Automotive Spark Plugs

Automotive Spark Plugs is an important component of the gasoline engine ignition system, It can introduce high voltage into the combustion chamber and make it cross the electrode gap to generate a spark, thereby igniting the combustible mixture in the cylinder. Automotive Spark Plugs mainly composed of a connecting nut, an insulator, a connecting screw, a center electrode, a side electrode and a housing. The side electrode is welded to the housing.

According to the calorific value, there are cold type and hot type. According to the electrode materials, here are nickel alloys, iridium gold and platinum, etc.If we are more professional, the types of spark plugs are generally as follows:

1. Standard spark plug: Its insulator skirt is slightly retracted into the end face of the housing, and the side electrodes are outside the end face of the housing. It is the most widely used type.

2. Insulator protruding spark plug: The insulator skirt is relatively long and protrudes beyond the end face of the housing. It has the advantages of large heat absorption and good anti-fouling ability, and can be directly cooled by the intake air to lower the temperature. Therefore, it is not easy to cause hot ignition, and thus has a wide thermal adaptability range.

3. Electrode type spark plugs: Their electrodes are very thin. Their characteristics are strong sparks, good ignition ability, ensuring the engine starts quickly and reliably even in cold seasons, and a wide thermal range, which can meet various applications.

4. Pedestal spark plug: Its housing and the screw thread are made into a conical shape, so it can maintain a good seal without a gasket, thereby reducing the volume of the spark plug and being more beneficial to the design of the engine.

5. Polar spark plugs: The side electrodes are usually two or more. Their advantages are reliable ignition and the gap does not need to be adjusted frequently. Therefore, they are often used in gasoline engines where the electrodes are prone to erosion and the gap of the spark plugs cannot be adjusted frequently.

6. Surface spark plug: Also known as the surface gap type, it is the coldest type of spark plug, and the gap between the central electrode and the end face of the shell is concentric.

7. Standard type and protruding type spark plugs

The standard spark plug is a single-sided electrode spark plug with the insulator skirt end slightly lower than the threaded end face of the shell. It adopts the traditional ignition end structure that is most widely used in side-mounted valve engines. To distinguish it from the later emerging "prominent type", this structure is called the "standard type".

The protruding spark plug was originally designed for overhead valve engines. Its insulator skirt protrudes from the threaded end face of the shell and extends into the combustion chamber. It absorbs more heat in the burning mixed gas, has a higher working temperature at the breathing rate, and avoids contamination. At high speed, due to the top-mounted valve, the inhaled airflow is directed at the skirt of the insulator, cooling it. As a result, the maximum temperature increase is not significant, and thus the thermal range is relatively large. Protruding spark plugs have many turns in the intake passage, and the airflow has little cooling effect on the insulator skirt. Therefore, they are not suitable for side-mounted valve engines.

8. Single-pole and multi-pole spark plugs

The traditional single-pole spark plug has an obvious defect, that is, the side electrode covers the center electrode. When high-voltage discharge occurs between the two poles, the mixed gas in the spark gap will absorb the heat of the spark and be activated due to ionization to form a "fire core". The place where the nucleon forms is generally close to the side electrodes. More heat will be absorbed by the side electrodes, that is, the "flame suppression effect" of the electrodes, which reduces the spark energy and lowers the spark skipping performance.

Thus, in the 1920s, three-sided pole spark plugs emerged. Compared with single-sided electrodes, the spark gap of multi-sided electrodes is composed of the cross-sections of multiple side electrodes (punched into circular holes) and the cylindrical surface of the central electrode. This side-mounted spark gap eliminates the drawback of side electrodes covering the central electrode, increases the "accessibility" of the spark, has greater spark energy, and is more likely to penetrate into the cylinder interior, which helps improve the combustion condition of the mixture and reduce exhaust emissions. Due to the multi-side pole providing multiple spark jumping channels, the service life is prolonged and the reliability of ignition is improved. It must be pointed out here that at the moment of discharge, only one channel can have a spark jump; it is impossible for multiple electrodes to have a spark jump simultaneously. The discharge process of high-speed photography proves this point.

The suffix letters D, J, and Q in domestic spark plug models (the letters after the calorific value number) respectively represent double-sided pole, triple-sided pole, and four-sided pole.

9. Nickel-based alloy and copper core electrode spark plugs

The most fundamental requirements for the electrodes extending into the combustion chamber are resistance to ablation (electrical erosion and chemical corrosion) and good thermal conductivity. With the development of materials science and process technology, electrode materials have undergone an evolution process from iron, nickel, nickel-based alloys, nickel-copper composites to precious metals. The most commonly used ones nowadays are nickel-based alloys. Generally, pure metals have better thermal conductivity than alloys, but pure metals (such as nickel) are more sensitive to the chemical corrosion reaction of combustion gases and the solid deposits they form than alloys. Therefore, the electrode material adopts nickel-based materials with the addition of elements such as chromium, manganese, and silicon. Chromium enhances the resistance to electrical erosion, while manganese and silicon improve the resistance to chemical corrosion, especially against the highly harmful sulfur oxide.

10. Common type and resistive type spark plugs

As a spark discharge generator, As a spark discharge generatoris a broadband continuous type of electromagnetic radiation interference source. Since the 1960s, countries around the world have accelerated the development of resistive spark plugs to suppress the strong interference of electromagnetic radiation caused by sparks to the radio field, protect radio communications and prevent malfunctions of on-board electronic devices. China has also issued a series of mandatory national standards for electromagnetic compatibility, imposing strict restrictions on the radio interference characteristics of vehicle devices driven by spark plug ignition engines. As a result, the demand for resistive spark plugs has significantly increased. Resistive spark plugs have no significant structural difference from the common type. The only difference is that the conductor sealant inside the insulator is changed to a resistive sealant

In the standards of Automotive Spark Plugs, calorific value is generally used to characterize the thermal characteristics of spark plugs. The calorific value of a spark plug indicates the balance ability of heat absorption and dissipation of the insulator skirt of the spark plug. The higher calorific value, The stronger the balance between heat absorption and dissipation, the lower the heat value of the hot type spark plug and the higher the heat value of the cold type spark plug. Generally, for engines with high power and large compression ratio, cold-type spark plugs with high calorific value are selected. On the contrary, engines with low power and small compression ratio should select hot-type spark plugs with low calorific value. The selection of spark plugs is generally determined by the factory through product type approval tests and should not be replaced at will.