An article that takes you through spark plugs

Spark plug is an important original component to support the work of gasoline engines (diesel engines are compression ignition to do work, no spark plug). In the ignition system of gasoline engine, high voltage current is introduced into the cylinder to produce electric spark to ignite the combustible gas mixture. It is mainly composed of wiring nut, insulator, wiring screw, center electrode, side electrode and shell, and the side electrode is welded to the shell.

Copper core is recommended to be replaced every 20-30,000 km; nickel alloy is replaced around 40-60,000 km; platinum core is recommended to be replaced every 80,000 km; iridium core is recommended to be replaced every 100,000 km. Specific information needs to check the vehicle maintenance manual.

I. Working principle and role

Gasoline engine is through the timely combustion of fuel and gas mixture to produce power, but as a fuel, gasoline is difficult to spontaneous combustion even at high temperatures, in order to make it timely combustion is necessary to use the “fire” to ignite. The role of the spark plug is to release the ignition coil pulse of high-voltage electricity in the tip of the line into an electric spark, ignite the gas mixture in the cylinder to do work, most commonly known as the equivalent of a lighter flint, an activation component.

Second, the spark plug structure

The main structure of the spark plug are: 1, wiring screw; 2, central electrode; 3, ground electrode; 4, metal shell; 5, insulator, of which the most important is the two electrodes.

From the appearance, the top part is called “terminal screw cap”, it is connected to the cylinder line, the role is to complete the docking of the cylinder line, when plugging and unplugging the cylinder line feel a sense of inhalation or ejection is from here, at the same time, it is also the place to receive electricity.

The following ceramic part of the insulation, heat resistance, thermal conductivity, these are the characteristics of ceramic material, ceramic surface has several grooves ripples, its role is to prevent the generation of flying arc, that is, between the terminal screw cap and the main body of the metal generated by the firing phenomenon (because the terminal screw cap and the main body of the metal in the ignition between the continuous high-voltage electricity, high-voltage electricity will try to slip away along the surface of the insulator, in order to stop the high-voltage electricity, so set up layers of grooves).

And the ceramic part is next to the main metal, the hexagonal (there are sizes) to facilitate the disassembly of the spark plug, from the manufacturing process, its surface also took the electroplating treatment, so that the high temperature, corrosion resistance. The thread is used to fasten the cylinder head part, screw diameter and screw length also due to the engine and divided into different categories.

The end is the spark plug electrode, there are center electrode and outer electrode, the two may take two different materials, and we often say iridium or white gold and other precious metal material refers to the material of the center electrode (some spark plug outer electrode will also use the same material), compared to the electrode for nickel-manganese alloy material of ordinary spark plug, their ignition capacity is stronger, but the price difference is several times.

In addition, in order to make the spark plug in the engine high-speed and low-speed operation can have a strong adaptability, in the center of the spark plug internal also embedded copper core, it has a great contribution to heat dissipation.

Three, the hard indicators of spark plugs


Each spark plug has its model number printed on it, the second letter in the string of characters represents the size of the spark plug, which contains both the diameter and length of the thread.

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1)Thread diameter

The thread diameter is mainly 10mm, 12mm and 14mm, in China’s models on sale, 14mm is the most mainstream size, but with the engine design more and more compact, all kinds of parts will follow the miniaturization, spark plugs are no exception, smaller and thinner trend has been set, the future 10mm, 12mm and other finer diameter spark plugs will become the mainstream.

2)Thread length

There is another important dimension is the length of the thread, many friends also commonly called it “tooth length”, there are many kinds of models in the list, but for ordinary users to remember these models are too difficult and not too meaningful, you just need to remember what size of spark plugs you need to replace your car. Some friends will ask what model is my car? This question is in the product description of the major spark plug manufacturers, find the corresponding model of their own spark plug on the line, not a difficult task.

