Denso, Japan's largest automotive parts manufacturer and a key member of Toyota's supplier group, ranks first or second globally in nearly 20 component categories.  Denso's spark plugs fall under the auspices of its Powertrain Control Systems business, representing 22% of Denso's total sales. 

In January 2005, Matthew Beecham talked with Marko Wowczyna, manager for Denso's UK aftermarket operations about how the company is pushing back the technical boundaries in the spark plug arena. What are the factors pushing innovations in spark plugs?

Marko Wowczyna: Spark plugs are increasingly required to deliver improved ignitability and a longer life, be smaller in size, and prevent ignition failure.  Amongst these, demand for smaller plugs and the prevention of ignition failure have become particularly important recently.  This is because vehicle manufacturers require smaller spark plugs to help increase engine design flexibility; because ignition failures are often caused by carbon contamination of the ceramic part -- with a smaller plug size outside temperature is lower); or because the plug is used for gasoline direct injection.  New technologies are already pushing towards these aims, with Denso having pioneered many of the sector's innovations both past and present.  An illustration of this is Denso's Iridium technology.  In 1997, Denso introduced its Iridium Spark Plug featuring a central electrode made of an iridium alloy; significantly improving plug ignitability and lengthening life.  In 1998 Denso developed the technology further to launch a spark plug with the world's thinnest iridium-alloy central electrode - 0.4 mm diameter - improving ignitability still further.  The company is continuing to develop new materials and structures that will deliver even greater ignitability and lifespan.  Denso is also working on new ways of making the spark plugs smaller and further reducing ignition failures; mainly by improving the ignition component (including both earth and centre electrodes) and the ceramic part. We've heard a lot about precious metal spark plugs becoming increasingly popular in Europe and North America, though technically speaking, what are you seeing in terms of copper core technologies?

MW:  Copper core technology is widely used as a way of releasing heat from the ceramic sleeve that covers the central electrode.  Some suppliers also use copper core technology for the earth electrode - it increases thermal resistance when the spark plug is inserted into the engine cylinder more deeply than before, improving ignitability. 

In Denso's case although we have copper core technology - mass-produced for some applications -  we have recently developed a unique new manufacturing process technology and alloy material for the earth electrode that provides better thermal resistance.  Known as Super Thermal Resistant Ni alloy (or High Al. content Ni alloy) the material contains 3% aluminium; compared to the conventional technologies of Bosch and NGK at only 0.5%.  The Denso spark plug featuring this unique earth electrode was launched in 2002 (Patent pending) and is now supplied to major vehicle manufacturers.  Such is the difficulty of welding the aluminium content alloy electrode to the metal housing that Denso is the only manufacturer able to supply this technology. Even though spark plug technology is improving, can it really catch up with engine life?  i.e. is a 'life of engine' spark plug a possibility?

MW:  We believe it is possible to develop a spark plug that lasts as long as an engine, and this is one of our goals.  However, whilst latest technologies ensure extremely long life - potentially even exceeding the life of the car itself - Denso does recommend the periodical replacement of any spark plug to benefit fuel economy and optimal engine performance.  For example, we advise drivers to change our Iridium spark plugs at 100,000 km, although they have the capability to last for 200,000 km.  With longer life spark plugs, what is the impact on the aftermarket?

MW:  We see the entire aftermarket volume of spark plugs, including long-life spark plugs as well as nickel spark plugs, declining due to the increase in OE installation.  We estimate this amounts to about a 1 - 2% decline each year on average in Europe.  We are also seeing the most marked decrease in middle and northern Europe where the installation ratio of longer-life spark plugs is high, and the smallest decrease in southern and eastern Europe where the installation ratio of longer-life spark plugs is low.  Whilst volume is declining, however, it is fair to say that the value of the overall spark plug market remains strong due to the growth of higher technology plugs, maintaining sales revenues. Turning to glow plugs, what are the factors pushing back the technical boundaries?

MW:  In addition to rapid start, glow plugs are required to have a higher temperature, a smaller diameter, and longer life.  A higher temperature induces better combustion to improve engine-starting performance; whilst a smaller diameter (thinner) glow plug allows the engine to have a stronger structure.   Denso is working to meet not only rapid start but all of these requirements.  Further, in diesel engines the compression ratio has been decreased to reduce harmful substances including NOx and PM in emissions, and this requires the glow plug to hold a higher temperature for a longer period of time - requiring a longer life. 

To comply with the requirements for higher temperature, longer life, and rapid start, the ceramic glow plug is growing in popularity.  In particular this is being seen in regions such as Europe and North America, which have strict emission regulations.  In 1991, Denso launched the world's first ceramic glow plug with an entirely ceramic heating component.  We are now working to improve ceramic materials for higher heating resistances, as well as to reduce cost.

Denso is also developing temperature control technology for glow plugs.  By precisely controlling the temperature-raising characteristics of the glow plug we aim to raise the temperature more quickly, induce better combustion at a higher temperature, and deliver a longer life.