Ignition System

Table of Contents

For burning any fuel we need two things, oxygen and heat. Fuels which has a low self ignition temperature can even be burnt by applying high pressure like, Diesel. But the case of petrol or gasoline is different. Here we need an ignition system to ignite the fuel.

In spark ignition engines, compression ratio is lower, and self ignition temperature of petrol is higher. Hence, to ignite the mixture for the initiation of combustion an ignition system is must.

Requirements of an ignition system

It should provide good spark at correct timing.
It should function efficiently for all engine speeds.
It should be light, effective and reliable in service.
It should be compact and easy to maintain.
It should be cheap and convenient to handle.
The magnetic field generated from the voltage source of the ignition system should not affect radio and television inside the automobile.

There are basically two types of ignition systems are used in automobiles. One is battery ignition system and another one is magneto ignition system.

Lets first discuss battery ignition system

1. Battery Ignition System

In a battery ignition system, a battery is used as a source of energy for the spark plug. This battery is rechargeable and derives energy for its recharging from an alternator.

This alternator is connected to the crankshaft of the engine and converts its mechanical energy into electrical energy.

Essential components of battery ignition system

Battery
Ignition switch
Ballast resistor
Ignition Coil
Contact breaker
Capacitor
Distributor
Spark plug

Characteristics battery ignition system

Battery is necessary. Difficult to start the engine when battery is discharged.
Maintenance problem is more due to battery.
Power for ignition is obtained from the battery.
Good spark is available, even at low engine speed.
As engine speed increases, efficiency of battery ignition system decreases.
Occupies more space.
Commonly employed in cars and light commercial vehicles.

2. Magneto ignition system

A magneto ignition system uses its own electric generator instead of a battery to derive power for electric spark. In a magneto ignition system, all the parts of battery ignition system are replaced except the spark plug.

While in operation, a magneto is capable of generating very high voltage and hence, replaces the need of a battery as a source of external power.

As the machine speed increases the voltage generated by magneto also increases. At the time of machine starting, magneto generates a very small voltage hence in some applications a separate battery is used for machine starting. Magneto ignition system is best suited for high speeds.

Characteristics magneto ignition system

No battery is needed and therefore no problem of battery discharge.
Maintenance problem is less, as there is no battery.
The power for producing spark is obtained from magneto.
At low speed efficiency of magneto ignition system is low.
As speed increases the efficiency of magneto ignition system increases.
Occupies less space
Mainly used in racing cars and two wheeler.

Comparison between Magneto and battery ignition system

Magneto Ignition System	Battery Ignition System
Generally used in two wheelers and racing cars	Generally used in commercial vehicles
No need of recharging	Battery needs to be recharged regularly
It is compact	It occupies more space
Its efficiency increases with engine speed	Its efficiency decreases with engine speed
Spark quality is poor at low speed	Spark quality is good even at low speed
Power for ignition is obtained from magneto	Power for ignition is obtained from battery
No problem of battery discharge	Problem of battery discharge
No battery hence no battery maintenance is required	Battery maintenance is required

Image (also featured) attribution: By Andy Dingley (scanner) – Scan from (1911) Mechanical Transport, HMSO, Public Domain, https://commons.wikimedia.org/w/index.php?curid=9884580