Investigation of Pressure Distribution and Frictional Heat on Self-Lubricated Piston Rings in Reciprocating Compressors

Piston ring sealing is of great importance in oil-free reciprocating compressors for high pressure application. Pressure distribution and frictional heat on piston rings have been investigated with the aim of finding the key factors influencing the life time of piston rings. A mathematical model simulating the unsteady flow within the gaps of piston rings was established to present the pressure distribution and disclose the mechanism of the uneven abrasion of different rings. Meanwhile, the test rig was built to validate the mathematic model, on which the pressure distributions between the piston rings were measured using pressure sensors. The results showed that the severe non-uniformity of the pressure distribution between piston rings was suggested to be the root cause of premature failure of the sealing rings. The pressure distributions between the rings were always dramatically nonuniform with the same ring cut, and the first ring afforded more than 75% of the total pressure difference. Then the method to equalize the pressure difference through each ring was proposed by re-distributing the cutting size of each ring, and it was also validated experimentally. Another factor that influenced the life time of piston ring was the high temperature caused by the frictional heat, so this paper also investigated the frictional heat generation and conduction between piston rings and cylinder by the Finite Element Method.