Thermodynamics-II
Lab Manual
SUBMITTED TO:
Engr. Yasir Hussain Siddiqui
SUBMITTED BY:
MECHANICAL ENGINEERING DEPARTMENT
Khwaja Fareed University of Engineering
& Information Technology,
Rahim Yar Khan
List of Experiments
Sr. No.
Lab Sessions
1.
To Draw the Layout of Thermodynamics Laboratory
2.
To learn different terms and properties of a Thermodynamics system
3.
To determine the pressure with a bourdon tube pressure gauge
4.
To determine the pressure with different pressure measuring devices and
then compare the measured values
5.
To perform the analysis on a single stage centrifugal compressor
6.
To demonstrate the functions of various parts of a 4 stroke Diesel Engine
using 4 stroke Diesel Engine Demonstration Model
7.
To demonstrate the working cycle of a 4 stroke Diesel Engine using 4 stroke
Diesel Engine Demonstration Model
8.
To demonstrate the functions of various parts of a 4 stroke Petrol Engine
using 4 stroke Petrol Engine Demonstration Model
9.
To demonstrate the working cycle of a 4 stroke Petrol Engine using 4 stroke
Petrol Engine Demonstration Model
10.
To demonstrate the functions of various parts of a 2 stroke Petrol Engine
using 2 stroke petrol engine demonstration model
11.
To learn about the working cycle of a 2 stroke Petrol Engine using 2 stroke
petrol engine demonstration model
12.
To study about the working of a Turbo Jet Engine using Turbo Jet Engine
demonstration model
13.
To determine efficiency of a convergent nozzle and to Jet speed at which air
leaves the nozzle
Signature
Lab Session No. 01
Objective:
To draw the layout of Thermodynamics laboratory
Lab Session No: 02
Objective:
To learn different terms and properties of a Thermodynamics system
Thermodynamics:
It is the branch of engineering-sciences which deals with the energies associated with the
gases and vapours and also conversion of these energies into mechanical work.
Thermodynamics System:
It is the area or space in which some thermodynamics process takes place. Each
thermodynamics system has some boundaries in which a thermodynamics process takes
place. Anything outside the boundary is called its surroundings.
Types of Thermodynamics System:
There are three main types of Thermodynamics system;
1) Closed System
2) Open System
3) Isolated System
1) Closed System
A system of fixed mass is known as a closed system. In this system, the working substance
cannot cross the boundary of the system. Heat or work may cross he boundary of system.
2) Open System:
A system in which working substance crosses the boundary of the system is called an open
system. In this system, heat and work may also cross the boundary of the system.
3) Isolated System:
A system of fixed mass and no heat or work cross the boundary of the system is called an
isolated system.
Thermodynamics Properties:
Thermodynamics properties are divided into two types;
1) Extensive Properties
2) Intensive Properties
1) Extensive Properties:
These are the properties of a Thermodynamics system whose sum for the individual parts of a
Thermodynamics system is equal to the properties of the whole system. These include mass,
volume and total energy etc.
2) Intensive Properties:
These are the properties of a Thermodynamics system whose sum for the individual parts of a
Thermodynamics system is not equal to the properties of the whole system. These include
pressure, temperature, density etc.
Laws of Thermodynamics:
Laws of thermodynamics are classified as;
1) Zeroth Law of Thermodynamics
2) 1st Law of Thermodynamics
3) 2nd Law of Thermodynamics
4) 3rd Law of Thermodynamics
1) Zeroth Law of Thermodynamics:
It states that;
“When two bodies are in thermal equilibrium with a third body, they are also in thermal
equilibrium with each other”.
Thermal equilibrium:
When a hot body is connected to a cold body, then heat flows from hot body to a cold body at
faster rate. The rate of heat transfer decreases with the time. The hot body begins to cool and
the cold body begins to hot. A time reaches when no heat flows from hot body to cold body
and the temperature of both the bodies becomes equal. This condition in which no heat flows
from hot body to cold body and temperature of both bodies becomes equal is named as
thermal equilibrium.
1st Law of Thermodynamics:
It states that;
“Energy can neither be created nor be destroyed, but it only changes from one from to
another form”.
It can also be stated as; “Heat and work are convertible quantities”.
When a gas in a container is heated, then this heat will be converted into the internal energy
and the work done.
If
Q = Heat supplied to the system
W = Work done by the expansion of the gas
E = Internal energy of the gas
So, according to 1st law of Thermodynamics;
Q = W+E
The phenomenon of the expansion of gas is shown in the figure below;
2nd law of Thermodynamics:
It states that;
“There is a limit on the amount of mechanical work that can be obtained from a given amount
of heat”.
It can also be stated as;
“It is not possible for a self-acting machine to transfer heat from cold body to hot body,
without the aid of external energy”.
It can also be stated as;
“It is not possible for an engine, to convert whole heat into work”.
This law is also known as “law of degradation of energy”.
3rd law of Thermodynamics:
It states that;
“The entropy of a system at absolute zero is exactly zero”.
