Spark Plug replacement - All you need to know from the experts at DENSO

Spark plug replacement intervals depend on the technology and materials used during plug manufacture, especially in terms of the electrical and heat corrosion resistance of those materials. So what should you know?

Here Gilbert Couvert, Product Manager, Spark Plugs at DENSO Europe Aftermarket advises on all aspects of spark plug replacement.

Estimated mileage

The estimated mileage of standard nickel spark plugs is between 30,000 and 45,000 km, platinum spark plugs around 70,000 km, and double platinum spark plugs more than 80,000 km. The estimated mileage of iridium spark plugs – depending on the thickness of the central electrode and the construction of the ground electrode – ranges from 60,000 km up to 120,000 km in the case of DENSO Super Ignition Spark Plugs, which feature a protruding ground electrode, like DENSO’s Twin Tip (TT) Spark Plugs.

Construction matters

The central electrode and construction of the ground electrode both have a huge impact on the combustion process. The smaller the surface area of the central electrode, the lower the voltage required for combustion. In addition, you also have to take into consideration the distance between the electrodes.

The ground electrode is of key importance. In 1974 DENSO developed a ground electrode with a now-familiar U-groove design, allowing more focused sparks on a smaller surface area; increased ignition efficiency. Another way to increase ignitability is the use of precious metal plates welded to the ground electrode.

Lower cost and improved performance?

In 2003, DENSO introduced Super Ignition Spark Plugs (SIP) featuring a fine tip on the platinum ground electrode.

Based on this construction, DENSO then developed and introduced Twin Tip (TT) Spark Plugs to the aftermarket; which proved a huge success. DENSO’s TT Spark Plugs are produced without using precious metals on the electrodes – making their price comparable to standard nickel spark plugs – and feature a nickel centre and a ‘twin’ protruding ground electrode with a slimmer 1.5 mm diameter. The complete TT Spark Plugs range is highly consolidated, comprising 15 part numbers that together offer 87% coverage of the top selling EU car parc. If you are looking for a highly ignitable, high quality, durable spark plugs without the costs usually associated with high performance, choose DENSO TT.

In both of these cases – SIP and TT Spark Plugs – the ground electrode facilitates the optimal use of electricity, to greatly limit energy loss caused by a fall in temperature through the ground electrode. This solution also allows for a heavier air/fuel mixture around the spark, resulting in better combustion in the combustion chamber – as well as lower fuel consumption, increased engine efficiency and smooth engine running. In low temperature conditions, start-up performance, response times and initial ignition are significantly reduced.

Gas operated engines

What about gas operated engines? The operating temperature in a LPG, CNG or LNG engine is much higher than in petrol engines, as the gas/air mixture burns at higher temperature. This higher temperature, together with increased electrical erosion from alternative fuels, gives a different service lifetime of a spark plug compared with normal petrol engines. This difference can be quite significant and depends on the vehicle application.

What is more, the ignition voltage required to ignite the LPG gas/air mixture is much higher than to ignite a gasoline/air mixture. In the case of a gas/air mixture, an ignition voltage of 10-15 kV is usually sufficient. LPG engines require higher ignition voltage; approx. 25-30 kV.

The increased voltage and combustion temperature of LPG engines means that the spark plugs used in these engines should be replaced more often.

It is therefore recommended to use iridium spark plugs with platinum ground electrodes in gas operated engines. DENSO After Market’s Iridium Tough Spark Plug range delivers the highest ignitability available in the market, featuring a 0.4mm iridium centre electrode in combination with four times the lifetime of a normal nickel plug. In terms of coverage, DENSO has the highest Iridium coverage for LPG in the market which is around 90% of the popular car parc.

DENSO TT Spark Plugs

In regions where LPG systems are fitted on older car parc, the price is often more sensitive than having the very low replacement rate of iridium plugs. Then DENSO has the very effective alternative to Iridium Tough plugs, the DENSO TT Spark Plugs. These plugs compensate for the required higher ignition voltage with smaller diameter center and ground electrodes when using alternative fuels. DENSO TT Spark Plugs provide greater ignitability than platinum spark plugs, and their hardened ground electrode is more resistant to temperature and electrical erosion than standard nickel plugs. This makes the use of TT in LPG engines highly effective for an affordable price.

Details of DENSO’s extensive Spark Plug programme are available online at www.denso-am.eu, on TecDoc or from DENSO Europe B.V.’s Business Unit Aftermarket on +31 (0) 294 493 493.