驴Qu茅 es un Turbocargador de Geometr铆a Variable, y c贸mo funciona?

Los turbocompresores de geometr铆a variable (VGT o turbocompresores de geometr铆a variable) es un t茅rmino que se le asigna alagunos turbos en su mayor铆a a diesel. Los VGT tienen turbinas con 谩labes que se mueven seg煤n las necesidades del motor al que est谩n conectados.

La forma en que se mueven los alabes depende del dise帽o de VGT; algunos fabricantes los dise帽an para pivotar y otros para deslizarlos. Los primeros VGT regulaban las posiciones de las piezas utilizando actuadores de presi贸n o vac铆o, pero la mayor铆a de los dise帽os actuales utilizan unidades de control electr贸nico para determinar las posiciones de las piezas.

Cuando se alteran las posiciones de los alabes, cambia la geometr铆a de la carcasa de la turbina. Estos cambios afectan la velocidad de la turbina giratoria, lo que permite optimizarla para el rendimiento del motor.

Cuando la velocidad del motor es baja, el espacio en el turbo se expande, disminuyendo la velocidad del aire que fluye a trav茅s de la turbina. Cuando la velocidad del motor es alta, el espacio en el turbo se restringe, aumentando la velocidad del aire que fluye a trav茅s de la turbina.

Es importante recordar que los VGT cambian la velocidad de la turbina, no la cantidad de aire de escape. La cantidad de aire de escape nunca cambia.

Los VGT se crearon para trabajar con sistemas EGR para controlar las emisiones y son esenciales para la regeneraci贸n del filtro de part铆culas di茅sel (DPF). Durante la regeneraci贸n del DPF, la velocidad del aire debe controlarse por completo para que la temperatura del aire de escape sea lo suficientemente alta como para quemar la materia acumulada en el filtro.

Un turbo de geometr铆a variable (VGT) es una soluci贸n de potencia compleja y costosa que prevalece especialmente en los motores di茅sel. Un VGT tiene un anillo de 谩labes de forma aerodin谩mica en la carcasa de la turbina que puede alterar su relaci贸n de 谩rea a radio para igualar las revoluciones del motor. A bajas revoluciones, la relaci贸n 谩rea-radio crea m谩s presi贸n y velocidad para acelerar el turbo de manera m谩s efectiva. A revoluciones m谩s altas, la relaci贸n aumenta para dejar entrar m谩s aire. El resultado es un rango de impulso m谩s amplio y menos retraso.

Ventajas

鈥 Curva de par amplia y plana. Turbocompresor eficaz en un rango de RPM muy amplio.
鈥 Requiere un solo turbo, lo que simplifica una configuraci贸n turbo secuencial en algo m谩s compacto.

Desventajas

鈥 Por lo general, solo se usa en aplicaciones di茅sel donde los gases de escape son m谩s bajos para que las paletas no se da帽en con el calor.
鈥 Para las aplicaciones de gasolina, el costo generalmente las mantiene fuera, ya que se deben usar metales ex贸ticos para mantener la confiabilidad. La tecnolog铆a se ha utilizado en el Porsche 997, aunque existen muy pocos motores de gasolina VGT como resultado del costo asociado.

驴Qu茅 es el Turbocompresor El茅ctrico de Audi y c贸mo funciona?

El聽turbocompresor el茅ctrico聽es un dispositivo mec谩nico el茅ctrico que ayuda a optimizar la eficiencia y reducir el turbolag a bajas revoluciones en el autom贸vil, incorpora un motor el茅ctrico que hace la funciona de la turbina y un compresor est谩 instalado en el sistema de admisi贸n de aire que entra al motor, antes del turbo principal y del intercooler y normalmente es accionado a un r茅gimen de giro determinado por el fabricante en este caso Audi

Sin embargo, a muy bajas revoluciones, cuando salimos de un sem谩foro, por ejemplo, el aire que es enviado al turbo principal no ser铆a suficiente como para activarlo, entonces el turbo el茅ctrico entra en funcionamiento y empuja el aire con mucha m谩s fuerza en el motor, eliminando el聽Turbolag.

Las ventajas de la instalaci贸n de un sobrealimentador el茅ctrico residen en su total independencia de los gases de escape, modific谩ndose el sistema el茅ctrico debido a la necesidad de tensiones de trabajo de 48 voltios como m铆nimo.

