The middle ring is commonly referred to as which type of ring?

The middle ring of a piston assembly is commonly referred to as the wiper ring. Its primary function is to control the amount of oil that is allowed to reach the combustion chamber. This is crucial because excessive oil can lead to higher emissions and poor engine performance. The wiper ring is designed to scrape off the excess oil from the cylinder walls as the piston moves, effectively "wiping" them.

Understanding the role and functionality of the wiper ring helps in grasping how engine components work together to ensure efficiency and longevity. While the other terms like Napier and scraper may relate to different types of rings or contexts, they do not specifically define the middle ring in the traditional piston ring setup as accurately as the term "wiper" does. Therefore, the wiper ring's designation underscores its specific role in managing oil consumption and maintaining optimal engine conditions.