us army principles of internal combustion engines

SUBCOURSE EDITIONOD1619 8

PRINCIPLES OF INTERNALCOMBUSTION ENGINES

USARMYBRADLEYFIGHTINGVEHICLESYSTEMSMECHANICCORRESPONDENCECOURSE

MOS/SKILLLEVEL:63T30

PRINCIPLESOFINTERNALCOMBUSTIONENGINES

SUBCOURSENO.OD1619

USArmyCorrespondenceCourseProgram

7CreditHours

GENERAL

The purpose of this subcourse is to increase the mechanic's knowledge of theprinciples,components,andoperationofinternalcombustionengines.

Sevencredithoursareawardedforsuccessfulcompletionofthissubcourse.

Lesson1: INTERNALCOMBUSTIONENGINES

TASK1: Describe the principles, components, and operation of both the twostrokeandfourstrokegasolineengines.

TASK2: Describe the principles, components, and operation of both the twostrokeandfourstrokedieselengines.

Lesson2: INTERNALCOMBUSTIONENGINESUBSYSTEMS

TASK1: Describetheprinciples,components,andoperationofturbochargers,intake,andexhaustsystems.

TASK2: Describetheprinciples,components,andoperationofthelubricationsystem.

TASK3: Describe the principles, components, and operation of the coolingsystem.

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PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619

TABLEOFCONTENTS

Section Page

TITLE......................................................................... i

TABLEOFCONTENTS............................................................. ii

Lesson1: INTERNALCOMBUSTIONENGINES..................................... 1

Task1: Describetheprinciples,components,andoperationofboththetwostrokeandfourstrokegasolineengines......................................................... 1

Task2: Describetheprinciples,components,andoperationofboththetwostrokeandfourstrokedieselengines......................................................... 27

PracticalExercise1..................................................... 44

AnswerstoPracticalExercise1.......................................... 46

Lesson2: INTERNALCOMBUSTIONENGINESUBSYSTEMS...................................................... 47

Task1: Describetheprinciples,components,andoperationofturbochargers,intake,andexhaustsystems..................................... 47

Task2: Describetheprinciples,components,andoperationofthelubricationsystem.............................................. 58

Task3: Describetheprinciples,components,andoperationofthecoolingsystem.................................................. 79

PracticalExercise2..................................................... 97

AnswerstoPracticalExercise2.......................................... 98

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PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619

REFERENCES.................................................................... 99

*** IMPORTANT NOTICE ***

THE PASSING SCORE FOR ALL ACCP MATERIAL IS NOW 70%.

PLEASE DISREGARD ALL REFERENCES TO THE 75% REQUIREMENT.

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PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 1/TASK 1

LESSON1

INTERNALCOMBUSTIONENGINES

TASK1. Describe the principles, components, and operation of both the twostrokeandfourstrokegasolineengines.

CONDITIONS

Withinaselfstudyenvironmentandgiventhesubcoursetext,withoutassistance.

STANDARDS

Withintwohours

REFERENCES

Nosupplementaryreferencesareneededforthistask.

1. Introduction

Militaryvehiclesincorporateallformsofwheeledandtrackedvehicles,includingthefullrangeofbodytypesfoundincommercialvehicles.However,therearealsobodiesandequipmentthatareuniquetomilitaryoperations. Theyincludealltypes of trucks, tractors, truck tractors, personnel carriers, tanks, selfpropelledguns,motorizedandmechanizedspecialpurposeequipment,trailers,vans,andspecialpurposetowedvehicles.

Theprincipaldistinctionbetweenthesevehiclesandtheircommercialcounterpartsisthatmilitaryvehiclesarespecificallydesignedformilitarypurposes.Theseincludecombatoperationsandthetransportationofcargo,personnel,orequipment;towingothervehiclesorequipment;andoperations,bothcrosscountryandoverroads,inclosesupportofcombatvehiclesandtroops.Suchvehiclesaredesignedandconstructedtoenduretherigorsofthemilitaryenvironmentandtocontinuetooperateat,orabove,aprescribedminimumperformance

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level.Theyhaveexcellentcrosscountryperformancecapabilitiesoveralltypesofterrainwheretacticalorcombatoperationscanbeconducted. Thisincludessnowandice,rockyterrain,swamps,anddesertsands.Inordertonegotiatewaterbarriers with a minimum of preparation, all sensitive equipment is eitherpermanentlywaterproofedordesignedtofunctionunderwater.

Themajorityofthevehiclesdescribedintheparagraphsabovehaveaninternalcombustionengine. Forthisreason,amechanicshouldknowtheprinciplesofoperationofthisengineanditsvariouscomponents.Aninternalcombustionengineisanyenginewithinwhichthefuelisburned. Thefourstrokeandtwostrokecycle gasoline and diesel engines are examples of internal combustion enginesbecausethecombustionchamberislocatedwithintheengine. Inthistask,aninternalcombustionengine,referredtoasthepistonengine,willbedescribed.

2. PistonEngineCharacteristics

a. EngineOperation.

(1) General.Becausethemostwidelyusedpistonengineisthefourstrokecycletype,itwillbeusedastheexampleforthisparagraphandasthebasisforcomparisoninTask2.Theoperationofthepistonenginecanbestbeunderstoodbycomparingittoasimplecannon.InviewAoffigure1onthefollowingpage,acannonbarrel,chargeofgunpowder,andacannonballareillustrated.InviewBoffigure1,thegunpowderisignited. Thegunpowderburnsveryrapidlyandasitburnsthereisarapidexpansionoftheresultinggases. Thisrapidexpansioncausesatremendousincreaseinpressurethatforcesthecannonballfromthebarrel.

InviewAoffigure2onthefollowingpage,thecannonbarrelhasbeenreplacedbyacylinderandacombustionchamber.Thecannonballhasbeenreplacedbyapiston.Amixtureofvaporizedfuelandairhasreplacedthegunpowder. InviewBoffigure2,thegasolineisignited.Thistime,theresultingforceactstopushthepistondownward.

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FIGURE1.PISTONENGINEPRINCIPLES.

FIGURE2.PISTONENGINEOPERATION.

(2) ReciprocatingMotiontoRotaryMotion.Theforceofthepistonactinginadownwardnotionisoflittleimmediatevalueifitistoturnthewheelsofavehicle.Inordertousethisstraightlineorreciprocatingmotion,itmustbetransformed into rotary motion. This is made possible through the use of acrankshaft.Thecrankshaftisconnectedtothedrivingwheelsofavehiclethroughthedrivetrainononeend. Ontheotherendoftheshaftisacrankwithacrankpinoffsetfromtheshaft'scenter.Figure3onthefollowingpage

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FIGURE3.PISTONANDCRANKSHAFT.

illustrateshowthepistonandthecrankshaftareconnectedthroughtheconnectingrodandthecrankpin.Figure4onthefollowingpageillustrateshowreciprocatingnotionofthepistonischangedtorotatingmotionofthecrankshaft.

A more detailed explanation of the parts that perform this reciprocating androtatingmotionwillbedescribedinparagraph3onpage15.

(3) IntakeandExhaust. Iftheengineisgoingtooperate,thefuelandairmixturemustbefedintothecombustionchamber. Theburntgasesalsomustbeexhausted.Toaccomplishthis,thereisapassagetothecombustionchambercalledtheintakeport,andapassagefromthecombustionchambertotheexhaustsystemcalledtheexhaustport.Asimplifiedarrangementisshowninfigure5onpage6.

Byputtingopeningsinthecombustionchamber,aproblemiscreated;theforceoftheburningfuelandairmixturewillbelostthroughtheexhaustandintakeportsratherthanusedtopushdownthepiston. Tosolvethisproblem,theremustbesomethingthatopensandclosestheintakeandexhaustportstothecombustionchambers. Toaccomplishthis,avalveisaddedtoeachoftheseports;thesevalvesarecalledtheintakeand

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FIGURE4.PISTONTOCRANKSHAFTRELATIONSHIP.

exhaustvalves. Asimplifiedarrangementisshowninfigure6onthefollowingpage.

Theintakeandtheexhaustvalvesareopenedandclosedinatimedsequencebythevalvetrain.Thevalvetrainwillbediscussedinparagraph2a(5)onpage8.

(4) ActionintheCylinder. Whenthepistonisatitshighestpointinthecylinder,itisinapositioncalledtopdeadcenter.Whenthepistonisatitslowestpointinthecylinder,itisinapositioncalledbottomdeadcenter.Asthepistonmovesfromtopdeadcentertobottomdeadcenter,orviceversa,thecrankshaftrotatesexactlyonehalfofarevolution,asshowninfigure6onthefollowingpage.

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FIGURE5.INTAKEANDEXHAUSTPORTSANDVALVES.

FIGURE6.PISTONPOSITIONS.

Eachtimethepistonmovesfromtopdeadcentertobottomdeadcenter,orviceversa,itcompletesamovementcalledastroke. Therefore,thepistoncompletestwostrokesforeveryfullcrankshaftrevolution.Therearefourdefinitephasesofoperationthatanenginegoesthroughinone

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completeoperatingcycle.Eachoneoftheseoperatingphasesiscompletedinonepistonstroke. Becauseofthis,eachoperatingphaseisalsoreferredtoasastrokeand,becausetherearefourstrokesofoperation,theengineisreferredtoasafourstrokecycleengine. Thefourstrokesareintake,compression,power,andexhaust. Becausetherearefourstrokesinoneoperatingcycle,itmaybeconcludedthattherearetwocompletecrankshaftrevolutionsineachoperatingcycle.

(a) IntakeStroke(figure7onpage9).Theintakestrokebeginsattopdeadcenter.Asthepistonmovesdown,theintakevalveopens.Thedownwardmovementofthepistonwiththeexhaustvalveclosedcreatesavacuuminthecylinder.Thevacuumcausesafuelandairmixturetobedrawnthroughtheintakeportintothecombustionchamber. Asthepistonreachesbottomdeadcenter,theintakevalvecloses.

(b) CompressionStroke. Thecompressionstrokebeginswiththepistonatbottomdeadcenter.Boththeintakeandtheexhaustvalvesremainclosed.Asthepistonmovestowardtopdeadcenter,theamountofspaceintheuppercylindergetssmaller.Thefuelandairmixtureiscompressedandthepotentialenergyinthefuelisconcentrated.Thecompressionstrokeendswhenthepistonreachestopdeadcenter.

(c) PowerStroke. Asthepistonreachestopdeadcenter,endingthepowerstroke,thesparkplugignitesthecompressedfuelandairmixture.Becausebothvalvesareclosed,theforceoftheresultingexplosionpushesthepistondown,givingapowerfuldrivingthrusttothecrankshaft.Thepowerstrokeendsasthepistonreachesbottomdeadcenter.

(d) ExhaustStroke. Asthepistonreachesbottomdeadcenter,endingthepowerstroke,theexhaustvalveopens,beginningtheexhauststroke.Asthepistonmovesupwardtowardtopdeadcenter,itpushestheburntgasesfromthefuelandairmixtureoutofthecombustionchamberthroughtheexhaustport.Asthepistonreachestopdeadcenter,endingtheexhauststroke,theexhaustvalvecloses.Astheexhaustvalvecloses,theintakevalveopenstobegintheintakestrokeinthenextcycle.

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(5) ValveTrain.Itisveryimportanttooperatethevalvesinatimedsequence.Therefore,theengineisfittedwithavalvetrain,whichoperatesthevalves.Iftheexhaustvalveweretoopeninthemiddleoftheintakestroke,thepistonwoulddrawburntgasesintothecombustionchamberwithafreshmixtureoffuelandair.As the piston continued to the power stroke, there would be nothing in thecombustionchamberthatwouldburn.

