Combustion chamber, Turbine section, and Exhaust section Flashcards
must contain the
burning mixture of air, and fuel, in
order to generate the maximum
heat release,
combustion chamber or
combustor
combustion chamber, or
combustor, must contain the
burning mixture of air, and fuel, in
order to generate the maximum
heat release, at a substantially
constant ________, so the turbine
receives a uniformly expanded,
heated, and accelerated stream
of gas.
pressure
increasingly becomes more important
because of the rise in the cost of
the fuel, and the increasing
awareness of the aviation
industry and the general public of
the dangers of atmospheric
pollution from the exhaust
smoke.
efficient combustion
Air enters the combustion
chamber at a slightly lower/higher rate
than which it enters the intake of
the engine.
lower
flame rate of kerosene
30 ft/s
the air has
a reduction in air velocity and
there is an increase in pressure. This is achieved by passing it
through a ________.
divergent duct
The air is divided after it exits the
high pressure compressor into ________.
Primary, Secondary, and Tertiary
air flows
a region of
lower velocity recirculation
immediately downstream of the
fuel spray nozzle. Stable
combustion is achieved within
this zone.
primary zone
is about 20% of
the total airflow exiting the high
pressure compressor.
primary air
The primary air is about _______ of
the total airflow exiting the high
pressure compressor.
20%
the primary air is mixed, in a ratio of approximately _______ by weight, with fuel, and burnt.
15:1
By being passed to the flare and
swirl vanes, the velocity of the
primary air is ________.
reduced
what enables the recirculation of flow within the primary zone?
shape and position of the flare and swirl vanes
The remaining 80% of the output
of the high-pressure compressor
air goes into the space between _________.
flame tube and air casing
Some of the remaining air from the high-pressure compressor,
approximately another ________, is
allowed into the flame tube
through the secondary air holes.
20%
Some of the remaining air from the high-pressure compressor,
approximately another 20%, is
allowed into the flame tube
through the ________.
secondary air holes
these are remaining air from the high-pressure compressor,
approximately another 20%, is
allowed into the flame tube
through the secondary air holes.
secondary air
secondary air reacts with the primary air,
which is flowing through the swirl
vanes to form a ________.
toroidal vortex
The temperature of the gases in
the primary zone reaches about
_________.
2,000 degrees Celsius
The remaining 60% of the air
leaving the HP compressor is called ________.
tertiary air
the tertiary air, is fed into the flame
tube through ________ in the
flame tube.
corrugated joint sand dilution air holes
is fed into the flame
tube through corrugated joint
sand dilution air holes in the
flame tube.
tertiary air
is used to cool
both the air casing and the gas
exiting the chamber.
tertiary air
A gas turbine engine would
probably start quite readily with
only one igniter operating.
However, most gas turbine
engines have ________ igniters.
two
Because there are only two
igniters, an ________ has to
pass the starting flame between
the combustion chambers.
inter-connector
The ________ in a combustion
chamber which has a flame in it
drives those flames into adjacent
combustion chambers, where the
mixture is unlit through the inter-
connector pipe work.
pressure
The pressure in a combustion
chamber which has a flame in it
drives those flames into adjacent
combustion chambers, where the
mixture is unlit through the ________.
inter-connector pipe work
allows for elongation of the
chamber due to expansion.
sealing ring
allows the
chamber to expand into the
nozzle box, which is the portion of
the engine immediately
preceding the nozzle guide vanes
while maintaining a gas tight
seal.
sealing ring
the sealing ring allows the
chamber to expand into the
________, which is the portion of
the engine immediately
preceding the nozzle guide vanes
while maintaining a gas tight
seal.
nozzle box
this combustion chamber
system was supplied with air by a
centrifugal compressor.
multiple combustion chamber system
the multiple combustion chamber system was later used on some
earlier types of axial flow engine,
and is still in use on centrifugal
compressor engines, such as the ________.
rolls royce dart
consists of a
number of the individual
combustion chambers, which
each consist of flame tube, which
has its own air casing.
multiple combustion chamber system
The multiple combustion
chamber system consists of a
number of the individual
combustion chambers, which
each consist of ________.
flame tube, which has its own air casing
is the primary air scoop.
snout
allow the passage of the starting flame.
interconnectors
allow the
drainage of excess fuel from the
combustion chambers in the
unlikely event of the engine
failing to start.
drain tubes
If the fuel is not removed before
the next attempt to start, the
result will be excessively high gas
temperatures in the turbine
region, and _________, which is a
very dangerous jet of flame from
the rear of the engine.
