Naturally aspirated engine
In stroke 1 , the piston sucks mixture into the combustion chamber through the open inlet valve (left)
A combustion engine in which the combustion air is not additionally pre-compressed by a compressor or a turbocharger ( engine supercharging ) is now referred to as a naturally aspirated or free-aspirating engine . Until the 2000s, the term was used differently for carburettor engines in order to differentiate them from engines with manifold injection .
Previous use & change of meaning
Until the 1980s, when was gasoline engines , the mixture preparation with carburetor the rule, the more complex injection came only in larger or more powerful engines. Turbochargers were not widely used. The term “suction” refers here to the fuel that is sucked in from a nozzle in the carburetor engine by the air flowing past, whereas it is actively injected in the injection engine . With the extinction of the carburettor engines from the 1990s, this distinction became superfluous. At the same time, turbocharging spread more and more, which is why the term experienced a change in meaning and from then on referred to the intake air.
Usage and function today
In four-stroke engines , the first working stroke is the intake stroke, in which the movement of the piston in the direction of the crankshaft creates a negative pressure in the combustion chamber . In this case, through the opened inlet valve in Otto engines with external mixture formation, an air-mixture fuel sucked in, diesel engines and direct injection , however, pure gasoline engines air, since the fuel is supplied only in the combustion chamber ( internal mixture formation ).
The naturally aspirated engines also include two-stroke engines with crankcase scavenging, in which the mixture is first sucked into the crankcase .
Advantages and disadvantages (compared to supercharged engines)
Advantages:
- more prompt throttle response instead of turbo lag
- lower production and development costs
- higher reliability because fewer individual parts
- easier maintenance
Disadvantage:
- poorer power to weight ratio and poorer efficiency
Small internal combustion engines are often naturally aspirated, but the trend is towards turbocharging, as it is more efficient. Some sports cars deliberately use naturally aspirated engines because they have no turbo lag .
Sound image
Naturally aspirated engines differ in sound from turbo engines, as intake and exhaust port noises are not muffled by turbo compressors and exhaust gas turbines. In the case of engines with mechanical charging, only the intake noise is dampened; depending on the design, additional tonal components are added (howling). Due to their high speed, depending on the number of turbine blades, turbo engines generate very high-frequency noise components (turbo whistles). When the load changes from high to low load, the excess boost pressure is released via the blow-off valve, which can be heard as a hissing sound in some vehicles.
literature
- Richard van Basshuysen, Fred Schäfer: Handbook Internal Combustion Engine; Basics, components, systems, perspectives . 3rd edition, Vieweg, Wiesbaden 2005, ISBN 3-528-23933-6 .
Individual evidence
- ↑ HR Etzold - So it's done, Volume 40, p. 42ff (and others)