英语翻译第6课

1LessonSixCOMBUSTIBLEMIXTUREFORMATIONANDCOMBUSTIONINDIESELENGINES（柴油机可燃混合气的形成与燃烧）1.INTRODUCTION（引言）Theincreasinginterestinthestudyofdieselenginecombustion,emissionsandeconomyiscausedbygrowingconcernaboutenergyresourcesandtheenvironment.(对能源和环境的日益关注导致对柴油机燃烧、排放和经济性的研究兴趣的日益增加)Thedieselengine,beingthemosteconomicalknownpowerplant,hasgainedpopularityinmanyapplications,includingheavyandmediumdutyvehicles.(柴油发动机是最经济的已知的能源机器，已在许多应用中得到普及，包括重型和中型车辆。)Morerecentlyithasbeenconsideredinmanypartsoftheworldasareplacementfortheregularsparkignition,orS.I.(gasolineorpetrol)engineinsomepassengercarapplications.(近来，它已经在世界许多地方，作为一种常规的火花点火的替换，或一些轿车应用中汽油发动机的替换)Thehighthermalefficiencyofthedieselengineismainlycausedbytherelativelyhighcompressionratiorequiredtostarttheautoignitionprocess,thelowerpumpinglossesasaresultoftheabsenceofthethrottlevalve(whichisneededinS.I.enginestocontrolthepoweroutput),andtheoverallleanmixturerequiredtoachieveanefficientheterogeneouscombustionprocess.（柴油机的热效率高，主要是由启动所需的自燃过程相对较高的压缩比，由于节流阀的缺失（这是在汽油发动机中需要控制的输出功率）造成的泵气损失降低，并要求达到高效的异构燃烧过程的整体精益混合物，所引起的。）MostdieselenginesemitlesscarbonmonoxideandunburnedhydrocarbonsthancomparableS.I.engines.Therearesomepollutants,however,characteristicoftheheterogeneousmixtureusedinthedieselcombustionprocesswhicharenotfoundwiththeS.I.engine.（大多数柴油机排放比同比的汽油发动机排出的一氧化碳和未燃烧的碳氢化合物更少。然而柴油机燃耗过程中使用异构混合物，多了一些在汽油机燃烧中没有的污染物）Theseareodorconstituents,visiblesmoke,andnoise.（包括气味成分，可见烟雾，噪声。）Thischapterdealswiththesepollutantsaswellaswithunburnedhydrocarbons,carbonmonoxide,nitricoxide,oxygenatedhydrocarbons,sulfurcompounds,andparticulates.（本章讨论这些污染物以及未燃烧的碳氢化合物，一氧化碳，氮氧化物，含氧化合物，硫化合物，和微粒。）Sincealltheseemittedpollutantsarearesultofthecombustionprocess,itisnecessaryfirsttostudythemechanismsofcombustionindieselengines.（由于所有这些排放的污染物是燃烧过程的结果，有必要首先研究柴油机燃烧机理。）Thiscombustionprocessisverycomplexanditsdetailedmechanismsarenotwellunderstood.（该燃烧过程是非常复杂的，其详细的机理还不是很清楚。）Autoignitionoccursatseverallocationsinthecombustionchamberwherethereisacombustiblemixture,meanwhile,insomeotherlocationsthefuelmaystillbeintheliquidphase.（在有可燃混合物的燃烧室内一些位置发生自燃，同时，在其他位置的燃料仍可能是液相。）Undermostengineoperatingconditions,ignitionstartswhilesomeportionofthefuelhasnotyetbeeninjected.（大多数发动机在工作条件下点火启动，但有部分燃料尚未注入）Theproportionoffuelpresentinthecombustionchamberatthestartofcombustiontothetotalamountoffuelinjectedgreatlyaffectsthecombustionprocess.（在燃烧开始到所有燃料注射完这段时间，燃烧室中的燃料比例很大的影响燃烧过程。）Alsothedistributionofthefuelwithinthecombustionspacehasagreateffectonthemechanismsofcombustionandemissionformation.