9-21
9-34E A six-cylinder, four-stroke, spark-ignition engine operating on the ideal Otto cycle is considered. The power
produced by the engine is to be determined.
c
v
= 0.171 Btu/lbm·R, and k = 1.4 (Table A-2Ea).
20.10
09801
1
2
1
v
v
v
v
.
r
1
P
3
9-22
9-35E An Otto cycle with non-isentropic compression and expansion processes is considered. The thermal efficiency, the
heat addition, and the mean effective pressure are to be determined.
Assumptions 1 The air-standard assumptions are applicable. 2 Kinetic and potential energy changes are negligible. 3 Air is
Analysis We begin by determining the temperatures of the cycle
states using the process equations and component efficiencies. The
P
3
9-23
9-36E An ideal Otto cycle with air as the working fluid has a compression ratio of 8. The amount of heat transferred to the
air during the heat addition process, the thermal efficiency, and the thermal efficiency of a Carnot cycle operating between
the same temperature limits are to be determined.
Assumptions 1 The air-standard assumptions are applicable. 2 Kinetic and
3
Btu/lbm92.04
1
u
Btu/lbm 241.42
28.21170.452
23
3
uuq
in
(b) Process 3-4: isentropic expansion.
4
v
4
qin
qout
9-26
Diesel Cycle
9-40C A diesel engine differs from the gasoline engine in the way combustion is initiated. In diesel engines combustion is
9-27
9-44 An air-standard Diesel cycle with a compression ratio of 16 and a cutoff ratio of 2 is considered. The temperature after
the heat addition process, the thermal efficiency, and the mean effective pressure are to be determined.
Assumptions 1 The air-standard assumptions are applicable. 2 Kinetic and potential energy changes are negligible. 3 Air is
an ideal gas with variable specific heats.
9-28
9-45 An air-standard Diesel cycle with a compression ratio of 16 and a cutoff ratio of 2 is considered. The temperature after
the heat addition process, the thermal efficiency, and the mean effective pressure are to be determined.
= 1.4 (Table A-2).
Analysis (a) Process 1-2: isentropic compression.
4
1
1
k
v
P
2
3
qin
9-32
9-49 An ideal dual cycle has a compression ratio of 14 and cutoff ratio of 1.2. The thermal efficiency, amount of heat added,
and the maximum gas pressure and temperature are to be determined.
k = 1.4 (Table A-2).
Analysis The specific volume of the air at the start of the compression is
K) 253)(K/kgmkPa 287.0( 3
3
1
RT
9-36
9-53 A diesel engine with air as the working fluid has a compression ratio of 20. The thermal efficiency and the mean
effective pressure are to be determined.
Assumptions 1 The air-standard assumptions are applicable. 2 Kinetic and potential energy changes are negligible. 3 Air is
9-37
9-54 Problem 9-53 is reconsidered. The effect of the compression ratio on the net work output, mean effective
pressure, and thermal efficiency is to be investigated. Also, T–s and P–
v
diagrams for the cycle are to be plotted.
Analysis Using EES, the problem is solved as follows:
Procedure QTotal(q_12,q_23,q_34,q_41: q_in_total,q_out_total)
n=1.35
{r_comp = 20}
R=0.287 [kJ/kg-K]
V[2] = V[1]/ r_comp
“Conservation of energy for process 1 to 2″
q_12 – w_12 = DELTAu_12
q_12 =0“isentropic process”
P[3]/P[4] =(V[4]/V[3])^n
s[4]=entropy(air,T=T[4],P=P[4])
P[4]*v[4]=R*T[4]
“Conservation of energy for process 3 to 4″
q_34 – w_34 = DELTAu_34 “q_34 is not 0 for the ploytropic process”
9-38
MEP = w_net/(V[1]-V[2])
rcomp
th
MEP
[kPa]
wnet
[kJ/kg]
14
47.69
970.8
797.9
16
50.14
985
817.4
18
52.16
992.6
829.8
20
53.85
995.4
837.0
22
55.29
994.9
840.6
24
56.54
992
841.5
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
s [kJ/kg-K]
T [K]
95 kPa
340.1 kPa
5920 kPa
0.044
0.1
0.88 m3/kg
Air
2
1
3
4
10-2 10-1 100101102
101
102
103
104
101
102
103
104
P [kPa]
293 K
1049 K
2200 K
5.69
6.74 kJ/kg-K
Air
9-39
14 16 18 20 22 24
790
800
810
820
830
840
850
rcomp
wnet [kJ/kg]
14 16 18 20 22 24
47
49
51
53
55
57
rcomp
th
14 16 18 20 22 24
970
975
980
985
990
995
1000
MEP [kPa]
9-40
9-55 A four-cylinder ideal diesel engine with air as the working fluid has a compression ratio of 22 and a cutoff ratio of 1.8.
The power the engine will deliver at 2300 rpm is to be determined.
k = 1.4 (Table A-2).
Analysis Process 1-2: isentropic compression.
4
1
1
k
V
P
2
Qin