AsimplifiedvalvetrainisillustratedinviewAoffigure8onpage10. Acamshaftismadetorotatewiththecrankshaftthroughthetiminggears. Theraisedpieceonthecamshaftiscalledacamlobe.AsillustratedinviewBoffigure8,thevalvespringisdesignedtoholdthevalveclosed.

Thecamlobecontactsthebottomofthelifterasitrotateswiththecamshaft,asshowninviewCoffigure8.Asthecamlobepushesuponthelifteritwill,inturn,pushthevalveopenagainstthepressureofthespring.InviewDoffigure8,thecamlobehaspassedthecenterofthelifterbottom. Asitrotatesawayfromthelifter,thevalvespringpullsthevalveclosed.

Byproperpositionofthecamlobesonthecamshaft,asequencecanbeestablishedfortheintakeandexhaustvalves. Itisdescribed,insubparagraphs2a(4)(a)through2a(4)(d)onpage7,howtheintakevalveandtheexhaustvalvemusteachopenonceforeveryoperatingcycle. Asexplainedinsubparagraph2a(4),thecrankshaftmustmaketwocomplete revolutions tocompleteoneoperatingcycle.Usingthesetwofacts,acamshaftspeedmustbeexactlyonehalfthespeedofthecrankshaft.Toaccomplishthis,thetiminggearsaremadesothatthecrankshaftgearhasexactlyonehalfasmanyteethasthecamshaftgear,asshowninviewAoffigure9onpage11.Thetimingmarksindicatedareusedtoputthecamshaftandthecrankshaftintheproperpositionrelativetoeachother.

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FIGURE7.FOURSTROKECYCLEOPERATIONS.

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FIGURE8.VALVETRAINOPERATION.

(6) EngineAccessorySystems.

(a) Fuel System. The fuel system supplies the engine with the properlyproportionedfuelandairmixture. Italsoregulatestheamountofthemixturesuppliedtotheenginetocontrolenginespeedandpoweroutput.

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FIGURE9.TIMINGGEARSANDFLYWHEEL.

(b) IgnitionSystem.Theignitionsystemignitesthefuelandairmixtureinthecombustionchamberattheprecisemomentneededtomaketheenginerun.

(c) Cooling System. The cooling system removes the excess heat from theengine,generatedbycombustion.

(d) LubricationSystem.Thelubricationsystemprovidesaconstantsupplyofoiltotheenginetolubricateandcoolthemovingparts.

(e) Flywheel (figure 9, view B). As discussed previously, for every tworevolutionsthecrankshaftmakes,itonlyreceivesonepowerstrokewhichlastsforonlyonehalfofonerevolutionofthecrankshaft.Thismeansthattheenginemustcoastthroughoneandonehalfcrankshaftrevolutionsineveryoperatingcycle.Thiswouldcausetheenginetoproduceveryerraticpoweroutput.Tosolvethisproblem,aflywheelisaddedattheendofthecrankshaft.Theflywheel,whichisveryheavy,willabsorbtheviolentthrustofthepowerstroke. Itwillthenreleasetheenergybacktothecrankshaftsothattheenginewillrunsmoothly.

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b. ComparisonofEngineTypes.

(1) InternalCombustionEngineVersusExternalCombustionEngine.

(a) InternalCombustionEngine (figure10,viewA). Aninternalcombustionengineisanyengineinwhichthefuelisburnedfromwithin.Afourstrokecycleengineisaninternalcombustionenginebecausethecombustionchamberislocatedwithintheengine.

FIGURE10.INTERNALCOMBUSTIONENGINEVERSUSEXTERNALCOMBUSTIONENGINE.

(b) ExternalCombustionEngine (figure10,viewB). Anexternalcombustionengineisanengineinwhichthefuelisburnedoutsideoftheengine. Asteamengineisaperfectexample. Thefuelisburnedinanoutsideboilerwhereitmakessteam.Thesteamispipedtotheenginetomakeitrun.

(2) FourStrokeCycleVersusTwoStrokeCycle. Theenginedescribeduntilnowhasbeenafourstrokecycleengine. Thereisanotherformofgasolinepistonenginewhichrequiresnovalvemechanismsandwhichcompletesoneoperatingcycleforeveryrevolutionofthecrankshaft.Itiscalledatwostrokecycleengineandisillustrated

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infigure11.Insteadofplacingtheintakeandexhaustportsinthecombustionchamber,theyareplacedinthecylinderwall. Inthisengine,thepistongoesthroughapowerstrokeeverytimeitmovesfromtopdeadcentertobottomdeadcenter. Thedownwardstrokeisalsoanintakeandanexhauststroke. Asthepistonmovesfrombottomdeadcenterbacktotopdeadcenter,itisgoingthroughacompressionstroke.

FIGURE11.TWOSTROKECYCLEENGINE.

(a) DownwardStroke (figure12,viewA,onthefollowingpage). Thepistonbeginsthepowerstrokeattopdeadcenter.Astheexplodingfuelandairmixturepushes the piston downward, it first covers the inlet port. This seals thecrankcase. As the piston continues downward, it uncovers the intake and theexhaustports. Thepressurebuiltupinthecrankcaseforcesthefuelandairmixtureintothecylinderthroughtheintakeport.Thetopofthepistonisshapedtodivertthemixtureupwardandawayfromtheexhaustport.Asthemixtureentersthecylinder,itdisplacesandpushestheburntgasesoutthroughtheexhaustport.

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(b) UpwardStroke(figure12,viewB).Asthepistonmovesupward,itcoverstheintakeandexhaustports. Thissealstheuppercylindersothattheupwardmovementofthepistoncompressesthefuelandairmixture.Atthesametime,theupwardmovementofthepistoncreatesasuctioninthecrankcasesothatastheinletportisuncovered,amixtureoffuelandairisdrawnintothecrankcase.Asthe piston reaches top dead center, the spark plug ignites the fuel and airmixture,beginningthedownwardpowerstrokeagain.

FIGURE12.THETWOSTROKECYCLE.

(c) TheFuelandLubricationSystem.Thefuelandairmixturemustfirstpassthroughthecrankcasebeforeitgetstothecombustionchamber.Forthisreason,the fuel and air mixture must also provide lubrication for the rotating andreciprocatingparts.Thisisaccomplishedbymixingasmallpercentageofoilwiththefuel.Theoil,mixedwiththefuelandairmixture,entersthecrankcaseinavaporthatconstantlycoatsthemovingparts.

(d) PowerOutput.Itmayseemthatatwostrokeenginewillputouttwiceasmuchpowerasacomparablefourstrokecycleenginebecausetherearetwiceasmanypowerstrokes.However,thisisnotthecase.Becausetheforceofthefueland

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airmixtureenteringthecylindermustbereliedupontogetridoftheburntgasesinthecylinderfromthelastpowerstroke,thereissomedilutionofthemixture.Themixingoftheintakemixturewithexhaustgasesreducesthepotentialpoweroutput.Also,withtheinletandexhaustportsopenedtogether,acertainamountofthefuelandairmixtureislost.Thereisalsoamuchshorterperiodinwhichtheinletportisopen.Thesefactorsreducetheamountofpowerfromeachpowerstroke.

(e) Advantage and Usage. The two stroke cycle engine is used almostexclusivelyinverysmallequipment. Itislightweightandabletorunatveryhighspeedsduetotheabsenceofamechanicalvalvetrain.

3. RotatingandReciprocatingParts

a. Piston.

(1) General(figure13).Thepistonisthepartofboththetwoandfourstrokeengines that receives the energy from the combustion and transmits it to thecrankshaft. The piston must withstand heavy stress under severe temperatureextremes.Thefollowingareexamplesofconditionsthatapistonmustwithstandatnormalhighwayspeeds.

FIGURE13.PISTON.

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(a) Asthepistonmovesfromthetopofthecylindertothebottom(orviseversa),itacceleratesfromastoptoaspeedofapproximately50milesperhour(mph)(80kilometersperhour[kph])atmidpoint,andthendeceleratestoastopagain.Itdoesthisapproximately80timespersecond.

(b) Theheadofthepistonissubjectedtopressuresinexcessof1000poundspersquareinch(psi)(6895kPa).

(c) Thepistonheadissubjectedtotemperatureswellover600F(316C).

(2) Construction Materials. When designing pistons, weight is a majorconsideration. Thisisbecauseofthetremendousinertialforcescreatedbytherapidchangeinpistondirection.Forthisreason,ithasbeenfoundthataluminumisthebestmaterialforpistonconstruction. Ithasaveryhighstrengthtoweight ratio and, in addition to being lightweight, aluminum is an excellentconductorofheatandismachinedeasily.Pistonsarealsomanufacturedfromcastiron.Castironisanexcellentmaterialforpistonsinlowspeedengines.Itisnotsuitableforhighspeedsbecauseitisaveryheavymaterial.

(3) ControllingExpansion(figure14onthefollowingpage).Pistonsmusthavebuiltinfeaturestohelpthemcontrolexpansion.Withoutthesefeatures,pistonswouldfitlooselyinthecylinderswhencold,thenbindinthecylindersastheywarmup. Thisisaproblemwithaluminumbecauseitexpandssoreadily. Tocontrolexpansion,pistonsmaybedesignedwiththefollowingfeatures:

(a) Itisobviousthatthecrownofthepistonwillgethotterthantherestofthepiston.Topreventitfromexpandingtoalargersizethantherestofthepiston,itismachinedtoadiameterthatisapproximately0.03to0.04in.(0.762to1.106mm)smallerthantheskirtarea.

(b) Oneofthewaystocontrolexpansionintheskirtareaistocutaslotupthesideoftheskirt.Asasplitskirtpistonwarmsup,thesplitwillcloseup,therebykeepingtheskirtfromexpandingoutwardandbindingthepistoninthecylinder.

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FIGURE14.CONTROLLINGPISTONEXPANSION.

(c) AvariationofthesplitskirtpistonistheTslotpiston. TheTslotpistonissimilartothesplitskirtpiston,withtheadditionofahorizontalslotthatretardsheattransferfromthepistonheadtothepistonskirt.

(d) Some aluminum pistons have steel braces cast into them to controlexpansion.

(4) CamGrinding (figure15onthefollowingpage). Bymakingthepistoneggshaped,itwillbeabletofitthecylinderbetterthroughoutitsoperationaltemperaturerange.Apistonofthisconfigurationiscalledacamgroundpiston.Camgroundpistonsaremachinedsothattheirdiameterissmallerparalleltothepistonpinaxisthanitisperpendiculartoit.Whenthepistoniscold,itwillbebigenoughacrossthelargerdiametertopreventrocking.Asitwarmsup,itwillexpandacrossitssmallerdiameteratamuchhigherratethanatitslargerdiameter. This will tend to make the piston round at operating temperature.Virtuallyallpistonsinautomotiveapplicationsarecamground.

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FIGURE16.CAMGROUNDPISTON.

(5) PartialSkirted (SlipperSkirt) Pistons (figure 16). The purpose of thepistonskirtistokeepthepistonfromrockinginthecylinder.Theslipperskirtpistonhaslargeportionsofitsskirtremovedinthenonthrustareas.Removaloftheskirtintheseareasservesthefollowingpurposes:

(a) Lightensthepiston,which,inturn,increasesthespeedrangeoftheengine.

FIGURE16.FULLANDPARTIALSKIRTEDPISTONS.

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(b) Reducesthecontactareawiththecylinderwall,whichreducesfriction.

(c) Allowsthepistontobebroughtdownclosertothecrankshaftwithoutinterferencewithitscounterweights.

(6) StrengthandStructure(figure17onthefollowingpage).Whendesigningapiston,weightandstrengtharecriticalfactors.Twoofthewayspistonsaremadestrongandlightareasfollows:

FIGURE17.PISTONSTRUCTURE.

