UMLAZI KWAZULU-NATAL
P.O. Box 1263 Jacobs 4026 Durban Tell: 031 907 7111 Fax: 031 907 2892
THERMODYNAMICS APPLIED III: TUTORIAL #4
GAS ENGINE CYCLES (APPLICATION)
1. A four stroke SI engine has the compression ratio of 6 and swept volume of 0.15 m 3. Pressure and
temperature at the beginning of compression are 98 kPa and 60ºC. Determine the pressure, volume
and temperatures at all salient points if heat supplied to it is 150 kJ/kg. Also find out entropy change,
work done, efficiency and mean effective pressure of cycle assuming Cp = 1 kJ/kg · K, Cv = 0.71
kJ/kg · K. Also plot the cycle on T-s diagram. Ans. (∆S = 0.1287 kJ/kg.K; Wnet = 76.75 kJ; Eff.
=51.17% and m.e.p = 511.67).
Note: m.e.p = P/∆V and
swept volume (V2 -V1) or (V4 – V3), see page #2
2. In a Diesel engine during the compression process, pressure is seen to be 138 kPa at 1/8th of stroke
and 1.38 MPa at 7/8th of stroke. The cut-off occurs at 1/15th of stroke. Calculate air standard
efficiency and compression ratio assuming indicated thermal efficiency to be half of ideal
efficiency, mechanical efficiency as 0.8, calorific value of fuel = 41800 kJ/kg and γ = 1.4. Ans.
(Compression ratio = 19.37 and Air standard efficiency = 63.25%)
3. In an air standard Brayton cycle the minimum and maximum temperature are 300 K and 1200 K,
respectively. The pressure ratio is that which maximizes the net-work developed by the cycle per
unit mass of air flow. Calculate the compressor and turbine work, each in kJ/kg air, and thermal
efficiency of the cycle. Ans. (Compressor work = 301.71 kJ/kg, Turbine work = 603.21 kJ/kg,
and Thermal efficiency = 50.02%)
P.O. Box 1263 Jacobs 4026 Durban Tell: 031 907 7111 Fax: 031 907 2892
THERMODYNAMICS APPLIED III: TUTORIAL #4
GAS ENGINE CYCLES (APPLICATION)
1. A four stroke SI engine has the compression ratio of 6 and swept volume of 0.15 m 3. Pressure and
temperature at the beginning of compression are 98 kPa and 60ºC. Determine the pressure, volume
and temperatures at all salient points if heat supplied to it is 150 kJ/kg. Also find out entropy change,
work done, efficiency and mean effective pressure of cycle assuming Cp = 1 kJ/kg · K, Cv = 0.71
kJ/kg · K. Also plot the cycle on T-s diagram. Ans. (∆S = 0.1287 kJ/kg.K; Wnet = 76.75 kJ; Eff.
=51.17% and m.e.p = 511.67).
Note: m.e.p = P/∆V and
swept volume (V2 -V1) or (V4 – V3), see page #2
2. In a Diesel engine during the compression process, pressure is seen to be 138 kPa at 1/8th of stroke
and 1.38 MPa at 7/8th of stroke. The cut-off occurs at 1/15th of stroke. Calculate air standard
efficiency and compression ratio assuming indicated thermal efficiency to be half of ideal
efficiency, mechanical efficiency as 0.8, calorific value of fuel = 41800 kJ/kg and γ = 1.4. Ans.
(Compression ratio = 19.37 and Air standard efficiency = 63.25%)
3. In an air standard Brayton cycle the minimum and maximum temperature are 300 K and 1200 K,
respectively. The pressure ratio is that which maximizes the net-work developed by the cycle per
unit mass of air flow. Calculate the compressor and turbine work, each in kJ/kg air, and thermal
efficiency of the cycle. Ans. (Compressor work = 301.71 kJ/kg, Turbine work = 603.21 kJ/kg,
and Thermal efficiency = 50.02%)
