Abstract: The cylinder liner of a diesel generator set is a pair of friction pairs that work under harsh working conditions such as high temperature, high pressure, poor lubrication, alternating loads, and corrosion. After using the diesel generator set for a period of time, there may be obvious cylinder blowby, burning of lubricating oil, and insufficient power, which is caused by excessive early wear of the cylinder. When early wear occurs on the cylinder liner, it can affect the power, economy, and service life of diesel generator sets. After conducting market research by the company, it was found that some users have purchased diesel generators that have not reached the overhaul period. However, many generator sets have experienced premature damage to the cylinder sleeves. The main reasons for this are that they have not strictly followed their maintenance and repair requirements, and are not familiar with the performance characteristics of generator sets. They still use them according to traditional misconceptions and habits.
1、 Analysis of factors affecting early wear of cylinder liners
Many users have experienced premature wear of cylinder liners during use, and some have also experienced issues such as cylinder pulling and piston ring breakage. The reasons for this damage are as follows:
1. Not following the running in specifications
New or overhauled diesel generators are directly put into load operation without strictly following the running in specifications, which can cause severe wear and tear on the cylinder liner and other parts of the diesel generator in the initial stage, shortening the service life of these parts. Therefore, it is required that new and overhauled diesel generators must strictly follow the requirements for running in and trial operation.
2. Careless maintenance
Some diesel generator sets often work in dusty environments, and some operators do not carefully maintain the air filter, resulting in air leakage in the sealing part, allowing a large amount of unfiltered air to enter the cylinder directly, exacerbating the wear of the cylinder liner, piston, and piston rings. Therefore, it is required that maintenance personnel must strictly and carefully inspect and maintain the air filter on schedule to prevent unfiltered air from entering the cylinder. In addition, after maintenance, the air filter was not installed correctly, with some missing rubber pads and some fastening bolts not tightened, resulting in early wear of the cylinder liner.
3. Overload usage
When diesel generators are often operated under overload, the body temperature rises, the lubricating oil becomes thinner, and the lubrication conditions deteriorate. At the same time, due to the large fuel supply during overload operation, the fuel is not completely burned, and carbon deposits in the cylinder are severe, which exacerbates the wear of the cylinder liner, piston, and piston rings. Especially when the piston ring gets stuck in the groove, the cylinder liner may be pulled. Therefore, attention should be paid to preventing overloaded operation of diesel generators and maintaining good technical conditions. In addition, there are too many deposits on the surface of the water tank. If not cleaned in time, it will affect the heat dissipation effect and cause a sharp increase in the working temperature of the diesel generator, resulting in piston sticking to the cylinder.
4. Long term no-load use
Long term use of diesel generators without load can also accelerate the wear of compression system components. This is mainly because the engine operates at a low throttle for a long time, and the temperature of the body is low. When fuel is injected into the cylinder and encounters colder air, it cannot completely burn, and it washes the lubricating oil film on the cylinder wall. At the same time, it produces electrochemical corrosion, which intensifies the mechanical wear of the cylinder. Therefore, diesel generators are not allowed to idle for a long time at low throttle.
5. Assembly error
The first ring of the diesel generator is a chrome plated air ring, and the chamfer should be facing upwards during maintenance and assembly. Some maintenance workers install the piston rings upside down and chamfer them downwards, which has a scraping effect and worsens the lubrication conditions, exacerbating the wear of the cylinder liner, piston, and piston rings. Therefore, it is necessary to be careful not to install the piston rings upside down during maintenance.
6. Improper maintenance standards
(1) During maintenance, pay attention to the cleanliness of parts, tools, and your own hands. Do not bring abrasive materials such as iron filings and mud into the cylinder, which may cause early wear of the cylinder liner.
(2) During maintenance, it was not found that the cooling nozzle for lubricating the piston was blocked, which prevented oil from spraying onto the inner surface of the piston. This caused the piston head to overheat due to poor cooling, accelerating the wear of the cylinder liner and piston. In severe cases, it also caused the piston ring to jam and break in the groove, and the ring bank to be damaged.
7. Improper maintenance procedures
(1) When adding lubricating oil during maintenance, it is important to pay attention to the cleanliness of the lubricating oil and oiling tools, otherwise dust will be carried into the oil pan. This will not only cause early wear of the bearing shells, but also cause early wear of parts such as the cylinder liner. Therefore, it is necessary to pay attention to the cleanliness of lubricating oil and filling tools. Additionally, it is important to maintain cleanliness and hygiene in the place of use.
