A naturally aspirated engine, also known as a normally aspirated engine, and abbreviated to N/A or NA, is an internal combustion engine in which air intake depends solely on atmospheric pressure and does not have forced induction through a turbocharger or a supercharger. [1]
In a naturally aspirated engine, air for combustion (Diesel cycle in a diesel engine or specific types of Otto cycle in petrol engines, namely petrol direct injection) or an air/fuel mixture (traditional Otto cycle petrol engines), is drawn into the engine's cylinders by atmospheric pressure acting against a partial vacuum that occurs as the piston travels downwards toward bottom dead centre during the intake 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 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 −127.3 °F (−88.5 °C) 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.
Most automobile petrol engines, as well as many small engines used for non-automotive purposes, are naturally aspirated. [2] Most modern diesel engines powering highway vehicles are turbocharged to produce a more favourable power-to-weight ratio, a higher torque curve, 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.
The advantages and disadvantages of a naturally aspirated engine in relation to a same-sized engine relying on forced induction include:
The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values.
In an internal combustion engine, a turbocharger is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into the engine in order to produce more power for a given displacement.
In engineering, the Miller cycle is a thermodynamic cycle used in a type of internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, U.S. Patent 2,817,322 dated Dec 24, 1957. The engine may be two- or four-stroke and may be run on diesel fuel, gases, or dual fuel. It uses a supercharger to offset the performance loss of the Atkinson cycle.
In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters.
A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:
The Roots-type blower is a positive displacement lobe pump which operates by pumping a fluid with a pair of meshing lobes resembling a set of stretched gears. Fluid is trapped in pockets surrounding the lobes and carried from the intake side to the exhaust. The most common application of the Roots-type blower has been the induction device on two-stroke diesel engines, such as those produced by Detroit Diesel and Electro-Motive Diesel. Roots-type blowers are also used to supercharge four-stroke Otto cycle engines, with the blower being driven from the engine's crankshaft via a toothed or V-belt, a roller chain or a gear train.
Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the equivalent volume of the fresh air drawn into the cylinder during the intake stroke to the volume of the cylinder itself. The term is also used in other engineering contexts, such as hydraulic pumps and electronic components.
In an internal combustion engine, forced induction is where turbocharging or supercharging is used to increase the density of the intake air. Engines without forced induction are classified as naturally aspirated.
A Nitrous Oxide Engine, or Nitrous Oxide System commonly referred to and known as NOS, is an internal combustion engine in which oxygen for burning the fuel comes from the decomposition of nitrous oxide, N2O, as well as air. The system increases the engine's power output by allowing fuel to be burned at a higher-than-normal rate, because of the higher partial pressure of oxygen injected with the fuel mixture. Nitrous injection systems may be "dry", where the nitrous oxide is injected separately from fuel, or "wet" in which additional fuel is carried into the engine along with the nitrous. NOS may not be permitted for street or highway use, depending on local regulations. N2O use is permitted in certain classes of auto racing. Reliable operation of an engine with nitrous injection requires careful attention to the strength of engine components and to the accuracy of the mixing systems, otherwise destructive detonations or exceeding engineered component maximums may occur. Nitrous oxide systems were applied as early as World War II for certain aircraft engines.
In automotive engineering, an inlet manifold or intake manifold is the part of an engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English word manigfeald and refers to the multiplying of one (pipe) into many.
Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.
The manifold absolute pressure sensor is one of the sensors used in an internal combustion engine's electronic control system.
A twincharger refers to a compound forced induction system used on some internal combustion engines. It is a combination of an exhaust-driven turbocharger and a mechanically driven supercharger, each mitigating the weaknesses of the other.
Twin-turbo refers to an engine in which two turbochargers work in tandem to compress the intake fuel/air mixture. The most common layout features two identical or mirrored turbochargers in parallel, each processing half of a V engine's produced exhaust through independent piping. The two turbochargers can either be matching or different sizes.
The term turbo-diesel, also written as turbodiesel and turbo diesel, refers to any diesel engine equipped with a turbocharger. As with other engine types, turbocharging a diesel engine can significantly increase its efficiency and power output, especially when used in combination with an intercooler.
Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work. There are two classifications of thermal engines-
In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement.
A two-stroke diesel engine is a diesel engine that uses compression ignition in a two-stroke combustion cycle. It was invented by Hugo Güldner in 1899.
An electric supercharger is a specific type of supercharger for internal combustion engines that uses an electrically powered forced-air system that contains an electric motor to pressurize the intake air. By pressurizing the air available to the engine intake system, the air becomes more dense, and is matched with more fuel, producing the increased horsepower to the wheels.
An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.
Most motor vehicle engines are naturally-aspirated engines; however, turbocharging and supercharging are currently a very popular way of boosting power output for a number car marques.