AIRCRAFT PROPULSION SYSTEM seminar report

A

Seminar Report

On

AIRCRAFT PROPULSION SYSTEM

Submitted in partial fulfilment for the

Award of degree of

Bachelor of Technology

In

Mechanical Engineering

2015-2016

Submitted to: Submitted by:

Mr. Krishna kumar Deepak Singh

Mr. Dhruv Kr. Prajapati Roll No:-1321640055

Assistant Professor B.Tech, 3rd year

Deptt. of Mechanical Engg.

Department of Mechanical Engineering

IIMT COLLEGE OF ENGINEERING, GREATER NOIDA

CONTENT

Serial No. Title

1. Introduction

2. Propulsion System

3. Aircraft motion

4. Aircraft Engine

5. Gas Turbine

5.1 Air Intake

5.2 Compressor

5.3 Combustion Chamber

5.4 Turbine

5.5 Outlet

6. Jet Propulsion

6.1 Turbojet

6.2 Ramjet

6.3 Rocket

7. Conclusion

8. References

ACKNOWLEDGEMENT

I express my sincere thanks to my guide Mr. Krishna kumar, Assistant Professor,

Mechanical Department, IIMT College Engineering, Greater Noida, for guiding me right

from the inception till the successful completion. I sincerely acknowledge him for extending

his valuable guidance, support for literature, critical reviews of seminar report and above all

the moral support he had provided to me with all stages of the seminar.

Finally, I would like to add few heartfelt words for the people who were the part of the

seminar in various ways, especially my friends and classmates who gave me unending

support right from the beginning. My family has been the most significant in my life so far

and this part of my life has no exception. Without their support, persistence and love I would

not be where I am today.

DEEPAK SINGH

Mechanical Engineering

3rd

Year, 5th

Sem.

IIMT COLLEGE ENGINEERING, GREATER NOIDA

1. Introduction

An aircraft is a machine that is able to fly by gaining support from the air. It counters the

force of gravity by using either static lift or by using the dynamic lift of an air foil, or in a few

cases the downward thrust from jet engines.

The human activity that surrounds aircraft is called aviation. Crewed aircraft are flown by an

on-board pilot, but unmanned aerial vehicles may be remotely controlled or self-controlled by

on-board computers. Aircraft may be classified by different criteria, such as lift type, aircraft

propulsion, usage and others.

Propulsion is a means of creating force leading to movement. The term is

derived from two Latin words: pro, meaning before or forward; andpellere, meaning to drive.

A propulsion system consists of a source of mechanical power, and a propulsor (means of

converting this power into propulsive force).

A technological system uses an engine or motor as the power source, and wheels and

axles, propellers, or a propulsive nozzle to generate the force. Components such

as clutches or gearboxes may be needed to connect the motor to axles, wheels, or

propellers.

Biological propulsion systems use an animal's muscles as the power source, and limbs such

as wings, fins or legs as the propulsors.

Some aircraft, like airliners and cargo planes, spend most of their life in a

cruise condition. For these airplanes, excess thrust is not as important as high engine

efficiency and low fuel usage. Since thrust depends on both the amount of gas moved and

the velocity, we can generate high thrust by accelerating a large mass of gas by a small

amount, or by accelerating a small mass of gas by a large amount. Because of the

aerodynamic efficiency of propellers and fans, it is more fuel efficient to accelerate a large

mass by a small amount. That is why we find high bypass fans and turboprops on cargo

planes and airliners.

Some aircraft, like fighter planes or experimental high speed aircraft require very high

excess thrust to accelerate quickly and to overcome the high drag associated with high

speeds. For these airplanes, engine efficiency is not as important as very high thrust.

Modern military aircraft typically employ afterburners on a low bypass turbofan core. Future

hypersonic aircraft will employ some type of ramjet or rocket propulsion.

2. Propulsion System

Propulsion is a means of creating force leading to movement. The term is derived from two

Latin words: pro, meaning before or forward; and puller, meaning to drive. A propulsion

system consists of a source of mechanical power, and a propulsor (means of converting this

power into propulsive force).

An aircraft propulsion system generally consists of an aircraft engine and some means to

generate thrust, such as a propeller or a propulsive nozzle.

An aircraft propulsion system must achieve two things. First, the thrust from the propulsion

system must balance the drag of the airplane when the

airplane is cruising. And second, the thrust from the

propulsion system must exceed the drag of the airplane

for the airplane to accelerate. In fact, the greater the

difference between the thrust and the drag, called the

excess thrust, the faster the airplane will accelerate.