torching
two means of getting rid of the fuel:
(1) fuel drainage system
(2) Evaporation of the remaining
traces of fuel from the
combustion chambers, the
turbine, and the jet pipe
connect the
lowest part of each chamber with
the next chamber below it.
drain tubes
Any remaining traces of fuel
within the engine must be
evaporated by
motoring the engine on a blowout cycle
the engine is rotated for the time
normally allocated to a full start
cycle, but with the HP fuel cock
shut, and the ignition system
deselected.
blowout cycle
is sometimes
also called the cannular or can-
annular system.
tubo-annular combustion chamber system
The tubo-annular combustion
chamber system is sometimes
also called the _________.
cannular or can-annular system
how does the tubo-annular combustion chamber system differ to the multiple combustion chamber system?
it does not have individual air casings for each of the flame tubes
A number of the flame tubes are
fitted within an inner and outer
air casing, which makes this
system a more compact unit.
tubo-annular system
has only one
flame tube, which is contained by
an inner and outer air casing.
annular combustion chamber system
advantages of an annular combustion chamber sytem:
- It can have a shorter length with
the same diameter for the same
power output. - No flame propagation problems.
- Less cooling air required.
- High combustion efficiency.
- Improved pressure distribution to
turbine.
To obtain the maximum heat
release from burning the mixture
of fuel and air in the combustion
chambers, the chemically correct
or stoichiometric ratio of air and
fuel of ________ must be used.
15:1
The addition of secondary and
tertiary air dilutes the mixture to
between _________.
45:1 to 130:1
A small loss in ________ does
occur in the combustion
chamber as the gases passes
through it.
pressure
A small loss in pressure does
occur in the combustion
chamber as the gases passes
through it. Losses vary from ________ of the pressure at the
entrance to the combustion
chamber.
3% to 8%
During normal engine running
conditions, the ignition system is ________ as soon as the
engine has attained self
sustaining speed.
switched off
means
smooth burning of the mixture,
coupled with the ability to remain
alight over a large range of
air/fuel and air mass flows.
combustion stability
Restarting the engine in
the air while it is windmilling is
called a _________.
relight
Outside the ________, it is
more difficult to start combustion
than it is to sustain it once it has
started.
ignition loop
what to do to when the
engine flame out at a high speed
or altitude?
slow down and/or descend
supply sufficient air to support
combustion. All that is required is
fuel and a spark.
windmilling compressor
The windmilling compressor is
supply sufficient air to support
combustion. All that is required is ________.
fuel and spark
is the
efficiency with which the
combustor assembly extracts the
potential heat actually contained
in the fuel.
Combustion efficiency
At high power operating
conditions, combustion
efficiencies are as great as ________.
99%
At idle, combustion efficiency can
still be as high as ________.
95%
is typically
located directly between the
compressor diffuser and turbine
section.
combustion section
4 basic elements of combustion sections:
- one or more combustion chambers (combustors)
- fuel injection system
- ignition source
- fuel drainage system
meters
the appropriate amount of fuel
through the fuel nozzles into the
combustors.
fuel injection system
in a fuel injection system, fuel is delivered
through the nozzles into the
liners in a ________ to
ensure thorough mixing with the
incoming air.
finely atomized spray
A typical ignition source for gas
turbine engines is the ________.
high-energy capacitor discharge system
consisting of an exciter unit, two
high-tension cables, and two spark
igniters.
high-energy capacitor discharge system
A typical ignition source for gas
turbine engines is the high-energy
capacitor discharge system,
consisting of an ________.
exciter unit, two high-tension cables, and two spark igniters
high-energy capacitor discharge system produces how many sparks?
60 to 100 sparks per minute
accomplishes the important task of
draining the unburned fuel after
engine shutdown.
fuel drainage system
helps to
prevent gum deposits in the fuel
manifold, nozzles, and combustion
chambers which are caused by fuel
residue.
fuel drainage system
where the fuel
and air are mixed and burned.
combustion chamber (combustor)
consists of a series of
individual combustor cans which
act as individual burner units. It is
well suited to centrifugal
compressor engines because of the
way compressor discharge air is
equally divided at the diffuser.
multiple-can / tubular
One of the major advantages of the
multiple can combustion chamber system
multiple cans can be removed individually for inspection
There are how many
cans in a typical multiple-can
combustion section?
