Spark plugIntroduction to knowledge and types
In a gasoline engine, gasoline and air are mixed and enter the cylinder. At the end of the compression stroke, it needs to be ignited to do work to generate power. The heavy task of igniting the mixed steam depends on a small spark plug.
The role of the spark plug is toIgnition coilsThe generated high-voltage electricity of more than 10,000 volts is introduced into the cylinder, and a spark is generated between the spark plug electrodes to ignite the mixture. The working environment of spark plugs is extremely harsh. In the cylinder of an ordinary four-stroke gasoline engine, the temperature of the intake stroke is only 60 degrees Celsius and the pressure is 90 kPa. During ignition and combustion, the temperature will rise to 3000 degrees Celsius and the pressure will reach 4 MPa. Changes in engine work place very stringent requirements on spark plug materials.
The spark plug consists of two parts: an insulator and a metal shell: the metal shell is threaded for screwing into the cylinder; the shell is equipped with an insulator, which runs through a center electrode, and there is a terminal nut on the upper end of the center electrode. From the distributorHigh-voltage lineThere is a ground electrode welded on the lower end surface of the shell, and there is a gap of 0.6-1.0 mm between the center electrode and the ground electrode. High-voltage electricity passing through this gap will burst into the ground and spark to ignite the mixture.
The key part of the spark plug is the insulator. The insulator must have good mechanical properties and the ability to withstand high voltage, high temperature impact, and chemical corrosion. Common spark plug insulators are mostly made of alumina-based ceramics. When the spark plug insulator is maintained at 500-600 degrees Celsius, the oil droplets falling on the insulator can be burned off immediately without forming carbon deposits. Above this temperature, it will burn prematurely, and below this temperature will form carbon deposits. The length of the insulator skirt determines the temperature adaptability of the spark plug.The skirt is short and the heating area is small and the heat dissipation is fast. It is called cold spark plug, which is suitable for highRotating speedEngines with high compression ratio; slender skirts with large heating area and slow heat dissipation are called hot spark plugs, which are suitable for engines with low and medium speeds and low compression ratios.
How to reasonably choose the calorific value of the spark plug depends on the specific use conditions and driving habits. The calorific value of spark plugs is generally marked with 5 degrees, 6 degrees, 7 degrees, etc. In daily use, spark plugs of 5 degrees to 8 degrees can be selected. In urban areas, it is recommended to use 7 degrees, while spark plugs above 9 degrees are only used in hot weather. The car is only available. Selecting a spark plug with a high number of heights will make the low-speed operation unstable, and long-term low-speed operation will cause serious carbon deposits in the engine; if the selected spark plug is too low, the spark plug electrode will be There is a risk of sintering, and the burned insulating ceramic debris falling into the engine will cause the cylinder to pull.
Spark plugkind of:
1. Standard spark plug: The insulator skirt is slightly retracted 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 one.
2. Spark plug with protruding edge body: the insulator skirt is longer and protrudes out of the end surface 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 and has a wide thermal adaptation range.
Take out the spark plug to check the electrode burnout
3. Electrode type spark plug: The electrode is very thin, the spark is strong, and the ignition ability is good. It can ensure the engine to start quickly and reliably even in the severe cold season. It has a wide thermal adaptation range and can meet a variety of purposes.
4. Seat-type spark plug: The casing and screw thread are made into a cone, and a good seal can be maintained without a gasket, thereby reducing the size of the spark plug, which is more beneficial to the design of the engine.
5. Polar type spark plugs: There are generally two or more side electrodes. The advantage is reliable ignition, and the gap does not need to be adjusted frequently. It is often used in gasoline engines where the electrode is easily ablated and the spark plug gap cannot be adjusted frequently.
6. Surface flashover spark plug: the surface gap type, which is the coldest spark plug. The gap between the center electrode and the end surface of the shell is concentric.
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