La sobrealimentaci贸n el茅ctrica promete importantes mejoras en consumos, rendimientos m谩s eficaces del motor y un optimo desempe帽o de las normas ambientales y de gases, Estos principios b谩sicos de la evoluci贸n de los motores actuales permiten tener un mejor mercado automotriz.

Turbolag

Uno de los principales problemas a los que se enfrentan los fabricantes de veh铆culos, independientemente del tipo de sobrealimentaci贸n que incorporan, son las prestaciones a bajo r茅gimen debido al famoso聽TURBOLAG聽(tiempo de reacci贸n) tiempo que transcurre desde que pisamos el acelerador hasta que notamos el empuje total del motor, siendo esta idea tan antigua como el propio turbo.

Caracter铆sticas

Las cifras que ofrece el sobrealimentador el茅ctrico de Audi son demoledores, alcanzando una聽velocidad de giro de 70.000 rpm en apenas cent茅simas de segundo.

脡sta es su principal ventaja como elemento complementario al dise帽o de doble turbocompresor en serie, pues聽el retraso del turbo 鈥 efecto lag 鈥 es totalmente contrarrestado聽por la velocidad que alcanza la turbina el茅ctrica en muy poco tiempo.

Pero las ventajas de este sobrealimentador el茅ctrico van m谩s all谩, y es que esta peque帽a turbina es capaz de alcanzar valores de presi贸n relativa de 2,4 bares, consiguiendo unos registros m谩s que interesantes para llenar cada uno de los cilindros.

驴Qu茅 es el Turbo Lag en el auto y c贸mo se produce?

Para ir entendiendo el concepto r谩pidamente determinamos que el Lag (retraso) es un lapso de tiempo (retraso de respuesta), que transcurre desde que se pisa el acelerador hasta que la fuerza se transmite a las ruedas y se genera un movimiento

El lag se genera聽cuando los gases de escape entran en contacto con la inercia de las propias turbinas聽que conforman el sistema del turbo, ya que su peso hace que no puedan funcionar de manera inmediata. Pero tambi茅n por el tiempo que transcurre聽hasta que las turbinas giran lo suficiente聽como para que su presi贸n sea capaz de empujar el veh铆culo.

Es decir, cuando la turbina gira con lentitud, el motor se comporta como si no llevara turbo, hasta que 茅ste alcanza la velocidad de giro necesaria para comprimir el aire de admisi贸n.

En algunos motores, con el turbocompresor muy grande, cuesta mucho mover la turbina cuando no est谩 girando o cuando lo hace despacio, por lo que los gases de escape necesitan vencer una fuerte inercia.

Para solucionarlo, se utilizan turbocompresores cada vez m谩s peque帽os; turbos con materiales muy ligeros pero que resistan muy bien el calor, como la cer谩mica o el titanio, o turbocompresores de geometr铆a variable. o en su defecto turbo compresores electricos como el que incorpor贸 AUDI, o el actualmente desarrollado por Garrett

驴Qu茅 es una v谩lvula de alivio (Wastegate) y c贸mo funciona en el turbocargador?

Una valvula de alivio o Wastegate es un dispositivo integrado en un turbocompresor que controla la presi贸n de sobrealimentaci贸n m谩xima permitida.  La v谩lvula de descarga es un componente en un turbocompresor que desv铆a los gases de la turbina. La funci贸n principal de la v谩lvula de descarga es regular la presi贸n de sobrealimentaci贸n 贸ptima en los sistemas de turbocompresor para proteger el turbocompresor y el motor. El desv铆o de los gases de escape ajusta la velocidad de la turbina, que en sinton铆a ajusta la velocidad de rotaci贸n del compresor.

Es en esta etapa que la rueda de la turbina traduce la energ铆a t茅rmica (energ铆a potencial) del escape del motor en energ铆a mec谩nica. Si el flujo de escape se desv铆a de manera que no fluya a trav茅s de la rueda de la turbina de un turbocompresor, entonces su energ铆a potencial no es convertida por la turbina. En pocas palabras, la reducci贸n del flujo de escape a trav茅s de la turbina reduce y / o controla la presi贸n de refuerzo. En una palabra,

Tipos de V谩lvulas de alivio

Hay dos tipos de alivios; interno y externo. Una compuerta de desechos interna est谩 integrada en el conjunto de la carcasa de la turbina. Se instala una v谩lvula de descarga externa en el tubo ascendente de escape entre el colector de escape y la entrada de la carcasa de la turbina. En cualquier caso, se requiere un actuador para operar la v谩lvula de v谩lvula de descarga. Cuando se abre la v谩lvula, el flujo de escape se desv铆a de su trayectoria normal a trav茅s de la rueda de la turbina y, en su lugar, sale directamente al tubo de escape.

