Universidad de Guanajuato, DICIS.
Termodinámica.
Homework #9. Gas Power Systems.
9.3. At the beginning of the compression process of an air-standard Otto cycle, p1 =1bar, T1 = 290K,
V1 = 400 cm3. The maximum temperature in the cycle is 2200 K and the compression ratio is 8.
Determine
(a) the heat addition, in kJ.
(b) the net work, in kJ.
(c) the thermal efficiency.
(d) the mean effective pressure, in bar.
9.9. At the beginning of the compression process in an air-standard Otto cycle, p1 = 14.7 lbf/in2 and
T1 = 530°R. Plot the thermal efficiency and mean effective pressure, in lbf/in 2, for maximum cycle
temperatures ranging from 2000 to 5000°R and compression ratios of 6, 8 and 10.
9.12. The compression ratio of a cold air-standard Otto cycle is 9. At the end of the expansion
process, the pressure is 95 lbf/in2 and the temperature is 1000°R. the heat rejection from the cycle is
86 Btu per lb of air. Assuming k =1.4, determine
(a) the net work, in Btu per lb of air.
(b) the thermal efficiency.
(c) the mean effective pressure, in lbf/in2.
9.21. The compression ratio of an air-standard Diesel cycle is 17 and the conditions at the beginning
of compression are p1 = 14.0 lbf/in2, V1 = 2 ft3, and T1 = 520°R. The maximum temperature in the
cycle is 4000°R. Calculate
(a) the net work for the cycle, in Btu.
(b) the thermal efficiency.
(c) the mean effective pressure, in lbf/in2.
(d) the cutoff ratio.
9.22. Solve Problem 9.21 on a cold air-standard basis with specific heats evaluated at 520°R.
9.29. An air-standard Diesel cycle has a maximum temperature of 1800 K. At the beginning of
compression, p1 = 95 kPa and T1 = 300 K. the mass of air is 12 kg. For compression ratios ranging
from 15 to 25 plot
(a) the net work of the cycle, in kJ.
(b) the thermal efficiency.
(c) the mean effective pressure, in kPa.
9.32. An air standard dual cycle has a compression of 9. At the beginning of compression, p1 = 100
kPa and T1 = 300 K. The heat addition per unit mass of air is 1400 kJ/kg, with one half added at
constant volume and one half added at constant pressure. Determine
(a) the temperatures at the end of each heat addition process, in K.
(b) the net work of the cycle per unit mass of air, in kJ/kg.
(c) the thermal efficiency.
(d) the mean effective pressure, in kPa.
Dr. Francisco Elizalde Blancas
Universidad de Guanajuato, DICIS.
Termodinámica.
9.35. The thermal efficiency, η, of a cold air-standard dual cycle can be expressed as
1 𝑟𝑝 𝑟𝑐𝑘 − 1
𝜂 =1− [ ]
𝑟 𝑘−1 (𝑟𝑐 − 1) + 𝑘𝑟𝑝 (𝑟𝑐 − 1)
where r is the compression ratio, rc is cutoff ratio, and rp is the pressure ratio for the constant
volume heat addition. Derive this expression.
9.37. The pressure and temperature at the beginning of compression in an air-standard dual cycle
are 14.0 lbf/in2 and 520°R, respectively. The compression ratio is 15 and the heat addition per unit
mass of air is 800 Btu/lb. At the end of the constant volume heat addition process, the pressure is
1200 lbf/in2. Determine
(a) the net work of the cycle per unit mass of air, in Btu/lb.
(b) the heat rejection for the cycle per unit mass of air, in Btu/lb.
(c) the thermal efficiency.
(d) the cutoff ratio.
(e) To investigate the effects of varying compression ratio, plot each of the quantities
calculated in parts (a) through (d) for compression ratios ranging from 10 to 28.
Dr. Francisco Elizalde Blancas
