2. Carnot cycle :-
• Carnot devised an ideal cycle of operation for a heat
engine and know as carnot cycle
Carnot heat engine:
• A heat engine which works on the reversible carnot
• Nicolas Léonard Sadi Carnot was the first person
who developed the basic modle for this engine in
• The carnot’s diagram is
3. • Idealized thermodynamic cycle consisting of four
• 1-Reversible isothermal expansion
• 2-Reversible adiabatic expansion
• 3-Reversible isothermal compression
• 4-Reversible adiabatic compression
• Source:- A reservoir at high temperature is called a
source or high temp. Reservoir (HTR) or boiler.
• Sink:- A reservoir at low temperature is called a sink
or low temp. reservoir (LTR) or condenser
• The gas is allowed to expand iso-
Thermally at temperature T1 by absorbing
Heat Q from the hot reservoir. This step
Is shown by curve AB in Fig
The gas is allowed to expand adiabatically.
No heat enter or leaves the system (Q=0)
And temperature of the gas is deceased form
T1 to T2. This step is shown by curve BC in
Isothermal compression :
The gas is compressed isothermally by increasing the pressure on gas at
temperature T2. The heat Q is rejected to low temperature reservoir.
This step is shown by curve CD in Fig
.Adiabatic compression :
The gas is allowed to compress adiabatically . No heat enter or leave the system
(Q=0) and temperature of the gas is increased from T2 to T1.This step is shown y
the path DA in the Fig
*All types of vehicles that we use cars, motorcycles, trucks, ships, aero planes, and
many other types work on the basis of second law of thermodynamics and carnot
* All the refrigerators, deep freezers, industrial refrigerator system, heat pumps etc
work on the basis of the carnot cycle
7. Efficiency of Carnot cycle :
• Efficiency of Carnot cycle=work done/heat
• Efficiency of Carnot cycle depends upon the
• Efficiency increase with decrease in
8. Combustion Cycle :
• A cycle in which the process of combustion of fuel takes place
is known as Combustion cycle.
• Combustion of fuel may occur inside the engine cylinder( in
ICE) or outside the engine cylinder (in ECE).
• Combustion cycle may be take place in four stroke or in two
stroke engines .
• In a combustion cycle the combustion of fuel takes place with
an oxidizer in a combustion chamber.
• An oxidizer is used for the process of combustion
9. History :
• The first internal combustion engine was created by
Etienne Lenoir in 1859.
• It was the first internal combustion engine which
was used commercially .
• Seigfried Marcus was the first person who invented
the first modren combustion engine in 1864.
11. Combustion process :
• There are two type of combustion process
• 1-Internal combustion process
• 2-External combustion process
• Working principle :
• An internal combustion engine works on the
temperature difference. Simply works on the Carnot
12. • Internal combustion engine:-
• In which process of combustion of fuel take place
inside the engine cylinder a chemical energy
obtained from the combustion is converted into the
mechanical energy further converted into
• E.g petrol engine ,gas engine ,diesel engine
13. • Four stroke combustion engine:-
• An internal combustion engine in which piston completes
the four separate stroke while turning the crankshaft
• A stroke is that refers to full travel of the piston along the
cylinder, in either directions.
• The four separate strokes are given below:
• Intake stroke.
• Compression stroke.
• Combustion stroke /working stroke.
• Exhaust stroke.
14. • Intake stroke:
This stroke of the piston begins at top dead center (T.D.C.)
and ends at bottom dead center (B.D.C.). In this stroke the
intake valve must be in the open position while the piston
pulls an air-fuel mixture into the cylinder by producing
vacuum pressure into the cylinder through its downward
• Compression stroke:
This stroke begins at B.D.C, or just at the end of the suction
stroke, and ends at T.D.C. In this stroke the piston
compresses the air-fuel mixture in preparation for ignition
during the power stroke (below). Both the intake and
exhaust valves are closed during this stage.
15. • Combustion stroke:
This is the start of the second revolution of the four stroke
cycle. At this point the crankshaft has completed a full 360
degree revolution. While the piston is at T.D.C. (the end of
the compression stroke) the compressed air-fuel mixture is
ignited by a spark plug (in a gasoline engine) or by heat
generated by high compression (diesel engines), forcefully
returning the piston to B.D.C. This stroke produces
mechanical work from the engine to turn the crankshaft.