Perfect Gas:
A state of a substance whose evaporation from its liquid state is complete is known as a
perfect gas. In other words, superheated vapours are known as perfect gas.
Vapours:
A state of a substance whose evaporation from its liquid state is partial i.e. it contains some
suspended liquid particles in it is called vapour.
Laws of perfect Gases:
Following are the laws of perfect gases;
Boyle’s Law:
It states that;
“The absolute pressure of a given mass of a perfect gas is inversely proportional to its volume
at constant temperature”.
Mathematically;
P α 1/V
(At Constant T)
P = Constant/V
PV = Constant
Where;
P = Absolute pressure of the gas
T = Absolute temperature of the gas
V = Volume of the gas
Charles’s Law:
It states that;
“The volume of the given mass of a perfect gas is directly proportional to its absolute
temperature at constant pressure”.
Mathematically;
Vα T
(At constant P)
V = Constant*T
V/T = Constant
Where;
P = Absolute pressure of the gas
T = Absolute temperature of the gas
V = Volume of the gas
General Gas Equation:
According to Boyle’s Law
Vα1/P (Keeping T constant)________________ (1)
According to Charles’s Law
VαT (Keeping P constant)_________________ (2)
Combining (1) and (2)
VαT/P
V = Constant*T/P
PV = Constant*T
(for unit mass of the gas)
PV = Constant *m*T (for mass ‘m’ of the gas)
PV = m*R*T
Where R = General Gas constant
For atmospheric air, the value of R = 287J/Kg-K.
Avogadro’s Law:
It states that;
“Equal volumes of all the gases at same temperature and pressure contain equal number of
molecules”.
Joule’s Law:
It states that;
“The change in internal energy of a perfect gas is directly proportional to the change of
temperature”.
Mathematically;
dU α dT
dU = Constant*dT
( for unit mass of the gas)
dU = m* C*dT
(for mass ‘m’ of the gas)
Where;
dU = Change in Internal Energy of the gas
dT = Change in absolute temperature of the gas
C = Constant of proportionality known as specific heat of the gas
Specific Heat:
The amount of heat required to increase the temperature of unit mass of a gas through 1 0C is
known as specific heat of a gas.
Molar Specific Heat:
The amount of heat required to increase the temperature of one mole of a gas through 1 0C is
known as molar specific heat of a gas.
Specific Heat at Constant Pressure:
The amount of heat required to increase the temperature of unit mass of a gas through 10C at
constant pressure is known as specific heat of a gas at constant pressure. It is denoted by ‘Cp’.
Specific Heat at Constant Volume:
The amount of heat required to increase the temperature of unit mass of a gas through 1 0C at
constant volume is known as specific heat of a gas at constant volume. It is denoted by ‘Cv’.
Adiabatic Index:
It is the ratio of Cp and Cv. It is denoted by ‘γ’.
γ = Cp / Cv
Its value is 1.4 for air.
Also
Cp - Cv = R
Where R = General Gas Constant
Lab Session No: 03
Objective:
To determine the pressure with a Bourdon tube pressure gauge
Apparatus:
Dead Weight Tester
Figure:
Piston
Weights
Pressure gauge
Valve 2
Valve 1
Cylinder
Procedure:
1. First of all remove the piston from the unit, open the valve V2 and close the valve V1.
2. Fill the cylinder with oil and close the valve V2.
3. Now place the piston back at its position and with both valves V1 and V2 closed.
4. Apply weights on the piston and calculate the theoretical value of pressure.
5. This applied pressure will be transferred to the gauge through oil.
6. Note the experimental value of the pressure from gauge reading.
7. Repeat the same procedure by decreasing the weights.
8. Compare the theoretical and experimental values of the pressures and draw the graphs
between the gauge pressure (Y-axis) and true pressure (X-axis). Also draw the graph between
% age error (Y-Axis) and Gauge Pressure (X-axis).
Observations & Calculations:
Diameter of the piston = d = 0.018m
Mass of the piston = m = 0.5 Kg.
Area (m2) = A = [π/4]*d2
Total Weight Applied (kg) = M = mass of the piston (kg) + Mass applied (Kg)
Total Force (N) = F = Mg
Where
g = 9.81m/s2
Theoretical (True) Pressure (N/m2) = P = F/A
Sr.
No.
Force
Applied
‘F’
(N)
True
Pressure
P=F/A
(N/m2)
Gauge Pressure
‘G’
(N/m2)
Increasing
Order
1.
2.
3.
4.
5.
Specimen Calculations:
Decreasing
Order
Percentage Error
E=[(G-P)/G]*100
(% age)
Mean
Comments:
Lab Session No: 04
Objective:
To determine the pressure with different pressure measuring devices and then compare the
measured values
Apparatus:
Humidity (Pressure Measurement Bench)
Figure:
Procedure:
1. First of all attach compressor with the pressure regulator and pressure regulator to the
desired gauges.
2. Fill up the U-tube manometer and inclined manometer up to half of the height of the tube
with water.
3. For comparison of pressures, a three way valve is used. One side of valve is attached to the
pressure regulator output and other two to the desired gauges.
