Diesel generator set piston ring, gas ring function and working principle?

The piston ring is an elastic metal open ring, which can be divided into two types: gas ring and oil ring according to their functions. Installed on the upper end of the piston head are 2 to 4 air rings, and the lower end is 1 to 2 oil rings.
The function of the    gas ring is to ensure the seal between the piston and the cylinder wall and prevent the high pressure gas on the upper part of the piston from leaking into the crankcase. When the seal is not good, the gas in the compression stroke will leak more, which will reduce the pressure at the end of compression, which will cause difficulty in starting the internal combustion engine. The leakage of high-temperature gas into the crankcase will also increase the temperature of the piston, and the oil will be oxidized and deteriorated due to heat. In addition to the sealing function, the gas ring also plays the role of heat transfer. Most of the heat absorbed by the top of the piston is transmitted to the cylinder wall through the gas ring (because the piston head does not touch the cylinder wall), and then taken away by the external cooling medium.
The gas ring, especially the first gas ring, in addition to the high-speed reciprocating linear motion along the cylinder wall with the piston, is also affected by the pressure of high temperature and high pressure gas and poor lubrication conditions, which reduces the mechanical properties of the gas ring. The elasticity is reduced, and it will cause carbonization of the lubricating oil, and may even cause cylinder pulling and air leakage. Therefore, it is required that the gas ring should have enough elastic force to make the surrounding of the ring close to the cylinder wall. At this time, it is impossible for high-pressure gas to leak through the contact surface between the gas ring and the cylinder wall. The gas acting on the upper end face of the ring presses the ring tightly in the piston ring groove, so that the lower end face is in close contact with the ring groove. The gas entering between the inner side of the ring and the groove of the ring presses outward, making the ring more tightly against the cylinder wall. Therefore, the leakage of high-pressure gas can be prevented by using the elastic force of the gas ring itself and the pressure of the gas.
Piston rings are usually made of high-quality gray cast iron or alloy cast iron. In order to improve the working performance of the first gas ring and improve its wear resistance, a porous chromium layer or a molybdenum layer is often plated on the surface of the first gas ring. In recent years, the first gas ring is also made of ductile iron or steel. In the free state, the outer diameter of the ring is slightly larger than the diameter of the cylinder. After being installed in the cylinder, the piston ring generates elastic force and is pressed against the cylinder wall, and a certain gap should be reserved at the opening (called end gap or opening gap, the internal combustion engine piston ring The opening clearance is usually 0.4~0.8mm) to prevent the piston ring from being stuck in the cylinder when it is heated and expanded. After the piston ring is installed in the ring groove, there should also be a certain clearance in the height direction (called side clearance, the side clearance of the piston ring of an internal combustion engine is usually 0.08-0.16mm). When the piston ring is installed on the piston, the openings of each ring should be staggered by 120°~180°, and the piston ring opening should be staggered by more than 45 from the piston pin seat hole to prevent leakage after the piston ring is installed in the cylinder. gas phenomenon.
In order to improve the working conditions of the piston ring and make the piston ring and the cylinder fit better, some piston rings use different sections, so special attention should be paid during installation. The basic cross-sectional shape of the gas ring is a rectangle. The rectangular ring is easy to manufacture and widely used, but its running-in performance is relatively poor, and it cannot meet the increasingly strengthened requirements of the engine. This common compression ring can be freely installed in the gas ring groove. Some engines use a conical ring structure. The working surface of the ring is made into a taper angle of 0.5° to 1.5, so that the contact surface between the working surface of the ring and the cylinder wall is reduced, and the running-in can be faster. The cone angle also has the function of scraping oil. However, the wear of the cone ring is fast, which affects the service life. Install with the angled side down.
Some internal combustion engines use twist rings. A part of the upper edge of the inner circle or the lower edge of the outer circle of the twisted ring is cut off to form a stepped section. This kind of section is asymmetric inside and outside. After the ring is loaded into the cylinder and compressed, under the action of the asymmetric internal force, a significant section inclination occurs, so that the outer surface of the ring forms a tapered surface with a small top and a large bottom, which reduces the size of the ring. The contact area of ​​the cylinder wall makes the ring easy to run in and has the effect of scraping oil downward. Moreover, the upper and lower end faces of the ring are in contact with the upper and lower end faces of the ring groove in the corresponding places, which not only increases the sealing performance, but also prevents the piston ring from moving up and down in the groove and causing pump oil and wear. When installing the ring, it is necessary to pay attention to its up and down direction. It cannot be installed reversely. The inner cut should be upward and the outer cut should be downward. On some internal combustion engines with large heat load, in order to improve the anti-coking ability of the gas ring, trapezoidal rings are often used. The matching gap between the end face of the ring and the ring groove changes with the lateral swing of the piston under the action of lateral force, which can crush the carbon deposits in the ring groove and prevent the piston ring from being glued and stuck. This ring can be installed at will like ordinary gas rings.
There is also a form of gas ring barrel face ring, its working surface is convex arc, and its upper and lower directions are wedge-shaped with the cylinder wall, easy to run in, good lubrication performance, and strong sealing. Such rings have been commonly used to strengthen internal combustion engines. Like ordinary compression rings, this ring can be freely installed in the gas ring groove.


Post time: Aug-04-2022