柴油机喷油与EGR耦合控制机理数值模拟研究
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摘要
随着排放法规的日益严格和对经济性越来越高的要求,柴油机高效清洁燃烧理论与技术一直都是柴油机研究的前沿课题。在柴油机燃烧控制技术中,喷油与EGR控制是柴油机燃烧控制的重要技术措施,本文使用三维CFD计算软件AVL-Fire,在其现有的柴油机ECFM-3Z燃烧模型基础上,研究了EGR控制的低温燃烧模式局部物性空间及时间特性以及其如何实现同时降低NOx及Soot机理,研究了柴油机单次喷射喷油定时与EGR耦合控制的燃烧机理。
本文首先借助于数值模拟手段研究通过单次喷射耦合废气再循环的方法实现的低温燃烧中主要参数对NOx及Soot排放的影响机理;随着EGR率不断增大Soot排放先增加后减少,增加主要是EGR抑制Soot氧化速率更为明显,Ф-T路径并没有明显脱离高Soot生成区域。局部火焰温度随氧浓度的降低而降低,当氧浓度降到某一转捩点时,滞燃期延长使Ф-T图中的燃烧路径明显避开的Soot生成区域;火焰局部温度降低导致NOx排放大量减少,达到同时降Soot和NOx的目的。
提高喷油压力,增加了燃油对空气的卷吸,加快了油气之间的混合,燃烧持续期缩短, NOx增加,而Soot生成峰值相当,但后期氧化增加,从而导致Soot排放降低。
低氧浓度时,进气压力增加,滞燃期缩短,燃烧放热加快,燃烧后期温度随进气压力增加而降低,Soot降低,NOx增加;主要原因是氧的绝对量增加,Soot后期氧化速率增加,NOx增加主要是因局部温度大于1900K的区域随进气压力增加而增加。
最后,作者通过调节喷油定时和EGR率使主燃烧相位CA50保持在几乎相同的时刻,以探讨喷油时刻控制与EGR控制对燃烧及排放的影响。实验及计算结果均表明:喷油定时提前耦合大EGR率的燃烧效率及热效率均较喷油定时推迟耦合小EGR率的高,但前者最大爆发压力、压力升高率和NOx较高,而Soot则先增加后降低。随着主燃烧相位CA50的推迟,缸内局部温度及平均温度均降低,燃烧效率降低,NOx降低;Soot先增加后降低。
In the context of low consumption and low emissions engines development, the clean and high-efficiency combustion theory and technology of diesel engine has been widely researched. Fuel injection strategy and EGR are the important measures for combustion control in diesel engine. This paper mainly studied all spatial and temporal characteristics as well as local properties of LTC by applying the available diesel combustion model (ECFM-3Z) implemented in a commercial AVL-FIRE code and considered how LTC reduced NOx and soot simultaneously, and then studied the combustion controlling mechanism of single injection timing coupled with EGR.
A single fuel injection strategy has been deployed to push the diesel cycle into low temperature combustion with EGR. When increasing EGR from low levels to a level that corresponds to low temperature combustion, soot emissions initially increase due to soot oxidation lower than formation before decreasing to almost zero due to very low soot formation. When the oxygen concentration dropped to some threshold, longer ignition delay madeФ-T avoid the soot formation region. The flame temperature considerably decreased with decreasing oxygen concentration in the ambient gas. NOx level was decreased greatly by the low flame temperature.In other words, it decreased NOx and soot simultaneously.
The simulation results indicated that a higher injection pressure can increase air entrainment, improve the mixing between the fuel and air and then reduce the combustion duration. Soot emissions lower due to more oxidation while NOx increasing due to higher temperature.
With the increase of intake pressure at low oxygen concentration, the ignition delay shortened, the combustion heat release accelerated, the temperature in the post-combustion was lower, the combustion efficiency and NOx emissions increased because the local temperature in more area was larger than 1900K and oxygen absolute content increased; soot emissions decreases, more oxygen content increased the soot oxidation.
The last part mainly studied that the injection timing coupled with EGR had effects on the combustion and emissions, the simulation and experiment results both showed advanced SOI coupled with large EGR(CaseA) can reach CA50 at the same time as delayed SOI with small EGR(CaseB),the heat release rate of the former increased rapidly and its peak was higher, thermal efficiency of CaseA is more than of CaseB. But for the former, the top pressure, pressure rise rate and NOx are higher, soot increases firstly then decreases. As CA50 delayed, the local and mean combustion temperature both decrease, the combustion efficiency reduced, NOx emissions decrease, while soot emission increases firstly and then decreases.
