What is the use of Piston Rings?

A piston ring is a split ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.

The three main functions of piston rings in reciprocating engines are :

1. Sealing the combustion chamber so that there is no transfer of gases from the combustion chamber to the crank 
2. Supporting heat transfer from the piston to the cylinder wall.
3.  Regulating engine oil consumption.