Page 240 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Main part of spark plug
Following are the main parts of spark plug
Terminal
The topmost part of the spark plug is called the terminal. A bangle cut cap is fitted on it, through which HT is
connected to the spark plug. Lead is added.
Central electrode
The central electrode is in the form of a wire attached below the terminal, through which the IHT reaches the
terminal. The current jumps to the side electrode and produces a spark.
Insulator
A ceramic insulator fits in the center of the spark plug. It separates the central electrode from other parts and HT.
Prevents the ghara from being unnecessarily earthed, due to which it usually ‘cracks’ due to carelessness.
In such a situation the spark plug should be changed otherwise HT. The current will be wasted in the engine parts
itself, due to which the ignition will not be able to function.

Side electrode
To tighten the spark plug, a thick wire is attached to the part where the bangle is cut, which is bent till below the
central electrode. HT reaching the central electrode. With its help the stream becomes earth and jumps.

Insulator nut
This nut is used to tighten the insulator with the plug. On this, the bangle is cut in the lower part on the outside.
This part is screwed to the engine. It is made of strong enough mild steel. The bangles cut on it are of 14 mm and
18 mm.
Copper gasket
There is a copper washer at the bottom of the spark plug, which acts as a gasket. By using this the gas from the
cylinder does not leak.
Working of spark plug
The first function of the ignition system is to generate a high voltage to produce a spark in the spark plug gap.
The spark plug has an end cap, which has some gap. When the mixture of air and fuel is compressed, some of it
enters the compressed mixture gap, due to which spark is generated and ignition starts in the gap.

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CITS : Automotive - Mechanic Diesel - Lesson 71 - 75