Supercharger

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A supercharger (item 6) on a piston engine Supercharger Animation by Tyroola.gif
A supercharger (item 6) on a piston engine
Roots-type supercharger (right) on a 2006 GM Ecotec LSJ four-cylinder engine 2006 Saturn Ion Red Line engine.jpg
Roots-type supercharger (right) on a 2006 GM Ecotec LSJ four-cylinder engine

In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement.

Contents

The current categorisation is that a supercharger 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 gasses. [1] However, up until the mid-20th century, a turbocharger was called a "turbosupercharger" and was considered a type of supercharger. [2]

The first supercharged engine was built in 1878, [3] 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/or increase power outputs.

Design

Types

There are two main families of superchargers defined according to the method of gas transfer: positive displacement and dynamic superchargers. Positive displacement superchargers deliver an almost constant level of boost pressure increase at all engine speeds (RPM), while dynamic superchargers cause the boost pressure to rise exponentially with RPM (above a certain RPM threshold). [4] Another family of supercharger, albeit rarely used, is the pressure wave supercharger.

Roots blowers (a positive displacement design) tend to be only 40–50% efficient at high boost levels, compared with 70-85% for dynamic superchargers.[ citation needed ] 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.

Positive displacement

Internals of a rotary-screw (Lysholm) supercharger Lysholm screw rotors.jpg
Internals of a rotary-screw (Lysholm) supercharger

Positive displacement pumps deliver a nearly fixed volume of air per revolution of the compressor (except for leakage, which typically has a reduced effect at higher engine speeds). The most common type of positive-displacement superchargers is the Roots-type supercharger. Other types include the rotary-screw, sliding vane and scroll-type superchargers.

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 71 cu in (1.2 L) each, resulting in an engine with a total displacement of 426 cu in (7.0 L)). 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 339 cu in (5.6 L) per revolution. Other supercharger manufacturers have produced blowers rated up to 16–71.

Dynamic

Dynamic compressors rely on accelerating the air to high speed and then exchanging that velocity for pressure by diffusing or slowing it down.

Major types of a dynamic compressor are:

Drive system

Common methods of driving a supercharger include:

Electric superchargers

A more recent concept is to drive the compressor using an electric motor rather than a mechanical power sources.

Effects of fuel octane rating

Fuels with a higher octane rating are better able to resist auto ignition and detonation. As a result, the amount of boost supplied by the superchargers could be increased, resulting in an increase in engine output. The development of 100-octane aviation fuel, pioneered in the USA in the 1930s, enabled the use of higher boost pressures to be used on high-performance aviation engines and was used to vastly increase the power output for several speed record airplanes.

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. [6] The German Luftwaffe also had supplies of a similar fuel. [7] [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 2,000 hp (1,500 kW). [9] [10] [11] [12]

Heating of intake air

One disadvantage of forced induction (i.e. supercharging or turbocharging) is that compressing the intake air increases its temperature. For an internal combustion engine, the temperature of the intake air becomes a limiting factor in engine performance. Extreme temperatures can cause pre-ignition or knocking, which reduces performance and can cause engine damage. The risk of pre-ignition/knocking increases with higher ambient air temperatures and higher boost levels.

Supercharging versus turbocharging

Turbocharged engines use energy from the exhaust gas that would normally be wasted, compared with a supercharged which mechanically draws power from the engine. Therefore turbocharged engines usually produce more power and better fuel economy than supercharged engines. However, turbochargers can cause turbo lag (especially at lower RPM), where the exhaust gas flow is initially insufficient to spin the turbocharger and achieve the desired boost level, thus leading to a delay in the throttle response. For this reason, supercharged engines are common in applications where throttle response is a key concern, such as drag racing and tractor pulling competitions.

A disadvantage of supercharging is that the engine must withstand the net power output of the engine plus the power to drive the supercharger.[ citation needed ]

Turbocharged engines are more prone to heat soak of the intake air (since turbocharging can place the hot exhaust components near the intake air system), although this can be overcome through the use of an intercooler.

