二冲程船用柴油机扫气过程CFD模拟分析
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摘要
二冲程船用柴油机的扫气过程在很大程度上影响了柴油机可燃混合气形成的质量,进而决定了柴油机在燃烧等方面的性能。扫气口作为二冲程直流扫气柴油机的重要组成部分,其结构直接影响了扫气过程中新鲜空气的充入量和燃烧废气排出的干净程度,另外,柴油机的转速也对扫气过程的进行有重要影响。本文针对6S50MC-C二冲程船用柴油机,运用CFD(计算流体力学)方法,应用大型CFD软件Fluent,首先改变扫气口数目、扫气口仰角、径向倾角的大小以及扫气口的结构,对该模型的扫气过程进行数值模拟,然后改变柴油机的转速,再进行上述模拟。可以得出流场关于压力、温度、湍流强度、进出口质量流量、速度等参数以及这些参数的分布情况。通过分析其流动状况后,找到较为合理的结构参数和运转参数。
本文首先对扫气口、气缸内部和上部一段排气道的流体空间进行建模,得到物理模型；接着使用GAMBIT对模型划分网格,并设定压力进出口等边界条件；然后导入Fluent中,设定参数,启用动网格模型,开始计算；最后应用后处理程序得到大量数据、云图、矢量图、流线图等,对流场进行分析。通过研究发现,对于6S50MC-C大型低速船用柴油机,在适当的范围内以较低转速运行,增加扫气口数目、使用0°的仰角以及20°的径向倾角比较有利于扫气过程和可燃混合气形成。并发现当转速较低或较高时,仰角大小对扫气过程的影响会变得更小。本文可以为优化柴油机结构和参数,进而解决燃烧与排放等问题提供理论依据,具有一定的现实意义。
Scavenging process of two-stroke marine diesel engines largely determines the formation quality of fuel mixture, and then determines the performance of combustion etc. As an important part of the two-stroke uniflow scavenging diesel, the scavenging port's structure directly affects the intake flux of fresh air and the exhaust cleanliness of combustion gas. In addition, the diesel's rotational speed, also affect the process of scavenging.6S50MC-C diesel engine is studied by using the method of CFD (Computational Fluid Dynamic), and CFD software Fluent is applied. First, the number, the elevation/radial angle and the structure of scavenging port are changed, and the scavenging process is simulated. Then the simulation is carried out like above mentioned at different diesel's rotational speed. Some parameters like pressure, temperature, turbulence intensity, mass flow of inlet, velocity etc. and the distribution of these parameters can be obtained. By analyzing its flow status, some reasonable structural and operating parameters can be found.
Firstly, the fluid space of port, in-cylinder part, and exhaust passage above the cylinder is modeled. Then, GAMBIT is used to mesh the model, meanwhile, pressure inlet/outlet boundary condition is set. Afterwards, the mesh is imported to Fluent, parameters are set, the dynamic mesh model is enabled, and then calculate begins. Finally, with the help of post-processing procedure, lots of data, contours, vector, path lines etc. can be obtained, so analysis can be done. It can be found with the appropriate range, operating in low rotational speed, increasing the number of scavenging ports, using 0°elevation angle and 20°radial angle may benefit scavenging process and the formation of oil and air. Meanwhile, when operating in lower or higher rotational speed, the influence of elevation angle becomes smaller on the scavenging process. So it can provide theoretical basis for diesel's structural optimization and solving problem of combustion, emission etc., therefore there is a certain practical significance.