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2, thermal value

Thermal value of this parameter is also very important, the most common explanation is the ability of the spark plug itself to dissipate heat, but different manufacturers for the thermal value of the spark plug naming rules vary, so can not be summarized as the thermal value of “high” or “low”, can be simply divided into good heat dissipation capacity The “cold” spark plugs and “hot” spark plugs for low speed engines. For example, the larger the value of the Champion spark plug means the more the spark plug is biased towards the “hot type”, while the NGK spark plug is the larger the value means the month is biased towards the “cold type”. In the purchase of spark plugs must be based on the thermal value of the vehicle to choose, if the choice does not match, it will affect the performance of the engine.

Cold spark plugs: the higher the thermal value of spark plugs, on behalf of the better heat dissipation capacity, this type of spark plugs are more suitable for high horsepower engines, the downside is that it is faster heat dissipation, so for small displacement engines are more likely to produce carbon, and the most serious consequence of carbon is ignition misfire, if you drive a car with high horsepower or often high RPM “racing”, then you can consider this kind of spark plugs.

Thermal spark plug: in the same working temperature, not easy to produce carbon, but the heat dissipation ability is relatively poor, suitable for not pursuing the power performance of the family car use. The disadvantage is that if the thermal value of the thermal spark plug is too high, it may produce early ignition and explosive shock.

Fourth, the impact of spark plug material on performance

Spark plug is made of iron shell, the central ceramic body of the two major components, which also contains a ceramic body wiring screw and electrode, and we usually select the spark plug said “a certain gold” is the material of the small electrode, and other parts of the material for the engine performance can be ignored.

Now on the market common electrode materials are copper, nickel alloy, white gold, iridium four (white gold and iridium commonly known as precious metals), metal conductivity from left to right in increasing order (copper < nickel alloy < white gold < iridium), ignition needs voltage from left to right in decreasing order (copper > nickel alloy > white gold > iridium), so the precious metal spark plug for the engine load is smaller, for reducing fuel consumption is beneficial; In addition, the life of the precious metal is also longer, of course, the price is also increased with the performance, the price of iridium spark plugs generally in a single hundred dollars or more.

Five, spark plug replacement cycle

Spark plug material used for its replacement cycle has a decisive impact, the current market mainstream spark plug copper core, nickel alloy core, white gold core, iridium core, copper core recommended every 20-30,000 kilometers to replace a nickel alloy cycle is slightly longer than the copper core, in about 40-60,000 kilometers to replace, and iridium and white gold core spark plug metal properties are more stable, good oxidation resistance, so the service life will be relatively much longer, white gold core recommended every 80,000 kilometers to replace a; iridium core recommended every 100,000 kilometers to replace a, the following table is the recommended replacement cycle corresponding to different materials.

Six, how to determine whether the spark plug needs to be replaced

If the electrode and the insulator are light yellow, it means that the working condition of the spark plug is healthy; if the spark plug electrode has black adhesion, it is a disease, which may be caused by “burning oil” or improper mixer ratio.

Seven, naturally aspirated and turbocharged engines for the requirements of spark plugs

Naturally aspirated engines and turbocharged engines for spark plug requirements are different, not that there is a turbocharged special spark plug, but there are considerations in the selection. Because the turbocharged engine power than the same displacement of naturally aspirated engines, the temperature and pressure of the gas mixture explosion is also greater, so the relative wear and tear is more serious, the use of precious metal spark plugs to extend the service life is very necessary.

Eight, the difference between single-pole, three-pole, four-pole?

Many people may have asked this question, that is, why the number of electrodes on the spark plug is not the same? What is the impact? On this point I’ll explain, first of all, do not be too entangled in this number, the number of electrodes above the spark plug does not mean that the performance must be good, one of the aspects of multi-electrode design is to extend the life of the spark plug, because in one of the electrodes after excessive aging there are other can continue to ensure normal ignition, this is for the short life of the metal spark plug to make up for the design, and not to improve the ignition performance. And now with the development of technology, the metal material used in the manufacture of spark plugs is more and more stable, life has also increased, fully capable of rated replacement mileage, so the multi-electrode design naturally faded out of the mainstream market, in general, the choice of single-electrode spark plug is sufficient.