cengel ch08
TRANSCRIPT
CHAPTER
8
Gas Power Cycles
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8-1
FIGURE 8-1Modeling is a powerful engineering tool that provides great insight and simplicity at the expense of some loss in accuracy.
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8-2
FIGURE 8-2The analysis of many complex processes can be reduced to a manageable level by utilizing some idealizations.
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FIGURE 8-6P-v and T-s diagrams of a Carnot cycle.
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8-4
FIGURE 8-7A steady-flow Carnot engine.
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8-5
FIGURE 8-8T-s diagram for Example 8–1.
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FIGURE 8-10Nomenclature for reciprocating engines.
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FIGURE 8-11Displacement and clearance volumes of a reciprocating engine.
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8-8
FIGURE 8-12The net work output of a cycle is equivalent to the product of the mean effective pressure and the displacement volume.
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FIGURE 8-13Actual and ideal cycles in spark-ignition engines and their P-v diagrams.
8-9
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8-10
FIGURE 8-14Schematic of a two-stroke reciprocating engine.
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8-11
FIGURE 8-16Thermal efficiency of the ideal Otto cycle as a function of compression ratio (k = 1.4).
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FIGURE 8-18The thermal efficiency of the Otto cycle increases with the specific heat ratio k of the working fluid.
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8-13
FIGURE 8-21T-s and P-v diagrams for the ideal Diesel cycle.
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8-14
FIGURE 8-22Thermal efficiency of the ideal Diesel cycle as a function of compression and cutoff ratios (k = 1.4).
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8-15
FIGURE 8-23P-v diagram of an ideal dual cycle.
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8-16
FIGURE 8-26T-s and P-v diagrams of Carnot, Stirling, and Ericsson cycles.
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8-17
FIGURE 8-27The execution of the Stirling cycle.
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FIGURE 8-28A steady-flow Ericsson engine.
8-18
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FIGURE 8-29An open-cycle gas-turbine engine.
8-19
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8-20
FIGURE 8-30A closed-cycle gas-turbine engine.
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FIGURE 8-31T-s and P-v diagrams for the ideal Brayton cycle.
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FIGURE 8-32Thermal efficiency of the ideal Brayton cycle as a function of the pressure ratio.
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8-23
FIGURE 8-33For 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.
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8-24
FIGURE 8-36The deviation of an actual gas-turbine cycle from the ideal Brayton cycle as a result of irreversibilities.
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8-25
FIGURE 8-38A gas-turbine engine with regenerator.
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8-26
FIGURE 8-39T-s diagram of a Brayton cycle with regeneration.
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8-27
FIGURE 8-40Thermal efficiency of the ideal Brayton cycle with and without regeneration.
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8-28
FIGURE 8-42Comparison of work inputs to a single-stage compressor (1AC) and a two-stage compressor with intercooling (1ABD).
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8-29
FIGURE 8-43A gas-turbine engine with two-stage compression with intercooling, two-stage expansion with reheating, and regeneration.
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8-30
FIGURE 8-44T-s diagram of an ideal gas-turbine cycle with intercooling, reheating, and regeneration.
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8-31
FIGURE 8-45As the number of compression and expansion stages increases, the gas-turbine cycle with intercooling, reheating, and regeneration approaches the Ericsson cycle.
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8-32
FIGURE 8-48Basic 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.]
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8-33
FIGURE 8-51Energy supplied to an aircraft (from the burning of a fuel) manifests itself in various forms.
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8-34
FIGURE 8-52A turbofan engine.
[Source: The Aircraft Gas Turbine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]
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FIGURE 8-53A 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).
Photo Courtesy of Pratt&Whitney Corp.
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8-36
FIGURE 8-54A turboprop engine.
[Source: The Aircraft Gas Turbine Engine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]
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8-37
FIGURE 8-55A ramjet engine.
[Source: The Aircraft Gas Turbine Engine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]
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8-38
FIGURE 8-57Under 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).
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8-39
FIGURE 8-62Aerodynamic drag increases and thus fuel economy decreases rapidly at speeds above 55 mph.
(Source: EPA and U.S. Dept. of Energy.)