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Performance required of spark plugs – DENSO SPARK PLUG

Performance required of spark plugs

The effect on the spark plugs of ignition and combustion of the running engine is severe and various aspects of performance for withstanding this are required.


Can withstand sudden heat and sudden cold

The temperature received by the inside surface of the spark plug reaches as high as 2000°C during combustion of the air-fuel mixture and during the intake stroke, the spark plug is subject to sudden cooling by low-temperature gas. In 4-cycle engines, this sudden heating and sudden cooling is repeated every other rotation as long as the engine is running.
As the same time that it must provide such capacity to withstand heat, the spark plug must also give off enough heat to avoid becoming a starting point for surface ignition.

Mechanical strength

Can withstand severe pressure changes.

In the intake stroke, the pressure is less than 0.1MPa, but in the combustion stroke it reaches 4.5MPa or higher. The mechanical strength to withstand this severe pressure change is required.


Has insulation at high voltage

In an environment in which the temperature and pressure are constantly changing drastically, spark plugs must have adequate insulation to withstand high voltages that reach about 10-30kV.


Maintains an airtight seal in a harsh environment

Spark plugs must maintain an airtight seal between the housing and the insulator under conditions of drastic temperature and pressure change and high voltage.
DENSO’s heat staking process provides stable air tightness.


Minimizes electrode wear

Spark plugs must have the wear-proof resistance to minimize electrode wear in a severe usage environment.
DENSO’s patented iridium alloy is effective against wear.


Minimizes soiling from combustion

It is required that under severe usage conditions, spark plugs minimize soiling of electrodes by the combustion of the air-fuel mixture and have self-cleaning that burns away carbon deposits with heat. Therefore, it is desirable that the spark plug temperature rise quickly even when the vehicle is moving at low speed and that the insulator section reach the self-cleaning temperature (about 500°C).