Some aircraft, like airliners and cargo planes, spend

most of their life in a cruise condition. For these

airplanes, excess thrust is not as important as high

engine efficiency and low fuel usage. Since thrust depends on both the amount of gas

moved and the velocity, we can generate high thrust by accelerating a large mass of gas by

a small amount, or by accelerating a small mass of gas by a large amount. Because of the

aerodynamic efficiency of propellers and fans, it is more fuel efficient to accelerate a large

mass by a small amount. That is why we find high bypass fans and turboprops on cargo

planes and airliners.

Some aircraft, like fighter planes or experimental high speed aircraft, require very high

excess thrust to accelerate quickly and to overcome the high drag associated with high

speeds. For these airplanes, engine efficiency is not as important as very high thrust.

Modern military aircraft typically employ afterburners on a low bypass turbofan core. Future

hypersonic aircraft will employ some type of ramjet or rocket propulsion.

A propeller or airscrew comprises a set of small, wing-like aerofoil blades set around a

central hub which spins on an axis aligned in the direction of travel. The blades are set at

a pitch angle to the airflow, which may be fixed or variable, such that spinning the propeller

creates aerodynamic lift, or thrust, in a forward direction.

A tractor design mounts the propeller in front of the power source, while a pusher design

mounts it behind. Although the pusher design allows cleaner airflow over the wing, tractor

configuration is more common because it allows cleaner airflow to the propeller and provides

a better weight distribution.

3. Aircraft Motion

This slide shows some rules for the simplified motion of an aircraft. By simplified motion we mean that some of the four forces acting on the aircraft are balanced by other forces and that we are looking at only one force and one direction at a time. In reality, this simplified motion doesn't occur because all of the forces are interrelated to the aircraft's speed, altitude, orientation, etc. But looking at the forces ideally and individually does give us some insight and is much easier to understand.

In an ideal situation, an airplane could sustain a constant speed and level flight in which the weight would be balanced by the lift, and the drag would be balanced by the thrust. The closest example of this condition is a cruising airliner. While the weight decreases due to fuel burned, the change is very small relative to the total aircraft weight. In this situation, the aircraft will maintain a constant cruise velocity as described by Newton's first law of motion.

If the forces become unbalanced, the aircraft will move in the direction of the greater force. We can compute the acceleration which the aircraft will experience from Newton's second law of motion

F = m * a

Where a is the acceleration, m is the mass of the aircraft, and F is the net force acting on the aircraft. The net force is the difference between the opposing forces; lift minus weight, or thrust minus drag. With this information, we can solve for the resulting motion of the aircraft.

If the weight is decreased while the lift is held constant, the airplane will rise:

Lift > Weight - Aircraft Rises

If the lift is decreased while the weight is constant, the plane will fall:

Weight > Lift - Aircraft Falls

Similarly, increasing the thrust while the drag is constant will cause the plane to accelerate:

Thrust > Drag - Aircraft Accelerates

And increasing the drag at a constant thrust will cause the plane to slow down:

Drag > Thrust - Aircraft Slows

4. Aircraft Engine

The Merriam-Webster dictionary defines an engine as a machine for converting any of

various forms of energy into mechanical force and motion. The engine is thus an energy

transformer. Energy (also called work, and quantified in Joules) can itself be interpreted as a

force in motion. In the well-known case of a car engine, the thermal energy coming from the

20 combustion of petrol and air is transformed into mechanical energy which is applied to the

wheels of the vehicle (the force allowing to turn the wheels).The more familiar notion of

power, quantified in Watts (or in horse-power by our parents and grandparents – 1 horse

power = 736 Watts) expresses the quantity of energy used in one unit of time.

This transformation is unfortunately not perfect and is necessarily accompanied by certain

losses. This introduces the notion of efficiency. The efficiency is defined as the ratio between

the result obtained (the mechanical energy transmitted to the wheels in the example of a car

engine) and the means used to produce it (thermal energy contained in the petrol-air mixture

in this example). Its value is always less than 1 (or

100%). As an example, a petrol engine and a diesel

engine give respectively efficiencies of the order of 35%

and 46%. In a traffic jam, this efficiency can reduce to

15%. The lost energy is generally transformed into heat.

