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Internal combustion engines Systems

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UNIT NO:-IV

UNIT NO:-IVENGINE SYSTEMS & COMPONENTS

Requirements of Ignition system:-Supply Minimum energyInitiate the combustionEstablishment of Flame under all operating.Ignition System for S.I. Engines

Produce high voltage (30,000V) spark across spark plugDistribute high voltage spark to each spark plug in correct sequenceTime the spark so it occurs as piston is nearing top dead centerVary spark timing with load, speed, and other conditions

IGNITION FUNCTION

Battery-CoilMagnetoElectronic a. Transistorized Coil Ignition(TCI) b. Capacitor Discharge Ignition (CDI)Types of Ignition Systems

BATTERYIGNITION SWITCHIGNITION COILSWITCHING DEVICE SPARK PLUGIGNITION SYSTEM WIRES

BATTERY IGNITION SYSTEM COMPONENTS

Battery supplies power to entire systemIgnition Switch turns engine on or offCoil transforms voltageSwitching device triggers ignition coilSpark Plug and wires distribute spark

The Ignition System (Reasons for)To make a spark inside the engines cylinders which is strong enough to ignite the air/fuel mixture. In normal atmospheric conditions only about 600 Volts are needed to make a spark, however in the pressurised environment of the engines cylinders, 8000 to 30,000 volts will be required.To ensure the spark happens at the right time for each cylinder going through the 4 Stroke Cycle i.e. just at the end of the compression stroke. The ignition system also has to change the time at which the spark occurs (the ignition timing) depending on engine operating conditions e.g. how fast the engine is turning.

System ComponentsThe Battery provides the electricity (12 Volts) for the Low Tension LT or Primary side of the ignition system.The Ignition Switch, this turns the system on and off by controlling the Low Tension/Primary side of the ignition system.The Ignition Coil, this transforms or boosts the Batteries 12 Volts up to a voltage strong enough to produce a spark in the engines cylinders. The Coil is connected to both the Low Tension (12 Volts) and High Tension HT (8000 to 30000 Volts) sides of the ignition system. The High Tension HT leads, these allow the spark from the coil to travel to the spark plugs Please note, the H.T Spark is produced when the coils primary windings are turned offThe Distributor, this sends the HT spark form the ignition coil to the correct cylinder . It may also turn the coil on and off so that the coil can produce the HT spark at the correct time when required by the engine to start the air/fuel mixture burning. Inside the distributor in modern systems, a electronic device, called a pick up (pulse generator) and control module turns the coils primary winding on and off. The distributor may also change the ignition timing depending on engine requirements, it is driven by the engine at half crankshaft speed.The Spark Plugs, these screw into the combustion chamber and have two electrodes with a set gap between them which the spark has to jump to ignite the air/fuel mixture.

The Ignition Coil

The ignition coil is switched off and by an electronic switch (pulse generator) and control unit as shown. When the coil is switched on,electricty(current) flows from the battery, through the ignition switch, through the several hundred turns of the thick coil primary windings, through the electronic switch and finally back to the battery. This sets up a magnetic field in the coil itself. When the primary current is switched off by the electronic switch, the magnetic field collapses through the several thousand turns of the fine secondary windings, producing a very high voltage (electrical pressure) in the form of a spark which is delivered by the H.T. circuit to the spark plug.

Block diagram of the Ignition System

Ignition Components - The Ignition CoilCoil contains primary and secondary windings, separated by a ceramic insulator.The windings are immersed in oil and contained within a slotted iron sheath.The core is made from soft iron laminations to produce a strong magnetic field and minimize losses.The coil has 3 terminals for circuit connection.- terminal+ terminal

Secondary terminal

Casing

Insulator

Primary windingsSecondary windingsInsulation paper

Laminated iron core

Ignition Coil Operation300 turns18000 turnsSpark plug gap

Primary turned on, current flows through primary winding, building up strong magnetic field, known as Dwell Period.Primary turned off, no current flows (suddenly stopped), producing a BACK EMF in the primary winding.Secondary EMF = turns ratio x primary BACK EMF= 18000/300 x 200 = 12000V.

BACK EMF = 200VControl unitBatteryPrimary windingSoft iron core

Secondary winding

The collapsing magnetic field induces an EMF in the secondary winding.

Distributor

It distributes the coils high voltage to the plugs wires. Actuates the on/off cycle of current flow through the ignition coil primary windings.

