In this post I will talk about ignition plug, one of the most important components to ignition system.
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How it works?
The ignition plug conduct high voltage around 20,000V generated by autotransformer which is conducted by distributer to the nickel electrodes loosen the spark to explode the mix of air with fuel and move the pistons. The space between the electrodes must have a properly size. If the distance is too large, the voltage won’t be enough, if is too small, will have spark in the wrong time.
Parts of plug
The ceramic insulators serve to thermal dissipation and electrical isolation. The central electrode inside the plug is made of copper with tip of nickel. The copper for being one of the best conductors and the nickel to reduce weariness and corrosion. The interference supressor is a resistor to suppress interference by radio waves. The metallic seal above the external ceramic serve to reduce oxidation and corrosion. The metallic rings and a powder prevent the gas escape and keep the heat dissipation uniform.
Cold and hot plug
There are two types of plug: hot and cold. In the hot plug the internal ceramic tip is bigger and has a bigger way to dissipation, therefore dissipate less heat and the cold plug has a smaller tip which dissipate more heat with smaller dissipation way.
To lower speeds the hot plug is better because since it has a bigger dissipation way, the temperature is kept high. The cold plug is more adequate to high performance motors.
The plugs must operate in a temperature band between 450°C and 850°C. Below this band will have carbonization which produce failures in sparks.
Above 850ºC will have overheating.
To avoid the two cases, must be installed the plugs according to the thermal degree (dissipation degree). Thermal degree above the needed produce carbonization and below overheating.
It is recommended the inspection of plugs for each 10,000 km traveled by the vehicle.