Wikicars - User contributions [en]

Talk:Edsel/

2008-12-18T18:15:08Z

196.25.52.36: FIELD_OTHER

http://www.FIELD_MESSAGE_varmonrono.com/

Supercharged Engine

2008-12-17T21:33:57Z

196.25.52.36:

A '''[[Supercharged Engine|supercharger]]''' (also known as a '''blower''') is an air compressor used to force air into the combustion chamber(s) of an [[internal combustion engine]] at pressures higher than would otherwise be the case. Any device which does this is a [[Supercharged Engine|supercharger]].

The additional mass of oxygen-containing air that is forced into the engine improves its [[volumetric efficiency]] which allows it to burn more fuel - which in turn makes it produce more power. A [[Supercharged Engine|supercharger]] can be powered mechanically by belt-, gear- or chain-drive from the engine's crankshaft. It can also be driven by a gas turbine powered by the exhaust gasses from the engine. Turbine-driven [[Supercharged Engine|superchargers]] are correctly referred to as [[Turbo Engine|turbo]]-[[Supercharged Engine|superchargers]] - or more commonly as [[Turbo Engine|turbocharger]]s.

== Types of [[Supercharged Engine|Supercharger]] ==
There are two main types of [[Supercharged Engine|supercharger]] defined according to the method of compression. Positive displacement and dynamic compressors.

===Positive displacement===
[[Image:800px-2006_Saturn_Ion_Red_Line_engine.jpg|right|thumb|250px|An Eaton M62 Roots-type supercharger is visible at the front of this Ecotec LSJ engine in a 2006 [[Saturn ION|Saturn ION Red Line]]]]
[[Image:Lysholm_screw_rotors.jpg|right|thumb|250px|Lysholm screw rotors. Note the complex shape of each rotor which must run at high speed and with close tolerances. This makes this type of supercharger quite expensive.(This unit has been blued to show close contact areas)]]
Positive displacement pumps deliver a fixed volume of air per revolution at all speeds (minus leakage which is nearly constant at all speeds for a given pressure and so its importance decreases at higher speeds). The device divides the air mechanically into parcels for delivery to the engine, mechanically moving the air into the engine bit by bit.

Major types of positive displacement pumps include:

*Roots
*Lysholm screw
*Sliding Vane
*Piston
*Wankel
*G-lader

Positive displacement pumps are further divided into internal compression and external compression types.

Roots [[Supercharged Engine|superchargers]] are typically external compression only (although high helix roots blowers attempt to emulate the internal compression of the Lysholm screw.)
*External compression refers to pumps which transfer air at ambient pressure into the engine . If the engine is running under boost conditions, the pressure in the intake manifold is higher than that coming from the [[Supercharged Engine|supercharger]]. That causes a back flow from the engine into the [[Supercharged Engine|supercharger]] until the two reach equilibrium. It is the back flow which actually compresses the incoming gas. This is a higly inefficient process and the main factor in the lack of efficiency of roots [[Supercharged Engine|superchargers]] when used at high boost levels. The lower the boost level the smaller is this loss and roots blowers are very efficient at moving air at low pressure differentials, which is what they were first invented for (hence the original term "blower").

All the other types have some degree of internal compression.
*Internal compression refers to the air being compressed within the [[Supercharged Engine|supercharger]] itself and this compressed air, already at or close to boost level, can be delivered smoothly to the engine with little or no back flow. This is much more efficient than backflow compression and allows very high efficiencies to be achieved. Internal compression devices usually use a fixed internal compression ratio. When the boost pressure is equal to the compression pressure of the [[Supercharged Engine|supercharger]] then back flow is zero. If the boost pressure exceeds that compression pressure then backflow can still occur as in a roots blower.

===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 dynamic compressor are:

* Centrifugal
* Multi stage axial flow

-Comprex [[Supercharged Engine|superchargers]] do not fit neatly into either dynamic or positive displacement categories. The Comprex design uses the exhaust gas to directly compress the incoming charge.

===[[Supercharged Engine|Supercharger]] drive types===
[[Supercharged Engine|Superchargers]] are further defined according to their method of drive (mechanical - or turbine).

Mechanical:

*Belt(V belt, Toothed belt, Flat belt)
*Direct drive
*Gear drive
*Chain drive

Exhaust gas turbines:

*Axial turbine
*Radial turbine

All types of compressor may be mated to and driven by either gas turbine or mechanical linkage. Dynamic compressors are most often matched with gas turbine drives due to their similar high-speed characteristics, while positive displacement pumps usually use one of the mechanical drives. However, all of the possible combinations have been tried with various levels of success.

==Automobiles==
[[Image:800px-1929_Bentley_front_34_right.jpg|right|thumb|250px|1929 "Blower" [[Bentley]] from the Ralph Lauren collection. The large "blower" (supercharger) is located at the front, in front of the radiator, and gave the car its name.]]

In cars, the device is used to increase the "effective [[engine displacement|displacement]]" and [[volumetric efficiency]] of an engine, and is often referred to as a '''blower'''. By pushing the air into the cylinders, it is as if the engine had larger valves and cylinders, resulting in a "larger" engine that weighs less.

