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In an internal combustion engine, a supercharger is a device which compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement. It is a form of forced induction that is mechanically powered (usually by a belt from the engine's crankshaft), as opposed to a turbocharger, which is powered by the kinetic energy of the exhaust gases. However, up until the mid-20th century, a turbocharger was called a "turbosupercharger" and was considered a type of supercharger.
The first supercharged engine was built in 1878, with usage in aircraft engines beginning in the 1910s and usage in car engines beginning in the 1920s. In piston engines used by aircraft, supercharging was often used to compensate for the lower air density at high altitudes. Supercharging is less commonly used in the 21st century, as manufacturers have shifted to turbochargers to reduce fuel consumption and increase power outputs, especially with reduced engine displacements.
A variant of the supercharger is the electric supercharger or e-supercharger, which uses an electric motor as its power source instead of a belt drive.
(a positive displacement lobe pump design) tend to be only 40–50% efficient at high boost levels, compared with 70-85% for dynamic superchargers. Lysholm-style blowers (a rotary-screw design) can be nearly as efficient as dynamic superchargers over a narrow range of load/speed/boost, for which the system must be specifically designed.
The rating system for positive-displacement superchargers is usually based on their capacity per revolution. In the case of the Roots blower, the GMC rating pattern is typical. The GMC rating is based on how many two-stroke cylinders - and the size of those cylinders - that it is designed to scavenge, with GMC's model range including 2–71, 3–71, 4–71 and 6–71 blowers. The 6–71 blower, for example, is designed to scavenge six cylinders of each, resulting in an engine with a total displacement of ). However, because 6–71 is the engine's designation rather than that of the blower, the actual displacement of the blower is less; for example, a 6–71 blower pumps per revolution. Other supercharger manufacturers have produced blowers rated up to 16–71.
Major types of a dynamic compressor are:
Military use of high-octane fuels began in early 1940 when 100-octane fuel was delivered to the British Royal Air Force fighting in World War II.Payton-Smith 1971, pp. 259–260. The German Luftwaffe also had supplies of a similar fuel.Mankau and Petrick 2001, pp. 24–29.Griehl 1999, p. 8. Increasing the octane rating became a major focus of aero engine development for the remainder of the war, with later fuels having up to a nominal 150-octane rating. Using such fuels, aero engines like the Rolls-Royce Merlin 66 and Daimler-Benz DB 605 DC produced power outputs of up to .Price, 1982. p. 170.Berger & Street, 1994. p. 199.Mermet 1999, pp. 14–17.Mermet 1999, p. 48.
In design, superchargers have relatively simple piping from the air intake, through the supercharger and into the engine. Turbochargers have more complicated piping where the intake operates as with the supercharger but the exhaust must also pass through the turbocharger, requiring both intake and exhaust piping to come close together in an often crowded engine bay. As well, turbocharged engines are more prone to heat soak of the intake air, as extremely hot exhaust and turbo components are directly alongside the intake air system, although this can be solved through the use of an intercooler. Turbocharged engines often utilize intercoolers more often than supercharged engines as a result.
Turbocharged piston engines are also subject to many of the same operating restrictions as those of gas turbine engines. Turbocharged engines also require frequent inspections of their turbochargers and exhaust systems to search for possible damage caused by the extreme heat and pressure of the turbochargers. Such damage was a prominent problem in the early models of the American Boeing B-29 Superfortress high-altitude used in the Pacific War during 1944–45.
Turbocharged piston engines continued to be used in a large number of postwar airplanes, such as the B-50 Superfortress, the KC-97 Stratofreighter, the Boeing 377 Stratocruiser, the Lockheed Constellation, and the C-124 Globemaster II.
Twincharged engines have occasionally been used in production cars, such as the 2005-2013 Volkswagen 1.4 litre and the 2017-present Volvo B4204T43/B4204T48 2.0 litre four-cylinder engines.
In March of 1878, German engineer Heinrich Krigar obtained the first patent for a screw-type compressor. The design was a two-lobe rotor assembly with identically-shaped rotors, however the design did not reach production.
Also in 1878, Scottish engineer Dugald Clerk designed the first supercharger which was used with an engine. This supercharger was used with a two-stroke gas engine. Gottlieb Daimler received a German patent for supercharging an internal combustion engine in 1885. Louis Renault patented a centrifugal supercharger in France in 1902.
Supercharged racing cars from around this time included the 1923 Fiat 805-405, the 1923 Miller 122 the 1924 Alfa Romeo P2, the 1924 Grand Prix season car from Sunbeam, the 1925 Delage, and the 1926 Bugatti Type 35C.
Amongst the most famous supercharged cars is the Bentley 4½ Litre ("Blower Bentley"), which was introduced in 1929.
In 1935, the development of screw-type superchargers reached a milestone when Swedish engineer Alf Lysholm patented a design for a rotary-screw compressor with five female and four male rotors.
In the 21st century, supercharged production car engines have become less common, as manufacturers have shifted to turbocharging to achieve higher fuel economy and power outputs. For example, Mercedes-Benz's Kompressor engines of the early 2000s (such as the C 230 Kompressor straight-four, C 32 AMG V6, and CL 55 AMG V8 engines) were replaced around 2010 by turbocharged engines in models such as the C 250 and CL 65 AMG models. However, there are exceptions, such as the Audi 3.0 TFSI supercharged V6 (introduced in 2009) and the Jaguar AJ-V8 supercharged V8 (upgraded to the Gen III version in 2009).
In 1942, two-speed two-stage supercharging with aftercooling was applied to the Rolls Royce Merlin 61 aero engine. The improved performance allowed the aircraft they powered to maintain a crucial advantage over the German aircraft they opposed throughout World War II, despite the German engines being significantly larger in displacement. Two-stage superchargers were also always two-speed. After the air was compressed in the low-pressure stage, the air flowed through a heat exchanger ("intercooler") where it was cooled before being compressed again by the high-pressure stage and then possibly also aftercooled in another heat exchanger.
While superchargers were highly used in the mid-1900s and during WWII, they have largely fallen out of use in modern piston-driven aircraft. This can largely be attributed to the higher temperature and lighter alloys that make Turbocharger more efficient than superchargers, as well as the lower maintenance due to less moving parts.
Since a supercharger is usually designed to produce a given amount of boost at high altitudes (where the air density is lower), the supercharger is often oversized for low altitude. To prevent excessive boost levels, it is important to monitor the intake manifold pressure at low altitude. As the aircraft climbs and the air density drops, the throttle can be progressively opened to obtain the maximum safe power level for a given altitude. The altitude at which the throttle reaches full open and the engine is still producing full rated power is known as the critical altitude. Above the critical altitude, engine power output will reduce as the supercharger can no longer fully compensate for the decreasing air density.
Another issue encountered at low altitudes (such as at ground level) is that the intake air is warmer than at high altitude. Warmer air reduces the threshold at which engine knocking can occur, especially in supercharged or turbocharged engines. Methods to cool the intake air at ground level include intercooler, anti-detonant injection, two-speed superchargers and two-stage superchargers.
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