(a) Theheadofthepistonismadeasthinasispractical;tokeepitstrongenough,ribsarecastintotheundersideofit.

(b) Theareasaroundthepistonpinarereinforced;theseareasarecalledthepinbosses.

(7) Coatings. Aluminumpistonsareusuallytreatedontheiroutersurfacestoaidinenginebreakinandtoincreasehardness.Thefollowingarethemostcommonprocessesfortreatmentofaluminumpistons.

(a) Thepistoniscoatedwithtinwhichwillworkintothecylinderwallsastheengineisbrokenin.Thisprocessresultsinamoreperfect

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fit,shorteningthebreakinperiod,andanincreaseisoverallenginelongevity.

(b) Thepistonisanodizedtoproduceaharderoutsidesurface.Anodizingisaprocessthatproducesacoatingonthesurfacebyelectrolysis. Theprocesshardensthesurfaceofthepiston.Thishelpsitresistpickingupparticlesthatmaybecomeembeddedinthepiston,causingcylinderwalldamage.

b. PistonRings.

(1) General(figure18).Pistonringsservethreeimportantfunctions:

FIGURE18.PURPOSEOFPISTONRINGS.

(a) Theyprovideasealbetweenthepistonandthecylinderwalltopreventthe force of the exploding gases from leaking into the crankcase from thecombustionchamber.Thisleakageisreferredtoasblowby.Blowbyisdetrimentaltoengineperformancebecausetheforceoftheexplodinggaseswillmerelybypassthepistonratherthanpushitdown.Italsocontaminatesthelubricatingoil.

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(b) Theypreventthelubricatingoilfrombypassingthepistonandgettingintothecombustionchamberfromthecrankcase.

(c) Theyprovideasolidbridgetoconducttheheatfromthepistontothecylinderwall.Aboutonethirdoftheheatabsorbedbythepistonpassestothecylinderwallthroughthepistonrings.

(2) Description (figure19). Pistonringsaresplittoallowforinstallationand expansion, and they exert an outward pressure on the cylinder wall wheninstalled.Theyfitintogroovesthatarecutintothepiston,andareallowedtofloat freely in these grooves. A properly formed piston ring, working in acylinderthatiswithinlimitsforroundnessandsize,willexertanevenpressureand maintain a solid contact with the cylinder wall around its entirecircumference.Althoughpistonringshavebeenmadefrommanymaterials,castironhasprovedmostsatisfactoryasitwithstandsheat,formsagoodwearingsurface,andretainsagreateramountofitsoriginalelasticityafterconsiderableuse.Therearetwobasicclassificationsofpistonrings.

(a) The Compression Ring. The compression ring seals the force of theexplodingmixtureintothecombustionchamber.

FIGURE19.PISTONRINGTYPESANDDESCRIPTION.

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(b) The Oil Control Ring. The oil control ring prevents the engine'slubricationoilfromgettingintothecombustionchamber.

(3) Configurations. Pistonringsarearrangedonthepistonsinthreebasicconfigurations.Theyare:

(a) Thethreeringpiston(figure20,viewA)hastwocompressionringsnearthehead,followedbyoneoilcontrolring.Thisisthemostcommonpistonringconfiguration.

FIGURE20.CONFIGURATIONSOFPISTONRINGS.

(b) Thefourringpiston(figure20,view8)hasthreecompressionringsnearthehead,followedbyoneoilcontrolring.Thisconfigurationiscommonindieselenginesbecausetheyaremorepronetoblowby,duetothemuchhigherpressuresgeneratedduringthepowerstroke.

(c) Thefourringpiston(figure20,viewc)hastwocompressionringsnearthehead,followedbytwooilcontrolrings.Thebottomoilcontrolringmaybelocatedaboveorbelowthepistonpin.

Thisisnotaverycommonconfigurationincurrentenginedesign.Inadditiontotheconfigurationsmentioned,therearesomedieselenginesthatusefiveormorepistonringsoneachpistontocontrolthehigheroperatingpressures.

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(4) CompressionRing.Asstatedinparagraph3b(2)(a)onpage21,thepurposeofthecompressionringistomaintainagastightsealbetweenpistonandcylinder,andtoholdthepressurefromthepowerstrokeinthecombustionchamber.Therearemanydifferentcrosssectionalshapesofpistonringsavailable(figure21).

FIGURE21.TYPESOFCOMPRESSIONRINGS.

Thevariousshapesofringsallservetopreloadtheringsothatitsloweredgepressesagainstthecylinderwall.Asshowninfigure22onthefollowingpage,thisservesthefollowingfunctions:

(a) Thepressurefromthepowerstrokewillforcetheupperedgeoftheringintocontactwiththecylinderwall,formingagoodseal.

(b) Asthepistonmovesdownward,theloweredgeoftheringscrapesanyoilthatworkspasttheoilcontrolringsfromthecylinderwalls.

(c) Onthecompressionandtheexhauststrokes,theringwillglideovertheoil,increasingthering'slife.

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FIGURE22.OPERATIONOFCOMPRESSIONRINGS.

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FIGURE23.STAGGERINGRINGGAPS.

(5) SecondCompressionRing(figure23).Theprimaryreasonforusingasecondcompressionringistoholdbackanyblowbythatmayhaveoccurredatthetopring.Asignificantamountofthetotalblowbyatthetopringwillbefromtheringgap.Forthisreason,thetopandthesecondcompressionringsareassembledonthepistonwiththeirgaps60offset.

(6) OilControlRings(figure24onthefollowingpage).Theoilcontrolringsservetocontrolthelubricationofthecylinderwalls.Theydothisbyscrapingtheexcessoilfromthecylinderwallsonthedownstroke.Theoilisthenforcedthroughslotsinthepistonringandthepistonringgroovedrainingbackintothecrankcase. Theringsaremadeinmanydifferentconfigurations,fromonepieceunitstomultipieceassemblies.Regardlessoftheconfiguration,alloilcontrolringsworkbasicallyinthesameway.

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FIGURE24.OILCONTROLRINGS.

4. Conclusion

Thistaskdescribedtheoperationofboththetwostrokeandfourstrokegasolineengines.Inthenexttask,theoperationalinformationforthedieselenginewillbediscussed.

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LESSON1

INTERNALCOMBUSTIONENGINES

TASK2. Describe the principles, components, and operation of both the twostrokeandfourstrokedieselengines.

CONDITIONS


STANDARDS

Withinonehour

REFERENCES


1. Introduction

Intask1,thegasolinepistonenginewasdiscussed.Inthistask,theoperationofafourstrokegasolineengineandafourstrokedieselenginewillbecompared.Inaddition,informationwillbeprovidedonthetwostrokedieselengineandthecombustionchambers.

2. GasolineEngineVersusDieselEngine

a. General.Inmanyrespects,thefourstrokecyclegasolineengineandthefourstrokecycledieselengineareverysimilar.Theybothfollowanoperatingcycleconsistingofintake,compression,power,andexhauststrokes.Theyalsosharethesamesystemforintakeandexhaustvalves.Thecomponentpartsofadieselengineareshownin(figure25).Themaindifferencesbetweengasolineenginesanddieselenginesfollow:

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(1) Inadieselenginethefuelandairmixtureisignitedbytheheatgeneratedbythecompressionstroke,versustheuseofasparkignitionsysteminagasolineengine.Thedieselenginethereforeneedsnoignitionsystem.Forthisreason,thegasolineengineisreferredtoasasparkignitionengineandadieselengineisreferredtoasacompressionignitionengine.

(2) Inadieselenginethefuelandairmixtureiscompressedtoaboutonetwentiethofitsoriginalvolume. Incontrast,thefuelandairmixtureinagasolineengineiscompressedtoaboutoneeighthofitsoriginalvolume. Thedieselenginemustcompressthemixturethistightlytogenerateenoughheattoignitethefuelandairmixture.Thecontrastbetweenthetwoenginesisshowninfigure26onthefollowingpage.

FIGURE25.THEFOURSTROKECYCLEDIESEL.

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(3) Thegasolineenginemixesthefuelandairbeforeitreachesthecombustionchamber.Adieselenginetakesinonlyairthroughtheintakeport.Fuelisputintothecombustionchamberdirectlythroughaninjectionsystem.Theairandfuelthenmixinthecombustionchamber. Thisisillustratedinfigure27onthefollowingpage.

(4) Theenginespeedandthepoweroutputofadieselenginearecontrolledbythequantityoffueladmittedtothecombustionchamber.The

FIGURE26.COMPARISONOFDIESELANDGASOLINEENGINECOMPRESSIONSTROKES.

29


amountofairisconstant.Thiscontrastswiththegasolineenginewherethespeedandpoweroutputareregulatedbylimitingtheairenteringtheengine. Thiscomparisonisillustratedinfigure28onthefollowingpage.

FIGURE27.COMPARISONOFDIESELANDGASOLINEENGINEINTAKESTROKES.

b. Operation.

(1) Intake(figure29,viewA,onpage32).Thepistonisattopdeadcenteratthebeginningoftheintakestroke.Asthepistonmovesdownward,theintakevalveopens.Thedownwardmovementofthepistondrawsairintothecylinder.Asthepiston reaches bottom dead center, the intake valve closes, ending the intakestroke.

(2) Compression(figure29,viewB).Thepistonisatbottomdeadcenteratthebeginningofthecompressionstroke.Thepistonmovesupward,

30


FIGURE28.COMPARISONOFGASOLINEANDDIESELENGINEREGULATIONOFPOWER.

compressingtheair.Asthepistonreachestopdeadcenter,thecompressionstrokeends.

(3) Power (figure29,viewC,onthefollowingpage). Thepistonbeginsthepowerstrokeattopdeadcenter. Atthistime,airiscompressedintheuppercylindertoasmuchas500psi(3448kPa). Thetremendouspressureintheuppercylinderbringsthetemperatureofthecompressedairtoapproximately1000F(538C).Thepowerstrokethenbeginswiththeinjectionofafuelchargeintotheengine. Theheatofcompressionignitesthefuelasitisinjected. Theexpandingforceoftheburninggasespushesthepistondownward,providingpowertothecrankshaft. Thepowergeneratedinadieselengineiscontinuousthroughoutthepowerstroke.Thiscontrastswithagasolineengine,whichhasapowerstrokewithrapidcombustioninthebeginningandlittleornocombustionattheend.

(4) Exhaust(figure29,viewD).Asthepistonreachesbottomdeadcenteronthepowerstroke,thepowerstrokeendsandtheexhauststrokebegins. Theexhaustvalveopensandthepistonpushesthe

31


burntgasoutthroughtheexhaustport.Asthepistonreachestopdeadcenter,theexhaustvalveclosesandtheintakevalveopens.Theengineisthenreadytobeginanotheroperatingcycle.

FIGURE29.FOURSTROKECYCLEDIESEL.

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c. Advantages.

(1) Thedieselengineismuchmoreefficientthanagasolineengineduetothemuchtightercompressionofthefuelandairmixture.Thedieselengineproducestremendouslowspeedpower,andgetsmuchgreaterfuelmileagethanitsgasolinecounterpart.Thismakestheengineverysuitableforlargetrucks.

(2) Thedieselenginerequiresnoignitiontuneupsbecausethereisnoignitionsystem.

(3) Becausedieselfuelisofanoilyconsistency andislessvolatilethangasoline,itisnotaslikelytoexplodeinacollision.

d. Disadvantages.

(1) The diesel engine must be made very heavy to have enough strength towithstandthetightercompressionofthefuelandairmixture.

(2) Thedieselengineisverynoisy.

(3) Dieselfuelcreatesalargeamountoffumes.

