STUDY OF JET PROPULSION

INTRODUCTION

Propulsion is a combination of two Latin words namely pro meaning forward and pellere meaning
to drive.
Thus, propulsion means to push forward or drive forward an object.
Propulsion system is a machine that produces necessary thrust to drive an object forward.
Jet propulsion devices are used to propel aircrafts, rockets, missiles etc.
The operation of these devices is based on Newton’s second and third laws of motion.
In jet propulsion a high velocity jet is produced by expanding the high pressure and high
temperature gases in the nozzle situated at the rear end of the aircraft.
This accelerating mass of the gases produces a force and its reaction. This is called as propulsive
force or thrust is used to propel the aircraft in forward direction.
The propulsive devices or the jet engines which make use of jet propulsion are mainly classified
as follows:
1. Air stream jet engine (which use atmospheric air)
o Indirect reaction: E.g. Propeller, turboprop, turbofan
o Direct reaction: E.g. Turbojet, Turbofan and Athodyd (Ram jet and pulse jet)
2. Self-contained jet engines (which do not use atmospheric air): Rockets.
Rockets are further subdivided into three groups
o Chemical (Solid propellant, liquid propellant)
o Nuclear
o Electric

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PRINCIPLE OF JET PROPULSION

Jet propulsion is a practical application of Sir Isaac Newton's third law of motion, which
states that, “for every force acting on a body there is an opposite and equal reaction.” For aircraft
propulsion, the “body” is atmospheric air that is caused to accelerate as it passes through the
engine. The force required to give this acceleration has an equal effect in the opposite direction
acting on the apparatus producing the acceleration. A jet engine produces thrust in a similar way
to the engine/propeller combination. Both propel the aircraft by thrusting a large weight of air
backwards , one in the form of a large air slipstream at comparatively low speed and the other in
the form of a jet of gas at very high speed.

This same principle of reaction occurs in all forms of movement and has been usefully
applied in many ways. The earliest known example of jet reaction is that of Hero's engine (Figure
2-5) produced as a toy in 120 B.C. This toy showed how the momentum of steam issuing from a
number of jets could impart an equal and opposite reaction to the jets themselves, thus causing the
engine to revolve.
The familiar whirling garden sprinkler (Figure 2-6) is a more practical example of this
principle, for the mechanism rotates by virtue of the reaction to the water jets. The high pressure
jets of modern firefighting equipment are an example of “jet reaction,” for often, due to the reaction
of the water jet, the hose cannot be held or controlled by one firefighter. Perhaps the simplest
illustration of this principle is afforded by the carnival balloon, which when the air or gas is
released, rushes rapidly away in the direction opposite to the jet.

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Jet reaction is definitely an internal phenomenon and does not, as is frequently assumed,
result from the pressure of the jet on the atmosphere. In fact, the jet propulsion engine, whether
rocket, athodyd, or turbojet, is a piece of apparatus designed to accelerate a stream of air or gas
and to expel it at high velocity. There are, of course, a number of ways of doing this, as described
next, but in all instances the resultant reaction or thrust exerted on the engine is proportional to the
mass or weight of air expelled by the engine and the velocity change imparted to it. In other words,
the same thrust can be provided either by giving a large mass of air a little extra velocity or a small
mass of air a large extra velocity. In practice the former is preferred, since by lowering the jet
velocity relative to the atmosphere, a higher propulsive efficiency is obtained.

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COMPONENTS OF JET PROPULSION

1. Intake
2. Low pressure compression
3. High pressure compression
4. Combustion
5. Exhaust
6. Hot section
7. Turbines Low and High pressure
8. Combustion chambers
9. Cold section
10. Air inlet

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TYPES OF JET PROPULSION

There are two general types of jet propulsion

1.AIR-BREATHING
Air-breathing engines use oxygen from the atmosphere in the combustion of fuel. They
include the turbojet, turboprop, ramjet, and pulse-jet. The term jet is generally used only in
reference to air-breathing engines.

2.NONAIR-BREATHING
Nonair-breathing engines carry an oxygen supply. They can be used both in the
atmosphere and in outer space. They are commonly called rockets and are of two kinds liquid-
propellant and solid-propellant.
Air-breathing engines may be further divided into two groups, based on the way in which
they compress air for combustion. The turbojet and turboprop each has a compressor, usually
turbine-driven, to take in air. They are called gas-turbine engines. The ramjet and the pulse-jet do
not have compressors.

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TYPES OF REACTION ENGINE

1. Jet engine
A jet engine is a reaction engine which uses ambient air as the working fluid, and converts
it to a hot, high-pressure gas which is expanded through one or more nozzles. Two types of jet
engine, the turbojet and turbofan, employ axial-flow or centrifugal compressors to raise the
pressure before combustion, and turbines to drive the compression. Ramjets operate only at high
flight speeds because they omit the compressors and turbines, depending instead on the dynamic
pressure generated by the high speed (known as ram compression). Pulse jets also omit the
compressors and turbines, but can generate static thrust and have limited maximum speed.

