HISTORY OF JET ENGINE INTRODUCTION

Long before humans appeared on earth, nature had given some creatures of the sea, such as the squid and the, the ability to jet propel themselves through the water.

THE AEOLIPILE Hero, an Egyptian scientist who lived in Alexandria around 100

B.C., is generally given credit for conceiving and building the first “jet engine.”

LEONARDO DA VINCI Around A.D. 1500 Leonardo Da Vinci describes the

chimney jack, a device which was later widely used for turning roasting spits.

ROCKETS AS A FORM OF JET PROPULSION

Chinese scholar named Wan Hu intended to use his rockets as a means of propulsion. His plan was simple.

BRANCA’S STAMPING MILL A further application of the

jet-propulsion principle, utilizing what was probably

the first actual impulse turbine, was the invention of

a stamping mill built in 1629 by Giovanni Branca, an

Italian engineer.

SIR ISAAC NEWTON

• in 1687 Sir Isaac Newton formulated the laws of motion on which all devices utilizing the jet propulsion theory are based.

THE FIRST GAS TURBINE• In 1781 John Barber, an

Englishman, was the first to patent a design utilizing the thermodynamic cycle of the modern gas turbine

• use for jet propulsion, basically the same as the modern gas turbine , had a compressor, a combustion chamber, and a turbine.

• In 1930 Frank Whittle submitted his patient application for a jet aircraft engine.

• During the period between 1791 and 1930, many people supplied ideas which laid the foundation for the modern gas turbine engines

Theory of a jet engine

Consider a balloonAccording to Newton's first law

P2+T = P1

F = 0 [P2+T- P1 = 0]

By Newton’s second law

P1 T

P2

F= P1-P2

F = m (V-0)

tF = ma

P1

mu = 0

m

V

P2 t

T : Surface tension

P1

P1

• By Newton’s third law

F

For every action there is an equal and opposite reaction.

Balloon analogy of the jet engine

• Pressure are equal in all directions.

• An unbalance of force is created when the stem is opened.

• Maintaining presser in the balloon

• Replacing the hand pump with a compressor

Raising the air temperature and increasing the volume.

The turbine extracts some of energy in the air to turn the compressor.

Low pressure compressor

P1 P2>P1

UV

Air Intake

Exhaust

A Whittle-type turbo-jet engine.

METHODS OF JET PROPULSION

A ram jet engine

A turbo/ram jet engine

A pulse jet engine

Lorin's jet engine.

A Whittle-type turbo-jet engine.

A rocket engine

A turbo-rocket engine

Types of jet engines

According to power usage produces

Turbojet engines Turbofan engines Turboprop engines Turboshaft engines

• Turbojet engines are about the simplest jet engine possible

• Flow is undivided all the way through the engine

• Turbojets were used extensively in both military and civilian applications

• Turbofan engines use the traditional jet scheme for some of their thrust, but much of it comes from a fan mounted on the shaft in front of the compressor

• The fan is driven by the turbine.

• The fan duct surrounds the core engine.

• A turboprop engine bears a functional similarity to a turbofan

• the shaft of the engine is used to drive another system

• The other system is in this case a gearbox and a propeller, rather than a ducted fan

• The core engine is designed much more in focus on creating toque, rather than providing thrust

• A turboshaft engine is similar in concept, but instead of the propeller, the gearbox exits to some other device

• The most common use is to power a helicopter rotor.

A comparison between the working cycle of a turbo-jet engine and a piston engine

Compressors

A Typical Centrifugal flow Compressor

Typical impellers for centrifugalcompressors

The Axial Flow Compressor

Typical triple spool compressor

Combustion Chambers

An early combustion chamber

Flame stabilizing and general airflow pattern

A vaporizer combustion chamber

An early Whittle combustion chamber

Multiple combustion chambers

Turbo-annular combustion chamber

Annular combustion chamber

Turbines

A triple-stage turbine with single shaft system

A twin turbine and shaft arrangement

T triple turbine and shaft arrangement

A typical free power turbine

Free power contra-rotating turbine

Exhaust System

Abasic exhaust system

Exhaust system with thrust reverser, noise suppressor and two position propelling nozzle

A low by-pass air mixer unit

High by-pass ratio engine exhaust systems

Accessory drives

Mechanical arrangement of accessory drives

Mechanical arrangement of internalgearboxes

An internal gearbox

An external gearbox and accessory units

An external gearbox with auxiliary gearbox drive

Thrust reversal

Method of Thrust reversal

Hot stream thrust reverser installations

A cold stream thrust reverser installation

AFTERBURNING

TWO-POSITION NOZZLE

Examples of afterburning jet pipes and propelling nozzles

Methods of afterburning ignition

Typical afterburning jet pipe equipment.

VARIABLE-AREANOZZLE

Afterburning and its effect on the rate of climb

Vertical / short take-off and landing

Lift/Propulsion engine.

Thrust deflector systems.

Vectored thrust engine.

Flap blowing engine.

Thrust distributionA diagram of a typical single-spool axial flow turbo-jet engine and illustrates where the main forward and rearward forces act.

Thrust distribution of a typical single-spool axial flow engine.

METHOD OF CALCULATING THE THRUST FORCES

total thrust at outlet

resultant thrust for a particular flow section

total thrust at outlet

Wvj

gThrust = (A X P) +

A = Area of flow sectionP = Pressure W = Mass flow VJ = Velocity of flowg = Gravitational constant

For To obtain the thrust on the compressor casing at the above figure

The pressure and the velocity at the inlet to the compressor are zerothe force at the outlet from the compressor.

Outlet Area (A) = 182 sq.in.Pressure (P) = 94 lb. per sq.in.(gauge)Velocity (VJ) = 406 ft. per sec.Mass flow(W) = 153 lb. per sec.