En funci贸n del modo de apertura, se distinguen dos variantes de v谩lvulas de descarga:

  • V谩lvula de descarga de tipo 芦push . En estas v谩lvulas de descarga, la apertura es accionada mediante un muelle. Este muelle, tarado a una determinada fuerza, aprieta el pist贸n de la v谩lvula manteni茅ndola cerrada. Cuando la presi贸n en la admisi贸n vence la fuerza del muelle, se abre la v谩lvula para permitir la salida del aire comprimido.
  • V谩lvula de descarga de tipo 芦pull禄.En las v谩lvulas de descarga de tipo jalar, la apertura es accionada por medio de una membrana en vez de por muelles. A diferencia de la versi贸n tipo 鈥減ush鈥, estas v谩lvulas tienen la ventaja de que no necesitan regulaci贸n ya que se adaptan autom谩ticamente a cualquier valor de presi贸n. Se trata de un modelo m谩s sofisticado y m谩s caro que la opci贸n tipo 鈥減ush鈥, que permite un funcionamiento m谩s optimizado y suave. Las v谩lvulas de descarga tipo 鈥減ull鈥 aseguran la estanqueidad m谩xima al ralent铆 y no sufren fugas bajo ning煤n rango de presi贸n de soplado del turbo. 

V谩lvula de descarga blow off

Como es la que expulsa el aire sobrante al exterior, . Tambi茅n suele llamarse v谩lvula de descarga atmosf茅rica, precisamente por lanzar al aire a presi贸n a la atm贸sfera. Este tipo de v谩lvulas es caracter铆stica de los sonidos realizados al revolucionar el veh铆culo

V谩lvula de descarga de bypass

Una v谩lvula de compresi贸n bypass, tambi茅n llamada v谩lvula de recirculaci贸n, no saca el aire sobrante fuera. En su caso lo env铆a a la admisi贸n, pero antes del turbo. Es decir, en la parte de donde el turbo saca el aire para luego presurizarlo y meterlo en el motor. Es importante que lo env铆e a un lugar donde el caudal铆metro pueda medir bien el aire que entra realmente. De lo contrario la mezcla de aire y combustible ser谩 incorrecta.

Control de la V谩lvula de Alivio Wastegate

Uno de los m茅todos m谩s simples para controlar una v谩lvula de descarga es mediante la presi贸n del m煤ltiple de admisi贸n (presi贸n absoluta del m煤ltiple o MAP). Una l铆nea o manguera conecta el colector de admisi贸n a un actuador de v谩lvula de descarga, que es esencialmente un diafragma mec谩nico y un dispositivo de resorte. El resorte dentro del actuador de la v谩lvula de descarga mantiene la v谩lvula en la posici贸n cerrada. Al igual que la presi贸n del colector de admisi贸n (presi贸n de refuerzo), tambi茅n lo hace la presi贸n en el actuador de la v谩lvula de descarga, aplicando una fuerza al diafragma. Cuando la fuerza ejercida sobre el diafragma excede la fuerza del resorte, la v谩lvula de descarga comienza a abrirse. A medida que cae la presi贸n de refuerzo, el resorte cierra la compuerta de desechos.

Una implementaci贸n m谩s moderna del control de la v谩lvula de descarga es mediante un actuador el茅ctrico; Esto se est谩 volviendo cada vez m谩s popular en motores turboalimentados. En lugar de depender de una presi贸n m煤ltiple o una fuente de vac铆o, estas compuertas de desag眉e cuentan con un solenoide el茅ctrico que es controlado directamente por el PCM y ajusta la posici贸n de la v谩lvula de compuerta de desag眉e.

WASTEGATES Y TURBOCOMPRESORES DE GEOMETR脥A VARIABLE (VGT)

Tradicionalmente (con excepciones), un turbocompresor de geometr铆a variable (VGT) no requiere el uso de una valvula de alivio, ya que el impulso se controla perpetuamente por la posici贸n de los 谩labes en la carcasa de la turbina. El un VGT ajusta f铆sicamente el tama帽o efectivo de la carcasa de la turbina al aumentar o disminuir las presiones de los gases de escape que act煤an sobre la rueda de la turbina. En lugar de desviar los gases de escape alrededor de la rueda de la turbina, un VGT simplemente abre las paletas, simulando un efecto similar al de una v谩lvula de descarga. 