In flight, an aircraft does not have wheels in contact with the ground. We therefore need to

define the way of generating energy to allow it to advance. The principle of aeronautical

propulsion is a direct application of Newton’s third law of motion (principle of opposite action

or action-reaction) which says that any body A exerting a force on a body B experiences a

force of equal intensity, exerted on it by body B. In the case of aeronautical propulsion, the

body A is atmospheric air which is accelerated through the engine. The force – the action –

necessary to accelerate this air has an equal effect, but in the opposite direction – the

reaction -, applied to the object producing this acceleration (the body B, that is the engine,

and hence the aircraft to which it is attached).

It is possible to imagine much simpler examples based on the same principle. The first,

probably the most simple, is that of the fairground balloon, which is first inflated then

released. The air (body A) is ejected from the balloon (body B)

through a small opening and at high speed. The balloon is

propelled in the opposite direction to the ejected air – this is the

reaction. The second example is that of a rotating watering

system.

The speed of water (body A) is increased by its passage

through small ejection holes. The two arms of the watering

system (body B) are pushed in the opposite direction (reaction), thus driving the rotation.

5. Gas Turbine

A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It

has an upstream rotating compressor coupled to a downstream turbine, and a combustion

chamber in between.

The basic operation of the gas turbine is similar to that of the steam power plant except that

air is used instead of water. Fresh atmospheric air flows through a compressor that brings it

to higher

pressure. Energy is then

added by spraying fuel into

the air and igniting it so the

combustion generates a

high-temperature flow. This

high-temperature high-

pressure gas enters a

turbine, where it expands

down to the exhaust

pressure, producing a shaft work output in the process. The turbine shaft work is used to

drive the compressor and other devices such as an electric generator that may be coupled to

the shaft. The energy that is not used for shaft work comes out in the exhaust gases, so

these have either a high temperature or a high velocity. The purpose of the gas turbine

determines the design so that the most desirable energy form is maximized. Gas turbines

are used to power aircraft, trains ships, electrical generators, or even tanks.

The example proposed here is the simplest that can be imagined for an engine. This is

composed of 5 main parts:

the air intake

the compressor

the combustion chamber

the turbine

the outlet (jet pipe and propelling nozzle)

The purpose of the following parts are-

1. Suck atmospheric air into the engine (air describe briefly these components. Their inte-

intake and compressor) gration serves to:

2. Increase the energy of this air by means of the compressor (increasing the pressure)

and the combustion chamber (increasing the temperature by burning a mixture of air and

kerosene)

3. Transforming this energy into speed (kinetic energy) by means of the outlet tube in order

to apply the principle of aeronautical propulsiondescribed above.

5.1 The Air Intake

The air intake is one of the most visible parts of an aircraft

engine. A typical photo of this component is shown on the

right picture. This envelope which precedes the main part

of the engine is attached to a strut, which is itself fixed to a

wing or the fuselage. The main purposes of this nacelle

are:

to present as little air resistance (drag) as possible

to guarantee optimal functioning of the engine during

the different phases of flight (take-off, cruise, landing)

to limit the acoustical disturbance of the engine by absorbing some of the noise

to protect the inlet parts of the engine from phenomena relating to icing (the local

temperature at 10 000 metres altitude is between -40° and -50°C)

5.2 The Compressor

The compressor, situated just behind the air intake, is the first element which allows

transformation of energy, in this case from mechanical

energy into energy in the form of pressure. This machine is

presented at the bottom left, where the flow is from left to

right.

The compressor is composed of a series of fixed blades, both

fixed (stators – coloured in grey in the figure) and moving

(rotors – coloured in blue, yellow and red in the figure). The

function of these blades is to transform the mechanical

energy which turns the rotors into pressure energy. This

transformation operates by directing in a precise way the flow

which develops in the channels defined by the blades and the envelope of the engine. The

rotor which is best known is the one coloured in blue in Figure at the left; this is also called

the fan and can be seen at the entrance of the engine.

Air from the atmosphere is sucked into the engine by the compressor in the same way that a

ventilator fan (which is nothing else but a type of

compressor) sucks air into a polluted room.

The compressor of a modern engine allows pressures

typically 30 or 40 times greater to be reached at the outlet

of this element. The fan turns at a rotational speed of the

order of 5000 revolutions per minute: the largest

diameters are of the order of 3.25 metres, the length of

the blades of the largest fans is greater than 1.20 metres.

The centrifugal force undergone by transport aircraft

these rotating blades is comparable to the weight of a

railway carriage (80 000kg) being attached to the end of

one of these blades.

