SPARK PLUG DESIGN
Every year the range of NGK spark plugs grows to accommodate the ever increasing demands of modern engines. Spark plug design must take into consideration many features
of an engine including physical dimensions; combustion chamber shape; cooling abilities; fuel and ignition systems. Spark plugs play a vital role in producing the maximum power from an engine whilst keeping fuel consumption and emissions to a minimum. Choosing the correct spark plug type will help a vehicle manufacturer meet legislated emission targets and assists the motorist in getting the best from their engine.
Increases in the size and the requirement to improve the cooling of the inlet and exhaust valves have meant that the space available for the spark plug is severely restricted on some cylinder heads. A change in spark plug design; possibly the adoption of a taper seat and extended reach (threaded portion) or even the use of a smaller diameter is often the answer. Some engines require the use of two spark plugs per cylinder and again due to space restrictions these might be of different sizes.
Changes in fuelling systems and the fuel itself have meant some special features being adopted at the ‘firing end’ of the spark plug. Extra projected types push the spark position into the heart of the combustion chamber to promote better combustion of the fuel/air mixture; which is weaker than ever in an effort to improve economy. Modern engines manufacturers often require increased spark gaps to allow a longer spark duration; which again aids more efficient combustion.
To combat the ‘cold fouling’ effect that can occur in some engines using unleaded fuels specially arranged ground electrodes are sometimes used. These can force the spark to discharge across the insulator and thus burn away any built up carbon that could cause poor starting or misfires. It is not uncommon to find two; three or four ground electrode arrangements in new vehicles. The use of precious metals on the tips of the spark plug electrodes is not uncommon especially on higher performance engines. Whilst these spark plugs do have increased service life they are often specified because of their superior ignition qualities.
Our engineering departments work very closely with the engine and vehicle manufacturers to produce the ideal spark plug type for each application. Any change in production is expensive for a manufacturer and therefore new spark plug types are only produced where necessary. NGK employ the very latest production technology to ensure that every aspect is catered for – performance; economy and value.
HEAT RANGE AND HEAT DISSIPATION
Spark plugs do not produce heat in the combustion chamber. One of the functions of the spark plug is to dissipate some of the heat produced during combustion. This is mostly transferred into the cylinder head. The ´Heat Range´ indicates the measure of the spark plug´s ability to do this. A ´hot´ spark plug is designed to maintain a sufficiently high temperature at the insulator nose to burn off carbon and oil deposits. A ´cold´ spark plug is designed to allow a faster transfer of heat to the cylinder head thus preventing overheating and premature failure.
The heat range selection is obviously a complex task with many factors to take into account. NGK engineers therefore make specific recommendations for each engine and the use
to which it is put.
WIDE HEAT RANGE
A wide range spark plug is more flexible and performs equally well in a hot or cold engine under stop and go city driving or fast motorway cruising. Engines that tend to run hot need cold type plugs. Those that run cold demand a hotter type. The specific plug for any engine is determined by the plug´s heat range. That is the minimum and maximum temperatures between which the plug will offer optimum performance.
The heat range of NGK Spark Plugs is wider than ordinary plugs therefore they are suitable for both high speed and low speed driving. Compared with conventional plugs of the same
pre-ignition rating they have more resistance to fouling.
Compared to ordinary plugs with equal anti-fouling resistance; NGK Spark Plugs have a higher pre-ignition rating.
NGK´S HEART OF COPPER
Copper wire used in place of the iron core in conventional plugs is the secret of NGK´s Wide Heat Range. Copper´s superior heat conductivity dissipates heat quicker. It cools the
electrode tip and insulator tip which prevents hot spots that could cause pre-ignition. Increased heat resistance does not affect fouling resistance; which is primarily determined by the insulator nose length. The longer the nose; the more susceptible it is to heat and the more free from fouling. By raising the pre-ignition rating with the high conduction copper and leaving the insulator nose long; NGK produces the Wide Range Plug. One that meets the broad thermal requirements of engines under high and low RPM conditions. With the exception of a couple of older applications all the spark plugs in this motorcycle catalogue employ copper core technology.
As a result of our policy of continuous research and development NGK can offer special spark plugs designed to give optimum performance under a high range of conditions.
‘VX’ TYPE (e.g. B8EVX)
These plugs have an even smaller centre electrode (0.8mm) than the V types and this is made of platinum. This combined with a taper cut ground electrode means an even lower required voltage than the V types. The result is better ignitability along with
improved starting; idle stability and anti-fouling performance.