The document discusses gas power cycles including the Carnot cycle, which is recognized for its theoretical efficiency and consists of four reversible processes. The Carnot principle asserts that reversible heat engines are more efficient than irreversible ones and that efficiency only depends on the temperatures of the reservoirs. Additionally, the document introduces the ideal Otto and Diesel cycles as models for spark-ignition and compression-ignition engines, respectively.

1. BITS
Pilani
Dubai Campus
2.Gas power Cycles
Gas power Cycles

2. THE CARNOT
CYCLE
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 Heat engine operates on a cycle.
 The efficiency of heat engine depends on how the
individual processes are executed.
 The most efficient cycles are reversible cycles, that is,
the processes that make up the cycle are all reversible
processes.
 Reversible cycles cannot be achieved in practice.
However, they provide the upper limits on the
performance of real cycles.

3.  The fundamental thermodynamic cycle proposed by
French engineer Sadi Carnot in 1824, in an attempt to
explain the working of the steam engine.
 Carnot cycle is one of the best-known reversible
cycles.
 The Carnot cycle is composed of four reversible
processes.
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4. CARNOT CYCLE
 Consider an adiabatic piston-cylinder device that contains gas.
 The four reversible processes that make up
the are as follows:
 1-2 Isothermal Expansions
 2-3 Adiabatic expansions,
 3-4 Isothermal compressions and
 4-1 Adiabatic compressions.
Carnot cycle

5. • Figure : A Carnot cycle acting as a heat engine, illustrated on a temperature-entropy
diagram. The cycle takes place between a hot reservoir at temperature TH and a
cold reservoir at temperature TC. The vertical axis is temperature, the horizontal
axis is entropy.
:

6. The Carnot Cycle (1-2): Reversible Isothermal Expansion
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7. The Carnot Cycle (2-3): Reversible Adiabatic Expansion
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8. The Carnot Cycle (3-4): Reversible Isothermal Compression
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9. The Carnot Cycle (4-1): Reversible Adiabatic Compression
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10. •The Carnot principle states that the reversible heat engines have the highest
efficiencies when compared to irreversible heat engines working between the same two
reservoirs.
•And the efficiencies of all reversible heat engines are the same if they work between
the same two reservoirs.
 The efficiency of a reversible heat engine is independent
 on the working fluid used and its properties,
 The way the cycle operates,
 The type of the heat engine.
The efficiency of a reversible heat engine is a function of the reservoirs'
temperature only.
The Carnot principle
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11. ηth = 1 - QL/QH = g(TH,TL)
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or
QH/QL = f(TH,TL)
Where QL= the
heat transferred to
reservoir which has a temperature of TL
low-temperature
QH
=
heat
reservoir
transferred
from which
has a
the high-temperature
temperature of TH
g, f = any function

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IDEAL OTTO CYCLE - IDEAL CYCLE FOR SPARK-
IGNITION ENGINES
Otto cycle is the ideal cycle for
spark-ignition engines, in honor of
Nikolaus Otto, who invented it in
1867.
In ideal Otto cycles, air-standard
assumption is used.
The ideal Otto cycle consists of four
internal reversible processes:
 1-2 Isentropic compression
 2-3 Constant volume heat addition
 4-1 Constant volume heat rejection

13. Otto cycle is the ideal cycle for
spark-ignition
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16. Example:
1
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18. Example:
2
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22. Example:
3
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23. Example:
4
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27. Diesel Cycle - Ideal Cycle for Compression-ignition Engines
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30. Engine Swept Volume (Vec) : where: Vc = engine swept volume or
Cylinder volume [cm3 (cc) or L] n = number of cylinders Vec = cylinder
swept volume [cm3 (cc) or L] =Vc n Ac = cylinder area [cm2 or
cm2/100] dc = cylinder diameter [cm or cm/10] The units of cylinder
swept volume is measured in (cm3, cubic centimeter (cc), or liter).

31. Example:
1
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32. Example:
2
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33. Example:
3
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34. Example:
4
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35. Example:
5
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38. Example:
6
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40. Example:
7
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46. Example:
1
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