A naturally aspirated engine is one common type of reciprocating piston internal combustion engine that depends solely on atmospheric pressure to counter the partial vacuum in the induction tract to draw in combustion air.
A naturally aspirated engine is the default type of reciprocating piston internal combustion engine, in contrast to a supercharged or forced induction engine. Naturally aspirated engines depend solely on atmospheric pressure against the partial vacuum in the induction tract to draw in combustion air.