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ShipsShipsarelarge,complexvehicleswhichmustbeself-sustainingintheirenvironmentforlongperiodswithahighdegreeofreliability.Ashipistheproductoftwomainareasofskill,thoseofthenavalarchitectandthemarineengineer.Thenavalarchitectisconcernedwiththehull,itsconstruction,form,habitabilityandabilitytoendureitsenvironment.Themarineengineerisresponsibleforthevarioussystemswhichpropelandoperatetheship.Morespecifically,thismeansthemachineryrequiredforpropulsion,steering,anchoringandshipsecuring,cargohandling,airconditioning,powergenerationanditsdistribution.Someoverlapinresponsibilitiesoccursbetweennavalarchitectsandmarineengineersinareassuchaspropellerdesign,thereductionofnoiseandvibrationintheship'sstructure,andengineeringservicesprovidedtoconsiderableareasoftheship.Ashipmightreasonablybedividedintothreedistinctareas:thecargo-carryingholdsortanks,theaccommodationandthemachineryspace.Dependinguponthetypeeachshipwillassumevaryingproportionsandfunctions.Anoiltanker,forinstance,willhavethecargo-carryingregiondividedintotanksbytwolongitudinalbulkheadsandseveraltransversebulkheads.Therewillbeconsiderablequantitiesofcargopipingbothaboveandbelowdecks.Thegeneralcargoshipwillhavevariouscargoholdswhichareusuallythefullwidthofthevesselandformedbytransversebulkheadsalongtheship'slength.Cargohandlingequipmentwillbearrangedondeckandtherewillbelargehatchopeningsclosedwithsteelhatchcovers.Theaccommodationareasineachoftheseshiptypeswillbesufficienttomeettherequirementsfortheship'screw,provideanavigatingbridgeareaandacommunicationscentre.Themachineryspacesizewillbedecidedbytheparticularmachineryinstalledandtheauxiliaryequipmentnecessary.Apassengership,however,wouldhavealargeaccommodationarea,sincethismightbeconsideredthe"cargospace".Machineryspacerequirementswillprobablybelargerbecauseofairconditioningequipment,stabilizersandotherpassengerrelatedequipment.Dependingonthenatureoftheircargo,andsometimesalsothewaythecargoisloaded/unloaded,shipscanbedividedintodifferentcategories,classes,andtypes,someofwhicharementionedinTable1.2 ■—balsocombinations,e.g.oil/chemicaltankers.Table1providesonlyaroughoutline.Inrealitytherearemanyothercombinations,suchas"Multipurposebulkcontainercarriers",tomentionjustoneexample.DryCargaLiquidCargoPasseagerUnitCargo-Containervessel-Roll-on/Roll-off-Heavycargovessel-CattleshipBulkCargo-Bulkcarrier-Orecarrier-Crudecarrier-Producttanker-Chemicaltanker-LPG/LNCcarriers-Passengership-Carandpassengerferries-CruiseshipMulli-purpos?shipNavyFishingDredgers,etcWorkships-Trawler-Othertypesoffishingvessels-Trailinghoppersuctiondredger-Cuttersuctiondredger-Rock-dumper-Cranevessel-Cable-layer-Buoy-layer-Oil-recoveryvessel-ShearlegcraneAuxiliarycraftPleasurecraftVariousOffshorematerial-seagoingtug-Harbortug-Icebreaker-PilotvesselCoastguardvessel-Researchvessel-Motoryacht-Sailingyachi-Hydrofoil-Floatingdock-Submersibleplatform-Pontoon,barge-Drillingrig/Jackup-Drill-ship-Pipelayer-FloatingstorageandoffloadingvesselShip'$size^told,oftherelevantloadedship,normallyinseawaterwithamassdensityof1.025t/m.totheship'sloadedcapacity,includingbunkersandothersuppliesnecessaryfortheship'spropulsion.Thedeadweightatanytimethusrepresentsthedifferencebetweentheactual3displacementandtheship'slightweight,allgivenintons:Incidentally,theword"ton"doesnotalwaysexpressthesameamountofweight.Besidesthemetricton(1,000kg),thereistheEnglishton(1,016kg),whichisalsocalledthe"longton".A"shortton"isapprox.907kg.Thelightweightofashipisnotnormallyusedtoindicatethesizeofaship,whereasthedeadweighttonnage(dwt),basedontheship'sloadingcapacity,includingfuelandlubeoilsetc,oftenis.MachineryArrangement*.Thethreelayoutsinvolvetheuseofdirect-coupledslow-speeddieselengines,medium-speedTheslow-speeddieselenginerotatesatthislowspeedandthecrankshaftisthusdirectlycoupledcannotthereforebedirectlycoupledtothepropellershaft.AgearboxisusedtoprovideaSlow-speeddiesel**.exchangerwouldbelocatedintheuptakeregionleadingtothefunnel.VariousworkshopsandGearedmedium-speeddiesel***.Fig.1-2.Thegearunitsprovideatwin-screwdriveat170r/mintocontrollablepitchpropellers.Thegearunitsalsopowertake-offsforshaft-drivengeneratorswhichprovideallpower4starboardagainstthesideshellplating.It-saferSectionlookingtoport SectionlookingtoforwardFig.1-1Low-speeddieselmachineryarrangement

mmm^tmnmwmb**wpu"k*Fig.1-2Medium-speeddieselmachineryarrangementLesson2HowDoesaMarineDieselEngineWorkusedonships.Theprincipleofitsoperationisasfollows:movingpistontoveryhighpressure.Theoperationbetweentwoinjectionsiscalledacycle,whichconsistsofafixedsequenceoffuelinjector deadcenter(BDC),withtheairinletportsorscavengeportsinthesidesofthecylinderbeing7Eng?sricdMamefcngintfeingAsthepistonmovesaboutonefifthofthewayup,itclosestheinletportsandtheexhaustports.Theairisthencompressedasthepistonmovesup(Fig.2-1<b)).exhaustports.Theburntgasesbegintoexhaust(Fig.2-1(d))andthepistoncontinuesdownuntilitopenstheinletports.Tpulsiondieseloperatesonthetwo-strokecycle.Atthislowspeedtheenginerequiresnoreductiongearboxbetweenitandpropeller.Thefour-strokeengine(usuallyrotatingatmediumgearboxtoprovideapropellerspeedofbetween90to120r/min.WorkingcyclesAdieselenginemayhedesignedtoworkonthetwo-strokeoronthefour-strokecycle.Bothofthemareexplainedbelow.Thefour-strokQcycle-*.Proceedingclockwiseroundthediagram,bothinlet(orsuction)andexhaustvalvesareinitiallyopen.(Allmodernfour-strokeengineshavepoppetvalves.)Iftheengineisnaturallyaspirated,(ATDC).1000r/minwillalmostcertainlybeturbochargedandwillbedesignedtoallowagenerousthroughflowofscavengeairatthispointinordertocontroltheturbinebladetemperature.Inthis8casetheexhaustvalvewillremainopenuntilexhaustvalveclosure(EVC)at50-60°ATDC.Asthepistondescendstoouterorbottomdeadcenter(BDC)onthesuctionstroke,itwillinhaleafreshchargeofair.Tomaximizethis,balancingthereducedopeningasthevalveseatsagainsttheslightramorinertiaeffectoftheincomingcharge,theinlet(suction)valvewillnormallybeheldopenuntilabout25-35°ABTC(145-155°BTDC).Thiseventiscalledinletvalveclosure(IVC).Thechargeisthencompressedbytherisingpistonuntilithasattainedatemperatureofsome550°C.Atabout10-20"BTDC(firing),dependingthetypeandspeedoftheengine,theinjectoradmitsfinelyatomizedfuelwhichigniteswithin2-7°(dependingonthetypeagain)andthefuelburnsoveraperiodof30-50°,whilethepistonbeginstodescendontheexpansionstroke.

