Chapter 2 - Force Induction System.pptx

1. Chapter 2 – Force
Induction System
By:
Mr. Mohd Faizullah Bin Abd Karim
Mechanical Engineering Department
Ungku Omar Polytechnic
DJA3013 Automotive Technology 2

2. What is Force Induction
System?
• Forced induction is the process of delivering compressed air to the
intake of an internal combustion engine. A forced induction engine
uses a gas compressor to increase the pressure, temperature and
density of the air. An engine without forced induction is considered
a naturally aspirated engine.
• Forced induction is used in the automotive and aviation industry to
increase engine power and efficiency. A forced induction engine is
essentially two compressors in series. The compression stroke of the
engine is the main compression that every engine has. An additional
compressor feeding into the intake of the engine causes forced
induction. A compressor feeding pressure into another greatly
increases the total compression ratio of the entire system. This
intake pressure is called boost. This particularly helps aviation
engines, as they need to operate at higher altitudes with lower air
densities.

3. • Higher compression engines have the benefit of maximizing the amount
of useful energy evolved per unit of fuel. Therefore, the thermal
efficiency of the engine is increased in accordance with the vapour
power cycle analysis of the second law of thermodynamics.[1] The
reason all engines are not higher compression is because for any given
octane, the fuel will prematurely detonate with a higher than normal
compression ratio. This is called preignition, detonation or knock and
can cause severe engine damage. High compression on a naturally
aspirated engine can reach the detonation threshold fairly easily.
However, a forced induction engine can have a higher total compression
without detonation because the air charge can be cooled after the first
stage of compression, using an intercooler.
• One of the primary concerns in internal combustion emissions is a factor
called the NOx fraction, or the amount of nitrogen/oxygen compounds
the engine produces. This level is government regulated for emissions as
commonly seen at inspection stations. High compression causes high
combustion temperatures. High combustion temperatures lead to
higher NOx emissions, thus forced induction can give higher NOx
fractions.

4. Types of compressor
•Turbocharged
•Supercharged

5. Turbocharged
• A turbocharger is a centrifugal compressor driven by the flow of
exhaust gasses.
• A turbocharger relies on the volume and velocity of exhaust gases to
spin (spool) the turbine wheel, which is connected to the compressor
wheel via a common shaft. The boost pressure produced can be
regulated by a system of release valves and electronic controllers. The
chief benefit of a turbocharger is that it consumes less power from the
engine than a supercharger; the main drawback is that engine response
suffers greatly because it takes time for the turbocharger to come up to
speed (spool up). This delay in power delivery is referred to as turbo lag.
Any given turbo design is inherently one of compromise; a smaller turbo
will spool quickly and deliver full boost pressure at low engine speeds,
but boost pressure will suffer at high engine RPM. A larger turbo, on the
other hand, will provide improved high-rev performance at the expense
of low-end response. Other common design issues include limited
turbine lifespan, due to the high exhaust temperatures it must
withstand, and the restrictive effect the turbine has upon exhaust flow.

6. Turbocharger System

7. Operation of turbocharged
system
• The way a turbo works is the exhaust gas coming out of the engine is
pushed through a turbine.
• This turbine is mounted on a shaft, which in turn spins an air
compressor. The compressor draws air in and blows it into the inlet
manifold, and this produces BOOST.
• The whole point of forcing the air/fuel mixture into an engine is to
allow it to burn more fuel and make more power with the same
engine capacity. This can get complicated, as there are several
factors that get in the way of efficency gain. For one thing when you
compress air (with a turbo) it gets hotter. The problem with hotter
air is that it contains less oxygen than cooler air, so there is less
oxygen to help burn extra fuel that’s going into the engine. This is
why many turbocharged cars use “intercooling” of various types, to
cool the pressurised air back down into the engine.
Compressed Air = Hot Air

