With the continuous improvement of the effective pressure, rotational speed and specific power of modern diesel generator sets, the specific mass is getting smaller and smaller, the structure is getting more compact, and the wall thickness of the cylinder liner tends to be thinner, which makes its anti-cavitation ability to some extent decrease. We found in the maintenance practice that the cavitation damage of diesel generator sets is very serious. The cylinder liners of many diesel generator sets are not replaced because they exceed the wear limit, but are often forced to be replaced due to cavitation damage.
Cavitation means that the surface of the outer wall of the wet cylinder liner of the diesel generator set in contact with the coolant is destroyed into some needle-shaped holes, which gradually expand and deepen, and finally form deep holes or cracks; the holes are generally very clean, and there is no corrosion product. The wet cylinder liner is in direct contact with the coolant and is inevitably cavitated gradually; while the dry cylinder liner is not in direct contact with the coolant, the liner seat is also cavitated, and the liner seat is gradually cavitated into through holes or cavities. After the crack, it will further damage the dry liner.
It is generally believed that cavitation is caused by high-frequency vibration of the cylinder liner. The mechanical vibration causes the coolant pressure to change, causing bubbles in the coolant to burst, which is the cause of cavitation. Due to the gas dissolved in the cooling liquid, when the high-frequency vibration of the cylinder reduces the local pressure of the cooling liquid to a certain critical value, the gas dissolved in the cooling liquid is separated in the form of bubbles, and these bubbles flow to the high-pressure area. When the pressure exceeds the bubble pressure, the diesel generator set will collapse.
The gas in the bubble state is re-liquefied or dissolved in the cooling liquid, and the volume is suddenly reduced, and the cooling liquid moves at a high speed to the center of the bubble to produce a water hammer phenomenon, resulting in a great impact force and high temperature, and supersonic speed in the form of a pressure wave. It spreads around, and when it acts on the outer surface of the cylinder liner, it produces great impact, extrusion and high temperature. Under the repeated action of this force, the outer surface of the cylinder liner of the diesel generator set is fatigued and gradually falls off, showing pitting and needle-shaped holes, and gradually expands with the progress of cavitation.
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