Page 93 - Entrophy Analysis in Thermal Engineering Systems

86 Entropy Analysis in Thermal Engineering Systems

Fig. 7.1 A schematic of the T-s diagram of the irreversible closed Brayton, Otto,
Atkinson, and Diesel cycles operating between a high- and a low-temperature reservoir.

Table 7.1 The processes of the irreversible Brayton, Otto, Atkinson, and Diesel cycles.
Processes
Engine Compression Heat addition Expansion Heat removal

Brayton Nonisentropic Isobaric Nonisentropic Isobaric
Otto Nonisentropic Isochoric Nonisentropic Isochoric
Atkinson Nonisentropic Isochoric Nonisentropic Isobaric
Diesel Nonisentropic Isobaric Nonisentropic Isochoric

pressure (isobaric). In the Diesel cycle, the heat addition is isobaric, whereas
the heat removal is isochoric. Table 7.1 summarizes the processes of the four
engines.

7.2 Brayton cycle
The isentropic efficiencies of the compression and expansion pro-
cesses are defined as

η ¼ T 2s T 1 (7.1)
com
T 2 T 1
η ¼ T 3 T 4 (7.2)
exp T 3 T 4s
The temperature of the air at states 2 and 4 can be obtained using the fol-
lowing relationships.