turbocharging

TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /1

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.


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.


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

= 105540

× 0

= 90 %.


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.


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.


Figure : 7.4.2 : The root –type blower


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


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.


Figure 7.5.2: A complete turbocharger unit for an automobile.


Figure 7.5.3: A cutaway view of a turbocharger.

Figure 7.5.4: Turbocharger located on the side the engine


Graph 7.1 : Graph of turbo charging performance

Legend of graph; Normal aspirated engine Turbocharged engine


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.


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;

Figure A.7.2 : Turbocharger Check your answers…….

a

c

d h

g

f

i e

b

j


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!.

turbocharging

Automotive

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