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  • Internal combustion Engines: Carburetor Fuel injectionInternal combustion Engines: Carburetor, Fuel injection

    Dr. Primal Fernando

    1

    [email protected]: (081) 2393608

    CIvs.SIEnginesg SIenginesdrawfuelandairintothecylinder. Fuelmustbeinjectedintothecylinderatthedesiredtimeof

    b ti i CI icombustioninCIengines. AirintakeisthrottledtotheSIengine nothrottlinginCI

    engines. Compression ratios must be high enough to cause auto ignition Compressionratiosmustbehighenoughtocauseautoignition

    inCIengines(CI:12to24),compressedtopressureabout4Mpaandtemperatureabout800K.

    Upper compression ratio in SI engines is limited by the autoUppercompressionratioinSIenginesislimitedbytheautoignitiontemperature(SI:8to12).

    FlamefrontinSIenginessmoothandcontrolled. CIcombustionisrapidanduncontrolledatthebeginning. ThevalvetiminginbothCIandSIaresimilar.

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    ComparisonofSIandCIEnginesp g

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    TypicalBrakeThermalEfficienciesofCIandSIEngines

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  • 5 6

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    FourStroke&TwostrokeSIEnginesEngines

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  • FourStroke&TwoStrokeCIEnginesg

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    Dieselengine(CI)g ( )

    The liquid fuel jet atomizes into drops and entrains air; Theliquidfueljetatomizesintodropsandentrainsair;evaporatesfuelvapormixeswithairairtemperatureandpressureareabovethefuelsignitionpoint.Afterashortdelay

    t i iti t tautoignitionstarts. Atfullloadairfuelratiois20:1

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    Dieselfuelinjectionsystemconsistsofj y

    1. Injectionpump

    2. Deliverypipes

    3. Fuelinjectornozzles

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    THEDIESELFUELSYSTEM

    InjectionPumpusuallymechanicaldriveB lt d ll t d d h i

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    Beltsandrollersnotgood,usegearsandchains Notespilllinefrominjector,pump,separator

  • Timing setsTiming sets

    Gear setsGear sets Cam and crank rotate in opposite directions Noisy if not free of burrs

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    Helical and spur cut gears

    Timing setsTiming sets

    Timing chainsTiming chains Single and double roller Tensioners

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    FuelInjectionSystemsj y

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    GeneralCharacteristics

    P t i d How does timing vary with load? PumprunsatenginespeedControlsQuantityANDtimingofinjectionMax fuel limited by smoke

    Howdoestimingvarywithload?IgnitiondelayisSHORTER(higherdensity)BUT:Althoughignitiondelayisshorted,ll d d llMaxfuellimitedbysmoke

    limitTimingvarieswithloadandspeed

    stillneedmoreadvancetoensureallfuelisburntduringstroke

    Atmaxloadfuelvarianceamongcylindersshouldbelessthan3%speed

    Timingaccurateto1o crankangle

    yotherwisepowerlimitedbysmokyexhaustofrichestcyl.

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  • Apumpaintsosimple!p p p

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    Valve trainsValve trains

    OHV (overhead valve)Pushrod configurationgMany reciprocating partsHigher valve spring pressure required

    i i d

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    Compact engine size compared to OHC

    Valve trainsValve trains

    OHC (overhead cam)Fewer reciprocating partsReduced valve spring pressure requiredHigher RPM capabilit

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    Higher RPM capabilityCylinder head assemblies are taller

    Valve trainsValve trains

    Cam in headCam-in-headNo pushrodsUse rocker arms

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    Use rocker arms

  • ValveLocations

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    Combustion process: stratified chargeCombustion process: stratified charge

    jet guided wall guided inlet air guided

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    ChargeStratificationg

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    CombustionChamberDesignsg

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  • CombustionChamberDesigng

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    CombustionChamberDesigng

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    CombustionChamberDesigng

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    CombustionChamberDesigng

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  • CombustionChamberDesigng

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    CLASSIFICATIONOFINTERNALCOMBUSTIONENGINES

    CoolingCooling

    1. DirectAircooling

    2. IndirectAircooling(LiquidCooling)

    3. LowHeatRejection(Semiadiabatic)engine.

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    Cooling system operationCooling system operation

    Engine heat is transfered . . . through walls of the combustion chambers through the walls of cylinders

    Coolant flows . . . to upper radiator hose through radiator through radiator to water pump through engine water jacketsthrough engine water jackets through thermostat back to radiator

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    Cooling system operationCooling system operation

    Fans increase air flow through radiator Hydraulic fan clutches Hydraulic fans consume 6 to 8 HP

    El t i f Electric fans

    Coolant (ethylene glycol)Coolant (ethylene glycol) 50/50 mixture increases boiling point to 227F pressurizing system to 15 PSI increases to 265Fp g y

    Coolant (propylene glycol) Less protection at the same temperatures

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    Less protection at the same temperatures Less toxic