本文首先借助于数值模拟手段研究通过单次喷射耦合废气再循环的方法实现的低温燃烧中主要参数对NOx及Soot排放的影响机理;随着EGR率不断增大Soot排放先增加后减少,增加主要是EGR抑制Soot氧化速率更为明显,Ф-T路径并没有明显脱离高Soot生成区域。局部火焰温度随氧浓度的降低而降低,当氧浓度降到某一转捩点时,滞燃期延长使Ф-T图中的燃烧路径明显避开的Soot生成区域;火焰局部温度降低导致NOx排放大量减少,达到同时降Soot和NOx的目的。
提高喷油压力,增加了燃油对空气的卷吸,加快了油气之间的混合,燃烧持续期缩短, NOx增加,而Soot生成峰值相当,但后期氧化增加,从而导致Soot排放降低。
低氧浓度时,进气压力增加,滞燃期缩短,燃烧放热加快,燃烧后期温度随进气压力增加而降低,Soot降低,NOx增加;主要原因是氧的绝对量增加,Soot后期氧化速率增加,NOx增加主要是因局部温度大于1900K的区域随进气压力增加而增加。
最后,作者通过调节喷油定时和EGR率使主燃烧相位CA50保持在几乎相同的时刻,以探讨喷油时刻控制与EGR控制对燃烧及排放的影响。实验及计算结果均表明:喷油定时提前耦合大EGR率的燃烧效率及热效率均较喷油定时推迟耦合小EGR率的高,但前者最大爆发压力、压力升高率和NOx较高,而Soot则先增加后降低。随着主燃烧相位CA50的推迟,缸内局部温度及平均温度均降低,燃烧效率降低,NOx降低;Soot先增加后降低。
In the context of low consumption and low emissions engines development, the clean and high-efficiency combustion theory and technology of diesel engine has been widely researched. Fuel injection strategy and EGR are the important measures for combustion control in diesel engine. This paper mainly studied all spatial and temporal characteristics as well as local properties of LTC by applying the available diesel combustion model (ECFM-3Z) implemented in a commercial AVL-FIRE code and considered how LTC reduced NOx and soot simultaneously, and then studied the combustion controlling mechanism of single injection timing coupled with EGR.
A single fuel injection strategy has been deployed to push the diesel cycle into low temperature combustion with EGR. When increasing EGR from low levels to a level that corresponds to low temperature combustion, soot emissions initially increase due to soot oxidation lower than formation before decreasing to almost zero due to very low soot formation. When the oxygen concentration dropped to some threshold, longer ignition delay madeФ-T avoid the soot formation region. The flame temperature considerably decreased with decreasing oxygen concentration in the ambient gas. NOx level was decreased greatly by the low flame temperature.In other words, it decreased NOx and soot simultaneously.
The simulation results indicated that a higher injection pressure can increase air entrainment, improve the mixing between the fuel and air and then reduce the combustion duration. Soot emissions lower due to more oxidation while NOx increasing due to higher temperature.
With the increase of intake pressure at low oxygen concentration, the ignition delay shortened, the combustion heat release accelerated, the temperature in the post-combustion was lower, the combustion efficiency and NOx emissions increased because the local temperature in more area was larger than 1900K and oxygen absolute content increased; soot emissions decreases, more oxygen content increased the soot oxidation.
The last part mainly studied that the injection timing coupled with EGR had effects on the combustion and emissions, the simulation and experiment results both showed advanced SOI coupled with large EGR(CaseA) can reach CA50 at the same time as delayed SOI with small EGR(CaseB),the heat release rate of the former increased rapidly and its peak was higher, thermal efficiency of CaseA is more than of CaseB. But for the former, the top pressure, pressure rise rate and NOx are higher, soot increases firstly then decreases. As CA50 delayed, the local and mean combustion temperature both decrease, the combustion efficiency reduced, NOx emissions decrease, while soot emission increases firstly and then decreases.
