This document discusses pure substances and the phases of pure substances. Some key points include: - A pure substance has a fixed chemical composition throughout and can exist in different phases like solid, liquid, and gas. - Pure substances can undergo phase changes through processes like melting, vaporization, and condensation. - The properties of a pure substance depend on its phase and conditions like temperature and pressure. - Mixtures of substances qualify as pure substances as long as they are homogeneous. Examples include liquid water and water vapor mixtures. The document then discusses concepts like saturation, latent heat, quality, and moisture content which are important for understanding phase equilibria of pure substances.

1. Made by:
Assistant Professor : NAPHIS AHAMAD
MECHANICAL ENGINEERING
06/10/17Naphis Ahamad (ME) JIT 1

2. 06/10/17 Naphis Ahamad (ME) JIT 2

3. What is Pure Substances?
06/10/17 JIT 3
 A substance that has a fixed
chemical composition throughout
is called a pure substance.
 A pure substance does not have
to be of a single chemical
element or compound, however.
A mixture of various chemical
elements or compounds also
qualifies as a pure substance as
long as the mixture is
homogeneous.

4. 06/10/17 JIT 4
 A mixture of liquid and water vapor is a pure substance, but a
mixture of liquid and gaseous air is not.
Examples:
 Water (solid, liquid, and vapor phases)
 Mixture of liquid water and water vapor
 Carbon dioxide, CO2
 Nitrogen, N2
 Mixtures of gases, such as air, as long as there is no
change of phase.

5. 06/10/17 JIT 5
Phases of A Pure Substance
 The substances exist in different phases, e.g. at room temperature
and pressure, copper is solid and mercury is a liquid.
 It can exist in different phases under variations of condition.
 There are 3 Principal phases
• solid
• Liquid
• gas
Each with different molecular structures.

6. 06/10/17 JIT 6
Phase-change Processes of Pure
Substances There are many practical situations where two phases of a pure
substances coexist in equilibrium.
 Solid: strong intermolecular bond
 Liquid: intermediate intermolecular bonds
 Gas: weak intermolecular bond
Solid Liquid Gas
 E.g. water exists as a mixture of liquid and vapor in the boiler and etc.

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Phase-change Processes

8. 06/10/17 JIT 8
s
This constant
pressure heating
process can be
illustrated as:

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Property Diagram

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Saturation
 Saturation is defined as a condition in which a mixture of vapor and
liquid can exist together at a given temperature and pressure.
 Saturation pressure is the pressure at which the liquid and vapor phases
are in equilibrium at a given temperature
 For a pure substance there is a definite relationship between saturation
pressure and saturation temperature. The higher the pressure, the higher
the saturation temperature

11. 06/10/17 JIT 11
Latent Heat
 Latent heat: The amount of energy absorbed or released during a phase-
change process.
 Latent heat of fusion: The amount of energy absorbed during melting. It
is equivalent to the amount of energy released during freezing.
 Latent heat of vaporization: The amount of energy absorbed during
vaporization and it is equivalent to the energy released during
condensation.
 At 1 atm pressure, the latent heat of fusion of water is 333.7 kJ/kg

12. 06/10/17 JIT 12
Quality
 When a substance exists as part liquid and part vapor at saturation conditions,
its quality (x) is defined as the ratio of the mass of the vapor to the total mass
of both vapor and liquid.
 The quality is zero for the saturated liquid and one for the saturated
vapor(0≤x≤1)
 For example, if the mass of vapor is 0.2 g and the mass of the liquid is 0.8
g, then the quality is 0.2 or 20%.
x
mass
mass
m
m m
saturated vapor
total
g
f g
= =
+

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Quality
Mixture of liquid and vapor

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Moisture Content
 The moisture content of a substance is the opposite of its quality. Moisture
is defined as the ratio of the mass of the liquid to the total mass of both
liquid and vapor
Recall the definition of quality x
Then
x
m
m
m
m m
g g
f g
= =
+
m
m
m m
m
x
f g
=
−
= −1

15. 06/10/17 JIT 15
Moisture Content
 Take specific volume as an example. The specific volume of the
saturated mixture becomes
v x v xvf g= − +( )1
 The form that is most often used
v v x v vf g f= + −( )
 Let Y be any extensive property and let y be the corresponding
intensive property, Y/m, then
y
Y
m
y x y y
y x y
where y y y
f g f
f fg
fg g f
= = + −
= +
= −
( )

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Important Definition
o Critical point - the temperature and pressure above which there
is no distinction between the liquid and vapor phases.
o Triple point - the temperature and pressure at which all three
phases can exist in equilibrium.
o Sublimation - change of phase from solid to vapor.
o Vaporization - change of phase from liquid to vapor.
o Condensation - change of phase from vapor to liquid.
o Fusion or melting - change of phase from solid to liquid.

