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17.1 THE GAS TURBINE CYCLE        383




                        (a)                              (b)
                                 Constant
                                               3                  3
                                 pressure                    2
                         Temperature, T  2                Pressure, p     Isentropic




                                                4
                                                                                 4
                                                                  1
                                             Isentropic     Constant
                                 1                          pressure
                                           Specific entropy, s                   Volume, V
               FIGURE 17.2
               Property diagrams for gas turbine cycle. (a) Temperature–entropy (T–s) diagram. (b) Pressure–volume (p–V )
               diagram.

               hot exhaust gas but no shaft power. This engine is depicted in Fig.17.3(a) and the cycle is shown in
               Fig. 17.3(b).
                  In the basic jet engine there is a power balance between the compressor and turbine and no shaft
               work is delivered. The output of a jet engine is the net thrust provided by the engine, which is a result of
               the momentum change of the air across the engine and, in the case of sonic exhaust, the pressure

                                                        (b)                      3

                                                          Temperature, T          p =p 3
                                                                                  2

                    (a)

                                 Combustion  Propulsion                         4
                            Fuel
                                 chamber     nozzle
                    Air                          Exhaust        2
                           2       3
                    1                  4           5                              p =p 5
                                                                                   1
                         C          T                                            5


                                                                1

                                                                                      Entropy, s
               FIGURE 17.3
               Jet gas turbine. (a) Schematic of engine. (b) Temperature–entropy (T–s) diagram for cycle.
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