引文
[1]周龙保,高宗英,内燃机学第二版.北京:机械工业出版社,2005.1
[2]蒋德明,陈长佑,杨嘉林,杨中极.高等内燃机原理(上下册),西安交通大学出版社,2006.4
[3] Kamimoto T, and Bae M. High Combustion Temperature for the Reduction of Particulate in Diesel Engines. SAE Paper 880423, 1988
[4] Akihama K, Takatori Y, Inagaki K. Mechanism of the smokeless rich Diesel combustion by reducing temperature. SAE Paper 2001-01-0655, 2001
[5] Kitamura, T Ito T and J Senda et al. Mechanism of smokeless diesel combust ion with oxygenated fuels based on the dependence of the equivalence ratio and temperature on soot particle formation. International Journal of Engine Research.2002, Vol. 3(4): a223-247,2002
[6] Bae C, Miles P C, Pickett L M. The Influence of Charge Dilution and Injection Timing on Low-Temperature Diesel Combustion and Emissions. SAE Paper 2005-01-3837, 2005
[7] Kelly-Zion P L and Dec J E. A Computational Study of the Effect of Fuel Type on Ignition Time in HCCI Engines. Proceedings of the Combustion Institute, 2000, Vol. 28(1): 1187-1194,2000
[8] Han Z Y, Uludogan A, Reitz R D. Mechanism of Soot and Nox Emission Reduction Using Multiple-Injection in a Diesel Engine.SAE Paper 960633, 1996
[9] Sj?berg M, Dec J E. An investigation into lowest acceptable combustion temperatures for hydrocarbon fuels in HCCI engines. Proceedings of the Combustion Institute 30, 2005, 2719-2726
[10] Lachaux T, Musculus M P. In-cylinder unburned hydrocarbon visualization during low-temperature compression-ignition engine combustion using formaldehyde PLIF.Proceedings of the Combustion Institute 31, 2007, 2921-2929
[11] Kee R J, Rupley F M and Miller et al. Chemkin-II: A Fortran Chemical Kinetics Package for the Analysis of Gas Phase Kinetics.Sandia National Laboratories, SAND89-8009B, UC-706; 1992
[12] Aceves S, Flowers D. A Detailed Chemical Kinetic analysis of Low Temperature Non-Sooting Diesel Combustion. SAE Paper 2005-01-0923,2005
[13] Zheng Ming, Mulenga M, Reader G, et al. Biodiesel Engine Performance and Emissions in Low Temperature Combustion [OL ] . [2007-12-26 ].doi :10. 1016/j. fuel. 2007. 05. 039.
[14] Alrikisson M,Rente T,Denbratt I.Low Soot and NOx in a Heavy Duty Diesel Engine Using High Levels of EGR .SAE Paper 2005-01-3836,2005
[15] Alriksson M, Denbratt I. Low Temperature Combustion in a Heavy Duty Diesel Engine Using High Levels of EGR[C] .SAE Paper 2006-01-0075,2006
[16] Musculus M. Multiple Simultaneous Optical Diagnostic Imaging of Early2Injection LowTemperatureCombustion in a Heavy Duty Diesel Engine[C] . SAE Paper 2006-01-0079,2006
[17] Kook S, Bae C, Miles P, et al. The Influence of Charge dilution and Injection Timing on Low Temperature Diesel Combustion and Emissions [C] . SAE Paper 2005-01-3837,2005
[18] J B Heywood. Internal combustion engine fundamentals. New York: McGraw-Hill Book Company, 1998
[19] Ciajolo, A. D'Anna, A Barbella, R., Tregrossi, A.The Effect of Temperature on Soot Inception in Premixed Ethylene Flames.Proceedings of the Combustion Institute 26, 1996, 2327-2333.
[20] T Kitamura T Ito, J Senda, H Fujimoto. Mechanism of smokeless diesel combust ion with oxygenated fuels based on the dependence of the equivalence rat io and temperature on soot particle formation. International Journal of Engine Research, 2002, Vol. 3(4): a223-247
[21] CD adapco Group.STARCD USER GUIDE(Version 3.26).Japan:Yokohama Computational Dynamics Limited,2006.
[22] AVL公司AVL-FIRE Version 8 FIRE-Manuals CFD-SOLVER v85,2006.11.
[23]解茂昭,内燃机计算燃烧学,大连:大连理工大学出版社,2004.
[24] AVL-FIRE Version 8 SPRAY, 2006.11.
[25] Liu A B, Reitz R D.Modeling the effects of Drop Drag and Break-up on Fuel Sprays. SAE Paper 930072, 1993.
[26] Su T F, Patterson M A. Reitz, R.D. and Farrell, P.V., Experimental and Numerical Studies of High Pressure Multiple Injection Sprays, SAE Paper 960861, 1996.
