17453088 How Does Variable Turbine Geometry Work

7/27/2019 17453088 How Does Variable Turbine Geometry Work

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Variable Turbine GeometryVariable Turbine Geometry

A National Maritime Academy A National Maritime Academypresentationpresentation


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On a conventional turbocharger, the exhaustOn a conventional turbocharger, the exhaustflow drives a turbine that is connected to aflow drives a turbine that is connected to acompressor on the intake side. Bycompressor on the intake side. By

compressing the incoming air, the amount ofcompressing the incoming air, the amount ofoxygen in a given volume is increased.oxygen in a given volume is increased.ince compression also causes an increaseince compression also causes an increase

in temperature, the air must be cooled in ain temperature, the air must be cooled in a

device known as a !intercooler". #ith moredevice known as a !intercooler". #ith moreoxygen present in each cylinder charge,oxygen present in each cylinder charge,more fuel can be burnt yielding greatermore fuel can be burnt yielding greaterenergy.energy.


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ince higher exhaust pressuresince higher exhaust pressures

generate greater loads on thegenerate greater loads on theintake side, the intake pressureintake side, the intake pressuremust be carefully controlled inmust be carefully controlled inorder to protect the engine.order to protect the engine.

$he %boost pressure& is limited$he %boost pressure& is limitedusing %waste gate& valves thatusing %waste gate& valves thatbypass excess pressure aroundbypass excess pressure aroundthe twin exhaust turbines.the twin exhaust turbines.


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ince a smaller turbine has a lower mass,ince a smaller turbine has a lower mass,it responds more 'uickly to increasingit responds more 'uickly to increasingpressure, spinning up easily to its optimumpressure, spinning up easily to its optimumspeed. $he key disadvantage of using aspeed. $he key disadvantage of using a

smaller turbo is that the back(pressuresmaller turbo is that the back(pressuregenerated at higher engine speedsgenerated at higher engine speedscauses a significant reduction incauses a significant reduction inperformance. )esistance is caused by theperformance. )esistance is caused by the

smaller cross(sectional area throughsmaller cross(sectional area throughwhich the exhaust is re'uired to flow.which the exhaust is re'uired to flow.


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*arger turbo units, which create lower*arger turbo units, which create lowerback(pressure at higher rpm, takeback(pressure at higher rpm, takeconsiderably longer to spin up underconsiderably longer to spin up underpower due to the large cross(sectionalpower due to the large cross(sectional

area and relative inertia of the heavierarea and relative inertia of the heavierturbine. +enerally, this type of turbo willturbine. +enerally, this type of turbo willonly be effective in the medium rpmonly be effective in the medium rpmrange. $his phenomenon, known asrange. $his phenomenon, known as%turbo lag&, means there is virtually no%turbo lag&, means there is virtually noturbo charging effect at lower engineturbo charging effect at lower enginespeeds.speeds.


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Variable TurbineVariable TurbineGeometryGeometry technology is the nexttechnology is the next

generation in turbochargergeneration in turbochargertechnology where the turbotechnology where the turbo

uses variable vanes to controluses variable vanes to controlexhaust flow against theexhaust flow against the

turbine blades.turbine blades.


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$he problem with the$he problem with the

turbocharger that we&ve all cometurbocharger that we&ve all cometo know and love is that bigto know and love is that bigturbos do not work well at slowturbos do not work well at slow

engine speeds, while smallengine speeds, while smallturbos are fast to spool but runturbos are fast to spool but runout of steam pretty 'uick. oout of steam pretty 'uick. o

how dohow do VTG turbosVTG turbos solve thissolve thisproblemproblem


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A A Variable Turbine GeometryVariable Turbine Geometry turbocharger is also known as aturbocharger is also known as avariable geometry turbochargervariable geometry turbocharger

(VGT)(VGT) ,,

or aor a Variable Nozzle Turbine (VNT)Variable Nozzle Turbine (VNT) ..


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A turbocharger e'uipped with A turbocharger e'uipped with-ariable $urbine +eometry has-ariable $urbine +eometry haslittle movable vanes which canlittle movable vanes which candirect exhaust flow onto thedirect exhaust flow onto theturbine blades. $he vane anglesturbine blades. $he vane anglesare ad usted via an actuator. $heare ad usted via an actuator. $heangle of the vanes varyangle of the vanes varythroughout the engine )/M rangethroughout the engine )/M rangeto optimi0e turbine behaviour.to optimi0e turbine behaviour.


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Below, you can see the vanes in a angle which isBelow, you can see the vanes in a angle which isalmost closed. Variable vanes are highlighted.almost closed. Variable vanes are highlighted.


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$he -+$ vanes look like when they are open.$he -+$ vanes look like when they are open.


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In this diagram, you can see the direction o e!haustIn this diagram, you can see the direction o e!haustlow when the variable vanes are in an almost closedlow when the variable vanes are in an almost closed

angle. The narrow "assage o which the e!haust gasangle. The narrow "assage o which the e!haust gashas to low through accelerateshas to low through accelerates the e!haust gas towardsthe e!haust gas towardsthe turbine blades,the turbine blades,ma#ing them s"inma#ing them s"in

aster. The angle o aster. The angle o the vanes alsothe vanes alsodirects the gas todirects the gas tohit the blades at thehit the blades at the "ro"er angle."ro"er angle.


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$iagram shows the e!haust gas low when the variable$iagram shows the e!haust gas low when the variableturbine vanes are ully o"en. The high e!haust low at highturbine vanes are ully o"en. The high e!haust low at highengine s"eeds are ully directed onto the turbine blades byengine s"eeds are ully directed onto the turbine blades bythe variable vanes.the variable vanes.


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$hank 1ou 2$hank 1ou 2


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17453088 How Does Variable Turbine Geometry Work