In 1900 Gottlieb Daimler (of [[Daimler-Benz]] / [[DaimlerChrysler|Daimler-Chrysler]] fame) became the first person to patent a forced-induction system for internal combustion engines. His first [[Supercharged Engine|superchargers]] were based on a twin-rotor air-pump design first patented by American Francis Roots in 1860. This design is the basis for the modern Roots type supercharger.

It wasn't long before the [[Supercharged Engine|supercharger]] was applied to custom racing cars, with the first [[Supercharged Engine|supercharged]] production vehicles being built by [[Mercedes-Benz|Mercedes]] and [[Bentley]] in the 1920's. Since then [[Supercharged Engine|superchargers]] (as well as turbochargers) have been widely applied to both racing and production cars, although their complexity and cost have largely relegated the [[Supercharged Engine|supercharger]] to pricey performance cars.

Boosting, or adding a [[Supercharged Engine|supercharger]] to a stock [[naturally-aspirated]] engine, has made something of a comeback in recent years due largely to the increased quality of the alloys and machining used in modern engines. In the past, boosting would dramatically shorten an engine's life due to the extreme temperature and pressure created by the [[Supercharged Engine|supercharger]], but modern engines produced with modern materials provide considerable overdesign and boosting is no longer a serious reliability concern. For this reason boosting is commonly used in smaller cars, where the added weight of the [[Supercharged Engine|supercharger]] is less than the weight of a larger engine delivering the same amount of power. This also results in better gas mileage, as mileage is often a function of the overall weight of the car, a sizeable percentage of which is weight of the engine. Nevertheless, adding boost to a car will often void the drivetrain warranty. Also, improperly installed or excessive boost will greatly reduce the life expectancy of both the engine as well as the [[transmission]] (which may not have been designed to cope with additional torque).

===Supercharging and Turbocharging===
[[Image:717px-MINICooperS.jpg|thumb|right|250px|A 2004 [[MINI (BMW)|MINI Cooper S]], with intercooled 1.6 l centrifugal belt-driven supercharger. Note the [[hood scoop]] which supplies cool air to the [[intercooler]].]]

The term ''supercharging'' technically refers to any pump that forces air into an engine - but in common usage, it refers to pumps that are driven directly by the engine as opposed to turbochargers that are driven by the pressure of the exhaust gasses.

Positive displacement [[Supercharged Engine|Superchargers]] may absorb as much as a third of the total crankshaft power of the engine, and in many applications are less efficient than turbochargers. In applications where engine response and power is more important than any other consideration, such as top-fuel dragsters and vehicles used in tractor pulling competitions, positive displacement [[Supercharged Engine|superchargers]] are extremely common. [[Supercharged Engine|Superchargers]] are generally the reason why tuned engines have a distinct high-pitched whine upon acceleration. Cars that signify this well include the [[Mercedes SLR]] and the [[MINI|MINI Cooper S]].

There are three main styles of [[Supercharged Engine|supercharger]] for automotive use:

* Centrifugal turbochargers - driven from exhaust gasses.
* Centrifugal [[Supercharged Engine|superchargers]] - driven directly by the engine via a belt-drive,
* Positive displacement pumps (such as the Roots and the Lysholm (Whipple) blowers.

The thermal efficiency, or fraction of the fuel/air energy that is converted to output power, is less with a mechanically driven [[Supercharged Engine|supercharger]] than with a [[Turbo Engine|turbocharger]], because turbochargers are using energy from the exhaust gasses that would normally be wasted. For this reason, both the economy and the power of a [[Turbo Engine|turbocharged]] engine are usually better than with [[Supercharged Engine|superchargers]]. The main advantage of an engine with a mechanically driven [[Supercharged Engine|supercharger]] is better throttle response. With the latest [[Turbo Engine|Turbo]] Charging technology, throttle response on [[Turbo Engine|turbocharged]] cars is nearly as good as with mechanical powered [[Supercharged Engine|superchargers]].

Roots blowers tend to be 40-50% efficient at high boost levels. Centrifugal [[Supercharged Engine|Superchargers]] are 70-85% efficient. The Lysholm style blowers are nearly as efficient as their Centrifugal counterparts.

Keeping the air that enters the engine cool is an important part of the design of both [[Supercharged Engine|superchargers]] and turbochargers. Compressing air makes it hotter - so it is common to use a small radiator called an [[intercooler]] between the pump and the engine to reduce the temperature of the air.

Centrifugal Supercharging and Lysholm [[Supercharged Engine|Superchargers]] respond very well to intercooling because the air is compressed in the blower itself, so when the air passes through the intercooler, the air is as hot as it is going to get. In Roots style [[Supercharged Engine|superchargers]], the air is not compressed in the blower itself, the air is compressed by being packed into the engine faster than the engine can use it, thus creating boost. Because the air from a Roots style blower is compressed in the engine, they do not utilize intercoolers as well.

Small turbochargers can suffer from significant heat transfer from the hot exhaust gasses into the air they are compressing. This exacerbates the heating of the air and can reduce the benefits gained over [[Supercharged Engine|superchargers]].

