Chapter 9 | 539PROBLEMS*Actual and Ideal Cycles, Carnot Cycle, Air-Standard
Assumptions, Reciprocating Engines
9–1C Why is the Carnot cycle not suitable as an ideal cycle
for all power-producing cyclic devices?
9–2C How does the thermal efficiency of an ideal cycle, in
general, compare to that of a Carnot cycle operating between
the same temperature limits?
9–3C What does the area enclosed by the cycle represent
on a P-vdiagram? How about on a T-sdiagram?
9–4C What is the difference between air-standard assump-
tions and the cold-air-standard assumptions?
9–5C How are the combustion and exhaust processes mod-
eled under the air-standard assumptions?
9–6C What are the air-standard assumptions?
9–7C What is the difference between the clearance volume
and the displacement volume of reciprocating engines?
9–8C Define the compression ratio for reciprocating engines.
9–9C How is the mean effective pressure for reciprocating
engines defined?
9–10C Can the mean effective pressure of an automobile
engine in operation be less than the atmospheric pressure?
9–11C As a car gets older, will its compression ratio change?
How about the mean effective pressure?
9–12C What is the difference between spark-ignition and
compression-ignition engines?
9–13C Define the following terms related to reciprocating
engines: stroke, bore, top dead center, and clearance volume.
9–14 An air-standard cycle with variable specific heats is
executed in a closed system and is composed of the following
four processes:
1-2 Isentropic compression from 100 kPa and 27°C to
800 kPa
2-3 vconstantheat addition to 1800 K
3-4 Isentropic expansion to 100 kPa
4-1 Pconstantheat rejection to initial state
(a) Show the cycle on P-vand T-sdiagrams.
(b) Calculate the net work output per unit mass.
(c) Determine the thermal efficiency.
9–15 Reconsider Problem 9–14. Using EES (or other)
software, study the effect of varying the temper-
ature after the constant-volume heat addition from 1500 K to
2500 K. Plot the net work output and thermal efficiency as a
function of the maximum temperature of the cycle. Plot the
T-sand P-vdiagrams for the cycle when the maximum tem-
perature of the cycle is 1800 K.
9–16 An air-standard cycle is executed in a closed system
and is composed of the following four processes:
1-2 Isentropic compression from 100 kPa and 27°C to
1 MPa
2-3 Pconstantheat addition in amount of 2800
kJ/kg
3-4 vconstantheat rejection to 100 kPa
4-1 Pconstantheat rejection to initial state
(a) Show the cycle on P-vand T-sdiagrams.
(b) Calculate the maximum temperature in the cycle.
(c) Determine the thermal efficiency.
Assume constant specific heats at room temperature.
Answers:(b) 3360 K, (c) 21.0 percent
9–17E An air-standard cycle with variable specific heats is
executed in a closed system and is composed of the following
four processes:
1-2 vconstantheat addition from 14.7 psia and
80°F in the amount of 300 Btu/lbm
2-3 Pconstantheat addition to 3200 R
3-4 Isentropic expansion to 14.7 psia
4-1 Pconstantheat rejection to initial state
(a) Show the cycle on P-vand T-sdiagrams.
(b) Calculate the total heat input per unit mass.
(c) Determine the thermal efficiency.
Answers:(b) 612.4 Btu/lbm, (c) 24.2 percent
9–18E Repeat Problem 9–17E using constant specific heats
at room temperature.
9–19 An air-standard cycle is executed in a closed system
with 0.004 kg of air and consists of the following three
processes:
1-2 Isentropic compression from 100 kPa and 27°C to
1 MPa
2-3 Pconstantheat addition in the amount of 2.76 kJ
3-1 Pc 1 v+ c 2 heat rejection to initial state (c 1 and
c 2 are constants)
(a) Show the cycle on P-vand T-sdiagrams.
(b) Calculate the heat rejected.
(c) Determine the thermal efficiency.
Assume constant specific heats at room temperature.
Answers:(b) 1.679 kJ, (c) 39.2 percent- Problems designated by a “C” are concept questions, and students
are encouraged to answer them all. Problems designated by an “E”
are in English units, and the SI users can ignore them. Problems
with a CD-EES icon are solved using EES, and complete solutions
together with parametric studies are included on the enclosed DVD.
Problems with a computer-EES icon are comprehensive in nature,
and are intended to be solved with a computer, preferably using the
EES software that accompanies this text.