本文首先对扫气口、气缸内部和上部一段排气道的流体空间进行建模,得到物理模型；接着使用GAMBIT对模型划分网格,并设定压力进出口等边界条件；然后导入Fluent中,设定参数,启用动网格模型,开始计算；最后应用后处理程序得到大量数据、云图、矢量图、流线图等,对流场进行分析。通过研究发现,对于6S50MC-C大型低速船用柴油机,在适当的范围内以较低转速运行,增加扫气口数目、使用0°的仰角以及20°的径向倾角比较有利于扫气过程和可燃混合气形成。并发现当转速较低或较高时,仰角大小对扫气过程的影响会变得更小。本文可以为优化柴油机结构和参数,进而解决燃烧与排放等问题提供理论依据,具有一定的现实意义。
Scavenging process of two-stroke marine diesel engines largely determines the formation quality of fuel mixture, and then determines the performance of combustion etc. As an important part of the two-stroke uniflow scavenging diesel, the scavenging port's structure directly affects the intake flux of fresh air and the exhaust cleanliness of combustion gas. In addition, the diesel's rotational speed, also affect the process of scavenging.6S50MC-C diesel engine is studied by using the method of CFD (Computational Fluid Dynamic), and CFD software Fluent is applied. First, the number, the elevation/radial angle and the structure of scavenging port are changed, and the scavenging process is simulated. Then the simulation is carried out like above mentioned at different diesel's rotational speed. Some parameters like pressure, temperature, turbulence intensity, mass flow of inlet, velocity etc. and the distribution of these parameters can be obtained. By analyzing its flow status, some reasonable structural and operating parameters can be found.
Firstly, the fluid space of port, in-cylinder part, and exhaust passage above the cylinder is modeled. Then, GAMBIT is used to mesh the model, meanwhile, pressure inlet/outlet boundary condition is set. Afterwards, the mesh is imported to Fluent, parameters are set, the dynamic mesh model is enabled, and then calculate begins. Finally, with the help of post-processing procedure, lots of data, contours, vector, path lines etc. can be obtained, so analysis can be done. It can be found with the appropriate range, operating in low rotational speed, increasing the number of scavenging ports, using 0°elevation angle and 20°radial angle may benefit scavenging process and the formation of oil and air. Meanwhile, when operating in lower or higher rotational speed, the influence of elevation angle becomes smaller on the scavenging process. So it can provide theoretical basis for diesel's structural optimization and solving problem of combustion, emission etc., therefore there is a certain practical significance.
引文
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[3]陈慧.船用大功率柴油机的技术发展和国内产业现状分析[J].重发科技,2009,4：17-20.
[4]蒋炎坤,钟毅芳等.二冲程发动机扫排气道—缸内系统三维瞬态数值模拟研究[J].内燃机学报.2001,19(2)：159-164.
[5]赵峰.直流扫气柴油机扫气过程仿真分析及优化[D].大连：大连海事大学.2010,6.
[6]Bruce. J. Tobis, et al, "Scavenging of Firing Two-Stroke-Spark-Ignition Engine", SAE 94039.
[7]李玉林,邓高雄.船用低速二冲程柴油机废气排放控制技术[J].造船工业.2010,(9)：60-61.
[8]A.A.Arnden, et al. "KIVA-H a Computer Program for Chemically Reactive Flows with S prays",1985.
[9]W.C.Reynolds“内燃机中流体运动的模拟”.刘龚俊译,内燃机燃烧模拟.机械工业出版社,1987.8.
[10]Chang-Su, KIM, Dong-Ho, LEE, Young-Sam, CHO. The Comparison about CFD-Simulation & Measurement Result of Large Two-Stroke Diesel Engine:CIMAC Congress 2001, Hamburg.
[11]宋如刚,杨延相等.扫气道对二冲程直喷汽油机扫气和喷雾过程影响的多维数值模拟[J].内燃机工程,2008,29(5)：3]-36.
[12]魏明锐,刘永长等.二冲程汽油机分层进气系统数值模拟及试验研究[J].内燃机学报,2003,21(6)：395-400.
[13]韩古忠等. FLUENT-流体工程仿真计算实例与应用[M].北京：北京理工大学.2004,6.
[14]王瑞金,张凯等Fluent技术基础及应用实例[M].北京：清华大学出版社,2007,2.
[15]段树林,辛颖等.柴油机缸内气体流动过程的数值计算[J].大连海事大学学报,2001,27(4)：43-48.
[16]吴春杰.二冲程柴油机气口结构对扫气过程影响的数值模拟研究[D].大连：大连理工大学,2001,6.
[17]来海菊.小型二冲程汽油机扫气过程的模拟与改进[D].镇江,江苏大学,2007.5.