Ignition Components - The Distributor CapMade from hard plastic and fabricated with locating lugs or hollows to ensure accurate placement.The cap has moulded HT terminals, which contain brass terminals for electrical connections to the spark plugs and the coil.The terminals protrude inside the cap, the centre terminal is a spring loaded carbon button, the outer terminals are small brass contacts.Spark plug HT terminal

Coil HT terminal

Brass contact

Spring loaded contact

Securing / Locating lug

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Ignition Components - The Rotor ArmThe rotor arm fits onto the distributor shaft, using a locating slot and a spring to ensure correct fitment.Distributes high voltage from the centre button to each outer terminal.The rotor arm should be periodically replaced, as contacts wear and corrode. Made from hard plastic and contains brass contacts for voltage transferral.

End contactCentre contact

Locating slot and spring

The centre contact may be spring loaded.

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Distributor OperationThe distributor shaft turns the rotor arm, transferring voltage from the centre terminal in the cap, to each outer terminal.The distributor shaft cam rotates, a signal is generated which is usedTo switch on and off the primaryIgnition coil windingsA distributor contains vacuum and centrifugal advance mechanisms to change ignition timing.This action determines when a spark will occur and is known as ignition timing.This action determines which spark plug will receive a spark.Rotor armOuter terminalCentre terminal

From coil

To spark plugs

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Ignition Components - Spark Plug HT LeadsLeads carry voltage from the distributor to each spark plug, constructed using a conductor and an insulator.The conductor is made from carbon.The conductor has an internal resistance to reduce radio frequency interference (RFI).The terminals at the ends of the leads are protected by rubber boots, which keep out moisture and dirt.Rubber bootTerminal

Silicone jacket

Distributorend

Spark plug end

The insulator is made from silicone.

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AdvantagesIt is cheapProvides better spark at low speedsVariation of ignition timing can be achieved easilyMaintenance is negligible except for batteryCan be effectively used in cars and buses

DisadvantagesHeavy due to battery & Occupies more spaceProvides weaker spark as speed increases as primary vtg decreases The engine cannot be started if battery is dischargedMaintenance Cost of battery is high

IGNITION SYSTEM Magneto SystemIgnition SwitchDistribution

Contact Breaker

CoilMagneto

Condenser

Power GenerationSpark GenerationMagneto UnitRotor Arm

IGNITION SYSTEM Dynamo/Alternator SystemDynamo/ AlternatorDistributor

Contact Breaker

CoilIgnition SwitchSecondary Windings

Primary Windings

Condenser

Battery

AdvantagesLess MaintenanceLight in weight & occupies less spaceProvides High Intensity Spark at high speedsSystem is reliableUsed in Two wheelers, racing cars, AeroplanesDisadvantagesSince wiring carry high voltage current there is strong possibility of leakage causing misfiring.At low speeds it develops poor Quality of SparkRequires extensive shielding to prevent leakage of high voltage current.

Ignition SwitchCoil Packs

IGNITION SYSTEM Electronic Systems

Control UnitTiming Sensor

Timing Disc

Engine Speed Sensing Unit

Alternator

Battery

1.Electronic Ignition Systema.Transistorized discharge ignition systemb.Capacitor Discharge Ignition

Ignition Components - The Spark PlugCentre electrode receives coil voltage.Insulator prevents high voltages from shorting to ground.Terminal

Gap

Insulator

GasketThreadMetal shellHex

Centre electrodeSide electrode

Spark plug is located in the cylinder head, it ignites the air and fuel mixture.Has centre and side electrodes, with an air gap between them.High voltage jumps the air gap, creating a spark.Side electrode is grounded.

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Spark Plug

Two or four stroke operationCompression RatioCylinder head designLocation of sparkMix. DensitySpeed of engineCooling arrangementOctane value of fuelParameters responsible

Types of Spark Plug

Ignition TimingA spark has to occur at precisely the right moment in an engine cycle, to ignite a pressurized mixture of air and fuel.In theory, a spark should occur just after TDC (top dead centre), as a piston starts downward on its power stroke.Therefore, a spark has to occur before a piston reaches top dead centre (BTDC).In practice, the air and fuel mixture has to burn for a finite length of time.This is known as ignition timing.Ignition timing changes with engine speed and load requirements.

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Ignition Timing Change Due to Engine SpeedIgnition timing has to advance, because as an engine speeds up, the point at which combustion occurs, comes around quicker.An ignition system must be able to advance and retard the spark, with regard to engine speed.Early DI systems use a centrifugal advance mechanism.Electronic and distributor less ignition systems calculate spark advance from sensor information.

