1. CHAPTER
8
Gas Power Cycles

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FIGURE 8-1
Modeling is a
powerful
engineering tool
that provides
great insight and
simplicity at the
expense of some
loss in accuracy.
8-1

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FIGURE 8-2
The analysis of
many complex
processes can be
reduced to a
manageable level
by utilizing some
idealizations.
8-2

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FIGURE 8-6
P-v and T-s diagrams of a
Carnot cycle.
8-3

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FIGURE 8-7
A steady-flow Carnot
engine.
8-4

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FIGURE 8-8
T-s diagram for
Example 8–1.
8-5

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FIGURE 8-10
Nomenclature for
reciprocating engines.
8-6

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FIGURE 8-11
Displacement and
clearance volumes
of a reciprocating
engine.
8-7

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FIGURE 8-12
The net work
output of a cycle is
equivalent to the
product of the
mean effective
pressure and the
displacement
volume.
8-8

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FIGURE 8-13
Actual and ideal cycles in
spark-ignition engines and
their P-v diagrams.
8-9

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FIGURE 8-14
Schematic of a two-
stroke reciprocating
engine.
8-10

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FIGURE 8-16
Thermal efficiency
of the ideal Otto
cycle as a function
of compression ratio
(k = 1.4).
8-11

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FIGURE 8-18
The thermal
efficiency of the
Otto cycle increases
with the specific
heat ratio k of the
working fluid.
8-12

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FIGURE 8-21
T-s and P-v
diagrams for the
ideal Diesel cycle.
8-13

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FIGURE 8-22
Thermal efficiency of the
ideal Diesel cycle as a
function of compression
and cutoff ratios (k = 1.4).
8-14

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FIGURE 8-23
P-v diagram of an
ideal dual cycle.
8-15

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FIGURE 8-26
T-s and P-v diagrams of Carnot,
Stirling, and Ericsson cycles.
8-16

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FIGURE 8-27
The execution of the
Stirling cycle.
8-17

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FIGURE 8-28
A steady-flow Ericsson
engine.
8-18

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FIGURE 8-29
An open-cycle gas-turbine engine.
8-19

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FIGURE 8-30
A closed-cycle
gas-turbine engine.
8-20

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FIGURE 8-31
T-s and P-v
diagrams for the
ideal Brayton cycle.
8-21

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FIGURE 8-32
Thermal efficiency
of the ideal Brayton
cycle as a function
of the pressure
ratio.
8-22

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FIGURE 8-33
For fixed values of
Tmin and Tmax , the
net work of the
Brayton cycle first
increases with the
pressure ratio, then
reaches a maximum
at rp = (Tmax /Tmin) k/
[2(k – 1)],
and finally
decreases.
8-23

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FIGURE 8-36
The deviation of an
actual gas-turbine
cycle from the ideal
Brayton cycle as a
result of
irreversibilities.
8-24

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FIGURE 8-38
A gas-turbine
engine with
regenerator.
8-25

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FIGURE 8-39
T-s diagram of a
Brayton cycle with
regeneration.
8-26

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FIGURE 8-40
Thermal efficiency of
the ideal Brayton
cycle with and
without
regeneration.
8-27

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FIGURE 8-42
Comparison of
work inputs to a
single-stage
compressor (1AC)
and a two-stage
compressor with
intercooling
(1ABD).
8-28

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FIGURE 8-43
A gas-turbine
engine with two-
stage compression
with intercooling,
two-stage
expansion with
reheating, and
regeneration.
8-29

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FIGURE 8-44
T-s diagram of an
ideal gas-turbine
cycle with
intercooling,
reheating, and
regeneration.
8-30

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FIGURE 8-45
As the number of
compression and
expansion stages
increases, the gas-
turbine cycle with
intercooling,
reheating, and
regeneration
approaches the
Ericsson cycle.
8-31

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FIGURE 8-48
Basic components of a
turbojet engine and the
T-s diagram for the ideal
turbojet cycle.
[Source: The Aircraft Gas Turbine Engine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]
8-32

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FIGURE 8-51
Energy supplied to an
aircraft (from the
burning of a fuel)
manifests itself in various
forms.
8-33

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FIGURE 8-52
A turbofan engine.
8-34 [Source: The Aircraft Gas Turbine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]

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FIGURE 8-53
A modern jet
engine used to
power Boeing 777
aircraft. This is a
Pratt & Whitney
PW4084 turbofan
capable of
producing 84,000
pounds of thrust.
It is 4.87 m (192
in.) long, has a
2.84 m (112 in.)
diameter fan, and
it weighs 6800 kg
(15,000 lbm).
8-35 Photo Courtesy of Pratt&Whitney Corp.

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FIGURE 8-54
A turboprop engine.
8-36 [Source: The Aircraft Gas Turbine Engine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]

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FIGURE 8-55
A ramjet engine.
8-37 [Source: The Aircraft Gas Turbine Engine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]

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FIGURE 8-57
Under average
driving conditions,
the owner of a 30-
mpg vehicle will
spend $300 less each
year on gasoline
than the owner of a
20-mpg vehicle
(assuming $1.50/gal
and 12,000
miles/yr).
8-38

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FIGURE 8-62
Aerodynamic drag
increases and thus
fuel economy
decreases rapidly
at speeds above
55 mph.
8-39 (Source: EPA and U.S. Dept. of Energy.)