The core hint: the cavitation erosion and prevention of the cylinder liner of the diesel engine of engineering machinery: the cavitation erosion of the cylinder liner is one of the common failure modes of the diesel engine, studying the causes of its formation so as to take preventive measures to delay the formation of the cavitation, and to reduce the mechanical failure and prolong the mechanical life of the machine, which is of ten important significance.
The cavitation erosion of cylinder liner is one of the common failure modes of diesel engine. It is of great significance to study the causes of its formation so as to take preventive measures to delay the formation of cavitation, and to reduce mechanical failure and prolong the mechanical life of the machine.
1. The formation and harm of cavitation erosion of cylinder liner
The surface of the cylinder liner of a diesel engine is in contact with the cooling water. It is characterized by a few needle like holes on the side of the main thrust of the piston. The surface of the hole is clean and does not corrode the product. With the passage of time, these needle holes gradually expand and deepen, so that the hole in the outer wall of the cylinder form a honeycomb hole, and even the cylinder wall is penetrated in serious case. This phenomenon is called cavitation.
When the diesel engine works, the cooling water in the water jacket is vibrate at high frequency under the action of the piston side pressure. The gas or air in the cooling water is separated in the form of bubbles; when the pressure rises and reaches a certain value, these bubbles collapse (blasting) and produce strong pressure waves, and the cylinder is severely impacted and denuded. This process is repeated, resulting in fatigue peeling of the cylinder liner, thus opening into a honeycomb hole, enlarging and deepening the small hole until it destroys and penetrates.
The cavitation erosion of the cylinder sleeve of the diesel engine is a common and very prominent problem, and with the improvement of the engine strengthening index (average effective pressure, the average speed of the piston, etc.), the speed of the cavitation erosion is quickened, even the inner wall of some cylinder sleeves is far from the wear limit, which is difficult to control because of the cavitation erosion of the outer wall of the cylinder liner. And repair the cylinder sleeve in advance.
2. Factors affecting cavitation erosion of cylinder liner
2.1 structure
(1) the structure of cylinder liner
The cause of cavitation erosion is the vibration of cylinder liner, and the vibration intensity is related to the structural strength of cylinder liner. Increasing the wall thickness of the cylinder liner can increase the structural strength and reduce the vibration intensity. It is generally believed that cavitation occurs rarely when the wall thickness reaches 0.08D (D is the diameter of the cylinder sleeve).
(2) piston structure
The location of the piston pin affects the proportion of the two parts of the piston. When the weight of the two parts of the upper and lower parts is too large, the piston has a larger torque when it swinging around the piston pin. When the upper weight of the piston is larger than the weight of the lower part, the impact force of the upper part of the piston on the cylinder wall is increased, and the local vibration intensity is increased. When the piston is long, the effect of the turnover can be weakened, and the contact area between the piston and the cylinder wall is increased, and the impact force on the unit area is reduced, thus the vibration intensity is reduced.
(3) section form of water cavity
The shape of the cross-section of the water chamber affects the velocity of water flow and changes the liquid pressure. At the small section, the flow velocity of water is high and the pressure is small. It is easy to evaporate and form bubbles. At the large section, the flow velocity of water is relatively low and the pressure is high. Therefore, the tendency of cavitation erosion is increased in the transition from small cross section to large section.
The gap between 2.2 piston and cylinder liner
When the clearance between piston and cylinder liner increases, the impact of piston on cylinder wall increases, thus cavitation is aggravated.
2.3 cooling water
When the cooling water contains corrosive medium, corrosion and cavitation will be formed. The cavitation erosion rate will be doubled or even dozens of times.
2.4 conditions of use
When the working process of the diesel engine is rough and the maximum explosive pressure increases, the lateral impact force will also increase correspondingly, and the cavitation erosion will increase.
3 measures to prevent cavitation erosion of cylinder liner
In addition to improving the capacity of cylinder sleeve to resist cavitation, the following measures should be taken in addition to improving the thickness and degree of cylinder sleeve in design and manufacture, reducing the deformation of cylinder liner and high frequency vibration to enhance the cavitation resistance of cylinder liner.
(1) properly reduce the fit gap between the cylinder sleeve and its upper and lower seats, so as to reduce the vibration frequency and amplitude of the cylinder liner.
(2) in the case of the normal moving conditions, the gap between the piston and the cylinder sleeve should be reduced as much as possible to reduce the cylinder liner motion caused by the swinging of the piston.
(3) timely remove the carbon in the combustion chamber, so as not to increase the compression ratio.
(4) clean the scale of the water jacket in time, ensure the clean and normal temperature of the cooling water, ensure the normal work of the cooling system, avoid the narrowing of the water jacket, short the water short, so that the local overheating or the temperature of the cooling system are too high, so as to reduce the production of "gas ditch" and slow down the development of the corrosion and cavitation of the gold.
(5) under the premise of guaranteeing power and economy, the oil supply advance angle is reduced properly to reduce the rough degree of the diesel engine and reduce the vibration of the cylinder liner.
(6) ensure the smooth operation of the diesel engine, in order to reduce the flow rate of cooling water and the repeated changes of water pressure, reduce the production of "bubble", and slow down the development of corrosion and cavitation.
(7) a proper amount of emulsion is added to the cooling water to reduce the surface tension of the cooling water, thus reducing the impact force produced by the "bubble" collapse (explosion) and reducing the effect of the cavitation erosion.
