1. BY
SRINATH R
ASST.PROFESSOR
DEPT. OF AERONAUTICS
INTRODUCTION OF AIRCRAFT
PROPULSION

2. OVER VIEW ON THE SUBJECT
 Power plants of aircrafts
 Classifications
 Gas turbine engines and its characteristics
 Brayton cycles
 Application of brayton cycle on gas turbines
 Comparative merits and demerits
 Principles of thrust augmentation.

3. AIRCRAFT POWER PLANT
• The airplane engine and propeller, often referred to as a powerplant.
• The powerplant propels the airplane and drives the various systems that
support the operation of an airplane.

4.  External combustion engine.
• Steam engine is the best example.
• Fuel burned in boiler heats water &
changes it into steam.
• It forces piston to move & turn a
crankshaft/ spins a turbine.
• They are quite in efficient.
 Internal combustion engine.
• It uses butane, propane, diesel etc..
• It converted into a fuel vapour.
• Then the fuel vapour is mixed with
some amount of air.
• It release the energy when the mixture
burns & it makes the expansion of air.
• It has greater mechanical simplicity &
higher overall efficiency.
BASIC CLASSIFICATION OF ENGINE

5. AEROSPACE ENGINES
• Comprehend the basic components of gas turbine engines and their basic
operations
• Comprehend the thermodynamic processes occurring in a gas turbine engines
• Comprehend the support systems associated with gas turbine engines

6. CLASSIFICATION OF AIRCRAFT ENGINES
 Reciprocating (piston) engines
I. In-line engine
II. V-type engine
III. Horizontally opposed engine
IV. Radial engine
V. Rotary engine
 Turbine-powered
I. Turboprop
II. Turbo shaft
 Reaction engines
I. Jets
a) Turbojet
b) Turbofan
I. Pulsejet
II. Rocket

7. CLASSIFICATION OF ENGINE
Jet Engines Reciprocating Engines
(Propulsive thrust is produced by jet)
Air Breathing Engine Non-Air Breathing Engine
(Using atm air to produced Power)
Engine
Gas Turbine Engine Non-Gas Turbine Engine
Turbojet Turboprop Turbofan Turbo-shaft
Ramjet Scramjet Pulsejet
(Presents of Fuel and absents of Air
instead of Air + Oxidizer. Hypersonic
vehicles, Operating Mach No : 15 to 20)
(Available moving parts like
Compressor and Turbine)
(No moving parts)
Rocket Engine
(No moving parts)

8. IN-LINE ENGINE
 "Inline engine" refers only to engines with a single row of cylinders.
 It can be mounted with up-right or inverted.
 Starts numbering @ anti propeller end & increase toward front.

9. V-TYPE ENGINE
 Two banks of cylinder inclined each other at an angle to each other with one crank shaft.
 Numbering at anti propeller end and increases toward the front
 Numbered according to position as well as bank

10. RADIAL TYPE ENGINE
• More than 2 cylinder in each row and equally spaced around the crank shaft.
• Piston of all cylinder are coupled to same crank shaft.
• They are numbered with top cylinder and continue around clockwise as viewed from anti
propeller end.

11. HORIZONTALLY OPPOSED ENGINE
• They have 2 cylinder banks located on same plane and on apposite of crank shaft
• Cylinder at anti propeller end on the right side is numbered one and cylinder on left is
numbered four and increases
• Depends on number of cylinder.

12. DEFINITION OF A JET ENGINE
• An engine that burns fuel and uses the expanding exhaust
gases to turn a turbine and/or produce thrust
• The concept of thrust is based on the principle of
Newton’s Third Law

13. NEWTON’S LAWS
• For every action there is an equal and opposite reaction
• Newton’s Second Law F=M x A
• Newton’s second law states - The force of an object is
equal to its mass times its acceleration
• The force of the spray nozzle is equal to the mass of the
water multiplied by the acceleration of the water when it
comes through the nozzle
• This is the same principle used in rocket and jet engines

14. NEWTON IN PRACTICE

15. WHERE ARE JET ENGINES USED

16. WHERE ARE JET ENGINES USED?

17. BASIC JET ENGINE

18. PARTS OF TURBOJET
• Housing – The rigid frame that supports and contains the
parts needed for operation as well as the combustion event
• Air inlet and diffuser – The area of the jet where fresh air
comes in, the design of the diffuser straightens and alters the
speed of the incoming airs
• Compressor – Compresses the incoming air at a ratio of
approximately 30:1
• Burner or combustion chamber – The area of the engine
where fuel is ignited

