Different Types of Spark Plugs


In our previous article we read about how car ignition system works and also the complete working of spark plugs. In this article we are going to discover various types of spark plugs available and their classification in detail. The design of spark plug is based on the type of engine used. Different designed spark plugs are used to suit the following parameters:-

  • loading and speed range of an engine
  • its combustion chamber design
  • varying fuel mixture strength
  • compression ratio and
  • operating temperatures
  1. Long reach spark plugIt is used where cylinder -head section is very deep (i.e. thickness is large) while in thinner head such plug would project too far into the combustion chamber and will have a short life.
  2. Short reach spark plugAs discussed in 1, it is used in thin cylinder- head cross section. In deeper head, its electrodes would lag behind thus producing inappropriate spark resulting in incomplete combustion of fuel.
  3. Tapered-shoulder plugThis type of design is incorporated where no gasket is used. Its tapered conical head is tightened into the cylinder head removing the need for gasket.
  4. Cold plugIt has a short insulator(less ceramic covering) i.e. more contact area with the metal part of the plug and cools faster thus preventing pre-ignition through overheating & making it apt for high performance engines.
  5. Hot plugIn contrary to cold plug it has long insulator i.e. less contact area with the metal part (having more ceramic covering), has a long heat flow which makes it apt for low performance engines. It also burns off any deposits on the plug.
  6. Side gap plugAs shown in the picture, it has the side gap between the electrodes which increases horsepower by enshrouding the spark. It allows the flame created to propagate faster resulting in proper combustion of the air fuel mixture. It is often used in highly tuned engines.
  7. Three gapA|three gap Plug-as the name suggests it has three gaps produced by the three earthed electrode (one is hidden behind in the picture) to give longer plug life.

In normal cars copper cored spark plugs are used. The reason behind using copper core is high conductivity but because of its inability to have a longer life makes it less usable (though some racers prefers it and replaces frequently). In custom engines and high rev engines, iridium and platinum alloy spark plugs are used.

These plugs have good longevity and durability. These are apt for high compression engines (turbocharged engines). The diameter of the central electrodes vary between 0.4 mm (Iridium) to 0.7 mm (platinum). These spark plugs with super fine tips (greater ignitability) exhibited its importance in high performance engines.


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