2. Rocket engine
The rocket is capable of operating in the vacuum of space, because it is dependent on the
vehicle carrying its own oxidizer instead of using the oxygen in the air, or in the case of a nuclear
rocket, heats an inert propellant (such as liquid hydrogen) by forcing it through a [[nuclear reactor

3. Plasma engine
Plasma thrusters accelerate a plasma by electromagnetic means.

4. Pump-jet
The pump-jet, used for marine propulsion, uses water as the working fluid, pressurized by
a ducted propeller, centrifugal pump, or a combination of the two.

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ADVANTAGES OF JET PROPULSION

1. Low-Specific Weight:
The specific weight of the jet propulsion is one-fourth to one-half of the reciprocating engine.
2. No Unbalance Force:
There are no reciprocating parts and so jet propulsion is free from unbalanced forces. Greater
reliability is thus achieved.
3. Small Frontal Area:
The frontal area of jet propulsion is less than one-fourth the frontal area of the reciprocating
engines which decreases drag greatly and hence makes available greater power, particularly at high
loads. This also reduces the air cooling problem.
4. No Restriction in Power Output:
Compared to reciprocating engine the jet propulsion with greatly increased power output can be
built because the power is not limited by detonation. The unit can work/operate over a large range
of mixture strength.
5. High-Speed:
The speed of jet propulsion is not limited by propeller. High speed can be obtained.
6. Neither Lubrication Nor Radiators:
Jet propulsion requires neither internal lubrication nor radiators as reciprocating engines require.
7. At high speed greater than 900 kmph and at an altitude greater than 10,000 metres, the efficiency
of the jet is much higher than that of a propeller.
8. Combustion and delivery of power is continuous, whilst peak and fluctuating pressures do not
occur.
9. There is no ship stream loss, the drag is reduced, and warm compressed air is available for cabin
heating.
10. The unit permits of a better position of the pilot whilst the absence of a propeller permits a
smaller under carriage

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DISADVANTAGES OF JET PROPULSION

1. Particularly at low pressure, the thermal efficiency is lower. At low altitude and speed upto 150
m/sec/540 kmph, the fuel consumption is 2 to 3 times that of a reciprocating engine.
2. The plant is very noisy, materials costly and life short.
3. The compression-pressure ratio is not constant as in the reciprocator, but varies approximately
with the square of the speed.
4. There are certain difficulties which are encountered in the running of the propulsive unit

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APPLICATIONS OF JET PROPULSION

(a) Turbo-Prop:
Turbo-prop jet engines are used for medium and long range transport and bomber aircraft. They
fly with subsonic speed.
(b) Turbojet:
Turbojets are mainly used in military as fighters, bombers and for transport applications. Generally
they fly with supersonic speeds, e.g. MIGS, Mirage, Knat, Jaugar etc. The only turbojet used for
civil aviation is concord.
(c) Turbofan:
Used mainly for civil aviation. Flies at subsonic speed.
(d) Ramjet:
Ramjets are used for misses, as pilotless aircraft. They fly at supersonic speed.
(e) Pulsejet:
They are used for missiles, applications and fly at supersonic speed.

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CONCLUSION

Tis project report present the constraints of the transition narratives, which argues that
innovation comes from individuals or corporate and academic research, opens up the analysis of
technical change many important sources of creativity lie in other places, including particularly in
industry. Looking at new places makes us aware not only that creativity emerges from these
places and the people who work there, but also that creativity builds on and is shaped by expertise.

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REFERENCES

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276. doi:10.1017/S0025315400057271. S2CID 84754313.
3. ^ Jump up to:a b Bone, Q.; Trueman, E. R. (2009). "Jet propulsion in salps (Tunicata:
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7998.1983.tb05071.x.
4. ^ Bone, Q.; Trueman, E. (1984). "Jet propulsion in Doliolum (Tunicata:
Thaliacea)". Journal of Experimental Marine Biology and Ecology. 76 (2): 105–
118. doi:10.1016/0022-0981(84)90059-5.
5. ^ Demont, M. Edwin; Gosline, John M. (January 1, 1988). "Mechanics of Jet Propulsion
in the Hydromedusan Jellyfish, Polyorchis Pexicillatus: I. Mechanical Properties of the
Locomotor Structure". J. Exp. Biol. 134 (134): 313–332. doi:10.1242/jeb.134.1.313.
6. ^ Demont, M. Edwin; Gosline, John M. (January 1, 1988). "Mechanics of Jet Propulsion
in the Hydromedusan Jellyfish, Polyorchis Pexicillatus: II. Energetics of the Jet Cycle". J.
Exp. Biol. 134 (134): 333–345. doi:10.1242/jeb.134.1.333.
7. ^ Demont, M. Edwin; Gosline, John M. (January 1, 1988). "Mechanics of Jet Propulsion
in the Hydromedusan Jellyfish, Polyorchis Pexicillatus: III. A Natural Resonating Bell;
The Presence and Importance of a Resonant Phenomenon in the Locomotor Structure". J.
Exp. Biol. 134 (134): 347–361. doi:10.1242/jeb.134.1.347.
8. ^ Madin, L. P. (1990). "Aspects of jet propulsion in salps". Canadian Journal of
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