Spark plugs — withstanding extremes

In order to operate as efficiently as possible, and to avoid any negative effects on a running engine’s ignition and combustion, spark plugs must be designed to withstand a wide range of extreme conditions.

What are these extreme conditions?

Spark plugs must be able to endure continuously changing temperatures. A spark plug’s surface reaches up to 3000°C during combustion of the air-fuel mixture. Then, during the intake stroke, the spark plug is subject to sudden cooling by low temperature gas. This sudden heating and cooling process is repeated every other rotation as long as the engine is running. At the same time it must be able to cool, the spark plug must release enough heat to avoid becoming a source of pre-ignition.

Spark plugs must be able to operate under severe pressure changes. In the intake stroke, the pressure is less than 1 atm, but in the combustion stroke, it reaches over 50 atm. Thus, spark plugs are required to have the mechanical strength to withstand this severe pressure. Spark plugs must also be able to maintain an airtight seal between the housing and the insulator in this environment where temperature and pressure are constantly changing.

Spark plugs must be able to channel high voltage of up to 10-30 kV from the terminal to the electrodes without leaking any energy. Leaking energy will lead to misfires. At the same time, the radio interference caused by the high voltage and current peaks must be suppressed to prevent errors on surrounding sensors.

In addition, spark plugs must have the wear-proof resistance to minimise electrode wear in a severe usage environment — some spark plugs even have electrodes made of precious metals for this exact purpose. Spark plugs must also be able to minimise fouling of electrodes and have self-cleaning properties that burn away carbon deposits. Therefore, it is desirable that the spark plug temperature rises quickly even when the vehicle is moving at low speed and that the insulator section reaches the self-cleaning temperature (about 500 °C).


How spark plug materials affect operation in extreme conditions

DENSO produces a multitude of different spark plugs comprised of unique materials that all impact the plug’s durability and performance within this unforgiving environment.

Direct fit

Leading OEMs choose DENSO Direct Fit spark plugs for their reliability and performance in both high-end and high-volume vehicles. They are made out of a range of materials including nickel, platinum, iridium and SIP.


Most of DENSO nickel spark plugs are equipped with U-Groove technology for improved ignition performance. In addition, the DENSO offers a more consolidated range than other manufacturers.


When lowering emissions became a goal of many manufacturers, it became necessary to replace the multi-ground nickel technology with a higher spec: platinum long life equipped with a platinum centre electrode and a platinum chip in the ground electrode. Platinum is often used for most modern spark plugs on the ground electrode for its excellent corrosion resistance.


Iridium, one of DENSO’s specialties, allows for even finer centre electrodes. This results in greater performance, and as iridium spark plugs can last a vehicle’s lifetime, leads to lower maintenance costs.

Super Ignition Plug (SIP)

Currently, super ignition is the best available technology for spark plugs. Produced with the smallest centre electrode used by OEMs, DENSO super ignition spark plugs provide the best performance even under the harshest conditions, maintaining a long lifetime.

Twin Tip

Though spark plugs with smaller electrodes perform better in almost every aspect, simply reducing electrode size reduces a spark plug’s lifetime. Because of this, DENSO has developed two types of spark plugs with small electrodes but designed with unique materials that help counteract this effect, known as twin tip electrodes.

Nickel TT

Patented by DENSO, Nickel TT uses a unique alloy containing nickel, silicone, yttrium and titanium (Ni-Si-Y-Ti). The compound has similar properties as nickel, but is 80% more resistant to oxidation and 40% more resistant to spark wear, which allows for fine Ø 1.5 mm electrodes with the same lifetime as a Ø 2.5 mm standard nickel electrodes, without affecting the lifetime.

Iridium TT

For manufacturers requiring even better performance and a longer lifetime, iridium spark plugs are the plug of choice. DENSO’s new Iridium TT spark plug, designed by combining Twin Tip technology with DENSO’s patented Ø 0.4 mm iridium centre electrode and a Ø 0.7 mm needle type platinum ground electrode, is the best performing spark plug available in the market. It reduces both exhaust emissions and fuel consumption whilst providing a long lifetime.

Iridium Power

Featuring a very fine Ø 0.4 mm iridium centre electrode, Iridium Power performs better than almost every other spark plug on the market. It is capable of handling high engine speeds and high powered engines such as those found in motorcycles, tuned cars, snowmobiles and jet skis.

Iridium Racing

Iridium racing spark plugs, designed with an ultra-fine 0.4 mm diameter iridium electrode and 0.8 mm platinum ground electrode, are trusted by drivers and racing teams for their reliability, durability and performance. Silicone-coated insulators repel water to prevent potential harm from moisture and carbon whilst a housing-end-face chamfer helps prevent carbon fouling.

Find out more

More information about spark plugs and the DENSO spark plug range are available online, on TecDoc or from your local DENSO Aftermarket sales contact.