哈工程輪機英語-lesson 9

LESSON9

TEXTSTARTINGSYSTEM第9課起動系統(tǒng)Prof.SongZhouNewWordsandExpressionsinText

reservoir容器(文中指空氣瓶)

ready準備好的

immediate立即的

drop下跌，下落bymeansof利用，用…方法

compressor壓縮機

feature功(能)，部件

drainage排放，排泄

facility設(shè)備

stringent嚴厲的，嚴格的

interlock連鎖

prevent防止

automatic自動的

pilot引導的，控制的，先導的

lever桿direct直接的

engage嚙合，從事further進一步地

deposit沉積物，沉淀

explosion爆炸

pipeline管路，管系

occurrence發(fā)生，事物

properly適當?shù)?/p>

careful謹慎的，小心的

attempt企圖；試圖

effect作用，影響，效果

trap擋板，收集器

burst爆發(fā)，沖破

disc盤

isolate隔絕，絕緣

fusible易熔的

plug塞，堵

melt熔化，融化

guard防護，防衛(wèi)，護罩

possibility可能性

burstingcap防爆帽Dieselenginesarestartedbysupplying

compressedair

intothecylinders

intheappropriatesequencefortherequireddirection.Asupplyofcompressedairisstoredinairreservoirsorbottlesorreceiversatpressuresabout30or40barreadyforimmediate

use.Sometimescompressedairpressureisdroppedtoalowervaluebymeansofareducingvalve(減壓閥)forotheruses.Thereceiversarechargedby

compressors.Thedesignofstartingairsystems,includingthenumberandcapacityofcompressorsandreceivers,theprovision（規(guī)定）offeaturesanddrainagefacilitiesarethesubjectofstringent(嚴格)requirementsbyClassificationSocieties(船級社).Upto12startsarepossiblewiththestoredquantityofcompressedair.Thestartingairsystemusuallyhasinterlockstopreventstartingifanythingisnotinorder.Thecompressedairissuppliedbyalargeborepipetoaremoteoperatingnon-returnorautomaticvalveandthentothecylinderairstartvalves(氣缸起動閥).Theopeningofeachcylinderairstartvalveswilladmitcompressedairintothecorrespondingcylinder.Theautomaticvalveandthecylinderstartvalvesarecontrolledbyapilot

air

system.Eachcylinderstartvalvewillbeopenedimmediatelyafterthetopdeadcentre(TDC)positionhasbeenpassedandclosedjustbeforetheexhaustportsareduetoopenaccordingtothedirectionofrotationrequired.Thus,whencompressedairfromthemainsupplyissuppliedtothestartingsystemofanengineatrestitentersthosecylindersinwhichthepistonsareinapositioncorrespondingtosomepartofthepowerstroke,theresulting

pressureonthepistonscausestheenginetorotate.Whenasufficientlyhighspeed,sayabout20r/min,hasbeenachievedtheairsupplyiscutoffandfuelisinjectedcausingthecylinderstofireandcontinuetoruninthenormalway.CylinderairstartvalveAirdistributorMastervalve(automaticvalve)AirbottleAirstartleverapilotaircontrolvalveThepilotairisdrawnfromthelargepipeandpassestoapilotaircontrolvalvewhichisoperatedbytheengineairstartlever.Whentheairstartleverisoperated,supplyofpilotairenablesthepilotaircontrolvalvetoopeneithermanuallyorwithapneumaticcylinder

whenabridgecontrolsystemisfitted.Pilotairfortheappropriatedirectionofoperationisalsosuppliedtoanairdistributor(空氣分配器).Thisdeviceisusuallydrivenbytheenginecamshaftandsuppliespilotairtothecontrolcylindersofthecylinderairstartvalves.Thepilotairisthensuppliedinappropriatesequenceforthedirectionofoperationrequired.Thecylinderairstartvalvesareheldclosedbyspringswhennotinuseandopenedbythepilotairenablingthecompressedairdirectfromthereceiverstoentertheenginecylinder.Assoonastheenginefirestheairstartingleverisbroughtback.Thepilotaircontrolvalvereturnstotheoffposition,ventingthepilotairlinesandtheremoteairstartingvalveandallowingittoclose.Anumberofinterlocksareprovidedinconnectionwiththeairstartingsystemtosafeguardtheengineandpersonnel.Theseare:1.Theturninggear(盤車機)interlockvalvewhichisarrangedtoshutoffthestartingairpilotlinewhentheturninggearisengaged(嚙合),thuspreventingtheenginebeingstarted.2.Topreventoperationofthestartingairsystemwhilsttheengineisrunning

