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Spring 2006
1
ME 201
Thermodynamics
Homework #10 Solutions
1. Three of the process that occur in the piston cylinder device of an internal
combustion engine are:
Process 1: Constant pressure heat addition during which the volume doubles
Process 2: Isentropic expansion during which the volume increases 9 times
Process 3: Constant volume heat removal to a final pressure of 100 kPa
At the start of process 1 the engine contains 0.035 liters of air at 950 K and 5.7
MPa. For each of the three processes the air undergoes find the work and heat
transfer in kJ. What is the total work and heat transfer for all three processes
together?
Solution:
We will work this problem process by process.
System Type: Closed System
Working Fluid: Air (ideal gas)
Process: Isobaric
State 1
State 2
T
1
= 950 K
T
2
=
1900 K
P
1
= 5700 kPa
P
2
=
5700 kPa
V
1
= 0.035 liters
= 3.5 x 10
5
m
3
V
2
=
7.0 x 10
5
m
3
m
1
=
7.317 x 10
4
kg
m
2
=
7.317 x 10
4
kg
u
1
=
716.55 kJ/kg
u
2
=
1582.6 kJ/kg
v
1
=
4.783 x 10
2
m
3
/kg
v
2
=
9.566 x 10
2
m
3
/kg
Italicized
values are from ideal gas relations or air tables.
Bold
values are calculated.
Q = UNKNOWN
W
sh
= 0
W
bnd
= P(V
2
V
1
) (isobaric)
Initial State: Fixed
Final State: UNKNOWN
Conservation of Mass: m
1
= m
2
1st Law: U
2
 U
1
= QW
bnd
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Spring 2006
2
Approach: To fix the final state we will use our process description along with the
conservation of mass to determine the final specific volume. The boundary work is
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 Spring '06
 SOMERTON
 Combustion

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