A quasi-dimensional, multi-zone engine model of a four stroke compression-ignition engine was developed and applied to study the engine performance and emission characteristics with both reference diesel fuel and biodiesel fuel. At nine typical operating conditions, the engine model was calibrated for both diesel and biodiesel fuels. Pressure diagram and heat release curves at these operating conditions were compared between simulation and experiments. In addition, variations in pressure trace, ignition delay, brake specific fuel consumption, indicated specific nitrogen dioxide with respect to injection timing, injection pressure, load and speed, compression ratio, and percentage of exhaust gas recirculation were determined from both simulations with diesel and biodiesel fuel. Furthermore, focusing nitric oxides, the sensitivity studies and NO kinetics studies were made for both diesel and biodiesel case, and the results were compared between each other. Major results and conclusions can be summarized as follows:
1. The calibrated quasi-dimensional multi-zone model successfully predicted engine performance for both diesel and biodiesel fueled engine. Simulated pressure diagram and heat release curve at nine operating conditions showed good agreement with experimentally determined results.
2. Injection timing and compression ratio has the most significant effect on pressure diagram for both diesel and biodiesel fueled engine. Advanced injection timing and higher compression ratio leads to higher in-cylinder pressure, while retarded injection timing and small compression ratio lowers the pressure diagram. Comparing between diesel and biodiesel case, pressure diagram with biodiesel has lower peak pressure than that with reference diesel fuel for all the operating conditions and the parameters
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considered for investigation. This observation might be attributed to the lower calorific value of biodiesel relative to diesel fuel.
3. The ignition delays for biodiesel fueled case were higher (3% ~ 10%) than the corresponding values for the diesel fueled case for medium load and high load conditions.
In addition, variations in injection timing, injection pressure, and compression ratio would have certain effects (0.5~1.5 degree crank angle) on ignition delay for both biodiesel and diesel case.
4. The brake specific fuel consumption (bsfc) values for the biodiesel fueled engine were consistently higher (2%~12%) than the corresponding values for the diesel fueled case for all operating conditions and parameters studied. This results can be attributed to lower LHV of biodiesel. To achieve the same power output, more biodiesel fuel is required.
5. Results from sensitivity study shows injection timing and EGR percentage has the most significant effect on nitric oxides calculation (50%~100%) among the six parameters that is studied. In addition, changes in most of the parameters has greater effect on biodiesel fueled engine than the corresponding effect on diesel case. The NO kinetics study indicates that at the same base case, M&B kinetics predicted highest NO value while Baulch kinetics gave the lowest value.
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Due to the unknown characteristics of the biodiesel fuel, some observations from both the simulation and the experiment still cannot be well explained. With more accurate experimental data, recommendations for future work are,
1. Calibrate the model to match the emission data from experiment, especially the nitric oxides emission. Together with burned zone temperature profile, compare the results with diesel and biodiesel fueled engine and find out the cause of the difference if there is any.
2. After getting the map for rack position of the VGT, include the compressor and turbine in the simulation rather than using compressor-out condition and turbine-in condition as inputs.
3. To get better understanding of biodiesel combustion in the cylinder, it would be useful to integrate the 3D computational fluid mechanics and detailed chemical kinetics into the current one-dimensional engine model. The simulation of intake/exhaust system could still be one-dimensional and the combustion in the cylinder could be simulated by 3D CFD and detailed chemical kinetics.
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REFERENCES
1 US Department of Energy, Energy Information Administration, Available:
http://www.eia.doe.gov/emeu/aer/pdf/pages/sec1.pdf, Accessed: 01/08/2009.
2 Smaling, R. Biodiesel and air quality: HARC Brownbag Presentation, Available:
files.harc.edu/Documents/Announcements/2006/BiodieselAndAirQuality.pdf, Accessed: 03/22/2009.
3 Monyem, A., Van Gerpen, J. H., and Canakci, M. The effect of timing and oxidation on emissions from biodiesel--fueled engines. Trans. of the ASAE, 2001, 44 (1), 35–42.