4. Keep on increasing the pressure by pressure regulator and note down the pressure readings
from respective gauges and compare these values with each other.
Observations & Calculations:
U-tube manometer pressure will be given by the formula given below;
Pgauge = Punknown –Patm = ρgh;
Where;
ρ (Kg/m3) = Density of liquid in tube
g (m/sec2) = Acceleration due to gravity = 9.81
h (m) = Difference between the heights of the liquid in each limb
The pressure measured by the inclined manometer is given by the formula given below;
Pgauge = Punknown –Patm = ρgd ( A2/A1 + sinϴ)
Where;
Ρ (kg/m3) =Density of liquid in tube
g (m/sec2) = Acceleration due to gravity = 9.81
d (m) = distance of the liquid moved along the inclined limb
A2 (m2) = Cross sectional area of the reservoir = π/4*d22
d2 (m) = Diameter of the reservoir (Vertical limb)
A1 (m2) = Cross sectional area the inclined limb = π/4*d12
d1 (m) = Diameter of the inclined limb
ϴ = Angle of the inclined from the horizontal = 45o (Given)
As d1 = d2, So; A1 = A2; therefore; A2/A1 = 1;
So;
Pgauge = Punknown –Patm = ρgd ( 1 + sinϴ)
Sr. No.
1.
2.
3.
4.
5.
Bourdon Tube
Pressure Gauge
(N/m2)
Piezoelectric
Pressure Sensor
(N/m2)
Inclined Tube
Manometer
(N/m2)
U-tube
Manometer
(N/m2)
Specimen Calculations:
Comments:
Lab Session No: 05
Objective:
To perform the analysis on a single stage centrifugal compressor
Apparatus:
Single Stage Centrifugal Compressor Apparatus
Figure:
Pressure Transmitter
RPM Meter
Knob for Damper Positioning
Damper
Temperature, Flow Rate,
Pressure Controllers
Power Meter
Frequency Modulator
Emergency Switch
Compressor
Air Inlet
Procedure:
1. First of all switch on the main supply and press the Run button on the modulator.
2. Increase the speed by turning the variable potentiometer.
3. Set the desired speed and note down the different parameters (readings) with the damper
condition partially opened.
4. Note down the different parameters by changing the speed.
5. Using readings, calculate the volume flow rate of air, pressure ratios, and efficiency of the
compressor.
6. Draw the graphs between the RPM (x-axis) and compressor efficiency (y-axis).
Observations & Calculations:
Flowrate of air across the compressor = Qa = Cf *π*D22 2∆P1
4
ρ(1-d4)
Where;
Qa = Flowrate of air;
(m3/sec)
d = D2/D1
(D1˃ D2)
D1 = 70mm = 0.070m;
D2 = 40mm = 0.040m;
Cf = 0.63 (Coefficient of flow);
ρ = Density of Air = 1.14 kg/m3;
∆P1 = Differential pressure across orifice;
(N/m2)
Hydraulic Power of Compressor = Phyd = ∆P2*Qa ;
(Watt)
And
∆P2 = Differential pressure across compressor;
(N/m2)
Efficiency of the Compressor = ηc = Work Done on Air per Second
Work Done on Compressor
ηc = ∆P2*Qa
Pc
ηc = Phyd
Pc
*100
*100
*100
Where
Pc = Electrical Power Supplied to the Compressor;
Sr.
Intake Air
No. Temperature
T1
(oC)
1.
2.
3.
4.
5.
(Watt)
Discharge
Air
Temperature
T2
Differential
Pressure
Across orifice
∆P1
Differential
Pressure Across
Compressor
∆P2
RPM
N
(oC)
(N/m2)
(N/m2)
(rev/min)
Sr.
No.
Power
provided to
Compressor
Pc
Volume
Flowrate of Air
Qa
(watt)
(m3/sec)
1.
2.
3.
4.
5.
Specimen Calculations:
Power transferred
to Air
Phyd
(watt)
Efficiency of
Compressor
ηc
(%age)
Comments:
Lab Session No: 06
Objective:
To demonstrate the functions of various parts of a 4 stroke Diesel Engine using 4 stroke
Diesel Engine Demonstration Model
Apparatus:
4 Stroke Diesel Engine Model or 4 Stroke Diesel Engine (Sectioned)
Figure:
Rocker Arm
Air Cleaner
Exhaust Valve
Intake valve
Fuel Inlet Line
Injection Line
Suction Manifold
Exhaust Manifold
Inject
Injection
Pump
Cylinder
Delivery Valve Spring
Piston
Delivery valve
Connecting Rod
Control Rack
Water Jacket
Piston Spring
Spring Valve
Cam Follower
Flywheel
Oil Pan
Geared Sector
Cam Shaft
Timing System Gears
Basement
Crankshaft
Cooling Fins
Functions of Different Parts:
Functions of different parts of a 4 stroke diesel engine are explained below;
Injection Pump:
It pressurizes the fuel to the required level and injects it correctly into the fuel injector at the
end of compression stroke during each cycle of operation of engine.
