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Spark Plug Design |
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| 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 his 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 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 cars. Whilst these spark plugs do have increased service life they are often specified because of their superior ignition qualities. NGKs 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. |
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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 plugs 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 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 plugs 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. |
NGKs Heart of Copper |
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Copper wire used in place of the iron core in conventional plugs is the secret of NGKs Wide Heat Range. Coppers superior heat conductivity dissipates heat quicker. It cools the electrode tip and insulator tip which prevents hot spots that could cause pre-igniton. 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 |
Firing End Appearance |
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NGK Spark Plug Types |
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Wide Gap Types |
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Projected Types |
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3 Ground electrode types
e.g. BCP6ET 1) Used by VW/Audi 2) These plugs have longer service life |
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Double Platinum Types Platinum tips on the electrodes |
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Semi Surface Types 1)Used by VW/Audi |
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Supplementary Gap Types Spark discharge at the |
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Intermittent Gap Types Spark discharge at intermittent |
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ISO Types 1)The insulator length of NOTE: BKR6E-11 is V-grooved |
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V-Grooved Types 1)Improved cold starting NGK copper cored V-grooved |
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OE Iridium Types 1)Centre electrode with iridium tip |
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Resistor Types 1)Prevents interference on car |
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VX Types 1)Centre electrode diameter is |
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Iridium spark plug specifications and benefits |
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| Relatively recent advances in fabrication techniques have enabled the use of Iridium - an incredibly hard precious metal, for the construction of spark plug electrodes. Laser welding technology is used to weld the Iridium tip to spark plugs manufactured by both Denso and NGK. |
 Denso Iridium tip - click to enlarge |
| Notable properties of Iridium are its melting point - approximately 2450 degrees C, considerably higher than Platinum, and its strength - approximately 8 times that of platinum. The table below compares the characteristics of Iridium with those of other precious/semi-precious metals commonly used in the construction of spark plugs. |
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Advantages of Iridium spark plug types |
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Because of the properties of Iridium, the spark plugs centre electrode can be made with a much smaller diameter than with platinum types (0.8mm), Gold or gold palladium and copper/nickel types. This means that spark plugs potential difference is more concentrated and hence less spark jump voltage is required - this can be as much as 5,000 volts less than with standard plug types. Ignition is improved and less strain is placed on the ignition system. Benefits of improved ignition/combustion include better fuel economy, increased power/acceleration and especially better throttle response.
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NGK Iridium IX spark plugs |
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NGKs Iridium IX product range of spark plugs in the UK is aimed predominantly at the motorcycle market. There are now a few instances of cars officially imported into the UK (Mainly Renault vehicles) that now use Iridium IX spark plugs as standard equipment - proof that the motoring manufacturers have tried and tested and now trust the product. NGK Iridium IX plugs are much more freely available in the US and for a wider range of car applications. |
| Sparkplugs.co.uk keep most commonly requested Iridium IX parts in stock for immediate despatch and can obtain spark plugs to satisfy most other requirements on request. | |
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The Iridium part of the spark plug is usually the centre electrode alone although some OEM Iridium plugs are available which also contain a chip of Iridium in the ground electrode. Service life of some OEM Iridium spark plugs can be as much as 120000 miles with very little degrading of performance in that lifespan. NGK Iridium IX types have a centre electrode tipped with Iridium alloy with a 0.6mm diameter. NGK believe this gives the optimum balance between performance and service life. Service life estimates are up to 60000 miles for cars and 20000 to 30000 for motorcycles although this is subject to application of course.
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Denso Iridium Power spark plugs |
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Densos current Iridium Power product range is aimed mainly at the performance car market although they have begun to release application information for motorcycles. We can usually cross reference NGK parts to Denso parts and vice versa to provide a plug to your specification. |
| Construction of NGK and Denso plugs is similar for the most part, the big difference being Densos use of a 0.4mm Iridium tipped centre electrode - claimed to be the worlds smallest production centre electrode, where NGKs is 0.6mm. As with NGK Iridium, and indeed most other spark plugs, the narrower the centre electrode is, the lower the potential difference (voltage) that is required to jump the gap between centre and ground electrodes. It follows that the Denso plug will require an even lower spark jump voltage than the NGK plug. The Denso plug also utilises a u-grooved ground electrode which is claimed to aid in the production of a flame core which further improves the combustion process. In theory, all the benefits offered by the NGK Iridium are further improved by the Denso Iridium with the exception of service life. The smaller diameter of the Denso centre electrode means that less wear can take place before the plugs optimum service life is exceeded. | |
