Example
Prof.Naik © 2011
Air enters the cylinder of a spark-ignition engine at 0.95 bar
Air enters the cylinder of a spark ignition engine at 0.95 bar
and 17
C.
The engine has a compression ratio of 8.
At the
beginning of the compression stroke, the cylinder volume is
2.2 L.
It is known that 3.6 kJ of heat is added during the
constant volume process.
Consider that the engine can be
modeled as
cold air-standard
Otto cycle.
consider constant
specific heats for working fluid (air)
C l
l t
th
t
t
(K)
d
(b
) f
h
» Calculate the temperature (K) and pressure (bar) for each
state in the cycle.
» What is the thermal efficiency (%) of the cycle?
What is the thermal efficiency (%) of the cycle?
» Determine the mean effective pressure (bar) for the cycle.

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Example (contd.)
Prof.Naik © 2011
Given
P = 0 95 bar T = 17
C = 290 K
P
1
= 0.95 bar, T
1
= 17
r = V
1
/V
2
= 8
V
1
= 2.2 L = 2.2 × 10
-3
m
3
Q
in
= Q
23
= 3.6 kJ
Find
T
2
, P
2
T
3
, P
3
T
4
, P
4
(K and bar)
Thermal efficiency (%)
MEP (bar)
Assumptions
- Air ideal gas
- Cylinder is closed system
- Neglect change in KE and PE
- All processes internally reversible
- Isentropic compression and expansion