A piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine.
The main functions of piston rings in engines are:
Sealing the combustion chamber so that there is minimal loss of gases to the crank case.
Improving heat transfer from the piston to the cylinder wall.
Maintaining the proper quantity of the oil between the piston and the cylinder wall
Regulating engine oil consumption by scraping oil from the cylinder walls back to the sump.[1]