A medida que se cierran las paletas, aumenta la energ铆a de escape que act煤a sobre la rueda de la turbina. Este rango de movimiento se utiliza para proporcionar una respuesta deseable del turbocompresor mientras se controlan las caracter铆sticas de rendimiento y la presi贸n de refuerzo m谩xima en todas las condiciones.

驴Qu茅 es un supercargador y como funciona en el motor del AUTOM脫VIL?

SUPERCHARGER: TYPES, METHODS AND WORKING PRINCIPLE

Superchargers are basically compressors/blowers which takes air at normal ambient pressure & compresses it and forcefully pushes it into engine! Power to the compressor/ blower is transmitted from engine via the belt drive.

The addition of extra amount of air-fuel mixture into the cylinder increases the mean effective pressure of the engine. An increment in MEP makes the engine produce more power. In this way, adding a compressor to the engine makes it more efficient.

TYPES OF SUPERCHARGER

There are mainly two types of supercharger. The first one is known as positive displacement supercharger and other one is known as Dynamic supercharger. The basic difference between both of them is that the positive displacement supercharger maintains constant level of pressure at all engine speed whereas the dynamic supercharger delivers increasing pressure with increasing speed. This is basic fundamental difference between them. These superchargers further subdivided as given below.

1. POSITIVE DISPLACEMENT SUPERCHARGER:

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As we discussed in early section that these superchargers deliver the same volume of charge at any engine speed or these superchargers are not depended on speed of the engine. The major types of positive displacement supercharger are root style and twin screw.

1. Root style
This design has two specially designed rotors which rotate in opposite direction (one is clockwise and other is anticlockwise) to compress the air. According to the rotor design this supercharger is further subdivided into two type: Two lob rotor, three lob, four lob rotors etc. As the rotor rotate, they trap the air by these lobs coming from suction side or inlet port and forced it towards discharge side or outlet port. The amount of air compressed is independent on the engine speed and each time this supercharger compresses the same amount of air.

Advantages:
飩 Simple design
飩 Best suited with high speed engine

Disadvantages:
飩 Pulsing airflow at low speed.
飩 Less efficiency.
飩 Heavy in weight.
飩 Create lots of heat due to friction.
飩 Back leakage at low speed.
飩 Provide same amount of air at both low and high RPM.

2. Twin screw supercharger
As the name implies, this type of supercharger have two screws which rotate in different direction. One of the screw rotate clockwise and other one is anticlockwise direction. The working of this supercharger is same as root type. It also sucks air from one side and delivered it to outlet port. This device provide smother air flow comparatively root style.

Advantages:

No photo description available.


飩 No back leakage problem.
飩 Provide smother air flow.

Disadvantages:
飩 High heat generation due to friction.
飩 Noisy in operation.

3. Vane type supercharger
A number of vanes are mounted on the drum of the supercharger. These vanes are pushed outwards via pre-compressed springs. This arrangement helps the vane to stay in contact with the inner surface of the body.
Now due to eccentric rotation, the space between two vanes is more at the inlet & less at the outlet. In this way, the quantity of air which enters at the inlet decreases it鈥檚 volume on its way to outlet. A decrease in volume results in increment of pressure of air. Thus, the mixture obtained at the outlet is at higher pressure than at the inlet.

2. DYNAMIC SUPERCHARGER:

No photo description available.

As we discussed earlier, these type of supercharger gives increasing air pressure as increasing engine speed. The supercharging effect in this type is highly depended on the engine speed. It also subdivided into following types.

1. Centrifugal Type


As the name implies this type uses centrifugal force to compress the air. The design of this supercharger is same as the centrifugal compressor. It has a impeller which is connected with the crankshaft with the help of belt drive. When the engine rotates, it makes rotate the impeller which sucks the air from one side. The centrifugal action acts on this air which increase its kinetic energy and delivery it to a diffuser. The air enter into the diffusion have high velocity at low pressure. The diffuser converts this high speed low pressure air to low speed high pressurized air. This high pressurized air then sent to the engine.

Advantages:
飩 It is small in size.
飩 High efficiency.

Disadvantages:
飩 The amount of air is not fixed.

2. Pressure wave 
3. Axial flow

METHODS OF SUPERCHARGING

No photo description available.

