What does natural inhalation mean?

Natural inhalation is a kind of automobile air intake, which is a form of atmospheric pressure forcing air into the combustion chamber without any supercharger. Naturally aspirated type has no supercharger, that is to say, air simply passes through the air filter, throttle valve (commonly known as "throttle valve") and intake manifold to reach the cylinder, and gasoline is directly injected into the intake manifold through the fuel injector. Take a four-cylinder engine as an example, the piston does work with four strokes: downward (the intake valve is open, there is a pressure difference, and the mixture of air and fuel enters the cylinder under the pressure difference), upward (the intake valve is closed, the mixture is compressed, and the piston is ignited when it reaches the highest point), downward (the mixture burns and expands, pushing the piston to do work and output power), and upward (the exhaust valve is opened, and the piston is exhausted).