INTRODUCTIONWe know that in case of Internal Combustion (IC) engines, combustion of air and fueltakes place inside the engine cylinder and the products of combustion expand to producereciprocating motion of the piston. This reciprocating motion of the piston is in turnconverted into rotary motion of the crank shaft through connecting rod and crank.This rotary motion of the crank shaft is in turn used to drive the generators for generatingpower.We also know that there are 4-cycles of operations viz.: suction; compression; powergeneration and exhaust.These operations are performed either during the 2-strokes of piston or during 4-strokesof the piston and accordingly they are called as 2-stroke cycle engines and 4-stroke cycleengines.In case of petrol engines during suction operation, charge of air and petrol fuel will betaken in. During compression this charge is compressed by the upward moving piston.And just before the end of compression, the charge of air and petrol fuel will be ignitedby means of the spark produced by means of for spark plug. And the ignition systemdoes the function of producing the spark in case of spark ignition engines.

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 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 Spark Plug

Centre electrode receives coil voltage.

Insulator prevents high voltages from shorting to ground.

Terminal

Gap

Insulator

Gasket

Thread

Metal shell

Hex

Centre electro

deSide

electrode

Spark plug is located in the cylinder head, it ignites the air and fuel mixture.

Has center 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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Ignition Timing

A 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 center), as a piston starts downward on its power stroke.

Therefore, a spark has to occur before a piston reaches top dead center (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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Base Ignition Timing

Typically, a spark at idle speed will occur at 8 degrees BTDC.

On contact breaker ignition systems, base timing is determined by the position of the contact breaker relative to the distributor cam and is affected by the gap between the contacts.

On DI systems, the ICM determines base timing from speed sensor pulses.

On DIS / EI systems, the ICM / ECU determines base timing from crankshaft pulses.

This is known as base ignition timing.

Exhaust Inlet

8°BTDCTDC

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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 distributor less ignition systems calculate spark advance from sensor information. Next >

Produces 30,000 volt spark across spark plug

Distributes high voltage spark to each spark plug in correct sequence

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

Varies spark timing with load, speed, and other conditions

IGNITION FUNCTION

BASIC IGNITION SYSTEM

Battery supplies power to entire system

Ignition Switch turns engine on or off

Coil transforms volts

Switching device triggers ignition coil

Spark Plug and wires distribute spark

PRIMARY CIRCUIT Consists of

low voltage wiring and components

Uses conventional type automotive primary wires

Controls when ignition will take place. (When coil fires)

SECONDARY CIRCUIT

Distributes current to individual cylinders to jump spark plug gap

Must have thicker, heavier insulation on wires

Typical voltage to jump gap - 10K Volts

Ignition Parts

BATTERY provides power for system.

IGNITION SWITCH allows driver to turn ignition on and off.

IGNITION COIL changes battery voltage to 30,000V during normal operation and has a potential to produce up to 60,000V.

SWITCHING DEVICE mechanical or electronic switch that operates Ignition coil(Pick-up coil, Crank sensor, Cam sensor).

SPARK PLUG uses high voltage from ignition coil to produce an arc in the combustion chamber.

IGNITION SYSTEM WIRES connect components.

Objectives

After studying this term paper, you should be able to

• Explain the function of ignition systems.• Differentiate between battery and magneto ignition system• Know the basic ignition system.• You are able the component of

ignition system –spark plug• Appreciate the importance of ignition timing .

• COMPARISON BETWEEN BATTERY AND MAGNETO IGNITION SYSTEM

• Battery Ignition Magneto Ignition

• Battery is a must. No battery needed.

• Battery supplies current Magneto produces the required current

in primary circuit. for primary circuit. • A good spark is available During starting

the quality of spark is poor at low speed due to slow speed

• Occupies more space. Very much compact.

• Recharging is a must in No such arrangement required

case battery gets discharged• Mostly employed in car Used on

motorcycles, scooters, etc. and bus for which it is required to crank the engine• Battery maintenance is required No battery

maintenance problems

References:

http://www.google.co.in/url?sa=t&rct=j&q=ignition%20system%20pdf&source=web&cd=1&cad=rja&ved=0CCkQFjAA&url=http%3A%2F%2Fwww.ignou.ac.in%2Fupload%2Funit%25204.pdf&ei=N7wTUufENsiXrAfn24EQ&usg=AFQjCNEqTMr1qLrKhrtETcfCqS2Fh88vIQ&bvm=bv.50952593,d.bmk

http://en.wikipedia.org/wiki/Ignition_system#Modern_ignition_systems

I.C Engines By V.Ganesan ,TMH Punlication.