Delivery Valve:
Its function is to deliver fuel (Diesel) from high pressure pump to the combustion engine
without loss of pressure.
Fuel Inlet Line:
It is a passageway of fuel injection system.
Delivery Valve Spring:
It just helps in opening and closing the delivery valve.
Cylinder:
It is the place or space in which piston reciprocates or travels.
Piston:
In an engine the function of piston is to transfer force from expanding gas in the cylinder to
the crankshaft by means of connecting rod. It also transfers force from crankshaft to the
inside of cylinder for the purpose of compressing the fluid in the cylinder.
Wrist Pin:
Its function is to connect piston with connecting rod. It is also called gudgeon pin or piston
pin.
Cylinder Head:
The top of a cylinder is covered with the cylinder head. It contains holes for the valves.
Crankcase:
It is used to cover the crankshaft of the engine. Generally cover of crankshaft is called
crankcase.
Crankshaft:
It converts linear motion of piston into rotational motion that is transmitted to the load.
Connecting Rod:
It connects the piston to the crankshaft.
Camshaft:
The camshaft makes it possible for the valves to open and close. The lobes (cam) of the
camshaft correspond to the engine’s valves.
Flywheel:
A flywheel is used to store rotational energy. The power stroke of the engine provides the
power to the engine. The power for the remaining strokes is provided by the flywheel which
gives the stored energy to the engine during idle strokes.
Fuel Injector:
It is a small nozzle into which liquid fuel is injected at high pressure. Its function is to spray
atomized fuel into the combustion chamber of the engine.
Pre-Combustion Chamber:
It is an auxiliary space in which combustible gases are ignited and combustion started ahead
of main combustion chamber.
Pre-heating Plug:
These plugs or heaters are mounted on pre-combustion chamber and their function is to heat
fuel in order to get better engine ignition. It is a pencil shaped piece of metal with a heating
element at the tip. These plugs also help to start diesel engines especially in cold weather,
when high speed diesel engines can be difficult to start.
Air Cleaner:
It is a device composed of fibrous materials which removes solid particulates such as dust,
mould and bacteria from air.
Intake Manifold:
The function of inlet manifold (suction manifold) is to deliver air and in some case
recirculated exhaust gas (in modern diesel engine) to engine’s cylinder.
Exhaust manifold:
The function of exhaust manifold is to collect and contain cylinder end gases (exhaust gases)
and deliver them to the exhaust piping.
Oil Pan:
It is used to collect engine’s lubricating oil. It is situated below the engine crankshaft. It is
also called sump.
Rocker Arm:
It is used to convert the radial movement from the camshaft lobe to the linear motion at the
valve to open it. One end of the rocker arm is attached to the camshaft lobe while other end
acts as the valve stem.
Timing Gears:
These gears are responsible for the movement of camshaft and most of the engine’s
accessories.
Inlet Valve:
It is used to allow/disallow the air into the cylinder by opening/closing.
Exhaust Valve:
Its function is to expel the exhaust burnt gases into the exhaust piping.
Water Jacket:
It is used in water-cooled engines. It is a water-filled casing surrounding the engine’s cylinder
to keep the temperature of the cylinder at a moderate level.
Lab Session No: 07
Objective:
To demonstrate the working cycle of a 4 stroke Diesel Engine using 4 stroke Diesel Engine
Demonstration Model
Apparatus:
4 Stroke Diesel Engine Model or 4 Stroke Diesel Engine (Sectioned)
Figure:
Working Principle:
A 4 stroke compression ignition engine completes one cycle of events in two revolutions of
crankshaft or four piston strokes. The four phases of these strokes are;
1) Induction of fresh air
2) Compression and heating of this air
3) Expansion of fuel and its burning and expansion 4) Expulsion of products of combustion
Before knowing the working cycle of a 4 stroke diesel engine, we must know the following
basic terms;
Top Dead Centre (TDC):
It is the position of the piston in which it is farthest from crankshaft.
Bottom Dead Centre:
It is the position of the piston in which it is nearest to the crankshaft.
Stroke:
A stroke is referred to as full travel of the piston along the cylinder in either direction.
Working Cycle:
There are four strokes in the working cycle of a 4 stroke diesel engine;
1) Intake/Induction
2) Compression
3) Expansion/Power
4) Exhaust
1. Intake/Induction Stroke:
This stroke starts at top dead centre (TDC) and ends at bottom dead centre (BDC) or in other
words, in this stroke piston moves from TDC to BDC. This movement of the piston
establishes a depression or vacuum in the cylinder. The inlet valve opens and the pressure
difference established between outside and inside of the cylinder will induce the fresh air at
atmospheric pressure to enter and fill up the cylinder. In diesel engine only pure air is
introduced into the cylinder during intake stroke.
2. Compression Stroke:
In this stroke, piston moves from BDC to TDC. Both inlet and exhaust valve will remain
closed during this stroke. The air enclosed in the cylinder will be compressed into a much
smaller space. This compression of air generates heat which will increase the charge
temperature.