There are various other ways to force the air which doesn鈥檛 need extra power unlike compressors. The 2 most widely applied are 鈥

鈥 Ram effect supercharging 
Here, the inlet manifold is designed in such a way that the air gets automatically pushed into the cylinder. The air continuously tries into the cylinder but the intake valves open/close several times a second ! Every time the valve closes, the air just rams into it. This generates a pressure wave which travels in the opposite direction until it hits the plenum & gets reflected back.

Now if the resonant frequency of the plenum & engine matches, this pressure wave carries more air into the cylinder doing the work of a supercharger.

鈥 Under piston supercharging 鈥
This type of method is generally adopted in large marine engines. It utilizes the bottom side of the piston for compressing the air. With proper timing of valves, this system gives an adequate supply of compressed air, as there are 2 delivery strokes to each suction stroke of each stroke !

ADVANTAGES AND DISADVANTAGES OF SUPERCHARGER

Advantages of supercharging

1. Higher power output
2. Greater induction of charge mass
3. Better atomization of fuel
4. Better mixing of fuel and air
5. Better scavenging products
6. Better torque characteristics over whole range
7. Quick acceleration of vehicle
8. Complete and smooth combustion
9. Even fuel with poor ignition quality can be used
10. Improved cold starting
11. Reduced exhaust smoke
12. Reduced specific fuel consumption
13. Increased mechanical efficiency
14. Smooth operation and reduction in diesel knock tendency

Disadvantages of supercharging

1. Increased detonation tendency in SI engines
2. Increased thermal stress
3. Increased heat loss due to increased turbulence
4. Increased gas loading
5. Increased cooling requirements of the engine

TURBOCHARGER: COMPONENTS, WORKING PRINCIPLES, AND TYPES

A Turbocharger is a device that is used to increase the power of the engine or one can say the efficiency of an engine by increasing the amount of air entering into the combustion chamber. More air into the combustion chamber means more amount of fuel will be admitted into the cylinder and as a result, one will get more power from the same engine if the turbocharger is installed in it.

Very simply, a turbocharger is a kind of air pump taking air at ambient pressures (atmospheric pressure), compressing to a higher pressure and passing the compressed air into the engine via the inlet valves.

At the present time, turbos are used mainly on diesel engines, but there is now a move towards the turbocharging of production petrol engines.

The amount of engine that actually goes into the engine鈥檚 cylinder, compared with the theoretical amount if the engine could maintain the atmospheric pressure, is called volumetric efficiency and the aim of the turbocharger is to improve an engine鈥檚 volumetric efficiency by increasing density of the intake gas.

The turbocharger draws the air from the atmosphere and compresses it with the help of centrifugal compressor before it enters into the intake manifold at increased pressure. This results in more amount of air entering into the cylinders on each intake stroke. The centrifugal compressor gets power from the kinetic energy of the engine鈥檚 exhaust gases.

COMPONENTS OF TURBOCHARGER

The turbocharger has three main components
1. The turbine, which is almost a radial inflow turbine.
2. The compressor is almost a centrifugal compressor.
3. The center hub rotating assembly.

No photo description available.

A turbocharger is made up of two main sections: the turbine and the compressor.

The turbine consists of a turbine wheel and turbine housing. It is the job of the turbine housing to guide the exhaust gas into the turbine wheel. The energy from the exhaust gas turns the turbine wheel, and the gas then exits the turbine housing through an exhaust outlet area.

The compressor also consists of two parts: the compressor wheel and the compressor housing. The compressor鈥檚 mode of action is opposite that of the turbine. The compressor wheel is attached to the turbine by a forged steel shaft, and as the turbine turns the compressor wheel, the high-velocity spinning draws in air and compresses it. The compressor housing then converts the high-velocity, low-pressure air stream into a high-pressure, low-velocity air stream through a process called diffusion. The compressed air is pushed into the engine, allowing the engine to burn more fuel to produce more power.

WORKING PRINCIPLE

A turbocharger mainly consists of two main sections: the turbine and the compressor. The turbine consists of a turbine wheel and the turbine housing whose purpose is to guide the exhaust gases into the turbine wheel. The kinetic energy of the exhaust gases gets converted into the mechanical after striking it on turbine blades. The exhaust outlet helps the exhaust gases to get exit from the turbine. The compressor wheel in the turbocharger is attached to a turbine with the help of steel shaft and as the turbine turns the compressor wheel, it draws the high-velocity, low-pressure air stream and converts it into high-pressure, low 鈥搗elocity air stream. This compressed air is pushed into the engine with the more quantity of fuel and hence produce more power.

