INTRODUCTION
A gas turbine is a machine delivering
mechanical power or thrust. It does this using
a gaseous working fluid. The mechanical
power generated can be used by, for
example, an industrial device. The outgoing
gaseous fluid can be used to generate thrust.
In the gas turbine, there is a continuous flow
of the working fluid.
CONT…
This working fluid is initially compressed
in the compressor. It is then heated in
the combustion chamber. Finally, it goes
through the turbine.
The turbine converts the energy of the
gas into mechanical work. Part of this
work is used to drive the compressor.
The remaining part is known as the net
work of the gas turbine.
HISTORY OF GAS TURBINES
We can distinguish two important types of gas
turbines. There are industrial gas turbines and
there are jet engine gas turbines. Industrial gas
turbines were developed rather slowly. This was
because, to use a gas turbine, a high initial
compression is necessary. This rather troubled
early engineers. Due to this, the first working gas
turbine was only made in 1905 by the Frenchman
Rateau.
CONT.
The first gas turbine for power generation became
operational in 1939 in Switzerland. It was developed by the
company Brown Boveri.
Gas turbines had a rather low thermal efficiency. But they
were still useful. This was because they could start up
rather quickly. They were therefore used to provide power
at peak loads in the electricity network. In the 1980’s,
natural gas made its breakthrough as fuel. Since then, gas
turbines have increased in popularity. After world war 2, the
gas turbine developed rapidly.
CONT…
New high-temperature materials, new cooling
techniques and research in aerodynamics
strongly improved the efficiency of the jet
engine. It therefore soon became the primary
choice for many applications.
Currently, there are several companies
producing gas turbines. The biggest producer of
both industrial gas turbines and jet engines is
General Electric (GE) from the USA. Rolls
Royce and Pratt & Whitney are also important
manufacturers of jet engines.
THE IDEAL GAS TURBINE CYCLE
CONT…
The cycle that is present is known as the JouleBrayton cycle. This cycle consists of four important
points.
We start at position 1where the gas has passed
through the inlet, after that the gas then passes
through the compressor. We assume that the
compression is performed isentropically. So, s1 = s2.
The gas is then heated in the combustor. (Point 3.)
This is done isobarically (at constant pressure). So,
p2 = p3. Finally, the gas is expanded in the turbine.
(Point 4.) This is again done isentropic ally. So, s3 =
s4.
CONT…
The whole process is visualized in the temperatureentropy diagram as shown above. The cycle consists of
an isentropic compression of the gas from state 1 to state
2; a constant pressure heat addition to state 3; an
isentropic expansion to state 4, in which work is done;
and an isobaric closure of the cycle back to state 1.
Above Figure shows, a compressor is connected to a
turbine by a rotating shaft. The shaft transmits the power
necessary to drive the compressor and delivers the
balance to a power-utilizing load, such as an electrical
generator.
CONT…
When examining the gas turbine cycle, we do make
a few assumptions. We assume that the working
fluid is a perfect gas with constant specific heats cp
and cv. Also, the specific heat ratio k (sometimes
also denoted by ) is constant. We also assume that
the kinetic/potential energy of the working fluid
does not vary along the gas turbine. Finally,
pressure losses, mechanical losses and other kinds
of losses are ignored.
CLASSIFICATION
The gas turbine can be classified into two
categories, i.e. impulse gas turbine and
reaction gas turbine. If the entire pressure
drop of the turbine occurs across the fixed
blades, the design is impulse type, while if
the drop is taken place in the moving
blades, the fixed blades serving only as
deflectors, the design is called reaction
type.
11
The advantage of the impulse design is that there is
no pressure force tending to move the wheel in the
axial direction and no special thrust balancing
arrangement is required.
There being no tendency for gas to leak over the
tips of the moving blades. A purely reaction turbine
is not generally used. In a small multi-stage
construction the velocity change in the moving and
fixed blades is about the same, the design being
50% reaction types.