(2) The fuel injectors of a certain cylinder or several cylinders were not checked in a timely manner, resulting in diesel leakage and dilution of lubricating oil. Management personnel did not inspect them carefully enough, and a slightly longer period of time led to early wear of the cylinder liner.
8. Wear caused by structural reasons
(1) Poor lubrication conditions result in severe wear on the upper part of the cylinder liner. The upper part of the cylinder liner is adjacent to the combustion chamber, with high temperature and poor lubrication conditions. Fresh air and unexpired fuel wash and dilute, exacerbating the deterioration of upper conditions, causing the cylinder to be in a dry or semi dry friction state, which is the reason for severe wear on the upper part of the cylinder.
(2) The upper part bears a large amount of pressure, causing the cylinder to wear heavily and lightly. The piston ring is tightly pressed against the cylinder wall under its own elastic force and back pressure. The higher the positive pressure, the more difficult it is to form and maintain a lubricating oil film, and mechanical wear intensifies. During the work stroke, as the piston descends, the positive pressure gradually decreases, resulting in a heavier upper and lighter lower cylinder wear.
(3) Mineral acids and organic acids cause corrosion and peeling on the surface of the cylinder. After the combustion of the combustible mixture in the cylinder, water vapor and acidic oxides are produced, which dissolve in water to form mineral acids. In addition, the organic acids generated during combustion have a corrosive effect on the surface of the cylinder. The corrosive substances are gradually scraped off by the piston rings during friction, causing deformation of the cylinder liner.
(4) Entering mechanical impurities intensifies wear in the middle of the cylinder. Dust in the air and impurities in lubricating oil can enter the piston and cylinder wall, causing abrasive wear. When dust or impurities move back and forth with the piston in the cylinder, the wear in the middle of the cylinder is intensified due to the maximum movement speed in the middle position of the cylinder.
2、 Maintenance of cylinder liner wear
1. Characteristics of early wear and tear
The wear rate of cast iron cylinder liner is greater than 0.1mm/kh, and the surface of the cylinder liner is dirty, with obvious pulling or biting phenomena such as scratches, scratches, and tears. The cylinder wall has burning phenomena such as blueing; The particles of wear products are relatively large.
2. Effects and requirements of cylinder liner wear
(1) Impact: Wall thickness decreases, roundness and cylindricity errors increase. When the wear of the cylinder liner exceeds (0.4%~0.8%) D, the combustion chamber loses its sealing and the diesel engine power decreases.
(2) Requirement: Maintenance personnel should inspect cylinder liner wear according to the instructions, grasp and control the condition of cylinder liner wear, and prevent excessive wear.
3. Detection method for cylinder liner wear
The detection of wear on the inner circular surface of diesel engine cylinder liners can mainly be carried out through the following methods:
(1) Theoretical method: Based on the size, material, and degree of wear of the diesel engine cylinder liner, calculate or refer to theoretical curves to determine the degree of wear of the inner circle of the cylinder liner.
(2) Visual inspection method: Use naked eyes or a microscope to directly observe the wear on the inner surface of the cylinder liner. Usually, scale cards or specific rulers are used to assist in detecting the depth of wear.
(3) Parameter detection method: using detection instruments such as micrometers, oscilloscopes, etc., to detect the diameter or wear area of the inner circle of the cylinder liner, in order to determine the specific degree of surface wear.
(4) High precision detection method: Using high-precision detection technologies such as photoelectric detection and laser scanning, three-dimensional inspection is carried out on the inner surface of the cylinder sleeve to obtain accurate wear data.
(5) Instrumenless detection method
If there is no positioning template for measurement and there is a lack of instructions and other materials, the following four positions can be referred to for cylinder liner wear measurement:
① When the piston is at the top dead center, the position of the cylinder wall corresponding to the first piston ring;
② When the piston is at the midpoint of its stroke, the position of the cylinder wall corresponding to the first piston ring;
③ When the piston is at the midpoint of its stroke, the cylinder wall corresponding to the last oil scraper ring.
3、 Measures to prevent early wear and tear
1. Correct start-up
When starting a diesel engine with a cold engine, the low temperature, high oil viscosity, and poor fluidity result in insufficient oil supply from the oil pump. At the same time, the oil on the original cylinder wall flows down along the cylinder wall after shutdown, resulting in poor lubrication at the moment of starting, leading to increased wear on the cylinder wall during starting. Therefore. When starting for the first time, the diesel engine should be warmed up during no-load operation, and then used on load when the coolant temperature reaches around 60 ℃.