4 Tat, M. E., Van Gerpen, J. H., and Wang, P. S. Fuel property effects on injection timing, ignition timing, and oxides of nitrogen emissions from biodiesel--fueled engines. Transactions of the ASAE, 2007, 50 (4), 1123-1128.
5 Lu, X. M., Ge, Y. S., Wu, S. J., and Han, X. K. An experimental investigation on combustion and emissions characteristics of turbocharged DI engines fueled with blends of biodiesel. SAE paper 2005-01-2199, 2005.
6 Yuan, W. Q., Hansen, C. A., and Zhang, Q. Computational modeling of NOx emissions from biodiesel combustion. International Journal of Vehicle Design, 2007, 45 (1/2), 12-32.
7 Szybist, P. J., Kirby, R. S., and Boehman, L. A. NOx emissions of alternative diesel fuels: a comparative analysis of biodiesel and FT diesel. Energy & Fuels, 2005, 19, 1484-1492.
8 Wayne, A. E. Effects of methyl ester biodiesel blends on NOx emissions. SAE paper 2008-01-0078, 2008.
9 Chang, Y. Z., and Van Gerpen, J. H. Fuel properties and engine performance for biodiesel prepared from modified feedstock. SAE paper 971684, 1997.
10 Senatore, A., Cardone, M., Rocco, V., and Prati, V. M. A comparative analysis of combustion process in DI diesel engine fueled with biodiesel and diesel fuel. SAE paper 2000-01-0691, 2000.
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11 Parvate-Patil, G., Vasquez, M., and Payne, M. Effects of Different Biodiesel Blends on Heat Release and its Related Parameters. ASME Internal Combustion Engine Division 2006 Fall Technical Conference, November 5-8, 2006, Sacramento, California, USA.
12 Kinoshita, E., Myo, T., Hamasaki, K., Tajima, H., and Zhang, R. K. Diesel combustion characteristics of coconut oil and palm oil biodiesels. SAE paper 2006-01-3251, 2006.
13 Ban-Weiss, G. A., Chen, J. Y., Buchholz, B. A., and Dibble, R. W. A numerical investigation into the anomalous slight NOx increase when burning biodiesel, a new theory. Fuel Processing Technology, 2007, 88(7), 659-667.
14 Agarwal, A. Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines. Progress in Energy and Combustion Science, 2007, 33, 233–271.
15 Musculus, M. Measurements of the influence of soot radiation on in-cylinder temperatures and exhaust NOx in a heavy-duty DI diesel engine. SAE paper 2005-01-0925, 2005.
16 Yamane, K. Influence of physical and chemical properties of biodiesel fuels on injection, combustin and exhaust emission characteristics in a direct injection compression ignition engine. International Journal of Engine Research, 2001, 2(4), 249-261
17 Jung, D., and Assanis, D. Multi-zone DI diesel spray combustion model for cycle simulation studies of engine performance and emissions. SAE paper 2001-01-1246, 2001.
18 Arsie, I., Di Genova, F., Mogavero, A., Pianese, C., and Rizzo, G. Multi-zone predictive modeling of common rail multi-injection diesel engine. SAE paper 2006-01-1384, 2006.
19 Kouremenos, D., Rakopoulos, C., and Hountalas, D. Multi-zone combustion modeling for the prediction of pollutants emissions and performance of DI diesel engines. SAE paper 970635, 1997.
20 McCrady, J., Hansen, A., and Lee, C. Modeling biodiesel combustion using GT-Power. ASABE Meeting Presentation, Paper Number 076095.
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21 GT-Power User Manual, Version 6.2, Gamma Technology, Inc, September 2006.
22 Woschni, G. A universally applicable equation for the instantaneous heat transfer coefficient in the internal combustion engine. SAE Trans., 1967, 76, 3065.
