AME 436

Effect of compression ratio (Otto)"
Animation: T-s diagrams, increasing compression ratio (same
displacement volume, same fuel mass fraction (f), thus same heat input)
Higher compression clearly more efficient (taller Carnot strips)
800
Compression Combustion Expansion
Blowdown Intake Exhaust
Close T-s cycle 1 2
3 4 5
6 7
700
Temperature (K)
600
500
400
300
200
T-s diagram
(medium (high (low compression)
100
0
-100 0 100 200 300 400 500
Entropy (J/kg-K)
AME 436 - Lecture 8 - Spring 2013 - Ideal cycle analysis
9
Effect of heat input (Otto)"
Animation: P-V diagrams, increasing heat input via increasing f (same
displacement volume, same compression ratio)
Heat in = mC v ( T 4
!T 3 ) = m R " P 4
V 4
! !1 mR ! PV % (
3 3
$
# mR &
' = P ! P )V
4 3
! !1
Pressure (atm)
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
Compression Combustion Expansion
Blowdown Intake Exhaust
Intake start 1 2
3 4 5
6 7
P-V diagram
P-V diagram
(high (low heat input)
(medium heat
0.0
0.0E+00 1.0E-03 2.0E-03 3.0E-03 4.0E-03 5.0E-03 6.0E-03
Cylinder volume (m^3)
AME 436 - Lecture 8 - Spring 2013 - Ideal cycle analysis
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