2. Correct selection of lubricating oil
(1) Strictly select the best viscosity lubricating oil according to the season and diesel engine performance requirements, do not purchase inferior lubricating oil, and regularly check and maintain the quantity and quality of lubricating oil. Strengthening the maintenance of the “three filters” is an important measure to prevent mechanical impurities from entering the cylinder, reduce cylinder wear, and extend the service life of the engine. Especially important in rural and windy and sandy areas.
(2) Pay attention to checking the sealing inside the oil cooler. The inspection method is to observe that there is no water vapor in the ventilation pipe of the crankcase. If there is water vapor, it indicates that there is water in the engine oil. When this situation is severe, the engine oil will turn milky white. When opening the valve cover, water droplets can be seen. When removing the engine oil filter assembly, it is found that there is water accumulation inside. In addition, it is important to check whether there is an increase in oil in the oil pan during use, and whether there is diesel inside. If there is, the fuel injectors should be checked and calibrated.
3. Maintain the operating temperature of the diesel engine
The normal operating temperature of a diesel engine is 80-90 ℃. If the temperature is too low and good lubrication cannot be maintained, it will increase the wear of the cylinder wall. The water vapor inside the cylinder will condense into water droplets, dissolve acidic gas molecules in the exhaust gas, generate acidic substances, and cause corrosion and wear on the cylinder wall. Experiments have shown that when the cylinder wall temperature drops from 90 ℃ to 50 ℃, the wear of the cylinder is four times that of 90 ℃. If the temperature is too high, it will reduce the strength of the cylinder and intensify wear, which can lead to excessive piston expansion and cause “cylinder expansion” accidents. Therefore, the water temperature of the diesel generator should be maintained between 74~91 ℃ and not exceed 93 ℃. In addition, it is necessary to ensure the normal circulation of the cooling system. If any coolant overflow is found in the expansion tank, it must be checked and removed in a timely manner.
4. Improve maintenance quality
During use, promptly troubleshoot any issues and replace or repair damaged or deformed parts at any time. When installing the cylinder, it is necessary to strictly inspect and assemble according to technical requirements. In the warranty ring replacement operation, choose a piston ring with appropriate elasticity. If the elasticity is too small, gas will enter the crankcase and blow off the oil on the cylinder wall, increasing the wear of the cylinder wall; Excessive elasticity will directly exacerbate the wear of the cylinder wall, or exacerbate its wear due to the damage of the oil film on the cylinder wall.
5. Strengthen maintenance
(1) Strict maintenance system, improve maintenance quality, especially strengthen the maintenance of the “three filters”, and at the same time, do a good job in purifying air, fuel, and lubricating oil. Especially the air filter must be regularly maintained, the intake duct must be intact without any damage, cleaning must be done carefully, and assembly must be carried out correctly according to requirements without losing parts or taking shortcuts for air. When the air resistance filter indicator light on the instrument panel is on during use, it indicates that the filter resistance has reached 6kPa, and the filter element should be cleaned or replaced immediately.
(2) Minimize the number of cold starts of diesel engines as much as possible.
(3) Maintain the normal operating temperature of the diesel engine and avoid prolonged operation under high temperatures and heavy loads.
(4) Use lubricating oil that meets the requirements to ensure good lubrication; Strictly follow the operating procedures to use diesel generator sets.
(5) Absolute cleanliness of diesel must be ensured. Because the cleanliness of diesel directly affects the service life of high-pressure fuel pumps and injectors, manufacturers require that the diesel used be purified. Usually, diesel must undergo 48 hours of sedimentation before refueling. When refueling, attention should also be paid to the cleanliness of various refueling tools. In addition, it is necessary to adhere to the daily drainage work of the oil-water separator. It should be noted that even if purified diesel is used, it is difficult to ensure that it does not contain water. However, in practical operation, many operators often overlook this point, resulting in excessive water accumulation.
Summary:
It should be noted that the accuracy and precision of the testing instrument should be maintained during testing. Testing should be carried out in a clean environment to avoid errors, and the degree of wear should be judged based on actual application conditions to determine whether repair or replacement is necessary. Practice has proven that as long as the measures described in this article are strictly followed, early damage to the cylinder of diesel generator sets can be effectively prevented, and the service life of diesel generator sets can be effectively extended, thereby bringing considerable economic benefits.
Post time: Mar-14-2024