A.Y.DADABHAI TECHNICAL INSTITUTE (POLYTECHNIC) KOSAMBA.

CERTIFICATE

Mr. MUBASSIR I. GHONIYA has satisfactorily completed his PPT work on IGNITION SYSTEM OF SI ENGINE in T.E-II course in mechanical engineering department as per the GTU regulation.

Date :-

Guide External faculty H.O.D Sign Sign Sign

A.Y.DADABHAI TECHNICAL INSTITUTE, KOSAMBA

Subject:- IGNITION SYSTEM OF SI ENGINESUBMITTED BY

GHONIYA MUBASSIR AHMED IMTIYAZ AHMEDEnrolment No:- 136010319024

Guide BY:- Y.A.S

DEFINATION OF IGNITION SYSTEMThe system in an internal-combustion

engine that produces the spark to ignite the produces the spark to ignite the mixture of fuel and air: includes the battery , spark plugs, and associated switches and wiring.

It known as the ignition system

INFORMATION ABOUT IGNITION SYSTEM IN SI ENGINEThe term spark-ignition engine refers to internal

combustion engines generally, petrol engines.Where the combustion process of the air-fuel

mixture is ignited by a spark from a spark plug.Spark-ignition engines are commonly refer to as

“gasoline engines” in America ,and “petrol engines” in Britain and the rest of the world .

The working cycle of spark ignition engines may be either two stock or four stroke

A four stroke spark ignition engines is an Otto cycle

It consist following four stroke.1. Suction stroke2. Compression stroke3. Power stroke 4. Exhaust stroke The combustion in spark ignition engine is

initiated by an electrical discharge across the electrodes of a spark plug, which usually occurs fro 100 to 300 before TDC depending upon the chamber geometry and operating conditions.

The ignition system provides a spark of sufficient intensity to ignite the air fuel mixture at the predetermined position in the engine cycle under all speeds and load condition.

IGNITION SYTEM REQUIREMENTIt should provide a good spark between the

electrodes of the plugs at the correct timing The duration of the spark must be long enough

with sufficient energy to ensure that ignition of the mixture has a high chance of occurring

The system must distribute this high voltage to each of the spark plug at exact time in every cycle , i.e., i t must have in it a distributing device

It should function efficiently over the entire range of engine speed

It should be light, effective and reliable in service

The development of high speed, high compression internal combustion engine requires reliable high-speed ignition speed ignition system. This is met by a high-tension ignition system that uses a spark plugs as the source of ignition. The electrical energy to the spark plug is supplied by one of the following systems and is termed accordingly.

TYPES OF IGNITION SYSTEMCOIL IGNITION SYSTEMMAGNETO IGNITION SYSTEM ELECTRONIC IGNITION SYSTEM

1.COIL IGNITION SYSTEM

The primary circuit consists of the battery, ammeter, ignition switch, primary coil winding, capacitor, and breaker points. The functions of these components are:BATTERY PROVIDES THE POWER TO RUN THE SYSTEM

IGNITION SYSTEM

ALLOWS THE DRIVER TO RUN TURN THE SYSTEM ON AND OFF.

PRIMARY COIL PRODUCES THE MAGNETIC FIELD TO CREATE THE HIGH VOLTAGE IN THE SECONDARY COIL.

BREAKER POINT

A MECHANICAL SWICH THAT ACTS AS THE TRIGGERING MECHANISM.

CAPACITOR PROTECS THE POINT FROM BURNING OUT

The secondary circuit converts magnetic induction into high voltage electricity to jump across the sparkplug gap, firming the mixture at the right time. The function of the

SecondaryCoil

Coil wire

: the part of the coil that creates the high voltageElectricityA hire insulated wire to take high voltage to the distributor cap

Distributor cap

: a plastic cap which goes on top of the distributor,to hold the high tension wires in the right order

Rotor : spins around on the top of the distributor shaft,and distributes the spark to the right spark plug

Spark plugLeads

: another highly insulated wire that takes the highvoltage from the cap to the plugs

Spark plugs

: take the electricity from the wires, and give it anair gap in the combustion chamber to jump across,

The ignition switch provided, connects and disconnects the ignition system from the battery.hence the engine can be started or stopped a will. When the ignition system is “ON "the contact breaker points are closed.

This allows the current to flow from the battery trough primary winding of the ignition coil and back to battery through earthlings .

The magnetic field across the primary winding is developed. This will induce back e.m.f. this will oppose the battery current. With the result, the current in the primary will slowly developed.

This will delay the building up of magnetic field. A voltage is induced in the secondary windings. But the e.m.f.is too low to produce a spark at the spark plug.