GAS TURBINE POWER PLANT
The simple gas turbine power plant mainly consists of a
gas turbine coupled to a rotary type air compressor and a
combustor or combustion chamber which is placed
between the compressor and turbine in the fuel circuit.
Auxillaries, such as cooling fan, water pumps, etc. and
the generator itself, are also driven by the turbine. Other
auxillaries are starting device, lubrication system, duct
system, etc. A modified plant may have in
addition to the above, an inter-cooler, a regenerator and a
reheater. The arrangement of a simple gas turbine power
plant is shown in Figure in next slide
SCHEMATIC ARRANGEMENT
OF A SIMPLE GAS TURBINE
POWER PLANT
CONSTRUCTION
The basic construction of a gas turbine employs
vanes or blades mounted on a shaft and enclosed
in a casing. The flow of fluid through turbine in most
designs is axial and tangential to the rotor at a
nearly constant or increasing radius. There are two
types of blades used in all turbines : those that are
fixed on the rotor and
move with the shaft and those that are fixed to the
casing and help to guide and accelerate or
decelerate
the flow of fluid, being called fixed blades or vanes.
The power of the turbine depends upon the
size, shape and the speed of the blades used.
Multi-staging is employed to increase the
power output of the turbine by placing
additional sets of fixed and moving blades in
series. To prevent leakage of gas along the
shaft gas seals or glands are provided where
the shaft emerges from the turbine casing. The
extending lengths of the shaft on the two sides
of the turbine are supported on journal
bearings which also maintain it’s proper
alignment.
ACCESSORIES
There are several accessories fitted to the turbine.
These are : a tachometer driven through a gear box,
an over speed governor, a lubricating oil pump and
a fuel
regulator. The starting gear is mounted on the shaft
at one end. The tachometer shows the speed of the
machine and also actuates the fuel regulator in case
of
speed rises above or fall below the regulated speed,
so that the fuel regulator admits less fuel or more
fuel into the combustor and varies the turbine power
according to demand of load.
The governor back off fuel feed, if the exhaust
temperature from turbine exceeds the safe limit,
thermal switches at the turbine exhaust acting on
fuel control to maintain present maximum
temperature. The lubricating pump supplies oil to
bearing under pressure. Other auxillaries used on
the turbine plant include the starting motor or
engine with starting gear, oil coolers, filters and
inlet and exhaust mufflers. The turbine (and with
it the compressors) is driven by the starting motor
through a clutch and set-up gearing. A standby
motor driven pump is also provided for
emergency service. A failure of lubricating pump
system results in stopping of the unit
automatically.
COMPRESSOR
A compressor is a device that is used to supply
compressed air to the combustion chamber.
Compressors are broadly classified as positive
displacement type and rotodynamic type and may
be of single stage or multi-stage design.
In the positive displacement machine, successive
volumes of air are pressurized within a closed
space. These may be of reciprocating type or rotary
type. In reciprocating type machines, air is
compressed by a piston in a cylinder, while in the
rotary type, this is accomplished by positive action
of rotating elements.
The roto-dynamic compressors may be of radial flow,
axial flow or mixed flow type. In these machines,
compression takes place by dynamic action of rotating
vanes or impellers which impart velocity and pressure to
the air as it flows through the compressor. Roto-dynamic
type compressors include the centrifugal, axial and
mixed flow compressors which are all high speed
machines running at as high as 3,000 to 4,000 RPM
driven by turbines. These are designed to have high
value of air discharge capacity at moderate pressure.
These types of compressors are usually employed for
gas turbine applications.
COMBUSTOR
A combustor is a device inside which the combustion of fuel
takes place. For an efficient operation of gas turbine plant, it is
necessary to ensure good combustor performance. A good
combustor should achieve completeness of fuel combustion
and the lowest possible pressure drop in the gas, besides
being compact, reliable and easy to control. Complete
combustion of fuel depends upon three factors, viz.
temperature, time and turbulence. Temperature in the
combustor directly affects combustion and high temperature is
conductive to rapid combustion.
