Definition - What does Naturally Aspirated mean?
Naturally Aspirated refers to a favorable power production from an internal combustion engine. Drilling engines used on drilling rigs need to be naturally aspirated to perform to their maximum capacity in an efficient manner. In a naturally aspirated internal combustion engine, the air intake primarily depends on the atmospheric pressure and not on the force produced from any external device such as a turbocharger or supercharger.
Petropedia explains Naturally Aspirated
Engines that are driven by gasoline or petrol are naturally aspirated. This means that they automatically produce a favorable power to weight ratio torque, have better fuel efficiency, and low carbon emissions. These internal combustion engines are installed in most of the automobiles. At times many small engines and light weight are also used for captive purpose in the industries. Diesel-driven automobiles have a heavier and bigger internal combustion engine and because of this nature they are generally not naturally aspirated. Thus, so as to gain maximum torque, better power to weight ratio, and better fuel efficiency these engines are installed with a turbocharger or a supercharger that makes engine naturally aspirated, more refined and powerful.