turbo charger (vmm)

7/31/2019 Turbo Charger (Vmm)

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TURBOCHARGING & SUPERCHARGING

V.M.MURUGESAN

Faculty

Department of Automobile Engineering

PSG College of TechnologyCoimbatore


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TURBO CHARGER

The turbocharger is a device which is used to take the energy of one fluidsystem and put it into another fluid system.

In the specific application of the automobile, turbochargers are used to

recover heat from engine exhaust gases, and use their energy to compress

air to be taken into the engine.

Using a compressor, such as a turbocharger, to increase the air intake of

engines, and thus their power capabilities is called Forced Induction.

Modern turbochargers come in a wide range of sizes custom tailored to

provide maximum efficiency in certain areas such as acceleration and

efficiency in smaller turbochargers, maximum power output (hp) in larger

turbochargers.


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TURBO CHARGER


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Inside the turbine housing, which is usually made of steel or a

similar composite.

Turbines are generally made of steel, however some low RPM

turbochargers use ceramic turbines in an attempt to decrease

the inertia weight of the turbine.

The Waste Gate : A pressure sensitive valve, and a boost

controller, an electric waste gate controller, the pressure in the

turbocharger can be kept under control by allowing gases to

bypass the turbines when pressures are to high, allowing the

turbines to slow down to an acceptable speed.


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The turbine is connected to a shaft with what are called thrust bearings.

Since turbines hit such high speeds, eitherfluid bearings, or extremely high

precision ball bearing must be used to ensure safety, performance and

reliability.

The shaft connects the turbine wheel to the compressor wheel.

The compressor wheel is encased by the compressor housing, which like

the turbine housing, is snail-like in shape.

Here it is connected to the compressor wheel is a device which sucks in

air and expels it into the compressor housing. It is located in the center of

the housing, and for maximum intake, directly facing the air intake.

On the top of the compressor housing, or the end of its coil, is the

compressor outlet.


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TURBO CHARGER


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The energy converted in a turbocharged can raise the power

output of a street legal automobile around 30%-40%.

Possibly one of the best points of the turbocharger is the fact that

the faster the engine works, the harder the turbocharger works,

meaning that until the turbocharger hits its peak RPM, the

turbocharger delivers an extremely self sufficient method of adding

boost: added combustion pressure which raises the engines

cylindrical pressure to one higher than that of normal atmospheric

pressure.

The intense rise in pressure is what causes the sizeable rise in

engine power output observed when Forced Induction engines are

compared to Naturally Aspired, non-turbocharged, engines.


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How the Turbocharger Increases Automobile

Engine Performance To increase the power created in an engine,

(1) Increase the rate at which air is burned and expelled.

This can be done by raising an engines displacement (the volume of the

engines total combustion space), which calls for bigger engines and

more gasoline consumption,

(2) By adding forced induction: the use of a compressor to create

pressures in the engine cylinder higher than that of the atmosphere.

The raise in pressure above atmospheric pressure is called the

turbochargers boost, and is measured in pounds per square inch or

PSI.


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Turbine Lag

As the exhaust gases flow through the turbine housing, the turbine

wheel is spun faster and faster.

The turbine also pushes the exhaust fumes out through the turbine

exhaust outlet, which connects to the automobiles exhaust system.

Since the speed at which the turbine spins is directly proportional

to the pressure of the compressed air being made, it is important

that turbines reach large RPMs in a short period of time.

The time it takes for the turbine to reach a speed which will create

boost (the turbochargers boost threshold) is called the

turbochargerslag.


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Reducing Turbine Lag

Lag can be reduced in a few ways, the simplest being the

use of a smaller turbine.

Smaller specifications, means less inertia weight and

therefore less lag. Other methods include using

replacements for steel alloys for turbines such as

ceramics, which are extremely light, yet relatively fragile

and therefore not safe at extremely high RPMs.


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What is Knocking?

Abnormal combustion, more commonly known as knock or detonation,has been the limiting factor in internal combustion engine power

generation .

Knocking (also called knock, detonation, spark knock, pinging or

pinking) in spark-ignition internal combustion engines occurs when

combustion of the air/fuel mixture in the cylinder starts off correctly in

response to ignition by the spark plug, but one or more pockets of air/fuel

mixture explode outside the envelope of the normal combustion front.

The fuel-air charge is meant to be ignited by the spark plug only, and at a

precise time in the piston's stroke cycle.

The shock wave creates the characteristic metallic "pinging" sound, and

c linder ressure increases dramaticall .


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The Waste Gate

Turbochargers are so powerful that they can actually raise temperatures

enough to cause an engine destructing phenomenon called engine

knock.

This is where the temperature is so high in the combustion chamber that

the intake gases ignite before the spark plug ignites, famous for theknocking sound it creates.

