Construction of Ignition Coil, Spark Plug, Distributors, Ignition Switch Key – Parts Of a Ignition system

Ignition Coil

The ignition coil is used to convert
12 V D.C. from the battery to 20,000V to 30,000V A.C. It works on the principle of Faraday’s law of electromagnetic induction. It is also called as Step up transformer. The
primary coil is made up of thick wires with 150 to 300 turns. The secondary coil is made up of thin wires with 20000 to 25000 turn

Types of Ignition coil

1. Can type (or) Metal glad type
2. Core type

Spark plug

introduce spark to ignite the air-fuel mixture. Spark plug consists of a central electrode, a ground electrode, an insulator. There is a small gap (0.5mm to 0.7mm) is available between the central electrode and ground electrode. When the high tension current from the ignition coil through a distributor is applied between these electrodes, spark
is produced. This spark will ignite the air fuel mixture.

Types of spark plug

1. Hot spark plug
2. Cold spark plug

Hot spark plug

In this type of spark plug, the length
of the insulator is long and heat travel
path is long. This spark plug is widely
used in low-speed engine and engine
operating in the cold climatic area.

Cold spark plug

In this, the length of the insulator is
short and heat travel part is short. These spark plugs are widely used in high-speed engines and heavy loaded engines.

Ignition switch and key

The Ignition switch is used to
connect the battery to the required circuits via a key. It will have three terminal viz., The battery (B), Ignition (Ig) and Starter (St). The terminal B is always connected to the battery. Ignition system, fuel system, lighting and other electricalbaccessories are connected in the Ignition terminal via a fuse. The solenoid of the starter motor is connected in Starter (St)

When the ignition switch is positioned in Ignition (Ig), then the electricity from the battery will flow to all the electrical system (expect starting system) of the vehicle.
When the ignition switch is positioned in Starter (St), then the current will flow to the starter motor through the solenoid and thus the engine is started.


The Distributor does two functions. First, it has a set of contact breaker points, that works as a switch. When the CB points close, current flows through the coil. When the CB point open, current flow stops and coil produces a high tension current. A
condenser is connected in parallel to the CB points. The condenser aids in the collapse of the magnetic field and help to reduce arcing occurs between the CB points.Second, the distributor is used to distribute the high tension current from the ignition coil to the spark plugs in the correct firing order.

A coil wire delivers the high tension from the coil to the centre terminal of the distributor cap. Inside the cap, a rotor is on top of the distributor shaft. The distributor shaft is driven from the engine camshaft by a pair of spiral gears. When the rotor turns,. the centre terminal of the distributor cap
is connected by spark plug wires to the spark plugs. The spark plug wires carry the high tension current to the sparkplug in the cylinder that is ready to fire.

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