Analysis and Prevention of Abnormal Wear and Early Damage of Piston Rings in High-Strength Diesel Engines

Abstract

The piston ring is one of the important parts in a diesel engine. It works under harsh conditions. If the internal combustion engine is not used or maintained properly or the method of assembling the piston ring is incorrect, it will cause abnormal wear or premature damage to the piston ring. This article analyzes the types, characteristics and causes of abnormal wear and early damage of high-strength diesel engine piston rings in recent years, and discusses the measures and methods to extend the service life of piston rings.

Key words

Prevention methods for abnormal wear of diesel engine piston rings

The characteristics and causes of abnormal wear and early damage of piston rings

1.1 Fatigue Damage

1.1.1 Characteristics

The upper and lower working surfaces of the piston ring have severe scratches along the circumferential direction and are severely worn, and the color of the piston ring is dull. The contact surface between the first piston ring and the cylinder is severely worn, and most of the sliding surfaces of the cylinder piston rings have fine scratches in the direction of the cylinder axis. There is a large amount of sludge and adhesive film around the inner circle of the gas ring, the oil ring and the return oil hole of the piston ring groove.

1.1.2 Reasons

The main cause of fatigue damage to piston rings is improper operation mode and maintenance during the running-in period of diesel engines. For example, the engine works at high speed and heavy load for a long time during the running-in period, and suddenly stalls at high temperature. A short circuit in the connecting hose between the air filter and the intake pipe allowed dust to enter the cylinder. The grade of the lubricating oil added does not meet the specified requirements and is seriously contaminated. Poor fuel injection quality of the fuel injector or poor quality of the selected fuel; Diesel engines have been operating at low temperatures for a long time. The fuel supply advance Angle does not meet the requirements, etc.

1.2 Fracture

1.2.1 Features

The first piston ring broke and the piston ring groove was severely damaged: there were wavy pull marks on the working surface of the piston ring and the upper part of the cylinder. There is molten wear on the piston skirt and the upper part of the cylinder. The fracture often occurs in the high point area on both sides of the opening.

1.2.2 Reasons

The main cause of piston ring breakage is improper use or maintenance and assembly of the engine. For instance, when a diesel engine operates for a long time in an overheated state, the piston rings get stuck and eventually break. The viscosity of the lubricating oil added is too high. Unreasonable selection of piston rings or incorrect installation methods can cause concentrated stress on the piston rings. The fit clearance between the piston and the cylinder is too small. Diesel engines operate for a long time under deflagration conditions, etc.

1.3 Adhesive Ring

1.3.1 Features

There is a large amount of oil sludge, carbon deposits and gelatinous deposits at the piston rings and the piston ring grooves. The sliding surface of the piston ring shows a polished luster and has relatively deep longitudinal scratches. Weakened elasticity of piston rings, etc.

1.3.2 Reasons

The main causes of ring sticking are the adhesion of piston rings by oil sludge deposits and carbon deposits, as well as the deformation of piston rings and cylinders. For example: Severe thermal deformation of the piston rings and cylinders, too small side clearance and back clearance of the piston rings, causing the rings to get stuck in the ring grooves and unable to rotate. Diesel engines overheat or operate under long-term overload conditions, causing the lubricating oil to become gel-like or severely contaminated. Poor quality of lubricating oil; Poor fuel injection quality of the fuel injector and frequent deflagration; The crankcase ventilation device malfunctions, causing excessive negative pressure or poor cylinder airtightness, which leads to a decrease in the average effective pressure and results in oil leakage. Deformation caused by unreasonable selection of cylinder liners or improper press-fitting methods, etc.

1.4 Eccentric wear

1.4.1 Characteristics

The wear between the upper and lower end faces of the piston ring and the ring groove is relatively small, and the thickness wear is uneven on the single surface or the circumferential surface. There are longitudinal scratches on the sliding surface of the piston ring caused by adhesive wear. There are traces of gas leakage between the piston rings and the top of the piston.

1.4.2 Reasons

The main cause of the piston's uneven wear is that the piston is not centered in the cylinder. For example: A new engine or a diesel engine that has undergone major overhauls does not run well during the running-in period; The cylinder liner undergoes local deformation due to uneven heating, and the cylinder liner is not properly positioned in the cylinder block. The connecting rod is bent or twisted. Excessive axial clearance of the crankshaft, etc.