Comparison for aircraft engines

The majority of aircraft engines used during World War II used mechanically driven superchargers because they had some significant manufacturing advantages over turbochargers. However, the benefit to the operational range was given a much higher priority to American aircraft because of a less predictable requirement on the operational range and having to travel far from their home bases. Consequently, turbochargers were mainly employed in American aircraft engines such as the Allison V-1710 and the Pratt & Whitney R-2800, which were comparably heavier when turbocharged, and required additional ducting of expensive high-temperature metal alloys in the gas turbine and a pre-turbine section of the exhaust system. The size of the ducting alone was a serious design consideration. For example, both the F4U Corsair and the P-47 Thunderbolt used the same radial engine, but the large barrel-shaped fuselage of the turbocharged P-47 was needed because of the amount of ducting to and from the turbocharger in the rear of the aircraft. The F4U used a two-stage inter-cooled supercharger with a more compact layout. Nonetheless, turbochargers were useful in high-altitude bombers and some fighter aircraft due to the increased high altitude performance and range.

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 bombers used in the Pacific Theater of Operations 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 Stratoliner, the Lockheed Constellation, and the C-124 Globemaster II.

Twincharging

In the 1985 and 1986 World Rally Championships, Lancia ran the Delta S4, which incorporated both a belt-driven supercharger and exhaust-driven turbocharger. The design used a complex series of bypass valves in the induction and exhaust systems as well as an electromagnetic clutch so that, at low engine speeds, a boost was derived from the supercharger. In the middle of the rev range, a boost was derived from both systems, while at the highest revs the system disconnected the drive from the supercharger and isolated the associated ducting. [13] This was done in an attempt to exploit the advantages of each of the charging systems while removing the disadvantages. In turn, this approach brought greater complexity and affected the car's reliability in WRC events, as well as increasing the weight of engine ancillaries in the finished design.

Twincharged engines have occasionally been used in production cars, such as the 2005-2007 Volkswagen 1.4 litre and the 2017-present Volvo B4204T43/B4204T48 2.0 litre four-cylinder engines.

History

In 1849, G. Jones of Birmingham, England began manufacturing a lobe pump compressor to provide ventilation for coal mines. [14] In 1860, the Roots Blower Company (founded by brothers Philander and Francis Marion Roots) in the United States patented the design for an air mover for use in blast furnaces and other industrial applications. This air mover and Birmingham's ventilation compressor both used designs similar to that of the later Roots-type superchargers.

In March of 1878, German engineer Heinrich Krigar obtained the first patent for a screw-type compressor. [15] 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. [16] This supercharger was used with a two-stroke gas engine. [17] Gottlieb Daimler received a German patent for supercharging an internal combustion engine in 1885. [18] Louis Renault patented a centrifugal supercharger in France in 1902. [19] [20]

Usage in cars

1929 Blower Bentley with the supercharger ("blower") located in front of the radiator 1929 Bentley front 34 right.jpg
1929 Blower Bentley with the supercharger ("blower") located in front of the radiator

The world's first series-produced cars [21] with superchargers were the 1.6 litre Mercedes 6/25 hp and 2.6 litre Mercedes 10/40 hp, both of which began production in 1923. [22] [23] [24] They were marketed as Kompressor models, a term which was used for various models until 2012.

Supercharged racing cars from around this time included the 1923 Fiat 805-405,[ citation needed ] the 1923 Miller 122 [25] the 1924 Alfa Romeo P2, the 1924 Grand Prix season car from Sunbeam, [26] the 1925 Delage, [27] 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. [15]

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 engines of the early 2000s (such as the C230K straight-four, C32 AMG V6, and CL55 AMG V8 engines) were replaced around 2010 by turbocharged engines in models such as the C250 and CL S65 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).

Usage in aircraft

Centrifugal supercharger for a Bristol Centaurus radial engine Bristol Centaurus centrifugal supercharger.jpg
Centrifugal supercharger for a Bristol Centaurus radial engine

In the 1930s, two-speed drives were developed for superchargers for aero engines providing more flexible aircraft operation. The arrangement also entailed more complexity of manufacturing and maintenance. The gears connected the supercharger to the engine using a system of hydraulic clutches, which were initially manually engaged or disengaged by the pilot with a control in the cockpit. At low altitudes, the low-speed gear would be used, to prevent excessive boost levels. At higher altitudes, the supercharger could be switched to a higher gear to compensate for the reduced intake air density. In the Battle of Britain the Spitfire and Hurricane planes powered by the Rolls-Royce Merlin engine were equipped largely with single-stage and single-speed superchargers. [28] [29]

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. [30] [29] 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.

