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Roots blower
The Roots 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 Roots blower design does not incorporate any reduction in volume/increase in pressure as air or other fluid passes through, hence it can best be described as a blower rather than a supercharger unlike some other designs of "supercharger" such as cozette, centric, Shorrock supercharger, Powerplus supercharger and also the axial flow Eaton type supercharger which have internal "compression".
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.
The Roots-type blower is named after American inventors and brothers Philander and Francis Marion Roots, founders of the Roots Blower Company of Connersville, Indiana, who patented the basic design in 1860 as an air pump for use in blast furnaces and other industrial applications. In 1900, Gottlieb Daimler included a Roots-style blower in a patented engine design, making the Roots-type blower the oldest of the various designs available. Roots blowers are commonly referred to as air blowers or PD (positive displacement) blowers.
The Roots-type blower is simple and widely used. It can be more effective than alternative superchargers at developing positive intake manifold pressure (i.e., above atmospheric pressure) at low engine speeds, making it a popular choice for passenger automobile applications. Peak torque can be achieved by about 2000 rpm. Unlike the basic illustration, most modern Roots-type superchargers incorporate three-lobe or four-lobe rotors; this allows the lobes to have a slight twist[clarification needed] along the rotor axes, which reduces pulsing in the input and output (this is impractical with two lobes, as even a slight twist could open up a free path through the supercharger at certain angles)[citation needed].
Accumulated heat is an important consideration in the operation of a compressor in an internal combustion engine. Of the three basic supercharger types, the Roots design historically possessed the worst thermal efficiency, especially at high pressure ratios. In accordance with the ideal gas law, a compression operation will raise the temperature of the compressed output. Additionally, the operation of the compressor itself requires energy input, which is converted to heat and can be transferred to the gas through the compressor housing, heating it more. Although intercoolers are more commonly known for their use on turbochargers, superchargers may also benefit from the use of an intercooler. Internal combustion is based upon a thermodynamic cycle, and a lower temperature of the intake charge results in a greater thermodynamic expansion and vice versa. A hot intake charge provokes detonation in a petrol engine, and can melt the pistons in a diesel, while an intercooling stage adds complexity but can improve the power output by increasing the amount of the input charge, exactly as if the engine were of higher capacity. An intercooler reduces the thermodynamic efficiency by losing the heat (power) introduced by compression, but increases the power available because of the increased working mass for each cycle. Above about 5 psi (35 kPa) the intercooling improvement can become dramatic.[citation needed] With a Roots-type supercharger, one method successfully employed is the addition of a thin heat exchanger placed between the blower and the engine. Water is circulated through it to a second unit placed near the front of the vehicle where a fan and the ambient air-stream can dissipate the collected heat.
The Roots design was commonly used on two-stroke diesel engines (popularized by the Detroit Diesel [truck and bus] and Electro-Motive [railroad] divisions of General Motors), which require some form of forced induction, because there is no separate intake stroke. The Rootes Co. two-stroke diesel engine, used in Commer and Karrier vehicles, had a Roots-type blower; the two companies are not related.
The superchargers used on top fuel engines, funny cars, and other dragsters, as well as hot rods, are in fact derivatives of General Motors Coach Division blowers for their industrial diesel engines, which were adapted for automotive use in drag racing. The model name of these units delineates their size - the once-commonly used 4–71 and 6–71 blowers were designed for 71 series diesels. Current competition dragsters use aftermarket GMC variants similar in design to the 71 series, but with the rotor and case length increased for added capacity; hot rodders also use reproduction 6-71s.
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Roots blower
The Roots 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 Roots blower design does not incorporate any reduction in volume/increase in pressure as air or other fluid passes through, hence it can best be described as a blower rather than a supercharger unlike some other designs of "supercharger" such as cozette, centric, Shorrock supercharger, Powerplus supercharger and also the axial flow Eaton type supercharger which have internal "compression".
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.
The Roots-type blower is named after American inventors and brothers Philander and Francis Marion Roots, founders of the Roots Blower Company of Connersville, Indiana, who patented the basic design in 1860 as an air pump for use in blast furnaces and other industrial applications. In 1900, Gottlieb Daimler included a Roots-style blower in a patented engine design, making the Roots-type blower the oldest of the various designs available. Roots blowers are commonly referred to as air blowers or PD (positive displacement) blowers.
The Roots-type blower is simple and widely used. It can be more effective than alternative superchargers at developing positive intake manifold pressure (i.e., above atmospheric pressure) at low engine speeds, making it a popular choice for passenger automobile applications. Peak torque can be achieved by about 2000 rpm. Unlike the basic illustration, most modern Roots-type superchargers incorporate three-lobe or four-lobe rotors; this allows the lobes to have a slight twist[clarification needed] along the rotor axes, which reduces pulsing in the input and output (this is impractical with two lobes, as even a slight twist could open up a free path through the supercharger at certain angles)[citation needed].
Accumulated heat is an important consideration in the operation of a compressor in an internal combustion engine. Of the three basic supercharger types, the Roots design historically possessed the worst thermal efficiency, especially at high pressure ratios. In accordance with the ideal gas law, a compression operation will raise the temperature of the compressed output. Additionally, the operation of the compressor itself requires energy input, which is converted to heat and can be transferred to the gas through the compressor housing, heating it more. Although intercoolers are more commonly known for their use on turbochargers, superchargers may also benefit from the use of an intercooler. Internal combustion is based upon a thermodynamic cycle, and a lower temperature of the intake charge results in a greater thermodynamic expansion and vice versa. A hot intake charge provokes detonation in a petrol engine, and can melt the pistons in a diesel, while an intercooling stage adds complexity but can improve the power output by increasing the amount of the input charge, exactly as if the engine were of higher capacity. An intercooler reduces the thermodynamic efficiency by losing the heat (power) introduced by compression, but increases the power available because of the increased working mass for each cycle. Above about 5 psi (35 kPa) the intercooling improvement can become dramatic.[citation needed] With a Roots-type supercharger, one method successfully employed is the addition of a thin heat exchanger placed between the blower and the engine. Water is circulated through it to a second unit placed near the front of the vehicle where a fan and the ambient air-stream can dissipate the collected heat.
The Roots design was commonly used on two-stroke diesel engines (popularized by the Detroit Diesel [truck and bus] and Electro-Motive [railroad] divisions of General Motors), which require some form of forced induction, because there is no separate intake stroke. The Rootes Co. two-stroke diesel engine, used in Commer and Karrier vehicles, had a Roots-type blower; the two companies are not related.
The superchargers used on top fuel engines, funny cars, and other dragsters, as well as hot rods, are in fact derivatives of General Motors Coach Division blowers for their industrial diesel engines, which were adapted for automotive use in drag racing. The model name of these units delineates their size - the once-commonly used 4–71 and 6–71 blowers were designed for 71 series diesels. Current competition dragsters use aftermarket GMC variants similar in design to the 71 series, but with the rotor and case length increased for added capacity; hot rodders also use reproduction 6-71s.