19. • Exhaust Nozzle – accelerates the engine exhaust to the
most efficient and effective speed for producing thrust
• Turbine – Converts the energy from the heated and
expanding exhaust gasses to a rotating shaft which is used
to turn the compressors, or in the case of a turboshaft
engine, power the vehicle

20. COMPRESSOR
• Supplies high pressure air for combustion process
• Centrifugal flow and Axial flow
• Centrifugal Compressor
• Adv: simple design, good for low compression ratios (5:1), strong
• Disadvantage: Difficult to stage, less efficient, high frontal area

21. AXIAL COMPRESSOR

22. • Radial flow engines use a centrifugal compressor – they
push the air out radially rather than along the axis of the
engine
• Axial flow compressors – the air travels along the axis
of the engine

23. AXIAL COMPRESSOR
They may have more than one spool
Spool is group of compressor stages
Mean a shaft and one or two turbine stages rotating at
the same speed.
Low pressure turbine is attached to forward low
pressure compressor.
Flow will be in axial direction.

24. CENTRIFUGAL COMPRESSOR
Flow will be radial
Radial flow engines use a centrifugal compressor –
they push the air out radially rather than along the axis
of the engine
Lower efficiency than the axial flow compressor
It is used in early jet engines.

25. TURBINE
• Convert the kinetic energy into expansion work
• It is used to drive the compressor as well as propeller shaft

26. ABOUT TURBOJET
 Chemical energy is converted into mechanical energy
 100% Thrust produced by Nozzle
 Operating Mach No: 1 to 2
 Supersonic Aircraft (1 to 5)

27. ADVANTAGES
• High power to weight ratio
• No reciprocating parts
• Less parasitic power loss – no need to constantly
accelerate and decelerate pistons
• Less required maintenance

28. DISADVANTAGES
• The high speeds and high operating temperatures make
designing and manufacturing gas turbines complex from
both the engineering and materials standpoint
• These complexities lead to a higher price.

29. TURBOFAN
• It has a large fan in the front which sucks the air in, most of
the air flows around the outside core of the engine.
• Fan’s rotational speed is same as low pressure compressor’s
rotational speed.
• Only a portion of air from the inlet will be sent to the
compressor
• The secondary air leaves separately from primary air and
ducted back to mix with the air from engine core at the back.
• This fan air will account for 80% of total engines thrust.

30. • If one wanted to increase thrust you would either have to
increase the speed of the air being moved or increase the
mass of the air being moved (Thrust = Mass x
Acceleration) ... However…
• It is more efficient to accelerate a larger mass of air to a
lower velocity
• Due to this principle the turbofan is more efficient than the
turbojet
• Due to the lower velocity the turbofan is also significantly
quieter than a turbojet
• Almost all modern commercial aircraft use turbofan
engines.

31. • This separation is called bypass
• Cool bypass air flow
• Hot turbine discharge gases

32. ABOUT TURBOFAN
 They are again subdivided into
1. High by pass ratio
2. Low by pass ratio
 It depends on the amount of engine it bypasses the core of engine
 This bypassing will be given as ratio and called as bypass ratio
 20 to 40% of Thrust produced by Nozzle
 60 to 80% of Thrust produced by Fan
 Operating Mach No: 0.4 to 0.8
 High Subsonic Aircraft (0.3 to 0.8)

33. ADVANTAGES AND DISADVANTAGES
• Because the large inlet fan moves a larger volume of air at
a lower velocity, the turbofan is more efficient than the
turbojet
• Because of the lower exhaust speeds the noise level is
greatly reduced
• The large inlet fan creates a large frontal area which
negatively affects drag at high speeds (especially
supersonic)
• Most effective at speeds below supersonic
(Mach .5 – Mach .9)

34. TURBOPROP

35. TURBO PROPELLER
 It has an additional gear box attached in front to drive the
propeller.
 This engine uses almost all the exhaust gas to run the
propeller and very less thrust will be produced.
 Means thrust from the exhaust is only 10%
 The other 90% of energy is extracted by turbines that
drives the compressor and second turbine which drives the
propeller.

