Turbo Charger (Vmm)
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Transcript of 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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Supercharging versus turbocharging
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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Supercharging versus turbocharging
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