Turbochargers also suffer (to a greater or lesser extent) from so-called ''[[Turbo Engine|turbo]]-lag'' in which initial accelleration from low RPM's is limited by the lack of sufficient exhaust gas pressure. Once engine RPM is sufficient to start the [[Turbo Engine|turbo]] spinning, there is a rapid increase in power as higher [[Turbo Engine|turbo]] boost causes more exhaust gas production - which spins the [[Turbo Engine|turbo]] yet faster. This makes the maintenance of smoothly increasing RPM far harder with turbochargers than with belt-driven [[Supercharged Engine|superchargers]] which apply boost in direct proportion to the engine RPM.

=== Sequential and Twin turbochargers ===

Many efforts have been made to mitigate the effects of [[Turbo Engine|turbo]]-lag in exhaust-driven turbochargers.

Sequential [[Turbo Engine|Turbo]] Charging was used on the [[Toyota Supra]]. The MKIV Toyota Supra used one small [[Turbo Engine|turbo]] and one medium sized [[Turbo Engine|turbo]]. The smaller [[Turbo Engine|turbo]] being used at lower engine RPMs because it's small size enabled it to be spun with less exhaust pressure than the larger pump. Once the boost pressure reached a pre-set level, the exhaust was redirected to the larger [[Turbo Engine|turbo]] which was capable of higher air flow to maintain boost at those RPMs.

An alternative arrangement utilizes two turbochargers of the same size, known as a "Twin [[Turbo Engine|Turbo]]". Twin [[Turbo Engine|Turbo]] Charging can make more power than a single [[Turbo Engine|turbo]] of the same output for two reasons. One is the lower rotating mass of two smaller turbos vice one large [[Turbo Engine|turbo]], which allows the compressor to spin up to speed much more quickly. The second is the increased exhaust outlet area available for the exhaust gas to flow out of the twin [[Turbo Engine|turbo]] set ups. Increased exhaust flow will increase power in most situations.

Another style of [[Turbo Engine|turbo]] charging is called "Compound [[Turbo Engine|Turbo]] charging". This is gaining popularity for [[diesel|diesel engine]]s. Tractor engines which compete in tractor pulling use compound [[Turbo Engine|turbo]] charging in some classes. Compound [[Turbo Engine|Turbo]] Charging can create boost levels above 200psig. Compound turbochargers are set up in various fashions. The most popular set up is to use one medium and one large [[Turbo Engine|turbo]]. The large [[Turbo Engine|turbo]] compressor blows into the smaller [[Turbo Engine|turbo]] compressor. The exhaust is set up to first enter the turbine of the smaller [[Turbo Engine|turbo]], and then into the turbine of the larger [[Turbo Engine|turbo]]. Compound [[Turbo Engine|Turbo]] Charging has little "[[Turbo Engine|turbo]] lag" and can create high power levels.

Still other combinations are possible - there are after-market kits for several [[Supercharged Engine|supercharged]] cars to add a [[Turbo Engine|turbocharger]] either before, after or in parallel with the [[Supercharged Engine|supercharger]]. In this manner the [[Supercharged Engine|supercharger]] operates alone at lower RPM's and the [[Turbo Engine|turbo]] either takes over from - or adds to the [[Supercharged Engine|supercharger]] once there is sufficient exhaust gas pressure available.

==Aircraft==
A more natural use of the [[Supercharged Engine|supercharger]] is with aircraft engines. As an aircraft climbs to higher altitudes the pressure of the surrounding air quickly falls off—at 6000 m (18,000 ft) the air is at half the pressure of sea level. Since the charge in the cylinders is being pushed in by this air pressure it means that the engine will normally produce half-power at full throttle at this altitude.

===Altitude effects===
[[Image:800px-Rolls-Royce_Merlin.jpg|right|thumb|250px|A Rolls Royce Merlin engine]]

A [[Supercharged Engine|supercharger]] remedies this problem by compressing the air back to sea-level pressures, or even much higher. This can take some effort. On the single-stage single-speed [[Supercharged Engine|supercharged]] [[Rolls Royce Merlin]] engine for instance, the [[Supercharged Engine|supercharger]] uses up about 150 [[horsepower]] (110 kW). Yet the benefits are huge, for that 150 [[HP|hp]] (110 kW) lost, the engine is delivering 1000 [[HP|hp]] (750 kW) when it would otherwise deliver 750 [[HP|hp]] (560 kW). And while the engine might be fooled into thinking it's at sea level, the airframe is quite aware of the halved air density and the plane thus has half the drag. For this reason [[Supercharged Engine|supercharged]] planes fly much faster at higher altitudes.

A [[Supercharged Engine|supercharger]] is only able to supply so much pressure because the compression increases the air temperature, and the engine is limited in maximum charge-air temperature before [[engine knocking|engine knock]] occurs. The boost is typically measured as the altitude at which the [[Supercharged Engine|supercharger]] can still supply sea level pressure (100 kPa or 1000 mbar) and is referred to as the ''critical altitude''. Throughout WWII British [[Supercharged Engine|superchargers]] generally had higher critical altitudes than their German counterparts and, when combined with higher [[octane]] fuels that the Americans supplied, that allowed for higher boost levels. British engines were generally able to outperform German ones.

===Altitude efficiency===
Below the critical altitude the [[Supercharged Engine|supercharger]] is capable of delivering too much boost and must therefore be restricted lest the engine be damaged. Unless other measures are taken, this means that at least some of the power driving the [[Supercharged Engine|supercharger]] is wasted. Also, due to the denser air at lower altitudes, the [[Supercharged Engine|supercharger]] is not operating at its best efficiency, and this can cause an additional load on the engine.