[27] v. Künsberg-Sarre.C,Tatschl, R. Spray Modelling / Atomisation– Current Status of Break-up Models.IMECHE-Seminar, December 15-16, 1998, The Lawn.
[28] Reitz R D, Bracco F V. Mechanism of Atomization of a Liquid Jet. Physic of Fluids 25 (10), 1982.
[29] Reitz R D, Diwakar J. "Effect of Drop Break-up on Fuel Sprays", SAE 860469.
[30] O’Rourke P J, Amsden A. The Tab Method for Numerical Calculation of Spray Droplet Break-up. SAE Paper 872089, 1987.
[31] O'Rourke P J, Bracco, F V. Modelling of Drop Interactions in Thick Sprays and a Comparison with Experiments. IMECHE, 1980.
[32] Bai C, Gosman A D, Development of Methodology for Spray Impingement Simulation.SAE Paper 950283, 1995.
[33] O. Colin ,A. Benkenida,The 3-Zones Extended Coherent Flame Model (Ecfm3z) for Computing Premixed/Diffusion Combustion, Oil & Gas Science and Technology - Rev. IFP, Vol. 59 (2004), No. 6, pp. 593-609 DOI: 10.2516/ogst:2004043.
[34] Aberg P, Smith G P, Jeffries J B. Nitric Oxide Formation and Reburn in Low-pressure Methane Flames. 27th Symp. (Int.) on Combustion, The Combustion Institute, 1998.
[35] Monat J P, Hanson R K, Kruger C H. Shock tube determination of the rate coefficient for the reaction N2 + O→NO + O. 17th Symp. (Int.) on Combustion, the Combustion Institute, 1979.
[36] Hioyasu H, Nishida K. Simplified Three Dimensional Modeling of Mixture formation and Combustion in a DI Diesel Engine.SAE Paper 890269, 1989.
[37] Nagle J, Strickland-Constable R.F. Oxidation of Carbon between 1000 - 2000°C. Proceedings of the Fifth Conference on Carbon. New York: Pergamon. 1962.
[38] AVL公司,AVL-FIRE Version 8 FIRE-Examples,2006.11.
[2]蒋德明,陈长佑,杨嘉林,杨中极.高等内燃机原理(上下册),西安交通大学出版社,2006.4
[3] Kamimoto T, and Bae M. High Combustion Temperature for the Reduction of Particulate in Diesel Engines. SAE Paper 880423, 1988
[4] Akihama K, Takatori Y, Inagaki K. Mechanism of the smokeless rich Diesel combustion by reducing temperature. SAE Paper 2001-01-0655, 2001
[5] Kitamura, T Ito T and J Senda et al. Mechanism of smokeless diesel combust ion with oxygenated fuels based on the dependence of the equivalence ratio and temperature on soot particle formation. International Journal of Engine Research.2002, Vol. 3(4): a223-247,2002
[6] Bae C, Miles P C, Pickett L M. The Influence of Charge Dilution and Injection Timing on Low-Temperature Diesel Combustion and Emissions. SAE Paper 2005-01-3837, 2005
[7] Kelly-Zion P L and Dec J E. A Computational Study of the Effect of Fuel Type on Ignition Time in HCCI Engines. Proceedings of the Combustion Institute, 2000, Vol. 28(1): 1187-1194,2000
[8] Han Z Y, Uludogan A, Reitz R D. Mechanism of Soot and Nox Emission Reduction Using Multiple-Injection in a Diesel Engine.SAE Paper 960633, 1996
[9] Sj?berg M, Dec J E. An investigation into lowest acceptable combustion temperatures for hydrocarbon fuels in HCCI engines. Proceedings of the Combustion Institute 30, 2005, 2719-2726
[10] Lachaux T, Musculus M P. In-cylinder unburned hydrocarbon visualization during low-temperature compression-ignition engine combustion using formaldehyde PLIF.Proceedings of the Combustion Institute 31, 2007, 2921-2929
[11] Kee R J, Rupley F M and Miller et al. Chemkin-II: A Fortran Chemical Kinetics Package for the Analysis of Gas Phase Kinetics.Sandia National Laboratories, SAND89-8009B, UC-706; 1992
[12] Aceves S, Flowers D. A Detailed Chemical Kinetic analysis of Low Temperature Non-Sooting Diesel Combustion. SAE Paper 2005-01-0923,2005
[13] Zheng Ming, Mulenga M, Reader G, et al. Biodiesel Engine Performance and Emissions in Low Temperature Combustion [OL ] . [2007-12-26 ].doi :10. 1016/j. fuel. 2007. 05. 039.
