Definition of Spark Plugs
Spark plugs, commonly referred to as ignition plugs, serve to discharge high-voltage pulses delivered by the ignition cables. This discharge arcs across the gap between the electrodes, generating a spark that ignites the air-fuel mixture in the cylinder. The fundamental requirements for a high-performance engine include a high-energy stable spark, a well-mixed air-fuel mixture, and a high compression ratio. Upgrading spark plugs and ignition wires is often one of the first steps in enhancing a vehicle’s ignition system.

Types Based on Electrode Materials
Spark plugs are often categorized as standard, platinum, or iridium based on their electrode materials. Standard spark plugs, typically made of nickel-manganese alloy, are commonly used as original equipment and generally require inspection or replacement after about 10,000 km or one year. In contrast, platinum spark plugs can last up to 100,000 km without needing replacement. Similarly, iridium spark plugs, a more recent innovation, offer comparable longevity. This extended service interval adds convenience for vehicle owners. However, it’s important to note that repair shops will not automatically install platinum spark plugs during maintenance unless specifically requested. Standard spark plugs are inexpensive, often costing just a few dollars each, whereas original-equipment platinum plugs can cost significantly more—typically found in high-end vehicles like Mercedes-Benz, BMW, and some Toyota models. Therefore, it’s essential to adhere to the maintenance schedule for standard spark plugs and perform regular checks, such as examining electrode color and gap width.

Platinum and iridium spark plugs are more expensive due to the use of precious metals. Although the amount used is minimal—only a tiny weld at the tip of each electrode—this small amount plays a critical role. Precious metals are chosen primarily for their durability. During operation, the combustion process generates extreme temperatures and pressures, with electrode temperatures reaching approximately 900°C. While silver and gold have melting points too low for electrode use, nickel—with a melting point around 1,500°C—is widely used for standard plugs due to its affordability. Platinum, melting at nearly 2,000°C, offers superior stability and erosion resistance. Iridium, with an even higher melting point, is particularly suited for high-performance engines that operate at high speeds and under sustained load. Additionally, precious metals exhibit stable chemical properties, ensuring reliable and precise spark generation under extreme conditions. In contrast, standard spark plugs may produce inconsistent sparks or even misfire under such demands, compromising engine performance.

While upgrading to high-performance spark plugs can be beneficial, it’s important to choose based on individual driving habits and vehicle needs. Platinum spark plugs offer clear advantages, but whether they are necessary depends on the driver’s usage. Iridium plugs, being more expensive, are best suited for those who frequently push their engines to high performance. For everyday driving, high-quality platinum plugs can provide excellent performance without unnecessary expense.

Categories of Spark Plugs
Spark plugs can be classified based on heat range (cold vs. hot types) and electrode material (nickel alloy, silver alloy, platinum alloy, etc.). From a more technical perspective, spark plugs include the following types:

1. Standard Spark Plugs:
   The insulator skirt is slightly recessed from the shell end face, with the side electrode located outside the shell end. This is the most widely used type.

2. Extended Insulator Spark Plugs:
   The insulator skirt is elongated and protrudes beyond the shell end. These plugs offer greater heat absorption, better fouling resistance, and improved cooling from incoming air, reducing the risk of pre-ignition. They have a broad thermal operating range.

3. Fine-Wire Electrode Spark Plugs:
   These feature thin electrodes that produce a strong spark and reliable ignition, ensuring quick starts even in cold weather. They have a wide heat range and are versatile in application.

4. Tapered Seat Spark Plugs:
   The shell and threaded section are conical, eliminating the need for a gasket while maintaining a secure seal. This compact design benefits engine packaging.

5. Multi-Electrode Spark Plugs:
   Equipped with two or more side electrodes, these provide reliable ignition and require less frequent gap adjustment. They are often used in engines where electrodes are prone to erosion or where adjusting the gap is impractical.

6. Surface-Gap Spark Plugs:
   These are among the coldest types, featuring a concentric gap between the center electrode and the shell end face.

Additionally, to suppress radio frequency interference from the ignition system, there are resistor-type and shielded-type spark plugs. Resistor plugs contain an internal resistor (5-10 kΩ), while shielded plugs are enclosed in a metal shell for complete shielding. Shielded plugs not only prevent radio interference but are also used in waterproof and explosion-proof applications.