For the early years of the war this was simply how it was and this led to the seemingly odd fact that many early-war engines actually delivered less power at lower altitudes, because the [[Supercharged Engine|supercharger]] was still using up power to compress air that was not delivering any power back. As the war progressed two-speed [[Supercharged Engine|superchargers]] were introduced using better controllers and, notably, hydraulic clutches, that allowed the boost to be managed over a wide range of altitudes by operating at low rpm down low and at high rpm at higher altitudes. This generally "flattened out" the power below the critical altitude.

===Improving octane rating===
In 1940 a batch of 100 [[octane]] fuel was delivered from the USA to the RAF. This allowed the boost on Merlin engines to be increased to 48 inHg (160 kPa) and the power to rise by more than 10% (from 1030 to 1160 [[HP|hp]], or 770 to 870 kW). By mid-1940 another increased boost yielded 1310 [[HP|hp]] (980 kW). Supercharging by itself could not have achieved these improvements; however, when married with fuel improvements, the engine could respond to both.

===Multiple stages===
In the 1930s two-speed drives were developed for [[Supercharged Engine|superchargers]]. These provided more flexibility for the operation of the aircraft although they also entailed more complexity of manufacturing and maintenance. Ultimately it was found that for most engines (excepting those in high-performance fighters) a single-stage two-speed setup was most suitable.

A final improvement was the use of two compressors in series, which were introduced to solve combustion problems. Compressing a gas always causes its temperature to rise, and highly compressed fuel-air mixtures may prematurely ignite or may detonate or both. In order to avoid combustion problems the "two stage" design was used. After being compressed "half-way" in the ''low pressure stage'' the air flowed through an [[intercooler]] radiator where it was partially cooled down before being compressed the rest of the way in the ''high pressure stage'' and then ''aftercooled'' in another air/air or coolant/air radiator (heat exchanger). At low altitudes one stage could be turned off completely. The two-stage Merlin was losing 400 [[HP|hp]] (300 kW) to turn the [[Supercharged Engine|supercharger]] but developing between 1500 and 1700 [[HP|hp]] (1125 to 1275 kW) at the propeller shaft, depending on model.

It is interesting to compare all of this complexity to the same system implemented with a [[Turbo Engine|turbocharger]]. Since the [[Turbo Engine|turbo]] is driven off the exhaust gases, simply dumping some of the exhaust pressure is sufficient to drive the compressor at almost any desired speed. In addition the power in the exhaust would otherwise be wasted (except to the extent that the exhaust itself provided thrust) whereas in the [[Supercharged Engine|supercharger]] that power is being taken directly from the engine. Thus at low altitudes the [[Turbo Engine|turbo]] robs nothing and, as the altitude increases, it can use just as much power as it needs and no more. Better yet the amount of power in the gas is the difference between the exhaust pressure and air pressure, which increases with altitude, so turbochargers generally have much better altitude performance.

Yet the vast majority of WWII engines used [[Supercharged Engine|superchargers]], because they maintained three significant manufacturing advantages over turbochargers, which were larger, involved extra piping, and required exotic high-temperature materials in the turbine. The size of the piping alone is a serious issue; consider that the Vought F4U and Republic P-47 used the same engine but the huge barrel-like fuselage of the latter was, in part, needed to hold the piping to and from the [[Turbo Engine|turbocharger]] in the rear of the plane.

==Supercharging in jet engines==
Supercharging is not confined to internal combustion engines — jet engines rely on supercharging as one of the main routes to thrust growth and improved fuel efficiency.

For example, adding an additional (i.e. zero) stage to a compressor will not only increase the overall pressure ratio of the cycle, but induce more airflow into the unit, by supercharging the entry plane of the original compressor. Ideally, the corrected (i.e. non-dimensional) speed of original compressor should be maintained, by raising the mechanical shaft speed by a factor
√(Tstage1new/Tstage1old). If stress considerations prevent any shaft speed increase, there is only a modest increase in airflow.

Converting a turbojet into a turbofan, by adding a fan spool, also supercharges the compression system, thereby raising core flow.

Many of the large turbofan engine series (e.g. Pratt and Whitney PW4000) have gained core flow by adding one or more stages to the front of the gas generator, usually in the LP (or IP) compressor. If the fan flow is not increased, the bypass ratio will decrease.

Supercharging can also be achieved by improving the aerodynamics of the existing blading. Core flow will increase if the original compressor outlet (corrected) flow size is maintained

Either way, raising core flow increases core power and, thereby, the net thrust or shaftpower of the engine. Raising overall pressure ratio tends to improve specific fuel consumption (i.e. fuel efficiency).

==See also==
* [[Turbo Engine|Turbocharger]]
* [[Naturally-aspirated engine|Naturally aspirated engine]]
* [[boost gauge]]
* [[Intercooler]]

==References==
* '''Allied Aircraft Piston Engines of World War II''', ''Graham White'' 1995: Airlife Publishing Ltd, England and Society of Automotive Engineers, Inc., in the USA. ISBN 1 85310 734 4
*[http://www.americantrucks.com/ford-truck-supercharger.html Ford Truck Superchargers]
* http://www.howstuffworks.com

[[Category:Engine technology]]

Supercharged Engine

2008-12-17T21:32:21Z

196.25.52.36:

A '''[[Supercharged Engine|supercharger]]''' (also known as a '''blower''') is an air compressor used to force air into the combustion chamber(s) of an [[internal combustion engine]] at pressures higher than would otherwise be the case. Any device which does this is a [[Supercharged Engine|supercharger]].