8. Turbocharged parts
• Turbine/Exhaust Wheel
• The exhaust wheel is the unpainted steel housing where all the exhaust gas is flowed
through on its way through the exhaust system. The wheel of the turbine is spun by
the pressure of the exhaust gases which are of extreme speeds, these help the blades
in the housing turn a shaft, which is connected to the compressor wheel.
•
• Compressor/Impeller
• The compressor housing looks like a reverse of the exhaust version. It contains bare
cats aluminum on the outside with a centrifugal compressor wheel on the inside. This
wheel is shaped differently in turn from the exhaust turbine because whereas the
turbine is designed to generate spinning power, the compressor has to pressurise air.
•
• Shaft Housing
• Between the turbine and compressor is a compact housing which the connecting
shaft, supported by plain bearings and sealed at both ends. Oil is pumped from the
engine into the top pf the turbo. Then a much thicker pipe then allows the oil to drain
back into the sump. The pipe needs to be thicker to provide space for the oil coming
out of the turbo, as it is super heated and becomes very frothy. With technology now
increasing ball-bearing turbos have come on the scene, using a proper ball bearing
instead of a plain brass bearing. This free running nature allows the turbo to spin up
to boosting RPM up to 40% faster than a conventional turbo.
• Here you can see the exhaust housing (dark) and the compressor housing (light).
•

9. • Blow Off Valves
• The purpose of a blow off valve is to release excess pressure from the turbo when driving on
boost and changing gears. As the throttle is closed suddenly, the turbo is blowing air against a
closed throttle body, this causes back pressure and slows down the turbo, so when you accelerate
again the turbo needs to wind up. So the function of the blow-off valve is to vent this excess
pressure and allowing the turbo to keep spinning fast. This helps to maintain reasonably full boost
in the next gear. Some blow off valves release the excess air into the atmosphere, creating the
'psshhtt' sound while others recirculate the air back into the intake manifolding. There are split
feelings on blow off valves, with some people saying they are only needed for high boost
situations, and when you release the accelerator, there is less exhaust flow which will slow the
turbo down anyway, but it is a matter of personal opinion. They do not add any performance to
the engine though.
•
• Wastegates
• The wastegate is the most common form of boost control used in turbo charged cars. The function
of the waste gate is to limit the speed of the turbine, and in turn limiting the amount of boost the
turbo can produce. The way it works is based on the pressure produced by the compressor once
you get to the desired boost level, a valve bypasses exhaust gas around the turbine and stops it
from spinning any faster. As soon as the boost drops below the chosen level again, the valve will
close. The result is that boost rises until you reach full boost and from then on the waste gate
should make boost level off for the rest of the rev range.
•
• Intercooling
• Intercooling is a means of cooling down the pressurised “charge” air from the turbo, before it goes
into the inlet. This is done both to reduce the combustion chamber temperatures, and to improve
the oxygen-density of the charge air. The two main types you’ll see in streetcars are “air-to-air”
and “water-to-water”. Air-to-air system is more simple and efficient. It simply involves running the
charge air through a large heat exchanger (similar to a radiator), so that the heat is transferred to
the air flowing across the outside of the heat exchangers core. The best place to mount the
intercooler is at the front of the car so there is a better chance of cool air flowing through them.
The main disadvantage is that all the piping involved results in a long inlet travel, which can slow
throttle response. The water-to-water type solves the long inlet tract problem, as the charge air
simply goes through a chamber, which contains a liquid-filled heat resistor. Because the inlet
chamber is small it can usually be mounted directly between the turbo and throttle body. The
disadvantages of the system include slightly poorer efficiency and the added complexity of
needing an electric fluid pump that operates constantly.

10. Turbocharged Construction

14. Blow Off Valve (B.O.V)
• A blowoff valve (BOV), dump valve or compressor bypass valve (CBV)
is a pressure release system present in most turbocharged engines.
Its purpose is to prevent compressor surge, and reduce wear on the
turbocharger and engine. These valves relieve the damaging effects
of compressor "surge loading" by allowing the compressed air to
vent to the atmosphere (BOV case), making a distinct hissing sound,
or recirculate into the intake upstream of the compressor inlet (CBV
case).
• A blowoff valve is connected by a vacuum hose to the intake
manifold after the throttle plate. When the throttle is closed, the
relative manifold pressure drops below atmospheric pressure and
the resulting pressure differential operates the blowoff valve's
piston. The excess pressure from the turbocharger is then vented
into the atmosphere or recirculated into the intake upstream of the
compressor inlet.

16. When the throttle plate is open,
the air pressure on both sides of
the piston in the blow-off valve is
equal and the spring keeps the
piston down.
When the throttle is closed, a
vacuum forms in the manifold. This
in combination with the pressurized
air from the turbocharger moves the
piston in the valve up, releasing the
pressure into the inlet of the turbo
(Recirc.) or the atmosphere (BOV).