(4) Becausedieselfuelisnotveryvolatile,coldweatherstartingisdifficult.

(5) A diesel engine operates well only in lowspeed ranges in relation togasolineengines.Thiscreatesproblemswhenusingtheminpassengercars,whichrequireawidespeedrange.

e. Usage.Dieselenginesarewidelyusedinalltypesofheavytrucks,trains,andboats.Inrecentyears,moreattentionhasbeenfocusedonusingdieselsinpassengercars.

f. MultifuelEngine(figure30onthefollowingpage).Themultifuelengineisbasicallyafourstrokecycledieselenginewiththecapabilityofoperatingonawidevarietyoffueloilswithoutadjustmentormodification.Thefuelinjectionsystemisequippedwithadevicecalledafueldensitycompensator.Itsjobistovarytheamountoffuel,keepingthepoweroutputconstantregardlessofthefuelbeingused. Themultifuelengineusesasphericalcombustionchambertoaidinthoroughmixing,completecombustion,andminimizedknocks.

33


FIGURE30.MULTIFUELENGINE.

3. TwoStrokeCycleDiesel

a. General.Thetwostrokecyclediesel(figure31onthefollowingpage)isahybridenginesharingoperatingprinciplesofbothatwostrokecyclegasolineengineandafourstrokecycledieselengine.Themajorfeaturesoftheengineareasfollows:

(1) Itcompletesanoperatingcycleeverytwopistonstrokesoreverycrankshaftrevolution.Likeatwostrokecyclegasolineengine,itprovidesapowerstrokeeverytimethepistonmovesdownward.

(2) Itisacompressionignitionengine,makingitatruedieselengine.

(3) Itusesanexhaustvalveontopofthecombustionchamberasinafourstrokecycledieselengine. Intakeportsarecutintothecylinderwallasinatwostrokecyclegasolineengine.

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FIGURE31.THETWOSTROKECYCLEDIESELENGINE.

(4) Itmixesitsfuelandairinthecombustionchamberasinafourstrokecycledieselengine.Theairentersthroughtheintakeportsandthefuelisinjectedintothecombustionchamberbythefuelinjectionsystem.

(5) Theairsupplytotheengineisconstantwhilethespeedandpoweroutputoftheengineisregulatedbycontrollingthequantityoffuelinjectedintothecombustionchamber.

(6) Unlikeanyoftheotherenginetypes,thetwostrokecycledieselenginemusthaveasuperchargertoforcetheintakeairintotheuppercylinder. ThemostcommontypeusedistheRootes.

b. Operation(figure32onthefollowingpage).

(1) Scavenging. Scavengingbeginswiththepistonatbottomdeadcenter. Theintakeportsareuncoveredinthecylinderwallandtheexhaustvalveopens.Airisforcedintotheuppercylinderbythesupercharger.Astheairisforcedin,theburntgasesfromthepreviousoperatingcycleareforcedout.

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FIGURE32.THETWOSTROKEDIESELCYCLE.

(2) Compression. Asthepistonmovestowardtopdeadcenter,itcoverstheintakeports.Theexhaustvalveclosesatthispointsealingtheuppercylinder.Asthepistoncontinuesupward,theairinthecylinderistightlycompressed.Asinthefourstrokecyclediesel,atremendousamountofheatisgeneratedbythecompression.

36


(3) Power.Asthepistonreachestopdeadcenter,thecompressionstrokeends.Fuelisinjectedatthispoint.Theintenseheatofcompressioncausesthefueltoignite.Theburningfuelpushesthepistondown,givingpowertothecrankshaft.Thepowerstrokeendswhenthepistongetsdowntothepointwheretheintakeportsareuncovered.Ataboutthispoint,theexhaustvalveopensandscavengingbeginsagain.

c. Advantages.Thetwostrokecycledieselenginehasalloftheadvantagesthatafourstrokecycleenginehasoveragasolineengine,plusthefollowing:

(1) Becauseitisatwostrokecycleengine,itwillrunsmootherthanitsfourstrokecyclecounterpart. Thisisbecausethereisapowerstrokegeneratedforeverycrankshaftrevolution.

(2) Thetwostrokecycledieselhasalesscomplicatedvalvetrainbecauseitdoesnotuseintakevalves.

d. Disadvantages.

(1) Thetwostrokecycleenginemustuseasuperchargertoforceintheintakeairandpushouttheburntexhaustgases. Thisisbecausethemovementofthepistonisnotsuchthatitwillaccomplishthisnaturally.Thesuperchargerusesenginepowertooperate.

(2) The two stroke cycle diesel uses either two or four exhaust valves percylinder,whichcomplicatesthevalvemechanism.

(3) Aswiththetwostrokecyclegasolineengine,thedieselcounterpartwillnotproducetwiceasmuchpowerasafourstrokecycleengine,eventhoughitproducestwiceasmanypowerstrokes.Bystudyingfigure33onthefollowingpage,itcanbeseenthatthepowerstrokeoccupiesonlyaportionofthedownstrokeofthepistoninatwostrokecyclediesel. Inafourstrokecyclediesel,thepowerstrokelastsfromtopdeadcentertobottomdeadcenter.

e. Usage.Thetwostrokecycledieselisusedinmostofthesameapplicationsasthefourstrokecyclediesel.

37


FIGURE33.COMPARISONOFTWOANDFOURSTROKECYCLEDIESELPOWERSTROKELENGTHS.

4. CombustionChamberDesign

a. General. The fuel injected into the combustion chamber must be mixedthoroughly with the compressed air and be distributed as evenly as possiblethroughoutthechamberiftheengineistofunctionatmaximumdriveability.Thewelldesigneddieselengineusesacombustionchamberthatisdesignedfortheengine'sintendedusage. Theinjectorsusedintheengineshouldcomplimentthecombustion chamber. The combustion chambers described in the followingsubparagraphsarethemostcommonandcovervirtuallyallofthedesignsthatareusedincurrentautomotiveapplications.

b. OpenChamber (figure34onthefollowingpage). Theopenchamberisthesimplest form of chamber. It is suitable for slowspeed, four stroke cycleengines,andisusedwidelyintwostrokecycledieselengines. Intheopenchamber,thefuelisinjecteddirectlyintothespaceatthetopofthecylinder.Thecombustionspace,formedbythetopofthepistonandthecylinderhead,isusuallyshapedtoprovideaswirlingactionoftheairasthepistoncomesuponthecompressionstroke.

38


Therearenospecialpockets,cells,orpassagestoaidthemixingofthefuelandair. Thistypeofchamberrequiresahigherinjectionpressureandagreaterdegreeoffuelatomizationthanisrequiredbyothercombustionchamberstoobtainanacceptableleveloffuelmixing. Thischamberdesignisverysusceptibletoignitionlag.

FIGURE34.OPENCOMBUSTIONCHAMBER.

c. PrecombustionChamber (figure35onthefollowingpage). Theprecombustionchamberisanauxiliarychamberatthetopofthecylinder.Itisconnectedtothemain combustion chamber by a restricted throat or passage. The precombustionchamberconditionsthefuelforfinalcombustioninthecylinder.Ahollowedoutportionofthepistontopcausesturbulenceinthemaincombustionchamberasthefuel enters from the precombustion chamber to aid in mixing with air. Thefollowingstepsoccurduringthecombustionprocess:

(1) During the compression stroke of the engine, air is forced into theprecompressionchamberand,becausetheairiscompressed,itishot. Atthebeginningofinjection,theprecombustionchambercontainsadefinitevolumeofair.

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FIGURE35.PRECOMBUSTIONCHAMBER.

(2) Astheinjectionbegins,combustionbeginsintheprecombustionchamber.Theburningofthefuel,combinedwiththerestrictedpassagetothemaincombustionchamber,createsatremendousamountofpressureinthechamber.Thepressureandtheinitialcombustioncauseasuperheatedfuelchargetoenterthemaincombustionchamberatatremendousvelocity.

(3) Theenteringmixturehitsthehollowedoutpistontop,creatingturbulenceinthechambertoensurecompletemixingofthefuelchargewiththeair.Thismixingensures even and complete combustion. This chamber design will providesatisfactory performance with low fuel injector pressures and coarse spraypatterns,becausealargeamountofvaporizationtakesplaceinthecombustionchamber.Thischamberalsoisnotverysusceptibletoignitionlag,makingitmoresuitableforhighspeedapplications.

d. TurbulenceChamber(figure36onthefollowingpage).Theturbulencechamberis similar in appearance to the precombustion chamber, but its function isdifferent.Thereisverylittleclearancebetweenthetopofthepistonandthehead,sothatahighpercentageoftheairbetweenthepistonandthecylinderheadisforcedintothe

40


turbulence chamber during the compression stroke. The chamber usually isspherical,andtheopeningthroughwhichtheairmustpassbecomessmallerasthepistonreachesthetopofthestroke,therebyincreasingthevelocityoftheairinthechamber. Thisturbulencespeedisapproximately60timescrankshaftspeed.Thefuelinjectionistimedtooccurwhentheturbulenceinthechamberisthegreatest.Thisensuresathoroughmixingofthefuelandtheair,withtheresultthatthegreaterpartofcombustiontakesplaceintheturbulencechamberitself.Thepressurecreatedbytheexpansionoftheburninggasesistheforcethatdrivesthepistondownwardonthepowerstroke.

FIGURE36.TURBULENCECHAMBER.

e. SphericalCombustionChamber(figure37onthefollowingpage).Thesphericalcombustionchamberisprincipallydesignedforuseinthemultifuelengine. Thechamberconsistsofabasicopentypechamberwithasphericalshapedreliefinthetopofthepistonhead. Thechamberworksinconjunctionwithastrategicallypositionedinjectorandanintake portthatproducesaswirlingeffectontheintakeairasitentersthechamber.Operationofthechamberisasfollows:

41


FIGURE37.SPHERICALCHAMBER.

(1) Astheairentersthecombustionchamber,aswirleffectisintroducedtoitbytheshapeoftheintakeport(figure37,viewA).

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(2) Duringthecompressionstroke,theswirlingmotionoftheaircontinuesasthetemperatureinthechamberincreases(figure37,viewB,onthepreviouspage).

(3) Asthefuelisinjected,approximately95percentofitisdepositedontheheadofthepiston;theremaindermixeswiththeairinthesphericalcombustionchamber(figure37,viewC).

(4) Ascombustionbegins,themainportionofthefuelissweptoffthepistonheadbythehighvelocityswirlthatwascreatedbytheintakeandthecompressionstrokes. Asthefuelissweptoffthehead,itburnsthroughthepowerstroke,maintainingevencombustionandeliminatingdetonation(figure37,viewDandE).

6. Conclusion

This concludes the explanation of the gasoline and diesel internal combustionengines.Inthenextlesson,operationalinformationonthesubsystemsofinternalcombustionengineswillbediscussed.

43

PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 1/PE 1

PRACTICALEXERCISE1

1. Instructions

Readthescenarioandrespondtotherequirementsthatfollowthescenario.

2. Scenario

SSGFredrickhasbeenattendinganArmyNCOdevelopmentcourseforfourweeks.Thisweekthesubjecthasbeeninternalcombustionengines,whichheunderstandscompletely.Oneofhisclassmates,SSGOlson,isnotverysureaboutthissubjectandisnervousabouttheexamwhichiscomingupintwodays.

SSGOlsonasksSSGFredrickifhewouldmindhelpinghimstudyfortheexam.SSGFredrickagreestohelpanddecidesthatthebestwaytoprepareSSGOlsonfortheexamistogivehimapretest.

