What are the 3 functions of piston rings?

What is a Piston Ring?
Between the piston and cylinder, the piston ring is a part that is needed for an engine to work efficiently. Piston Rings have 3 main functions.

This means that the combustion chamber must be made as gas-tight as possible, so that the pressure generated by the quickly burning combustion gases will move the piston in the cylinder causing the Crankshaft to turn, making power available. Not only important for the combustion/expansion stroke, gas-tightness is also very important for the intake, compression and exhaust strokes as well. This general function can be simply called "gas sealing".

The piston rings act to carry heat away from the hot piston into the cooled cylinder wall/block of the engine. Heat energy flows from the piston groove into the piston ring and then into the cylinder wall, where it eventually will be transferred into the engine coolant. This heat transfer function is very important to maintaining acceptable temperatures and stability in the piston and piston rings, so that sealing ability is not impaired.

The piston rings require some oil for lubrication, however it is desirable to keep this amount to a minimum. The rings act in a scraping manner, keeping excess oil out of the combustion chamber. In this way, oil consumption is held at an acceptable level and harmful emissions are reduced.

The three boxes above show the primary functions performed by piston rings. In almost all cases, each individual ring in a three-ring set will be designed so as to optimize or help the functions of the other two rings. In this way, it's easy to understand that while each ring in the three-ring pack is unique, the ring pack as a whole is really designed as a 'system', where each ring is 'tuned' to make the complete 3-piece set work most effectively in the engine.