Usage in aircraft engines

Altitude effects

Due to the reduced air density at higher altitudes, supercharging and turbocharging have often been used in aircraft engines. For example, the air density at 30,000 ft (9,100 m) is 13 of that at sea level, resulting in 13 as much fuel being able to be burnt in a naturally aspirated engine, therefore the power output would be greatly reduced. [31] A supercharger/turbocharger can be thought of either as artificially increasing the density of the air by compressing it or as forcing more air than normal into the cylinder every time the piston moves down on the intake stroke. [31]

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 intercoolers/aftercoolers, anti-detonant injection, two-speed superchargers and two-stage superchargers.

Intake freezing

In supercharged engines which use a carburetor, a partially-open throttle reduces the air pressure within the carburettor. In cold conditions, this low pressure air can cause ice to form at the throttle plate. Significant quantities of ice can cause engine failure, even with the engine operating at full rated power.

See also

Related Research Articles

Turbocharger Forced induction device for internal combustion engines

A turbocharger, formally a turbosupercharger and colloquially known as turbo, is a turbine-driven, forced induction device that increases an internal combustion engine's power output by forcing extra compressed air into the combustion chamber. This improvement over a naturally aspirated engine's power output is because the compressor can force more air—and proportionately more fuel—into the combustion chamber than atmospheric pressure alone.

Rolls-Royce Merlin Aircraft engine family by Rolls-Royce

The Rolls-Royce Merlin is a British liquid-cooled V-12 piston aero engine of 27-litres capacity. Rolls-Royce designed the engine and first ran it in 1933 as a private venture. Initially known as the PV-12, it was later called Merlin following the company convention of naming its four-stroke piston aero engines after birds of prey.

Miller cycle Thermodynamic cycle

In engineering, the Miller cycle is a thermodynamic cycle used in a type of internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, U.S. Patent 2,817,322 dated Dec 24, 1957. The engine may be two- or four-stroke and may be run on diesel fuel, gases, or dual fuel.

Allison V-1710 Aircraft engine produced and manufactured by Allison Engine Company

The Allison V-1710 aircraft engine designed and produced by the Allison Engine Company was the only US-developed V-12 liquid-cooled engine to see service during World War II. Versions with a turbocharger gave excellent performance at high altitude in the twin-engined Lockheed P-38 Lightning, and turbo-superchargers were fitted to experimental single-engined fighters with similar results.

Four-stroke engine Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion. The piston is moving down as air is being sucked in by the downward motion against the piston.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust valve.
Roots-type supercharger A positive displacement lobe pump

The Roots-type blower is a positive displacement lobe pump which operates by pumping a fluid with a pair of meshing lobes resembling a set of stretched gears. Fluid is trapped in pockets surrounding the lobes and carried from the intake side to the exhaust. The most common application of the Roots-type blower has been the induction device on two-stroke diesel engines, such as those produced by Detroit Diesel and Electro-Motive Diesel. Roots-type blowers are also used to supercharge four-stroke Otto cycle engines, with the blower being driven from the engine's crankshaft via a toothed or V-belt, a roller chain or a gear train.

A centrifugal supercharger is a specialized type of supercharger that makes use of centrifugal force in order to increase the manifold air pressure, MAP. An increased MAP allows the engine to burn more fuel, which results in an increased power output. Centrifugal superchargers are generally attached to the front of the engine via a belt-drive or gear-drive from the engine's crankshaft.

Naturally aspirated engine Type of internal combustion engine

A naturally aspirated engine, also known as a normally aspirated engine, and abbreviated to N/A or NA, is an internal combustion engine in which air intake depends solely on atmospheric pressure and does not have forced induction through a turbocharger or a supercharger. Many sports cars specifically use naturally aspirated engines to avoid turbo lag.