8 or 10
consists of a housing and perforated
inner liner, or basket. It must be
removed as a single unit for repair or
replacement.
annular or basket type
represent a combination of the
multiple-can combustor and the
annular type combustor.
can-annular or tubo-annular type
who invented the can-annular or tubo-annular type of combustion chamber system?
pratt & whitney
characteristics of a good combustion chamber:
- Mix fuel and air effectively in the
best ratio for good combustion. - Burn the mixture as efficiently as
possible. - Cool the hot combustion gases to a temperature the turbine blades
can tolerate. - Distribute hot gases evenly to the
turbine section.
The situation wherein an excessively
high velocity airflow could literally
blow the flame out of the
engine/combustion chamber.
flameout
2 types of flameout:
- lean die out
- rich blow out
usually occurs at
high altitude where low engine
speeds and low fuel pressure
form a weak flame that can die
out in a normal airflow.
lean die out
occurs during
rapid engine acceleration when
an overly-rich mixture causes the
fuel temperature to drop below
the combustion temperature or
when there is insufficient airflow
to support combustion.
rich blow out
Air from the engine compressor
enters the combustion chamber
at a velocity up to ________.
500 ft/s
In normal operation, the overall
air/fuel ratio of a combustion
chamber can vary between_________.
45:1 and 130:1
Approximately ________ of the
air mass flow is taken in by the
snout or entry section.
20%
Combustion should be
completed ________ the dilution air
enters the flame tube.
before
initiates combustion and
the flame is then self-sustained.
electric spark (from an igniter)
Fuel is supplied to the airstream
by different methods. The most common is the ________.
injection of a fine
atomized spray into the
recirculating airstream through
spray nozzles
The first part of the turbine which directs
the air axially onto the blades of a
rotor section.
nozzle guide vane
extracts energy from
the hot gases that flow through
it, and converts that energy into
mechanical energy, to drive the
compressor and gearbox
connected to it.
turbine
The energy available in the gas
stream flowing through the
turbine takes several forms. These are:
heat energy, the potential
or pressure energy, and the
kinetic energy from the velocity
of the gas stream
The compressor adds energy to
the gas stream by ________.
increasing its pressure
The compressor adds energy to
the gas stream by increasing its
pressure. That energy is extracted
in the turbine by it ________ the
pressure of the gases flowing
through it.
reducing
The drop in pressure
energy occurs both as it is
converted to ________ in the
nozzle guide vanes, and also as it
is converted into ________ in the turbine blades.
kinetic energy; mechanical
energy
The drop in pressure
energy occurs both as it is
converted to kinetic energy in the
________, and also as it
is converted into mechanical
energy in the _________.
nozzle guide vanes; turbine blades
consists of two
elements, one row of stationary
nozzle guide vanes and one row
of rotating turbine blades.
turbine stage
The turbine stage consists of two
elements:
one row of stationary nozzle guide vanes;
one row of rotating turbine blades
affords longer and longer blades
to be fitted to each turbine stage
moving backwards in the engine.
This enables the velocity of the
gas stream to be controlled as
the gas expands to a larger
volume available to it.
divergent gas flow annulus
is fitted in an attempt to minimize losses due
to leakage across the turbine
blade tips and it also reduces the
vibration of the blades.
blade shroud
The clearance between the blade
tips and the turbine casing varies
because of the ________.
different rates of expansion and contraction of the materials involved
In some engines, an _________ is used in the turbine casing area, to reduce gas
leakage through this clearance
between the blade tips and the
turbine casing, but active
clearance control can be more
effective throughout the flight
cycle.
abradable lining
a turbine which is not
connected to the compressor, it is
connected only either to the
reduction gear for propeller.
free turbine or a free power
turbine
The power output of a turbine
can be increased by ________.
increasing its diameter
2 detrimental effects of increasing turbine diameter:
- increased drag factor
- greater stresses imposed
allows an increase in power
output with a reduction in
turbine diameter.
increase in the number of stages which comprise the turbine
The efficiency of a turbine blade
________ as its rotational speed
increases.
increases
The efficiency of a turbine blade
decreases as its rotational speed
_________.
decreases
the stresses in the blade ________ as the blade speed increases.
increase
as the blade speed decreases, the stresses in the blade ________ .
decrease
the advent of the high
bypass engine with its much
greater propulsive efficiency
means that for a given thrust, it
can have a ________ diameter turbine
small
The high bypass ratio engine
consists of three spools:
high pressure (hp) spool; intermediate pressure (ip) spool; low pressure (lp) spool
driven by the HP turbine, which
rotates at a relatively high speed.
high pressure (HP) spool
To the rear of the HP turbine is
the _______, driving the IP
compressor through a shaft
which spins inside that of a HP
turbine.
intermediate pressure (IP)
turbine
the rearmost turbine is
the ________ that
drives the LP compressor, more
commonly called the ________,
through a shaft which runs inside
the HP and IP shafts.