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Ignition Timing Change Due to Engine LoadEngine load and the mix of air and fuel affect burn time.A long burn time is required when the mixture is lean and engine load is light.A short burn time is required when the mixture is rich and engine load is heavy.An ignition system must be able to advance and retard the spark, with regard to engine load.Early DI systems use a vacuum advance mechanism.Electronic and distributorless ignition systems calculate spark advance from sensor information.

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At low speed, the springs hold the cam plate in base ignition timing position.Centrifugal Advance MechanismsTwo springs, two flyweights and a cam plate make up the advance system.Cam

StopBase plate

Flyweight

Tension spring

Cam plate

Rubbing block

PivotAssume distributor cam is rotating counter-clockwise.As speed increases, the cam plate turns counter-clockwise as the flyweights overcome spring pressure.The end stop limits cam plate travel.The point at which the rubbing block engages the cam has moved forward (spark occurs earlier).thrown outAngle of advance

meets cam lobe earlierat rest

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Vacuum Advance MechanismsAt idle speed, intake air and the spring keep the diaphragm in its home position.Advance angleThrottle plate at idle

Low load and speedAssume distributor cam is rotating counter-clockwise.The system consists of a diaphragm and a spring inside a sealed housing, with a link to the base plate.At low speed, vacuum pulls the diaphragm against the spring, turning the base plate clockwise.The pick up coil rotates clockwise and timing is advanced.The system does not function during low vacuum conditions (acceleration or full load).VacuumIntake air

Base plateDiaphragmSpringVacuumport

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Ignition Control Module

An electronic switch that turns the ignition coil primary current on/offLOCATIONEngine compartmentOn the side of distributorInside the distributorUnder vehicle dash

Methods of controlling TimingElectronic Advance Sensors input influences the ignition timing.Crank shaft Position Sensor (RPM)

Cam Position Sensor (tells which cylinder is on compression stroke)

Manifold Absolute Pressure (MAP)(engine vacuum and load)

Methods of controlling TimingElectronic Advance Sensors input influences the ignition timing.Intake Air Temperature Sensor

Knock Sensor (Retards timing when pinging or knocking is sensed)

Throttle Position Sensor(TPS)

Engine coolant Temperature

Primary Objectives:(i) To reduce friction between two moving parts so that there is minimum power loss.(ii) To minimize wear and tear of moving parts.2. Secondary objectives:(i) To provide cooling effect.(ii) Act as sealing.(iii) Act as cleaning agent.

LUBRICATION SYSTEM

Should Maintain required oil filmLeave no carbon residuePrevent wear of bearingsLow CostViscosity: It should ensure, hydrodynamic lubrication action should take place.Chemical stability: It should be chemically stable under different temperature conditions. Less tendency of oxidation.Resistance against corrosion : It should be good corrosion resistance agent.occurred in the engine.Physical stability: It should be able to stable under different condition of temperature.Flash point: It should be high to avoid flashing of oil vapors.Should contain no sulphur.Free from dirt & water.

There are following major requirement for a good lubricants.

Solid Lubricants:-Solid Lubricants are used when film lubrication is not possible.Graphite,soap stone, molbdenumPowdered very finely & mixed with oil or WaterSemi-Solid Lubricants:-Where retention of liquid lubricants is not possible and the mating parts are subjected to very high pressureGreases made by mixing oils and thickening agents.Liquid Lubricants:- (a) Animal oils : These are generally obtained from animal fat. But they are not good lubricants because they are easily oxidized and become gummy aftersome time of use.(b) Vegetables oils : These are generally obtained from vegetables like seeds, plants and trees etc. It has same problem like animal oil but has very goodlubricant proportion.(c) Mineral oil: It is generally derived from the petrochemical and it is most widely used in automobile sector because of following properties.(i) Greater chemical stability at higher temperature. (ii) Less reactive with water.(iii) More plentiful and cheaper.(d) Synthetic lubricants : These are made from silicon fluids, polyglycol ethers and aliphatic diester.

Types of Lubricants

The oil additives are added to the lubricating oil to reinforce some propertieswhich is not the natural properties of fluid or lubricating oil. These additive are added according to the property of lubricants.e.g. Phenols, metal salts of thiophosphoric acid and suiphurized waxes etc. Their important function are as follows:(i) Corrosion Inhilitors : Compounds such as metal salt of thiophasphoric acid and suiphurized waxes act as anti agent in the formation of acid which causecorrosion.(ii) Detergents These additions like polymers act as cleaning agent they break the sludge particles into finely divided particles which are easily scavenged throughexhaust port.(iii) Viscosity index improvers These are the addition which prevent minimisingthe decrease of oil viscosity with increase in temperature.

