Forced Induction: The Supercharger
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The only difference between them is done by their source of energy. The supercharger is mechanically powered by the engine crankshaft while the turbocharger is powered by the flow of the exhaust gas. Let's start looking at them one by one.
The supercharger is basically an air compressor which is mechanically powered by the engine itself via a belt, chain or gear connected to the engine's crankshaft. Being invented only a few years after the internal combustion engine (ed, 1885, by Gottlieb Daimler), the automotive supercharger is working like an added pump, therefore providing the engine with a forced increase in the air that goes in the combustion chamber.
The theory is this: the pressurized air going in via the supercharger (or turbocharger, since they're essentially the same thing) means that more fuel can be burned, which in turn means a bigger explosion in the cylinders and... ta daaa! more power.
In over 100 years of history, the ol' supercharger has evolved and branched into many different types but only three of them managed to resist the test of time:
The Roots blower is the oldest type, with a design first patented to ventilate mines in 1860 by the Philander and Francis Roots brothers. Using two meshing lobes inside a chamber that spin in different directions, the Roots supercharger compresses large quantities of air to create positive pressure. Because of their increased size, they usually sit on top of the engine.
The twin-screw supercharger is also called the Lysholm supercharger, after its inventor, Alf Lysholm. It operates in a very similar way to the Roots type blower. The main difference resides in the pair of rotor mesh lobes who look more like a pair of worm gears. This translates into a much more efficient delivery of compressed air compared to the Roots blower because the lobes have a conical taper, therefore decreasing the size of the air pockets as they travel from the filling side to the discharge side.
Because they're more complicated to make, the Lysholm type superchargers generally cost more then their counterparts. Another somewhat of a downside is the increased noise this supercharger makes, with its distinctive whistle at high rpm.
Using only one rotor instead of two, the centrifugal supercharger is probably the most wide-spread type. It looks very similar to a turbocharger, powering an inboard rotor to rapidly draw air into a small housing, therefore compressing it before forcing it into the engine.
From all the three surviving types of superchargers, the centrifugal one is the most efficient. Being also the lightest and the smallest, they can be easily attached to almost any kind of engine with minor modifications
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