low pressure (LP) turbine; fan
Nozzle guide vanes are of _________
shape.
airfoil
The space between two
nozzle guide vanes forms a
________.
convergent duct
Within the convergent duct,
some of the pressure energy in
the gas stream is converted into
________.
kinetic energy
3 types of turbine blades:
- impulse type
- reaction type
- impulse-reaction
turbine blade similar in action to a water wheel.
impulse type
these blades
rotate as a reaction to the lift they
create as the gas stream flows
over them.
reaction type
The shape of this blade changes
from its base to its tip.
impulse-reaction
The shape change of an impulse-reaction blade is accomplished by ________.
the blade having a greater stagger angle at
its tip than at its base
more commonly used turbine blade type
impulse-reaction
The method of fixing the blade to
the disc is extremely important. The most
commonly used system on
modern engines is the ________.
fir tree fixing
these are accurately machined, which form the fir tree to ensure that the enormous centrifugal
load is shared equally between
them.
serrations
The blade is ________ in the serrations
while the engine is not rotating,
but the ________ imposed
during operation holds it firmly in
place.
free; centrifugal force
On average, the energy loss in the
turbine is about ________.
8%
the 8% energy loss is 3.5% from aerodynamic losses in the ________, 1.5% from
aerodynamic losses in the ________, the rest is divided fairly equally between _________.
turbine blades; nozzle guide vanes; gas leakage over the blade tips and exhaust system losses
During normal engine operation,
the rotational speed of the
turbine may be such that the
blade tips travel faster than _________.
1500 ft/s
The temperature of the gases
driving the turbine can reach as
high as ________.
1,700 degrees Celsius
The temperature of the gases
driving the turbine can reach as
high as 1,700 degrees Celsius.
The speed of these gases comes
close to the ________ at
these temperatures.
speed of sound
This tensile loading under
tremendous heat, causes a
phenomenon called _________.
creep
is the stretching of the metal of
the blade, beyond its ability to
reform back to its original length.
creep
Turbine blades of early gas
turbine engines were made from
________. Use of
this material imposed a stringent
limit upon the turbine
temperature, and consequently,
because the gas turbine engine is
a heat engine, the power output
of such engines was limited.
high temperature steel
materials used in the making or turbine blades:
high temperature steel, nickel-based alloys, super alloys
a complex
mixture of chromium, cobalt,
nickel, titanium, tungsten,
carbon, etc.
super alloys
Blades manufactured from super
alloys have a maximum
temperature limit of
approximately _______, or if the blades are cooled internally, ________.
1,100 degrees Celsius; 1,425 degrees Celsius
Traditional metal manufacturing
processes produce a ________ in the material.
The ________ create a weakness in the
structure, and are usually the
starting point of any failure.
crystal lattice or grain; boundaries of the crystal
In the search for even stronger
materials, a procedure called
________ is now
being used in modern engines.
single crystal casting
This process virtually eliminates
corrosion and creates an
extremely creep resistant blade.
single crystal casting
transforms a portion of the
kinetic energy in the hot exhaust
gases into mechanical energy to
drive the compressor and
accessories.
turbine
encloses the
turbine rotor and stator assembly,
giving either direct or indirect
support to the stator elements.
case / turbine casing
A typical case has ________ on both
ends that provide a means of
attaching the turbine section to the
combustion section and the exhaust
assembly.
flanges
A stator element is most commonly
referred to as the _________.
turbine nozzle, turbine guide vanes, or nozzle diaphragm
It is typically exposed to the
highest temperatures. Its purpose is
to collect the high energy airflow
from the combustors and direct the
flow to strike the turbine rotor at the
appropriate angle.
turbine nozzle
The turbine nozzle assembly
consists of an ________ that retains and surrounds the nozzle vanes.
inner and outer shroud
The nozzle vanes
are rigidly welded or riveted into the
inner and outer shrouds. To allow for
expansion, the inner or outer shroud
ring is ________.
cut into segments
is a dynamically balanced unit
consisting of blades attached to a
rotating disk.
turbine wheel
is the anchoring
component for the turbine
blades and is bolted or welded to
the main shaft.
turbine disk
it is a phenomena
in which extreme stress on turbine
blades may cause the turbine
blades to grow in length due to
severe centrifugal loads imposed by
high rotational speeds.
growth or creep
airfoil shaped
components designed to extract the
maximum amount of energy from
the flow of hot gases.
turbine blades
Turbine blades
fit loosely into a turbine disk when
an engine is ________, but expand to fit
tightly at normal operating
temperatures.