To avoid this problem, the waste gate was developed; a device which

allows exhaust gases to bypass the turbine if combustion pressure is

getting to high.

This is usually regulated with a boost controller, a device which allows the

driver, or manufacturer, to control at exactly what pressure the waste gate

opens.


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The Shaft, Bearings, Lubrication System and

Cooling System

In the center of the turbine wheel is a bearing casing

containing either fluid bearings or high precision ball

bearings.

This casing is attached to the turbochargers shaft.Since

turbines can reach RPMs of up to 200,000, these bearings

must be extremely durable at high pressures, speeds, and

temperatures.

The Shaft connects to the compressor wheel which is in the

compressor housing.


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In between the turbine and compressor

housings is the turbochargers lubrication and

cooling system.

This is supplied by oil and sometimes

coolant inlets, which takes oil and coolant

from the engines reservoirs and spreads

them through the turbocharger through the

shaft.


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The Compressor When the turbine rotates, and in turn rotates the shaft, the

compressor wheel is rotated as well.

This wheel was designed to suck air in from the adjacent air

intake, and disperse it into the compressor housing where the air

is compressed and directed towards the turbochargers air

outtake.

The compressor is very similar to the turbine, except the turbine

takes heat to make kinetic energy, and the compressor uses that

kinetic energy to compress external air into pressurized air which

can be inducted into the engines air intake.


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The Intercooler and Induction of Air

Air does not go directly back into the engine.

It is sent through an intercooler.

The intercooler is placed in the front of the car where it is in

contact with fresh air.

A fan inside the intercooler sucks the cool air in and

disperses it over numerous pipelines containing the

pressurized air, cooling it, making it denser and more potent.

Once the air has cooled down it is forced into the engines

combustion chamber, causing a much higher internal

pressure than found in the atmosphere.


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SUPERCHARGING

To increase the quantity of air aspired beyond what is

taken in at full throttle and maximum engine speed.

For this the air is taken into the cylinder after it is

compressed by a blower or compressor and forced intothe engine cylinder.

The compressor is blown using power from the

crankshaft, as stored in the flywheel.

To pressurize the air, a supercharger must spin rapidly --

more rapidly than the engine itself.


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Making the drive gear larger than the compressor gear

causes the compressor to spin faster.

Superchargers can spin at speeds as high as 50,000 to

65,000 rpm.

Supercharging adds more horsepower and more torque.

In high-altitude situations, where engine performance

deteriorates because the air has low density and pressure, a

supercharger delivers higher-pressure air to the engine so itcan operate optimally.


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supercharger

A supercharger is an air compressor used for forced

induction of an internal combustion engine.

The greater mass flow-rate provides more oxygen to

support combustion than would be available in a

naturally-aspirated engine, which allows more fuel to be

burned and more work to be done per cycle, increasing

the power output of the engine.

Power for the unit can come mechanically by a belt, gear,

shaft, or chain connected to the engine's crankshaft.


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Types of supercharger

There are two main types of superchargers defined

according to the method of compression:

(1) positive displacement

It delivers a fairly constant level of pressure increase atall engine speeds (RPM).

Its importance decreases at higher speeds.Types of

pumps used are

Roots . Lysholm screw

Sliding vane, Scroll-type supercharger, also known

as the G-Lader


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Dynamic compressors

It delivers increasing pressure with increasing

engine speed.

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

Pressure wave supercharger


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Supercharger drive types

Superchargers are further defined according to

their method of drive (mechanical or turbine).

Mechanical Belt (V-belt, Synchronous belt, Flat belt)

Direct drive

Gear drive

Chain drive


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Supercharging versus turbocharging

Positive-displacement 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 for which engine response and power are

more important than any other consideration, such as top-

fuel dragsters and vehicles used in tractor pulling

competitions, positive-displacement superchargers are very

common.


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The thermal efficiency, or fraction of the fuel/air energy that is

converted to output power, is less with a mechanically-driven

supercharger than with a turbocharger, because turbochargers

are using energy from the exhaust gases that would normally be

wasted.

For this reason, both the economy and the power of a

turbocharged engine are usually better than with superchargers.

The main advantage of an engine with a mechanically-driven

supercharger is better throttle response, as well as the ability to

reach full-boost pressure instantaneously.


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With the latest turbocharging technology, throttle response on

turbocharged cars is nearly as good as with mechanically-

powered superchargers, but the existing lag time is still

considered a major drawback, especially considering that the vast

majority of mechanically-driven superchargers are now driven off

clutched pulleys, much like an air compressor.

Roots blowers tend to be 4050% efficient at high boost levels.

Centrifugal superchargers are 7085% efficient.

Lysholm-style blowers can be nearly as efficient as their

centrifugal counterparts over a narrow range of load/speed/boost,

for which the system must be specifically designed

turbo charger (vmm)

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