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Unit 7
Title: Turbo charging and Supercharging
General objective:
To understand the basic knowledge of supercharging and
operation of a turbocharger
Specific objectives:
At the end of this unit you should be able to:
1. state the definition of supercharging.
2. identify the parts and operation of the mechanical root-
type blower.
3. identify the parts and operation of a turbocharger.
4. draw a graph of turbo charging performance.

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Input
This section introduces the subject matter that you are going to learn.
7.0 Introduction
In this unit we will discuss and study the evolution of automobile
technology on how to increase the power output of a car. Many automobile
engines today use superchargers to increase the amount of air going into the
engine. Supercharging also helps to increase the horsepower characteristics of
the engine. The most common type of supercharger is called a turbocharger. In
addition, in some racing engines, mechanical roots-type blowers are used to
increase the amount of air going into the engine. Unit 7 introduces the principle
of turbocharging and explains the basic operations of the mechanical blower.
7.1 Why Supercharging is being use in automobile industry today?
With the increase use of fuel injection and computer controlled
combustion systems, turbocharging have become common components in
gasoline and diesel engines. In the past, only large engines had turbochargers.
Today, with the precise control afforded by computers, turbochargers are making
smaller engines more efficient and capable of producing more power. In this unit
we will look at volume efficiency, factor of volume efficiency, head efficiency,
turbochargers and supercharging.

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7.2 Volume efficiency
Another way to measure the efficiency of an engine is related to how
easily air flows in and out of the engine. As the piston starts moving down on the
intake stroke, air and fuel flow into the engine. As the engine increases in
revolutions per minute, the intake valves are not opened for long. This means
that the amount of air per time period may be less. Volume efficiency measures
this condition. The formula for measuring volume efficiency is ;
Volume efficiency = actual air used X 100
Maximum air possible
7.1 Example
One engine speed 40 cubic inches of fuel mixture enters the cylinder but to
completely fill the cylinder of 55 cubic,it needs volume efficiency; calculate the
volume efficiency.
As we know the formula is ;
Volume efficiency = actual air used X 100
Maximum air possible
40
= × 100
55
= 90 %.

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7.3 Factors of volume efficiency.
The following are other factors that affect volume efficiency .
1. exhaust restriction.
2. air cleaner restriction.
3. carbon deposits on cylinder and valve.
4. shape and design of valve.
5. amount of restriction in the intake and exhaust port by curve.
6. shape of the intake exhausts manifolds.
7. temperature of the air.
7.4 Supercharging
What is supercharging?. This is the process of forcing air into an engine
cylinder with an air pump. The forced air can come from a blower or
turbocharger.
The operation is, when the piston moves downward on the intake stroke, a
vacuum is created. This vacuum causes air and fuel to be drawn into the engine.
This process is called a naturally aspirated or normally aspirated engine. The
amount of air that enters the engine is based on atmospheric pressure. Most
engines are considered to be naturally aspirated. However, in smaller engines,
there may be a lack of power for certain driving conditions.
To overcome this lack of power, an engine can be supercharged.
Supercharging an engine means to deliver a greater volume of air to the
cylinders than the air delivered from the suction of the pistons alone. The engine
is not naturally aspirated, it is supercharged. When more air is forced into
cylinders, there must be a corresponding increase in fuel to maintain a 14.7 to 1
air-fuel ratio. If both these conditions occur, then a great increase in power will
occur. In some cases, this system can increase 50% more power by
supercharging an engine.

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7.4.1 Parts and operation
Supercharging have two important parts and they are:
7.4.1 Blower.
Either a blower or turbocharger can be used to supercharge an engine. A
blower is a mechanical air pump that forces air into the engine. It is driven
by a set of gears or belts from the crankshaft. It produces a substantial
friction loss on the engine because it requires horsepower from the engine
to operate.
Figure 7.3.1: Blower
7.4.2 : Root-Type blower
There are several types of mechanical blower which can be used on
engines. One most common blower is named after its inventor, the root-
type blower. (Figure 7.4.2), the rotors act like a positive displacement air
pump, drawing in huge amount of air, and forcing this air into the intake
manifold.

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Figure : 7.4.2 : The root –type blower

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Input
This section introduces the subject matter that you are going to learn.
7.5 Turbo charging principles
A turbocharging is a device that uses exhaust gas, rather than engine
power to turn an air pump or compressor. The air pump then forces an increased
amount of air into the cylinders. Both diesel and gasoline engines in the
automotive market use turbochargers. Figure 7.5.1a,b shows a typical
schematic of air and exhaust in a turbocharged engine and Figure 7.5.2 is a
complete turbo charging unit for the automobile. High velocity exhaust gases
are released from the exhaust part. From here they pass through a turbine
driven pump.
Here the exhaust gas causes the exhaust turbine to turn rapidly. The
exhaust turbine causes the intake compressor to turn rapidly too. As the
compressor turbine turns, it draws in a large amount of fresh air. The intake of air
is pressurized and forced into the intake port. The increase in pressure in the
intake manifold is called boost. Boost may produce pressure in the intake
manifold of about 6 to 10 psi or more, depending on the manufacturer.
7.5.1 Turbocharger contruction.
Figure 7.5.3 shows a complete turbocharger. The shafts on the intake and
xhaust turbines are connected together. The intake turbine acts as fan,
causing the shaft to turn. Housing surrounds both turbines. Flanges are
attached to the housing for mounting

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Figure 7.5.1a: Blower housing
Figure 7.5.1b: A turbocharging uses the exhaust gases to turn
an air pump or Compressor. The compressor
turbine forces extra air into the engine.

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Figure 7.5.2: A complete turbocharger unit for an automobile.

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Figure 7.5.3: A cutaway view of a turbocharger.
Figure 7.5.4: Turbocharger located on the side the engine

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Graph 7.1 : Graph of turbo charging performance
Legend of graph;
Normal aspirated engine
Turbocharged engine

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7.6 Graph of turbo charging performance
Graph 7.1 shows a comparison between a turbocharged and
normally aspirated engine. Note that both the torque and horsepower have been
increased at all RPM. For example, at 5,000 RPM the normally aspirated engine
produces about 80 hp. At this RPM, the turbocharged engine can produce
about 140 hp.

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Activity 7B
The questions in this section test your understanding of the subject
matter. You have to complete this section by following the instructions
carefully.
7.1 Draw the Graph of turbo charging performance
7.2 Label the components in Figure A.7.2 below;
a f
g
b
c
j
h
d
i
e
Figure A.7.2 : Turbocharger
Check your answers…….

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Self –Assessment
Self-assessment evaluates your understanding of each unit.
Question 7-1.
List 7 factors of volume efficiency
Question 7-2.
Define supercharger
Question 7-3.
Explain the principle of turbo charging
Question 7-4.
Explain the out put graph of turbo charging performance
Congratulations!!!!
If your answers are correct you can proceed to the
next unit. Good Luck!.