1. Steel shell: The lower part of the steel shell is a thin thread for fitting with the cylinder head spark plug hole, and the upper part has an external hexagon nut for the spark plug sleeve to tighten or unscrew the spark plug.
2. The metal rod is the center electrode. The lower end of the metal rod is in contact with the upper end of the center electrode through a conductive glass body, and the upper end of the metal rod is provided with a wiring nut.
3. There is a high alumina ceramic insulator between the steel casing and the center electrode, so that the center electrode is insulated when the power is applied.
4. The lower part of the steel case is equipped with a curved side electrode.
5. There is a copper washer in the middle of the outer part of the steel shell.
The spark plug skirt has a small heating area and fast heat dissipation, so the skirt temperature is lower. It is called a cold spark plug, which is suitable for high-speed and high compression ratio engines.
In the standard of the spark plug, the heat value is usually used to characterize the thermal characteristics of the spark plug. The spark plug heat value represents the balance of the heat absorption and heat dissipation of the spark plug insulator skirt. The higher the heat value. The stronger the balance between heat absorption and heat dissipation, the lower the thermal value of the hot spark plug and the higher the thermal value of the cold spark plug. Generally, engines with high power and large compression ratios use cold spark plugs with high heating value; on the contrary, engines with low power and small compression ratios select thermal spark plugs with low heat value. In general, the selection of spark plugs is determined by the factory through product sizing experiments, and should not be changed at will.
Under the action of high voltage, the air between the center electrode and the side electrode of the spark plug will rapidly ionize, forming positively charged ions and negatively charged free electrons. When the voltage between the electrodes reaches a certain value, the number of ions and electrons in the gas is increased like an avalanche, so that the air loses insulation, and the gap forms a discharge channel, and a “breakdown” phenomenon occurs. At this time, the gas forms a luminous body, that is, “spark”. With its thermal expansion, a “snap” sound also occurs. The temperature of this electric spark can be as high as 2000 ~ 3000 ℃, which is enough to ignite the mixture in the combustion chamber of the cylinder.