柴油机冷却系统设计毕业论文.doc

I摘要柴油机运转时气缸内的燃烧温度达到1800到2000，瞬时温度高达3000，与高温燃气相互接触的零件（如缸盖，活塞，气缸，气阀，喷油器等）受到强烈的加热，如不加以适当的冷却，发动机会过热，充气系数下降，燃烧不正常，发生早燃和爆燃现象，与高温接触零件过热，导致材料机械性能降低，和产生严重的热应力，导致变形和裂纹，另外温度过高会使得机油变质，烧损和结焦失去润滑性能，破坏润滑油膜，零件的摩擦和磨损加剧，从而导致发动机的动力性，可靠性，经济性，耐久性，全面恶化。如果系统的冷却能力过强，机油被燃油稀释（即因缸壁过冷，可燃混合气体在缸壁冷凝并聚集，冲刷缸筒上的润滑油膜，未蒸发的燃油经缸壁流到油底壳，稀释机油），同时恶化混合气体形成及燃烧，增加机油粘度和摩擦效率，造成零件间的磨损加剧，摩擦损失增加，柴油机工作粗暴，另外通过冷却系统带走的热量是燃油燃烧的热量，一般约占燃烧热量的20%-30%，这是一种损失，如果冷却过强，散热损失增加，会降低发动机的经济性。因此发动机过冷或者过热（即发动机冷却能力过强或者过弱）都会对发动机的动力性，经济性，工作可靠性带来不利的影响。因此设计良好的冷却系统，能够保证发动机始终处于最适宜的温度下工作，已获得较高的发动机经济性能，动力性能，工作可靠性指标等。冷却系统的功用就是使发动机在各种工况下都保持在适当的温度范围内，冷却系统既要防止发动机过热，又要防止冬季发动机过冷，在冷态下的发动机启动之后，冷却系统还要保证发动机迅速升温，尽快达到正常的工作温度。关键词：散热器；风扇；冷却水泵；硅油风扇离合器；节温器IIAbstractCylinderdieselenginerunninginsidethecombustiontemperaturereaches1800to2000,theinstantaneoustemperatureupto3000,andthehightemperaturegascomponentsincontactwitheachother(suchascylinderhead,piston,cylinder,valve,injector,etc.)bythestrongheating,Ifnotproperlycooled,theenginewilloverheat,inflatablecoefficientdecreased,abnormalcombustion,burningandexplodingphenomenonoccurredearly,withthehightemperaturecontactpartsoverheat,resultinginlowermechanicalpropertiesofmaterials,andsevereheatstress,leadingtodeformationandcrackInaddition,theoiltemperatureistoohighwillcausedeterioration,lossofcokeburningandlubricatingproperties,destructionofoilfilm,partofthefrictionandwearincreased,resultinginenginepower,reliability,economy,durability,overalldeterioration.Ifthesystemscoolingcapacityistoostrong,oilisthefueldilution(ie,coolingduetocylinderwall,combustiblegasmixtureinthecylinderwall,condensationandaggregationoferosiononthecylinderlubricatingoilfilm,notbyevaporationofthefuelflowtothesumpcylinderwall,dilutedoil),whiledeteriorationofgasmixtureformationandcombustion,increasingefficiencyofoilviscosityandfriction,causingincreasedwearbetweenparts,frictionlossesincreaseingrossenginework,whiletheheatthroughthecoolingsystemisthefuelburnawaytheheat,generallyaboutburningcalories-30%to20%,whichisaloss,ifthecoolingistoostrong,increasetheheatlosswillreducetheengineseconomy.Sotheenginecoldorhot(ie,enginecoolingistoostrongortooweak)willbetheengineofpower,economy,adverselyaffectthereliabilityofwork.Therefore,well-designedcoolingsystemensurestheenginealwaysworkunderthemostsuitabletemperature,theenginehasbeenhigheconomicperformance,dynamicperformance,operationalreliabilityindicators.Functionofthecoolingsystemistomaketheengineinvariousoperatingconditionsaremaintainedattheappropriatetemperaturerange,coolingsystems,itisnecessarytopreventtheengineoverheating,andalsotopreventthewintercoldengine,theengineundercoldIIIstart,thecoolingsystemalsoensurethattheenginequicklywarminguptonormaloperatingtemperatureasquicklyaspossible.Keywords:radiator；fan；coolingwaterpump；siliconoilfanclutch；Thermostats辽宁工程技术大学毕业设计目录1绪论.11.1汽车发动机冷却系统概述.11.2汽车发动机冷却系统的发展和现状.21.3汽车发动机冷却系统向高效化发展.52散热器的设计.62.1发动机散热量计算.62.2散热器材料的选择.62.3结构设计及选择.63节温器的设计.1