17. Wastegate
• A wastegate is a valve that diverts exhaust gases away from
the turbine wheel in a turbocharged engine system.
• Diversion of exhaust gases regulates the turbine speed, which
in turn regulates the rotating speed of the compressor. The
primary function of the wastegate is to regulate the maximum
boost pressure in turbocharger systems, to protect the engine
and the turbocharger. One advantage of installing a remote
mount wastegate to a free-float (or non-WG) turbo includes
allowance for a smaller A/R turbine housing, resulting in less
lag time before the turbo begins to spool and create boost

19. Intercooler
• An intercooler is any mechanical device used to cool a fluid,
including liquids or gases, between stages of a multi-stage
heating process, typically a heat exchanger that removes
waste heat in a gas compressor.[1] They are used in many
applications, including air compressors, air conditioners,
refrigerators, and gas turbines, and are widely known in
automotive use as an air-to-air or air-to-liquid cooler for
forced induction (turbocharged or supercharged) internal
combustion engines to improve their volumetric efficiency by
increasing intake air charge density through nearly isobaric
(constant pressure) cooling.

21. Supercharged
• Superchargers use various different types of compressors but are all
powered directly by the rotation of the engine, usually through a belt
drive. The compressor can be centrifugal or a Roots-type for positive
displacement compression. An example of an internal compressor is a
screw-type supercharger or a piston compressor.
• Superchargers have almost no lag time to build pressure because the
compressor is always spinning proportionally to the engine speed. They
are not as common as turbochargers because they use the torque
produced from the engine to operate. This results in some loss in power
and efficiency. A Roots-type supercharger uses paddles on two rotating
drums to push air into the intake.[2] Because it is a positive
displacement device, this compressor has the advantage of producing
the same pressure ratio at any engine speed. A screw-type supercharger
is also a positive displacement device, like a Roots-type supercharger.
Screw-type superchargers are more complex to manufacture than
Roots-type superchargers, but are more efficient to operate, producing
cooler air output. A centrifugal-type supercharger is not a positive
displacement device and will usually have better thermal efficiency than
a Roots-type supercharger. Centrifugal superchargers are also more
compact and easier to use with an intercooler.

22. • A supercharger is an air compressor that increases the
pressure or density of air supplied to an internal combustion
engine. This gives each intake cycle of the engine more
oxygen, letting it burn more fuel and do more work, thus
increasing power.
• Power for the supercharger can be provided mechanically by
means of a belt, gear, shaft, or chain connected to the
engine's crankshaft. When power is provided by a turbine
powered by exhaust gas, a supercharger is known as a
turbosupercharger[1] – typically referred to simply as a
turbocharger or just turbo. Common usage restricts the term
supercharger to mechanically driven units.

23. Types of supercharger
• There are two main types of superchargers defined according
to the method of gas transfer: positive displacement and
dynamic compressors. Positive displacement blowers and
compressors deliver an almost constant level of pressure
increase at all engine speeds (RPM). Dynamic compressors do
not deliver pressure at low speeds; above a threshold speed,
pressure increases with engine speed
• Major types of positive-displacement pumps include:
 Roots
 Lysholm twin-screw
 Sliding vane
 Scroll-type supercharger, also known as the G-Lader

24. • 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

25. Roots supercharger
Roots type supercharger on AMC V8 engine for dragstrip racing

26. Twin screw supercharger
Lysholm screw rotors with complex shape of each rotor, which must
run at high speed and with close tolerances. This makes this type of
supercharger expensive.

