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The Knowledge Of Spark Plug

- Mar 09, 2018-

So far, spark plug flashover has two main methods: One is under the action of a pulsed high voltage, which breaks through the air gap existing between the center electrode and the side electrode to generate spark; the other is the flashover along the surface, that is, the discharge route. It is along the surface of the insulator between the center electrode and the side electrode. The former has a short discharge distance and poor flashover performance, and the traditional one-side pole spark plug is even worse. Because the size of the air gap is limited by the power supply voltage, it is generally about 0.6 to 0.9 mm. Shorter discharge distances do not allow sufficient "development" of the fire nucleus and heat is absorbed by the side electrodes, reducing the spark energy. If you increase the air gap, you need to increase the ignition voltage, which can easily lead to "fire." The creeping discharge occurs at the interface between the ceramic surface of the insulator and the air. The distortion of the electric field at the surface of the ceramic increases the local field strength, causing local discharge to occur first, thereby promoting the further development of the discharge until the breakdown of the electrode gap. This discharge mechanism reduces the creepage voltage of the creepage gap over an air gap of the same width. If the breakdown voltage is the same, the creepage distance is longer than the air gap. A longer discharge distance can greatly increase the spark energy. Because the spark discharge is composed of two parts with very different energy densities, namely the capacitor discharge part and the inductor discharge part. The former has a high energy density, a high voltage, and can be emitted in a very short time; the latter has a small energy density but works for a long time. From the EDM energy distribution, it can be seen that the energy of the inductance part is 20 to 30 times that of the capacitor part, which is a true “hot flame” and plays a major role in heating the surrounding mixture to form a fire core. The longer the inductor duration, the better the ignitability. Increasing the discharge distance will reduce the "flame-out effect" of the side electrodes. The spark burns the oil deposits along the surface of the insulator, avoids cross-connections between the electrodes, and also prevents current leakage between the insulator and the casing due to the adhesion of combustion deposits, and ensures ignition reliability under idle conditions. The insulation of the creeping spark plug has no skirt and can not quickly absorb the heat of the combustion chamber. It is an extremely cold spark plug. Widely used is a "sliding-air gap" in which "face gap" and "air gap" are combined, and an air gap exists between the insulator skirt and the side electrodes. Sparks “slip” from the surface of the insulator and jump to the side electrode during flashover. The breakdown voltage is reduced due to the electric field surface distortion on the insulator. The insulator of this spark plug has a normal skirt and thus can adapt to different thermal loads.

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