The effective pressure, rotational speed and specific power of the modern diesel engine have been improved, the quality is smaller and smaller, the structure is more compact, and the wall thickness of the cylinder liner is thinner. We found in the maintenance practice, cavitation of modern diesel engine damage is very serious, many of the diesel engine cylinder is not because more than wear limit and change, is often due to cavitation damage was forced to change. Cavitation has become an important factor affecting the life and reliability of modern diesel engine.
1, cavitation erosion
Cavitation refers to the surface of the diesel engine cylinder liner and the outer wall of the cooling liquid contact holes are broken into some acicular, these holes gradually expand and deepen, and finally the formation of deep hole or crack; holes generally very clean, no corrosion products. Wet cylinder liner in direct contact with the cooling liquid, inevitably gradually by cavitation; and dry liner while not directly contact with the cooling liquid, but also by the cavitation of cylinder block, cylinder block was gradually cavitation through holes or cracks, will further damage of dry liner.
It is generally believed that cavitation caused by high frequency vibration of cylinder liner. The mechanical vibration causes the change of the cooling fluid pressure, so that the bubbles in the coolant can be broken. Because the cooling liquid in dissolved gas, when the high-frequency vibration so that the local pressure of the cooling liquid drops to a critical value, the form of soluble coolant gas bubbles will separate these bubbles flow to the high pressure zone, when the pressure exceeds the pressure occurs when the bubble collapse. In the gas bubble state re liquefied or dissolved in the coolant, the volume suddenly decreases, the cooling liquid to the high-speed bubble center and produce water hammer phenomenon, have a great impact and high temperature, and the pressure wave form of supersonic propagation when acting on the cylinder outer surface, have a great impact. Extrusion and high temperature. Under the repeated action of the force, the outer surface of the cylinder liner is tired and gradually falls off, which is a bit like a needle and a pinhole.
2, prevention of cavitation erosion
(1) the coolant temperature which is most vulnerable to cavitation erosion is -60 DEG C at a temperature of 40 DEG C by using factor A., so the working temperature (-85 DEG C) should be kept as normal as possible in use. B. to add the cooling fluid by the manufacturer of the cooling water, without water or containing more impurities (liquid). The experiment showed that salt and alkali water than clean water cavitation rate several times. C. minimize idle, heavy load and overload time. D. in accordance with the provisions of the use of fuel to reduce the combustion caused by diesel engine rough.
(2) repair factor A. replace the coolant according to the regulations, and clean the cooling system in time, so that the cooling system often keep a good technical state. B. according to the regulation of fuel supply advance angle and fuel system assembly, to maintain good fuel system performance, reduce the harm caused by abnormal combustion. C. to maintain a good cylinder clearance, Baotou North Benz parts crankshaft bearing clearance and connecting rod bearing clearance, in order to reduce knocking and vibration. Baotou North Benz D. installation accessories, cylinder liner, piston rods and other parts, to try to reach the verticality and parallelism, reduce the impact on normal cylinder piston.
(3) A. manufacturing factors of anti cavitation materials and vibration absorbing substances in the water jacket wall coating. B. to improve the hardness of the outer surface of the cylinder liner of the North Benz parts in Baotou; to reduce the roughness of the outer surface; to choose the material with strong cavitation resistance. C. select the appropriate cylinder wall thickness, increase its stiffness to avoid resonance.