The breaker point is opened by the distributor arm when we want a spark in the engine. This opens the primary circuit.

The magnetic field in the primary field collapses. The resulting induced current will flows in the same directiopn as the battery current. It charge the condenser. When the voltage of the battery across the condenser plates, the flows of the current is reversed.

The magnetic field in the coil of the primary winding reverses due to the quick reversal of the current in the primary winding.

This will cause a very high voltage to be induced in the secondary winding.

This depends upon the number of turns of the secondary to primary wind.

This induced voltage is of the order of 10 KV to 20 KV.

When the contact breaker in the primary circuits is opened, the distributor rotor connects with a contact to the spark plug.

This high induced voltage jumps across the air gap of the spark plug.

This will produce the spark for ignition system battery of 6V to V used. The voltage induced is 6 V to 24 V used.

The voltage induced is 6kV to 10kV.

ADVANTAGES OF THE COIL IGNITION SYSTEM1. At the time of starting and idling at low

speed good sparkling is available.2. Initial expenditure is less . Hence, this

system is used in cars and commercial vehicles.

3. Maintenance cost is less.4. Distributor drive is simple and non-

complicated.5. By adjusting spark-timing complete

ignition system is not adversely affected.

DISADVANTAGE OF COIL IGNITION SYTEM 1. If the battery is discharged, then it is not

possible to start the engine.2. Battery is to be checked regularly.3. It occupies more space.4. Its wiring is complicated.5. The intensity of spark decreases with

increase in speed.

2. Magneto ignition system The high powered, high speed spark ignition

engines like aircraft, sports and racing cars use magneto ignition system. The basic components of a magneto ignition system consist of a magneto, breaker points, capacitor, ignition switch, distributor, spark plug leads, and spark plugs.

Magneto can either be rotating armature type or rotating magneto type. In the former, the armature consisting of the primary and secondary windings all rotate between the poles of a stationary magneto, revolves and the winding are kept stationary.

oElectric circuits• Uses a changingmagnetic field togenerate currentin primary andsecondarycircuits

oMagnetic flux• As magnetapproaches,induces magneticflux in armature• Breaker points closeand currentdissipates throughprimary circuit

oSpark fires • After magnet rotate past armature flux reverses direction, and the breakerpoints open• Change in magneticflux produces 170volts in primary circuit• Induces 10,000 voltsin secondary circuit,firing spark plug

oBreaker points

• Crankshaft rotation causes mechanical actuation of breaker

ADVANTAGES OF MAGNETIC IGNITION SYSTEMSince there is no battery or connecting

table, the system is more reliable.For medium and very high speed engines,

the system is more suitable.The space require is less, by using cobalt

steel and nickel aluminium magnet metals energy.

This system in fairly reliable with resent development.

DISADVANTAGES OF MAGNETO IGNITION SYSTEMAt low speed and during cranking the voltage

is very low. Suitable modifications are necessary in the circuit to overcome this.

Adjustment of the spark timing has determined effect upon the spark voltage or energy.

The burning of the electrodes will result with powerful sparks at high engine speeds.

More costly.Starting is troublesome.

3. Electronic ignition system The disadvantage of the mechanical system is

that it requires regular adjustment to compensate for wear, and the opening of the contact breakers, which is responsible for spark timing, is subject to mechanical variations.

In addition, the spark voltage is also dependent on contact effectiveness, and poor sparking may lower the engine efficiency. Electronic ignition system has solved these problems

.

• In this system, the contact breaker points are replaced by an angular sensor of some kind - either optical, where a vane rotor breaks a light beam, or more commonly using a hall effect sensor, which responds to a rotating magnet mounted on a suitable shaft.•The sensor output processed by a suitable circuitry is then used to trigger a switching device such as a thyristor, which switches a large flow of current through the coil.•The rest of the system remains the same as the mechanical system. The lack of moving parts compared with mechanical system leads to greater reliability and longer service intervals. In some order cars, it was usually possible to retrofit an electronic ignition system in place of the mechanical one.

• The spark plug ignites the air-fuel mixture inside the cylinder. This occurs when high voltage, triggered atprecisely the right instant, bridges the gap between the center and the ground electrodes. It also provides a secondary purpose of helping to channel some heat away from the cylinder.

oSpark plugs

Firing order Firing order indicates the sequence or order

in which the firing impulses occur in a multi-cylinder spark ignition engine. It is chosen to give a uniform torque, and hence a uniform distribution of firing per revolution of the engine.

This is naturally dictated by the engine design, the cylinder arrangement and the crankshaft design. The firing order be such that there must always be a proper balance so as to minimize the engine Vibration.