According to the calorific value, there are cold and hot types; according to the electrode material, there are nickel alloys, silver alloys and platinum alloys; if more professional, the types of spark plugs are generally as follows:
1. Quasi-type spark plug: the insulator skirt is slightly retracted into the end face of the case, and the side electrode is outside the end face of the case, which is the most widely used.
2. Spark plug with protruding edge body: The insulator skirt is longer and protrudes beyond the end face of the housing. It has the advantages of large heat absorption and good anti-pollution ability, and can be directly cooled by the intake air to reduce the temperature, so it is not easy to cause fiery ignition, so the thermal adaptation range is wide.
3. Electrode-type spark plug: The electrode is very thin, characterized by strong sparks and good ignition ability. It can also ensure that the engine starts quickly and reliably in the cold season, the thermal range is wide, and it can meet a variety of uses.
4. Seat-type spark plug: its shell and screw-in thread are tapered, so it can maintain a good seal without a gasket, thereby reducing the volume of the spark plug, which is more beneficial to the design of the engine.
5. Polar spark plug: The side electrode is generally two or more. The advantage is that the ignition is reliable and the gap does not need to be adjusted frequently. Therefore, it is often used on some gasoline engines where the electrode is easy to ablate and the spark plug gap cannot be adjusted frequently.
6. Surface spark-type spark plug: It is the surface gap type. It is the coldest spark plug. The gap between the center electrode and the end surface of the housing is concentric.
7. Standard and protruding spark plugs
The standard type spark plug is a single-side electrode spark plug whose insulator skirt end is slightly lower than the threaded end surface of the casing. It adopts the traditional ignition end structure which is the most widely used side-mounted valve engine. In order to distinguish it from the "protruding type" that appeared later, this structure is called the "standard type".
The protruding spark cold was originally designed for overhead valve engines. Its insulator skirt protrudes from the threaded end surface of the shell and extends into the combustion chamber. Absorb more heat in the burning gas mixture, and have a higher working temperature at the rate of speed to avoid fouling; due to the overhead of the valve at high speed, the inhaled airflow is directed to the insulator skirt to cool it, so that the maximum temperature does not increase There are many, so the thermal range is large. The protruding spark plug has many turns in the intake port, and the air flow has little effect on the cooling of the insulator skirt, so it is not suitable for side valve engines.
8. Single-side pole and multi-side pole spark plugs
The traditional single-side pole spark plug has an obvious defect that the side electrode covers the center electrode. When the high voltage discharges between the two poles, the gas mixture at the spark gap will absorb the heat of the spark and be activated by ionization to form a "fire core". The place where the fire core is formed is generally near the side electrode, and the heat will be absorbed by the side electrode more, that is, the "flame suppression effect" of the electrode, which reduces the spark energy and reduces the flashover performance.
Thus, in the 1920s, three-sided spark plugs appeared. Compared with the single-side pole, the spark gap of the multi-side pole is composed of a plurality of side electrode cross sections (punched into a circular hole) and the cylindrical surface of the center electrode. This side-by-side spark gap eliminates the side electrode covering the center electrode. The shortcomings increase the "accessibility" of the spark, the spark energy is larger, and it is easier to penetrate into the cylinder, which helps to improve the combustion of the mixed gas and reduce exhaust emissions. Since the multi-side pole provides multiple channels for flashover, the service life is extended and the reliability of ignition is improved. It must be pointed out here that the moment of discharge can only be a channel flashover, it is impossible for multiple side poles to flashover simultaneously. The discharge process of high-speed photography proves this.
The suffix letters (the letters after the calorific value) in the domestic spark plug models D, J, and Q indicate the double-sided pole, three-sided pole, and four-sided pole, respectively.
9. Nickel-based alloy and copper core electrode spark plug
The most basic requirements for electrodes extending into the combustion chamber are resistance to ablation (electrical and chemical corrosion) and good thermal conductivity. With the development of materials science and process technology, electrode materials have undergone the evolution of iron, nickel, nickel-based alloys, nickel-copper composite materials, and precious metals. The most commonly used nowadays are nickel-based alloys. Generally, pure metals have better thermal conductivity than alloys, but pure metals (such as nickel) are more sensitive to chemical corrosion reactions of combustion gases and the solid deposits they form than alloys. Therefore, the electrode material uses nickel-based elements such as chromium, manganese, and silicon. Chromium increases the resistance to electrical corrosion, and manganese and silicon increase the resistance to chemical corrosion, especially to the highly harmful sulfur oxide.