The waste exhaust gases of the engine are utilized to drive a turbine wheel, which is connected to a compressor wheel by a shaft. The compressor or air wheel sucks in air through the air filters and passes this into the engine.
As the waste gases are expelled from the engine, they are directed to the turbine or hot wheel of the turbo and so completes the cycle.

1. Capture

Instead of escaping through the exhaust pipe, hot gases produced during combustion flow to the turbocharger. The cylinders inside an internal combustion engine fire in sequence (not all at once), so exhaust exits the combustion chamber in irregular pulses.
Conventional single-scroll turbochargers route those irregular pulses of exhaust into the turbine in a way that causes them to collide and interfere with one another, reducing the strength of the flow. In contrast, a twin-scroll turbocharger gathers exhaust from pairs of cylinders in an alternating sequence.

2. Spin

The exhaust strikes the turbine blades, spinning them at up to 150,000 rpm. The alternating pulses of exhaust help eliminate turbo lag.

3. Vent

Having served their purpose, exhaust gases flow through an outlet to the catalytic converter, where they are scrubbed of carbon monoxide, nitrous oxides, and other pollutants before exiting through the tailpipe.

4. Compress

Meanwhile, the turbine powers an air compressor, which gathers cold, clean air from a vent and compresses it to 30 percent above atmospheric pressure, or nearly 19 pounds per square inch. Dense, oxygen-rich air flows to the combustion chamber.

The additional oxygen makes it possible for the engine to burn gasoline more completely, generating more performance from a smaller engine. As a result, the Twin Power engine generates 30 percent more power than a non-turbocharged one of the same sizes.

It follows the following process

1. The engine鈥檚 air intake sucks in cool air and sends to the compressor.
2. The compressor compresses the incoming air and heats it up. It then blows out the hot air.
3. The hot air cools down when passing through the heat exchanger and enters the cylinder鈥檚 air intake.
4. The cold air burns inside the combustion chamber at a faster rate because of carrying more oxygen.
5. Due to the burning of more fuel, the energy output will be bigger faster, and the engine will be able to send more power to the wheels.
6. Hot waste gasses will leave the chamber and blows past the turbine at the exhaust outlet.
7. The turbine rotates at a high speed and spins the compressor too as both are mounted on the same shaft.
8. The exhaust gasses leave the car through the exhaust pipe. They waste less energy than an engine not having a turbocharger.

TYPES OF TURBOCHARGER

1. Single-Turbo

Single turbochargers alone have limitless variability. Differing the compressor wheel size and turbine will lead to completely different torque characteristics. Large turbos will bring on high top-end power, but smaller turbos will provide better low-end grunt as they spool faster. There are also ball bearing and journal bearing single turbos. Ball bearings provide less friction for the compressor and turbine to spin on, thus are faster to spool (while adding cost).

Advantages
鈥 A cost-effective way of increasing an engine鈥檚 power and efficiency.
鈥 Simple, generally the easiest of the turbocharging options to install.
鈥 Allows for using smaller engines to produce the same power as larger naturally-aspirated engines, which can often remove weight.

Disadvantages
鈥 Single turbos tend to have a fairly narrow effective RPM range. This makes sizing an issue, as you鈥檒l have to choose between good low-end torque or better high-end power.
鈥 Turbo response may not be as quick as alternative turbo setups.

2. Twin-Turbo

Just like single turbochargers, there are plenty of options when using two turbochargers. You could have a single turbocharger for each cylinder bank (V6, V8, etc). Alternatively, a single turbocharger could be used for low RPM and bypass to a larger turbocharger for high RPM (I4, I6, etc). You could even have two similarly sized turbos where one is used at low RPM and both are used at higher RPM. On the BMW X5 M and X6 M, twin-scroll turbos are used, one on each side of the V8.

Advantages
鈥 For parallel twin turbos on 鈥榁鈥 shaped engines, the benefits (and drawbacks) are very similar to single turbo setups.
鈥 For sequential turbos or using one turbo at low RPM and both at high RPM, this allows for a much wider, flatter torque curve. Better low-end torque, but the power won鈥檛 taper at high RPM like with a small single turbo.