Forced induction is the process of delivering compressed air to the intake of an internal combustion engine. A forced induction engine uses a gas compressor to increase the pressure, temperature and density of the air. An engine without forced induction is considered a naturally aspirated engine.

Junkers Jumo 205

The Junkers Jumo 205 aircraft engine was the most famous of a series of aircraft diesel engines that were the first, and for more than half a century, the only successful aviation diesel powerplants. The Jumo 204 first entered service in 1932. Later engines of this type comprised the experimental Jumo 206 and Jumo 208, with the Jumo 207 produced in some quantity for the Junkers Ju 86P and -R high-altitude reconnaissance aircraft, and the 46-meter wingspan, six-engined Blohm & Voss BV 222 Wiking flying boat. All three of these variants differed in stroke and bore and supercharging arrangements. In all, more than 900 of these engines were produced, in the 1930s and through most of World War II.

Blowoff valve A pressure release system in turbocharged engines

A blowoff valve is a pressure release system present in most petrol turbocharged engines. Blowoff valves are used to reduce pressure in the intake system as the throttle is closed, thus preventing compressor surge.

Packard V-1650 Merlin Piston aircraft engine

The Packard V-1650 Merlin is a version of the Rolls-Royce Merlin aircraft engine, produced under license in the United States by the Packard Motor Car Company. The engine was licensed to expand production of the Rolls-Royce Merlin for British use. The engine also filled a gap in the U.S. at a time when similarly powered American-made engines were not available.

A wastegate is a valve that controls the flow of exhaust gases to the turbine wheel in a turbocharged engine system.

Junkers Jumo 213

The Junkers Jumo 213 was a World War II-era V-12 liquid-cooled aircraft engine, a development of Junkers Motoren's earlier design, the Jumo 211. The design added two features, a pressurized cooling system that required considerably less cooling fluid which allowed the engine to be built smaller and lighter, and a number of improvements that allowed it to run at higher RPM. These changes boosted power by over 500 hp and made the 213 one of the most sought-after Axis engine designs in the late-war era.

Twincharger refers to a compound forced induction system used on some piston-type internal combustion engines. It is a combination of an exhaust-driven turbocharger and a mechanically driven supercharger, each mitigating the weaknesses of the other. A mechanically driven supercharger offers exceptional response and low-rpm performance as it does not rely on pressurization of the exhaust manifold. A turbocharger sized to move a large volume of air tends to respond slowly to throttle input while a smaller, faster-responding turbo may fail to deliver sufficient volume through an engine's upper RPM range. The unacceptable lag time endemic to a large turbocharger is effectively neutralized when combined with a supercharger which tends to generate substantial boost pressure much faster in response to throttle input. The end result being a zero-lag powerband with high torque at lower engine speeds and increased power at the upper end. Twincharging is therefore desirable for small-displacement motors, especially those with a large operating rpm, since they can take advantage of an artificially broad torque band over a large speed range.

Twin-turbo refers to an engine in which two turbochargers compress the intake fuel/air mixture. The most common layout features two identical or mirrored turbochargers in parallel, each processing half of a V engine's produced exhaust through independent piping. The two turbochargers can either be identical or different sizes.

The Shvetsov ASh-73 was an 18-cylinder, air-cooled, radial aircraft engine produced between 1947 and 1957 in the Soviet Union. It was primarily used as the powerplant for the Tupolev Tu-4 heavy bomber, a copy of the American Boeing B-29 Superfortress.

Two-stroke diesel engine Engine type

A two-stroke diesel engine is an internal combustion engine that uses compression ignition, with a two-stroke combustion cycle. It was invented by Hugo Güldner in 1899.

Electrically-assisted turbocharger

An electrically-assisted turbocharger (EAT) is a turbocharger that includes an electric motor to assist in powering the compressor, particularly at times when the exhaust gas flow is insufficient to produce the desired boost.

An electric supercharger is a specific type of supercharger for internal combustion engines that uses an electrically powered forced-air system that contains an electric motor to pressurize the intake air. By pressurizing the air available to the engine intake system, the air becomes more dense, and is matched with more fuel, producing the increased horsepower to the wheels.

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