GENERATOR
It is a device that generates electricity. It is
coupled to the same shaft of turbine and
runs
at same speed to that of the turbine. The
capacity of generators depends on installed
capacity of the plant. The types of
generators to be used depend on the
purpose for which electrical energy is to be
produced.
TYPES OF GAS TURBINE
POWER PLANTS
The gas turbine power plants can be classified
mainly into two categories. These are :open
cycle gas turbine power plant and closed cycle
gas turbine power plant.
Open Cycle Gas Turbine Power Plant In this
type of plant the atmospheric air is charged into
the combustor through a compressor and the
exhaust of the turbine also discharge to the
atmosphere.
Closed Cycle Gas Turbine Power Plant In this
type of power plant, the mass of air is constant
or another suitable gas used as working
medium, circulates through the cycle over and
over again.
OPEN CYCLE GAS TURBINE
POWER PLANTAND ITS
CHARACTERISTICS
The schematic arrangement of a simple
open cycle gas turbine power plant is
shown in Figure in next slide
SIMPLE OPEN GAS TURBINE
POWER PLANT
In the process shown the cycles are :
2-3: Isentropic compression
3-4: Heat addition at constant pressure
4-1: Isentropic expansion
1-2: Heat rejection at constant pressure
The ideal thermal efficiency for the cycle,ç
t, is given by, Heat supplied - Heat
rejected/Heat supplied
where, r is the compression ratio=V2/V3and
k is the ratio of specific heat of the gas.
In actual operation the processes along 2-3 and 41 are never isentropic and the degree of
irreversibility of these processes and the
mechanical efficiencies of the machine
components greatly reduce the ideal value of
thermal efficiencies of the cycle. If the air entering
the combustor is preheated by the heat of exhaust
gases escaping from the turbine, some heat can
be recovered resulting into an increase in the
efficiency of the cycle improved. Such heating of
combustion air is known as regeneration and the
heat exchanger transferring heat from gas to air is
called regenerator.
Since most of the output of turbine is consumed by the
compressor, the actual efficiency of the cycle greatly
depends upon an efficient working of the compressor.
To attain higher compression ratios, it is necessary to
use multi-stage compression with inter-cooling. In
actual practice, all these modifications, viz.
regeneration, reheating and inter-cooling are combined
in a simple modified cycle and a substantial gain in the
overall plant efficiency is attained.
5 CLOSED CYCLE GAS
TURBINE POWER PLANTAND
ITS CHARACTERISTICS
In the closed cycle, quantity of air is constant,
or another suitable gas used as working
medium, circulates through the cycle over and
over again. Combustion products do not come
in contact with the working fluid and, thus,
remain closed.
CONT…
A development in the basic gas turbine cycle is the
use of the closed cycle which permits a great deal
of flexibility in the use of fuels. Moreover, working
medium of the plant could be any suitable
substance other than air which would give higher
efficiency. An arrangement of closed gas turbine
cycle is shown in Figure in next slide. In this cycle,
working fluid is compressed through the requisite
pressure ratio in the compressor, and fed into the
heater, where it is heated up to the temperature of
turbine itself.
ARRANGEMENT OF CLOSED
CYCLE GAS TURBINE PLANT
CONT…
The fluid is then expanded in the turbine and the
exhaust is cooled to the original temperature in the
pre-cooler. It then re-enter the compressor to begin
the next cycle. Thus, the same working fluid
circulates through the working parts of the system.
The heater burns any suitable fuel and provides the
heat for heating the working fluid. In fact, this
combustor is akin to an ordinary boiler furnace,
working at the atmosphere pressure and
discharging the gaseous products to the
atmosphere. There is, thus, a great deal of flexibility
in respect of furnace design and use of fuel,
allowing low cost fuel to be used.