3. Expansion/Power Stroke:
At the end of compression stroke, when both inlet and exhaust valve are closed, the fuel oil
(diesel) is injected into dense and heated air by fuel injector in the form of high pressure
spray of fine particles. These atomized and tiny droplets of liquid fuel, when distributed
throughout the air, are vaporized and ignited by the heat of compression. This highly
compressed mixture pushes the piston from TDC to BDC and expansion occurs. So, during
this stroke, piston moves from TDC to BDC.
4. Exhaust Stroke:
During this stroke, the piston again moves from BDC to TDC and exhaust valve opens at the
end of power stroke. This sudden opening of exhaust valve releases the exhaust burnt gases
or products of combustion to the atmosphere.
Lab Session No: 08
Objective:
To demonstrate the functions of various parts of a 4 stroke Petrol Engine using 4 stroke Petrol
Engine Demonstration Model
Apparatus:
4 Stroke Petrol Engine Model or 4 Stroke Petrol Engine (Sectioned)
Figure:
Air Cleaner
Carburettor
Fuel Intake
Spark Plug
Float
Cup
Starter
Valve Closing Spring
Intake Manifold
Exhaust manifold
Exhaust Valve
Throttle Valve
Intake Valve
Capacitor
Water Circulation
Space
Distributor
Piston
Cup
Camshaft
Flywheel
Automatic Spark
Advance
Coil
Connecting Rod
Sump
Timing Gears
Crankcase
Cooli
Basement
Coil Ignition
Cooling Fins
Driving Shaft
(Crankshaft)
Functions of Different Parts:
Functions of different parts of a 4 stroke petrol engine are explained below;
Carburettor:
The main function of a carburettor is to mix air and gasoline (petrol) in correct ratio to ensure
proper engine function. If the carburettor is not tuned properly, the engine receives poor airfuel ratio which can lead to poor performance of the engine.
The components of a carburettor are float chamber, diaphragm chamber, venturi, throttle
valve, choke valve etc. The functions of these parts of a carburettor are given below;
a) Float Chamber:
It is used to hold the fuel (Petrol) at atmospheric pressure. The fuel supply is refilled by a
float driven controller. When there is fuel drop in the chamber, float opens the inlet valve to
permit fuel pump to transfer extra fuel to the chamber.
b) Diaphragm Chamber:
In any orientation of the engine when float chamber is not suitable, then a diaphragm
chamber is used in place of float chamber. Function of diaphragm is same as that of a float in
a float chamber i.e., to regulate the fuel flow into the carburettor fuel chamber. The advantage
of the diaphragm is that it can be mounted in virtually any position.
c) Venturi:
A carburettor consists of a pipe which is in the form of a venturi through which the air passes
into the intake manifold of the engine. It widens in section and then narrows again. It causes
an increase in air flow speed in the narrowest section of the venturi.
d) Throttle Valve (Butterfly Valve):
Below the venturi, a butterfly valve also called throttle valve is present. It is in the form of a
rotating disc. This valve controls the quantity of air-fuel mixture that will enter into the
engine cylinder and thus regulating the engine power and speed.
e) Choke Valve:
In cold weather, when engine is cold, the fuel vaporizes less and began to condense on the
walls of intake manifold making the engine difficult to start. Hence a rich air-fuel mixture is
needed to start engine in this situation. To provide extra fuel, a choke is usually used. It is a
valve that restricts the flow of air at the entrance to the carburettor before the venturi. With
this restriction, extra vacuum is produced in the carburettor which pulls the extra fuel to enter
into the carburettor. It provides the rich mixture. Choke can be connected to the cam or other
such device, which prevents the throttle plate from closing fully, when the choke is in
operation.
Different parts of a carburettor are shown in the figure below;
Air Filter
Choke Valve
Fuel
Float
Gas and Air Mixture
Venturi
Throttle Valve
Float Chamber
Fig.1 (Float Type Carburettor)
Ignition System:
The coil ignition of a petrol engine consists of following components;
a) Battery b) Ignition coil c) Distributor d) Capacitor e) Spark Plug. Their functions are
given below;
a) Battery:
It provides a constant source of electricity i.e., current and voltage supply.
b) Ignition Coil:
It acts as a transformer. It is used to step the voltage up to the required needs of the ignition.
c) Distributor:
It is used to distribute the ensuing pulse to correct spark plug at correct time.
d) Capacitor:
It makes a parallel resonant circuit with the ignition coil. With this resonance, the duration of
spark is sustained and provides a good flame in air-fuel mixture. It is usually used to store
electric charge.
e) Spark Plug:
It is used to ignite air-fuel mixture. The electric pulse in spark plug provided by the
distributor is used to ignite air-fuel mixture. Different components of the coil ignition system
are shown in the figure below;
Direction of current flow
Ignition Key
+
-
Capacitor
Spark Plug
Battery
Coil
Distributor
Fig.2 (Coil ignition system schematic diagram)
Cylinder:
It is the place or space in which piston reciprocates or travels.
Piston:
In an engine the function of piston is to transfer force from expanding gas in the cylinder to
the crankshaft by means of connecting rod. It also transfers force from crankshaft to the
inside of cylinder for the purpose of compressing the fluid in the cylinder.
