Steam is a vapourised form of water. It is obtained by boiling
or evaporating the water in a boiler.
Steam is widely used as working fluid in thermal power plant
to produce Power.
Steam is working fluid in power plants, following advantages
High heat capacity
Can easily be condensed and evaporated
Work of compression is very small
3. STEAM BOILERS
Boiler or Steam generator is a closed steel shell in which steam
is generated from the water by combustion of fuel.
The water is pumped into the boiler at operating pressure.
The steam generated in the boiler is superheated in super
heater and is then expanded in engine or turbine to produce
4. The function of a boiler is to convert water into steam and
to supply the steam at required rate with desired quality.
Requirements of Good Boiler:
It should be capable of producing maximum amount of
It should be occupy less space and should be capable of
It should be safe in working
All parts should be easily accessible for inspection and
5. CLASSIFICATION OF BOILERS
According to the content in the tubes
Fire tube boilers
Water tube boilers
According to the location of furnace
Internally fired boilers
Externally fired boilers
According to the axis of the shell
According to the Circulation of Water:
Service to which they are employed
6. SELECTION OF BOILERS
Steam generating rate
Quality of steam required
Availability of floor space
Fuel to be used
Nature is the load on the boiler
8. Cylinder head:
Closes the cylinder to make a confined space.
Valves and Parts:
The admit the air and to discharge the spent gases.
Prevent the damage of Cylinder due to wear and tear.
To transmit the force in either direction between the piston
and the crank
To operate the valves.
9. Bore (d) :
The inside diameter of cylinder is called Bore, and is
measured in mm.
The piston reciprocates in the cylinder between two
fixed positions. The upper most position is termed as the
Top Dead Centre
The piston reciprocates in the cylinder between two
fixed positions. The Lower most position is termed as
the Bottom Dead Centre
Piston Stroke :
The distance travelled by the piston from one dead
Centre to the other is called the piston stroke. During
one stroke the crank shaft rotates half a turn.
10. Stroke Volume:
The volume displaced by the piston as it moves from one
dead Centre to the other is called stroke volume. It is
measured in liters or cubic centimeters.
The space between the cylinder head and the piston face at
the top dead Centre is known as the clearance volume.
The ratio of the whole cylinder Volume to the clearance
volume is called compression Ratio.
11. CLASSIFICATION OF I.C.ENGINES
Types of fuels used.
Nature of cycle used
Otto Cycle Engine
Diesel Cycle Engine
Dual combustion Cycle Engine
Number of strokes required
Four Stroke Engine
Two Stroke Engine
Method of Ignition
Spark ignition engines
Compression ignition engines
12. Number of Cylinders
Single Cylinder Engine
Multi Cylinder Engine
Method of Cooling
Air cooled engines
Water cooled engines
Method of governing
Hit and miss method governed engines
Quality governed engines
Quantity governed engines
Speed of Engines
Low Speed Engines
Medium Speed Engines
High Speed Engines
14. FOUR STROKE PETROL ENGINE (S.I ENGINE)
S.I engines are used in passenger cars, motor cycles, air
crafts and agricultural equipment.
Engine cycle is completed in two revolutions of
crankshaft. These two revolutions constitute the following
15. Suction Stroke:
During the suction stroke,
inlet valve opened and
the exhaust valve closed.
downwards create the
partial vacuum in the
16. Compression Stroke
During compression Stroke,
both valves are closed, piston
moving upwards compress the
charge to required pressure and
Near the end of compression
Stroke, the charge is ignited by
spark given by spark plug. Due
to combustion the pressure and
temperature are increased
further at nearly constant
17. Expansion Stroke
This is Power or working stroke.
In this stroke both valves are
closed and high pressure gas
At the end of expansions stroke,
exhaust valve opens, some of the
18. Exhaust Stroke
During this stroke, exhaust
valve is open, and inlet valve
remain closed; pistom moving
upwards forces the spent gases
through exhaust valve.
At the end of this stroke,
Exhaust valve closed and inlet
valve opens. The fresh charge is
taken into engine cylinder,
while the piston moving
19. FOUR STROKE DIESEL ENGINES
The diesel engine operates on a very similar to petrol
The major differences is that the ignition occurs
spontaneously due to the high temperature of the
compressed air, and spark plug of S.I engine replaced
with fuel injector.
20. Suction Stroke
During Suction Stroke only air is
admitted inti the cylinder.
In this stroke inlet valve open,
exhaust valve closed and piston
21. Compression Stroke:
Both valves remain closed. The
piston moving upwards
compress the air to high
pressure and temperature.
Fuel is injected into the cylinder
at the end of compression Stroke
and ignition occurs
spontaneously due to high
temperature of the compressed
22. Expansion Stroke
The Burnt gases expand
doing work on the piston.
Both valves closed, piston
moves downwards. This is
the power stroke of the
23. Exhaust Stroke:
Expanded gases are driven
out of the cylinder. Inlet valve
closed and Exhaust valve
Piston moves upwards. At
the end of exhaust Stroke
exhaust valve closed, inlet
valve opens to admit the air.