3.Requirement

BelowisalistofquestionsthatSSGFredrickfeelswillgiveSSGOlsonageneralunderstandingofinternalcombustionengines.

a. Iftheengineisgoingtooperate,thefuelandairmixturemustbefedintothe__________________________.

b. What component opens and closes the intake and exhaust valves in a timedsequence?

c. Howmanyrevolutionsdoesthecrankshaftrotatewhenthepistonmovesfromtopdeadcentertobottomdeadcenter?

d. Whatarethefourstrokesofoperationinapistonengine?

e. Whatsystemignitesthefuelandairmixtureinthecombustionchamberattheprecisemomentneededtomaketheenginerun?

f. Whattypeofengineisusedalmostexclusivelyinverysmallequipmentbecauseitislightweightandabletorunatveryhighspeedsduetotheabsenceofamechanicalvalvetrain?

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g. Whatpistonringkeepstheengine'slubricationoilfromgettingintothecombustionchamber?

h. Whyisadieselenginereferredtoasacompressionignitionengine?

i. Whyisthedieselenginemuchmoreefficientthanthegasolineengine?

j. Thetwostrokecycleenginemustuseasuperchargertoforceintheintakeairandpushouttheburntexhaustgasesbecause_______________________________________________________________________________________________________________________.

k. What type of combustion chamber is designed principally for use in themultifuelengine?

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LESSON1.PRACTICALEXERCISEANSWERS

1. Requirement

a. combustionchamber.

b. Thevalvetrain.

c. Exactlyonehalf.

d. Intake,compression,power,andexhaust.

e. Theignitionsystem.

f. Thetwostrokecycleengine.

g. Theoilcontrolring.

h. Thefuelandairmixtureisignitedbytheheatgeneratedbythecompressionstroke.

i. Thedieselengineismuchmoreefficientthanthegasolineengineduetothemuchtightercompressionofthefuelandairmixture.

j. themovementofthepistonisnotsuchthatitwillaccomplishthisnaturallyandthesuperchargerusesenginepowertorunit.

k. Thesphericalcombustionchamber.

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LESSON2

INTERNALCOMBUSTIONENGINESUBSYSTEMS

TASK1. Describe the principles, components, and operation of theturbochargers,intake,andexhaustsystems.

CONDITIONS


STANDARDS

Withinonehour

REFERENCES


1. Introduction

InLessonone,theprinciples,components,andoperationofdieselandgasolineenginesweredescribed.Theknowledgeobtainedfromthisinformationcanbeusedtounderstandthesubsystemsoftheinternalcombustionenginesdiscussedwithinthislesson.Thesesubsystemsare:intakesystem;exhaustsystem;turbochargers;lubricationsystem;andcoolingsystem.

Thistaskwillintroduceanddescribetheintakesystem,turbochargers,andexhaustsystem.

2. IntakeSystem

a. Purpose.Todrawairfromanoutsidesourceintotheenginecylinder.

b. IntakeManifold(figure38onthefollowingpage).Theintakemanifoldshould:

47


FIGURE38.TYPICALINTAKEMANIFOLD.

(1) Deliverthemixturetothecylindersinequalquantitiesandproportions.Thisisimportantforsmoothengineperformance. Thelengthsofthepassagesshouldbeasnearequalaspossibletodistributethemixtureequally. Inagasolineengine,thereisaseriesofpipesorpassagesthroughwhichthefuelairmixturefromthecarburetorisdirectedtotheenginecylindersontheintakestroke.Thedieselenginedoesnothaveacarburetorsotheairisdirectedintothecylinderandthefuelisinjectedtomixwiththeair.

(2) Helptokeepthevaporizedmixturefromcondensingbeforeitreachesthecombustionchamber.Becausetheidealmixtureshouldbevaporizedcompletelyasitentersthecombustionchamber,thisisveryimportant.Toreducethecondensingofthemixture,themanifoldpassages shouldbedesignedwithsmoothwalls andaminimumofbendsthatcollectfuel.Smoothflowingintakemanifoldpassagesalsoincreasevolumetricefficiency,themethodofmeasuringanenginesabilitytotakeinitsintakemixture.

(3) Aidinthevaporizationofthemixture. Todothis,theintakemanifoldshouldprovideacontrolledsystemofheating,asdescribedinparagraph3conpage53. This systemmustheat themixture enough toaidin vaporization withoutheatingtothepointofsignificantlyreducingvolumetricefficiency.

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FIGURE39.RAMINDUCTIONMANIFOLD.

c. RamInduction(figure39).Intakemanifoldscanbedesignedtoprovideoptimumperformanceforagivenenginespeedrangebyvaryingthelengthofthepassages.Theinertiaofthemovingintakemixturewillcauseittobouncebackandforthinthemanifoldpassagefromtheendofoneintakestroketothebeginningofthenextintakestroke.Ifthepassageistheproperlengthsothatthenextintakestrokeisjustbeginningasthemixtureisrebounding,theinertiaofthemixturewillcauseit to ramitselfinto thecylinder. Thiswillincrease thevolumetricefficiencyoftheengineinthedesignatedspeedrange.Itshouldbenotedthattherammanifoldwillservenousefulpurposeoutsideofitsdesignatedspeedrange.

d. Heating the Mixture. As stated in paragraph 2b(3) on page 48, providingcontrolledheatfortheincomingmixtureisveryimportantforgoodperformance.Theheatingofthemixturemaybeaccomplishedbyoneorbothofthefollowingmethods:

(1) Directingaportionoftheexhaustthroughapassageintheintakemanifold(figure40onthefollowingpage). Theheatfromtheexhaustwilltransferandheatthemixture.Theamountofexhaustthatisdivertedintotheintakemanifoldheatpassageiscontrolledbythemanifoldheatcontrolvalve.

49


FIGURE40.EXHAUSTHEATEDINTAKEMANIFOLD.

(2) Directingtheenginecoolant,whichisladenwithengineheat,throughtheintakemanifoldonitswaytotheradiator(figure41onthefollowingpage).

e. Intake Manifold Flame Heater System (figure 42 on page 52). Engines areequippedwithaflametypemanifoldheaterforheatingtheinductionairduringcoldweatherstartingandwarmupoperations.

(1) Operation.Theflameheaterassemblyiscomposedofahousing,sparkplug,flowcontrolnozzle,andtwosolenoidcontrolvalves.Thesparkplugisenergizedbytheflameheaterignitionunit.Thenozzlespraysfuelunderpressureintotheintakemanifoldelbowassembly.Thefuelvaporisignitedbythesparkplugandburnsintheintakemanifold,heatingtheairbeforeitentersthecombustionchambers.

(2) Because this system uses fuel from the fuel tank of the vehicle, itscomponentsmustbecompatiblewithallapprovedfuelswhenthesystemisusedwithamultifuelengine.

(a) Theflamefuelpumpassembly isarotarytype,drivenbyanenclosedelectricmotor.Thefuelpumpreceivesfuelfromthevehiclefueltankthroughthevehicle'ssupplypumpanddeliversittothespraynozzle.ThepumpisenergizedbyanONOFFswitchlocatedontheinstrumentpanel.

50


FIGURE41.WATERHEATEDINTAKEMANIFOLD.

(b) Theintakemanifoldflameheatersystemhasafiltertoremoveimpuritiesfromthefuelbeforeitreachesthenozzle.

(c) Twofuelsolenoidvalvesareusedintheflameheatersystem.Thevalvesareenergized(open)whenevertheflameheatersystemisactivated. Thevalvesensurethatfuelisdeliveredonlywhenthesystemisoperating.Theystopfuelflowtheinstanttheengineorheatersystemisshutdown.

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FIGURE42.MANIFOLDFLAMEHEATERSYSTEM.

3. ExhaustSystem

a. Purpose(figure43onthefollowingpage).Thewasteproductsofcombustionarecarriedfromtheenginetotherearofthevehiclebytheexhaustsystem,wheretheyareexpelledtotheatmosphere. Theexhaustsystemalsoservestolessenenginenoise.

52


FIGURE43.TYPICALEXHAUSTSYSTEM.

b. ExhaustManifold (figure44 onthefollowingpage). Theexhaustmanifoldconnectsalloftheenginecylinderstotheexhaustsystemandisusuallymadeofcastiron.Iftheexhaustmanifoldisformedproperly,itcancreateascavengingactionthatwillcauseallofthecylinderstohelpeachothergetridofexhaustgases. Backpressure(theforcethatthepistonsmustexerttopushouttheexhaustgases)canbereducedbymakingthemanifoldwithsmoothwallsandwithoutsharpbends. Allofthesefactorsaretakenintoconsiderationwhentheexhaustmanifoldisdesigned,andthebestpossiblemanifoldismanufacturedtofitintotheconfinesoftheenginecompartment.

c. ManifoldHeatControlValve(figure45onpage55).Avalveisplacedintheexhaustmanifoldonsomegasolineenginestodeflectexhaustgasestowardahotspotintheintakemanifolduntiltheenginereachesoperatingtemperature.Thisvalveisaflatmetalplatethatisthesameshapeastheopeningitcontrols.Itpivotsonashaftandisoperatedbyathermostaticcoilspring.Thespringpullsthevalveclosedagainstacounterweightbeforewarmup.Thespringexpandsastheenginewarmsupandthecounterweightpullsthevalveopen.

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FIGURE44.EXHAUSTMANIFOLD.

d. Muffler(figure46onpage56).Themufflerreducestheacousticpressureofexhaustgasestodischargethemtotheatmospherewithaminimumofnoise. Themufflerisusuallylocatedatapointaboutmidwayinthevehicle,withtheexhaustpipebetweenitandtheexhaustmanifold,andthetailpipeleadingfromittotherearofthevehicle.Theinletandtheoutletofthemufflerareusuallyslightlylargerthantheirconnectingpipessothatitmaybehookedupbyslippingoverthem.Themuffleristhensecuredtotheexhaustpipeandthetailpipebyclamps.Atypicalmufflerhasseveralconcentricchamberswithopeningsbetweenthem.Thegasenterstheinnerchamberandexpandsasitworksitswaythroughaseriesofholesin the otherchambersand finallyto the atmosphere. Mufflers mustbedesigned to quiet exhaust noise while creating a minimum of back pressure.Excessivebackpressurecouldcauselossofenginepower,economy,andalsocauseoverheating. Exhaust system components are usually made of steel. They areusuallycoatedwithaluminumorzinctoretardcorrosion.

54


Stainlesssteelisalsousedinexhaustsystems,inlimitedquantitiesduetoitshighcost.Astainlesssteelexhaustsystemwilllastindefinitely.

FIGURE45.MANIFOLDHEATCONTROLVALVE.

4. Turbochargers

Turbochargingisamethodofincreasingenginevolumetricefficiencybyforcingtheairfuelmixtureintotheintakeratherthanmerelyallowingthepistonstodrawitinnaturally.Aturbocharger(figure47onpage57)usestheforceoftheengineexhauststreamtoforcetheairfuelmixtureintotheengine. Itconsistsofahousing

55


containingtwo chambers. Onechamber containsa turbine thatisspun ashotexhaustgasesaredirectedagainstit.Theturbineshaftdrivesanimpellerthatislocatedintheotherchamber.Thespinningimpellerdrawsanairfuelmixturefromthecarburetorandforcesitintotheengine.Becausethevolumeofexhaustgasesincreaseswithengineloadandspeed,theturbochargerspeedwillincreaseproportionally,keepingthemanifoldpressurefairlyuniform.Adeviceknownasawastegateisinstalledonturbochargedenginestocontrolmanifoldpressure.Itisavalvewhich,whenopen,allowsengineexhausttobypasstheturbochargerturbine,effectivelyreducingintakepressure.Thewastegatevalveisoperatedbyadiaphragmthatisoperatedbymanifoldpressure. Thediaphragmwillopenthewastegatevalvewhenevermanifoldpressurereachesthedesiredmaximum.

