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3.4
Engine
Performance
Parameters
215
3.2
A
turbojet
engine
powers
an
aircraft
flying
at
a
speed
of
245
m/s,
which
has
an
exhaust
speed
of
560
m/s
and
a
specific
thrust
of
535
N
Á
s
=
kg.
Using
the
three
different
formulae,
calculate
the
propulsive
efficiency.
What
are
your
comments?
(Neglect
the
fuel-to-air
ratio).
3.3
A
turbojet
engine
is
powering
an
aircraft
flying
at
9
km
(ambient
temperature
and
pressure
are
229.74
K
and
30.8
kPa).
It
has
the
following
data:
m
_
a
¼
40
kg
=
s,
f
¼
0
:
02,
u
e
¼
950
m
=
s,
P
e
¼
100
:
0
kPa,
A
e
¼
0
:
25
m
2
Plot
(a)
The
relation
between
the
propulsive
efficiency
η
p
and
the
speed
ratio
(
u
/
u
e
)
(b)
The
relation
between
the
thrust
force
and
the
speed
ratio
(
u
/
u
e
)
The
flight
speed
u
–
varies
from
0
to
500
m/s.
3.4
A
turbojet
engine
is
being
flown
at
a
velocity
of
230
m/s.
It
is
burning
a
hydrocarbon
furl
with
a
heating
value
of
43,000
kJ/kg.
The
specific
thrust
is
500
N/(kg.s),
and
the
thrust
specific
fuel
consumption
is
0.08
kg/(N.h).
Calculate:
(a)
Fuel-to-air
ratio
(b)
Overall
efficiency
(c)
Exhaust
speed
of
gases
(d)
Propulsive
efficiency
(e)
Thermal
efficiency
3.5
The
GEnx
high-bypass-ratio
turbofan
engine
at
maximum
static
power
(
V
0
¼
0)
on
a
sea
level,
standard
day
(
P
0
¼
101
kPa,
T
0
¼
288.0
K)
has
the
following
data:
Total
air
mass
flow
rate
through
the
engine
is
1000
kg/s,
bypass
ratio
is
9.3,
the
exit
velocity
from
the
core
is
360
m/s,
the
exit
velocity
from
the
bypass
duct
is
265
m/s,
and
the
fuel
flow
rate
into
the
combustor
is
3750
kg/h.
For
the
case
of
exhaust
pressures
equal
to
ambient
pressure
(
P
0
¼
P
e
),
estimate
the
following:
(a)
The
thrust
of
the
engine
(b)
The
thermal
efficiency
of
the
engine
(heating
value
of
jet
fuel
is
43,000
kJ/kg)
(c)
The
propulsive
efficiency
and
thrust
specific
fuel
consumption
of
the
engine
3.6
A
commercial
airliner
has
a
dry
mass
of
the
aircraft
600
t
and
has
a
range
of
9000
km
using
150
t
of
hydrocarbon
fuel.
Estimate
the
range
of
the
aircraft
when
burning
the
same
volume
of
hydrogen
(both
gaseous
and
liquid).
The
hydrocarbon
heating
value
is
43,000
kJ/kg
and
its
density
is
804
kg/m
3
.
The
gaseous
and
liquid
hydrogen
has
heating
value
of
120
MJ/kg.
Density
of
liquid
and
gaseous
hydrogen
is
70
kg/m
3
and
0.08
kg/m
3
.
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