摘要
随着能源短缺和环境污染问题愈演愈烈,人们开始广泛关注实现汽车节能减排的相关技术。其中,汽车应用怠速-停止技术,即怠速时发动机熄火,行车时快速起动的技术,可以有效降低城市工况下燃油消耗量和整车排放,赢得了许多国家和地区政府的认可。传统进气道喷射汽油机从起动喷油到缸内着火做功最快也要2～3个冲程,致使重新起动产生较长时间延滞。而直喷汽油机可在1个冲程内着火做功,为快速起停技术提供了良好的载体。
在缸内直喷汽油机上采用怠速-停止技术,实现快速起动,可以直接向处于压缩行程或膨胀行程的气缸喷入燃油。但是由于发动机热机停止,活塞停止位置的随机性,导致滞留在气缸中的气体的质量是不确定的,而且这些气体直接受到高温气缸壁、气缸盖的加热,温度要高于普通工况进入气缸内的气体温度,所以在起动时其着火的初始边界条件具有特殊性。本文针对这种条件研究了不同冷却液温度、活塞停止位置以及喷油参数对首次喷油气缸内着火情况的影响。并且基于CFD商用软件FIRE对活塞处于不同初始位置时,气缸内气液混合流的浓度场、温度场和速度场的动态分布特点进行了数值模拟,分析了不同喷油时刻和喷油量对火花塞附近混合气浓度的影响。本文的主要研究结论如下:
1.当活塞从60°CA BTDC起动时,喷油后油束最前端出现卷吸现象,并在气缸内形成逆滾流,压缩上止点时缸内温度相对较低。喷油量较稀或适中时,均可点燃。喷油量较浓时,喷油时刻越早,失火的可能性越大。当活塞从90°CA BTDC起动时,喷油量适中时,喷油时刻对其燃烧情况影响不大。当活塞从120°CA BTDC或150°CA BTDC起动时,喷油量较多时,喷油时刻对其燃烧情况影响不大,但在150°CA BTDC起动时,喷油量较少时,自燃的可能性增加。当活塞从180°CA BTDC起动时,喷油时刻越晚,缸内温度越高,温度梯度越大。喷油量少或适中时,喷油时刻对其燃烧情况影响不大。喷油量较多时,喷油时刻过早或过晚时,自燃可能性增加。
2.喷油时刻在90°CA BTDC附近时,缸内产生两个运动方向相反的滾流,在其作用下,油束向燃烧室两侧扩散。喷油时刻较早或较晚时,油束主要在壁面的引导下向火花塞附近运动。
3.当冷却液温度在100℃,活塞初始位置距离压缩上止点小于90°曲轴转角时,在混合气偏浓和偏稀处出现失火区域,中间为点燃区域;随着活塞初始位置逐渐远离上止点,点燃区域逐渐增大,向偏浓失火区扩展。当活塞初始位置距离上止点大于120°曲轴转角时,在偏稀失火区和点燃区之间出现了自燃区,随曲轴转角逐渐增大,自燃区面积增加,向点燃区扩展。喷射时刻选择适中,处于压缩上止点前60°~90°曲轴转角并且采用较浓的混合气有助于避免自燃的发生。
4.当发动机热机起动,直接向处于压缩冲程的气缸喷油时,冷却液温度对缸内混合气能否发生自燃影响较大。冷却液温度越高,自燃区越大。
5.在点燃区内,对一定的喷油量,不同的喷油定时对其燃烧状况影响不大,燃烧始点一样,最高燃烧爆发压力相差不多。在自燃区内,不同的喷油定时对其燃烧状况影响较大,喷油定时越早,自燃始点随之提前,最高燃烧压力也相应增大。
Because of increasingly attention on the energy shortage and environmental pollution, energy saving and emission reduction technology was caused widely attention. The start-stop technology (the vehicle was flameout in idling period and then could start quickly) which could reduce fuel consuming and emissions in urban conditions was widely accepted by many countries. There would be 2-3 strokes in the period between injection and ignition on port fuel injection engine. As a result, a long time delay existed in restart. However, it only needed one stroke on gasoline direct injection engine which provided favorable support for quick start-stop technology.
