This system consists of a number of components such as: 1. Spark Plug 2. Distributor 3. Ignition Coil 4. Condenser 5. Ignition Switch 6. Dynamo 7. Storage Battery.
Component # 1. Spark Plug:
Spark plug ignites the fuel-air mixture in combustion chamber. It is a device for the high voltage current to jump and ignite the charge. It provides insulated and grounded electrode within the cylinders of the engine to form a gap across which the spark jumps and ignites the charge. Each spark plug consists of a threaded outer shell with an outside electrode, insulator and a copper gasket. Usually spark gap settings are kept between 0.50 and 0.85 mm. If the clearance is too wide, it does not give satisfactory results.
Spark plug is of following two types:
(a) Cold plug and
(b) Hot plug
(a) Cold Plug:
Cold plug has a short insulator, extending into the cylinder. It conducts the heat away from the point rapidly allowing it to be cooled by the cylinder jacket. The short path dissipates heat quickly, so it is named as Cold plug.
(b) Hot Plug:
Hot plug has comparatively longer insulator, so the heat has to pass through a longer path to reach the cooling water and hence the heat is not dissipated quickly.
Component # 2. Distributor:
It is a device for interrupting the low voltage primary current and distributing the resulting high voltage current to the engine cylinder in proper sequence and in proper time.
The main functions of distributor are:
(a) It closes and opens the primary circuit.
(b) It distributes the resulting high voltage current from the secondary circuit to the spark plugs.
The distributor consists of:
(a) Housing
(b) Drive shaft
(c) Cam
(d) Breaker point
(e) Condenser
(f) Rotor and
(g) Cap
It is a rotary switch that connects the high tension terminal from the ignition coil to the proper spark plug wires at the instant the breaker point opens. The rotor is mounted on the upper end of the shaft. A clip in the centre of the rotor serves to connect the rotor to the high tension lead from the coil.
The contactor at the end of the rotor directs the current to the proper terminal in the distributor cap. The rotor is always made of non-conducting material. Distributor cap is made of Bakelite or similar non-conducting material. High tension cables connect the terminals in the distributor cap to the spark plug.
Component # 3. Ignition Coil:
Ignition coil serves the purpose of a small transformer. It steps up low voltage to a very high voltage (may be 20,000 volts) necessary to jump the gap of the spark plug. The coil consists of primary winding and secondary winding, wound round a soft iron core. Primary winding is made of copper wire of about 0.8 mm diameter having less number of turns. Secondary winding consists of thousands of turn of very fine insulated copper wire of about 0.1 mm diameter.
The voltage varies as the ratio of turns of wire of the primary to the secondary winding. If the battery is connected in the primary circuit, current flows and forms an electromagnet. When the electrical circuit is suddenly broken, the electro-magnetism dies out very quickly and thereby induces very high voltage in secondary winding.
Component # 4. Condenser:
A condenser consists of a pair of flat metal plates, separated by air. The most common type of condenser is of metal foil strips, separated by wax impregnated paper. The condenser in the distributor is connected across the contact breaker points. It is used to produce a quick collapse of the magnetic field in the coil to obtain extremely high voltage. In doing so, the condenser prevents sparking across the contact breaker points, thus preventing the points from burning.
Component # 5. Ignition Switch:
A switch provided in the primary circuit for starting and stopping the engine is called Ignition switch. It may be push-pull type or key type.
Component # 6. Dynamo:
The purpose of the dynamo is to keep the battery charged and to supply current for ignition, light and other electrical accessories. The dynamo supplies direct current to the battery and keeps it fully charged. It consists of a frame, soft iron pole shoes, field winding, armature winding, commutator, brushes, brush holder, spring, terminals and drive pulley.
Component # 7. Storage Battery:
Storage battery is a device for converting chemical energy into electrical energy. There are several types of battery, but lead- acid battery is most common for I.C. engines, used for tractors and automobiles.