According to the calorific value, there are cold and hot; According to the electrode materials, there are nickel alloy, silver alloy and platinum alloy; If more professional, there are generally the following types of spark plugs:

1. Quasi-type spark plug: the insulator skirt is slightly contracted into the end face of the shell, and the side electrode is outside the end face of the shell, which is the most widely used [5].

2. Edge protruding spark plug: the insulator skirt is long, protruding beyond the end face of the shell. It has the advantages of large heat absorption and good pollution resistance, and can be directly cooled by the intake air to reduce the temperature, so it is not easy to cause hot ignition, so the thermal adaptation range is wide [5].

3. Electrode type spark plug: its electrode is very thin, characterized by strong spark and good ignition ability. It can guarantee the engine to start quickly and reliably in cold season, and has a wide thermal range, which can meet a variety of uses [5].

4, seat type spark plug: its shell and screw thread are made into a cone, so it can keep a good seal without a gasket, thus reducing the spark plug volume, which is more beneficial to the engine design [5].

5, polar spark plug: the side electrode is generally two or more than two, the advantage is reliable ignition, the gap does not need to be adjusted often, so in the electrode is easy to ablate and spark plug gap can not be adjusted often some gasoline machine is often used [5].

6. Surface jump spark plug: that is, the surface clearance type, which is the coldest type of spark plug, and the clearance between the central electrode and the end face of the shell is concentric [5].

7. Standard and protruding spark plugs

Standard spark plug is a one-side electrode spark plug whose insulator skirt end is slightly lower than the threaded end of the shell. It adopts the traditional ignition end structure which is most widely used in side-mounted valve engines. To distinguish it from the later "protruding type", this structure is called "standard type" [6].

Protruding spark plugs were originally designed for overhead valve engines. Its insulator skirt protrudes the threaded end face of the housing and extends into the combustion chamber. It absorbs more heat in the combustion mixture and has a higher working temperature at the speed of breath to avoid fouling. At high speed, because the valve is placed on the head, the inhaled air flow is directed at the insulator skirt and cooled, so that the maximum temperature is not increased much, so the thermal range is large. Protruding spark plugs are not suitable for side-mounted valve engines [6] because the inlet has many turns and the air flow has little cooling effect on the insulator skirt.

8. Single-pole and multi-pole spark plugs

Conventional single-side spark plugs have an obvious defect that the side electrode covers the central electrode. When a high voltage discharge occurs between the two poles, the mixture in the spark gap absorbs spark heat and is activated by ionization to form a "fire core". The place where the fire core is formed is generally close to the side electrode, and more heat will be absorbed by the side electrode, namely the "flame suppression effect" of the electrode, which reduces the spark energy and reduces the fire jumping performance [6].

Then, in the 1920s, came the three-side spark plug. Compared with the single pole, many side of the spark gap by multiple side of the electrode section (rushed into a round hole) and the center of cylinder electrode, the type of this kind of set of spark gap to eliminate the disadvantages of side electrode covering the center electrode, increased the spark of the "accessibility", spark energy is larger, easier to deep inside the cylinder, helps to improve mixture combustion and reducing emissions. The multi-pole provides multiple fire jumping channels, thus prolonging the service life and improving the reliability of ignition. It must be pointed out here that the moment of discharge can only be one channel fire, not multiple poles at the same time. The discharge process of high-speed photography proves this point [6].

The suffix letters (letters after calorific value) D, J and Q in domestic spark plug models represent double pole, three pole and four pole respectively [6].

9, Nickel base alloy and copper core electrode spark plug

The most basic requirements for electrodes inserted into the combustion chamber are ablative resistance (electrical and chemical) and good thermal conductivity. With the development of materials science and technology, electrode materials have undergone the evolution of iron, nickel, nickel base alloy, nickel-copper composite and precious metals. The most commonly used alloy is nickel - base alloy. In general, pure metals have better thermal conductivity than alloys, but pure metals (e.g., nickel) are more sensitive than alloys to the chemical corrosion of combustion gases and the solid deposits they form. Therefore, nickel base is used to add chromium, manganese, silicon and other elements into the electrode material. Chromium improves the resistance to electrocorrosion, while manganese and silicon improve the resistance to chemical corrosion, especially the resistance to the very harmful sulfur oxide [6].

10, general type and resistance type spark plug

The spark plug

The spark plug

As a spark discharge generator, spark plug is a kind of broadband continuous electromagnetic radiation interference source. In order to suppress the strong interference of electromagnetic radiation caused by fire to radio field, protect radio communication and prevent the misoperation of vehicle electronic device, the development of resistive spark plug has been accelerated since the 1960s in the world. China has also issued a series of mandatory electromagnetic compatibility (EMC) national standards, which strictly limit the radio interference characteristics of vehicle devices driven by spark plug ignition engines. Therefore, the demand for resistive spark plugs has increased greatly. Resistive spark plug has no big difference in structure with ordinary type, only the conductor sealant in the insulation body is changed to resistance sealant