For achieving quick start-stop technology on gasoline direct injection engine, fuels would be jetted into cylinder which is in the compression stroke or expansion stroke. However, in consider of hot stop and randomness of piston stop position, the mixture quality is uncertain. Moreover, these mixtures are heated by high-temperature cylinder wall and cylinder head. Therefore, the initial boundary conditions of ignition in start were special. In the paper, the research was carried out on the influence of different cooling liquid temperature, piston stopping position and injection parameters on ignition in cylinder of first injection. Additionally, based on the CFD commercial software FIRE, in different piston initial positions, numerical simulation was made on the dynamic distribution characteristics of mixture concentration field, temperature field and velocity field. Moreover the influence of different injection timing and qualities on mixture concentration near spark plug was analyzed. The main conclusions are as follows:
a) When the engine started at 60°CA BTDC, the end of spray appeared entrainment phenomenon after injection and clockwise flow existed in cylinder. The temperature in cylinder was relatively low. Ignition was available near TDC when fuel quality was relatively more rarefied or proper. With fuel charge in cylinder being higher and injection timing being earlier, the possibility of misfire was lower. When the engine started at 90°CA BTDC, the influence of injection timing on combustion was little if the fuel charge was proper. When the engine started at 120°CA BTDC or 150°CA BTDC, the influence of injection timing on combustion was not obvious if the fuel charge was relatively more. However, to start at 150°CA BTDC, the possibility of self-ignition increased if the fuel charge was more rarefied. When the engine started at 180°CA BTDC, the later the injection timing was, the higher the temperature in cylinder was. The temperature gradient also increased if the injection timing was earlier. There was nearly no influence of injection timing on combustion when the fuel charge was proper or rarefied. For the fuel charge was relatively more, the possibility of spontaneous combustion increased if the injection timing was too early or too late.
b) When the injection timing was at 90°CA BTDC, there were two adverse flows in cylinder which caused jets diffusing to chamber wall. Jets mainly moved to spark plug along the chamber wall if the injection timing was relatively early or late.
c) When coolant temperature was 100°C, the initial piston position was less than 90°CA BTDC, it is available for ignition only based on the fuel charge being proper. Otherwise, there would be misfire phenomenon. As the crankshaft angle between the initial piston position and TDC was increasing gradually, the ignition zone expanded to the misfire zone of high fuel charge. When the angle was larger than 120°C, there was spontaneous combustion zone between misfire zone and ignition zone. Additionally, this zone expanded to ignition zone as the angle increased. The proper injection timing (60°CA BTDC --90°CA BTDC) and relatively high fuel charge were good for avoiding spontaneous combustion.
d) In the process of hot engine start, the coolant temperature played significant roles on avoiding spontaneous combustion of mixture in cylinder if the injection timing was in compression stroke. The higher coolant temperature was, the larger spontaneous zone was.
e) In ignition zone, for certain fuel charge, the influence of different injection timings on combustion was small. The pressure peak value of combustion was similar if the initial combustion positions were the same. In spontaneous combustion zone, the influence of different injection timings on combustion was large. As injection timing was earlier, the initial spontaneous combustion position was earlier, the pressure peak value also increased.
引文
[1]居钰生,张红燕.试论我国内燃机工业的可持续发展.内燃机燃油喷射和控制.1999年第2期
[2]王燕军,王建昕,帅石金.汽油机稀薄燃烧研究的新进展-从GDI到HCCI[J].汽车技术,2002,8:1-5
[3]孙天松.能源危机与内燃机发展前景.山东内燃机,2001年第3期
[4] C.N.Grimaldi, L.Postrioti, C.Stan and R.Tr?ger, Analysis Method for the Spray Characteristics of a GDI System with High Pressure Modulation. SAE, 2000-01-1043
[5]白云龙,王志,帅石金,王建昕.缸内直喷汽油机喷雾、混合气形成和燃烧过程的三维数值模拟[J].燃烧科学与技术,第16卷第2期,2010年4月
[6]周玉明,胡健丽,刘家全.缸内汽油直喷稀薄燃烧技术.内燃机,2006年8月
[7] Shi shao-xi,Recent Progress in Combustion Technologies for Automotive Engines. Journal of Comnustion Science and Technology, Vol.7(2001)No.1
[8]原满红,汽油机的稀薄燃烧系统分析,内燃机2002年第5期
[9]李克强,汽车技术的发展动向及我国的对策,汽车工程,2009年(第31卷)第11期
[10]杨妙梁,汽车怠速停止和起动系统的技术进展[J],汽车与配件,2004, NO.3,24-26
[11] Moritaka Matsuura, Koji Korematsu and Junya Tanaka. Fuel Consumption Improvement of Vehicles by Idling Stop[C]. SAE Paper, 2004-01-1896
[12] Shigeo Yamamoto, Dai Tanaka, Jun Takemura, Osamu Nakayama and Hiromitsu AndoMixing ,Control and Combustion in Gasoline Direct Injection Engines for Reducing Cold-Start Emissions[C].SAE Paper, 2001-01-0550
[13] John Bishop, Ashok Nedungadi, Gregory Ostrowski, et al. An Engine Start/Stop System for Improved Fuel Economy[C]. SAE Paper, 2007-01-1777.
