Novel crosshead type two-stroke uniflow scavenging piston assembly

Abstract

The invention provides a novel crosshead type two-stroke straight-flow scavenging piston assembly. The novel crosshead type two-stroke straight-flow scavenging piston assembly is characterized by comprising a scavenging piston and an air inlet valve, wherein the scavenging piston is composed of a detachable piston head and a piston seat ring, the air inlet valve is located in the scavenging piston and detachably connected with one end of a piston rod, a scavenging port is formed in the center of the top of the piston head, the air inlet valve is used in cooperation with the scavenging port, and the air inlet valve is opened or closed through movement of the piston rod. By means of the novel crosshead type two-stroke straight-flow scavenging piston assembly, the combustion efficiency can be improved, the ventilation quality is improved, and installation and maintenance are convenient and reliable to carry out.

Description

technical field [0001] The invention relates to the field of diesel engines, in particular to a piston of a crosshead two-stroke diesel engine. Background technique [0002] Compared with the four-stroke diesel engine, the two-stroke diesel engine has the advantages of high efficiency, high power, reliable operation, long life, and low-quality fuel, but it also has problems such as insufficient combustion and severe heat load, which cause this The important reason of this problem is the poor quality of air exchange, which is also one of the bottlenecks restricting the development of this type of diesel engine. Existing two-stroke diesel engines have two forms of ventilation: curved flow scavenging and direct current scavenging. Among them, the curved flow scavenging method has problems such as poor ventilation quality, uneven heating and easy deformation of the cylinder, and direct current scavenging. The method overcomes the above-mentioned shortcomings and is the main for...

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Problems solved by technology

[0002] Compared with the four-stroke diesel engine, the two-stroke diesel engine has the advantages of high efficiency, high power, reliable operation, long life, and low-quality fuel, but it also has problems such as insufficient combustion and severe heat load, which cause this An important reason for this problem is poor air exchange quality, which is also one of the bottlenecks restricting the development of this type of diesel engine

Existing two-stroke diesel engines have two forms of ventilation: curved flow scavenging and direct current scavenging. Among them, the curved flow scavenging method has problems such as poor ventilation quality, uneven heating and easy deformation of the cylinder, and direct current scavenging. The method overcomes the above shortcomings and is the main form of ventilation for large diesel engines used in modern ships.

[0003] Existing direct current scavenging methods such as figure 1 As shown, there is a scavenging hole on the lower peripheral surface of the cylinder liner, and the scavenging path is: scavenging box-scavenging port-inside of the cylinder liner-exhaust valve, the air enters the cylinder approximately tangentially at a certain elevation angle, and the intake air is If the horizontal direction is changed to the vertical direction, there is a large speed loss, and the air that rotates and rises has a long path before reaching the exhaust port (blowing off the exhaust gas), and on each cross-section, the air forms a swirl, and the combustion The center of the swirl flow is formed in the middle of the chamber. Compared with air, the exhaust gas has a lower density and higher viscosity, and is easy to accumulate in the center area of ​​the swirl flow. Above this area is the valve crown of the exhaust valve. The diameter of the conventionally designed valve crown is 0.32~ of the diameter of the cylinder liner. 0.5 times, the valve crown hinders the smooth discharge of these exhaust gases

According to data analysis, the size of the central area depends on the speed and air density of the scavenging air. The higher the speed, the greater the density, and the larger the diameter of the central exhaust gas area, which affects the exhaust quality. At the same time, the higher the scavenging speed, the more air entering the cylinder. The inner wall close to the cylinder flows upwards, thereby scouring the inner wall of the cylinder, forming a "chamber wall chilling effect", which causes the temperature of the cylinder wall to be too low and affects the combustion efficiency. In addition, because the scavenging hole is opened on the inner wall of the cylinder liner, when the piston ring moves with the piston Scratching up and down the air hole is likely to cause ring breakage accidents, and the top of the piston is also prone to ablation and cracking due to long-term action in a high-temperature and high-pressure environment. Under the existing DC scavenging structure, to replace the piston ring or piston, the piston, The piston rod and air seal box and other accessories are hoisted out together, which involves a large amount of engineering and is easy to pollute the crankcase, making maintenance difficult

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