Additives Used

Classification of lubricants is based on their viscosity.SAE has assigned numbers for gradationViscosity is measure of resistance of flow.Units are SUS (saybolt universal seconds) & CentipoisesUsually expressed at two temp:- (-18C & 99C)SAE 5W,10W, 20W,grades are defined in terms of viscosity at -18C SAE 20,30,40,50 grades are defined in terms of viscosity at 99C

Some Points About Oil & Grades

Multi-gradeThe temperature range the oil is exposed to in most vehicles can be wide, ranging from cold temperatures in the winter before the vehicle is started up, to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. A specific oil will have high viscosity when cold and a lower viscosity at the engine's operating temperature. The difference in viscosities for most single-grade oil is too large between the extremes of temperature.The SAE designation for multi-grade oils includes two viscosity grades; for example,10W-30designates a common multi-grade oil with viscosity equal to that of SAE 10W at -18C & SAE 30 for 99C

Provides Ease of starting & short warming period, Extends Battery life.Operates for wider range of tempReduces oil comsumptionReduces carbon deposits

Advantages of Multigrade oils

Mist or ChargeWet SumpSplashSplash & PressureFully PressureDry sump

TYPES OF LUBRICATION SYSTEM

Splash System

SPLASH & PRESSURE SYSTEM

Wet Sump

Working of Wet Sump Lubrication

Dry sump

Air cooling

ENGINE COOLING SYSTEM

(a)Air cooledengines operate satisfactorily in both hot and cold climates.(b) Theseengines can work at higher operating temperatures than their equivalent liquid-cooled counterparts.(c) The working temperature in theseengines is attained rapidly from cold condition. id) Theseengines are marginally lighter than liquid-cooledenginesofsame capacity. (e) Theseengines do not encounter coolant-leakage or freezing problems.

Cool circulating air comes in contact with the exposed and enlarged external surfacesofthe cylinder and head. Direct Air-cooledEngineSystem.Dis-advantages.(a)Thecoolingfans require a relatively large amountofpower to run.(b) Due to the large quantitiesofintake air passing into thecoolingsystem, theenginemay become noisy.(c)Thecoolingfins can vibrate and amplify noise under certain conditions.(d) For proper positioningofthe fins between cylinders, the pitch between cylinder centres has to be greater than in liquid-cooledengines.(e) Each cylinder is required to be cast individually unlike liquid-cooledengines where a rigid mono-block construction is used.(/) To prevent overheatingofthe lubricant, the air-coolingis frequently supplemented by an oil heat exchanger.(g) The presenceofthe guide cowling and baffles around the cylinders may hinder maintenance.Indirect Liquid-cooledEngineSystem.

Thermo-Syphon Cooling

Water cooling

Advantages.(a) Greater temperature-uniformity around the cylinders is achieved in liquid-cooledengines causing less distortion compared with air-cooledengines.(b) The power consumptionofthe coolantpumpand the fan together in liquid-cooledengines is less than thatofthe fan in air-cooledengines.(c) The liquid-cooledenginecylinders are much closer, providing a very rigid and compact unit unlike the air-cooledengine.(d) Both the coolant and the jackets dampen the mechanical noise from theengine.(e) Liquid-cooled units perform heavy-duty work more reliably than air-cooledengines.(f) Hot coolant can readily be circulated for interior heatingofthe vehicle.Disadvantages.(a)Liquid-coolant joints may develop leakage.(b)Care must be taken to avoid freezingofthe coolant.(c) Liquid-cooled units require more time to warm up than the air-cooledengines.(d) The boiling pointofliquid-coolant limits maximum temperatureofoperation, whereas air-cooledengines can operate at slightly higher temperatures.(c) Formationofscale takes place in the coolant passages, and the hoses and radiator tubes deteriorate with time.

The advantages ofthermo-syphoncoolingare :(a)Cheap as no water pump is required.(b)Reliable as there are no moving parts.(c)Circulation of water depends solely onenginetemperature. The hotter theengine, the greater is the circulation.Disadvantages ofthermo-syphoncooling(a) In order to achieve efficient circulation, the radiator top tank must be well above theengine. This needs a high bonnet (b) Cooled water enters theengineat the bottom of the cylinder, where theenginenormally runs fairly cool and it heats up to maximum as it reaches the top of the cylinders. Therefore, it has a reducedcoolingeffect on the hottest part of theengine.(c) Difficult to fit an interior heater successfully without a water pump.(d) Under conditions of very heavy load or in hot climates the water may not circulate as quickly as required.Incorporation of a water pump insures positive water circulation and removes all the disadvantages of thethermo-syphoncoolingprocess.