What is the main purpose of the compression ring?

The main purpose of the compression ring is to aid in sealing blow-by. Blow-by refers to the combustion gases that escape past the piston rings and into the crankcase. The compression ring plays a crucial role in maintaining the integrity of the combustion chamber by effectively sealing it during the compression stroke and combustion process. This helps to ensure that the engine operates efficiently and maintains the necessary pressure for optimal power output. By preventing blow-by, the compression ring also contributes to better fuel efficiency and reduces the amount of exhaust emissions from the engine.

In terms of the other options, while cleaning the piston and cylinder may be tasks associated with other components, they do not accurately describe the primary function of the compression ring, which is focused on sealing. Similarly, distributing oil is relevant to other rings such as the oil control ring, which is specifically designed for managing lubricating oil around the piston.