Superchargers squeeze extra air into engines, powered by the crankshaft itself
Force more air into an engine and it makes more power for its size. A supercharger does exactly that, driven usually by a belt off the crankshaft. That costs some fuel economy, but it avoids the lag a turbocharger suffers, which is why they stay common in drag racing and tractor pulling.
The idea is old. In 1878 the Scottish engineer Dugald Clerk fitted the first supercharger to a working engine, a two-stroke gas unit, and Gottlieb Daimler patented supercharging for combustion engines in 1885. The pumps behind it were older still: a Birmingham maker built lobe compressors to ventilate coal mines from 1849, and the Roots brothers in America patented a similar air mover in 1860. Mercedes put the first series-built supercharged cars on sale in 1923, badged Kompressor, and the Blower Bentley followed in 1929.
Two main families exist. Positive-displacement types, such as the common Roots blower or the rotary screw, for which Alf Lysholm patented a design in 1935, move a nearly fixed volume per turn, so boost stays fairly even across engine speeds. Dynamic types instead speed the air up and then slow it down to turn velocity into pressure; their boost climbs steeply with revs. At high boost a Roots blower manages only 40 to 50 per cent efficiency, against 70 to 85 for dynamic designs.
Aircraft adopted supercharging in the 1910s to make up for thin air at altitude, and fuel chemistry pushed it further. Higher-octane fuels resist knocking, allowing more boost, and 100-octane fuel reached the RAF in 1940. On later fuels, engines such as the Rolls-Royce Merlin 66 produced up to 2,000 horsepower. American designers often preferred turbochargers for range, at a cost in bulk: the P-47 Thunderbolt's barrel fuselage housed turbo ducting that the same engine in the Corsair did without.
Lancia tried to have it both ways in the Delta S4 rally car of 1985 and 1986, running a supercharger at low revs and a turbo at the top, at a price in weight and reliability. Today turbos dominate, as makers chase economy from smaller engines, while electric superchargers offer boost without drawing on the crankshaft.
Source: Supercharger
