∆ Ignition... System
The purpose of an Ignition system is to ignite the compres air-fuel mixer in the engine combustion chamber It delivers and electric spark that jump. a gap at the to two ends of this spark plug the heats from this ank ignite the air-fuel mixer and creatine mixer presere that pushes the piston down to the cylinder so the engine runs. there are two types of Ignition system ........
@. Battery Ignition system
b. Contact point Ignition system (same as battery ignition.
c. Magneto Ignition system.
e. Electronic Ignition system.
•The main components in Battery Ignition System are---
a) Battery
b) Ignition coil / [ HT coil ]
c) Contact Breaker
d) Condenser scroll down and see
e) Distributor the Diagram about
f) Spark plug ignition system
Ignition coil:- The ignition coil is simply a transformer to step up the voltage in the ignition system. It consists of a soft iron core, primary winding and secondary winding. The primary winding consists of 200-300 turns of thick wire (20 SWG) and the secondary winding 15,000-20,000 turns of fine wire (40 SWG). The core is formed by lamination of soft iron.
The ignition coils may be of two types:
1. Core type ignition coil. In this type of coil, the primary winding is wound around the iron core forming double C with air gaps. The secondary winding is wound outside the primary winding. The core is of rectangular cross-section and is made of soft iron lamination.
2. Can type ignition coil. In this type of coil, the secondary winding is wound around the core, and then the primary winding is wound over the secondary winding. The core assembly is placed in a steel casing which is fitted with a cap of moulded insulating materials. The terminals are provided in the cap. The windings are immersed in oil to improve insulation and to reduce moisture effect.
When the ignition switch is turned on, the current flows from the battery through the primary winding. When the contact breaker points open, the primary circuit breaks and the magnetic field collapses. Rapid collapsing of magnetic field induces high voltage in both the primary and secondary winding. The current flowing in the primary winding, runs towards contact breaker points and is observed by the condenser placed across them: and the circuit is completed through the earth. The high voltage current flowing through the secondary winding goes to the distributor from where it is distributed to the proper spark plug through the high tension lead, where it jumps the spark plug gap producing the spark.
Contact Breaker:-The contact breaker is mechanism to make and break the primary circuit of the ignition system for obtaining high voltage current in the secondary circuit. It consists of two points, known as ignition points or contact breaker points, one is fixed and other is movable. The movable point is operated by the rotation of a cam by which the two points come in contact and separate, thus making and breaking the primary circuit. The contact breaker is placed in the distributor housing itself. The cam is fitted to the distributor spindle.
Distributor:-The distributor consists of a housing, driving shaft with breaker cam, breaker plate with contact points, governor, condenser, rotor, advance mechanism and cap. The shaft is driven by the engine cam shaft directly or indirectly through the oil pump drive shaft. The drive shaft is rotated at half the engine speed in four-stroke engines. When the shaft moves, it opens and closes the breaker points. The breaker cam contains the same number of lobes as the number of cylinders in the engine. Arotor is mounted on the breaker cam which is carried by the drive shaft. The rotor connects the centre terminal of the cap with each outside terminal in turn, so that high voltage surges from the coil are directed first to one spark plug and them to another, according to the firing order.
Spark plug:- Spark plug is a device to produce electric spark to ignite the compressed air-fuel mixture inside the cylinder. The spark plug is screwed in the top of the cylinder so that its electrode projects in the combustion chamber.Construction. A spark plug consists of mainly three parts:
1. Centre electrode or insulated electrode.
2. Ground electrode or outer electrode. 3. Insulation separating the two electrodes.
The upper end of the centre electrode is connected to the spark plug terminal, where H.T. cable from the ignition coil is connected. It is surrounded by porcelain insulator. The lower half portion of the insulator is fastened with a metal shell. The lower portion of the shell has a short electrode attached to one side and bent in towards the centre electrode, so that there is a gap between the two electrodes. The two electrodes are thus separated by the insulator. The sealing gaskets are provided between the insulator and the shell to prevent the escape of gases under various temperature and pressure conditions. The lower part of the shell has screw threads and the upper part is made in hexagonal shape like a unt, so that the spark plug g may be screwed in or unscrewed from the cylinder head.
Materials. The materials used in the construction of different parts s of a spark plug are as follows:
1.Shell. Steel.
2. Insulation. Porcelain, mica, sintered alumina. The porcelain has disadvantages of brittleness and low resistance to thermal shocks. Mica is somewhat attacked by fuels. Sintered alumina is now almost extensively used for insulation.
3. Electrode. Nickel, alloy of nickel and manganese, alloy of nickel, manganese and silicon. Platinum alloy, addition of manganese (2.5-3.5%) improves tensile strength and resistance to sulphur attack at high temperatures. Platinum alloys are better for electrodes, but their high costs limit their use.
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