UNIT NO:-IV

ENGINE SYSTEMS &

COMPONENTS

Requirements of Ignition system:-

1. Supply Minimum energy2. Initiate the combustion3. Establishment of Flame

under all operating.

Ignition System for S.I. Engines

Produce high voltage (30,000V) spark across spark plug

Distribute high voltage spark to each spark plug in correct sequence

Time the spark so it occurs as piston is nearing top dead center

Vary spark timing with load, speed, and other conditions

IGNITION FUNCTION

1. Battery-Coil2. Magneto3. Electronic a. Transistorized Coil Ignition(TCI) b. Capacitor Discharge Ignition (CDI)

Types of Ignition Systems

BATTERY IGNITION SWITCH IGNITION COIL SWITCHING DEVICE SPARK PLUG IGNITION SYSTEM WIRES

BATTERY IGNITION SYSTEM COMPONENTS

Battery supplies power to entire system Ignition Switch turns engine on or off Coil transforms voltage Switching device triggers ignition coil Spark 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 Components The 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 off

The 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 Coil

Coil 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 windings

Secondary windings

Insulation paper

Laminated iron core

Ignition Coil Operation

300 turns 18000

turns

Spark 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 = 200V

Control unit

Battery

Primary winding

Soft 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 Cap

Made 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

Ignition Components - The Rotor Arm

The 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 contact

Centre contact

Locating slot and spring

The centre contact may be spring loaded.

Distributor Operation

The 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 windings

A 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 terminal

Centre terminal

From coil

To spark plugs

Ignition Components - Spark Plug HT Leads

Leads 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 boot

Terminal

Silicone jacket

Distributorend

Spark plug end

The insulator is made from silicone.

Advantages It is cheap Provides better spark at low speeds Variation of ignition timing can be achieved easily Maintenance is negligible except for battery Can 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 System

Ignition Switch

Distribution

Contact Breaker

Coil

Magneto

Condenser

Power Generation

Spark GenerationMagneto Unit Rotor Arm

IGNITION SYSTEM – Dynamo/Alternator System

Dynamo/ Alternator

Distributor

Contact Breaker

Coil

Ignition Switch

Secondary Windings

Primary Windings

Condenser

Battery

Advantages Less Maintenance Light in weight & occupies less space Provides High Intensity Spark at high speeds System is reliable Used in Two wheelers, racing cars, Aeroplane’s

Disadvantages Since wiring carry high voltage current there is

strong possibility of leakage causing misfiring. At low speeds it develops poor Quality of Spark Requires extensive shielding to prevent leakage

of high voltage current.

Ignition Switch

Coil Packs

IGNITION SYSTEM – Electronic Systems

Control Unit

Timing SensorTiming

Disc

Engine Speed Sensing Unit

Alternator

Battery

1.Electronic Ignition Systema.Transistorized discharge ignition system

b.Capacitor Discharge Ignition

Ignition Components - The Spark Plug

Centre electrode receives coil voltage.

Insulator prevents high voltages from shorting to ground.

Terminal

Gap

Insulator

Gasket

Thread

Metal shell

Hex

Centre electrode

Side 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.

Spark Plug

Two or four stroke operation Compression Ratio Cylinder head design Location of spark Mix. Density Speed of engine Cooling arrangement Octane value of fuel

Parameters 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.

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.

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.

At low speed, the springs hold the cam plate in base ignition timing position.

Centrifugal Advance Mechanisms

Two springs, two flyweights and a cam plate make up the advance system.

Cam

Stop

Base plate

Flyweight

Tension spring

Cam plate

Rubbing block

Pivot

Assume 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 out

Angle of advance

meets cam lobe earlier

at rest

Vacuum Advance Mechanisms

At idle speed, intake air and the spring keep the diaphragm in its ‘home’ position.

Advance angle

Throttle plate at idleLow load and speed

Assume 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).