[14] Alrikisson M,Rente T,Denbratt I.Low Soot and NOx in a Heavy Duty Diesel Engine Using High Levels of EGR .SAE Paper 2005-01-3836,2005
[15] Alriksson M, Denbratt I. Low Temperature Combustion in a Heavy Duty Diesel Engine Using High Levels of EGR[C] .SAE Paper 2006-01-0075,2006
[16] Musculus M. Multiple Simultaneous Optical Diagnostic Imaging of Early2Injection LowTemperatureCombustion in a Heavy Duty Diesel Engine[C] . SAE Paper 2006-01-0079,2006
[17] Kook S, Bae C, Miles P, et al. The Influence of Charge dilution and Injection Timing on Low Temperature Diesel Combustion and Emissions [C] . SAE Paper 2005-01-3837,2005
[18] J B Heywood. Internal combustion engine fundamentals. New York: McGraw-Hill Book Company, 1998
[19] Ciajolo, A. D'Anna, A Barbella, R., Tregrossi, A.The Effect of Temperature on Soot Inception in Premixed Ethylene Flames.Proceedings of the Combustion Institute 26, 1996, 2327-2333.
[20] T Kitamura T Ito, J Senda, H Fujimoto. Mechanism of smokeless diesel combust ion with oxygenated fuels based on the dependence of the equivalence rat io and temperature on soot particle formation. International Journal of Engine Research, 2002, Vol. 3(4): a223-247
[21] CD adapco Group.STARCD USER GUIDE(Version 3.26).Japan:Yokohama Computational Dynamics Limited,2006.
[22] AVL公司AVL-FIRE Version 8 FIRE-Manuals CFD-SOLVER v85,2006.11.
[23]解茂昭,内燃机计算燃烧学,大连:大连理工大学出版社,2004.
[24] AVL-FIRE Version 8 SPRAY, 2006.11.
[25] Liu A B, Reitz R D.Modeling the effects of Drop Drag and Break-up on Fuel Sprays. SAE Paper 930072, 1993.
[26] Su T F, Patterson M A. Reitz, R.D. and Farrell, P.V., Experimental and Numerical Studies of High Pressure Multiple Injection Sprays, SAE Paper 960861, 1996.
[27] v. Künsberg-Sarre.C,Tatschl, R. Spray Modelling / Atomisation– Current Status of Break-up Models.IMECHE-Seminar, December 15-16, 1998, The Lawn.
[28] Reitz R D, Bracco F V. Mechanism of Atomization of a Liquid Jet. Physic of Fluids 25 (10), 1982.
[29] Reitz R D, Diwakar J. "Effect of Drop Break-up on Fuel Sprays", SAE 860469.
[30] O’Rourke P J, Amsden A. The Tab Method for Numerical Calculation of Spray Droplet Break-up. SAE Paper 872089, 1987.
[31] O'Rourke P J, Bracco, F V. Modelling of Drop Interactions in Thick Sprays and a Comparison with Experiments. IMECHE, 1980.
[32] Bai C, Gosman A D, Development of Methodology for Spray Impingement Simulation.SAE Paper 950283, 1995.
[33] O. Colin ,A. Benkenida,The 3-Zones Extended Coherent Flame Model (Ecfm3z) for Computing Premixed/Diffusion Combustion, Oil & Gas Science and Technology - Rev. IFP, Vol. 59 (2004), No. 6, pp. 593-609 DOI: 10.2516/ogst:2004043.
[34] Aberg P, Smith G P, Jeffries J B. Nitric Oxide Formation and Reburn in Low-pressure Methane Flames. 27th Symp. (Int.) on Combustion, The Combustion Institute, 1998.
[35] Monat J P, Hanson R K, Kruger C H. Shock tube determination of the rate coefficient for the reaction N2 + O→NO + O. 17th Symp. (Int.) on Combustion, the Combustion Institute, 1979.
[36] Hioyasu H, Nishida K. Simplified Three Dimensional Modeling of Mixture formation and Combustion in a DI Diesel Engine.SAE Paper 890269, 1989.
[37] Nagle J, Strickland-Constable R.F. Oxidation of Carbon between 1000 - 2000°C. Proceedings of the Fifth Conference on Carbon. New York: Pergamon. 1962.
[38] AVL公司,AVL-FIRE Version 8 FIRE-Examples,2006.11.