The centrifugal-type supercharger is an engine-driven compressor

Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

 used to increase the power output of an internal-combustion engine by increasing the amount of available oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 by compressing air that is entering the engine. This type of supercharger is practically identical in operation to a turbocharger

Turbocharger

A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...

, with the exception that instead of exhaust gases driving the compressor via a turbine

Turbine

A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

, the compressor is driven from the crankshaft

Crankshaft

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

 by a belt, gear or chain drive.

Like any centrifugal pump, the boost provided by the centrifugal supercharger increases with the square of the speed

Angular velocity

In physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating. The SI unit of angular velocity is radians per second, although it may be measured in other units such as degrees per second, revolutions per...

. This means that the centrifugal design provides little boost at low engine speeds, in some cases allowing air to pass back through the supercharger, such as during deceleration. On the other hand, the design is also the most efficient, besting designs like the Roots type supercharger

Roots type supercharger

The Roots type supercharger or Roots blower is a positive displacement lobe pump which operates by pumping fluids with a pair of meshing lobes not unlike a set of stretched gears. Fluid is trapped in pockets surrounding the lobes and carried from the intake side to the exhaust...

 and twin-screw type supercharger, which have the advantage of producing boost at any speed.

Many World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 piston aircraft engines, such as the Rolls-Royce Merlin

Rolls-Royce Merlin

The Rolls-Royce Merlin is a British liquid-cooled, V-12, piston aero engine, of 27-litre capacity. Rolls-Royce Limited designed and built the engine which was initially known as the PV-12: the PV-12 became known as the Merlin following the company convention of naming its piston aero engines after...

 and the Daimler-Benz DB 601

Daimler-Benz DB 601

|-See also:-Bibliography:* Mankau, Heinz and Peter Petrick. Messerschmitt Bf 110, Me 210, Me 410. Raumfahrt, Germany: Aviatic Verlag, 2001. ISBN 3-92550-562-8.* Neil Gregor Daimler-Benz in the Third Reich. Yale University Press, 1998-External links:...

, utilized single-speed or multi-speed centrifugal superchargers. Because high-performance aircraft engines were typically mated to constant-speed propellers and did not see a great variation in engine speeds, the poor low-rpm performance of centrifugal superchargers was not an issue. Superchargers have since fallen from use in the aviation world, replaced by turbochargers of ever-improving quality.

Due to its design and lack of low-RPM boost it is often employed on near-standard compression engines. This means that it can facilitate airflow at higher engine RPMs, when most motors tend to have poor volumetric efficiency

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 cylinders. More specifically, volumetric efficiency is a ratio of what quantity of fuel and air actually enters the cylinder during induction to the...

, without substantially increasing cylinder pressures at low- to mid-RPM operation, causing knock. This principle makes this type of supercharger ideally fit for a "bolt-on" type power adder, with no modification of the pistons and/or compression ratio necessary. Since gasoline must mix with air in a fairly narrow ratio to achieve combustion, the fact that centrifugals do not add much air at low and mid-range RPM's means fuel mileage is near-stock in the cruise RPM range. They appear to be most popular with cars that have a sufficiently large engine to provide adequate acceleration from a standing start without boost, while at the same time avoiding wheelspin. Then, the engine encounters breathing limitations in the mid-RPM range, often because it may only use two valves per cylinder. Centrifugals are also popular in places where the power-adder must be removed for frequent government engine inspections, as the exhaust system is unaffected (as it would be with a turbocharger).

Compared to a turbocharger (which uses an almost identical compressor design, but instead is powered by exhaust gasses), a supercharger has the benefit of being able to reach peak boost earlier in the RPM range. A turbocharger will maintain the desired boost pressure by leaking excess gasses using a Wastegate, to keep the boost pressure at the desired level and also allow the engine to continue accelerating. A centrifugal supercharger does not have the ability to do this, so it will always make peak boost at the engine's own peak RPM (provided that the engine's peak RPM isn't beyond the peak efficiency of the compressor). The flaw in this application is that the engine will not have the same torque at lower RPM, using a centrifugal supercharger.

All supercharger types benefit from the use of an intercooler

Intercooler

An intercooler , or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through nearly isobaric cooling, which removes...

to remove heat produced during compression.