（燃烧室中燃料的分布也对燃烧和排放形成的机制有很大影响。）Thisdistributiondependsmainlyonthe2injectionprocessandtheairmotion.（这种分布主要取决于注射过程和空气运动。）Thefirstpartofthisarticlewillbeconcernedwiththeprocessofinjectionandsprayformation.(本文的第一部分将关注的注射过程和喷雾的形成。)Thiswillbefollowedbyastudyoftheautoignitionprocessandtheignitiondelay.(这将是其次的自燃过程和点火延迟时间的研究。)Inthestudyofdirectinjection(D.I.)engines,theairmotionwillbeanalyzed(在直接喷射的研究（直喷）发动机，空气运动将分析)2.FUELINJECTION(燃料喷射)(1)SprayFormation(喷雾形成)Thefuelisintroducedintothecylinderofthedieselenginethroughanozzleintheformofaliquidsprayundertheeffectofahighpressuredifferential.(燃料是在高压力差的作用下，以液体喷雾的形式通过喷嘴被引入柴油发动机的气缸。)Thenozzlemayhavedifferentdesignssuchasthethrottle,pintle,singleorifice,ormultiorificetype.(喷嘴可以有不同的设计，如节流阀，针阀，单孔或多孔型。)Thefueldeliveredfromthenozzleisdisintegratedintodropletsofdifferentsizesandconcentrationsinthespray.(从喷嘴输送的燃料被分解成喷雾中不同大小和浓度的液滴。)Fig.1showsasprayformedbyinjectingaliquidfromasingleholeinstagnantair.(图1显示了从一个单孔向静止的空气中喷入液体形成的喷雾。)Afterthejetleavesthenozzleitbecomescompletelyturbulentataveryshortdistancefromthepointofdischarge.(注射液在离开喷嘴后，在从喷射点开始的很短一段距离内完全变成紊流)Duetojet-turbulence,theemergingjetbecomespartlymixedwiththesurroundingair.(由于射流湍流，新形成的射流与周围的空气部分混合。)Particlesoftheairarecarriedawaybythejet.Asaresultthemass-flowincreasesinthex-direction.(空气中的粒子被由射流带走，因此，在X方向的质量流量增加。)Concurrentlythejetspreadsoutinthey-direction.(同时射流在Y方向扩散。)Byapplyingtheprincipleofconservationofmomentum,wefindthatthejetvelocitydecreases.Also,thevelocityofthejetwillfurtherdecreaseasitmovesinthex-directionbecauseoffrictionaldrag.应用动量守恒原理，我们发现射流速度减小。同时，在X方向移动时由于摩擦阻力，射流的速度将进一步减小。Fig.1givesthevelocitydistributionattwocrosssections.图1给出了两个截面的速度分布。Thefuelvelocityishighestatthecenterlineanddecreasestozeroattheinterfacebetweenthezoneofdisintegration(ortheconicalenvelopeofthespray)andtheambientair.燃料的速度在中心线是最高的，并在分解区域（或喷雾的锥面）和周围空气的分界面处减小到零。Indieselenginesitisofparticularinteresttoknowwhichdropletshavebeenintroducedatthebeginningoftheinjectionprocess.在柴油发动机中，知道液滴在注射过程开始时已经被引入气缸是很有利的。Atthebeginningofinjection.thefuelisretardedbythedragofairwhichstartstomovealongthesprayaxis.在注射开始时，燃料在空气阻力的阻碍下开始沿喷雾轴线移动。Thefollowingfueldropletsencounterasmallerresistance,overtaketheretardeddroplets,andforcethemtowardtheperipheryofthespray.后面的燃料液滴遇到的阻力变小，赶上落后的液滴，并把它们压迫到喷雾的外围。Thedropletsattheaxisbecomelessatomized.在轴心的液滴变得更少的雾化。Atthesprayfrontthedropletsmeetthehighestaerodynamicresistance,butthespraypenetratestheairbecausethedropletsretardedatthefrontarecontinuouslyreplacedbynewhighmomen