Wrist Pin:
Its function is to connect piston with connecting rod. It is also called gudgeon pin or piston
pin.
Cylinder Head:
The top of a cylinder is covered with the cylinder head. It contains holes for the valves.
Crankcase:
It is used to cover the crankshaft of the engine.
Crankshaft:
It converts linear motion of piston into rotational motion that is transmitted to the load.
Connecting Rod:
It connects the piston to the crankshaft.
Camshaft:
The camshaft makes it possible for the valves to open and close. The lobes (cams) of the
camshaft correspond to the engine’s valves.
Flywheel:
A flywheel is used to store rotational energy. The power stroke of the engine provides the
power to the engine. The power for the remaining strokes is provided by the flywheel which
gives the stored energy to the engine during idle strokes.
Air Cleaner:
It is a device composed of fibrous materials which removes solid particulates such as dust,
mould and bacteria from air.
Intake Manifold:
The function of inlet manifold (suction manifold) is to deliver air fuel mixture to engine’s
cylinder.
Exhaust manifold:
The function of exhaust manifold is to collect and contain cylinder end gases (exhaust gases)
and deliver them to the exhaust piping.
Oil Pan:
It is used to collect engine’s lubricating oil. It is situated below the engine crankshaft. It is
also called sump.
Timing Gears:
These gears are responsible for the movement of camshaft and most of the engine’s
accessories.
Inlet Valve:
It is used to allow the air fuel mixture to enter into the cylinder.
Exhaust Valve:
Its function is to expel the exhaust burnt gases into the exhaust piping.
Water Jacket:
It is used in water-cooled engines. It is a water-filled casing surrounding the engine’s cylinder
to keep the temperature of the cylinder at a moderate level.
Lab Session No: 09
Objective:
To demonstrate the working cycle of a 4 stroke Petrol Engine using 4 stroke Petrol Engine
Demonstration Model
Apparatus:
4 Stroke Petrol Engine Model or 4 Stroke Petrol Engine (Sectioned)
Figure:
Working Principle:
A 4 stroke spark ignition engine completes one cycle of events in two revolutions of
crankshaft or four piston strokes. The four phases of these strokes are;
1) Induction of fresh air/fuel mixture
2) Compression and heating of this air/fuel mixture
3) Expansion of air fuel mixture and its burning
4) Expulsion of products of combustion
Working Cycle:
There are four strokes in the working cycle of a 4 stroke Petrol engine;
1) Intake/Induction
2) Compression
3) Expansion/Power
4) Exhaust
1. Intake/Induction Stroke:
This stroke starts at top dead centre (TDC) and ends at bottom dead centre (BDC) or in other
words in this stroke piston moves from TDC to BDC. In this stroke inlet valve opens and
allows the air-fuel mixture to enter into the cylinder. It is done by vacuum pressure which is
created by the difference of pressure between outside and inside of the engine’s cylinder.
Exhaust valve ill remain closed during this stroke.
2. Compression Stroke:
In this stroke, piston moves from BDC to TDC. In this stroke, the piston compresses the airfuel mixture to prepare it for ignition during power / expansion stroke. This compression
will increase the temperature inside the cylinder. At the end of the compression stroke, spark
plug ignites the air-fuel mixture. Both inlet and exhaust valves remain closed during this
stroke.
3. Expansion/Power Stroke:
At the end of compression stroke, the compressed air-fuel mixture is ignited/burns by heat
generated by the spark plug, forcefully returning the piston from TDC to BDC. This
movement of the piston by ignited air-fuel mixture from TDC to BDC is the expansion
stroke.
4. Exhaust Stroke:
During this stroke, the piston again moves from BDC to TDC and exhaust valve opens.
Exhaust valve is opened at the end of expansion stroke. This opening of the exhaust valve
expels the exhaust/spent or burnt gases out of engine’s cylinder.
Lab Session No: 10
Objective:
To demonstrate the functions of various parts of a 2 stroke Petrol Engine using 2 stroke petrol
engine demonstration model
Apparatus:
2 Stroke Petrol Engine Model or 2 Stroke Petrol Engine (Sectioned)
Figure:
Spark Plug
Fuel Tank
Carburettor
Cylinder
Cooling Fins
Piston
Fuel Line
Flywheel
Basement
Air Filter
Functions of Different Parts:
Functions of different parts of a 2 stroke petrol engine are explained below;
Spark Arrestor:
It prevents the fire and ignition of combustible carbon deposits and thus prevents the engine
from unwanted explosion.
Muffler:
It helps to decrease the noise level produced by exhaust emissions of the engine.
Ignition Coil:
It transforms the low voltage into high voltage required to create an electric spark in spark
plug to ignite air-fuel mixture.
Fuel Line:
It is a pipe from which fuel is transferred from fuel tank to the carburettor.
Carburettor:
It is a device in which air-fuel mixture is prepared in correct ratio in order to make it possible
for ignition.
