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Spark Plugs & Glow Plugs Explained

Spark plugs and glow plugs are a critical part of the combustion process but are a commonly misunderstood component.

Spark plugs & glow plugs have a seemingly simple but critical job: to ignite the fuel and air mixture within the piston chamber, which in turns forces the piston down and produces the power of the engine.

One thing that's vital to remember about spark plugs & glow plugs is the operating temperature.

A plug uses a lot of voltage in order to produce an ignition-worthy spark of "electrical performance", which in turn causes heat. The trick is to keep this temperature low enough to prevent pre-ignition, but high enough to prevent fouling "thermal performance". That's why it's critical you get the right plug fitted.

There are many fundamental factors that separate one plug out from another:

• Length of the insulator nose
• Thermal conductivity of the centre electrode
• Structure of the centre electrode - copper iridium etc.
• Relative position of the insulator tip to the end of the shell "projection"
• Heat rating; the longer the insulator nose the hotter the capacity

Spark plugs & glow plugs can be used to diagnose an ill-performing engine. They offer insight into fuel richness, heat, air to fuel ration and contamination within the combustion process... so take notice of damaged or unhealthy looking plugs.