哈工程轮机英语-lesson 9

LESSON9

TEXTSTARTINGSYSTEM第9课起动系统Prof.SongZhouNewWordsandExpressionsinText

reservoir容器(文中指空气瓶)

ready准备好的

immediate立即的

drop下跌，下落bymeansof利用，用…方法

compressor压缩机

feature功(能)，部件

drainage排放，排泄

facility设备

stringent严厉的，严格的

interlock连锁

prevent防止

automatic自动的

pilot引导的，控制的，先导的

lever杆direct直接的

engage啮合，从事further进一步地

deposit沉积物，沉淀

explosion爆炸

pipeline管路，管系

occurrence发生，事物

properly适当地

careful谨慎的，小心的

attempt企图；试图

effect作用，影响，效果

trap挡板，收集器

burst爆发，冲破

disc盘

isolate隔绝，绝缘

fusible易熔的

plug塞，堵

melt熔化，融化

guard防护，防卫，护罩

possibility可能性

burstingcap防爆帽Dieselenginesarestartedbysupplying

compressedair

intothecylinders

intheappropriatesequencefortherequireddirection.Asupplyofcompressedairisstoredinairreservoirsorbottlesorreceiversatpressuresabout30or40barreadyforimmediate

use.Sometimescompressedairpressureisdroppedtoalowervaluebymeansofareducingvalve(减压阀)forotheruses.Thereceiversarechargedby

compressors.Thedesignofstartingairsystems,includingthenumberandcapacityofcompressorsandreceivers,theprovision（规定）offeaturesanddrainagefacilitiesarethesubjectofstringent(严格)requirementsbyClassificationSocieties(船级社).Upto12startsarepossiblewiththestoredquantityofcompressedair.Thestartingairsystemusuallyhasinterlockstopreventstartingifanythingisnotinorder.Thecompressedairissuppliedbyalargeborepipetoaremoteoperatingnon-returnorautomaticvalveandthentothecylinderairstartvalves(气缸起动阀).Theopeningofeachcylinderairstartvalveswilladmitcompressedairintothecorrespondingcylinder.Theautomaticvalveandthecylinderstartvalvesarecontrolledbyapilot

air

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

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

whenabridgecontrolsystemisfitted.Pilotairfortheappropriatedirectionofoperationisalsosuppliedtoanairdistributor(空气分配器).Thisdeviceisusuallydrivenbytheenginecamshaftandsuppliespilotairtothecontrolcylindersofthecylinderairstartvalves.Thepilotairisthensuppliedinappropriatesequenceforthedirectionofoperationrequired.Thecylinderairstartvalvesareheldclosedbyspringswhennotinuseandopenedbythepilotairenablingthecompressedairdirectfromthereceiverstoentertheenginecylinder.Assoonastheenginefirestheairstartingleverisbroughtback.Thepilotaircontrolvalvereturnstotheoffposition,ventingthepilotairlinesandtheremoteairstartingvalveandallowingittoclose.Anumberofinterlocksareprovidedinconnectionwiththeairstartingsystemtosafeguardtheengineandpersonnel.Theseare:1.Theturninggear(盘车机)interlockvalvewhichisarrangedtoshutoffthestartingairpilotlinewhentheturninggearisengaged(啮合),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(安全阀)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(独立的)units.Themechanismcanbedividedintotwoparts,aspeedsensingportionandanactuatingportion.Acommonformofsensingdevicesistheballhead.Itconsistsofarevolvingcarrier(旋转支架)onwhicharemountedtwoweightshavingcrankedlevers.Theyarepivoted(装在枢轴上)sothattheleverscompressaspringastheweightsflyoutundercentrifugalforce.Theforceexertedbythespringiscontrolledbythepressureofanadjustmentonitsotherendwhichisdecidedbythemaincontrollevermechanismoftheengine.Thisadjustmentisthespeedcontrolfortheengine.Whereverthisissettheweightswillassumeacorrespondingpositionaccordingtothespeedatwhichtheyarerotated.Thispositionissignaledtotheactuatingportionofthegovernorbythepositionofthecontrolspindle.Thecontrolspindleisconnectedtoapilotvalvewhichadmitsoilasrequiredtotheactuatingpistonandcylinder.Thepositiontakenupbythisactuatingpistonis‘fedback(反馈)’topilotvalvesothattheoiliscontrolledtogivetheactuatorthedesiredfinalposition.Theactuatorspindleisconnectedtoaleveroutputfromthegovernor.Thisleverisconnectedtothelinkagewhichcontrolsthefuelquantity.Foranyspeedsettingofthegovernortherewillbearangeoffueloutputaccordingtowhethertheloadtorque(扭矩)ishighorlow.Itwillvaryfromfullatoneendofthetraveloftheactuatorpistontonofuelattheother.Thesetwopositionscorrespondtotwoslightlydifferentvaluesofthespeed.Thedifferencebetweenthesevaluesisknownasthegovernor

drop.Itisusuallyexpressedasapercentageofthesetspeed.Electronicgovernorsarecomingintouseonmodernengines.Theygivequickerresponseandamorepowerfuloutput.Thespeed-sensingdeviceisasmallelectricgenerator(发生器)orsmallmachinewhichproduceasignal,usuallyintheformofapulsedcurrentorvoltagehavingafrequencyproportionaltoenginespeed.Thisiscomparedwithadesiredspeedsettingandanydifferenceproducesanoutputsignal.Theoutputsignalenergizes(激活，使…活跃)theactuatingequipmentwhichoperatesthefuelcontrolmechanism.Withallgovernorsitisusualpracticetoprovideamanualover-ride(优势，优先权)bywhichthelinkagecanbereturnedtothenofuelpositioninanemergencyorshouldthegovernorfailinanyway.Theengineisstoppedfornormalmaneuveringpurposesbybringingthemaincontrollevertothenofuelposition.Automaticshutdownsystemsarealsoprovidedtostoptheengineinthecaseoffailureoflubricatingoilorofcoolingwateroriftheenginespeedexceedsthemaximumallowabler/min.c.StartingairsystemTheengineisstartedwithcompressedairofmax.30bar.Minimumpressurerequiredis15bar.Apressuretransmitter(变送器)PT301mountedonthestartingairlinebeforethemainstartingvalvehasanindicatorintheinstrumentpanel.Thesupplylinefromthestartingairbottleisprovidedwithanon-returnvalveandadrainvalve.Thesolenoidvalve(电磁阀)iselectrical(remotecontrol)ormanual(ontheengine)operatedandsendsafteractivation(带电)apilotairsignaltothemainstartingairvalve.Interruption(阻断,中断)ofthecontrolairclosesthemainstartingairvalve.Afterthemainstartingairvalveisactivated,theairflowsthroughtheflamearresters(trap)tothestartingairvalvesinthecylinderheads.Partofairflowsviathestartingairdistributortoeachofthemainstartingairvalvesinthecylinderheads.Thestartingairdistributorcontrolsthetimingofopeningandclosingofthemainstartingairvalves.Onthemomentthemainstartingairvalveisoperatedthegovernorbooster(调速器升压器)isalsoenergized.Themainsta