[14] Domenic A. Santavicca and James V. Zello. Fuel Injection Pressure Effects on the Cold Start Performance of a GDI Engine[C]. SAE Paper, 2003-01-3163
[15]韩立伟、洪伟、苏岩、段伟等,发动机停机后曲轴停止相位的研究,车用发动机,2010年6月,第3期
[16]黄勇成,周龙保,李维,蒋德明,缸内直喷周向分层燃烧系统火花塞附近油束发展历程的试验,内燃机学报,第19卷(2001)第6期
[17] C. Preussner,C. D?ring,S. Fehler and S. Kampmann, GDI:Interaction Between Mixture Preparation,Combustion System and Injector Performa- nce,SAE 980498
[18] Carlos Queiroz, Eduardo Tomanik, Gasoline Direct-injection Engines~a Bibliographical Review, SAE,973113
[19] H.Baecker, A. Kaufmann and M.Tichy, Experiment and Simulative Investigation on Stratification Potential of Spray-guided GDI Combustion Systems, SAE Paper, 2007-01-1407
[20] Hiroshi Tajima,Masayoshi Nakashima,Masashi Sawada and Masayuki Aoyama, Visual Study Focused on the Combustion Problem in Gasoline Direct Injection Engine,SAE,2003-32-0014
[21]周华,张晓辉,韩玉环,汽油机缸内直喷稀薄燃烧技术(GDI),客车技术与研究,2007年第4期
[22] Cheng Y.K., Hamrin D, Heywood B, etal. An overview of hydrocarbon emissions mechanisms in spark-ignition engines. SAE Paper: 932708.
[23] Pisehinger F, Walzer P. Future trends in automotive engine technology[A]. FISITA Technical Paper, No.P1303[C]. 1996.
[24] Domenic A. Santavicca and James V. Zello. Fuel Injection Pressure Effects on the Cold Start Performance of a GDI Engine.SAE Paper, 2003-01-3163
[25] Xu M. Recent Advances in direct injection gasoline injector technology and fuel preparation strategy[A]·Proceedings of the Second Intenational Workshop on Advanced Spray Combustion[C]. Hiroshima, JaPan:1998:201-213.
[26] C. Stan、A. Stanciu、R. Troeger,GDI Compact Four Stroke Engine - an Advanced Concept for Vehicle Application,2004 SAE World Congress, Michigan,USA,2004
[27]尚秀镜,江俊峰,张建昭,傅茂林,汽油机缸内直喷的关键技术和发展现状,汽车技术,2001年3期
[28] L. Araneo、A. Coghe、G. Brunello and R. Dondé,Effects of Fuel Temperature and Ambient Pressure on a GDI Swirled Injector Spray,SAE 2000-01-1901
[29] Changsoo Jang、Sangmin Choi、Choongsik Bae Jooyoung Kim and Seung kook Baik,Performance of Prototype High Pressure Swirl Injector Nozzles for Gasoline Direct Injection,SAE 1999-01-3654
[30]陆展华,GDI发动机及其稀燃优化技术,柴油机,第6期,2003年
[31] N.Collings,K.S.Kalsi,S.Regitz, Cyclically Resolved Measurements of In-CylinderNOxConcentration in a Gasoline Engine .SAE Paper, 2006-08-0186
[32] H.Nakajima,Y.Yamaguchi,K.Tashiro.et.al.Study of TWC in NOx Adsorber Catalyst System for Gasoline Direct Injection Engine.SAEpaper,2001-01-1300
[33] K. Ueda, K. Kaihara, K. Kurose and H. Ando. Idling Stop System Coupled with Quick Start Features of Gasoline Direct Injection[C].SAE Paper 2001-01-0545.