CONT…
Another advantages in use of closed cycle is the choice
of selecting a convenient pressure range, once the
pressure ratio has been selected. The volume of the air
or the working fluid in the cycle depends upon the
pressure range which, in turn, affects the sizes of the air
heater, compressor, turbine, etc. In a closed cycle, there
is no restriction to keep the pressure low and this could
be kept at any suitable value say 7.03 kg/cm2(68.9 N/cm
) abs.
CONT…
The pre-cooler in a closed cycle plant is an
important equipment and corresponds to the
condenser of a steam plant. However, unlike the
condenser, cooling water in the pre-cooler could
be heated to a fairly high temperature depending
upon temperature of exit gas from the turbine, and
then used elsewhere in the plant. The design of
pre-cooler is commonly of the shell and tube type,
and water is the coolant commonly used. The air
heater of the closed cycle corresponds to the
water heaters of the steam plant, but with one
important difference that it has very small heat
storage capacity .
FUEL FOR GAS TURBNE
POWER PLANTS
Natural gas is the ideal fuel for gas turbines, but this is not
available everywhere. Blast furnace and producer gas
may also be used for these plants. However, liquid fuels
of petroleum origin, such as, distillate oils or residual oils
are most commonly used for gas turbine power plants.
The essential qualities of these fuels include proper
volatility, viscosity and calorific value. At the same time,
the fuel should be free from any content of moisture and
suspended impurities that may clog the small passages of
the nozzles and damage valves and plungers of the fuel
pump.
CONT…
However, liquid fuels of petroleum origin, such distillate oils or
residual oils are most commonly used for gas turbine plants.
Residual oils burns with less ease than distillate oils and the heaters
are often used to start the unit from cold, after which the residual oils
are red into the combustor. Pre-heating of residual oils may be
necessary in cold climates. Use of solid fuel, such as coal in
pulverized form in gas turbines presents several difficulties, most of
which have been only partially overcome.
TYPES OF GAS TURBINES
Jet engines
Airbreathing jet engines are gas turbines optimized
to produce thrust from the exhaust gases, or from
ducted fans connected to the gas turbines. Jet
engines that produce thrust from the direct impulse
of exhaust gases are often called turbojets,
whereas those that generate thrust with the
addition of a ducted fan are often called turbofans
or (rarely) fan-jets.
Gas turbines are also used in many liquid
propellant rockets, the gas turbines are used to
power a turbopump to permit the use of lightweight,
low pressure tanks, which saves considerable dry
mass.
DIAGRAM OF A GAS TURBINE
JET ENGINE
TURBOPROP ENGINES
A turboprop engine is a type of turbine
engine which drives an external aircraft
propeller using a reduction gear.
Turboprop engines are generally used on
small subsonic aircraft, but some large
military and civil aircraft, such as the
Airbus A400M, Lockheed L-188 Electra
and Tupolev Tu-95, have also used
turboprop power.
AERODERIVATIVE GAS
TURBINES
Aeroderivatives are also used in electrical power
generation due to their ability to be shut down, and
handle load changes more quickly than industrial
machines. They are also used in the marine industry to
reduce weight. The General Electric LM2500, General
Electric LM6000, Rolls-Royce RB211 and Rolls-Royce
Avon are common models of this type of machine.
AMATEUR GAS TURBINES
In its most straightforward form, these are
commercial turbines acquired through
military surplus or scrapyard sales, then
operated for display as part of the hobby
of engine collecting. In its most extreme
form, amateurs have even rebuilt
engines beyond professional repair and
then used them to compete for the Land
Speed Record
AUXILIARY POWER UNITS
APUs are small gas turbines designed to supply
auxiliary power to larger, mobile, machines such as an
aircraft. They supply:
compressed air for air conditioning and ventilation,
compressed air start-up power for larger jet engines,
mechanical (shaft) power to a gearbox to drive shafted
accessories or to start large jet engines, and
electrical, hydraulic and other power-transmission
sources to consuming devices remote from the APU.