Disadvantages
鈥 Cost and complexity, as you鈥檝e nearly doubled the turbo components.
鈥 There are lighter, more efficient ways of achieving similar results (as discussed below).

3. Twin-Scroll Turbo

A turbo is powered by exhaust gases that are redirected to spin turbine blades and force air into the engine. Now, an engine鈥檚 cylinders fire in sequence, meaning that exhaust gases enter the turbo in pulses. As you can probably imagine, these pulses can easily overlap and interfere with one another when powering the turbo, and a twin-scroll turbocharger solves this issue by using a divided-inlet turbine housing and a specific exhaust manifold that pairs the right cylinders to each scroll. In a four-cylinder vehicle, you can then have the first and fourth cylinders powering one scroll, and two and three powering another. This means that there are less pulse overlap and less lag.

Advantages
鈥 More energy is sent to the exhaust turbine, meaning more power.
鈥 A wider RPM range of effective boost is possible based on the different scroll designs.
鈥 More valve overlap is possible without hampering exhaust scavenging, meaning more tuning flexibility.

Disadvantages
鈥 Requires a specific engine layout and exhaust design (eg: I4 and V8 where 2 cylinders can be fed to each scroll of the turbo, at even intervals).
鈥 Cost and complexity versus traditional single turbos.

4. Variable Geometry Turbocharger (VGT)

A variable geometry turbo (VGT) is an expensive and complex power solution that鈥檚 especially prevalent in diesel engines. A VGT has a ring of aerodynamically-shaped vanes in the turbine housing that can alter their area-to-radius ratio to match the revolutions of the engine. At low revs, area-to-radius ratio creates more pressure and velocity to spool up the turbo more effectively. At higher revolutions, the ratio increases to let in more air. The result is a wider boost range and less lag.

Advantages
鈥 Wide, flat torque curve. Effective turbocharging at a very wide RPM range.
鈥 Requires just a single turbo, simplifying a sequential turbo setup into something more compact.

Disadvantages
鈥 Typically only used in diesel applications where exhaust gases are lower so the vanes will not be damaged by heat.
鈥 For gasoline applications, the cost typically keeps them out as exotic metals have to be used in order to maintain reliability. The tech has been used on the Porsche 997, though very few VGT gasoline engines exist as a result of the cost associated.

5. Variable Twin-Scroll Turbocharger

A variable twin-scroll turbo combines a VGT with a twin-scroll setup, so at low revolutions, one of the scrolls is closed completely, forcing all the air into the other. This results in good turbo response and low-end power. As you speed up, a valve opens to allow air into the other scroll (this is a completely variable process, meaning the valve opens in small increments), you get good high-end performance. You get the sort of performance from a single turbo that you鈥檇 normally only be able to get from a twin-turbo set-up.

Advantages
鈥 Significantly cheaper (in theory) than VGTs, thus making an acceptable case for gasoline turbocharging.
鈥 Allows for a wide, flat torque curve.
鈥 More robust in design versus a VGT, depending on the material selection.

Disadvantages
鈥 Cost and complexity versus using a single turbo or traditional twin-scroll.
鈥 The technology has been played with before (eg: quick spool valve) but doesn鈥檛 seem to catch on in the production world. There are likely additional challenges with technology.

6. Electric Turbochargers

A very recent development is the introduction of turbos with electric compressors. An example is BorgWarner鈥檚 booster, which is an electrically powered compressor. The compressor provides an instant boost to the engine until the turbocharger has spooled up enough. A similar version of this can be found in Audi鈥檚 SQ7. With the instant boost, lag becomes a thing of the past, but again, the system is expensive and complex. A compressor needs a motor, which in turn needs to be powered, so this is not a simple system to implement.

Advantages
鈥 By directly connecting an electric motor to the compressor wheel, turbo lag and insufficient exhaust gases can be virtually eliminated by spinning the compressor with electric power when needed.
鈥 By connecting an electric motor to the exhaust turbine, wasted energy can be recovered (as is done in Formula 1).
鈥 A very wide effective RPM range with even torque throughout.

Disadvantages
鈥 Cost and complexity, as you now must account for the electric motor and ensure it remains cool to prevent reliability issues. That goes for the added controllers as well.
鈥 Packaging and weight become an issue, especially with the addition of a battery onboard, which will be necessary to supply sufficient power to the turbo when needed.
鈥 VGTs or twin-scrolls can offer very similar benefits (though not at quite the same level) for a significantly lower cost.

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