The function of piston rings in an internal combustion engine is

Explanation:

Piston rings fulfill the following important tasks for engine operation:

• Sealing of the combustion chamber, in order to maintain the pressure of the combustion gas. The combustion gas must not enter the crankcase, and oil must not reach the combustion chamber.
• Transfer of heat built up in the piston to the cylinder surface.
• Controlling the oil balance, where a minimum of oil is needed on the cylinder surface to create a hydrodynamic situation, while oil consumption needs to be kept as low as possible.

These tasks are performed by the piston rings as follows:

1st piston ring:

Compression of combustion air or gas mixture, and the resulting gas pressure in the combustion cycle, transfer of generated heat to the cylinder surface, and to a slight degree, scraping of the residual oil from the cylinder surface.

2nd piston ring:

Support of the remaining gas pressure due to blow-by past the 1st piston ring, scraping of oil from, and transfer of generated heat to the cylinder surface.

3rd piston ring:

Scraping of the oil.