When it comes to spark plugs, the section most people are aware of and the part that without it the plug would not function – is the insulator. The familiar white ‘ceramic’ is a part that cannot be taken for granted. It has to prevent the escape of in excess of 30,000 volts writes, Ron Merralls, NGK Technical Services Assistant Manager – Aftermarket
‘NGK’ is a name synonymous with spark plugs. When the full Japanese name is translated, it means Japan Insulator Company. The company also trades under the NTK brand for the Technical Ceramics arm of the business. NGK Insulators was established in 1919 and in 1936 the first spark plug factory was built. This shows us that the pedigree of NGK in this area is second to none.
The insulator is in fact Alumina – which is aluminium oxide. A mined substance obtained from bauxite. It is chosen because after being processed, formed, sintered and glazed it offers superior insulation properties, resistance to chemical attack, extreme hardness and high strength. Although the insulator looks remarkably similar on a modern plug to those of days gone by, NGK’s expertise in this field means that design and production methods have remarkably increased the dielectric strength and resistance to thermal shock.
Most modern plugs incorporate a resistor to guard against electrical ‘noise’. NGK’s accurate and stable resistor material is constructed from glass impregnated with carbon. Altering the ratio of the substances means that the vehicle manufacturers (VMs) required value can be met and will not break down or alter over the service life of the plug.
The historical preferred choice of material for the centre electrode has been a copper cored nickel alloy. Nickel alloy is a material which provides a good service life and the copper provides a great method of ensuring heat is conducted away from the electrode tip quickly.
Platinum and Iridium alloy plugs are more often the choice of vehicle manufacturers now. NGK laser welds small pins of these precious metals to the electrode tip. Iridium is the best material. It is truly a precious metal – being one of the least abundant elements. It is chosen for its hardness, resistance to heat, oxidisation and wear. Although the pin can be just 0.4mm in diameter, it will last longer than a conventional 2.5mm diameter nickel alloy electrode plug whilst also significantly improving ignition performance. Worth noting is that all NGK precious metal plugs still incorporate NGK’s pioneering copper core in the main centre electrode. As a result of these benefits, Iridium plugs in particular are used extensively in race engines and becoming increasingly popular as the upgrade choice for road vehicles.
Ground electrodes can be visually different when comparing different part numbers – some plugs have one and others can have up to four. However, plugs that look the same often have unseen differences in this area. Subtle differences in their shape, construction and material often exist. High specification alloys are often required and some are a layered copper design. This is the result of working closely with VMs to produce the perfect plug for the engine. Design characteristics and material is often crucial to the engine type to guard against overheat and vibration fatigue. Developed for the VMs and more recently available to the aftermarket are the DFE (double fine electrode) plugs which incorporate a precious metal pin welded to the ground as well as one welded to the centre electrode. This pin to pin spark discharge design is the most sophisticated in obtaining superb ignition performance coupled with long life.
Another technology is the SPE (special platinum electrode). For instance, Ford uses the NGK SILZNAR8C7H in their 1.0L Ecoboost engine. The small three-cylinder engine puts plugs under stressful combustion conditions, resulting in bespoke requirements. It has a fine Iridium centre electrode and a strong ground electrode material construction which incorporates a taper cut on the ground electrode tip (to reduce the amount of material shielding flame kernel growth). The ground electrode is of the SPE type (special platinum electrode) which incorporates a platinum chip at the leading edge to guard against wear. The ground electrode is of the layered copper design to ensure efficient dissipation of heat away from the electrode tip.
The NGK factory invests heavily in quality, research and development and pushes technology forward to meet the VMs requirements both now and in the future. Like most companies, advances in technology and alternative concepts are closely guarded by the company.
NGK’s ethos is to continue development of technology products for automotive and associated industries to help lower the ecology burden, enhance operator comfort and drivability experience whilst maintaining operational reliability.