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18. 06/10/17 JIT 18
Ideal Gas Law
 Robert Boyle formulates a well-known law that states the pressure of a gas
expanding at constant temperature varies inversely to the volume, or
constant2211 == VPVP
 As the result of experimentation, Charles concluded that the pressure of a gas
varies directly with temperature when the volume is held constant, and the
volume varies directly with temperature when the pressure is held constant, or
2
1
2
1
2
1
2
1
T
T
P
P
or
T
T
V
V
==

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 By combining the results of Charles'
and Boyle's experiments, the following
relationship can be obtained
 The constant in the above equation is
called the ideal gas constant and is
designated by R; thus the ideal gas
equation becomes
 In order to make the equation applicable to
all ideal gas, a universal gas constant RU is
introduced
constant=
T
Pv
mRTPVorRTPv ==
M
R
R U
=

20. 06/10/17 JIT 20
 For example the ideal gas constant for air, Rair
KkgkJ
M
R
R
air
airU
air ./2871.0
96.28
3144.8
)(
)(
===
 The amount of energy needed to raise the temperature of a unit of mass of
a substance by one degree is called the specific heat at constant volume Cv
for a constant-volume process and the specific heat at constant pressure
Cp for a constant pressure process. They are defined as
P
P
v
v
T
h
Cand
T
u
C 





∂
∂
=





∂
∂
=

21. 06/10/17 JIT 21
 Using the definition of enthalpy (h = u + Pv) and writing the differential of
enthalpy, the relationship between the specific heats for ideal gases is
 The specific heat ratio, k is defined as
v
P
C
C
k =
P V
P V
h u Pv
dh du RT
C dt C dt RdT
C C R
= +
= +
= +
= +

22. 06/10/17 JIT 22
 For ideal gases u, h, Cv, and Cp are functions of temperature alone. The Δu
and Δh of ideal gases can be expressed as
)( 1212 TTCuuu v −=−=∆
)( 1212 TTChhh P −=−=∆

23. Simple Rankine cycle
06/10/17 JIT 23

24. The main components of steam power plant are
i. BOILER
ii. TURBINE
iii. CONDENSER
iv. COOLING TOWER
v. PUMP .
06/10/17 JIT 24

25. From graph
1-2 = isentropic process
2-3 = isobaric process
3-4 = isentropic process
4-1 = isobaric process .
06/10/17 JIT 25

26. Boiler :-
Boiler is used to produce steam .
Heat energy produced by coal is used to produce steam.
Water is allowed to heat until it becomes into vapor state.
Vapor is sent into turbine.
TURBINE :-
Turbine produces the work.
Work produced is used to run the generator.
The enthalpies at the enter and exit of the turbine are different.
Then Vapor is sent into the condenser.
CONDENSER :-
The vapor is condensed to water in the condenser and sent into the pump.
PUMP :-
Pump send the water again into the Boiler and the cycle repeats again.
06/10/17 JIT 26

27. By considering the devices as steady flow devices and by applying the energy
balance we get
Steam turbine :
W turbine = h1 - h2
Condenser :-
Q rejected = h2 – h3
Pump :-
W pump = h4 – h3
Boiler :-
Q added = h1 – h4
06/10/17 JIT 27

28.  Turbine produces the more work if the water is heated to super heated region.
 If the water is heated to super heated then the turbine will produce the more
work .
06/10/17 JIT 28

29.  But there is a problem if water is heated to super heated i.e. when it is condensed the
vapor is not converted into water completely . It remains still as a mixture.
 It is difficult for the pump to handle both liquid and water which leads to CAVITATION
.
06/10/17 JIT 29

30. INTRODUCTION What is IC Engine?
An internal combustion engine is a thermal system (power plant) that
converts heat obtained from chemical energy sources (gasoline, natural gas)
into mechanical work.
Where are IC Engines Used?
IC engines are used as the propulsion systems for land transport vehicles
such as automobiles (cars, etc.), marine vehicles (boats, etc.) and small
airplanes. IC engines are also used in portable electrical generators and as
prime mover in grass cutting machine, etc.
06/10/17 JIT 30

31. 06/10/17 JIT 31
Basic Components of IC Engines
• Cylinder, piston, inlet valve and exhaust
valve.
• Piston moves from the top dead center
(TDC) to the bottom dead center (BDC).
• Clearance volume, Vc is a spacing
between the top of the piston and the
valve’s heads when the piston is at the end
of the delivery stroke.
• Swept volume or displacement volume,
Vs is the volume between TDC and BDC.

