The spark plug is an essential component that supports the operation of a gasoline engine (while diesel engines operate by compression and do not require spark plugs). In the ignition system of a gasoline engine, high-voltage current is introduced into the cylinder to generate an electric spark, which ignites the combustible mixture. It is mainly composed of a terminal nut, an insulator, a terminal screw, a center electrode, a side electrode, and a housing. The side electrode is welded onto the housing.

The copper core should be replaced every 2-3 thousand kilometers; the nickel alloy core should be replaced around 4-6 thousand kilometers; the platinum core should be replaced every 8 thousand kilometers; and the iridium core should be replaced every 10 thousand kilometers. 

I. Working Principle and Function 

The gasoline engine generates power through the timely combustion of fuel and the mixture gas. However, even when gasoline is in a high-temperature environment, it is difficult for it to ignite spontaneously. To make it combust in a timely manner, it is necessary to ignite it with "fire". The function of the spark plug is to create an electric spark at the tip by releasing the pulse high voltage from the ignition coil, igniting the gasoline and air mixture in the cylinder for work. In the simplest terms, it is equivalent to the striker of a lighter, an activated component.

II. Spark Plug Structure 

The main components of a spark plug are: 1. Terminal screw; 2. Central electrode; 3. Ground electrode; 4. Metal housing; 5. Insulator. Among them, the two electrodes are the most important.

From the appearance, the top part is called the "terminal screw cap". It is connected to the cylinder wire and its function is to complete the connection of the cylinder wire. When plugging or unplugging the cylinder wire, the sensation of suction or ejection that you feel is precisely from this part. At the same time, it is also the place where electrical energy is received. 

The following ceramic part is electrically insulating, heat-resistant and heat-conductive. These are all characteristics of ceramic materials. The surface of the ceramic has several grooved patterns, which serve to prevent the occurrence of arcing, that is, the sparking phenomenon that occurs between the terminal screw cap and the main body metal (because when igniting, a continuous high voltage is generated between the terminal screw cap and the main body metal. The high voltage attempts to flow along the surface of the insulator. To stop the high voltage, a series of grooves are set up). 

Immediately adjacent to the ceramic part is the main metal. The hexagonal shape (with different sizes) on it facilitates the disassembly and assembly of the spark plug. From the manufacturing perspective, its surface has also undergone electroplating treatment, which can prevent high temperatures and resist corrosion. The threads are the part used for fastening with the cylinder head. The diameter and length of the screws also vary according to the type of engine. 

At the very end are the electrodes of the spark plug, which are divided into the central electrode and the outer electrode. Both of them may be made of different materials, and the precious metal materials we often refer to (such as iridium or platinum) mostly refer to the material of the central electrode (some of the outer electrodes of the spark plugs may also use the same material). Compared to the ordinary spark plugs with nickel-manganese alloy electrodes, they have stronger ignition capabilities, but the price can differ by several times.

Furthermore, in order to ensure that the spark plugs have strong adaptability during both high-speed and low-speed engine operation, a copper core is embedded in the center of the spark plugs. This copper core makes a significant contribution to heat dissipation.