27. Construction of Supercharger

28. • The Basics
• An ordinary four-stroke engine dedicates one stroke to the process of air intake. There are three steps
in this process:
• The piston moves down.
• This creates a vacuum.
• Air at atmospheric pressure is sucked into the combustion chamber.
• Once air is drawn into the engine, it must be combined with fuel to form the charge — a packet of
potential energy that can be turned into useful kinetic energy through a chemical reaction known as
combustion. The spark plug initiates this chemical reaction by igniting the charge. As the fuel
undergoes oxidation, a great deal of energy is released. The force of this explosion, concentrated
above the cylinder head, drives the piston down and creates a reciprocating motion that is eventually
transferred to the wheels.
• Getting more fuel into the charge would make for a more powerful explosion. But you can’t simply
pump more fuel into the engine because an exact amount of oxygen is required to burn a given
amount of fuel. This chemically correct mixture — 14 parts air to one part fuel — is essential for an
engine to operate efficiently. The bottom line: To put in more fuel, you have to put in more air.
• That’s the job of the supercharger. Superchargers increase intake by compressing air above
atmospheric pressure, without creating a vacuum. This forces more air into the engine, providing a
“boost.” With the additional air in the boost, more fuel can be added to the charge, and the power of
the engine is increased. Supercharging adds an average of 46 percent more horsepower and 31
percent 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 it can
operate optimally.
• Unlike turbochargers, which use the exhaust gases created by combustion to power the compressor,
superchargers draw their power directly from the crankshaft. Most are driven by an accessory belt,
which wraps around a pulley that is connected to a drive gear. The drive gear, in turn, rotates the
compressor gear. The rotor of the compressor can come in various designs, but its job is to draw air in,
squeeze the air into a smaller space and discharge it into the intake manifold.

29. • To pressurize the air, a supercharger must spin rapidly —
more rapidly than the engine itself. 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 rotations per minute (RPM).
• A compressor spinning at 50,000 RPM translates to a boost of
about six to nine pounds per square inch (psi). That’s six to
nine additional psi over the atmospheric pressure at a
particular elevation. Atmospheric pressure at sea level is 14.7
psi, so a typical boost from a supercharger places about 50
percent more air into the engine.
• As the air is compressed, it gets hotter, which means that it
loses its density and can not expand as much during the
explosion. This means that it can’t create as much power
when it’s ignited by the spark plug. For a supercharger to
work at peak efficiency, the compressed air exiting the
discharge unit must be cooled before it enters the intake
manifold. The intercooler is responsible for this cooling
process. Intercoolers come in two basic designs: air-to-air
intercoolers and air-to-water intercoolers. Both work just like
a radiator, with cooler air or water sent through a system of
pipes or tubes. As the hot air exiting the supercharger
encounters the cooler pipes, it also cools down. The
reduction in air temperature increases the density of the air,
which makes for a denser charge entering the combustion
chamber.
ProCharger D1SC centrifugal
supercharger

30. • Root Superchargers
• There are three types of superchargers: Roots, twin-
screw and centrifugal. The main difference is how they
move air to the intake manifold of the engine. Roots
and twin-screw superchargers use different types of
meshing lobes, and a centrifugal supercharger uses an
impeller, which draws air in. Although all of these
designs provide a boost, they differ considerably in
their efficiency. Each type of supercharger is available
in different sizes, depending on whether you just want
to give your car a boost or compete in a race.
• The Roots supercharger is the oldest design. Philander
and Francis Roots patented the design in 1860 as a
machine that would help ventilate mine shafts. In
1900, Gottleib Daimler included a Roots supercharger
in a car engine.
• As the meshing lobes spin, air trapped in the pockets
between the lobes is carried between the fill side and
the discharge side. Large quantities of air move into
the intake manifold and “stack up” to create positive
pressure. For this reason, Roots superchargers are
really nothing more than air blowers, and the term
“blower” is still often used to describe all
superchargers.
• Roots superchargers are usually large and sit on top of
the engine. They are popular in muscle cars and hot
rods because they stick out of the hood of the car.
However, they are the least efficient supercharger for
two reasons: They add more weight to the vehicle and
they move air in discrete bursts instead of in a smooth
and continuous flow.

31. • Twin-screw Superchargers
• A twin-screw supercharger operates by pulling
air through a pair of meshing lobes that
resemble a set of worm gears. Like the Roots
supercharger, the air inside a twin-screw
supercharger is trapped in pockets created by
the rotor lobes. But a twin-screw
supercharger compresses the air inside the
rotor housing. That’s because the rotors have
a conical taper, which means the air pockets
decrease in size as air moves from the fill side
to the discharge side. As the air pockets
shrink, the air is squeezed into a smaller
space.
• This makes twin-screw superchargers more
efficient, but they cost more because the
screw-type rotors require more precision in
the manufacturing process. Some types of
twin-screw superchargers sit above the engine
like the Roots supercharger. They also make a
lot of noise. The compressed air exiting the
discharge outlet creates a whine or whistle
that must be subdued with noise suppression
techniques.