23 Hohenberg, G. Advanced approaches for heat transfer calculations. SAE paper 790825, 1979.
24 Heywood, J. Internal Combustion Engine Fundamentals, 1988 (McGraw-Hill, New York).
25 Yoshizaki, T., Nishida, K., and Hiroyasu, H. Approach to low NOx and smoke emission engines by using phenomenological simulation. SAE Paper 930612, 1993.
26 Baluch, D. L., Drysdale, D. D., Horne, D. G., and Lloyd, A. C. Evaluated Kinetic Data for High Temperature Reactions, Vol. 2 – Homogeneous Gas Phase Reactions of the H2-N2-O2 System, 1973 (Butterworths & Co. Ltd, London).
27 Hanson, R. K. and Salimian, S. Survey of Rate Constants in the N/H/O System, in Combustion Chemistry, ed. W. C. Gardiner, Jr., 1984 (Springer-Verlag, New York).
28 Miller, J. A. and Bowman, C. T. Mechanism and modeling of nitrogen chemistry in combustion. Progress in Energy and Combustion Science, 1989, 15, 287-338.
29 Dean, A. M. and Bozzelli, J. W. Combustion Chemistry of Nitrogen, in Gas-Phase Combustion Chemistry, ed. W. C. Gardiner, Jr., 2000 (Springer-Verlag, New York).
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APPENDIX I
PROPERTIES OF BIODIESEL AND DIESEL FUEL
Table 8 Properties comparison between diesel 2 and biodiesel
State Item Unit Diesel No.2 Biodiesel
Vapor
C Atoms per Molecule 13.5 18.82
H Atoms per Molecule 23.6 34.39
O Atoms per Molecule 0 2
N Atoms per Molecule 0 0
Lower Heating Value kJ/kg 43250 37150
Critical Temperature K 569.4 785.87
Critical Pressure bar 24.6 12.07
Enthalpy kJ/kg See Table 9 See Table 9
Viscosity Pa-s See Table 10 See Table 11
Thermal Conductivity W/m-K See Table 10 See Table 11
Liquid
Heat of Vaporization kJ/kg 250 357
Density kg/m^3 830 890.7
Enthalpy kJ/kg See Table 12 See Table 12
Viscosity kg/m-s See Table 13 See Table 14 Thermal Conductivity W/m-K See Table 13 See Table 14
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Table 9 Enthalpy constants for vapor diesel and biodiesel Enthalpy Constants Diesel No.2 Biodiesel
a1 1634.3 1675
a2 1.8191 1
a3 0 0
a4 0 0
a5 0 0
Note: The enthalpy of the vapor in J/kg is determined from the following curve-fit equation where href is the enthalpy at the reference temperature, Tref, of 298 K.
2 3 4 5
1( ) 2( ) 3( ) 4( ) 5( )
ref ref ref ref ref ref
h h− =a T−T +a T−T +a T−T +a T−T +a T−T
Table 10 Viscosities and thermal conductivities of diesel vapor Temperature Dynamic Viscosity Thermal Conductivity
[K] [Pa-s] [W/m-K]
303.15 8.02e-006 0.00829904
373.55 6.75e-006 0.00829904
475.35 475.35 475.35
Table 11 Viscosities and thermal conductivities of biodiesel vapor Temperature Dynamic Viscosity Thermal Conductivity
[K] [Pa-s] [W/m-K]
617 8.05715E-05 0.023996841
620 8.09543E-05 0.024174589
640 8.34962E-05 0.025364339
660 8.60214E-05 0.026562371
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Table 11 Continued
680 8.85297E-05 0.027768685
700 9.10212E-05 0.02898328
720 9.34959E-05 0.030206157
740 9.59537E-05 0.031437315
760 9.83948E-05 0.032676755
780 0.000100819 0.033924477
800 0.000103226 0.03518048
820 0.000105617 0.036444765
840 0.000107991 0.037717331
860 0.000110348 0.038998179
880 0.000112688 0.040287309
900 0.000115011 0.04158472
