Editing Naturally aspirated engine (section)

== Description ==
In a naturally aspirated engine, air for combustion ([[Diesel cycle]] in a [[diesel engine]] or specific types of [[Otto cycle]] in petrol engines, namely [[Gasoline direct injection|petrol direct injection]]) or an air/fuel mixture (traditional Otto cycle petrol engines), is drawn into the engine's [[cylinder (engine)|cylinders]] by atmospheric pressure acting against a [[Vacuum|partial vacuum]] that occurs as the [[piston]] travels downwards toward [[Dead centre (engineering)|bottom dead centre]] during the intake [[stroke (engine)|stroke]]. Owing to innate restriction in the engine's inlet tract, which includes the [[Inlet manifold|intake manifold]], a small pressure drop occurs as air is drawn in, resulting in a [[volumetric efficiency]] of less than 100&nbsp;percent—and a less than complete air charge in the cylinder. The density of the air charge, and therefore the engine's maximum theoretical [[power (physics)|power output]], in addition to being influenced by induction system restriction, is also affected by engine speed and atmospheric pressure, the latter of which decreases as the operating [[altitude]] increases.

This is in contrast to a [[forced-induction]] engine, in which a mechanically driven [[supercharger]] or an exhaust-driven [[turbocharger]] is employed to facilitate increasing the mass of intake air beyond what could be produced by atmospheric pressure alone. [[Nitrous oxide]] can also be used to artificially increase the mass of oxygen present in the intake air. This is accomplished by injecting liquid nitrous oxide into the intake, which supplies significantly more oxygen in a given volume than is possible with atmospheric air. Nitrous oxide is 36.3% available oxygen by mass after it decomposes as compared with atmospheric air at 20.95%. Nitrous oxide also boils at {{convert|-127.3|F}} at atmospheric pressures and offers significant cooling from the latent heat of vaporization, which also aids in increasing the overall air charge density significantly compared to natural aspiration.