The spark plug consists of a central electrode, a ceramic insulator with a housing and a ground electrode. The ignition spark, which ignites the air-fuel mixture, jumps between the central electrode and the ground electrode. It is not recommended to deviate from the prescribed type of candles, which, among other things, is also determined by the glow number.
The glow number indicates the degree of maximum allowable thermal load of one spark plug. With a decrease in the heat number, the allowable thermal load increases. In this case, heat removal from the candle improves, resulting in a reduced risk of glow ignition (engine operation after ignition off). The main disadvantage of candles with a high thermal load capacity is that the self-cleaning temperature of the candle is also high. In this case, the working part of the candle is covered with deposits, especially when the engine does not warm up to operating temperature while driving.
The glow rating of the spark plug is specified by the car manufacturer. Spark plugs differ from each other in the presence of one or more side electrodes and the diameter and length of the thread, therefore, for normal operation of the engine, it is necessary to use only spark plugs prescribed by the manufacturer.
The service life of candles is mainly determined by the material of the electrodes. Nickel-chromium alloy electrodes have high thermal conductivity and high corrosion resistance. The use of silver ensures maximum thermal conductivity. Platinum electrodes have the highest anti-corrosion properties and burnout resistance. The service life of the plugs depends on the electrode material used and the design of the spark plugs and ranges from 20,000 to 100,000 km.
Two constructive types of seals are used between the spark plug and the cylinder head.
With a flat sealing surface, a non-removable outer o-ring is installed on the spark plug. If the plug has a conical seal, then no additional o-rings are required. Due to the downsizing of the engine, spark plugs with a flat seal and a reduced spanner size or plugs with a conical seal are used.
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