Q 1. An ideal Otto cycle has a compression ratio of 8.
At the beginning of the compression process, air is at 100 kPa
and 17ºC, 0.832 m3/kg and 800 kJ/kg of heat is transfer to the air during constant volume heat addition process.
Accounting for the variation of specific heat of air with temperature, determine a) the maximum temperature and
pressure that occurring during the cycle, b) Net work output, c) thermal efficiency and mean effective pressure of
cycle.
Ans. T 1575.1 K, 4.35 MPa, 418.17 kJ/kg, 52.3%, 574 kPa
Q 2. The idea diesel cycle with air is working fluid has a compression ratio of 18 and the cut off ratio of 2. At the
beginning of the compression process, the working fluid is at 100 kPa, 27ºC, and 1917 cm3. Utilizing the cold air
standard assumption, determine (a) temperature and pressure of air at the end of each process, b) network output
and the thermal efficiency, and c) mean effective pressure.
Ans. T2 953 K, P2=5720, T3=1906 K, T4=791 K, P4= 264 kPa, W= 1.35 kJ, ȵ= 63.2% MEP= 746 kPa
Note: properties of the air are R = 0.287 kPa-m3/kg K and its other properties is room temperature are Cp 1.005 kJ/kg
K, Cv 0.718 kJ/kg K.
Q 3. A gas turbine power plant operating on an ideal Brayton cycle has a pressure ratio of 8. The gas temperature is
300 K at the compressor inlet and 1300 K at the turbine inlet utilizing the air standard assumption, determine (a) the
gas temperature at the exit of the compressor and the turbine, (b) back work ratio and (c) the thermal efficiency.
Ans. T2 540 K, P4 = 770 K, Rbk= 0.403, ȵ= 42.6% ȵ Brayton = 44.8%
Q 4. An engine working an Otto cycle is supplied with air at 0.1 MPa, 35ºC. the compression ratio is 8. Heat supplied is
2100 kJ/kg. calculate the maximum pressure and temperature of the cycle, the cycle efficiency and the mean effective
pressure. For air R = 0.287 kPa-m3/kg K and Cp 1.005 kJ/kg K, Cv 0.718 kJ/kg K.
Ans. 56.5%, T=3633 K, P=9.426 MPa, MEP=1.533 MPa
Q 5. A diesel engine has a compression ratio of 14 and cut-off takes place at 6% of the stroke. Find the air standard
efficiency.
Ans. 60.5%
Q 6. In air standard diesel cycle, the compression ratio is 16, and at the beginning of isentropic compression, the
temperature is 15ºC. and the pressure is 0.1 MPa. Heat is added until the temperature at the end of constant pressure
process is 1480 ºC. calculate (a) the cut of ratio, (b) the heat supplied per kg of air (c) the cycle efficiency and the (d)
mean effective pressure.
Ans. Rc =2.01, 61.2%, mep=698.45 kPa