FIGURE46.MUFFLER.

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FIGURE47.TURBOCHARGER.

5. Conclusion

Thistaskdescribedthreesubsystemsofaninternalcombustionengine. Thenexttaskwilldefinethelubricationsystem.

57


LESSON2


TASK2. Describetheprinciples,components,andoperationofthelubricationsystem.

CONDITIONS


STANDARDS

Withinonehour

REFERENCES


1. Introduction

Thelubricationsystem(figure48onthefollowingpage)inanautomotiveenginesuppliesaconstantsupplyofoiltoallmovingparts. Thisconstantsupplyoffreshoilisimportanttominimizewear,flushbearingsurfacesclean,andremovethelocalizedheatthatdevelopsbetweenmovingpartsasaresultoffriction.Inaddition,theoilthatissuppliedtothecylinderwallshelpsthepistonringsmakeagoodsealtoreduceblowby.

This task will describe the characteristics, components, and function of aninternalcombustionenginelubricationsystem.

2. PurposeofLubrication

a. OilasaLubricant.Theprimaryfunctionofengineoilistoreducefrictionbetweenmovingparts(lubricate).Friction,inadditiontowastingenginepower,createsdestructiveheatandrapidwearofparts.Thegreaterthefrictionpresentbetweenmovingparts,thegreatertheenergyrequiredtoovercomethatfriction.The

58


increaseinenergyaddstotheamountofheatgenerated,causingmovingpartsthataredeprivedofoiltomelt,fuse,andseizeafteraveryshortperiodofengineoperation.Theeffectivenessofamodernlubricationsystemmakespossibletheuseoffrictiontypebearingsinanengine. Frictionbetweenthepistonsandthecylinderwallsissevere,makingeffectivelubricationofthisareaimperative.Lubricationoftheconnectingrodandmainbearingsiscrucialbecauseoftheheavyloadsthatareplacedonthem. Therearemanyotherlesscriticalenginepartsthatalsoneedaconstantsupplyofoil,suchasthecamshaft,valvestems,rockerarms,andtimingchains.

FIGURE48.TYPICALENGINELUBRICATIONSYSTEM.

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b. OilasaCoolant.Engineoilcirculatedthroughouttheenginealsoservestoremoveheatfromthefrictionpoints. Theoilcirculatesthroughtheengineanddrainstothesump. Theheatpickedupbytheoilwhileitiscirculatedisreducedbyanairflowaroundtheoutsideofthesump.Insomeinstances,wherethesumpisnotexposedtoaflowofair,itisnecessarytoaddanoilcoolingunitthattransferstheheatfromtheoiltotheenginecoolingsystem.

3. EngineOils

a. General.Mineraloilisusedinmostinternalcombustionengines.Engineoilsgenerally are classified according to their performance qualities and theirthickness.

(1) HowOilLubricates(figure49onthefollowingpage).

(a) Everymovingpartoftheengineisdesignedtohaveaspecificclearancefrom its adjacent surface. As oil is fed to the surface it forms a film,preventingthemovingpartfromactuallytouchingthesurface.

(b) Asapartrotates,thefilmofoilactsasaseriesofrollers.Becausethemovingpartsdonotactuallytoucheachother,frictionisreducedgreatly.

(c) Itisimportantthatsufficientclearancebeallowedbetweenthepartandthebearing; otherwise thefilmmight betoo thin. Thiswould allow contactbetweentheparts,causingthebearingtowearorburnup.

(d) Italsoisimportantthattheclearancenotbetoolargebetweenrotatingpartsandtheirbearings.Thisistrueparticularlywithheavilyloadedbearingslikethosefoundontheconnectingrods.Theheavyloadscouldthencausetheoilfilmtobesqueezedout,resultinginbearingfailure.

(2) OilContamination(figure50onpage62).Oildoesnotwearout,butitdoesbecomecontaminated.Whenforeignmatterentersthroughtheairintake,someofitwillpassbythepistonringsandenterthecrankcase.Thisdirt,combinedwithforeignmatterenteringthroughthecrankcase

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breatherpipe,mixeswiththeoil,andwhenforcedintothebearings,greatlyaccelerateswear. Water,oneoftheproductsofcombustion,willseepbythepistonringsassteamandcondenseinthecrankcase.Thewaterinthecrankcasethen will emulsify with the oil to form a thick sludge. Products of fuelcombustionwillmixwiththeoilastheyenterthecrankcasethroughblowby.Theoil,whenmixedwiththecontaminants,losesitslubricatingqualitiesandbecomesacidic.Engineoilmustbechangedperiodicallytopreventcontaminatedoilfromallowingexcessivewearandcausingetchingofbearings. Oilcontaminationiscontrolledinthefollowingways:

FIGURE49.HOWOILLUBRICATES.

(a) Controlenginetemperature;ahotterrunningengineburnsitsfuelmorecompletelyandevaporatesthewaterproducedwithinitbeforeanyappreciableoilcontaminationoccurs.

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FIGURE50.SOURCESOFOILCONTAMINATION.

(b) Theuseofoilfiltersremovesdirtparticlesfromtheoilbeforeitreachesthebearings,minimizingwear.

(c) An adequate crankcase ventilation system will purge the crankcase ofblowbyfumeseffectivelybeforealargeamountofcontaminantscansixwiththeoil.

(d) Theuseofairintakefilterstrapforeignmaterialandkeepitfromenteringtheengine.

(3) OilDilution (refertofigure50). Engineoilthinsoutwhenmixedwithgasoline,causingadramaticdropinitslubricatingqualities.Someofthecausesofoildilutionarethefollowing:

(a) Excessiveuseofahandchokecausesanoverrichmixtureandanabundanceofunburnedfueltoleakpastthepistonringsintothecrankcase. Thesameconditioncanoccuronvehiclesequipped

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withanimproperlyadjustedormalfunctioningautomaticchokesystem.

(b) Avehiclewithadefectiveignitionsystemcancauseoildilutionduetomisfiringsparkplugs.Wheneverasparkplugmisfires,mostoftheunburnedfuelwillbeforcedintotheexhaustsystembutasmallportionofitwillalsopasstheringsandenterthecrankcase.

(c) Anenginewithamalfunctioningthermostat,oranenginethatisoperatedforshortdurationsonly,willneverreachasufficienttemperaturetoburnthefuelcompletely.Asmallamountofoildilutionoccursinallenginesfrominitialstartupthroughwarmup. When,however,theenginereachesitsoperationalrange(180F(82.2C]to200F[93.3C]),thisconditioniscorrectedastheexcessgasolinevaporizesinthecrankcaseandiscarriedoffbythecrankcaseventilationsystem.

b. AmericanPetroleumInstitute(API)RatingSystem.

(1) General. TheAPIsystemforratingoilclassifiesoilaccordingtoitsperformancecharacteristics.Thehigherratedoilscontainadditivesthatprovidemaximumprotectionagainstrust,corrosion,wear,oiloxidation,andthickeningathigh temperatures. There are currently six oil classifications for gasolineengines(SA,SB,SC,SD,SE,andSF)andfourclassificationsfordieselengines(CA,CB,CC,andCD).Thehigherthealphadesignation,thehigheristhequalityoftheoil.

(2) APIDesignations.

(a) SA(UtilityGasolineEngines).Adequateforutilityenginessubjectedtolight loads, moderate speeds, and clean conditions. SArated oils generallycontainnoadditives.

(b) SB(MinimumDutyGasAutomotive). Adequateforautomotiveuse underfavorable conditions (light loads, low speeds, and moderate temperatures) withrelatively short oil change intervals. SBrated oils generally offer minimalprotectiontotheengineagainstbearingscuffing,corrosion,andoiloxidation.

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(c) SC. Meets all automotive manufacturers' requirements for vehiclesmanufacturedfrom1964to1967.

(d) SD. Meets all automotive manufacturers' requirements for vehiclesmanufacturedfrom1968to1970.SDoiloffersadditionalprotectionoverSCoils,necessarywiththeintroductionofemissioncontrols.

(e) SE. Meets all automotive manufacturers' requirements for vehiclesmanufacturedfrom1971to1979.Stricteremissionrequirementsduringtheseyearscreatedtheneedforthisoiltoprovideprotection.

(f) SF. Meets all automotive manufacturers' requirements for vehiclesmanufacturedafter1980. SFoilisdesignedtomeetthedemandsofthesmall,highrevvingenginesmadenecessarybythetrendtowardsmallervehicles. AnSFoilcanbeusedinallautomotivevehicles. APIserviceratingshaverelatedmilitaryspecificationdesignations.

c. ViscosityandViscosityMeasurement.

(1) General.Theviscosityofanoilreferstoitsresistancetoflow.Whenoilis hot, it will flow more rapidly than when it is cold. In cold weather,therefore,oilshouldbethin(lowviscosity)topermiteasyflow.Inhotweather,oilshouldbeheavy(highviscosity)topermitittoretainitsfilmstrength.Theambienttemperatureinwhichavehicleoperatesdetermineswhetheranengineoilofhighorlowviscosityshouldbeused.If,forexample,toothinanoilwereusedinhotweather,consumptionwouldbehighbecauseitwouldleakpastthepistonringseasily.Thelubricatingfilmwouldnotbeheavyenoughtotakeupbearingclearancesorpreventbearingscuffing.Incoldweather,heavyoilwouldnotgiveadequate lubrication because its flow would be sluggish; some parts might notreceiveoilatall.

(2) ViscosityMeasurement. OilsaregradedaccordingtotheirviscositybyaseriesofSocietyofAutomotiveEngineers(SAE)numbers.TheviscosityoftheoilwillincreaseprogressivelywiththeSAEnumber.AnSAE5oilwouldbeverylight(lowviscosity)andanSAE90oilwouldbe

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veryheavy(highviscosity). TheviscosityoftheoilusedingasolineenginesgenerallyrangesfromSAE5(arcticuse)toSAE60(desertuse). ItshouldbenotedthattheSAEnumberoftheoilhasnothingtodowiththequalityoftheoil.Theviscositynumberoftheoilisdeterminedbyheatingtheoiltoapredeterminedtemperature and allowing it to flow through a precisely sized orifice whilemeasuringtherateofflow.Thefasteranoilflows,thelowertheviscosity.Thetestingdeviceiscalledaviscosimeter. AnyoilthatmeetsSAElowtemperaturerequirementswillbefollowedbytheletterW.AnexamplewouldbeSAE10W.

(3) Multiweight Oils. Multiweight oils are manufactured to be used in mostclimatesbecausetheymeettherequirementsofalightoilincoldtemperaturesandaheavyoilinhottemperatures.Theirviscosityratingwillcontaintwonumbers.

Anexampleofthiswouldbe10W30.Anoilwithaviscosityratingof10W30wouldbeasthinasa10Wweightoilat0F(17.7C)andasthickasa30weightoilat210F(99C).

(4) DetergentOils.Detergentoilscontainadditivesthathelpkeeptheenginecleanbypreventingtheformationofsludgeandgum. AllSEandSFoilsaredetergentoils.