The additional mass of oxygen-containing air that is forced into the engine improves its [[volumetric efficiency]] which allows it to burn more fuel - which in turn makes it produce more power. A [[Supercharged Engine|supercharger]] can be powered mechanically by belt-, gear- or chain-drive from the engine's crankshaft. It can also be driven by a gas turbine powered by the exhaust gasses from the engine. Turbine-driven [[Supercharged Engine|superchargers]] are correctly referred to as [[Turbo Engine|turbo]]-[[Supercharged Engine|superchargers]] - or more commonly as [[Turbo Engine|turbocharger]]s.

== Types of [[Supercharged Engine|Supercharger]] ==
There are two main types of [[Supercharged Engine|supercharger]] defined according to the method of compression. Positive displacement and dynamic compressors.

===Positive displacement===
[[Image:800px-2006_Saturn_Ion_Red_Line_engine.jpg|right|thumb|250px|An Eaton M62 Roots-type supercharger is visible at the front of this Ecotec LSJ engine in a 2006 [[Saturn ION|Saturn ION Red Line]]]]
[[Image:Lysholm_screw_rotors.jpg|right|thumb|250px|Lysholm screw rotors. Note the complex shape of each rotor which must run at high speed and with close tolerances. This makes this type of supercharger quite expensive.(This unit has been blued to show close contact areas)]]
Positive displacement pumps deliver a fixed volume of air per revolution at all speeds (minus leakage which is nearly constant at all speeds for a given pressure and so its importance decreases at higher speeds). The device divides the air mechanically into parcels for delivery to the engine, mechanically moving the air into the engine bit by bit.

Major types of positive displacement pumps include:

*Roots
*Lysholm screw
*Sliding Vane
*Piston
*Wankel
*G-lader

Positive displacement pumps are further divided into internal compression and external compression types.

Roots [[Supercharged Engine|superchargers]] are typically external compression only (although high helix roots blowers attempt to emulate the internal compression of the Lysholm screw.)
*External compression refers to pumps which transfer air at ambient pressure into the engine . If the engine is running under boost conditions, the pressure in the intake manifold is higher than that coming from the [[Supercharged Engine|supercharger]]. That causes a back flow from the engine into the [[Supercharged Engine|supercharger]] until the two reach equilibrium. It is the back flow which actually compresses the incoming gas. This is a higly inefficient process and the main factor in the lack of efficiency of roots [[Supercharged Engine|superchargers]] when used at high boost levels. The lower the boost level the smaller is this loss and roots blowers are very efficient at moving air at low pressure differentials, which is what they were first invented for (hence the original term "blower").

All the other types have some degree of internal compression.
*Internal compression refers to the air being compressed within the [[Supercharged Engine|supercharger]] itself and this compressed air, already at or close to boost level, can be delivered smoothly to the engine with little or no back flow. This is much more efficient than backflow compression and allows very high efficiencies to be achieved. Internal compression devices usually use a fixed internal compression ratio. When the boost pressure is equal to the compression pressure of the [[Supercharged Engine|supercharger]] then back flow is zero. If the boost pressure exceeds that compression pressure then backflow can still occur as in a roots blower.

===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 dynamic compressor are:

* Centrifugal
* Multi stage axial flow

-Comprex [[Supercharged Engine|superchargers]] do not fit neatly into either dynamic or positive displacement categories. The Comprex design uses the exhaust gas to directly compress the incoming charge.

===[[Supercharged Engine|Supercharger]] drive types===
[[Supercharged Engine|Superchargers]] are further defined according to their method of drive (mechanical - or turbine).

Mechanical:

*Belt(V belt, Toothed belt, Flat belt)
*Direct drive
*Gear drive
*Chain drive

Exhaust gas turbines:

*Axial turbine
*Radial turbine

All types of compressor may be mated to and driven by either gas turbine or mechanical linkage. Dynamic compressors are most often matched with gas turbine drives due to their similar high-speed characteristics, while positive displacement pumps usually use one of the mechanical drives. However, all of the possible combinations have been tried with various levels of success.

==Automobiles==
[[Image:800px-1929_Bentley_front_34_right.jpg|right|thumb|250px|1929 "Blower" [[Bentley]] from the Ralph Lauren collection. The large "blower" (supercharger) is located at the front, in front of the radiator, and gave the car its name.]]

In cars, the device is used to increase the "effective [[engine displacement|displacement]]" and [[volumetric efficiency]] of an engine, and is often referred to as a '''blower'''. By pushing the air into the cylinders, it is as if the engine had larger valves and cylinders, resulting in a "larger" engine that weighs less.

In 1900 Gottlieb Daimler (of [[Daimler-Benz]] / [[DaimlerChrysler|Daimler-Chrysler]] fame) became the first person to patent a forced-induction system for internal combustion engines. His first [[Supercharged Engine|superchargers]] were based on a twin-rotor air-pump design first patented by American Francis Roots in 1860. This design is the basis for the modern Roots type supercharger.