The thrust= (A x P) + Wvj/g= (182 x 94) + (153 x 406)/32 - 0= 19,049 lb. of thrust in a forward direction.

CALCULATING THE THRUST OF THE ENGINE

Diffuser ductdiffuser duct inlet are the same as the conditions at the compressor outlet, i.e. 19,049 lb

ThereforeOutlet Area (A) = 205 sq.in.Pressure (P) = 95 lb. per sq.in.(gauge)Velocity (VJ) = 368 ft. per sec.Mass flow(W) = 153 lb. per sec.

The thrust= (A x P) + Wvj/g - 19,049= (205 x 95) + 153 x 368/32 - 19,049= 21,235 - 19,049= 21,186 lb. of thrust in a forward direction.

Combustion chambers

The conditions at the combustion chamber inlet are the same as the conditions at the diffuser outlet, i.e. 21,235

Therefore

Outlet Area (A) = 580 sq.inPressure (P) = 93 lb. per sq.in.(gauge)Velocity (VJ) = 309 ft. per sec.Mass flow(W) = 153 lb. per sec.

The thrust= (A x P) + Wvj/g - 21,235lb= (580 x 93) + (153 x 309)/32 - 21,235= 55,417 - 21,235= 34,182 lb. of thrust in aforward direction.

Turbine assemblyThe conditions at the turbine inlet are the same as the conditions at the combustion chamber outlet, i.e. 55,417 lb.

Therefore

Outlet Area (A) = 480 sq.inPressure (P) = 21 lb. per sq.in.(gauge)Velocity (VJ) = 888 ft. per sec.Mass flow (W) = 153 lb. per sec.

The thrust = (A x P) + Wvj/32 - 55,417lb = (480 x 21) + 153 x 888/32 - 55,417 = 14,326 - 55,417 = -41,091

This negative value means a force actingin a rearward direction.

Exhaust unit and jet pipeThe conditions at the inlet to the exhaust unit are the same as the conditions at the turbine outlet, i.e. 14,326 lb.

Outlet Area (A) = 651 sq.inPressure (P) = 21 lb. per sq.in.(gauge)Velocity (VJ) = 643 ft. per sec.Mass flow (W) = 153 lb. per sec.

Therefore

The thrust= (A x P) + Wvj/32 - 14,326lb= (651 x 21) + (153 x 643)/32 - 14,326= 16,745 - 14,326= 2,419lb. of thrust in a forward direction.

Propelling nozzleThe conditions at the inlet to the propelling nozzle are the same as the conditions at the jet pipe outlet, i.e. 16,745 lb.

Therefore

OUTLET Area (A)= 332 sq.in. Pressure (P) = 6 lb. per sq.in. (gauge) Velocity (VJ) = 1,917 ft. per sec. Mass flow (W) = 153 lb. per sec.

The thrust= (A + P) + Wvj/32 - 16,745= (332 x 6) + (153 x 1,917)/32 -16,745= 11,158 - 16,745= 5,587lb. acting in a rearward direction

• It is emphasized that these are basic calculations and such factors as the effect of air offtakes have been ignored.

Based on the individual calculations,

the sum of the forward or positive loads = 57,836 lb.

the sum of the rearward or negative loads

= 46,678 lb.

Therefore the resultant (gross or total) thrust = 57,836 lb 46,678 lb.-= 11,158 lb.

EngineCalculate the thrust of the engine by considering the engine as a whole

The resultant thrust= Sum of the individual gas loads

The momentum change of the gas stream produces most of the thrust developed by the engine

an additional thrust is produced when the engine operates with the propelling nozzle in a 'choked' condition

This thrust results from the aerodynamic forces which are created by the gas stream and exert a pressure across the exit area of the propelling nozzle (pressure thrust).

Algebraically, this force is expressed as

(P - P0) A. A = Area of propelling nozzle insq. in.P = Pressure in lb. per sq.in.P0 = Atmospheric pressure in lb.per

sq.in.

assuming values of mass flow, pressure and area to be the same as in the previous calculations

Area of propelling nozzle (A) = 332 sq.in.Pressure (P) = 6 lb. persq.in (gauge)Atmospheric Pressure (P0) = 0 lb. persq.in (gauge)Mass flow (W) = 153 lb.per sec.Velocity (VJ) = 1,917ft.per sec.

The thrust= (P - P0) + Wvj/g - 0= (6-0) 332+ (153 x 1,917)/32 -0= 1,992 - 9,166= 11,158lb.

Then

The same as previously calculated by combining the gasloads on the individual engine locations.

On engines that operate with a non-choked nozzle, the (P - P0) A function does not apply and the thrust results only from the gas stream momentum change.

Inclined combustion chambers

The axial thrust = the sum of the outlet thrust x cosine of the angle

If the inlet and outlet are at different angles to the engine axis, it is necessary to multiply the inlet and outlet thrusts separately by the cosine of their respective angles.

AFTERBURNINGThe gases passing through the exhaust system are reheated by the afterburning system to provide additional thrust.

Assuming that an afterburner jet pipeand propelling nozzle are fitted to the engine

The new conditions at the propelling nozzle are

Outlet Area (A) = 455 sq.in.Pressure (P) = 5 lb. per sq.in.

(gauge)Velocity (VJ) = 2,404 ft. per sec.Mass flow (W) = 157 lb. per sec.

The thrust= (A x P) + Wvj/g - 16,745 (jet pipe outlet) = (455 x 5) + (157 x 2,404) -16,745= 14,069 - 16,745

= 2,676lb. acting in a rearward direction.

• Compared with the previous calculation, it will be seen that the negative thrust is reduced from -5,587 lb. to -2,676 lb.

• The overall positive thrust is thus increased by 2,911 lb• That is equivalent to a thrust increase of more than 25

per cent.