SPARK PLUG A spark plug which produce electric current from an ignition system to the combustion chamber

A spark plug which produce electric current from an ignition system to the combustion chamber. The high voltage of electric current is required to ignite an engine. Spark plugs consist of an insulated center electrode which is connected by a heavily insulated wire to an ignition coil on the outside.

Parts of the spark plug

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Insulator tip.


Metal case/shell.

Central electrode.

Spark plug construction:
The spark plug which contains a terminal to connect to the ignition system. Plugs are used for these applications often have the end of the terminal serve a unique purpose as the nut on a thin threaded shaft so that they can be used for either type of connection.

The physical shape of the ribs function to improve the insulator and prevent electrical energy from leaking from the terminal to the metal case along the side of the insulator. The interrupted and longer path makes the electricity encounter more resistance along the surface of the spark plug.

The insulator is typically made from an aluminum oxide ceramic as is designed to withstand 550° C and 60,000 V. It would extend from the metal case into the combustion chamber. The length of the insulator partly determines the heat range of the spark plug.

As the spark plug also seals the combustion chamber of the engine when installed, the seals would ensure that there is no leakage from the combustion chamber. The seals are generally made of copper in the form of washer so that it can get compressed to give a good seal.

Metal case
The metal case of the plug bears the torque of tightening, which leads to remove heat from the insulator and pass it to the cylinder head. It also acts as the ground for the sparks passing through the center electrode to the side electrode to body.

Insulator tip
The tip of the insulator surrounding the center electrode is within the combustion chamber which would directly affects the spark plug performance and the heat range.

Side electrode
The side electrode is made up of high nickel steel and is welded to the side of the metal case. The side electrode also runs hot, especially on projected nose plugs. Some spark plug is designed with multiple side electrode which do not overlap the center electrode.
Center electrode
The center electrode which is connected to the terminal through an internal wire and commonly a ceramic series resistance to reduce emission of noise from the sparking. The center electrode is usually designed to eject the electrons because it is the hottest part of the plug
Spark plug gap
Spark plugs are designed to have a gap which can be adjusted by the technician for installing the spark plug, by the simple mechanism of bending the ground electrode.


The plug is being connected to the high voltage generated by an ignition coil .The voltage difference will develop between the center electrode and side electrode, as the electrons flows through the coil. No current can flow in between because the fuel and air in the gap is an insulator, but as the voltage rises to an extent, it begins to change the structure of the gases between the electrodes. Once the voltage exceeds the dielectric strength of the gases, the gases gets ionized. The ionized gas becomes a conductor and allows certain electrons to flow across the gap.

When the spark is being ignited and the air and fuel mixture is being combined and then it starts up the engine by moving the piston thus engine gets warmed. The piston will be compressed and released, where a high temperature is being created this will make the engine to burn. The heat and pressure which is being produced from the combustions force the gases to react with each other and at the end of the spark event there would be a small ball of fire in the spark gap which makes the gases burn.

The symptoms where we need to change the spark plug
The engine idles roughly.

Trouble starting car in the morning
Car’s engine misfires
Engine surge or hesitation
High fuel consumption
Lack of acceleration