It wasn't long before the [[Supercharged Engine|supercharger]] was applied to custom racing cars, with the first [[Supercharged Engine|supercharged]] production vehicles being built by [[Mercedes-Benz|Mercedes]] and [[Bentley]] in the 1920's. Since then [[Supercharged Engine|superchargers]] (as well as turbochargers) have been widely applied to both racing and production cars, although their complexity and cost have largely relegated the [[Supercharged Engine|supercharger]] to pricey performance cars.

Boosting, or adding a [[Supercharged Engine|supercharger]] to a stock [[naturally-aspirated]] engine, has made something of a comeback in recent years due largely to the increased quality of the alloys and machining used in modern engines. In the past, boosting would dramatically shorten an engine's life due to the extreme temperature and pressure created by the [[Supercharged Engine|supercharger]], but modern engines produced with modern materials provide considerable overdesign and boosting is no longer a serious reliability concern. For this reason boosting is commonly used in smaller cars, where the added weight of the [[Supercharged Engine|supercharger]] is less than the weight of a larger engine delivering the same amount of power. This also results in better gas mileage, as mileage is often a function of the overall weight of the car, a sizeable percentage of which is weight of the engine. Nevertheless, adding boost to a car will often void the drivetrain warranty. Also, improperly installed or excessive boost will greatly reduce the life expectancy of both the engine as well as the [[transmission]] (which may not have been designed to cope with additional torque).

===Supercharging and Turbocharging===
[[Image:717px-MINICooperS.jpg|thumb|right|250px|A 2004 [[MINI (BMW)|MINI Cooper S]], with intercooled 1.6 l centrifugal belt-driven supercharger. Note the [[hood scoop]] which supplies cool air to the [[intercooler]].]]

The term ''supercharging'' technically refers to any pump that forces air into an engine - but in common usage, it refers to pumps that are driven directly by the engine as opposed to turbochargers that are driven by the pressure of the exhaust gasses.

Positive displacement [[Supercharged Engine|Superchargers]] may absorb as much as a third of the total crankshaft power of the engine, and in many applications are less efficient than turbochargers. In applications where engine response and power is more important than any other consideration, such as top-fuel dragsters and vehicles used in tractor pulling competitions, positive displacement [[Supercharged Engine|superchargers]] are extremely common. [[Supercharged Engine|Superchargers]] are generally the reason why tuned engines have a distinct high-pitched whine upon acceleration. Cars that signify this well include the [[Mercedes SLR]] and the [[MINI|MINI Cooper S]].

There are three main styles of [[Supercharged Engine|supercharger]] for automotive use:

* Centrifugal turbochargers - driven from exhaust gasses.
* Centrifugal [[Supercharged Engine|superchargers]] - driven directly by the engine via a belt-drive,
* Positive displacement pumps (such as the Roots and the Lysholm (Whipple) blowers.

The thermal efficiency, or fraction of the fuel/air energy that is converted to output power, is less with a mechanically driven [[Supercharged Engine|supercharger]] than with a [[Turbo Engine|turbocharger]], because turbochargers are using energy from the exhaust gasses that would normally be wasted. For this reason, both the economy and the power of a [[Turbo Engine|turbocharged]] engine are usually better than with [[Supercharged Engine|superchargers]]. The main advantage of an engine with a mechanically driven [[Supercharged Engine|supercharger]] is better throttle response. With the latest [[Turbo Engine|Turbo]] Charging technology, throttle response on [[Turbo Engine|turbocharged]] cars is nearly as good as with mechanical powered [[Supercharged Engine|superchargers]].

Roots blowers tend to be 40-50% efficient at high boost levels. Centrifugal [[Supercharged Engine|Superchargers]] are 70-85% efficient. The Lysholm style blowers are nearly as efficient as their Centrifugal counterparts.

Keeping the air that enters the engine cool is an important part of the design of both [[Supercharged Engine|superchargers]] and turbochargers. Compressing air makes it hotter - so it is common to use a small radiator called an [[intercooler]] between the pump and the engine to reduce the temperature of the air.

Centrifugal Supercharging and Lysholm [[Supercharged Engine|Superchargers]] respond very well to intercooling because the air is compressed in the blower itself, so when the air passes through the intercooler, the air is as hot as it is going to get. In Roots style [[Supercharged Engine|superchargers]], the air is not compressed in the blower itself, the air is compressed by being packed into the engine faster than the engine can use it, thus creating boost. Because the air from a Roots style blower is compressed in the engine, they do not utilize intercoolers as well.

Small turbochargers can suffer from significant heat transfer from the hot exhaust gasses into the air they are compressing. This exacerbates the heating of the air and can reduce the benefits gained over [[Supercharged Engine|superchargers]].

Turbochargers also suffer (to a greater or lesser extent) from so-called ''[[Turbo Engine|turbo]]-lag'' in which initial accelleration from low RPM's is limited by the lack of sufficient exhaust gas pressure. Once engine RPM is sufficient to start the [[Turbo Engine|turbo]] spinning, there is a rapid increase in power as higher [[Turbo Engine|turbo]] boost causes more exhaust gas production - which spins the [[Turbo Engine|turbo]] yet faster. This makes the maintenance of smoothly increasing RPM far harder with turbochargers than with belt-driven [[Supercharged Engine|superchargers]] which apply boost in direct proportion to the engine RPM.