36.  Modern engines have propeller with smaller diameter but large number
of blades.
 20 to 25% of Thrust produced by Nozzle
 75 to 80% of Thrust produced by Propeller
 Operating Mach No: 0.4 to 0.65
 Subsonic Aircraft (0.1 to 0.8)

37. TURBO SHAFT
 High pressure turbine is used to rotate HP & LP Compressor
 Low pressure turbine is used to rotate output Shaft
 No Thrust produced in the exit turbine gas
 Kinetic energy is converted to Shaft power
 100% Thrust produced by Shaft
 Operating Mach No: 0.4 to 0.8
 High speed Subsonic helicopter (0.3 to 0.8)

38. PASSENGER AIRPLANES
SI.No Description Less Moderate High
1 Specific fuel
consumption
Turbofan Turboprop Turbojet
2 Noise Level Turbofan Turboprop Turbojet
3 Operating Mach No Turboprop Turbofan Turbojet
4 Take off Thrust Turbojet Turbofan Turboprop
5 Altitude Turboprop Turbofan Turbojet
6 Load Carrying capacity Turbojet Turboprop Turbofan
7 Specific Impulse Turbojet Turboprop Turbofan

39. BRAYTON CYCLE APPLICATION
• A Brayton-type engine consists of three components:
I. a compressor
II. a mixing chamber
III. an expander
• The term Brayton cycle has more recently been given to the gas turbine engine. This also
has three components:
I. A gas compressor
II. A burner (or combustion chamber)
III. An expansion turbine

40. IDEAL BRAYTON CYCLE:
 Isentropic process – ambient air is drawn into the compressor, where it
is pressurized.
 Isobaric process – the compressed air then runs through a combustion
chamber, where fuel is burned, heating that air—a constant-pressure
process, since the chamber is open to flow in and out.
 Isentropic process – the heated, pressurized air then gives up its
energy, expanding through a turbine (or series of turbines). Some of
the work extracted by the turbine is used to drive the compressor.
 Isobaric process – heat rejection (in the atmosphere).

41. ACTUAL BRAYTON CYCLE:
 adiabatic process – compression
 isobaric process – heat addition
 adiabatic process – expansion
 isobaric process – heat rejection
 A closed Brayton cycle recirculates the working fluid.
 The air expelled from the turbine is reintroduced into the compressor
 This cycle uses a heat exchanger to heat the working fluid instead of an internal
combustion chamber.
 The closed Brayton cycle is used for example in closed-cycle gas turbine and space
power generation.

42. BRAYTON CYCLE EFFICIENCY

43. THRUST AUGMENTATION
 Is a method of extracting more power from Internal Combustion
Engines.
 It’s a form of ‘Power Boosting’
 We shall examine two main types of augmentation systems,
 Water Injection
and
 Reheat or Afterburning

44. WATER INJECTION METHOD
 Operation of either Water or Water Methanol systems cools the
turbine, and allows water to be injected into the fuel spray nozzles
 Which cools the air flow in the combustor allowing more fuel to be
added.
 Water Injection allows water to be injected via additional nozzles
built into the fuel spray nozzles.
 The water injection system automatically resets the fuel control unit
to allow more fuel to flow.
 Water cools the turbine,
 and a cooler turbine means more fuel can be added.

45.  Increases the exhaust jet velocity, and provides extra thrust without
increasing the engine's frontal area.
 System is heavy and not used in most of the aircrafts

46. METHODS OF THRUST AUGMENTATION
 After burning
 High thrust for short duration
 It is used only in take-off (or) for high climbing rates
 Additional fuel is burning in the tail pipe between the turbine and exhaust
nozzle
 It is increased the jet velocity
 Oxidizer-Fuel Mixture
 Increase the mass flow rate
 Evaporative cooling which produces higher pressure and higher mass flow
rate
 Increase the compressor pressure ratio due to reduced compressor air flow
 Water and menthol or alcohol Mixture

49. ADVANTAGES OF GAS TURBINE ENGINES
 Weight reduction of 70%
 Simplicity
 Reduced manning requirements
 Quicker response time
 Faster Acceleration/deceleration
 Modular replacement
 Less vibrations
 More economical

50. DISADVANTAGES OF GAS TURBINE ENGINES
 Many parts under high stress
 High pitched noise
 Needs large quantities of air
 Large quantities of hot exhaust (target)
 Cannot be repaired in place

51. RAM JET ENGINES

52. ROCKET ENGINES
 A rocket is a machine that develops thrust by the rapid expulsion of matter
 A rocket is called a launch vehicle when it is used to launch a satellite or
other payload into space
 Rocket engines are reaction engines
 The highest exhaust velocities
 It is used in missile