920 0.000117318 0.042890413
940 0.000119608 0.044204387
960 0.000121881 0.045526643
980 0.000124137 0.046857181
1000 0.000126376 0.048196
Table 12 Enthalpy constants for liquid diesel and biodiesel Enthalpy Constants Diesel No.2 Biodiesel
a1 2050 2050
a2 0 0
a3 0 0
Note: The enthalpy of the liquid in J/kg at pressure=1 bar is determined from the following curve-fit equation,
where the reference enthalpy is defined as: href = (href)vapor - hvaporization and Tref = 298 K
2 3
1( ) 2( ) 3( )
ref ref ref ref
h h− =a T−T +a T−T +a T−T
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Table 13 Viscosities and thermal conductivities of liquid diesel Temperature Dynamic Viscosity Thermal Conductivity
[K] [Pa-s] [W/m-K]
273.15 0.00219 0.116645
290.15 0.00171 0.113925
310.15 0.00133 0.110725
330.15 0.0011 0.107525
350.15 0.00096 0.104325
373.15 0.00088 0.100645
400.15 0.00087 0.096325
450.15 0.00112 0.088325
Table 14 Viscosities and thermal conductivities of liquid biodiesel Temperature Dynamic Viscosity Thermal Conductivity
[K] [Pa-s] [W/m-K]
300 0.000045993 0.17887
310 0.000036646 0.17719
320 0.00002994 0.17549
330 0.000024982 0.17377
340 0.000021223 0.17205
350 0.000018309 0.17031
360 0.000016007 0.16855
370 0.000014157 0.16678
380 0.000012649 0.165
390 0.000011402 0.1632
400 0.00001036 0.16139
410 0.00000948 0.15955
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Table 14 Continued
420 0.000008729 0.1577
430 0.000008083 0.15584
440 0.000007523 0.15395
450 0.000007034 0.15204
460 0.000006604 0.15011
470 0.000006224 0.14816
480 0.000005886 0.14618
490 0.000005584 0.14418
500 0.000005313 0.14216
510 0.000005069 0.14011
520 0.000004848 0.13803
530 0.000004647 0.13591
540 0.000004463 0.13377
550 0.000004296 0.13159
560 0.000004142 0.12937
570 0.000004 0.12711
580 0.000003869 0.12481
590 0.000003748 0.12247
600 0.000003636 0.12007
610 0.000003531 0.11762
620 0.000003434 0.11511
630 0.000003343 0.11253
640 0.000003259 0.10988
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APPENDIX II
DISCHARGE COEFFICIENTS WITH LIFT
Table 15 Intake valve flow coefficients
L/D Ratio Forward Flow Coefficient Reverse Flow Coefficient
0 0 0
0.0304053 0.1071826 0.1071826
0.0608812 0.2031018 0.2031018
0.0911371 0.2788924 0.2788924
0.1215096 0.3513742 0.3513742
0.1519005 0.4214792 0.4214792
0.1823885 0.4814215 0.4814215
0.2128395 0.5291767 0.5291767
0.243119 0.5648113 0.5648113
0.2734641 0.5883421 0.5883421
0.3038992 0.6019374 0.6019374
0.3344928 0.6113458 0.6113458
0.3646257 0.6184707 0.6184707
0.3952485 0.6262355 0.6262355
Table 16 Exhaust valve flow coefficients
L/D Ratio Forward Flow Coefficient Reverse Flow Coefficient
0 0 0
0.0309989 0.1052954 0.1052954
0.0620698 0.2117053 0.2117053
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Table 16 Continued
0.0929163 0.3008259 0.3008259
0.1238818 0.385439 0.385439
0.154866 0.4794244 0.4794244
0.1859492 0.5483239 0.5483239
0.2169947 0.5985104 0.5985104
0.2478653 0.6431867 0.6431867
0.2788029 0.6792136 0.6792136
0.3098321 0.7080437 0.7080437
0.341023 0.733009 0.733009
0.3717443 0.7526495 0.7526495
0.4029648 0.7682453 0.7682453