• Exhaust stroke:
During the exhaust stroke, the piston once again returns
from B.D.C. to T.D.C. while the exhaust valve is open. This
action expels the spent air-fuel mixture through the
18. • Two stroke combustion engine:-
• It's called a two-stroke engine because there is
a compression stroke and then a combustion stroke.
• In a four-stroke engine, there are separate intake,
compression, combustion and exhaust strokes.
• 2 Stroke cycle engine
• Mix special two-stroke oil in with the gasoline
• Mix oil in with the gas to lubricate the crankshaft,
connecting rod and cylinder walls
• Note: If you forget to mix in the oil, the engine isn't going
to last very long!
20. Intake :
The fuel/air mixture is first drawn into the
crankcase by the vacuum that is created
during the upward stroke of the piston.
• Many engines use a rotary value
incorporated into the crankshaft.
• But in this case we use poppet
21. Compression :
The piston then rises, driven by flywheel
momentum, and compresses the fuel mixture.
(At the same time, another intake stroke is
happening beneath the piston)
During the downward stroke, the
poppet valve is forced closed
by the increased crankcase
The fuel mixture is then compressed
in the crankcase during remainder
of the stroke.
22. Power :
At the top of the stroke, the spark plug ignites the fuel
mixture. The burning fuel expands, driving the
piston downward, to complete
the cycle. (At the same time, another
crankcase compression stroke is
happening beneath the piston.)
23. Exhaust :
Toward the end of the stroke, the piston
exposes the intake port, allowing
the compressed fuel/air mixture
in the crankcase to escape around
the piston into the main cylinder.
This expels the exhaust gasses out
the exhaust port, usually located
on the opposite side of the cylinder.
Unfortunately, some of the fresh
fuel mixture is usually expelled as well
24. Compression Stroke :
• Now the momentum in the crankshaft starts
driving the piston back toward the spark plug for
the compression stroke. As the air/fuel mixture in
the piston is compressed, a vacuum is created in
the crankcase. This vacuum opens the reed
valve and sucks air/fuel/oil in from the carburetor.
• Reed valves are a type of check valve which
restrict the flow of fluids to a single direction,
opening and closing under changing pressure on
25. Piston functions :
• On one side of the piston is the combustion chamber,
where the piston is compressing the air/fuel mixture
and capturing the energy released by the ignition of
• On the other side of the piston is the crankcase, where
the piston is creating a vacuum to suck in air/fuel from
the carburetor through the reed valve and then
pressurizing the crankcase so that air/fuel is forced into
the combustion chamber.
• Meanwhile, the sides of the piston are acting
like valves, covering and uncovering the intake and
exhaust ports drilled into the side of the cylinder wall
27. Difference b/w four and two stroke engine
• Four stroke
• It has one power stroke for every two
revolutions of the crankshaft.
• Engine is heavy
• Engine requires more space
• Less fuel consumption and complete
burning of fuel.
• Less noise is created by engine.
• Engine design is complicated due to
• Heavy flywheel is required and
engine runs unbalanced because
turning moment on the crankshaft is
not even due to one power stroke for
every two revolutions of the
• Used in cars, buses, trucks etc.
• Two stroke
• It has one power stroke for each
revolution of the crankshaft.
• Engine is light
• Engine requires less space
• More fuel consumption and fresh
charge is mixed with exhaust gases
• More noise is created by engine
• Engine design is simple due to
absence of valve mechanism
• Lighter flywheel is required and
engine runs balanced because
turning moment is more even due to
one power stroke for each revolution
of the crankshaft.
• Used in mopeds,
28. • External combustion engine:-
• In which combustion of the fuel take place outside
the engine a chemical energy obtained from the
combustion is converted into mechanical energy
further converted into the mechanical work
• Steam engine
30. Difference b/w ICE and ECE engine
• Internal combustion engine :
• In an internal combustion engine,
the working fluid consists of a
combustible fluid placed inside a
• It can work at high temperature
• It takes less place for installation.
• It is more reliable and useful.
• External combustion engine :
• In external combustion engines,
combustion occurs outside the
cylinder. The heat needs to be
transferred into the working fluid
• It cannot work at high temperature
• It takes more place for installation.
• It is not very reliable and useful.