Leave the turbine exit at station 4 still hot and at

leave the turbine exit at station 4, still hot and at a stagnation pressure well above the
ambient. These gases then expand through a nozzle that converts the excess pressure and
thermal energy into a high-kinetic-energy jet at station 5. The forward thrust on the
engine, according to Newton’s Second Law, is produced by the reaction to the internal
forces that accelerate the internal flow rearward to a high jet velocity and the excess of
the nozzle exit plane pressure over the upstream ambient pressure.
Diffuser Analysis

Consider a fluid element passing through a given point at the inlet diffuser. The
pressure, temperature and density feel when the measurements device feel is the static
condition (the condition when you feel when you ride along with the gas at the local flow
velocity). However along the fluid element journey from the inlet to the outlet of the
diffuser, the fluid element is adiabatically slow it down to zero velocity. Thus, the change
in fluids kinetic energy must be taken into account (become total condition). The relation
between static and total pressure is given as;
a
k
k
static
total
p
p
M
k
P
P
' 1
1
2
2
1
1 =






-
+ =
-
The effects of friction, turbulence and other irreversibilities in the inlet flow are
represented by the diffuser efficiency. The adiabatic diffuser efficiency is defined as the
ratio of the actual isentropic enthalpy change to the ideal isentropic enthalpy change. In
terms of the static and total pressures, the diffuser efficiency becomes;
a
a
d
p p
p p
-
-
=
' 1
1 η
Other parameter in measuring diffuser efficiency are called recovery factor and
pressure drop specific which are defined as;
Recovery factor;
a
a
r
p
p
1
= η
Pressure drop specific;
' 1
1 ' 1
p
p p
E
r
-
=

Isentropic process
k
k
p
p
T
T
1
0
' 1
0
' 1
-








=
1 ' 1
T T =
Diffuser work (jet)- work in
2
) (
2
1
0 1
V
T T cp w
d
= - =
kJ/kg
Compressor Analysis
Compressor efficiency;
1 2
1 ' 2
1 2
1 ' 2
T T
T T
h h
h h
leWork Irrevessib
Work Isentropik
c
-
-
=
-
-
= = η

Isentropic process
k
k
p
p
T
T
1
1
' 2
1
' 2
-








=
2 ' 2
P P =
Compressor work (shaft)- work in
) (
1 2 1 2
T T cp h h w
c
- = - =
kJ/kg
Combustor Analysis
Combustor efficiency
f
a s
b
m
m
x
V H L
h h
V H L
Q


. . . .
2 3
-
= = η
Combustor pressure specific

2
3 2
p
p p
E
b
-
=
Heat source-in
) (
2 3 2 3
T T cp h h q
s
- = - =
Turbine Analysis
Turbine efficiency;
3 ' 4
3 4
3 ' 4
3 4
T T
T T
h h
h h
Work Isentropik
leWork Irrevessib
t
-
-
=
-
-
= = η
Isentropic process
k
k
p
p
T
T
1
' 4
3
' 4
3
-








=
4 ' 4
P P =

Turbine work (shaft)- work out
) (
4 3 4 3
T T cp h h w
t
- = - =
kJ/kg
Nozzle Analysis
Nozel efficiency
' 5 4
5 4
T T
T T
n
-
-
= η
Jet efficiency
' 5
5
'
V
V
V
V
j
j
j
= = η
) (
2
5 4 5 4
2
5 T T cp h h
V
- = - =

) (
2
' 5 4 ' 5 4
2
' 5 T T cp h h
V
- = - =
n j
η η =
Isentropic process
k
k
p
p
T
T
1
' 5
4
' 5
4
-








=
0 5 ' 5
P P P = =
Nozel work (jet)- work out
2
) (
2
5
5 4
V
T T cp w
n
= - =
kJ/kg
Turbojet Thrust
The thrust of the engine is obtained by applying Newton’s Second Law to a
control volume, as shown in Figure 5. If the mass flow rate through the engine is m  , the