INDUSTRIAL GAS TURBINES
FOR POWER GENERATION
Industrial gas turbines differ from aeronautical designs
in that the frames, bearings, and blading are of heavier
construction. They are also much more closely
integrated with the devices they power—electric
generator—and the secondary-energy equipment that is
used to recover residual energy (largely heat).
They range in size from man-portable mobile plants to
enormous, complex systems weighing more than a
hundred tonnes housed in block-sized buildings.
TURBOSHAFT ENGINES
Turboshaft engines are often used to drive
compression trains (for example in gas pumping
stations or natural gas liquefaction plants) and are
used to power almost all modern helicopters. The
primary shaft bears the compressor and the high speed
turbine (often referred to as the Gas Generator), while a
second shaft bears the low-speed turbine (a power
turbine or free-wheeling turbine on helicopters,
especially, because the gas generator turbine spins
separately from the power turbine).
MICROTURBINES
Microturbines are one of the most promising
technologies for powering hybrid electric
vehicles. They range from hand held units
producing less than a kilowatt, to
commercial sized systems that produce tens
or hundreds of kilowatts. Basic principles of
microturbine are based on micro
combustion.
CONT…
Microturbine systems have many claimed
advantages over reciprocating engine
generators, such as higher power-to-weight
ratio, low emissions and few, or just one,
moving part. Nevertheless reciprocating engines
overall are still cheaper when all factors are
considered. Microturbines also have a further
advantage of having the majority of the waste
heat contained in the relatively high temperature
exhaust making it simpler to capture, whereas
the waste heat of reciprocating engines is split
between its exhaust and cooling system.
EXTERNAL COMBUSTION
Most gas turbines are internal combustion engines
but it is also possible to manufacture an external
combustion gas turbine which is, effectively, a
turbine version of a hot air engine. Those systems
are usually indicated as EFGT (Externally Fired Gas
Turbine) or IFGT (Indirectly Fired Gas Turbine).
External combustion has been used for the purpose
of using pulverized coal or finely ground biomass
(such as sawdust) as a fuel.
GAS TURBINES IN SURFACE VEHICLES
Gas turbines are often used on ships, locomotives,
helicopters, tanks, and to a lesser extent, on cars,
buses, and motorcycles.
Gas turbines offer a high-powered engine in a very
small and light package. However, they are not as
responsive and efficient as small piston engines
over the wide range of RPMs and powers needed in
vehicle applications. Turbines have historically been
more expensive to produce than piston engines,
though this is partly because piston engines have
been mass-produced in huge quantities for
decades, while small gas turbine engines are
rarities; however, turbines are mass-produced in the
closely related form of the turbocharger.
TURBOCHARGER
The turbocharger is basically a compact and
simple free shaft radial gas turbine which is
driven by the piston engine's exhaust gas. The
centripetal turbine wheel drives a centrifugal
compressor wheel through a common rotating
shaft. This wheel supercharges the engine air
intake to a degree that can be controlled by
means of a wastegate or by dynamically
modifying the turbine housing's geometry (as in
a VGT turbocharger). It mainly serves as a
power recovery device which converts a great
deal of otherwise wasted thermal and kinetic
energy into engine boost.
CONCEPT CARS
The first serious investigation of using a gas
turbine in cars was in 1946 when two
engineers, Robert Kafka and Robert Engerstein
of Carney Associates, a New York engineering
firm, came up with the concept where a unique
compact turbine engine design would provide
power for a rear wheel drive car. The original
General Motors Firebird was a series of
concept cars developed for the 1953, 1956 and
1959 Motorama auto shows, powered by gas
turbines.
Toyota demonstrated several gas turbine
powered concept cars such as the Century gas
turbine hybrid in 1975, the Sports 800 Gas
Turbine Hybrid in 1979 and the GTV in 1985.
RACING CARS
The first race car (in concept only) fitted with a
turbine was in 1955 by a US Air Force group as a
hobby project with a turbine loaned them by Boeing
and a race car owned by Firestone Tire & Rubber
company.[31] The first race car fitted with a turbine
for the goal of actual racing was by Rover and the
BRM Formula One team joined forces to produce the
Rover-BRM, a gas turbine powered coupe, which
entered the 1963 24 Hours of Le Mans, driven by
Graham Hill and Richie Ginther.