[18]E.Sher. "Modeling the scavenging Process in the Two-Stroke Engine-An overview". SAE 890414.
[19]王亮亮.船用大型二冲程柴油机工作过程数值模拟[D].大连：大连海事大学,2009,6.
[20]傅德薰.计算流体力学[M].北京：高等教育出版社.2002,7.
[21]沈建平.内燃机气缸内空气湍流运动试验研究及数值模拟[D].武汉：华中理工大学,1995.
[22]刘超,任福安.工程流体力学[M].大连：大连海事大学出版社.2003,9
[23]来海菊.二冲程汽油机扫气过程的模拟[J].拖拉机与农用运输车.2006,33(6)：54-55.
[24]Dr.German Weisser, E. NOX emission from a two-stroke Engine ship engine:Part 2-Laboratory test. Applied Thermal Engineering.2009.
[25]傅德薰等.可压缩湍流直接数值模拟[M].北京：科学出版社.2010.
[26]王福军.计算流体动力学分析-CFD软件原理与应用[M].北京：清华大学出版社.2004,9.
[27]Sweeney M E G. Swann G B G, Kenny R G, Blair G P. Computational Fluid Dynamics Applied to Two-Stroke Engine Scavenging. SAE paper 851519.
[28]何志霞,干谦等.数值热物理过程：基本原理及CFD软件应用[M].镇江：江苏大学出版社.2009.
[29]Fluent6.3 user's guide[Z]. Fluent Inc.2006,9.
[30]江帆,黄鹏Fluent高级应用与实例分析[M].北京：清华大学出版社.2008,7.
[31]陈秋亮.缸内直喷式柴油/天然气双燃料转子发动机的数值模拟研究[D].长沙：中南大学.2008.
[32]M.M.Rahman, T.Siikonen and A.Mietinen, "A Pressure-correction Method for Solving Fluid Flow problems on a Colloca-ted grid", numerical heat transfer PART-B. FUNDAMENTALS, Vol.32 No.1.1997.
[33]M. Mugele. J. Tribulowski,IL Peters and U. Spicher. Numerical Analysis of Gas Exchange and Combustion Process in a Small Two-Stroke Gasoline. University of Karlsruhe. SAE Paper 2001013602,2001.
[34]李长春UG NX 4.0基础教程[M].北京：人民邮电出版社.2007.
[35]白京元,刘兵等.二冲程汽油机扫气过程多维数值模拟及扫气系统优化设计[J].内燃机工程.2005,26(1)：36-42.
[36]GAMBIT user's guide[Z]. Fluent Inc.2006.
[37]李辉.基于CFD方法的全方向推进器水动力性能研究[D].哈尔滨：哈尔滨工程大学.2009.
[38]Haworth DC. Multi-Dimension Calculation for a Two-Stroke-Cycle Engine:A Detailed Scavenging Model Validation [c]. SAE 932712,1993.
[39]王海燕,任光.船用大型低速二冲程柴油机的动态模拟[J].内燃机学报.2006,24(6)：543-547.
[40]杜涛.CFD模拟分析在二冲程汽油机性能改进中的应用探讨[J].内燃机与动力装置.2010,3：30-32,36.
[41]Anthony. A.Amsden, Peter. J. O. Rourke and TDaniel. Butier, "Comparisons of Computed and Measured Three-Dimensional Velocity Fields in a Motored Two-Stroke Engine". SAE 92041.
[42]陈登.二冲程缸内直喷汽油机扫气和喷油过程的多维数值模拟[D].天津：天津大学.2005,1.
[43]丰琳琳.二冲程低速柴油机工作过程与增压系统的计算研究[D].上海：上海交通大学.2007.
[44]Golverk A A. The Method for Development of a Diesel Engine Universal Performance. SAE paper941928,1994.
[45]夏兴兰,陈大陆等.内燃机气道性能的评价方法[J].现代车用动力.2007,(2)：7-12.
[46]J.G.Smyth, R.G. Kenny and G. P. Blair, "Motored and Steady Flow Boundary Conditions Applied to the Prediction of Scavenging Flow in a Loop Scavenging Two-Stroke Cycle Engine", SAE 90080.
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