice region), while they were mainly concentrated in the piston bowl region when injected after BTDC 30°. (4) In the comparison to the biodiesel emissions with those of diesel fuel, biodiesel fuel showed lower nitrogen oxides (NOx) and soot emissions at the same injection quantity and engine operating conditions. The lower heating value (LHV) and oxygen content in biodiesel fuel influenced the simultaneous reduction of NOx and soot emissions compared to those of diesel fuel. On the other hand, CO and HC emissions from biodiesel fuel showed similar trends. The CO emissions from biodiesel fuel were somewhat low, and the HC emissions in
6. Conclusions In this work, the spray, combustion and exhaust emissions characteristics of biodiesel fuel were numerically calculated using KIVA-3 V code. The calculated results were compared to experimental results observed at the same test conditions. Following is a summary of the results and discussion on biodiesel application in a diesel engine. (1) At the same 6177
Energy Fuels 2010, 24, 6172–6178
: DOI:10.1021/ef100962a
Park et al.
biodiesel fuel were somewhat high compared to those of normal diesel fuel.
Nomenclature ATDC = after top dead center BTDC = before top dead center CA = crank angle (degree) mfuel = injected fuel mass (mg) Pamb = ambient pressure (MPa) Pinj = injection pressure (MPa) SME = soybean oil methyl ester (biodiesel) SOE = start of energizing ULSD = ultra low sulfur diesel
Acknowledgment. This work was supported in part by the CEFV (Center for Environmentally Friendly Vehicle) of the EcoSTAR project of the MOE (Ministry of the Environment in Seoul, Republic of Korea). Also, this study was also supported by the Second Brain Korea 21 Project in 2006. This work was supported by the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (Grant 2010-000-0000-0432).
6178