Spark Plug:
It is used to ignite compressed air-fuel mixture by an electric spark. Or in other words, it is a
device used to transfer electric current from ignition system to the combustion chamber of the
spark ignition engine.
Fuel Tank:
It is used to store and keep the fuel i.e. petrol in this engine.
Cooling Fins:
These are the projections made around the combustion chamber or cylinder of the engine.
These fins increase the surface area and this increase in surface area helps to remove heat
from the cylinder at a much faster rate. They are most commonly made in air-cooled engines.
Cylinder:
It is the place or space in which piston reciprocates or travels.
Piston:
In an engine the function of piston is to transfer force from expanding gas in the cylinder to
the crankshaft by means of connecting rod. It also transfers force from crankshaft to the
inside of cylinder for the purpose of compressing the fluid in the cylinder.
Wrist Pin:
Its function is to connect piston with connecting rod. It is also called gudgeon pin or piston
pin.
Crankcase:
It is used to cover the crankshaft of the engine.
Crankshaft:
It converts linear motion of piston into rotational motion that is transmitted to the load.
Connecting Rod:
It connects the piston to the crankshaft.
Magneto Ignition System:
This ignition system provides current for ignition without any external source of electricity. It
is mostly used in small powered engines like lawn movers etc. The flywheel contains a
magnet and outside the magnet, there is a coil which has primary and secondary windings.
The secondary coil has larger number of turns than primary coil. As the flywheel rotates, the
magnet attached to it produces a magnetic flux. This magnetic flux produces the
electromotive force and induces a current into the surrounding coil according to Faraday’s
law of electromagnetic induction. From the primary windings, the induced current is
transferred to the secondary windings. As the secondary windings has larger number of turns,
and according to Faraday’s law the current induced is directly proportional to the number of
turns, so secondary coil will have larger current than the primary coil. This larger current is
then transferred to the spark plug and through this current, spark plug ignites air-fuel mixture.
A set of contact breaker points travelling over a cam lobe regulates the electrical impulse to
set the timing. These points allow a fixed charge to enter the secondary coil circuit. A
condenser acts as a ground to disperse the primary’s magnetic charge until the next armature
rotation. The faster the speed of flywheel, firing the primary windings will be more often. A
magneto ignition system is shown in the fig. below;
Air Gap (Spark Plug)
Condenser
Primary Windings
Secondary Windings
Points
Armature
Coil
Flywheel Magnets
Fig.3 (Magneto ignition system schematic diagram)
Magnetic Field
Lab Session No: 11
Objective:
To learn about the working cycle of a 2 stroke Petrol Engine using 2 stroke petrol engine
demonstration model
Apparatus:
2 Stroke Petrol Engine Model or 2 Stroke Petrol Engine (Sectioned)
Figure:
Cylinder Head
Spark Plug
Cooling Fins
Exhaust Port
Inlet Port
Piston
Transfer Port
Connecting Rod
Crankcase
Crankshaft
Working Principle:
A 2 stroke petrol engine completes one cycle of events in only one revolution of crankshaft or
2 piston strokes. It has following 2 strokes
1) Intake of air fuel mixture in crankcase and compression of air-fuel mixture in cylinder
2) Expansion of air-fuel mixture in cylinder and exhaust of burnt gases through exhaust port
These strokes are explained as;
1st Stroke:
In this stroke, piston moves from BDC to TDC. The top of the piston covers the exhaust port
and bottom of the piston uncovers the inlet port. This opening of the inlet port allows the
fresh charge of air-fuel mixture to enter into the crankcase. Also the upward movement of the
piston compresses the air-fuel mixture above it i.e. in the cylinder. At the end of this
compression, spark plug ignites the air-fuel mixture in the cylinder creating high temperature
or heat and pressure.
2nd Stroke:
In this stroke, the piston moves from TDC to BDC. The high pressure created by the spark
plug ignition forces the piston to move downwards. During downward movement, the top of
the piston uncovers the exhaust port thus expels the burnt gases of the cylinder out of exhaust
port. Also top of the piston uncovers the transfer port and thus transfer air-fuel mixture from
crankcase to the cylinder. For this purpose, the pistons are usually made special shaped to
direct the air-fuel mixture from crankcase to the cylinder and prevents this mixture to go out
of the exhaust port. The downward movement of the piston also compresses the air-fuel
mixture in the crankcase that has been entered into the crankcase by inlet port during 1st
stroke.
Lab Session No. 12
Objective:
To study about the working of a Turbo Jet Engine using Turbo Jet Engine demonstration
model
Apparatus:
Turbo Jet Demonstration Model
Figure:
Compressor
Combustion Chamber
Turbine
Nozzle
Turbojet Engine:
Gas turbines are particularly suited for aircraft propulsion because of their favourable power
to weight ratio. The turbojet engine is commonly used for this purpose as shown in fig.
below;
Air In
Gas out
Diffuser
Nozzle
C Combustion Chamber T
T = Turbine; C = Compressor
This type of engine consists of three main sections, diffuser, gas generator and the nozzle.