4. OilPumps.

a. General. Oilpumpsaremountedeitherinsideoroutsideofthecrankcase,dependingonthedesignoftheengine.Theyareusuallymountedsothattheycanbedrivenbyawormorspiralgeardirectlyfromthecamshaft.Oilpumpsgenerallyareofthegearortherotortype.

b. RotorTypeOilPump (figure51onthefollowingpage). Therotoroilpumpmakesuseofaninnerrotorwithlobesthatmatchsimilarlyshapeddepressionsintheouterrotor.Figure51showsthemannerinwhichthetworotorsfittogether.Theinnerrotorisoffcenterfromtheouterrotor.Theinnerrotorisdrivenand,asitrotates,itcarriestheouterrotoraroundwithit.Theouterrotorfloatsfreelyinthepumpbody. Asthetworotorsturn,theopeningsbetweenthemarefilledwithoil.Thisoilisthenforcedoutfrombetweentherotorsastheinnerrotorlobesenterthe

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FIGURE51.ROTARYPUMPS.

openingsintheouterlobes.Thisactionismuchlikethatinthegeartypepump.

c. GearTypeOilPump(figure52onthefollowingpage).Geartypeoilpumpshaveaprimarygearthatisdrivenbyanexternalmember,andwhichdrivesacompaniongear.Oilisforcedintothepumpcavity,aroundeachgear,andouttheothersideintotheoilpassages.Thepressureisderivedfromtheactionofthemeshedgearteeth,whichpreventsoilfrompassingbetweenthegears,forcingitaroundtheoutsideofeachgearinstead.Theoilpumpincorporatesapressurereliefvalve,aspringloadedballthatriseswhenthedesiredpressureisreached,allowingtheexcessoiltobedeliveredtotheinletsideofthepump.

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FIGURE52.GEARTYPEPUMPS.

FIGURE53.OILPICKUPANDSTRAINER.

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d. OilStrainerandPickup(figure53onthepreviouspage).MostmanufacturersofinlineandVtypeenginesplaceatleastoneoilstrainerorscreeninthelubricationsystem. Thescreenisusuallyafinemeshbronzescreen,locatedintheoilsumpontheendoftheoilpickuptube. Theoilpickuptubeisthenthreadeddirectlyintothepumpinletormayattachtothepumpbyaboltedflange.Afixedtypestrainer,liketheonedescribed,islocatedsothataconstantsupplyofoilwillbeassured.Someautomotiveenginesuseapickupthatishingedfromtheoilpump.Thepickupisdesignedtofloatontopoftheoil,thuspreventingsedimentfrombeingdrawnintotheoilingsystem.

e. OilFilters.

(1) General (figure54onthefollowingpage).Theoilfilterremovesmostoftheimpuritiesthathavebeenpickedupbytheoilasitiscirculatedthroughtheengine. Thefilterismountedoutsidetheengineandisdesignedtobereadilyreplaceable.

(2) Filter Configurations (figure 54). There are two basic filter elementconfigurations:thecartridgetypeandthesealedcamtype.

(a) Thecartridgetypefilterelementfitsintoapermanentmetalcontainer.Oilispumpedunderpressureintothecontainerwhereitpassesfromtheoutsideofthefilterelementtothecenter. Fromheretheoilexitsthecontainer. Theelementischangedeasilybyremovingthecoverfromthecontainerwhenthistypeoffilterisused.

(b) The sealed camtype filter element is completely selfcontained,consistingofanintegralmetalcontainerandfilterelement.Oilispumpedintothecontainerontheoutsideofthefilterelement.Theoilthenpassesthroughthefiltermediumtothecenteroftheelementwhereitexitsthecontainer.Thistypeoffilterisscrewedontoitsbaseandisremovedbyspinningitoff.

(3) FilterMediumMaterials(figure55onpage70).

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FIGURE54.OILFILTERS.

(a) Cottonwasteorresintreatedpaperarethetwomostpopularautomotivefiltermediums.Theyareheldinplacebysandwichingthembetweentwoperforatedmetalsheets.

(b) Someheavydutyapplicationsuselayersofmetalthatarethinlyspacedapart.Foreignmatterisstrainedoutastheoilpassesbetweenthemetallayers.

(4) FilterSystemConfigurations. Therearetwofiltersystemconfigurations,the fullflow system and the bypass system. Operation of each system is asfollows:

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FIGURE55.OILFILTERINGMEDIUMS.

(a) Thefullflow(figure56,viewA,onthefollowingpage)isthemostpopularincurrentautomotivedesign.Alloilinafullflowsystemiscirculatedthroughthefilterbeforeitreachestheengine.Whenafullflowsystemisused,itisnecessarytoincorporateabypassvalveintheoilfiltertoallowtheoiltopassthroughtheelementintheeventitbecomesclogged.Thiswillpreventtheoilsupplyfrombeingcutofftotheengine.

(b) Thebypasssystem(figure56,viewB)divertsonlyasmallquantityoftheoileachtimeitiscirculatedandreturnsitdirectlytotheoilpanafteritisfiltered.Thistypeofsystemdoesnotfiltertheoilbeforeitissenttotheengine.

f. OilCoolers.

(1) Purpose. Some automotive configurations do not allow sufficient airflowaroundthecrankcasetoallowtheoiltodissipateheat.Enginesinheavydutyanddesertusemustbeabletodissipatemoreheatfromtheiroilthannormalairflowcanaccomplish.Anoilcoolerisinstalledinallofthesecases.

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FIGURE56.FILTERSYSTEMCONFIGURATIONS.

(2) OilTemperatureRegulator (figure57,viewA,onthefollowingpage). Theoiltemperatureregulatorisusedtopreventtheoiltemperaturefromrisingtoohighinhotweather,andtoassistinraisingthetemperatureduringcoldstartsinwinterweather.Theregulatormakesuseofthe

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liquidinthecoolingsystem.Itprovidesamorepositivemeansofcontrollingoiltemperaturethandoescoolingbyradiationofheatfromtheoilpanwells.

FIGURE57.OILTEMPERATUREREGULATORANDOILCOOLER.

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Theregulatorunitismadeupofacoreandahousing.Thecorethroughwhichtheoilcirculatesisofcellularorbellowsconstruction,builttoexposeasmuchoilaspossibletothecoolantthatcirculatesthroughthehousing.Theregulatorisattachedto the enginesothat theoil will flowthroughthe regulatorafterpassingthroughthepump.Theoilleavestheregulatoreitherheatedorcooled,dependingonthetemperatureofthecoolant,andisthencirculatedthroughtheengine.

(3) OilCooler (figure57,viewB,onthepreviouspage). Thetypesofoilcoolers used with combat vehicles consist of a radiator through which air iscirculatedbymovementofthevehicle,orbyacoolingfan.Oilfromtheengineiscirculatedthroughthisradiatorandbacktothesumporsupplytank. Inthissystem,theradiatorwillactonlytocooltheoil.Itwillnotheatoilinacoldengine.

FIGURE58.OILLEVELINDICATOR.

g. OilLevelIndicator (figure58). Theoillevelindicatorisusuallyofabayonettype. Itconsistsofasmallrod,knownasadipstick,thatextendsthroughatubeintothecrankcase.Itismarkedtoshowwhenthecrankcaseisfullor,ifitislow,howmuchoilisneeded. Readingsaretakenbypullingthedipstickoutandnotingtheoillevelwhichitindicates.

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h. PressureRegulator(figure59).Theoilpumpwillproducepressuresingreatexcesstothosenecessary. Thisexcesspressure,ifuncontrolled,wouldcauseexcessoilconsumptionduetofloodedcylinderwallsandleakagethroughoilseals.Aspringloadedregulatorvalveisinstalledinthelubricationsystemtocontrolpumppressure. Thevalvewillopenasthepressurereachesthevaluethatisdeterminedbythespring,causingexcessoiltobedivertedbacktothecrankcase.

FIGURE59.OILPRESSUREREGULATOR.

5.TypesofLubricationSystems

a. SplashSystem(figure60onthefollowingpage).Thesplashlubricationsystemisnolongerusedinautomotiveengines,thoughitisusedinsmallequipmentengines.Inasplashlubricationsystem,dippersontheconnectingrodsentertheoilinthecrankcasewitheachcrankshaftrevolution,thussplashingtheoil.Astheoilisthrownupward,itfindsitswayintothevariousengineparts. Apassageisdrilledfromthedippertothebearingineachconnectingrodtoensurelubrication.Thissystemistoouncertainformodernautomotiveapplications.Onereasonisthatthelevelofoilinthecrankcasewillgreatlyvarytheamountoflubricationreceivedbytheengine;ahighlevelresultsinexcesslubricationandoilconsumptionandevenaslightlylowlevelresultsininadequatelubrication.

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FIGURE60.SPLASHTYPELUBRICATIONSYSTEM.

FIGURE61.COMBINATIONSPLASHANDFORCEFEEDLUBRICATIONSYSTEM.

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b. CombinationSplashandForceFeedSystem(figure61onthepreviouspage).Inthecombinationsystem,oilisdeliveredtosomepartsbymeansofsplashandtootherpartsthroughoilpassages,underpressurefromapumpinthecrankcase.Themainandthecamshaftbearingsareusuallytheitemsthatareforcefedwhiletheconnectingrodsarefittedwithdippersthatsupplyoiltotherestoftheenginebysplash.Someconfigurationsusesmalltroughsundereachconnectingrod,keptfullbysmallnozzlesthatdeliveroilunderpressurefromtheoilpump.Theseoilnozzlesdeliveranincreasinglyheavystreamasspeedincreases. Atveryhighspeeds,theseoilstreamsarepowerfulenoughtostrikethedippersdirectly.Thiscausesamuchheaviersplashsothatadequatelubricationofthepistonsandtheconnectingrodbearingsisprovidedathigherspeeds.Ifacombinationsystemisusedonanoverheadvalveengine,theuppervalvetrainislubricatedbypressurefromtheoilpump.

FIGURE62.FORCEFEEDLUBRICATIONSYSTEM.

c. ForceFeed Lubrication System (figure 62). A somewhat more completepressurizationoflubricationisachievedintheforcefeedlubricationsystem.Oilisforcedbytheoilpumpfromthecrankcasetothemainbearingsandthe

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camshaftbearings.Unlikethecombinationsystem,theconnectingrodbearingsarealso fed oil under pressure from the pump. Oil passages are drilled in thecrankshaftinordertoleadoiltotheconnectingrodbearings. Thepassagesdeliveroilfromthemainbearingjournalstotherodbearingjournals.Insomeengines,theseopeningsareholesthatindex(lineup)onceforeverycrankshaftrevolution. Inotherengines,thereareannulargroovesinthemainbearingsthrough which oil can feed constantly into the hole in the crankshaft. Thepressurizedoilthatlubricatestheconnectingrodbearingsgoesontolubricatethepistonsandwallsbysquirtingoutthroughstrategicallydrilledholes.Thislubrication system is used in virtually all engines that are equipped withsemifloatingpistonpins.

FIGURE63.FULLFORCEFEEDLUBRICATIONSYSTEM.

d. Full ForceFeed Lubrication System (figure 63). In the full forcefeedlubricationsystem,allofthebearingsmentionedinparagraph5bonpage76arelubricated by oil under pressure. This includes main bearings, rod bearings,camshaftbearings,andthecompletevalvemechanism.Inaddition,thefullforcefeedlubricationsystemprovideslubricationunderpressuretothepistons

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andthepistonpins. Thisisaccomplishedbyholesdrilledthelengthoftheconnectingrod,creatinganoilpassagefromtheconnectingrodbearingtothepistonpinbearing.Thispassagenotonlyfeedsthepistonpinbearings,butalsoprovides lubrication for the pistons and cylinder walls. A full forcefeedlubricationsystemisusedinvirtuallyallcurrentautomotiveenginesthatareequippedwithfullfloatingpistonpins.

6. Conclusion

Thelubricationsystemplaysanimportantroleinkeepinganinternalcombustionengineoperational. Thecoolingsystem,describedinthenexttask,isanothersubsystemessentialforproperoperationofaninternalcombustionengine.

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LESSON2


TASK3. Describe the principles, components, and operation of the coolingsystem.

CONDITIONS


STANDARDS

Withinonehour

REFERENCES


1. Introduction

All internal combustion engines are equipped with some type of cooling systembecauseofthehightemperaturesgeneratedduringoperation.Hightemperaturesarenecessarytoproducethehighgaspressuresthatactontheheadofthepiston.Powercannotbeproducedefficientlywithouthightemperatures.However,itisnotpossible to use all of the heat of combustion without harmful results. Thetemperatureinthecombustionchamberduringtheburningofthefueliswellabovethemeltingpointofiron.Therefore,ifnothingisdonetocooltheengineduringoperation,valveswillburnandwarp,lubricatingoilwillbreakdown,andbearingsandpistonswilloverheat,resultinginengineseizure.

Thistaskwilldescribetheprinciples,components,andoperationofthecoolingsystem.

2. CoolingEssentials

a. CoolingMediums.

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(1) Liquid. Liquidisthemostpopularcoolantinautomotiveuse. Aliquidcoolingsystemprovidesthemostpositivecoolingandisbestformaintaininganevenenginetemperature.

(2) Air.Aircoolingismostpracticalforsmallvehiclesandequipmentbecausenoradiatororhosesarerequired.Aircoolinggenerallywillnotbeusedwhereverwatercoolingispractical.Thisisbecauseaircooledenginesdonotrunateventemperaturesandrequireextensiveuseofaluminumtodissipateheat.

b. OtherSourcesofEngineCooling.Thereareothersourcesofheatdissipationfortheengineinadditiontothecoolingsystem.

(1) Theexhaustsystemdissipatesassuch,ifnotmore,heatthanthecoolingsystem,althoughthatisnotitspurpose.

(2) Theengineoil,asstatedinparagraph1onpage58,removesheatfromtheengineanddissipatesittotheairfromthesump.

(3) Thefuelprovidessomeenginecoolingthroughvaporization.

(4) Ameasurableamountofheatisdissipatedtotheairthroughradiationfromtheengine.

3. LiquidCoolingSystems

a. FlowofCoolant (figure64onthefollowingpage). Asimpleliquidcooledcoolingsystemconsistsofaradiator,coolantpump,piping,fan,thermostat,andasystemofjacketsandpassagesinthecylinderheadandcylinderblockthroughwhichthecoolantcirculates.Someenginesareequippedwithawaterdistributiontubeinsidethecoolingpassages;thesedirectadditionalcoolanttothepointswherethetemperaturesarehighest.Coolingoftheenginepartsisaccomplishedbykeeping the coolant circulating and in contact with the metal surfaces to becooled. Thepumpdrawsthecoolantfromthebottomoftheradiator,forcesitthroughthejacketsandpassages,andejectsitintotheuppertankonthetopoftheradiator.Thecoolantthenpassesthroughasetoftubestothebottomoftheradiatorfromwhichthecoolingcyclebeginsagain. Theradiatorissituatedinfrontofafandriveneitherbythewaterpumporbyanelectric

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motor.Thefanensuresanairflowthroughtheradiatorattimeswhenthereisnovehiclemotion.Itshouldbenotedthatthedownwardflowofcoolantthroughtheradiatorcreateswhatisknownasathermosiphonaction.Thissimplymeansthatasthecoolantisheatedinthejacketsoftheengine,itexpands.Asitexpands,itbecomeslessdenseandthereforelighter.Thiscausesittoflowoutofthetopoutletoftheengineandintothetoptankoftheradiator. Asthecoolantiscooledintheradiator,itagainbecomesmoredenseandheavier.Thiscausesthecoolanttosettletothebottomtankoftheradiator.Theheatingintheengineandthecoolingintheradiator,therefore,createsanaturalcirculationthataidsthewaterpump.Theearliestautomotivevehiclesreliedonthermosiphonactionandusednowaterpump.

FIGURE64.LIQUIDCOOLEDSYSTEM.

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b. EngineWaterJackets(figure64onthepreviouspage).Thewaterpassagesinthecylinderblockandcylinderheadformtheenginewaterjacket.Inthemajorityofcylinderblocks,thewaterjacketcompletelysurroundsallcylindersalongtheirfulllength.Withinthejacket,narrowpassagesareprovidedbetweencylindersforcoolantcirculation. Insomeengineconfigurations,however,thecylinderboresareattachedtoeachotherandacoolantpassagewayisnotprovidedbetweenbores.Anengineofthisdesignoftenisreferredtoashavingsiamesecylinders.Thistypeofenginetendstooperatewithcylindertemperaturesslightlyhigherbetweenthebores,andslightlycoolerwherewaterjacketscomeincontactwiththebores.Inaddition,allenginesareprovidedwithwaterpassagesaroundtheexhaustvalveseat.Thisprovidescoolingforthevalvewhenitcomesincontactwiththeseat.

Inthecylinderhead,thewaterjacketcoversthecombustionchambersatthetopofthecylindersandcontainswaterpassagesaroundthevalveseatswhenthesearelocated in the head. The coolant flows from the cylinder block up into thecylinderheadthroughpassagescalledwatertransferports. Atightsealattheportsbetweenthecylinderheadandblockisveryimportant.Thewatertightsealattheports,aswellasthegastightsealatthecombustionchamberopenings,isobtainedwithonelargegasketcalledthecylinderheadgasket.

c. Coolants.Waterisbyfarthemostpopularcoolantforliquidcooledengines.It is plentiful, inexpensive, and its boiling point is within the efficientoperationaltemperaturerangeoftheengine.

(1) Antifreeze Protection. When a vehicle is operated in areas where thetemperaturefallsbelow32F(0C),anantifreezesolutionmustbeaddedifwaterisusedasthecoolant. Themostcommonantifreezeisethyleneglycol. Otherantifreezesthatarelittleusedareglycerin,methylalcohol,andethylalcohol.Ethylandmethylalcoholprovideadequateprotectionasanantifreezewhenusedinsufficientquantities.Themainobjectiontotheseliquids,however,isthattheyevaporatebelowtheoperatingtemperatureofmodernautomotiveengines,makingthemimpractical. Glycerinoffersthesamedegreeofprotectionasalcohol,butdoesnotevaporateinuse,hasahigh

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boilingpoint,isnoncorrosive,hasnoodor,andgivescompleteprotectionagainstfreezing in normal use. Ethylene glycol gives a maximum protection againstfreezingto65F(53.8C)whenitismixedtoasolutionof60percentwith40percentwater.

Iftheproportionsofethyleneglycolareraisedinthesolution,itwillresultinahigherfreezingpointforthesolution,consequentlyhavinglessprotection.Ifa100percentsolutionofethyleneglycolwereused,itsfreezingpointwouldbemuchbelowthatofwater.Otherantifreezesolutions,however,donotshowthisincreaseoffreezingpointwithincreasingconcentration. Twogoodexamplesaremethylalcoholwhichfreezesat144F(97.8C),andethylalcoholwhichfreezesat174F(114.3C).

(2) CorrosionResistance.Thecoolingsystemmustbefreeofrustandscaleinordertomaintainitsefficiency.Theuseofinhibitorsorrustpreventativeswillreduce or prevent corrosion and the formation of scale. Inhibitors are notcleaners and, therefore, will not remove rust and scale that have alreadyaccumulated.Mostcommerciallyavailableantifreezesolutionscontaininhibitors.Ifwateraloneisusedasacoolant,aninhibitorshouldbeadded.

d. Radiators(figure65onthefollowingpage).Radiatorsforautomotivevehiclesusingliquidcoolingsystemsconsist oftwotankswithaheatexchangingcorebetweenthem.Theuppertankcontainsanoutsidepipecalledaninlet.Thefillerneckgenerallyisplacedonthetopoftheuppertank;attachedtothisfillerneckisanoutlettotheoverflowpipe.Thelowertankalsocontainsanoutsidepipethatservesastheradiator'soutlet.Operationoftheradiatorisasfollows:

(1) Theuppertankcollectsincomingcoolantand,throughtheuseofaninternalbaffle,distributesitacrossthetopofthecore.

(2) Thecoreismadeofnumerousrowsofsmallverticaltubesthatconnecttheupperandlowerradiatortanks. Sandwichedbetweentherowsoftubesarethinsheetmetalfins.Asthecoolantpassesthroughthetubestothelowertank,thefinsconducttheheatawayfromitanddissipateit

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FIGURE65.ENGINERADIATORCONSTRUCTION.

into the atmosphere. The dissipation of the heat from the fins is aided bydirectingaconstantairflowbetweenthetubesandoverthefins.

(3) Thelowertankcollectsthecoolantfromthecoreanddischargesittotheenginethroughtheoutletpipe.

(4) Theoverflowpipeprovidesanopeningfromtheradiatorforescapeofcoolantorsteamifpressureinthesystemexceedstheregulatedmaximum.Thispreventsruptureofcoolingsystemcomponents.

Someradiatorsaredesignedwiththeirtanksonthesidesinaverticalposition.They are connected by a core that contains horizontal tubes. This radiatorconfigurationiscalledacrossflowradiatorandoperatesinthesamemannerastheconventionalverticalflowradiator,thoughitshouldbenotedthatthereisnothermosiphoneffectwithacrossflowradiator.

e. WaterPump(figure66onthefollowingpage).Allmoderncoolingsystemshavewaterpumpsto

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circulatethecoolant.Thepump,usuallylocatedonthefrontsideoftheengineblock,receivescoolantfromthelowertankandforcesitthroughthewaterjacketintotheupperradiatortank. Thepumpisofacentrifugaltypeandhasanimpellerwithbladesthatforcecoolantoutwardastheimpellerrotates. Itisusually driven by the engine crankshaft through a Vbelt. Advantages of acentrifugalpumpasawaterpumparethatitisinexpensive, circulatesgreatquantitiesofcoolantforitssize,andisnotcloggedbysmallamountsofforeignmatter.Anotheradvantageisthatacentrifugalpumppermitsalimitedamountofthermosiphonactionaftertheengineisshutdowntohelppreventboilover. Thepumphousingusuallyiscastfromironoraluminum.Theimpellercanbemadeofiron,aluminum,orplastic.Itridesonashaftthatissupportedinthehousingonasealeddoublerowballbearing.Thepumpshaftalsohasaspringloadedsealtopreventcoolantleakage.

FIGURE66.WATERPUMPCONSTRUCTION.

f. FanandShrouding(referbacktofigure64onpage81).Thefanpullsalargevolumeofairthroughtheradiatorcoresothatengineheatcanbedissipatedeffectively.Inmostcases,thefan

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worksinanenclosurecalledashroudtoensuremaximumefficiencyofthefan.Therearetwomethodsofdrivingafan.Onemethodistoattachittotheendofthewaterpumpshaft.Theothermethod,becomingincreasinglypopular,istouseanelectricmotor.

(1) ThermostaticallyControlledEngineDrivenFan. Somevehiclesareequippedwithasevenbladefan,particularlythoseforheavydutyuseorthosewithairconditioning.Thisfanconfigurationwillmovetremendousamountsofairthroughtheradiatortoprovideextracoolingcapacity.Theproblemwithahighcapacityfanisthatitcancausetheradiatorcoretofreezeincoldweather. Otherproblemsassociatedwithahighoutputfanareexcessivepowerconsumptionandnoiseat highway speeds. Most sevenbladefans are drivenbythe waterpumpthroughaviscous(fluid)clutch(figure67)tocorrecttheseconditions.Thefanclutchisdesignedtolimitthefanspeedbasedonthetemperatureoftheairdrawnthrough the radiator. The clutch will provide controlled slippage if thetemperatureofthisairisbelowapresetminimum.Afanclutchalsowillcontrolthenoiseandthepowerconsumptionofthefanbylimitingitsspeedtoapresetmaximum.

(2) Electrically Motorized Fan (figure 68 on the following page). Theelectricallymotorizedfanisgainingpopu

us army principles of internal combustion engines

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