Naturally-aspirated engine


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 (petrol) engines are naturally-aspirated, although turbochargers and superchargers have enjoyed periods of success, particularly in the late 1980s and the current 2000s era. Most road-going diesel-engined vehicles use turbochargers and intercoolers because naturally-aspirated diesels generally cannot offer power-to-weight ratios acceptable in the modern car market.

Air or air/fuel mixtures are forced into the cylinders by vacuum caused by piston movement, natural atmospheric pressure, and venturi effect upon opening of the inlet valve or valves. The pressure within the cylinder is lowered by the action of the piston moving away from the valves (so as to expand the volume available for incoming air). In some cases the lowering of the cylinder pressure is enhanced by a combination of the speed of the exhaust gases leaving the cylinder and the closing of the exhaust valve at the appropriate time. A tuned exhaust can help with this but generally only works at a narrow range of engine speeds and hence is most useful in very high performance cars, aircraft, and helicopters. Many N/A engines today make use of Variable Length Intake Manifolds to harness Helmholtz resonance, which has a mild forced-induction effect but is not considered true forced induction.

Cylinder head porting design is of premium importance in naturally aspirated engines. Camshafts usually will be more "aggressive", having greater lift and duration. Cylinder head gaskets will also be thinner, with the top of the piston rising up into the combustion chamber,= for high-performance N/A engines that benefit from higher compression.

Naturally-aspirated engines generally gives less power than either turbo or supercharged engines of the same engine displacement and development level but tend to be cheaper to produce. In drag racing naturally-aspirated vehicles are those that do not operate with a supercharger, a turbocharger, nor use nitrous oxide.

Many racing series specify N/A engines to limit power and speed. NASCAR, IndyCar, and Formula One are all in this category. Naturally-aspirated engines have been mandated in Formula One since 1989, in order to curb excessive power output and the high cost of engines with superchargers or turbochargers. The Indy Racing League mandated Naturally-aspirated engines in 1997.

Natural aspiration as defined above cannot occur in a two-stroke diesel engine. Some method of charging the cylinder with scavenging air must be integrated into the engine design, customarily 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 air flow volume in direct proportion to engine displacement and speed. A mechanically scavenged two-stoke diesel is considered to be naturally aspirated.

ee also

* Carburetor
* Forced induction
* Fuel injection
* Manifold vacuum
* Turbodiesel


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • 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… …   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