Every gasoline engine needs spark plugs, and each cylinder
has one, specific engine has even two. The drivers know
about this well.
When high-voltage electric current ( over 10000V) from
ignition coil entrains into the cylinder, it creates spark
between electrodes of spark plug and ignites mixed gas.
The working condition of spark plug is very hard, such
four-stroke engine as an example, on return stroke the
temperature is 60C and the pressure is 90 kPa only, but
on power stroke the temperature will raise up to 2000-3000C,
and pressure will reach 4000 kPa in a twinkling. And the
frequency of exchanging hot and cold is very high. Common
material can't bear. Especially under this working condition
the material must keep its good insulating performance
Spark plug is composed of insulator and metallic
housing mainly. The key part is insulator. It should be
providZd with good mechanical performance and high voltage-resisting,
thermo-shockproof, and chemical corrosion-resisting. Usually
the insulator is made of ceramic ( content of Al2O3
d®j—5%). The fundamental dimension of spark plugs is identical
in the all over the world, and therefore they can be suitable
for various vehicle. However, spark plugs are divided
into two versions due to the difference of gasoline engines
hot and cold versions. They express thermo-performance
of spark plugs. Spark plugs can work well only under proper
temperatY6ëjÀýthout carbon. According to practice when
insulators of spark plugs keep 450-900²¢ the oil adhered
to their sJrface can be burnt up without carbon. If the
temperature is higher, it will ignite earlier than expected.
Conversely, it will create carbon. Because of the different
working temperature of engines designers change the length
of insulator's skirt and the other factors to suit different
requirement. Short skirt has smaller area to be heated,
absorption ofheat is a little and ther9ä8Ò´the temperature
of skirt is lower. This kind of spark plugs is called
cold version. They are suitable to be used for engines
|[«j—´ with high speed, high compression ratio and strong power.
Conversely, they are called hot version. They are suitable
to be used for engines with medium or low speed, low compression
ratio and small pPwer. The users should select according
to the requirement of engine manufacturers.