Cavitation: it occurs around the engine combustion chamber, although we can see from the feedback of the vehicle water temperature gauge that it is at 90 ° But the engine combustion work, especially most of the wet cylinder liner, the local surface temperature exceeds the boiling point of water, which is much higher. When the water is near the boiling point, a large number of bubbles will be produced, which repeatedly impact the surface of the cylinder liner, and the micro shock wave pressure reaches 15-20000 psi. In our daily life, when a teapot is boiling, bubbles are produced at the bottom of the teapot. The reason is similar.

发动机使用的冷 却液，通常沸点温度超过130度。如果破坏冷 却液的成分比例，乙二醇成分减少。气缸套暴露在较低的沸点下，醇类物质无法附着在表面。穴 蚀发生将无法避免，例如200小时后，兑水后的冷 却液实验，康明斯CumminsNTC400发动机已经产生缸套激烈气蚀情况，产生更严重的穴蚀。

The engine coolant usually has a boiling point of more than 130 degrees. If the composition ratio of the coolant is destroyed, the glycol content will decrease. When the cylinder liner is exposed to low boiling point, alcohols cannot adhere to the surface. Cavitation erosion can not be avoided, for example, after 200 hours, after the coolant test, Cummins Cummins ntc400 engine has produced severe cavitation erosion of cylinder liner, resulting in more serious cavitation erosion.

为什么有些全自动混凝土搅拌机的发动机加水表面看起来很正常?

Why does the surface of some automatic concrete mixers look normal?

全自动混凝土搅拌机

Automatic concrete mixer

中等排量发动机：冷却系统要求不高腐蚀状况较突出

Medium displacement engine: low requirement of cooling system, prominent corrosion condition

国内中等排量的发动机，从上世纪70年代技术上演变而来，仅相当于国外50年代的水平，本质上并没有改变。因此发动机设计之初，冷却系统要求不高，燃烧室并没有强化，气蚀现象同样存在，但并非明显感受，相比腐蚀状况就比较突出，例如烂水堵。

The domestic medium displacement engine, which evolved from the 1970s in technology, is only equivalent to the level of the 1950s abroad, and has not changed in essence. Therefore, at the beginning of engine design, the cooling system requirements were not high, the combustion chamber was not strengthened, and the cavitation phenomenon also existed, but it was not obvious. Compared with the corrosion condition, it was more prominent, such as rotten water blocking.

现今国产大排量卡车发动机，采用了增压，高压缩比，活塞行程缩短，转速更低，这样的强化设计，燃烧室的局部温度，强制散热要求，多通过活塞机油喷嘴，更高的冷却液循环量，和使用更高沸点温度的冷却液来实现。因此冷却液少量补充水，短期内可以应急，长时间使用弊大于利，一个局部频繁“开锅”的发动机，寿命大大缩短。

Nowadays, the domestic large displacement truck engine adopts supercharging, high compression ratio, shorter piston stroke and lower speed. Such enhanced design, local temperature of combustion chamber and forced heat dissipation requirements are mostly realized through piston oil nozzle, higher coolant circulation and higher boiling point temperature coolant. Therefore, a small amount of supplementary coolant water can be used for emergency in a short period of time, and the disadvantages of long-term use outweigh the advantages. The service life of an engine with frequent local "boiling" is greatly shortened.