apilotairinterlockvalveisoperatedbythemaincontrollever.Thevalveremainsopenduringthestartingsequence,i.e.untilthemaincontrolleverisremovedjustbeyondthestartingposition,butremainsclosedafterthispointanddoesnotopenagainuntilthemainleverismovedbacktothestopposition.3.Amechanicalinterlockisprovidedinthecontrolboxtopreventthemaincontrolleverbeingmovedbeyondthestartingpositionwhilethestartingairleveriseithertheaheadorasternstartingposition.4.Anothermechanicalinterlockisprovidedtopreventthemaincontrolleverbeingmoveduntilstartingairisadmittedtothecylinders.Thispreventsfuelbeingadmittedtothecylinderswhentheengineisatrest.Lubricatingoilfromthecompressorwillpassalongtheairlinesanddepositonthem.Intheeventofacylinderairstartingvalveleaking,hotgaseswouldpassintotheairpipesandignitethelubricatingoil.Ifstartingairissuppliedtotheenginethiswouldfurtherfeedthefireandcouldleadtoanexplosioninthepipelines.Inordertopreventsuchanoccurrence,cylinderstartingvalvesshouldbeproperlymaintainedandthepipelinesregularlydrained.Alsooildischargedfromcompressorsshouldbekepttoaminimum,bycarefulmaintenance.Inanattempttoreducetheeffectsofanexplosion,flametraps(阻焰器),reliefvalves(安全閥)andburstingcapsordiscs

(防爆帽)arefittedinthepipelines.Inadditionanisolating

non-returnvalve(theautomaticvalve)isfittedtothesystem,whichpreventsfurthercompressedairbytheengineintosystem.Thelossofcoolingwaterfromanaircompressorcouldleadtoanoverheatedairdischargeandpossiblyanexplosioninthepipelinesleadingtotheairreservoir.Ahightemperaturealarmorafusibleplug(易溶塞),whichwillmelt(融化,熔化),isusedtoguardagainstthispossibility.ReadingmaterialA.STARTINGAspreviouslyexplained,theignitionofthefuelindieselengineiscausedbytheheatofcompressionoftheairpreviouslyadmittedintothecylinder.Thus,fortheenginetobeginfiring,airmustfirstbedrawnorpumpedintothecylinderandthisairmustbecompressedbytheupwardmovementofthepistontoobtainthehightemperaturenecessarytoburnthefuelwhenitisinjected.Hencetheenginemustbedrivenforafewrevolutionsbysomeoutsidesourcebeforeallowingthefuelintothecylinders.Inheavymarineenginethepracticeistodrivetheengineoncompressedairwhichhaspreviouslybeenstored(atpressurerangingfrom20to40bardependinguponthetypeofengine)instarting-airreservoirs.Thecompressedairisadmittedtoeachcylinderthroughacamoperatedstarting-airvalvewhenthepistonhasjustpasseditstopcenterandcommenceitspowerstrokeandremainingopenuntilthepistonhastraveledpartofthatstroke.Theperiodofopeningdependsupon(on)thenumberofcylindersandwhetheritisfour-strokeortwo-strokeengine.Whenthestarting-airvalveclosesononecylinder,anotherstarting-airvalvealreadyopenedonanothercylinderwhosepistonhasjustcommenceditsdownwardstroke.Thusnomatterinwhatpositiontheenginestopstherewillalwaysbeatleastoneofthecylinderswithitsstarting-airvalveopentoadmitcompressedairtostarttheengine.Whentheengineobtainssufficientspeed,thefuelpumpsandvalvesarebroughtintooperationandthestartingairvalvesputoutofcommission.B.EnginereversingWhererunningatmaneuveringspeed1.Wheremanuallyoperatedauxiliaryblowersarefittedtheyshouldbestarted.2.Thefuelsupplyisshutoffandtheenginewillquicklyslowdown.3.Thedirectionhandleispositionedastern.4.Compressedairisadmittedtotheenginetoturnitintheasterndirection.5.Whenturningasternundertheactionofcompressedair,fuelwillbeadmitted.Thecombustionprocesswilltakeoverandairadmissioncease.Whenrunningatfullspeed1.Theauxiliaryblowers,wheremanuallyoperated,shouldbestarted.2.Fuelisshutofffromtheengine.3.Blastsofcompressedairmaybeusedtoslowtheenginedown.4.Whentheengineisstoppedthedirectionhandleispositionedastern.5.Compressedairisadmittedtoturntheengineasternandfuelisadmittedtoacceleratetheengine.Thecompressedairsupplywillthencease.SpeedregulationInordertocontroltheenginespeed,itisnowcommonpracticetofitaspeedregulatororgovernortomakebalancebetweenthefuelinjectedintotheengineandtheengineload.Thegovernormaintainstheenginespeedatthedesiredvaluebycontinuallypositioningthemeteringdeviceinthefuelsystemtocontroltheamountoffuelbeinginjectedintoeachcylinderpercycle.Mostgovernorsarehydraulicactuatingtypesandself-contained(獨立的)units.Themechanismcanbedividedintotwoparts,aspeedsensingportionandanactuatingportion.Acommonformofsensingdevicesistheballhead.Itconsistsofarevolvingcarrier(旋轉(zhuǎn)支架)onwhicharemountedtwoweightshavingcrankedlevers.Theyarepivoted(裝在樞軸上)sothattheleverscompressaspringastheweightsflyoutundercentrifugalforce.Theforceexertedbythespringiscontrolledbythepressureofanadjustmentonitsotherendwhichisdecidedbythemaincontrollevermechanismoftheengine.Thisadjustmentisthespeedcontrolfortheengine.Whereverthisissettheweightswillassumeacorrespondingpositionaccordingtothespeedatwhichtheyarerotated.Thispositionissignaledtotheactuatingportionofthegovernorbythepositionofthecontrolspindle.Thecontrolspindleisconnectedtoapilotvalvewhichadmitsoilasrequiredtotheactuatingpistonandcylinder.Thepositiontakenupbythisactuatingpistonis‘fedback(反饋)’topilotvalvesothattheoiliscontrolledtogivetheactuatorthedesiredfinalposition.Theactuatorspindleisconnectedtoaleveroutputfromthegovernor.Thisleverisconnectedtothelinkagewhichcontrolsthefuelquantity.Foranyspeedsettingofthegovernortherewillbearangeoffueloutputaccordingtowhethertheloadtorque(扭矩)ishighorlow.Itwillvaryfromfullatoneendofthetraveloftheactuatorpistontonofuelattheother.Thesetwopositionscorrespondtotwoslightlydifferentvaluesofthespeed.Thedifferencebetweenthesevaluesisknownasthegovernor