BUSES
The arrival of the Capstone Microturbine
has led to several hybrid bus designs,
starting with HEV-1 by AVS of
Chattanooga, Tennessee in 1999, and
closely followed by Ebus and ISE
Research in California, and Design Line
Corporation in New Zealand (and later
the United States).
MOTORCYCLES
The MTT Turbine SUPERBIKE appeared in 2000 (hence
the designation of Y2K Superbike by MTT) and is the first
production motorcycle powered by a turbine engine specifically, a Rolls-Royce Allison model 250 turboshaft
engine, producing about 283 kW (380 bhp). Speed-tested
to 365 km/h or 227 mph (according to some stories, the
testing team ran out of road during the test), it holds the
Guinness World Records for most powerful production
motorcycle and most expensive production motorcycle,
with a price tag of US$185,000.
TRAINS
Several locomotive classes have
been powered by gas turbines, the
most recent incarnation being
Bombardier's JetTrain.
TANKS
The German Army's development division, studied a
number of gas turbine engines for use in tanks starting
in mid-1944. The first gas turbine engines used for
armoured fighting vehicle GT 101 was installed in the
Panther tank.
A turbine is theoretically more reliable and easier to
maintain than a piston engine, since it has a simpler
construction with fewer moving parts but in practice
turbine parts experience a higher wear rate due to their
higher working speeds. The turbine blades are highly
sensitive to dust and fine sand, so that in desert
operations air filters have to be fitted and changed
several times daily.
Like most modern diesel engines used in tanks, gas
turbines are usually multi-fuel engines.
MARINE APPLICATIONS
N AVA L
G A S T U R B I N E S A R E U S E D I N M A N Y N AVA L
V E S S E L S , W H E R E T H E Y A R E VA L U E D F O R T H E I R
H I G H P O W E R - T O - W E I G H T R AT I O A N D T H E I R
S H I P S ' R E S U LT I N G A C C E L E R AT I O N A N D A B I L I T Y
T O G E T U N D E R W A Y Q U I C K L Y.
T H E F I R S T G A S - T U R B I N E - P O W E R E D N AVA L
V E S S E L W A S T H E R O YA L N AV Y ' S M O T O R G U N
B O AT M G B 2 0 0 9 ( F O R M E R LY M G B 5 0 9 )
CONVERTED IN 1947.
ADVANCES IN TECHNOLOGY
Gas turbine technology has steadily advanced since
its inception and continues to evolve. Development
is active in producing both smaller gas turbines and
more powerful and efficient engines. Main drivers
are computer design (specifically CFD and finite
element analysis) and development of advanced
materials: Base materials with superior high
temperature strength (e.g., single-crystal superalloys
that exhibt yield strength anomaly) or thermal barrier
coatings that protect the structural material
underneath from ever higher temperatures. These
advances allowed higher compression ratios and
turbine inlet temperatures, more efficient
combustion and better cooling of engine parts.
AIRCRAFT GAS TURBINE ENGINES
ENGINE TYPES and APPLICATIONS
Most of modern passenger and military aircraft are powered by gas
turbine engines, which are also called jet engines. There are several
types of jet engines, but all jet engines have some parts in common .
Aircraft gas turbine engines can be classified according to (1) the type
of compressor used and (2) power usage produces by the engine.
Compressor types are as follows:
1. Centrifugal flow
2. Axial flow
3. Centrifugal-Axial flow.
Power usage produced are as follows:
1. Turbojet engines
2. Turbofan engines.
3. Turboshaft engines.
CENTRIFUGAL COMPRESSOR ENGINES
Centrifugal flow engines compress the air by
accelerating air outward perpendicular to the
longitudinal axis of the machine. Centrifugal
compressor engines are divided into Single-Stage
and Two-Stage compressor. The amount of thrust is
limited because the maximum compression ratio.
