A piston ring is a split ring that fits into a groove on the outer diameter of a piston in reciprocating engine such as an internal combustion engine or steam engine.The main function of piston rings in reciprpcating engine are:
1.Sealing the combustion chamber so that there is minimal loss of gases to the crank case.
2.Improving heat transfer from the piston to the cylinder wall .
3.Maintaing the proper quantity of the oil between the piston and the cylinder wall .
4.Regulating engine oil consumption by scraping oil from the cylinder walls back to sump.
The gap in the piston ring compresses to a few thousandth of an inch inside the cylinder bore.Piston rings are major factor in identifying if an engine is two stroke or four stroke.Three piston rings suggest that it is a four stroke engine whilw piston rings suggest that it is a two stroke engine.Most piston rings are made of a very hard and somewhat brittle cast iron.