Naturally aspirated engine

Naturally aspirated engine

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. This is in contrast to a forced induction engine, in which a mechanically driven supercharger, or an exhaust-driven turbocharger is employed to facilitate in increasing the mass of intake air beyond what could be produced by atmospheric pressure alone.

In a naturally aspirated engine; air for combustion (diesel cycle in a diesel engine, or specific types of Otto cycle in gasoline engines - namely gasoline direct injection), or an air/fuel mixture (traditional Otto cycle petrol engines) is drawn into the engines cylinders by atmospheric pressure acting against a partial vacuum that occurs as the piston travels downwards toward bottom dead centre during the induction stroke. Owing to innate restriction in the engine's inlet tract which includes the intake manifold, a small pressure drop occurs as air is drawn in, resulting in a volumetric efficiency of less than 100 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 output, in addition to being influenced by induction system restriction, is also affected by engine speed and atmospheric pressure, the latter which decreases as the operating altitude increases.

Most automobile petrol engines, as well as many small engines used for non-automotive purposes, are naturally aspirated. Most modern diesel engines powering highway vehicles are turbocharged to produce a more favourable power-to-weight ratio, as well as better fuel efficiency and lower exhaust emissions. Turbocharging is nearly universal on diesel engines that are used in railroad, marine engines, and commercial stationary applications (electrical power generation, for example). Forced induction is also used with reciprocating aircraft engines to negate some of the power loss that occurs as the aircraft climbs to higher altitudes.

A two-stroke diesel engine is incapable of natural aspiration as defined above. Some method of charging the cylinders with scavenging air must be integrated into the engine design. This is usually achieved with a positive displacement blower driven by the crankshaft. The blower does not act as a supercharger in this application, as it is sized to produce a volume of air flow that is in direct proportion to engine displacement and speed. A mechanically scavenged two-stroke diesel engine is considered to be naturally aspirated.

See also

References and further reading


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Naturally-aspirated engine — A naturally aspirated engine or normally aspirated engine (or N/A aspiration meaning breathing) refers to an internal combustion engine (normally petrol or diesel powered) that is neither turbocharged nor supercharged. Most automobile gasoline… …   Wikipedia

  • naturally aspirated engine — A conventional engine that takes in air at normal pressure, i.e. not turbocharged or supercharged. The opposite is forced induction engine …   Dictionary of automotive terms

  • naturally aspirated engine — A non supercharged reciprocating engine that uses atmospheric pressure to force the fuel air mixture into cylinders …   Aviation dictionary

  • aspirated engine — See naturally aspirated engine normally aspirated engine …   Dictionary of automotive terms

  • normally aspirated engine — An engine which uses the factory installed carburetor or fuel injection system with its normal air filter, etc. It does not use modified air flow systems which pump more air into the engine. Usually this expression is used as comparison as in My… …   Dictionary of automotive terms

  • engine — A device for changing fuel energy to mechanical energy. The term applies to the primary source of power generation. In Britain there is a desire to make a clear distinction between engine and motor so that motor refers only to electric power… …   Dictionary of automotive terms

  • Engine swap — Warning: in some jurisdictions with strict smog rules it may not be possible to register a late model vehicle with an engine swap, even if it can be proven that it produces less pollution than the original engine (owing to visual inspection… …   Wikipedia

  • Engine displacement — One complete cycle of a four cylinder, four stroke engine. The volume displaced is marked in orange. Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top… …   Wikipedia

  • Judd (engine) — Judd is a name brand of engines produced by Engine Developments Ltd. , a company founded in 1971 by John Judd and Jack Brabham in Rugby, Warwickshire, England. Engine Developments was intended to build engines for Brabham s racing efforts, and… …   Wikipedia

  • Diesel engine — Diesel engines in a museum Diesel generator on an oil tanker …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”