The function of the spark plug is to introduce a high-voltage current in the gasoline engine ignition system into the cylinder to generate an electric spark to ignite the combustible mixed gas. At present, ordinary spark plugs using nickel-based alloy electrodes have become less and less suitable for the needs of modern engines with high power, high speed, and large compression ratio. In order to make the spark plug have higher ignition performance and use n life, people began to aim at precious metals (precious metals such as platinum, rhodium, and titanium), used them for electrodes, and correspondingly improved the structure of the ignition end. The precious metal has a very high melting point, the melting point of titanium is 1668 degrees, the melting point of platinum is 1772 degrees, and the hardness of sheet metal is 2454 degrees. Adding certain elements (such as antimony and palladium) has a very high resistance to chemical attack. This was made into a thin electrode (diameter: 0.4-0.6 mm), directly sintered in the ignition end of the insulator, or laser-welded to the working surface of the front end of the center electrode and the side electrode by a wafer having a diameter of 0.4 to 0.8 mm. This electrode has a strong tip discharge effect and can ignite when the voltage is relatively low, and the spark gap can be increased to 1.1 to 1.5 mm. The precious metal causes a qualitative change in the performance of the spark plug: First, the high corrosion resistance of the electrode can keep the spark gap constant for a long time (in the 160,000 km test, the spark gap of the platinum electrode is only increased by 0.05 mm), so that the ignition voltage value is stable. The engine works smoothly. There is no need to adjust the corrected spark gap during the use of the spark plug. The second is suitable for cold start. Due to the tip discharge, ignition is easy, improving the performance of the engine under low speed conditions. The third is to reduce the heat absorption and flame elimination of the electrode and enhance the spark energy. The small electrode makes the enthalpy around the gap increase the accessibility of the mixture, making the combustion more complete and the emission lower. The spark plug is a wearing part, and the replacement time is only manifested in high fuel consumption, difficult to start, and slow acceleration. The timely replacement or replacement of the high-grade material spark plug can maximize the engine design power, and the combustion completely reduces fuel consumption.
There are common copper cores, nickel alloys, platinum, sheet metal, platinum-iridium alloys, etc. These materials themselves have good electrical conductivity. Among them, the precious metal spark plug has a relatively high melting point, high temperature and high pressure resistance, and good quality. Therefore, the precious metal spark plug can emit a stronger and more stable spark, and the service life is relatively longer. The original low-end car original spark plug is a nickel alloy spark plug, while the original > flower plugs of the high-end models are mostly platinum or sheet metal spark plugs.
Titanium spark plugs have good high temperature and low temperature performance. Titanium alloy can maintain good mechanical properties at around 500 °C. It maintains good elongation and toughness at temperatures from 196 °C to minus 253 °C. The density of titanium is 4.506- 4.516 g / cm 3 (20 ° C), higher than aluminum and lower than iron, copper, nickel. But the specific strength is at the top of the metal. Melting point 1668 ± 4 ° C, melting latent heat 3.7-5.0 kcal / gram atom, boiling point 3260 ± 20 ° C, vaporization latent heat 102.5-112.5 kcal / gram atom, critical temperature 4350 ° C, critical pressure 1130 atmosphere. Titanium has poor thermal conductivity and electrical conductivity, which is similar to or slightly lower than that of stainless steel. Titanium has superconductivity, and the superconducting critical temperature of pure titanium is 0.38-0.4K. At 25 ° C, the heat capacity of titanium is 0.126 cal/g atom·degree, the heat is 1149 cal/g atom, the entropy is 7.33 cal/g atom·degree, the metal titanium is a paramagnetic substance, and the magnetic permeability is 1.00004. Titanium spark plugs have a certain combustion-supporting effect.
The precious metals are on the center electrode and the side electrode. Generally, the center electrode is gold-plated platinum-titanium gold, and the side electrodes are all made of platinum. The popular double-gold-gold spark plug side electrode (grounding electrode) on the market is also platinum, but has a needle shape. Only.
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