32. • Centrifugal Superchargers
• A centrifugal supercharger powers an impeller — a
device similar to a rotor — at very high speeds to
quickly draw air into a small compressor housing.
Impeller speeds can reach 50,000 to 60,000 RPM. As
the air is drawn in at the hub of the impeller,
centrifugal force causes it to radiate outward. The air
leaves the impeller at high speed, but low pressure. A
diffuser — a set of stationary vanes that surround the
impeller — converts the high-speed, low-pressure air
to low-speed, high-pressure air. Air molecules slow
down when they hit the vanes, which reduces the
velocity of the airflow and increases pressure.
• Centrifugal superchargers are the most efficient and
the most common of all forced induction systems.
They are small, lightweight and attach to the front of
the engine instead of the top. They also make a
distinctive whine as the engine revs up — a quality that
may turn heads out on the street.
• Any of these superchargers can be added to a vehicle
as an after-market enhancement. Several companies
offer kits that come with all of the parts necessary to
install a supercharger as a do-it-yourself project. In the
world of funny cars and fuel racers, such customization
is an integral part of the sport. Several auto
manufacturers also include superchargers in their
production models.

33. Superchargers Advantages
• The biggest advantage of having a supercharger is the increased horsepower. Attach a
supercharger to an otherwise normal car or truck, and it will behave like a vehicle with a
larger, more powerful engine.
• But what if someone is trying to decide between a supercharger and a turbocharger? This
question is hotly debated by auto engineers and car enthusiasts, but in general,
superchargers offer a few advantages over turbochargers.
• Superchargers do not suffer lag — a term used to describe how much time passes between
the driver depressing the gas pedal and the engine’s response. Turbochargers suffer from
lag because it takes a few moments before the exhaust gases reach a velocity that is
sufficient to drive the impeller/turbine. Superchargers have no lag time because they are
driven directly by the crankshaft. Certain superchargers are more efficient at lower RPM,
while others are more efficient at higher RPM. Roots and twin-screw superchargers, for
example, provide more power at lower RPM. Centrifugal superchargers, which become
more efficient as the impeller spins faster, provide more power at higher RPM.
• Installing a turbocharger requires extensive modification of the exhaust system, but
superchargers can be bolted to the top or side of the engine. That makes them cheaper to
install and easier to service and maintain.

34. • Finally, no special shutdown procedure is
required with superchargers. Because they are
not lubricated by engine oil, they can be shut
down normally. Turbochargers must idle for
about 30 seconds or so prior to shutdown so
the lubricating oil has a chance to cool down.
With that said, a good warm-up is important
for superchargers, as they work most
efficiently at normal operating temperatures.
• Superchargers are common additions to the
internal combustion engines of airplanes. This
makes sense when you consider that airplanes
spend most of their time at high altitudes,
where significantly less oxygen is available for
combustion. With the introduction of
superchargers, airplanes were able to fly
higher without losing engine performance.
• Superchargers used with aircraft engines work
just like those found in cars. They draw their
power directly from the engine and use a
compressor to blow pressurized air into the
combustion chamber. The illustration above
shows the basic setup for a supercharged
airplane.
The basic setup for an airplane with a
centrifugal supercharger, or compressor.

35. Superchargers Disadvantages
• The biggest disadvantage of superchargers is also their defining
characteristic: Because the crankshaft drives them, they must steal
some of the engine’s horsepower. A supercharger can consume as
much as 20 percent of an engine’s total power output. But because a
supercharger can generate as much as 46 percent additional
horsepower, most think the trade-off is worth it.
• Supercharging puts an added strain on the engine, which needs to be
strong to handle the extra boost and bigger explosions. Most
manufacturers account for this by specifying heavy-duty components
when they design an engine intended for supercharged use. This makes
the vehicle more expensive. Superchargers also cost more to maintain,
and most manufacturers suggest high-octane premium-grade gas.
• Despite their disadvantages, superchargers are still the most cost-
effective way to increase horsepower. Superchargers can result in power
increases of 50 to 100 percent, making them great for racing, towing
heavy loads or just adding excitement to the typical driving experience.