32. Classifications:
Internal Combustion Engines (IC Engines)
External Combustion Engines (EC Engines)
Internal Combustion Engines (IC Engines):
IC Engines are those in which combustion of fuels take places inside engine
cylinder (Example: Petrol, Diesel, GAS)
External Combustion Engines (EC Engines):
EC Engines are those in which combustion of fuels take places outside engine
cylinder (Example: Steam Engine, Steam turbine)
06/10/17 JIT 32

33. Classification of IC Engines:
a. According to the cycle of operation
Spark ignition engines(Petrol or Constant volume or Otto cycle)
Compression ignition engines(Diesel or Constant Pressure)
b. According to the type of fuel used
Petrol, Diesel, Gas Engine.
c. According to the method of fuel
SI & CI
d. According to the Process of combustion
Otto cycle, Diesel cycle, Dual combustion cycle06/10/17 JIT 33

34. About Petrol Engine:
A petrol engine (also known as a gasoline engine in North America) is an
internal combustion engine with spark-ignition, designed to run on petrol (gasoline).
06/10/17 JIT 34

35. Working Cycles Four Stroke Petrol Engine:
 It is also known as Otto cycle or constant volume cycle.
 Cycle of operation is completed in 4-strokes of the piston or 2 revolutions of
the crankshaft.
 Each stroke consists of 180°, of crankshaft rotation and hence a cycle
consists of 720°of crankshaft rotation.
2-stroke: 1 power stroke per 1 crankshaft rev
4-stroke: 1 power stroke per 2 crankshaft rev
06/10/17 JIT 35

36. Principle of Operation:
The series of operations of an ideal four-stroke SI engine are as follows
Suction Stroke or charging stroke
Compression Stroke
Expansion or Power Stroke or working stroke
Exhaust Stroke
06/10/17 JIT 36

37. Principle of Operation
06/10/17 JIT 37

38. Principle of Operation:
Stroke Valve Position
Suction Stroke
Suction Valve open
Exhaust Valve closed
Compression Stroke Both Valves closed
Expansion or Power Stroke Both Valves closed
Exhaust Stroke
Exhaust Valve open
Suction Valve closed
06/10/17 JIT 38

39. Working Principles of Four Stroke Diesel Engine:
Increased pressure of combustion gases acts on piston -> converted to rotary motion
Can be 2 or 4 stroke engines
2-stroke: 1 power stroke per 1 crankshaft rev
4-stroke: 1 power stroke per 2 crankshaft rev
Engine stroke:
A stroke is a single traverse of the cylinder by the piston (from TDC to BDC)
1 revolution of crankshaft = 2 strokes of piston
06/10/17 JIT 39

40. Exhaust
Suction Compression Ign.-Combn. Expansion Exhaust
06/10/17 JIT 40

41. Working Principles Of Four Stroke Diesel Engine:
Intake stroke
Intake valve open, exhaust valve shut
Piston travels from TDC to BDC
Air drawn in
Compression stroke
Intake and exhaust valves shut
Piston travels from BDC to TDC
Temperature and pressure of air increase
06/10/17 JIT 41

42. Working Principles Of Four Stroke Diesel Engine:
Power stroke
Intake and exhaust valves shut
Fuel injected into cylinder and ignites
Piston forced from TDC to BDC
Exhaust stroke
Intake valve shut, exhaust valve open
Piston moves from BDC to TDC
Combustion gases expelled06/10/17 JIT 42

43. 06/10/17 JIT 43

44. 06/10/17 JIT 44
Two Stroke Cycle Petrol Engine
Construction :
•A piston reciprocates inside the cylinder
•It is connected to the crankshaft by means of connecting rod and crank
•There are no valves in two stroke engines, instead of valves ports are cut
on the cylinder walls.
•There are three ports, namely inlet, exhaust and transfer ports.
•The closing and opening of the ports are obtained by the movement of
piston. The crown of piston is made in to a shape to perform this.
•A spark plug is also provided.

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Two stroke cycle Petrol Engines - Working
• The piston moves up from Bottom Dead Centre (BDC) to
Top Dead Centre (TDC)
• Both transfer and exhaust ports are covered by the piston.
• Air fuel mixture which is transferred already into the engine
cylinder is compressed by moving piston.
• The pressure and temperature increases
• at the end of compression.