Atabout120-150"ATDCtheexhaustvalveopens(EVO).thetimingbeingchosentopromoteaveryrapidblow-downofthecylindergasestoexhaustThisisdone:(a)topreserveasmuchenergyasispracticabletodrivetheturbocharger.and(b)toreducethecylinderpressuretoaminimumbyBDCtoreducepumpingworkonthe"exhaust"stroke.Therisingpistonexpelstheremainingexhaustgasandatabout70-80°BTDCtheinletvalveopens(1VO)sothattheinertiaoftheoutflowinggas,plusthepositivepressuredifference,whichusuallyexistsacrossthecylinderbynow,producesathroughflowofairtotheexhaustto"scavenge"thecylinder.IftheengineisnaturallyaspiratedtheIVOisabout10°BTDC.Thecyclenowrepeats.77?etwo-strokecyclesFig.2-3showsthesequenceofeventsinatypicaltwo-strokecycle,which,asthenameimplies,isaccomplishedinonecompleterevolutionofthecrank.Two-strokeenginesinvariablyhaveportstoadmitatrwhenuncoveredbythedescendingpiston.Theexhaustmaybeviaportsadjacenttotheairportsandcontrolledbythesamepiston(loopscavenge)orviapoppetexhaustvalvesattheotherendofthecylinder(uniflowscavenge).9"￥-*"""? -■'StartingatTDCcombustionisalreadyunderthewayandtheexhaustopens(EO)at110-120°ATDCtopromotearapidblow-downbeforetheinletopens(10)about20-30"later(130-150°ATDC).Inthiswaytheinertiaoftheexhaustgases-movingataboutthespeedofsound-isstroke.f\g.2-3TheTwo-slrokecycleTheexhaustshouldclosebeforetheinletonthecompressionstroketomaximizethecharge,butinanenginewithexhaustvalves.130-150°BTDC)andtheexhaustinthesameregion.withthefour-stroke.LessonODieselEngineConstructionBedplateandFramepartofthedoublebottomoftheship.Itissecuredinthetransversedirectionbymeansofboltsmainbearings,eachconsistsoftwoshellswhicharesupportedinhousingsmachinedinthebedplateandsecuredbymeansofstudsandbearingcaps.Thethrustblockorthrustbearing,scavengingairbox,whichisbuiltofanumbersectionsprovidedwithverticalflangesenablingablockwith4-6cylindersaftofthechaintransmission.Thechaintransmission,formingthechaindrivecasing.Cylindersandcovers***knownascylinderblocksorcoolingjackets,whichareprovidedwithverticalflangesenablingairboxes.rigidconstructionwithlessdeformationinserviceandlowervibration.Thecylinderlinersaremadeofalloyedcastironandthecylindersurfacesaresometimessealingbetween(helinerandthe(opofthescavengingairboxisachievedbytherubberringsfittedintotheslotsmachine-turnedintheliners.scavengingairports.Theseportsarelocatedatsuchaheightthattheyarejustexposedby(heupperedgeofthepistonwhenthepistonisin(hebottomdead-centreposition.Theportsarerotarymovement.partofthecover.Thefittingofthesealingringintheconicalsurfacemustbecarriedoutwiththecylinderframes.waterattheuppermostpartofit.valvecoolingchamber.Pistonsandpistonrods-*.Apistonconsistofalowerpart-pistonskirtofcastiron-andaupperpartorcrownmadeofapininthecrown.Eachpistonisprovidedwithfiveorsixpistonringsfittedinchromiumplatedgroovesintheoilcylinderlinerduringtherunning-inperiodfornewpistonrings.modernengines.Inthiscase,thepistonhasaninternalinsertinthepistoncrown,whichserveseffect.Thepistonrodsareboredfromthetopflangetoapointoppositethecenterofthecrosshead.formedbetweenthepistonrodandthepipe.Thelowerendofthepistonrodisreducedindiametertofitaboreinthecrosshead,thisbeingsecuredtothepistonrodbyanut.Thepistonrodsareprovidedwithdowelpinstoensurethecorrectassemblyofthecomponents.17f^ ■ metaltoensureanadequatesupplyoflubricatingoil.Thecrossheadisshortandrigidandthebearingsaresoconstructedthatthebearingpressuretoimprovetheworkingconditionsofthebearings,thebearingpressureismadesmallerandtheperipheralspeedhigherinlaterdesigns.Thepistonsarecooledbyoilsuppliedfromtheforcedlubricatingsystem.Thecoolingoilistelescopicpipesorarticulatedpipes,androundtheinternalpipesofthepistonrods.Thecoolingcrossheads,aswellastheslottedpipesfromwhichtheoilisledto"controlboxes"withsightglassesontheengine.stuffingboxes,locatedinthebottomofthescavengingairboxes.Eachstuffingboxisprovidedwithtwosealingringsandthreescraperrings.Thesealingrings,whicharemounteduppermost,Connectingrodandmainbearings**.partsecuredtotheconnectingrodbymeansoffittingbolts,thenutsofwhicharesecured.Thebearingshavewhitemetalbearingsurfacesprovidedwithlubricationgroovesforthenecessarysupplyoflubricatingandcoolingoil.ShimsofdifferentthicknessesareinsertedThemainbearings,whichsupportthecrankshaft,eachconsistoftwoshellsofcaststeelwithsecuredbymeansofbearingcapsandstuds,thenecessaryclearance(approx,0.30mm)beingprovidedbymeansofshimsofdifferentthicknesses.Allbearingsarelubricatedfromtheforce-feedlubricationsystemoftheengine,theoilbeinglubricatingoilflowsthroughchannelstthecrankpinbearings.CrankshaftsThecrankshaftisbuiltup,theforgedmainbearingjournalbeingshrunkintocaststeelcrankLesson■rFuelOilSystemThe'Unifuel'Systemparticularlyinregardtotheremovalofcatalyticfines,isachievedwhenthecentrifugesareoperatedinseries,i.e.inpurifier/clarifiermode.treatingfuelswithdensitieshigherthan991kg/m3at15°C,itisrecommendedtofollowthemaker'sspecificinstructions.oiltreatmentoffuelswithhigherdensity.Withsuchequipment,adequateseparationofwaterandfuelcanbecarriedoutinthecentrifuge,limitfornewhighdensityfuelgrades.instructions.Designfeaturesandworkingprinciple^Thefueloilsystemisacommon,pressurisedsysteminwhichbothheavyfueloilanddieseloilcanbeused.Thepurposeofpressurisationisprimarilytoavoidboilingandcavitationintherequiredforinjection(Fig.4-1).24ToFWooolABpumpuiclfon|FMfolP"Operationatsea-*.Inthesupplysystem,thefuelispumpedbythesupplypumps,intoacirculatingsystemataoilconstantinletpressureof7-8barbeforetheengines.Theinletpressureismaintainedattheengines.releasedbyadeaeratingvalve,toavoidcavitationinthesystem.Theflexibilityofthesystemmakesitpossible,ifnecessary,tooperateanauxiliaryengineondieseloilbymeansofremotecontrolled3-wayvalves,whichshouldbelocatedclosetotheauxiliaryengines.ofablack-out,theboosterpumpmusthaveanimmediatepossibilityofbeingpoweredbycompressedairorbypowersuppliedfromtheemergencygenerator.pressurizedandtheopenMDO(MarineDieselOil)supplysystem.Intheeventofablack-out,the3-wayvalveateachauxiliaryenginewillautomaticallychangefewseconds,beflushedwithMDOandbereadyforstartup.Operationinport^.bekeptrunningwhenthereisheavyoilinthepiping.lineenginefueloilsystem.Duringthisby-pass,theoverflowvalvetakesoverthefunctionoftheinternaloverflowvalveofthemainengine.Lesson5CentralCoolingWaterSystemDesignfeaturesandworkingprinciplecentralcoolerandoneadditionalsetofpumps.MANHAW'sspecifications.themainandauxiliaryenginesduringstandstill.Asallfreshcoolingwaterisinhibitedandcommonforthecentralcoolingsystem,onlyonetemperature.theexpansiontank.Analarmdeviceisinsertedbetweenthedeaeratingtankandtheexpansionmalfunctionofenginecomponents.Operationatsea^.Theseawatercoolingpumpspumpseawaterfromtheseacheststhroughthecentralcooler,andwatertomaintainanoutletwatertemperatureof80-85°Cfromtheengine(Fig.5-1).