drop.Itisusuallyexpressedasapercentageofthesetspeed.Electronicgovernorsarecomingintouseonmodernengines.Theygivequickerresponseandamorepowerfuloutput.Thespeed-sensingdeviceisasmallelectricgenerator(發(fā)生器)orsmallmachinewhichproduceasignal,usuallyintheformofapulsedcurrentorvoltagehavingafrequencyproportionaltoenginespeed.Thisiscomparedwithadesiredspeedsettingandanydifferenceproducesanoutputsignal.Theoutputsignalenergizes(激活，使…活躍)theactuatingequipmentwhichoperatesthefuelcontrolmechanism.Withallgovernorsitisusualpracticetoprovideamanualover-ride(優(yōu)勢，優(yōu)先權(quán))bywhichthelinkagecanbereturnedtothenofuelpositioninanemergencyorshouldthegovernorfailinanyway.Theengineisstoppedfornormalmaneuveringpurposesbybringingthemaincontrollevertothenofuelposition.Automaticshutdownsystemsarealsoprovidedtostoptheengineinthecaseoffailureoflubricatingoilorofcoolingwateroriftheenginespeedexceedsthemaximumallowabler/min.c.StartingairsystemTheengineisstartedwithcompressedairofmax.30bar.Minimumpressurerequiredis15bar.Apressuretransmitter(變送器)PT301mountedonthestartingairlinebeforethemainstartingvalvehasanindicatorintheinstrumentpanel.Thesupplylinefromthestartingairbottleisprovidedwithanon-returnvalveandadrainvalve.Thesolenoidvalve(電磁閥)iselectrical(remotecontrol)ormanual(ontheengine)operatedandsendsafteractivation(帶電)apilotairsignaltothemainstartingairvalve.Interruption(阻斷,中斷)ofthecontrolairclosesthemainstartingairvalve.Afterthemainstartingairvalveisactivated,theairflowsthroughtheflamearresters(trap)tothestartingairvalvesinthecylinderheads.Partofairflowsviathestartingairdistributortoeachofthemainstartingairvalvesinthecylinderheads.Thestartingairdistributorcontrolsthetimingofopeningandclosingofthemainstartingairvalves.Onthemomentthemainstartingairvalveisoperatedthegovernorbooster(調(diào)速器升壓器)isalsoenergized.Themainsta