Spark Plugs
Chapter 2 Spark Plugs
12
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.
The temperature received by the inside
surface of the spark plug reaches as high
as 3000
°
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 pre ignition.
Can withstand sudden heat
and sudden cold
1
In the intake stroke, the pressure is less
than 1atm, but in the combustion stroke
it reaches 50 atm or higher. The
mechanical strength to withstand this
severe pressure change is required.
Can withstand severe
pressure changes.
2
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 10-30 kV.
Has insulation at high voltage
3
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.
Maintains an airtight seal in
a harsh environment
4
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 electrode wear
5
It is required that under severe usage
conditions, spark plugs minimize fouling
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 ).
Minimizes fouling from
combustion
6
●
Performance required of spark plugs
｛
3
4
1
2
5
6