Fig.60 Discharge coefficients against L/D ratio for intake and exhaust valves
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
Discharge Coefficient
L/D Ratio
Exhaust Valve
Intake Valve
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APPENDIX III
MODEL VALIDATION FOR BIODIESEL FUEL
Fig.61 Pressure diagram comparison @ 1400 rpm 50 ft-lbs for biodiesel
Fig.62 Heat release curve comparison
@ 1400 rpm 50 ft-lbs for biodiesel
Fig.63 Pressure diagram comparison @ 1400 rpm 150 ft-lbs for biodiesel case
Fig.64 Heat release curve comparison
@ 1400 rpm 150 ft-lbs for biodiesel case
Pressure Diagram @ 1400 rpm 50 ft-lb (bio)
Heat Release Comparison @1400 rpm 50 ft-lb (bio)
Pressure Diagram @ 1400 rpm 150 ft-lb (bio)
Heat Release Comparison @1400 rpm 150 ft-lb (bio)
"Experiment"
Simulation
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Fig.65 Pressure diagram comparison @ 1400 rpm 300 ft-lbs for biodiesel case
Fig.66 Heat release curve comparison
@ 1400 rpm 300 ft-lbs for biodiesel case
Fig.67 Pressure diagram comparison @ 1900 rpm 50 ft-lbs for biodiesel case
Fig.68 Heat release curve comparison
@ 1900 rpm 50 ft-lbs for biodiesel case
0
Pressure Diagram @ 1400 rpm 300 ft-lb (bio)
Heat Release Comparison @1400 rpm 300 ft-lb (bio)
Pressure Diagram @ 1900 rpm 50 ft-lb (bio)
Heat Release Comparison @1900 rpm 50 ft-lb (bio)
"Experiment"
Simulation
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Fig.69 Pressure diagram comparison @ 1900 rpm 150 ft-lbs for biodiesel case
Fig.70 Heat release curve comparison
@ 1900 rpm 150 ft-lbs for biodiesel case
Fig.71 Pressure diagram comparison @ 1900 rpm 300 ft-lbs for biodiesel case
Fig.72 Heat release curve comparison
@ 1900 rpm 300 ft-lbs for biodiesel case
Pressure Diagram @ 1900 rpm 150 ft-lb (bio)
Heat Release Comparison @1900 rpm 150 ft-lb (bio)
Pressure Diagram @ 1900 rpm 300 ft-lb (bio)
Heat Release Comparison @1900 rpm 300 ft-lb (bio)
"Experiment"
Simulation
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Fig.73 Pressure diagram comparison @ 2400 rpm 50 ft-lbs for biodiesel case
Fig.74 Heat release curve comparison
@ 2400 rpm 50 ft-lbs for biodiesel case
Fig.75 Pressure diagram comparison
@ 2400 rpm 150 ft-lbs for biodiesel case
Fig.76 Heat release curve comparison
@ 2400 rpm 150 ft-lbs for biodiesel case
Pressure Diagram @ 2400 rpm 50 ft-lb (bio)
Heat Release Comparison @2400 rpm 50 ft-lb (bio)
Pressure Diagram @ 2400 rpm 150 ft-lb (bio)
Heat Release Comparison @2400 rpm 150 ft-lb (bio)
"Experiment
"
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Fig.77 Pressure diagram comparison @ 2400 rpm 300 ft-lbs for biodiesel case
Fig.78 Heat release curve comparison
@ 2400 rpm 300 ft-lbs for biodiesel case
Pressure Diagram @ 2400 rpm 300 ft-lb (bio)
Heat Release Comparison @2400 rpm 300 ft-lb (bio)
"Experiment"
Simulation
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VITA
Name: Junnian Zheng
Address: Texas A&M University
Department of Mechanical Engineering 3123 TAMU
College Station TX 77843-3123 Email Address: [email protected]
Education: B.A., Mechanical Engineering, Shanghai Jiaotong University, 2007 M.S., Mechanical Engineering, Texas A&M University, 2009