For burning any fuel we need two things. First is oxygen and second is heat.
Fuels which has self ignition temperature can even be burnt with applying high pressure, like Diesel.
But the case of petrol or gasoline is different.
In a 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
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 from the crankshaft of the engine and converts its mechanical energy into electrical energy.
Essential components of battery ignition system
- Ignition switch
- Ballast resistor
- Ignition Coil
- Contact breaker
- 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.
Magneto ignition system
A magneto ignition system uses its own electric generator instead of a battery to derive power for electric spark.
All the parts of battery ignition system replaced except spark plug.
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.