1.5 Scratches on the working surface

1.5.1 Characteristics

There are longitudinal grooves on the unilateral or circumferential contact surface of the piston ring. Metal peeling or severe and large-scale longitudinal scratches occur on the contact surface. Scratches on the working surface and ring sticking often coexist.

1.5.2 Reasons

The main cause of piston ring abrasion is the damage of the lubricating oil film between the piston ring and the cylinder. For example: The clearance between the piston and the cylinder is too small; Improper assembly methods of piston rings or random compression or extension of the ring opening during assembly can cause deformation. The incorrect method of assembling the cylinder liner or tightening the cylinder head causes deformation of the cylinder liner. When diesel engines operate for a long time under high-temperature and heavy-load conditions, the lubricating oil film breaks. Insufficient lubricating oil or severe contamination, etc.

Measures to extend the service life of piston rings

2.1 Use and Maintain diesel engines correctly

When starting a diesel engine, the preheating start method should be adopted as much as possible. When running the engine in winter, the body temperature should be kept within the normal range. It is prohibited to have bad operating habits such as sudden acceleration, forced temperature increase, and emergency braking to stop. It is also necessary to prevent sudden and drastic load changes and prolonged idling in low-temperature conditions, and minimize the frequency of cold starts.

Effectively carry out the running-in operation, maintenance and cleaning work during the running-in period of new engines and diesel engines after major overhauls. During the operation of the carrier vehicle, maintain a medium speed and load reasonably.

Strengthen the maintenance of the "three filters" and replace the filter elements in a timely manner. According to the data, if 1g of dust enters the cylinder, it can cause the upper part of the cylinder to wear down by 0.01mm, the piston to lose 0.75g of mass, and the piston ring to wear down by 0.009mm. Therefore, it is necessary to regularly and compulsorily maintain the air filter, oil filter and diesel filter.

The correct selection, inspection and replacement of lubricating oil should be carried out. Lubricating oil of the same brand, from the same manufacturer, with the same viscosity and quality grade should be chosen. It is strictly prohibited to mix lubricating oils of different viscosities and quality grades. When refilling, it should be done in a windless and pollution-free environment to prevent dust, water and other contaminants from entering.

The fuel should be correctly selected based on factors such as the climate environment and the performance of the diesel engine. The fuel injection pressure of the fuel injector and the fuel supply advance Angle of the fuel injection pump should be accurately calibrated and adjusted to ensure that the diesel engine operates in the best condition.

Avoid running the diesel engine without cooling water or when it is overheated for a long time. Do not add coolant or rinse the engine block with water when the engine temperature is too high.

2.2 Improve the repair and maintenance quality of diesel engines

Strengthen the cleaning and anti-pollution work at every stage of the selection and assembly of spare parts.

Correctly select and assemble piston rings. Currently, the surfaces of piston rings in high-speed diesel engines are all treated with processes such as chromium plating and molybdenum plating. It is strictly prohibited to use the method of grinding the rings to adjust the "side clearance". When installing the piston rings, special tools should be used. The opening of the piston rings should not be expanded or compressed at will to prevent permanent deformation of the piston rings, which may cause them to twist up and down due to improper assembly methods. When the piston connecting rod assembly is installed into the cylinder. Do not strike forcefully to prevent the piston rings from colliding with the cylinder, which may cause damage, cracks, etc.

The axial clearance of the crankshaft should comply with the regulations. The bending and twisting of the connecting rod must be corrected to ensure the correct position of the piston in the cylinder.

The selection and installation methods of cylinder liners must be correct to prevent local deformation, tilting and stress concentration of the cylinder liners due to improper installation. The interference fit between the cylinder liner and the cylinder block, as well as the protrusion of the upper plane after the cylinder liner is installed, should be strictly controlled within the specified range. Tighten the cylinder head correctly. The torque of the bolts such as the cylinder head and the axle bearing cover should be uniform and comply with the specifications.

Attach great importance to the cold grinding and hot testing of diesel engines after assembly. The running-in time is preferably 16 hours. According to the data, the service life of the running-in piston rings is 20% to 30% longer than that of the unrunning-in ones. Therefore, it is necessary to pay attention and carefully carry out the debugging, disassembly inspection and cleaning work.

2.3 Strengthen the storage and management of piston rings

The storage of piston rings should be classified and stored according to different types of diesel engines to prevent mixed storage and loading. During storage and handling, prevent dropping and bumping to avoid damage, cracking, deformation, etc. During storage, piston rings should be placed flat to avoid unstable placement and prevent rust and other issues caused by poor management.