8/14/2019 How to Choose a Plug

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Spark plug heat dispersal

What is a spark plugs heat range ?

How to Choose a Plug

Various circumstances such as engine conditions and driving

conditions are rough measures for choosing a plug. For example, if

strenuous driving is continued for a long time using normal plugs, the

plug will overheat. This is why the idea of a regular plug for a regular

car doesnt work. Whats important is to inspect the condition of your

current plugs, and then choose a plug accordingly.

The degree to which a spark plug disperses the heat it

receives is called its "heat range". Spark plugs with a

high degree of heat dispersal are called high heat range

(cold type) and those with a low degree of heat dispersal

are called low heat range (hot type).

This is largely

determined by the

temperature of the

gas inside the

combustion

chamber and the

spark plug design.

The heat range will changewith the seasons.

When the air temperature is high, as in the summer,

the inlet air temperature becomes higher, increasing

the load on the engine. In times like this, it's better to

choose a plug with a higher heat range.

The more horsepower is increased,the higher the required heat range.

If the horsepower has been increased through tuning,

the increase in explosive power leads to an increase

in combustion chamber temperature, making pre-ignition more likely; in such cases it is necessary to

choose a plug with a higher heat range and a higher

level of heat resistance.

Glossary of spark plug terms

Low heat range and high heat rangeLow heat range plugs have long insulator leg sections and the surfacearea affected by the flame and the gas pocket capacity are large.Also, since the heat release path from the insulator leg section to the

housing is long, heat dispersal is low and the temperature of thecenter electrode rises easily.On the other hand, high heat range plugs have short insulator legsand the surface area affected by the flame and the gas pocketcapacity are small.Also since the heat release path from the insulator leg section to thehousing is short, heat dispersal is high and the temperature of thecenter electrode does not rise easily.

The relationship between the spark plugtemperature and vehicle speed and heat rangeThere are restrictions on the temperatures at which spark plugscan be used: the lower limit is the self-cleaning temperature andthe upper limit is the pre-ignition temperature.A spark plug onlyfunctions completely when its center electrode temperature isbetween these temperatures of about 500C and 950C.

Water1

Cooled by intakeair-tuel mixture

2

Low heatrange(hot type)

spark plugs

High heatrange(cold type)spark plugs

Gas pocket

Self-cleaning temperature1 Pre-ignition temperature2

Low heat range (hot type) spark plugs3 Standard spark plugs4

High heat range (cold type) spark plugs

S: Vehicle speed T: Spark plug temperature (C)

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HeatRange

31

27

24

22

20

To prevent plug overheat

Standard Plugs

Level of TuningLow High

To prevent carbon fouling/ oil fouling

Application

16 20 22 24 2714

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http://www.globaldenso.com/PLUG/

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