[34]刘凯,何仁,黄大星,汽车怠速停止和起动系统研究现状及发展趋势,轻型汽车技术,2008年Z4期
[35]杨妙梁,汽车怠速停止和起动系统的技术进展(二)[J],汽车与配件,2004.4期: 36-39.
[36]张科勋,童毅,李建秋,欧阳明高.一体式起动发电机系统概述[J].汽车工程,2005 (Vol. 27) No. 3:377-378.
[37]朱慧敏.马自达智能怠速停止系统[J].汽车与配件,2006.1:19
[38]吴明一,王红星,秦玉波等,CFD并行计算技术的研究进展,化工进展,2007年第26卷增刊
[39]蔡荣泉.船舶计算流体力学的发展与应用[J].船舶,2002(4): 8-13.
[40]肖柯则,夏艺.计算流体力学在铸造过程中的应用[J].内蒙古工业大学学报, 1995, 4(3): 30-38.
[41]傅晓英,刘俊,许剑峰.计算流体力学在城市规划设计中的应用研究[J].四川大学学报(工程科学版),2002,34(6):36-39.
[42]翟晓华,谢晶,徐世琼.计算流体力学在制冷工程中的应用[J].制冷, 2003, 22(1): 17-22.
[43]金杉,庄达民,张向阳.计算流体力学在现代建筑消防设计中的应用[J].消防科学与技术,2003, 22(3): 194.197.
[44]常思勤,扈圣刚.计算流体力学进展及其在汽车设计中的应用[J].武汉汽车工业大学学报,1997,19(4):12.15.
[45]傅德薰,第二届国际计算流体力学会议简介[J].力学进展, 2003(3): 388
[46] Mike Fry, Jason King, Carl White, A Comparison of Gasoline Direct Injection Systems and Discussion of Development Techniques(Ⅰ), SAE, 1999-01-0171
[47] M.Fry, J.King, C.White, A Comparison of Gasoline Direct-injection Systems and Discussion of Development Techniques(Ⅱ), SAE, 1999-04-0181
[48] M.Pontoppidan, G.Bella,A.demaio,V.Rocco, Enhanced use of 3-D CFD and combustion simulation to optimize the development of ecu-control algorithms for GDI spark ignited engines,SAE,1999-24-0066
[49] Edwards.S.Suh and Christopher.J.Rurland, Numerical Study of Fuel/Air Mixture Preparation in a GDI Engine, SAE, 1999-01-3657
[50] C.Arcoumanis, M.Cavaises, B.Argueyroues, F.Galzin, Modeling of Pressure-swirl Atomizers for GDI Engines, SAE Paper,1999-01-0500
[51] Miok Joh, Kang Y. Huh, Seok Hong Noh, Kyu Hoon Choi, Numerical Prediction of Stratified Charge Distribution in a Gasoline Direct Injection Engine Parametric Studies,SAE Paper 1999-01-0178
[52] T.Georjon, E.Bourguignon, T.Duverger, et.al. Characteristics of Mixture Formation and Combustion in a Spray-Guided Concept Gasoline Direct Injection Engine: An Experimental and Numerical Approach, SAE,Paper, 2000-01-0534
[53] Sang Jin Hong, Akihiro Nishimura, George Papageorgakis, Bruno Vanzieleghem, Studies of Spray Breakup and Mixture Stratification in a Gasoline Direct Injection Engine Using KIVA-3V,Transactions of the ASME,Vol. 122,JULY 2000
[54] Rolf B.Karlsson, John B.Heywood, Piston Fuel Film Obsernations in an Optical Access GDI Engine, SAE,Paper, 2001-01-2022
[55] Miok Joh, Kang Y. Huh, Seok Hong Noh, Kyu Hoon Choi, Numerical prediction and validation of fuel spray behavior in a gasoline direct-injection engine, SAE Paper 2001-01-3668
[56] Gerhard F.Meister, Ales Alajbegovic, et.al. Transient Simulation of DGI Engine Injector with Needle Movement, SAE,Paper, 2002-01-2663
[57] C. Stan, A. Stanciu and R. Troeger, et.al. Influence of Mixture Formation on Injection and Combustion Characteristics in a Compact GDI Engine, SAE,Paper, 2002-01-0997
