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XX设计外文翻译学生姓名：XXXX学号：XXXXX学院：机电工程学院专业：XXXXX设计(论文)题目：488Q天然气发动机总体方案设计和计算指导教师：XXXXXXXXX年X月XX日英文翻译CNGengineandaLPGengineisgasengine.FuelCNGengineiscompressednaturalgas,themaincompositionismethane,LPGenginefuelisliquefiedpetroleumgas(LPG),itsmaincompositionispropaneandbutane.Comparedwiththeoriginaldieselengine,gassinglefuelenginemainlyexistthefollowingdifferences:1,Thefuelsupplysystem:Canceltheoriginaldieselenginefuelinjectionsystemofrelatedpartsandcomponents,increasedtheevaporationpressureregulator(LPGengine),pressurereducer(CNGengine),andothersuppliesLPGorCNGrelatedspareparts.2,Theignitionsystem:Dieselengineisacompressionignitionengine,theLPGandCNGfuelfeatureduetothelimit(antiknockperformanceofvibration)isthesamelightasgasolineengine.Aftertheycancelledtheinjectorintheoriginalfuelinjectorholeoncylinderheadtothesparkplughole.Aftercanceledtheoilpump,oilpumpintheoriginalinstallationlocationonaignitiondrivingdevice,engineignitiontimingsignalswereobtainedthroughtheignitiontimingsensor.Addedtotheignitionmodule,ignitioncoilsandsparkplugignitionsystemcomposedofparts.3,Thecontrolsystem:LPGenginetoCNGengineadoptselectriccontrol,comparedwiththeoriginalmechanicaldieselengine,thepointofair-fuelratio,ignitionadvanceAngle,superchargingpressureformoreprecisecontrol,inordertomeetthecontrolrequirements,increasethecorrespondingMAP,MAT,ECT,ignitiontimingandoxygenconcentrationandothersensors.4,Compressionratio:Theselectionofcompressionratioiscloselyrelatedtothefuelantiknockperformance,antiknockperformanceismeasuredbythefueloctanenumber,thehighertheoctanenumberantiknockperformance,thebetter,thecommonlyusedseveralkindsoffuelaccordingtotherankofoctanenumber:dieselandCNG(methane),propane,butane(LPG)isamixtureofpropaneandbutane,andgasoline.BasedonthecharacteristicsofthiskindoffuelCNGenginecompressionratiothanLPGenginegenerallyhighbutislowerthandiesel,andLPGenginescompressionratiocanbeslightlyhigherthanthegasolineengine,ofcourse,becauseofLPGisamixtureofpropaneandbutane,differentmixingproportionalsoaffectthecompressionratio.OnthebasisofthedieselenginedesignimprovementsforLPGandCNGengine,inordertoreducethecompressionratioyouneedtoincreasethecombustionchambervolume,asaresultofthedieselenginecylinderheadstructuregenerallyhavenochange,onlythepistoncombustionchambervolumeincrease.Therefore,LPGandCNGengineinordertomeettherequirementsofcompressionratio,increasethecombustionchambervolume.ThebasicworkingprincipleofLPGengine:LPGsinglefuelenginegassystemincludes:theenginecontrolmodule,ignitioncontrolmodule,ignitioncoils,sparkplugs,electronicthrottle,mixer,themainfuelcontrolvalves(FTVvalve),idlespeedcontrolvalve,evaporatingpressureregulator,pressuresolenoidvalve,exhaustbypassvalveandsurgevalve.Inaddition,alsoincludingallkindsofsensorsandwiringharness.Thesystemcontrolstheengineandvehicleperformance,safetyandemissions.TheprinciplediagramoftheLPGenginesystemLiquidLPGcylindersfromoutinhighpressuresolenoidvalve,highpressuresolenoidvalveopeningiscontrolledbytheengineECM,LPGafterhighpressuresolenoidvalvetotheevaporationoftheliquidpressureregulator,theevaporatingpressureregulatorCanonoftwo-stagedecompressionevaporationvaporizationintogaseousLPG,duetotheLPGevaporationvaporizationneedtoabsorbalotofheat,sotheevaporationpressureregulatorwithenginecoolingwaterisheated,inordertopreventtheevaporationpressureregulatoricejam.Parttworoadfromtheevaporatingpressureregulator,allthewayisprimarydecompressionafteridlefuelcontrolvalvestothemixer,theotherissecondarystressthemainfuelcontrolvalveallthewaytothemixer.Levelofthereliefpressureisrelativelystable,higherthan1atmdozensofKpa,providemostofthefuelfortheengineidlespeedandtheECMonidlefuelcontrolvalveclosedloopcontrol,ensurethattheidlewhentheconcentrationofthemixture.Secondaryreliefpressuresuperchargingpressurefeedbackcontrol,toprovidefuelfortheengineallconditionandbytheECMtoclosedloopcontrol,themainfuelcontrolvalvestoguaranteeengineworkingconditionofeachpointoftheconcentrationofthemixture.IgnitiontimingcontroltableisstoredintheECMcalibrationonthepointofignitiontimeforopenloopcontrol.Throughtheexhaustbypasscontrolvalvecontrolsuperchargerby-passvalveopeningtocontrolthechargingpressure.ThebasicworkingprincipleoftheCNGengine:HighpressureofCNGcameoutfromthecylindertothehighpressuresolenoidvalve,highpressuresolenoidvalveopeningiscontrolledbytheengineECM,highpressureofCNGafterhighpressuresolenoidvalvetothepressurereducer,afterpressurereducerofCNGpressurefrom20Mpa(fullbottlesofoil-gaspressure)to6to9bar,becauseoftheCNGdecompressionafterthetemperaturedroppedsubstantially,soafterthepressurereducerhasaheatexchanger,theuseoftheenginecoolingwaterforheating,inordertopreventthepipelineicejam.Andintheheatexchangerhasathermostat,bycontrollingtheflowofcoolingwatertocontrolthetemperatureoftheCNG.CNGafterthermostattometeringvalve,meteringvalveisequippedwitheightnozzle,thenozzleopeningtimeiscontrolledbytheECM,controltheengineworkingconditionofeachpointoftheconcentrationofthemixture.CNGisoutofthemeteringvalvetothemixer,afterinthemixermixeswiththeairbytheelectronicthrottleintothecylinder.Ignitioncontrol,boostpressurecontrolandidlespeedandhighspeedcontrolofmotorspeedcontrolisthesameastheLPGengine.Atpresent,thedomesticcarusingnaturalgas,aretheoriginalcarpetrolordieselenginetobemodified,toadapttotheburningnaturalgas.Accordingtothecharacteristicsofthecombustiongasspecializeddesign,themanufactureofthemotorisless.Accordingtotheworkingprincipleofgasolineengineanddieselengine,theworkingsofaswitchtonaturalgascanhavethefollowingkinds:1,ThemodifiedgasolinevehiclesTheworkingprincipleofusingnaturalgasasafuelisthesameastheoriginalgasolineengine.Willbestoredinhigh-pressurecylindersafterpressurerelieftothemixerofnaturalgas,inthemixedwithair,intothecylinder.Stillusetheoriginalsparkplugintheengineignitionsystem.Theoriginalgasolineenginescompressionratiodoesntchange,thestructureoftheoriginalenginebasicallyremainunchanged,justinadditiontotheaircylinder,pressurereducingvalveofthegasandthecorrespondingswitch.Modificationcostislow,andusenaturalgasorgasolinebothfuelcanworkwhilegasantidetonatingqualityisverygood,allowedtoworkatahighercompressionratio,butbecauseinamodifiedinordertomaketheoriginalworkcanstillbeusedgasolineengine,sotheoriginalenginescompressionratiohasnotchanged,tolossofenginepowerare10%20%.Inordertoreducethepowerloss,canbeinwhenconvertedtoincreasethecompressionratiooftheoriginalgasolineengine(themostsimplewaytogoisdugcylindercoverpart),andchangingtheignitionadvanceAngleinordertomeettheneedsoftheworkofnaturalgas.Althoughthiscanreducetherateofloss,butwithgasolinetoworktherewillberiskofdetonation,evencantwork.Itisdifficulttoreturntotheoriginalgasolineengineworks.Sothecar,petrolenginecompressionratiogenerallyremainthesame.2,DieselcarmodifiedTherearetwokindsofmethod.Thefirstkindofmethodisbasicallyremainunchanged,theoriginaldieselenginestructureaccordingtoelectricignitionmethods,namely,accordingtotheworkingprincipleofgasolineengine(Ottocycle).Removeallofyouroriginaldieselenginefuelsystemwillbereducedtogascompressionratiocanundertakenumerical(higherthangasolineengines,general(810):1)inadditiontonaturalgasfuelsystemcomponents,aircylinder,pressurereducingvalve,mixer,etc,addelectricignitionsystem,shouldbeonlysinglecarfuelgasburningnaturalgas.Thismodifiedmethodissimpler,technologyismature,butcantworkwithdiesel,andenginepowerlossisbigger,isabout65%70%thatoftheoriginaldieselengine.Thesecondmethodistheoriginaldieselenginefuelsystemischangeless,coupledwiththesamegasfuelsystemasabove,averagecompressionratiowithoutchanging.Enginecylinderafterinhaledairandgasmixture,theoriginaldieselinjectorintoasmallamountofdieselfuelforignition.Aftercompressiveignitiondiesel,litthegasandairmixtureintothework,thisisdualfuelgasengine.Itsbasicworkingprincipleis:startwiththedieseloil,addloadtonegativepressureintheairandgasmixerdiaphragminstitutions,throughthepumproddieselhighpressureoilpumprackislimited,whilethedriveristheacceleratorpedalnowonlytoincreasetheflowofnaturalgas.Theworkingsofadualfuelnotonlylosepower,andbynaturalgascombustionperformanceisgood,alsothantheoriginaldieselenginepowerincreasesslightly.Thisisbecausetheenginecompressionratioishigh,theoriginalbecauseofexcessaircoefficientislarger.Themodifiedmethodsoftheoriginaldieselenginechangestheleast,andwhenthegasisinshortsupplycanalsobeconvertedtothediesel.Butthiswayofworkinginthemiddleandlowload,economyandemissionsarenotsogood.Therefore,withoutanadditionalmeansofovercomethesedisadvantages,isnotsuitableforcitybus.Itisbestthatinthelongterm,highloadofcarsandlong-distancetransportationvehiclesusemodifiedinthisway.Moderntechnologyadvancedautomotivefuelsystemsmostlywithcomputercontrolofelectronicfuelinjectionsystem.Istousethecomputerautomaticallyaccordingtotheconditionsofusetochangetheelectronicsprayvalvebodyemitsthegasolineordiesel,flowrateandignitiontime.Liketoswitchtonaturalgasasfuel,needtoreplacepetrolordieselelectronicinjectionvalvewithorelectronicinjectionvalveofthegas,tochangethecomputercontrolsoftwareprogram,suchascanbeburningnaturalgasnaturalgasengines.Ofcourse,theothercomponentsofnaturalgasfuelsystemandaircylinder,pressurereducingvalveisnecessary.中文译文CNG发动机和LPG发动机是气体发动机CNG发动机的燃料是压缩天然气，主要成分是甲烷；LPG发动机的燃料则为液化石油气，其主要成分是丙烷和丁烷。与原柴油机相比，气体单燃料发动机主要存在以下方面的差别：1、燃料供给系统：取消了原柴油机的燃油喷射系统相关的零部件，增加了蒸发调压器（LPG发动机）、减压器（CNG发动机）等供给LPG或CNG的相关零部件。2、点火系统：柴油机是压燃式发动机，而LPG和CNG由于受燃料特性限制（抗爆振性能）采用的是与汽油机一样的点燃方式。在取消了喷油器后，将原缸盖上的喷油器孔改为了火花塞孔。在取消了油泵后，在原油泵安装位置装上了一个点火传动装置，通过点火正时传感器获得发动机的点火正时信号。增加了以点火模块、点火线圈及火花塞等零件组成的点火系统。3、控制系统：LPG发动机与CNG发动机采用电控，与原机械式柴油机相比，各工况点的空燃比、点火提前角、增压压力都实现了更精确的控制，为满足这些控制要求，增加了相应的MAP、MAT、ECT、点火正时以及氧浓度等传感器。4、压缩比：压缩比的选取与燃料的抗爆震性能密切相关，抗爆震性能是用燃料的辛烷值来衡量，辛烷值越高抗爆震性能越好，常用的几种燃料按辛烷值高低排序依次为：柴油、CNG（甲烷）、丙烷、丁烷（LPG是丙烷和丁烷的混合物）和汽油。根据这种燃料特性，一般CNG发动机压缩比比LPG发动机高但比柴油机低，而LPG发动机的压缩比又可以比汽油机略高，当然，由于LPG是丙烷和丁烷的混合物，混合比例不同也影响其压缩比的选择。由于柴油机的缸盖结构上一般都没有改动的余地，只有将活塞上的燃烧室容积加大。因此，LPG和CNG发动机为了满足压缩比的要求，都加大了燃烧室容积。LPG发动机的基本工作原理：LPG单燃料发动机的燃气系统包含：发动机控制模块、点火控制模块、点火线圈、火花塞、电子节气门、混合器、主燃料控制阀（FTV阀）、怠速燃料控制阀、蒸发调压器、高压电磁阀、废气旁通控制阀和喘振阀构成。另外，还包括各种传感器和线束。整套系统控制着发动机和车辆的性能、排放和安全。液态的LPG从气瓶出来到高压电磁阀，高压电磁阀的打开受发动机ECM的控制，液态的LPG经高压电磁阀后到蒸发调压器，在蒸发调压器内经两级减压蒸发汽化变为气态LPG，由于LPG蒸发汽化需要吸收大量的热量，因此蒸发调压器接有发动机的冷却水进行加热，以防止蒸发调压器结冰堵塞。从蒸发调压器出来有两路气，一路是一级减压经怠速燃料控制阀后到混合器，另一路是二级减压经主燃料控制阀到混合器。一级减压的压力相对稳定，比1个大气压高几十千帕，为发动机怠速提供大部份燃料并由ECM对怠速燃料控制阀进行闭环控制，保证怠速时混合气的浓度。二级减压压力受增压压力反馈控制，为发动机全工况提供燃料并由ECM对主燃料控制阀进行闭环控制，以保证发动机各工况点混合气的浓度。点火时间控制是由储存在ECM中的标定表对各工况点的点火时间进行开环控制。通过废气旁通控制阀控制增压器旁通阀的开度来控制增压压力。CNG发动机的基本工作原理：高压的CNG从气瓶出来到高压电磁阀，高压电磁阀的打开受发动机ECM的控制，高压的CNG经高压电磁阀后到减压器，经减压器后CNG的压力由20MPa（满瓶时气压力）降到6到9Bar，由于CNG减压后温度大幅度下降，因此在减压器后接有一个热交换器，利用发动机的冷却水进行加热，以防止管路结冰堵塞。并且在热交换器后有一个节温器，通过控制冷却水的流量来控制CNG的温度。CNG经过节温器后到计量阀，计量阀上装有八个喷嘴，喷嘴的开启时间受ECM的控制，控制了发动机各工况点混合气的浓度。CNG从计量阀出来后到混合器，在混合器处与空气混合后经电子节气门进入气缸。点火控制、增压压力控制、怠速及高速调速控制与LPG发动机相同。目前，汽车使用天然气时，都是将原来的汽油车或柴油车的发动机进行改装，以适应燃烧天然气。按燃烧天然气的特点专门设计、制造的发动机还比较少。根据汽油机和柴油机工作原理不同，改用天然气的工作方式可以有以下几种:1、汽油车的改装使用
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