Page 241 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

After this the combusted mixture comes out of the orifice and ignites the remaining compressed mixture.

A gasket is used during installation of some spark plugs for the purpose of providing a leaf proof seat. Additionally,
some engines use a plug with a tapered seat, which acts as a perfect seal.

Types of spark plug
Two important properties of a spark plug are its heat range and accessibility. The heat range of a spark plug
refers to the temperature the spark plug will tolerate in the engine, which determines how hot the spark plug will
get. The heat range of a spark plug is controlled by its size and the distance it takes for the heat to reach the
center electrode of the plug and the cooler of the cylinder head. If this distance traveled by heat is large, the plug
becomes hot and if this distance is small, the plug is cold. Apart from the above description, on the basis of spark
plug cleaning etc., spark plugs are mainly of the following types:
Detachable spark plugs
The biggest advantage of this type of plug is that by opening it, the carbon deposited inside it can be cleaned
thoroughly. Similarly, among the other differences in the plugs, the difference in electrodes is important. Usually,
spark plugs have side electrodes installed below the central electrode, but in some plugs, two or more side
electrodes are also installed. Similarly, in some plugs, the side electrode is not placed below the central electrode
but is placed at 90°.
Cold Spark Plug

These types of spark plugs are relatively cold. In these, the length of the insulator is somewhat less, due to which
they are not able to retain much heat inside themselves. The path of heat is less in these, hence carbon etc. gets
deposited quickly.
This type of spark plugs is often used in engines in which the cylinder heads are made of aluminum alloy. Apart
from this, similar type of cold plugs is also used in engines which are fitted in the engine valve block.
These plugs should be cleaned from time to time, otherwise there is a possibility of pre-ignition fault in the engine
due to carbon accumulation. The structure of the spark plug is shown with the hot spark plug inserted.
If for some reason the spark plug becomes too cold, it is not able to burn the residue accumulated on the insulator
present around the center electrode and ignition fault occurs due to lack of spark.
The main reason for this is that the high voltage leaks around the residue collected on the insulator of the center
electrode and cannot reach the spark gap.

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CITS : Automotive - Mechanic Diesel - Lesson 71 - 75