[58] Ronny Lindgren, Mikael Skogsberg, et.al. The Infulence of Injection Deposists on Mixture Formation in a DISC SI Engine, SAE,Paper,2003-01-1771
[59] Yong Yi、Christopher M. DeMinco,Numerical Investigation of Mixture Preparation in a GDI Engine,SAE 2006-01-3375
[60] H. Baecker、A. Kaufmann and M. Tichy,Experimental and Simulative Investigation on Stratification Potential of Spray-Guided GDI Combustion Systems,SAE 2007-01-1407
[61] B.Befrui, G.Corbinelli, D.Robart and W.Reckers, LES Simulation of the Internal Flow and Near-Field Spray Structure of an Outward-Opening GDI Injector and Comparison with Imaging Data, SAE Paper 2008-01-0137
[62] Timothy D. Spegar, Shi-Ing Chang and Sudhakar Das, et.al. An Analytical and Experimental Studyof a High Pressure Single Piston Pump for Gasoline Direct Injection (GDi) Engine Applications, SAE, 2009-01-1504
[63] S.Malaguti, G.Cantore and S.Fontanesi,et.al. CFD Investigation of Wall Wetting in a GDI Engine under Low Temperature Cranking Operation, SAE,2009-01-0704
[64] Zheng Xu, Jianwen Yi, Steven Wooldridge, et.al. Modeling the Cold Start of the Ford 3.5L V6 EcoBoost Engine, SAE, 2009-01-1493
[65]王燕军,基于两次喷射的汽油缸内直喷式燃烧系统的研究,博士学位论文,清华大学,2004年
[66] Gao Jian、JIANGDe-ming、HUANG Zuo-hua、WANG Xi-bin,Numerical Study on Spray and Mixture Stratif ied Combustion in a Direct Injection Gasol ine Engine,内燃机学报(Trans actions of CSICE),第23卷(2005)第4期
[67]沈俊、傅立敏、黎妹红、王靖宇,CFD软件及其在汽车领域的应用,汽车研究与开发,2000年5期
[68] K.J.Richards,M.N.Subramaniam and R.D.Reitz,Modeling the Effects of EGR and Injection Pressure on Emissions in a High-Speed Direct Injection Diesel Engine,SAE2001-01-1004
[69] Han Zhiyu,ReitzRD,Claybaker P J, et al,Modeling the Effects of Intake Flow Structures on Fuel/Air Mixing in a Direct-injected Spark-ignition Engine[R].SAE paper 961192
[70]汪淼,王建昕等,汽油喷雾碰壁和油膜形成的可视化试验与数值模拟,车用发动机,2006年12月,第6期
[71]赵治国,解茂昭,伞形油雾与热多孔介质相互作用的数值模拟,燃烧科学与技术,2007年12月,第13卷,第6期
[72]成晓北,黄荣华,王志,朱梅林,喷雾撞壁油膜流动的研究,内燃机学报,第20卷(2002)第3期
[73] Bai C.Gosman A D. Development of Methodology for Spray Impingement Simulation. SAE Paper,950283,1995
[74] Kong S C、Senlcal P K and Reitz R D,Developments in spray Modeling in Diesel and direct-injection Gasoline Engines, Oil and Gas Science and Technology-Rev IFP,1999,54(2)
[75] Dukowicz,J.K, Quasi-steady Droplet Change in the Presence of Convection, Informal Report Los Alamos Scientific Laboratory, LA7997-MS
[76] AVL FIRE Version 8 Spray, December 2006
[77]王燕军,汽油高压旋流喷雾的数值模拟和试验研究[J],汽车工程,2004,26(6)
[78]于水,董光宇,高原,吴志军,李理光,基于循环分析的发动机快速起动瞬态燃烧特性,内燃机学报,第26卷(2008)第5期
[79] Brigitte M. Castaing, Jim S.Cowart and Wai K.Cheng, Fuel Metering Effects on Hydrocarbon Emissions and Engine Stability During Cranking and Start-up in a Port Fuel Injected Spark Ignition Engine[C], SAE Paper,2000-01-2836
