CHAPTER 8 Gas Power Cycles

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-1 FIGURE 8-1 Modeling is a powerful engineering tool that provides great insight and simplicity at the expense of some loss in accuracy.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-2 FIGURE 8-2 The analysis of many complex processes can be reduced to a manageable level by utilizing some idealizations.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-3 FIGURE 8-6 P-v and T-s diagrams of a Carnot cycle.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-4 FIGURE 8-7 A steady-flow Carnot engine.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-5 FIGURE 8-8 T-s diagram for Example 8–1.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-6 FIGURE 8-10 Nomenclature for reciprocating engines.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-7 FIGURE 8-11 Displacement and clearance volumes of a reciprocating engine.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-8 FIGURE 8-12 The net work output of a cycle is equivalent to the product of the mean effective pressure and the displacement volume.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. FIGURE 8-13 Actual and ideal cycles in spark-ignition engines and their P-v diagrams. 8-9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-14 Schematic of a two- stroke reciprocating engine.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-16 Thermal efficiency of the ideal Otto cycle as a function of compression ratio (k = 1.4).

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-18 The thermal efficiency of the Otto cycle increases with the specific heat ratio k of the working fluid.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-21 T-s and P-v diagrams for the ideal Diesel cycle.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-22 Thermal efficiency of the ideal Diesel cycle as a function of compression and cutoff ratios (k = 1.4).

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-23 P-v diagram of an ideal dual cycle.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-26 T-s and P-v diagrams of Carnot, Stirling, and Ericsson cycles.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-27 The execution of the Stirling cycle.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. FIGURE 8-28 A steady-flow Ericsson engine. 8-18

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. FIGURE 8-29 An open-cycle gas-turbine engine. 8-19

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-30 A closed-cycle gas-turbine engine.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. FIGURE 8-31 T-s and P-v diagrams for the ideal Brayton cycle. 8-21

8-22 FIGURE 8-32 Thermal efficiency of the ideal Brayton cycle as a function of the pressure ratio. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-36 The deviation of an actual gas- turbine cycle from the ideal Brayton cycle as a result of irreversibilities.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-38 A gas-turbine engine with regenerator.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-39 T-s diagram of a Brayton cycle with regeneration.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-40 Thermal efficiency of the ideal Brayton cycle with and without regeneration.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-42 Comparison of work inputs to a single-stage compressor (1AC) and a two- stage compressor with intercooling (1ABD).

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-43 A gas-turbine engine with two- stage compression with intercooling, two- stage expansion with reheating, and regeneration.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-44 T-s diagram of an ideal gas-turbine cycle with intercooling, reheating, and regeneration.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 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.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 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.]

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-51 Energy supplied to an aircraft (from the burning of a fuel) manifests itself in various forms.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-52 A turbofan engine. [Source: The Aircraft Gas Turbine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 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). Photo Courtesy of Pratt&Whitney Corp.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-54 A turboprop engine. [Source: The Aircraft Gas Turbine Engine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-55 A ramjet engine. [Source: The Aircraft Gas Turbine Engine and Its Operation. © United Aircraft Corporation (now United Technologies Corp.), 1951, 1974.]

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 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).

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 8-62 Aerodynamic drag increases and thus fuel economy decreases rapidly at speeds above 55 mph. (Source: EPA and U.S. Dept. of Energy.)