Chapter 1 Gas Power Cycle

Analysis of Air Standard Otto Cycle (cont’d)
Thermal efficiency
w
η th =
q
w
1
2
3
C
= c,
k =
C
P2v
2 − P1v
1
1w
2 =
1−
k
R(
T2
− T1
)
1w
2 =
1−
k
qL
4 q
or,
η th = 1−
= 1−
q q
Mean Effective Pressure
w
net
w =
Pv
k
net
= w + w
∫
net
in
Pdv
= MEP ( v − v )
4
H
1
p
v
2
2
1
3
P
T
3
2
v 2 =v 3
1
Pv k = c
2
s 1 =s 2
Pv k = c
v = const.
v =
const.
Spark-ignition Engine
1. The higher r v the higher thermal eff.
2. The higher r v cause Self-Ignition � engine knock
3. Higher Octane Number of fuel used retard the self-ignition
4. Typical r v of gasoline engine ~ 9.0 – 10.0
5. Thermal efficiency of actual spark ignition engine ~ 25-30%
v
w in
q in
q out
w out
4
1
v 1 =v 4
3
4
s3 =s 4
v
v
s