Spark Plug (Courtesy: Bosch)

How Does A Spark Plug Work In Engines? Read More

 | 5 minutes read

Spark Plug Construction & Working:

A spark plug is very important in a petrol engine when it comes to igniting the charge in the combustion chamber. As the name suggests, the spark plug creates a spark that burns the air-fuel mixture. It consists of a center electrode, a ground electrode, an insulator, and a shell/body. Ignition coil provides the electrode with a very high voltage of around 20,000 volts which produces a spark to burn the air-fuel mixture.

Spark plugs
Spark plugs


A typical spark plug consists of a steel-shell assembly which serves as a housing for the core-insulating assembly. It has the ground electrode fixed to its lower threaded portion. The upper part is hexagonal in shape; just like a nut. It acts as a surface for the wrench to screw and unscrew the plug from the cylinder head. The core assembly consists of an insulator that can withstand high voltages, pressures, and temperatures.  The center electrode is fastened into the insulator. The upper end of the center electrode is connected to the spark-plug wire terminal while its lower end projects beyond the insulator and forms a gap with the ground electrode. A gasket between the insulator & shell prevents the combustion gases to escape under high pressures & temperatures.

Spark Plug construction
Spark Plug construction

Spark Plug Material:

The material of the spark plug is of corrosion-resistant type. Earlier generation plugs used nickel. Nowadays, manufacturers use platinum and iridium-alloy on the central electrode. Iridium is one of the hardest metals in the world.

Iridium starts to melt at 2450°C. It is also very resistant to spark erosion. Iridium can reduce voltage demands by 24%, leading to longer life of spark plug. On average, Iridium spark plugs offer double the service life compared to standard nickel plugs.

Some of the spark plugs have a platinum plate on its central electrode. It provides a more constant output even under difficult conditions throughout its entire service life. It emits very little spark voltage, discharges the ignition coil quickly, and carries out optimal combustion.


Furthermore, the primary ignition circuit induces a high voltage current into the center electrode. This high voltage current travels down the center electrode; jumps the gap to the ground electrode and completes the secondary circuit. The sealing gasket provides the sealing between the plug shell and cylinder head and helps in the conduction of heat. Thus, the high voltage current, in order to be grounded, jumps the gap between the center & ground electrodes. This process produces a strong spark to burn the air-fuel mixture.

Don't miss out on Automotive Knowledge