An internal combustion engine that relies on atmospheric pressure to fill the cylinders with air is referred to as what?

An internal combustion engine that relies on atmospheric pressure to fill the cylinders with air is termed naturally aspirated. In such engines, air enters the combustion chamber purely through the natural pressure differential created by the downward movement of the pistons. This means that the intake air is at ambient atmospheric pressure without any mechanical assistance to force more air into the engine.

This is a critical aspect of engine design, as the amount of air available for combustion directly impacts engine performance. Naturally aspirated engines generally have simpler designs than their boosted counterparts, as they do not require additional components like turbochargers or superchargers to increase the intake air pressure. The simplicity often translates to less weight, fewer potential points of failure, and a more direct connection between the throttle input and engine response.

In contrast, turbocharged and supercharged engines use forced induction to increase air intake, and "boosted" generally refers to these types of engines as well. These methods enhance performance by compressing air before it enters the cylinders, allowing for a greater air-fuel mixture and enabling more power. However, that is outside the realm of naturally aspirated engines, which operate solely on atmospheric pressure.