=== Sequential and Twin turbochargers ===

Many efforts have been made to mitigate the effects of [[Turbo Engine|turbo]]-lag in exhaust-driven turbochargers.

Sequential [[Turbo Engine|Turbo]] Charging was used on the [[Toyota Supra]]. The MKIV Toyota Supra used one small [[Turbo Engine|turbo]] and one medium sized [[Turbo Engine|turbo]]. The smaller [[Turbo Engine|turbo]] being used at lower engine RPMs because it's small size enabled it to be spun with less exhaust pressure than the larger pump. Once the boost pressure reached a pre-set level, the exhaust was redirected to the larger [[Turbo Engine|turbo]] which was capable of higher air flow to maintain boost at those RPMs.

An alternative arrangement utilizes two turbochargers of the same size, known as a "Twin [[Turbo Engine|Turbo]]". Twin [[Turbo Engine|Turbo]] Charging can make more power than a single [[Turbo Engine|turbo]] of the same output for two reasons. One is the lower rotating mass of two smaller turbos vice one large [[Turbo Engine|turbo]], which allows the compressor to spin up to speed much more quickly. The second is the increased exhaust outlet area available for the exhaust gas to flow out of the twin [[Turbo Engine|turbo]] set ups. Increased exhaust flow will increase power in most situations.

Another style of [[Turbo Engine|turbo]] charging is called "Compound [[Turbo Engine|Turbo]] charging". This is gaining popularity for [[diesel|diesel engine]]s. Tractor engines which compete in tractor pulling use compound [[Turbo Engine|turbo]] charging in some classes. Compound [[Turbo Engine|Turbo]] Charging can create boost levels above 200psig. Compound turbochargers are set up in various fashions. The most popular set up is to use one medium and one large [[Turbo Engine|turbo]]. The large [[Turbo Engine|turbo]] compressor blows into the smaller [[Turbo Engine|turbo]] compressor. The exhaust is set up to first enter the turbine of the smaller [[Turbo Engine|turbo]], and then into the turbine of the larger [[Turbo Engine|turbo]]. Compound [[Turbo Engine|Turbo]] Charging has little "[[Turbo Engine|turbo]] lag" and can create high power levels.

Still other combinations are possible - there are after-market kits for several [[Supercharged Engine|supercharged]] cars to add a [[Turbo Engine|turbocharger]] either before, after or in parallel with the [[Supercharged Engine|supercharger]]. In this manner the [[Supercharged Engine|supercharger]] operates alone at lower RPM's and the [[Turbo Engine|turbo]] either takes over from - or adds to the [[Supercharged Engine|supercharger]] once there is sufficient exhaust gas pressure available.

==Aircraft==
A more natural use of the [[Supercharged Engine|supercharger]] is with aircraft engines. As an aircraft climbs to higher altitudes the pressure of the surrounding air quickly falls off—at 6000 m (18,000 ft) the air is at half the pressure of sea level. Since the charge in the cylinders is being pushed in by this air pressure it means that the engine will normally produce half-power at full throttle at this altitude.

===Altitude effects===
[[Image:800px-Rolls-Royce_Merlin.jpg|right|thumb|250px|A Rolls Royce Merlin engine]]

A [[Supercharged Engine|supercharger]] remedies this problem by compressing the air back to sea-level pressures, or even much higher. This can take some effort. On the single-stage single-speed [[Supercharged Engine|supercharged]] [[Rolls Royce Merlin]] engine for instance, the [[Supercharged Engine|supercharger]] uses up about 150 [[horsepower]] (110 kW). Yet the benefits are huge, for that 150 [[HP|hp]] (110 kW) lost, the engine is delivering 1000 [[HP|hp]] (750 kW) when it would otherwise deliver 750 [[HP|hp]] (560 kW). And while the engine might be fooled into thinking it's at sea level, the airframe is quite aware of the halved air density and the plane thus has half the drag. For this reason [[Supercharged Engine|supercharged]] planes fly much faster at higher altitudes.

A [[Supercharged Engine|supercharger]] is only able to supply so much pressure because the compression increases the air temperature, and the engine is limited in maximum charge-air temperature before [[engine knocking|engine knock]] occurs. The boost is typically measured as the altitude at which the [[Supercharged Engine|supercharger]] can still supply sea level pressure (100 kPa or 1000 mbar) and is referred to as the ''critical altitude''. Throughout WWII British [[Supercharged Engine|superchargers]] generally had higher critical altitudes than their German counterparts and, when combined with higher [[octane]] fuels that the Americans supplied, that allowed for higher boost levels. British engines were generally able to outperform German ones.

===Altitude efficiency===
Below the critical altitude the [[Supercharged Engine|supercharger]] is capable of delivering too much boost and must therefore be restricted lest the engine be damaged. Unless other measures are taken, this means that at least some of the power driving the [[Supercharged Engine|supercharger]] is wasted. Also, due to the denser air at lower altitudes, the [[Supercharged Engine|supercharger]] is not operating at its best efficiency, and this can cause an additional load on the engine.

