646 ENGINEERING THERMODYNAMICS

dharm

\M-therm\Th13-3.pm5

+Example 13.26. In an engine working on Dual cycle, the temperature and pressure at
the beginning of the cycle are 90°C and 1 bar respectively. The compression ratio is 9. The
maximum pressure is limited to 68 bar and total heat supplied per kg of air is 1750 kJ.
Determine :
(i)Pressure and temperatures at all salient points
(ii)Air standard efficiency
(iii)Mean effective pressure.
Solution. Refer Fig. 13.22.

Adiabatics

p (bar)

68 3 4

2

1

5

1(90°C)

V(m )^3

Fig. 13.22

Initial pressure, p 1 = 1 bar

Initial temperature, T 1 = 90 + 273 = 363 K

Compression ratio, r = 9

Maximum pressure, p 3 = p 4 = 68 bar

Total heat supplied = 1750 kJ/kg

(i) Pressures and temperatures at salient points :

For the isentropic process 1-2,

p 1 V 1 γ = p 2 V 2 γ

p 2 = p 1 ×

V

V

(^1) r
2
1
F
HG
I
KJ
=×
γ
()γ = 1 × (9)1.4 = 21.67 bar. (Ans.)
Also, T
T
V
V
(^2) r
1
1
2
1
=F^11419
HG
I
KJ

−
−−
γ
()γ ( ). = 2.408
∴ T 2 = T 1 × 2.408 = 363 × 2.408 = 874.1 K. (Ans.)
p 3 = p 4 = 68 bar. (Ans.)