cold
the blades merely change the
direction of airflow coming from
the turbine nozzle and cause
relatively no change in gas
pressure or velocity.
impulse turbine blades
produce a turning force based on
an aerodynamic action. To do
this, the turbine blades form a
series of converging ducts that
increase gas velocity and reduce
pressure.
reaction turbine blades
the workload along the length of this combination blade is
evenly distributed. The blade
base is ________ shaped while the
blade tip is ________ shaped.
impulse-reaction; impulse; reaction
In the turboprop engine, where
the thrust is provided by the
propeller, the turbine gas
temperature and back pressure
at the turbine are dictated by the ________.
design of the outlet nozzle
The temperature of the gases
entering the exhaust system can
be between _________.
550°C and 850°C
If the exhaust system runs
through the fuselage of the
aircraft, then the fuselage must
be protected from the very high
temperatures of the gases. This is
done by ________.
allowing a clearance between the jet pipe and the aircraft skin
The gas velocity leaving the
turbine is between ________,
around ________ Mach.
750 – 1,250 ft/s; 0.5
Although the shape of the jet
pipe outer casing appears to be
convergent at the point where
the gas leaves the turbine, the
shape of the volume within the
casing is in fact ________.
divergent
Although the shape of the jet
pipe outer casing appears to be
convergent at the point where
the gas leaves the turbine, the
_________ is in fact divergent.
shape of the volume within the casing
a conical shaped device
positioned close up to the rear
turbine disc rear face.
exhaust cone
helps to reduce the
velocity of the gases leaving the
turbine
exhaust cone
prevents the hot gases flowing
across the rear disc face of the
turbine, further reducing
disturbance, and preventing
overheating of the disc.
exhaust cone
The rear turbine bearing is also
supported inside the exhaust
cone via ________, which are streamlined by
_________.
turbine rear support
struts; fairings
straighten out
any residual whirl which could
cause additional losses through
generating turbulence in the jet
pipe.
fairings
The exhaust gases exit to
atmosphere via the ________.
convergent propelling nozzle
The convergent
nozzle increases the velocity to
speeds of ________ in a turbojet
engine at virtually all throttle
openings above idle.
Mach 1.0
The more powerful the engine, the
________ the danger zones will extend
from the engine.
further
Although the gas velocity and
temperature exiting the engine
are extremely high, the levels of
both drop quite dramatically with
________ distance from the
exhaust nozzle.
increasing
combines the bypass air and the
hot exhaust gases in a mixer unit.
low bypass
ensures thorough
mixing of the two streams before
they are ejected into the
atmosphere.
mixer unit
Two methods used to exhaust
the cold bypass air and the hot
exhaust gases:
standard method; fitting an integrated exhaust nozzle
Within this type
of unit, the two gas flows are
partially mixed together before
their ejection into the atmosphere.
fitted with an integrated exhaust nozzle
Some of the highest known levels
of noise are generated by ________.
aircraft engines
The main source of noise
emanating from an aircraft is
generated by the ________.
engine
The most significant sources of
noise from the engine originate
from the ________.
compressor, turbine, and exhaust
the level of noise from
the ________ is more affected by a
reduction in its velocity
exhaust
________ turbulence zone = high frequency noise
narrow
wide turbulence zone = ________ frequency noise
low
Manufacturers used different
types of _________
in the engine intake and the
bypass duct which is extremely
efficient in reducing noise in
those regions.
noise absorbing material
Older turbojet used other system
in reducing noise output. ________ cause the gases to flow in separate exhaust jets that
rapidly mix with slowly moving air
which is trapped by the lobes.
Lobe type nozzles
components of an exhaust section:
- exhaust cone
- exhaust duct or tailpipe
- exhaust nozzle
an extension of the
exhaust section that directs exhaust
gases safely from the exhaust cone
to the exhaust, or jet nozzle.
tailpipe
It is used almost exclusively with
engines that are installed within an
aircraft’s fuselage to protect the
surrounding airframe.
tailpipe
provides the exhaust gases with a final boost
in velocity.
exhaust or jet nozzle
The two types of exhaust nozzle
designs used on aircraft:
converging design; converging-diverging design
the convergent shape produces a
venturi that accelerates the
exhaust gases and increases
engine thrust.
converging exhaust nozzle
the converging portion of the
exhaust nozzle accelerates the
turbine exhaust gases to
supersonic speed at the
narrowest part of the duct, then,
they are accelerated further in
the nozzle’s divergent portion, so
the exhaust gases exit the nozzle
well above the speed of sound.
converging-diverging nozzle