29Operationinport^.airThemainengineandthestoppedauxiliaryenginesarepreheatedbytheoperatingauxiliaryengine(s).Lesson6StartingSystemDieselenginesarestartedbysupplyingcompressedairintothecylindersintheappropriatecompressorsandreceivers,theprovisionoffeaturesanddrainagefacilitiesarethesubjectofstringentrequirementsbyClassificationSocieties.Upto12startsarepossiblewiththestoredthingisnotinorder.airvalveandthentothecylinderairstartvalves.Theopeningofeachcylinderairstartvalvewillthepistonscausestheenginetorotate.Whenasufficientlyhighspeed,sayabout30r/min,hasbeenachievedtheairsupplyiscutoffandfuelisinjectedcausingthecylinderstofireandcontinuetoruninthenormalway.bytheengineairstartlever.Whentheairstartleverisoperated,asupplyofpilotairenablesthesystemisfitted.Pilotairfortheappropriatedirectionofoperationisalsosuppliedtoanairdistributor.Thisdeviceisusuallydrivenbytheenginecamshaftandsuppliespilotairtothesequenceforthedirectionofoperationrequired.Thecylinderairstartvalvesareheldclosedbyback.Thepilotaircontrolvalvereturnstotheoffposition,ventingthepilotairlinesandtheremoteairstartingvalveandallowingittocloseengineandpersonnel.Theseare:1.TheturninggearinterlockvalvewhichisarrangedtoshutoffthestartingairpilotlinewhenIhcturninggearisengaged,thuspreventingtheenginebeingstarted.Topreventoperationofthestartingairsystemwhenapilotairinterlockvalveisoperatedbythemaincontrolleverwhilsttheengineisrunning.Thevalveremainsopenduringthestartingsequence,i.e.untilthemaincontrolleverisremovedjustbeyondthestartingposition,butremainsclosedafterthispointanddoesnotopenagainuntilthemainleverismovedbacktothestopposition.Amechanicalinterlockisprovidedinthecontrolboxtopreventthemaincontrolleverbeingmovedbeyondthestartingpositionwhilethestartingairleverisineithertheaheadorasternstartingposition.Anothermechanicalinterlockisprovidedtopreventthemaincontrolleverbeingmoveduntilstartingairisadmittedtothecylinders.Thispreventsfuelbeingadmittedtothecylinderswhentheengineisatrest.Lubricatingoilfromthecompressorwillpassalongtheairlinesanddepositonthem.Intheeventofacylinderairstartingvalveleaking,hotgaseswouldpassintotheairpipesandignitethelubricatingoil.Ifstartingairissuppliedtotheenginethiswouldfurtherfeedthefireandcouldleadtoanexplosioninthepipelines.Inordertopreventsuchanoccurrence,cylinderstartingvalvesshouldbeproperlymaintainedandthepipelinesregularlydrained.Alsooildischargedfromcompressorsshouldbekepttoaminimum,bycarefulmaintenance.Idanattempttoreducetheeffectsofanexplosion,flametraps,reliefvalvesandburstingcapsordiscsarefittedinthepipelines.Inadditionanisolatingnon-returnvalve(theautomaticvalve)isfittedtothesystem,whichpreventsfurthercompressedairbytheengineintothesystem.Thelossofcoolingwaterfromanaircompressorcouldleadtoanoverheatedairdischargeandpossiblyanexplosioninthepipelinesleadingtotheairreservoir.Ahightemperaturealarmorafusibleplugwhichwillmeltisusedtoguardagainstthispossibility.DesignfeaturesandworkingprinciplesTwoaircompressors,withautomaticstartandstop,maintainastartingairpressureof30barinthestartingairreceivers.Themainengineissuppliedwith30barstartingairdirectlyfromthestartingairreceivers.Throughapressurereductionstation,compressedairat7barissuppliedascontrolairfortheenginemanoeuvringsystem,andassafetyairfortheemergencysystem.Startingairandcontrolairfortheauxiliaryengine(s)isalsosuppliedfromthesamestarlingairreceivers,viareducingvalvesthatlowerthepressuretoavaluesuitedtotheactualtypeofMANB&Wfour-strokeauxiliaryengineschosen.Anemergencyaircompressorandastartingairbottleareinstalledforredundantemergencystartoftheauxiliaryengines.33Ifhigh-humidityairissuckedinbytheaircompressors,anoilandwaterseparatorwillremoveslight.Consequently,furtherairdryingisconsideredunnecessary.Lesson/LubricatingSystemDutiesofLubricantlubricationwhichinvolvestheformationandmaintenanceofalubricatingoilfilmbetweentheproblemofthelubricationofitsmanypartswiththeirwidelyvaryingoperationconditions.carbonaceousdeposits,resistoxidationandwashawayweardetritus.offueltobeburned.coolingthepistons.Cylinderoilsystem^.onthelinerwallsunderconditionsinvolvingrapidlychangingspeedandreversalofdirectionofmotion.Oilissuppliedlothecylinderlinerwallandthepistonringsbymeansofmechanicalistimedsothattheoilimpingesonlyonthepistonringbelt,thusensuringthemostefficientlubrication.arenotonlyessentialforlubricationbutalsoplayanimportantpartinachievingagasseal.Inwhichinterferewiththecorrectoperationoftherings.Tocounteracttheseundesirableeffectscylinderoilsusuallycontainadditivesformulatedtoimpartahighdegreeofalkalinityandgrooves.37Mainlubricatingoilsystem^Operatingconditionsinthecrankchamberareverydifferentfromihoseinthecylinderanditistheneedfortheoiltoperformitsfunctionoveraverylongperiod,whichdeterminesthepropertiesrequiredinthelubricant.Thefollowingfeaturesareessentialforcrankchamberoils:1-Theymusthavegoodlubricatingpropertiesandbeabletoresistruptureofthefilmseparatingthemovingpartsinordertoensureminimumfrictionlosses.Theymustbeabletoremoveheatfromabearingandtodosotheviscosityshouldbehighenoughatoperatingtemperaturestoassistfilmmaintenance.Theymustbecapableofremovingheatfromoilcooledpistonsandindoingsomusthavethehighestpossibledegreeofresistancetooxidationandothereffectsofheat.Theuseofapoorqualityoilcanleadtorapiddeteriorationofitspropertieswiththeresultantformationofdepositsinthepistoncrownwhichinturnresultsinaconsiderablereductioninheattransferwithsubsequentoverheatingandthermalcracking.Thecoolingoilisusuallysuppliedtothepistonbymeansoftelescopicpipesconnectedtothecrossheadsandpassagesinthepistonrods.Toensureaconstantsupplyofcleanandtemperaturecontrolledoiltotheenginerequirestheprovisionofagreatdealofauxiliaryequipmentsuchaspumps,filterscentrifuges,coolers,drainandstoragetanksetc.LubricationThelubricationsystemofanengineprovidesasupplyoflubricatingoiltothevariousmovingpartsinanengine,itsmainfunctionistoenabletheformationofafilmofoilbetweenthemovingparts,whichreducesfrictionandwear.Thelubricatingoilisalsousedasacleanerandinsomeenginesasacoolant.LubricatingoilsystemsLubricatingoilforanengineisstoredinthebottomofthecrankcase,knownasthesump,orinadraintanklocatedbeneaththeengine.Theoilisdrawnfromthistankthroughastrainer,oneofapairofpumps,intooneofapairoffinefilters.Itisthenpassedthroughacoolerbeforeenteringtheengineandbeingdistributedtothevariousbranchpipes.Thebranchpipeforaparticularcylindermayfeedthemainbearing,forinstance.Someofthisoilwillpassalongadrilledpassageinthecrankshafttothebottomendbearingandthenupadrilledpassageintheconnectingrodtothegudgeonpinorcrossheadbearing.Analarmattheendofthedistributionpipeensuresthatadequatepressureismaintainedbythepump.Pumpsandfinefiltersarearrangedinduplicatewithoneasstandby.Thefinefilterswillbearrangedsothatonecanbecleanedwhiletheotherisoperating.Afteruseintheenginethelubricatingoildrainsbacktothesumpordraintankforreuse.Alevelgaugegivesalocalread-putofthedraintankcontents.Acentrifugeisarrangedforcleaningthelubricatingoilinthesystemandcleanoilcanbeprovidedfromastoragetank.Theoilcooleriscirculatedbyseawater,whichisatalowerpressurethantheoil.Asaresultanyleakinihecoolerwillmeanalossofoilandnotcontaminationoftheoilbyseawater.Cylinderlubrication^.Largeslowspeedenginesareprovidedwithaseparatedlubricatingsystemforthecylinderliners.Oilisinjectedbetweenthelinerandthepistonbymechanicallubricatorswhichsupplytheirindividualcylinder.Aspecialtypeofoilisusedwhichisnotrecovered.Inadditiontolubricating,itassistsinformingagassealandcontainsadditiveswhichcleanthecylinderliner.removalofexhaustgases.Thisisthegasexchange.Olderengineswere"naturallyaspirated"-takingfreshaironlyatatmosphericpressure.Byandthecylinder,theweightofairinducedperworkingstrokeisincreased,andtherebyagreaterinchargeairdensityisaccomplishedonmostmoderndicselenginetypesbyuseofexhaustgascentrifugaltypeaircompressor.Bothfour-strokeandtwo-strokecycleenginesmaybepressurepressuresandthermalloadswhichresult.Itisessentialtothescavengingprocessthattheairenteringthecylinderisatahigherpressuretheisusuallycooledtoincreasethechargeairdensity.theexhaustvalveclosing.Theairflowthroughthecylinderduringiheoverlapperiodhasatwo-strokecycleenginesthisoverlapislimitedbytheenginedesigncharacteristics,andsomeslightmixingofexhaustgasesandincomingairdoesmonuse:thecrossflow,theloopandtheuniflow.exhaustgasesthentraveldownandoutoftheexhaustports.airabovetheinletports.(invalve(inthepoppetvalveengine).fittingofapistonskirttopreventairorexhaustgasescapewhenthepistonisatthetopoftheoranexhaustvalveinthecylinderhead.Allthreesystemshavetheportsangledtoswirlthespeedenginesarenolongerinproductionandpoppetvalvesarcusedinthemajorityofnewdesigns.pressure"and"pulse"systems.ItistheconstantpressuresystemthatisnowusedbyallLesson9OperationandMaintenanceofMainEngineOperatingProceduresMedium-speedandslow-speeddieselengineswillfollowafairlysimilarprocedureforstartingshouldbeconsultedandused.Preparationsforstandby^.shouldbeobserved.forcedout. Theturninggearisremovedandifpossibletheengineshouldbeturnedoveronairbefore

-closingtheindicatorcocks, dependuponthesizeoftheengine.Enginestarting**.replylever.Thecamshaftisthuspositionedrelativetothecrankshafttooperatethevariouscamsforfuelinjection,valveoperation,hecorrectsequencetoturntheengineinthedesireddirection.Aseparateairstartbuttonmaybeused.admissionwillcease.Enginereversing^.463-Thedirectionhandleispositionedcesswilltakeoverandairadmissioncease. DieselenginesareremarkablysimpleinprincipleandrequirelittleinthewayofroutinelittleThenozzlesoftheengineshouldwhennecessarybefreedfromcoke,which,especiallywhenoutascheduleofnecessaryoperations.Thefollowingschedulemaybeusefulasaguide.Itfueloils.Afurtherconditionisthattheen