46. 06/10/17 JIT 46
Two stroke cycle Petrol Engines - Working
First Stroke : (b) Ignition and Inductance:
• Piston almost reaches the top dead centre
•The air fuel mixture inside the cylinder is ignited by means of an
electric spark produced by a spark plug
•At the same time, the inlet port is uncovered by the plane.
•Fresh air fuel mixture enters the crankcase through the inlet port

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Two stroke cycle Petrol Engines - Working
(c)Expansion and Crankcase compression
•The burning gases expand in the cylinder
•The burning gases force the piston to move down. Thus useful work is
obtained.
•When the piston moves down, the air fuel mixture in the crankcase is
partially compressed.
This compression is known as Crank case compression.

48. 06/10/17 JIT 48
Two stroke cycle Petrol Engines - Working
(d) Exhaust and transfer:
•At the end of expansion, exhaust port is uncovered.
•Burnt gases escape to the atmosphere.
•Transfer port is also opened. The partially compressed air fuel mixture enters
the cylinder through the transfer port.
•The crown of the piston is made of a deflected shape. So the fresh charge
entering the cylinder is deflected upwards in the cylinder.
•Thus the escape of fresh charge along with the exhaust
gases is reduced

49. Compression
Intake and exhaust valves shut
Piston travels from BDC to TDC
Temperature and pressure of air increase
Power stroke
Intake and exhaust valves shut
Fuel injected into cylinder and ignites
Piston forced from TDC to BDC
Working Principles Of Two Stroke Diesel Engine
06/10/17 JIT 49

50. Application Of Four stroke Cycle Engine
Used in heavy vehicles
Buses,
Lorries,
Trucks etc.,
Application Of Two stroke Cycle Engine
Used in light vehicles
Bikes,
Scooters,
Mopeds
Ship propulsion
06/10/17 JIT 50

51. Application Of Four stroke Petrol Engine
Buses ,Trucks
Mobile electric generating sets.
Small pumping sets with side cars
Application Of Four stroke Diesel Engine
30kw-Tractors
40to 100kw – jeeps, buses and trucks
200 to 400kw-Earthmoving m/c
100 to 35000kw-Marine application
06/10/17 JIT 51

52. 06/10/17 JIT 52
I.C ENGINE TERMINOLGY

53. 06/10/17 JIT 53
standard terms used in I.C Engines are
1. Bore: Inside diameter of the cylinder is termed as Bore and it is designated by the
letter d and is usually expressed in millimeter (mm)
2. Top Dead Center (TDC): The extreme position reached by the piston at the top of
the cylinder in the vertical engine is called Top Dead center. It is also called the Inner
dead centre (IDC).
3. Bottom Dead Center (BDC): The extreme position reached by the piston at the
Bottom of the cylinder in the vertical engine is called Bottom Dead center. It is also
called the Outer dead centre (ODC).

54. 06/10/17 JIT 54
5. Compression ratio (r): It is the ratio of Maximum cylinder volume to the
Clearance volume.
6. Cylinder volume (v): It is the sum of swept volume and the Clearance volume.
V = Vs + Vc
7. Displacement (or)Swept volume (Vs): It is the volume of space generated by
the movement of piston from one dead center to another dead center. It is expressed
in terms of cubic centimeter (cc) and given by
VS = A * L = π * d2
* L / 4
8. Clearance Volume( Vc): It is the space in the cylinder, when the piston is at Top
Dead Center It is designated as VC and expressed in cubic centimeter (cc).

55. 06/10/17 JIT 55
Petrol Engines
* A petrol engine draws a mixture of
petrol and air during suction stroke.
* The carburetor is employed to mix
air and petrol in the required
proportion and to supply it to the
engine during suction stroke.
* Pressure at the end of compression
is about 10 bar.
* The charge (i.e. petrol and air
mixture) is ignited with the help of
spark plug.
Diesel Engines
* A diesel engine draws only air
during suction stroke.
*The injector or atomizer is employed
to inject the fuel at the end of
combustion stroke.
*Pressure at the end of compression is
about 35 bar.
*The fuel is injected in the form of
fine spray. The temperature of the
compressed air is sufficiently high to
ignite the fuel.

56. 06/10/17 JIT 56
*The maintenance cost is less.
*The thermal efficiency is
about 26%.
*Overheating trouble is more
due to low thermal efficiency.
*These are high speed engines.
*The petrol engines are
generally employed in light
duty vehicle such as scooters,
motorcycles and cars. These
are also used in aeroplanes.
* The maintenance cost is
more.
* The thermal efficiency is
about 40%.
* Overheating trouble is less
due to high thermal
efficiency.
* These are relatively low
speed engines.
* The diesel engines are
generally employed in heavy
duty vehicles like buses,
trucks, and earth moving
machines.