Vacuum Intake air

Base plate

Diaphragm

Spring

Vacuumport

Ignition Control Module•An electronic switch that turns the ignition coil primary current on/off

LOCATION

•Engine compartment

•On the side of distributor

•Inside the distributor

•Under 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 film Leave no carbon residue Prevent wear of bearings Low Cost Viscosity: 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, molbdenum Powdered very finely & mixed with oil or Water Semi-Solid Lubricants:- Where retention of liquid lubricants is not possible and the mating parts

are subjected to very high pressure Greases 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 after some 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 good lubricant 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 properties which 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 cause corrosion. (ii) Detergents These additions like polymers act as cleaning agent they

break the sludge particles into finely divided particles which are easily scavenged through

exhaust port. (iii) Viscosity index improvers These are the addition which prevent

minimising the decrease of oil viscosity with increase in temperature.

Additives Used

Classification of lubricants is based on their viscosity.

SAE has assigned numbers for gradation Viscosity is measure of resistance of flow. Units are SUS (saybolt universal seconds) &

Centipoises Usually expressed at two temp:- (-18°C &

99°C) SAE 5W,10W, 20W,grades are defined in terms

of viscosity at -18°C SAE 20,30,40,50 grades are defined in terms

of viscosity at 99°C

Some Points About Oil & Grades

Multi-grade The 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-30 designates a common multi-grade oil with viscosity equal to that of SAE 10W at -18°C & SAE 30 for 99°C

Provides Ease of starting & short warming period, Extends Battery life.

Operates for wider range of temp Reduces oil comsumption Reduces carbon deposits

Advantages of Multigrade oils

Mist or ChargeWet Sump1. Splash2. Splash & Pressure3. Fully PressureDry sump

TYPES OF LUBRICATION SYSTEM

Splash System

SPLASH & PRESSURE SYSTEM

Wet Sump

Working of Wet Sump Lubrication

Dry sump

Air coolingENGINE COOLING SYSTEM

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

Cool circulating air comes in contact with the exposed and enlarged external surfaces of the cylinder and head.

Direct Air-cooled Engine System. Dis-advantages.

(a)The cooling fans require a relatively large amount of power to run.(b) Due to the large quantities of intake air passing into the cooling system, the engine may become noisy.(c)The cooling fins can vibrate and amplify noise under certain conditions.(d) For proper positioning of the fins between cylinders, the pitch between cylinder centres has to be greater than in liquid-cooled engines.(e) Each cylinder is required to be cast individually unlike liquid-cooled engines where a rigid mono-block construction is used.(/) To prevent overheating of the lubricant, the air-cooling is frequently supplemented by an oil heat exchanger.(g) The presence of the guide cowling and baffles around the cylinders may hinder maintenance.

Indirect Liquid-cooled Engine System.

Thermo-Syphon Cooling

Water cooling

Advantages.(a) Greater temperature-uniformity around the cylinders is achieved in liquid-cooled engines causing less distortion compared with air-cooledengines.(b) The power consumption of the coolant pump and the fan together in liquid-cooled engines is less than that of the fan in air-cooled engines.(c) The liquid-cooled engine cylinders are much closer, providing a very rigid and compact unit unlike the air-cooled engine.(d) Both the coolant and the jackets dampen the mechanical noise from the engine.(e) Liquid-cooled units perform heavy-duty work more reliably than air-cooled engines.(f) Hot coolant can readily be circulated for interior heating of the vehicle.

Disadvantages.(a)Liquid-coolant joints may develop leakage.(b)Care must be taken to avoid freezing of the coolant.(c) Liquid-cooled units require more time to warm up than the air-cooled engines.(d) The boiling point of liquid-coolant limits maximum temperature of operation, whereas air-cooled engines can operate at slightly higher temperatures.(c) Formation of scale takes place in the coolant passages, and the hoses and radiator tubes deteriorate with time.

The advantages of thermo-syphon cooling are :(a)Cheap as no water pump is required.(b)Reliable as there are no moving parts.(c)Circulation of water depends solely on engine temperature. The hotter the engine, the greater is the circulation.

Disadvantages of thermo-syphon cooling (a) In order to achieve efficient circulation, the radiator top tank must be well above the engine. This needs a high bonnet

(b) Cooled water enters the engine at the bottom of the cylinder, where the engine normally runs fairly cool and it heats up to maximum as it reaches the top of the cylinders. Therefore, it has a reduced cooling effect on the hottest part of the engine.(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 the thermo-syphon cooling process.