The diffuser placed before the compressor decelerates the incoming air relative to engine. A
pressure rise known as ram effect is associated with this deceleration. The gas generator
section consists of a compressor, combustion chamber and the gas turbine. In compressor this
high pressure air coming from the diffuser is compressed. This compressed air is then heated
by the fuel in the combustion chamber. This heated air is then expanded in the turbine. The
gases leave the turbine at a pressure significantly higher than atmospheric pressure and
expand through the nozzle at a high velocity. The overall change of velocity of gases relative
to the engine gives rise to the propulsive force or thrust to the engine. Some turbojets are
equipped with an afterburner. Afterburner is a reheat device in which additional fuel is
injected into the gas exiting the turbine and burned producing a high temperature at the
nozzle inlet which will increase its inlet velocity resulting in increased thrust.
Cycle of Operation:
3
2
4
1
T
5
a
s
Explanation:
a-1: Isentropic compression in diffuser
1-2: Isentropic compression in compressor
2-3: Constant pressure heat addition in combustion chamber
3-4: Isentropic expansion in gas turbine
4-5: Isentropic expansion in nozzle
5-a: Constant pressure heat rejection in atmosphere (Open cycle gas turbine)
If the burned gases after the turbine or nozzle reject heat in the atmosphere then it is called
open cycle gas turbine. If the hot exhaust rejects heat in the heat exchanger and then enters
again to the compressor after cooling, then it is a closed cycle gas turbine.
Lab Session No. 13
Objective:
To determine efficiency of a convergent nozzle and to Jet speed at which air leaves the nozzle
Apparatus:
Computer Controlled Nozzle Performance Test Unit
Figure:
System Diagram:
Explanation:
1. SP-1: Pressure at the entries to the chamber (Adjustable)
2. SP-2: Pressure in the chamber (Adjustable)
3. ST -1, ST-2: Air temperature at the entries of the chamber
4. ST-3: Temperature in the chamber
5. SC-1: Air volume
6. SF-1: Force Sensor to measure jet force on nozzle
Theory:
Efficiency of the Nozzle:
Efficiency of the nozzle is defined as;
𝜂=
Kinetic energy of the jet exhausting from the nozzle
Change of isentropic enthalpy through the nozzle
C2
𝜂=
2(h1 − h2 )
Installation of Nozzle in Equipment:
1. Close the air inlet valve.
2. Remove the exhaust ducts from the chamber in its upper part.
3. Unscrew the screws with cap to remove the upper lid of the chamber.
4. Once the chamber is open, screw in the nozzle to the upper part of the chamber. If, instead
of it, a blind cap is screwed in, remove first the latter.
5. Screw in the blind cap in the lowest part of the chamber, in the rod that contains the force
sensor.
6. Put again the chamber lid, making it safe with screws with cap.
7. Finally, put on again the air exhaust ducts on the chamber lid.
8. Make sure that the air inlet control valve is regulated, to make possible the air pass towards
the lower part of the chamber, and not towards the upper part.
Experimental Procedure:
1. Set the nozzle inlet pressure P1 on a constant value, with the chamber pressure valve fully
closed.
2. Notice the pressures, the air flux rate, temperatures and the readings of the force sensor.
3. Increase the chamber pressure P2 to any desired value by keeping the inlet pressure P1
constant.
4. Keep on increasing the chamber pressure P2 and by keeping the inlet air pressure P1
constant and note down the different parameters.
.Observations & Calculations:
Pressure Ratio = rp =
P2
P1
;
Where;
P2 = Chamber Pressure (kNm-2); P1= Air Inlet Pressure (kNm-2);
Jet Speed = C =
F
ṁ
(m/s);
Where;
F = Impact force taken from force measurer (N) ; ṁ = Mass flux rate (kg/s)
ṁ = Volume flow rate (m3/sec) * Density of air (1.225 kg/m3)
Specific Kinetic Energy = ke =
C2
2
(J/kg);
Isentropic Enthalpy Change = ∆h =
γ
γ−1
RT1 [1 − ( rp)
γ−1
γ
] (J/kg);
Where;
γ = Isentropic Index = 1.4 (for air); T1 = Inlet Air Temperature (K);
R = General Gas Constant = 287 Jkg-1K-1;
Nozzle Efficiency = η =
Sr.
No.
Specific Kinetic Energy
Change of Isentropic Enthalpy
*100=
Inlet
Chamber Pressure
Air
Air
Pressure
Ratio
Inlet
Pressure
Temperature
P2
P2
rp
(KN/m2)
(KN/m2)
Ke
∆h
Force
1.
2.
3.
4.
5.
Specific
Kinetic
Energy
Volum
e
Flow
Rate
of Air
Mass
Flow
Rate
of Air
Jet Speed
T1
F
V̇
ṁ
C
(K)
(N)
(m3/s)
(Kg/s)
(m/s)
1.
2.
3.
4.
5.
Sr. No.
∗100
Isentropic
Enthalpy
Change
Nozzle
Efficiency
ke
∆h
η
(J/kg)
(J/kg)
(%age)
Specimen Calculations:
Comments: