Naturally-aspirated engine

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Naturally-aspirated engine

A naturally-aspirated engine is a reciprocating internal combustion engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs in a combustion chamber inside and integral to the engine. In an internal combustion engine it is always the expansion of the high temperature and pressure gases that are produced by the combustion which apply force to the movable component of the engine, such as...
that depends solely on atmospheric pressure

Atmospheric pressure

Atmospheric pressure is sometimes defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the Earth's atmosphere....
to draw in combustion air. This is in contrast to a forced induction

Forced induction

Forced induction is a term used to describe internal combustion engines that are not naturally-aspirated engine. A gas compressor is added to the air intake instead, thereby increasing the quantity of oxygen available for combustion....
engine, in which a mechanical

Supercharger

A supercharger is an air Gas compressor used for forced induction of an internal combustion engine. The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally-aspirated engine, which allows more fuel to be provided and more work to be done per cycle, increasing the power output of the engine...
or exhaust-driven

Turbocharger

A turbocharger, or turbo, is a gas compressor used for forced induction of an internal combustion engine. Like a supercharger, the purpose of a turbocharger is to increase the mass of air entering the engine to create more power....
blower is employed to increase the volume of intake air beyond what could be produced by atmospheric pressure alone.

In a naturally-aspirated engine, air (Diesel cycle

Diesel cycle

The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the Diesel engine, invented by Rudolph Diesel in 1897....
) or an air/fuel mixture (Otto cycle) is forced into the cylinder

Cylinder (engine)

A cylinder is the central working part of a reciprocating engine, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically casting from aluminum or cast iron before precision features are machined into it....
by atmospheric pressure in response to a partial vacuum that occurs as the piston moves toward bottom dead center during the intake stroke.

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Encyclopedia

A naturally-aspirated engine is a reciprocating internal combustion engine

Internal combustion engine

Atmospheric pressure

Forced induction

Supercharger

Turbocharger

Diesel cycle

Cylinder (engine)

Volumetric efficiency

Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the Cylinder ....
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

Horsepower

Horsepower is the name of several non-International System of Units units of power . It was originally defined to allow the output of steam engines to be measured and compared with the power output of draft horses....
, 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

Altitude

Altitude has multiple uses depending on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object....
increases.

Most automobile

Automobile

An automobile or motor car is a wheeled motor vehicle for transportation passengers, which also carries its own car engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally f...
gasoline (petrol) engines, as well as many small engines used for non-automotive purposes, are naturally-aspirated. The majority of Diesel engines powering highway vehicles are turbocharged to produce a more favorable power-to-weight ratio

Power-to-weight ratio

Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another....
, as well as better fuel efficiency

Fuel efficiency

Fuel efficiency, in its basic sense, is the same as thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or Mechanical work....
and lower exhaust emissions

Automobile emissions control

Automobile emissions control covers all the technologies that are employed to reduce the air pollution-causing emissions produced by automobiles....
. Turbocharging is nearly universal on Diesel engines that are used in railroad, marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology....
and commercial stationary

Stationary

Stationary can mean:* Not moving .* Unchanging .* In statistics and probability: a stationary process.* In mathematics: a stationary point....
applications (for example, electrical power generation). Forced induction

Forced induction

Aircraft engine

An aircraft engine is a propulsion system for an aircraft. Aircraft engines are almost always either lightweight piston engines or gas turbines....
s to negate some of the power loss that occurs as the aircraft

Aircraft

An aircraft is a vehicle which is able to flight by being supported by the air, or in general, the atmosphere, of a planet. Examples include balloons, airplanes and helicopters....
climbs to higher altitudes.

It should be noted that 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, customarily achieved with a positive displacement blower driven by the crankshaft

Crankshaft

The crankshaft, sometimes casually abbreviated to crank , is the part of an engine which translates reciprocation linear piston motion into rotation....
. 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.

Naturally-aspirated engine

See also