For the early years of the war this was simply how it was and this led to the seemingly odd fact that many early-war engines actually delivered less power at lower altitudes, because the [[Supercharged Engine|supercharger]] was still using up power to compress air that was not delivering any power back. As the war progressed two-speed [[Supercharged Engine|superchargers]] were introduced using better controllers and, notably, hydraulic clutches, that allowed the boost to be managed over a wide range of altitudes by operating at low rpm down low and at high rpm at higher altitudes. This generally "flattened out" the power below the critical altitude.

===Improving octane rating===
In 1940 a batch of 100 [[octane]] fuel was delivered from the USA to the RAF. This allowed the boost on Merlin engines to be increased to 48 inHg (160 kPa) and the power to rise by more than 10% (from 1030 to 1160 [[HP|hp]], or 770 to 870 kW). By mid-1940 another increased boost yielded 1310 [[HP|hp]] (980 kW). Supercharging by itself could not have achieved these improvements; however, when married with fuel improvements, the engine could respond to both.

===Multiple stages===
In the 1930s two-speed drives were developed for [[Supercharged Engine|superchargers]]. These provided more flexibility for the operation of the aircraft although they also entailed more complexity of manufacturing and maintenance. Ultimately it was found that for most engines (excepting those in high-performance fighters) a single-stage two-speed setup was most suitable.

A final improvement was the use of two compressors in series, which were introduced to solve combustion problems. Compressing a gas always causes its temperature to rise, and highly compressed fuel-air mixtures may prematurely ignite or may detonate or both. In order to avoid combustion problems the "two stage" design was used. After being compressed "half-way" in the ''low pressure stage'' the air flowed through an [[intercooler]] radiator where it was partially cooled down before being compressed the rest of the way in the ''high pressure stage'' and then ''aftercooled'' in another air/air or coolant/air radiator (heat exchanger). At low altitudes one stage could be turned off completely. The two-stage Merlin was losing 400 [[HP|hp]] (300 kW) to turn the [[Supercharged Engine|supercharger]] but developing between 1500 and 1700 [[HP|hp]] (1125 to 1275 kW) at the propeller shaft, depending on model.

It is interesting to compare all of this complexity to the same system implemented with a [[Turbo Engine|turbocharger]]. Since the [[Turbo Engine|turbo]] is driven off the exhaust gases, simply dumping some of the exhaust pressure is sufficient to drive the compressor at almost any desired speed. In addition the power in the exhaust would otherwise be wasted (except to the extent that the exhaust itself provided thrust) whereas in the [[Supercharged Engine|supercharger]] that power is being taken directly from the engine. Thus at low altitudes the [[Turbo Engine|turbo]] robs nothing and, as the altitude increases, it can use just as much power as it needs and no more. Better yet the amount of power in the gas is the difference between the exhaust pressure and air pressure, which increases with altitude, so turbochargers generally have much better altitude performance.

Yet the vast majority of WWII engines used [[Supercharged Engine|superchargers]], because they maintained three significant manufacturing advantages over turbochargers, which were larger, involved extra piping, and required exotic high-temperature materials in the turbine. The size of the piping alone is a serious issue; consider that the Vought F4U and Republic P-47 used the same engine but the huge barrel-like fuselage of the latter was, in part, needed to hold the piping to and from the [[Turbo Engine|turbocharger]] in the rear of the plane.

==Supercharging in jet engines==
Supercharging is not confined to internal combustion engines — jet engines rely on supercharging as one of the main routes to thrust growth and improved fuel efficiency.

For example, adding an additional (i.e. zero) stage to a compressor will not only increase the overall pressure ratio of the cycle, but induce more airflow into the unit, by supercharging the entry plane of the original compressor. Ideally, the corrected (i.e. non-dimensional) speed of original compressor should be maintained, by raising the mechanical shaft speed by a factor
√(Tstage1new/Tstage1old). If stress considerations prevent any shaft speed increase, there is only a modest increase in airflow.

Converting a turbojet into a turbofan, by adding a fan spool, also supercharges the compression system, thereby raising core flow.

Many of the large turbofan engine series (e.g. Pratt and Whitney PW4000) have gained core flow by adding one or more stages to the front of the gas generator, usually in the LP (or IP) compressor. If the fan flow is not increased, the bypass ratio will decrease.

Supercharging can also be achieved by improving the aerodynamics of the existing blading. Core flow will increase if the original compressor outlet (corrected) flow size is maintained

Either way, raising core flow increases core power and, thereby, the net thrust or shaftpower of the engine. Raising overall pressure ratio tends to improve specific fuel consumption (i.e. fuel efficiency).

==See also==
* [[Turbo Engine|Turbocharger]]
* [[Naturally-aspirated engine|Naturally aspirated engine]]
* [[boost gauge]]
* [[Intercooler]]

==References==
* '''Allied Aircraft Piston Engines of World War II''', ''Graham White'' 1995: Airlife Publishing Ltd, England and Society of Automotive Engineers, Inc., in the USA. ISBN 1 85310 734 4
*[http://www.americantrucks.com/ford-truck-supercharger.html Truck Superchargers]
* http://www.howstuffworks.com

[[Category:Engine technology]]