TITLE.PM5

650 ENGINEERING THERMODYNAMICS

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3. Effect of variable specific heat, heat loss through cylinder walls, inlet and exhaust veloci-
   ties of air/gas etc. have not been taken into account.

+Example 13.28. A Diesel engine working on a dual combustion cycle has a stroke vol-
ume of 0.0085 m^3 and a compression ratio 15 : 1. The fuel has a calorific value of 43890 kJ/kg. At
the end of suction, the air is at 1 bar and 100°C. The maximum pressure in the cycle is 65 bar and
air fuel ratio is 21 : 1. Find for ideal cycle the thermal efficiency. Assume cp = 1.0 and cv = 0.71.
Solution. Refer Fig. 13.24.

p (bar)

1(100°C)

V(m )^3

5

1

65 3 4

2

V = 0.0085 ms^3

Fig. 13.24

Initial temperature, T 1 = 100 + 273 = 373 K

Initial pressure, p 1 = 1 bar

Maximum pressure in the cycle, p 3 = p 4 = 65 bar

Stroke volume, Vs = 0.0085 m^3

Air-fuel ratio = 21 : 1

Compression ratio, r = 15 : 1

Calorific value of fuel, C = 43890 kJ/kg

cp = 1.0, cv = 0.71

Thermal efficiency :

Vs = V 1 – V 2 = 0.0085

and as r =

V

V

1

2

= 15, then V 1 = 15V 2
∴ 15 V 2 – V 2 = 0.0085
or 14 V 2 = 0.0085

or V 2 = V 3 = Vc =
0 0085
14

.

= 0.0006 m^3

or V 1 = 15V 2 = 15 × 0.0006 = 0.009 m^3