Principal Advantages of Centrifugal Compressor
1. Light Weight
2. Simplicity
3. Low cost.
CONT…
AXIAL FLOW COMPRESSOR ENGINES
Axial flow compressor engines may
incorporate one , two , or three spools (Spool
is defined as a group of compressor stages
rotating at the same speed) . Two spool
engine , the two rotors operate
independently of one another. The turbine
assembly for the low pressure compressor is
the rear turbine unit .
CONT..
AXIAL-CENTRIFUGAL
COMPRESSOR ENGINE
Centrifugal compressor engine were used
in many early jet engines , the efficiency
level of single stage centrifugal
compressor is relatively low . The multistage compressors are some what better
, but still do not match with axial flow
compressors.
CONT…
CHARACTERISTICS AND APPLICATIONS
The turbojet engine : Turbojet engine derives its
thrust by highly accelerating a mass of air , all
of which goes through the engine. Since a high
" jet " velocity is required to obtain an
acceptable of thrust, the turbine of turbo jet is
designed to extract only enough power from the
hot gas stream to drive the compressor and
accessories . All of the propulsive force (100%
of thrust ) produced by a jet engine derived
from exhaust gas.
CONT…
The turboprop engine : Turboprop engine derives its propulsion by
the conversion of the majority of gas stream energy into mechanical
power to drive the compressor , accessories , and the propeller load.
The shaft on which the turbine is mounted drives the propeller
through the propeller reduction gear system . Approximately 90% of
thrust comes from propeller and about only 10% comes from
exhaust gas.
The turbofan engine : Turbofan engine has a duct enclosed fan
mounted at the front of the engine and driven either mechanically at
the same speed as the compressor , or by an independent turbine
located to the rear of the compressor drive turbine . The fan air can
exit seperately from the primary engine air , or it can be ducted back
to mix with the primary's air at the rear .
CONT…
The turboshaft engine : Turboshaft engine derives
its propulsion by the conversion of the majority
of gas stream energy into mechanical power to
drive the compressor , accessories , just like
the turboprop engine but The shaft on which
the turbine is mounted drives something other
than an aircraft propeller such as the rotor of a
helicopter through the reduction gearbox . The
engine is called turboshaft.
CONT…
ADVANTAGES
There are two big advantages:
Gas turbine engines have a great power-toweight ratio compared to reciprocating engines.
That is, the amount of power you get out of the
engine compared to the weight of the engine
itself is very good.
Gas turbine engines are also smaller than their
reciprocating counterparts of the same power.
The Gas Turbine Plant is simple in Design and
Construction. It has few Reciprocating Parts and
is lighter in weight.
The Gas Turbine is quite useful in the regions
where due to scarcity it is not possible to supply
water in abundance for raising steam.
CONT…
Other advantages include:
Moves in one direction only, with far less
vibration than a reciprocating engine.
Fewer moving parts than reciprocating engines.
Greater reliability, particularly in applications
where sustained high power output is required
Waste heat is dissipated almost entirely in the
exhaust. This results in a high temperature
exhaust stream that is very usable for boiling
water in a combined cycle, or for cogeneration.
CONT…
Low operating pressures.
High operation speeds.
Low lubricating oil cost and consumption.
Can run on a wide variety of fuels.
Very low toxic emissions of CO and HC due to
excess air, complete combustion and no
"quench" of the flame on cold surfaces
DISADVANTAGES
The main disadvantage of gas turbines is that, compared to a
reciprocating engine of the same size, they are expensive.
Because they spin at such high speeds and because of the high
operating temperatures, designing and manufacturing gas
turbines is a tough problem from both the engineering and
materials standpoint.
Gas turbines also tend to use more fuel when they are idling
and they prefer a constant load rather than a fluctuating load.
That makes gas turbines great for things like trans-continental
jet aircraft and power plants,
THANKS