Gas turbines are internal combustion engines that produce power by burning an air-fuel mixture to spin a turbine and drive a generator. They work by compressing air, igniting the air-fuel mixture at high temperatures, spinning turbine blades with the hot gases, and using the spinning turbine to power a generator and produce electricity. Gas turbines can operate on a wide range of gaseous, liquid, and solid fuels. Fuel injectors introduce fuel into the combustion chamber in atomized form. Emissions like CO, NOx, and UHC are controlled through techniques like optimized fuel-air ratios, improved mixing, and exhaust gas recirculation. CFD analysis is used to study internal cooling schemes in turbine blades.

1. Gas Turbines
By Harshith
M.Tech , Rotating Equipment

2. What is Gas Turbine :
 They are one of the most widely-used
power generating technologies. Gas
turbines are a type of internal combustion
(IC) engine in which burning of an air-fuel
mixture produces hot gases that spin a
turbine to produce power.

3. How they work :
 Air-fuel mixture ignites.
– The gas turbine compresses air and mixes it with
fuel that is then burned at extremely high
temperatures, creating a hot gas.
 Hot gas spins turbine blades.
– The hot air-and-fuel mixture moves through
blades in the turbine, causing them to spin
quickly.
 Spinning blades turn the drive shaft.
– The fast-spinning turbine blades rotate the turbine
drive shaft.

4.  Turbine rotation powers the generator.
– The spinning turbine is connected to the rod in a
generator that turns a large magnet surrounded
by coils of copper wire.
 Generator magnet causes electrons to move
and creates electricity.
– The fast-revolving generator magnet creates a
powerful magnetic field that lines up the electrons
around the copper coils and causes them to
move.
– The movement of these electrons through a wire
is electricity.

5. Brayton Cycle
• Gas turbines are described thermodynamically by the
Brayton cycle.
• In this cycle:
1. Air is compressed isentropically
2. Combustion occurs at constant pressure
3. Heated air expands through the turbine
4. Heat is rejected into the atmosphere.

6. Components :

7. Fuel Technology in GT
 Understanding the need to ensure fuel quality is
maintained at a high standard is a key to delivering
good operation in a gas turbine over long periods of
time.
 The choice of fuels used in GT applications is very wide
with the choice Based on availability and cost. Gas
Turbines can and do operate on a wide range of fuels as
shown in the graph,
 Combustion technology has moved forwards in
achieving low emissions without resorting to wet
abatement methods. Both conventional and low
emissions technologies associated with the fuels are
developed.

8.  Graph shows various gaseous,
liquid, and solid fuels and the
wide range of lower heating
values (LHV).
 “Gaseous fuels” are shown as
green triangles or yellow,
orange and green ellipses.
 The blue ellipses and solid
blue dots indicate all of the
common and less-common “liquid fuels” , including bio fuels
and liquefied petroleum gas (LPG), butane, and propane, which
are between the gaseous and the liquid phase.
 “Solid fuels” including lignite and hard coal and are indicated
by black squares.
Fuels :

9. Fuel Injection Technology :
 The Fuel Injector is used to introduce fuel into
the combustion chamber.
There are four primary types of fuel injectors :
1. Pressure-atomizing
2. Air blast
3. Vaporizing
4. Premix/prevaporizing injectors

10. 1. Pressure Atomizing
 Pressure atomizing fuel injectors rely on high fuel
pressures (500 psi) to atomize the fuel.
 This type of fuel injector has the advantage of being
very simple, but it has several disadvantages.
 The fuel system must be robust enough to
withstand such high pressures, and the
fuel tends to be heterogeneously
atomized, resulting in incomplete or
uneven combustion which has
more pollutants and smoke.

11. 2. Air blast
 The Air blast injector "blasts" a sheet of fuel with a
stream of air, atomizing the fuel into homogeneous
droplets.
 This type of fuel injector led to the first smokeless
combustors.
 The air used is just same amount
of the primary air that is diverted
through the injector, rather than
the swirler. This type of injector
also requires lower fuel pressures
than the pressure atomizing type.

12. 3. Vaporizing
 The vaporizing fuel injector is similar to the air blast
injector in which primary air is mixed with the fuel as it
is injected into the combustion zone.
 The fuel-air mixture travels through a tube within the
combustion zone. Heat from the combustion zone is
transferred to the fuel-air mixture, vaporizing some of
the fuel (mixing it better) before it is combusted. This
method allows the fuel to be combusted with
less thermal radiation, which helps protect the liner.
However, the vaporizer tube may have serious
durability problems with low fuel flow within it (the fuel
inside of the tube protects the tube from the combustion
heat).

13. 4. Premix/pre-vaporizing
injectors
 The premixing/pre-vaporizing injectors work by
mixing or vaporizing the fuel before it reaches
the combustion zone.
 This method allows the fuel to be very uniformly
mixed with the air, reducing emissions from the
engine. One disadvantage of this method is that
fuel may auto-ignite or otherwise combust
before the fuel-air mixture reaches the
combustion zone. If this happens the combustor
can be seriously damaged.

14. Emissions :
 Different types of emissions are CO, NO and UHC.
1. CO [Carbon monoxide]
Causes:
 CO is produced in all fuel/air ratios.
 At low temperatures, that corresponding to low fuel/air ratios (Φpz < 0.5),
CO cannot be burnt to CO2.
 At high temperatures or high fuel/air ratios (Φpz > 0.9) on the other hand,
CO2 dissociates to CO.
Reduction:
 Improved fuel atomization.
 Holding the primary-zone equivalence ratio to its optimum value by
redistributing the air flow.
 Increase the residence time or the primary’s zone volume.
 Use of fuel staging.
 Use of compressed air-bleed.

15. 2. UHC [Unburnt Hydrocarbons]
The parameters that influence CO emissions are also affecting
UHC emissions in the same way. So, UHC emissions reduction
requires the same treatment with CO emissions, but more attention
should be paid on the “reduction of film-cooling air” in the primary zone,
as well as on fuel atomization improvements. The latter could be
achieved with the use of airblast atomizers and air assist nozzles.
3. NO [Oxides of Nitrogen]
The principal parameter that governs NOx formation is temperature.
Reduction:
 Lean primary zone.
 Rich primary zone.
 Improved combustion’s homogeneity
 Use of water injection
 Recirculation of exhaust gas.

16. CFD Analysis
CFD Analysis of matrix cooling method in gas
turbine blades
 A sophisticated cooling scheme must be developed for continuing
the safe operation of gas turbines with high performances. Gas
turbine blades can be cooled internally as well as externally.
 This CFD analysis is focused on the internal cooling of turbine
blades and vanes of a gas turbine.
 Internal cooling can be achieved by passing coolant through
various enhanced serpentine passages inside the blade and
extracting heat from outside of the blades.
 As shown in the fig the slot in the blade has
matrix shaped ribs on top and bottom side of
Cooling channel.

17.  By using Ansys Design Modeler a fine mesh is generated near the
channel walls and the fluid flow domain so as to capture the velocity
variations because of and the temperature variations.
 The boundary conditions are used accordingly.
Different mass transfer rates will be used for
the ribbed matrix channel.
 The velocity and temperature contours have
been observed in order to analyze the variation of temperature and
velocity . along the blade’s surface as well as the fluid domain’s
surface.
Temperature contour on side walls, inlet
and outlet
Temperature contour on the bottom
surface of the blade

18. Gas Turbine Manufacturers :

20. Thank You