5.3 The Combustion Chamber

The combustion chamber, situated just downstream from the compressor, is the element in

which thermal energy is added to the pressure energy accumulated at the outlet of the

compressor. The transformation of energy considered here comes from the combustion of

the air/kerosene mixture (the combustible used in most aircraft engines) which generates an

increase in the temperature of the air passing through the engine.

Calculations show that the efficiency of the engine will be better if the temperature at the

outlet of the combustion chamber is higher. In the most recent engines, temperatures of the

order of 2100°C are achieved. To understand this temperature, it is useful to remember that

the temperature of the flame of a wood fire is only about 1000°C. The materials used for the

construction of a combustion chamber contain an important fraction of nickel and chrome.

The melting temperature of these two metals is less than this 2100°C and protection and

cooling of the metal parts is therefore absolutely necessary. A description of such

technologies is outside the scope of this document.

In summary then, at the outlet of the combustion chamber, there is a mixture of burnt air and

kerosene at very high temperature and pressure.

This energy (in the form of pressure and temperature) results from the transformation of

mechanical energy necessary to turn the compressor and the transformation of chemical

energy contained within the kerosene, which is stored in the fuel tanks of the aircraft. We

now need to define the source of mechanical energy required to turn the compressor. This is

the role of the turbine.

5.4 Turbine

The turbine is situated at the outlet of the combustion chamber. Its function is to transform

the energy available in the form of pressure and temperature into mechanical energy. In

other words, the turbine is the “motor” which turns the com- pressor. The pressure and

temperature of the airkerosene mixture will decrease during passage through this element.

This part of the machine is presented in Left Figure.

As for the compressor, the turbine is composed of a

series of blades, both fixed (stators – coloured in grey in

the figure) and moving (rotors – coloured in red, yellow

and blue in the figure). The function of these rotors is to

transform the temperature and pressure energy into

mechanical energy which turns the compressor. This

transformation is also made by precisely directing the

flow which develops in the channels defined by the

blades and the envelope of the engine. As an example,

the red rotor in Left Figure is generally composed of 30 to 40 blades. Each one of these

generates the same energy as is generated by the entire engine of a Formula One car!

Calculations show that the complete transfor- mation of the energy available in the form of

pressure and temperature and the energy available in the kerosene gives more mechanical

energy than is needed to turn the compressor (typically twice as much). The turbine serves

then to transform only the quantity of energy strictly required to achieve this function. The

50% available energy which remains in the air/kerosene mixture is transformed into kinetic

energy (the speed necessary to guarantee propulsion of the aircraft).

5.4 The Outlet

This last element, situated at the back of the turbine, is the

outlet tube. In this tube the last transformation of energy

takes place with the aim of creating a jet of air exiting the

engine at high speed, thus allowing the propulsion of the

aircraft according to the principle of action/reaction. This

transformation is achieved by a controlled variation of the

cross-section of the outlet tube.

In the case of Concorde (a now discontinued supersonic

civil transport aircraft) and in the case of a number of

military aircrafts, a final transformation of energy,

afterburning, is made in the outlet tube. The principle of this

transformation is to inject extra kerosene and burning the

mixture. The extra energy obtained gives an even higher

speed to the jet of air exiting the engine and hence an

even great propulsive power. A photo of the outlet jet, with

afterburn showm in fig. This technology is mainly used for

aircraft flying at speeds greater than the speed of sound.

6. Jet Propulsion

Jet propulsion is thrust produced by passing a jet of matter (typically air or water) in the

opposite direction to the direction of motion. By Newton's third law, the moving body is

propelled in the opposite direction to the jet. It is most commonly used in the jet engine, but

is also the favoured means of propulsion used to power various space craft.

A number of animals, including cephalopods sea

hares, arthropods, and fish have convergently evolved jet propulsion mechanisms.

Jet propulsion is most effective when the Reynolds number is high - that is, the object being

propelled is relatively large and passing through a low-viscosity medium.

In biology, the most efficient jets are pulsed, rather than continuous. at least when the

Reynolds number is greater than 6.

A jet engine is a reaction engine that discharges a fast moving jet of fluid to

generate thrust by jet propulsion and in accordance with Newton's laws of motion. This

broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse

jets and pump-jets. In general, most jet engines are internal combustion engines[4] but non-

combusting forms also exist.

6.1 Turbojets

The turbojet is an air breathing jet engine, usually used in aircraft. It consists of a gas

turbine with a propelling nozzle. The gas turbine has an air inlet, a compressor, a

combustion chamber, and a turbine (that drives the compressor). The compressed air from

the compressor is heated by the fuel in the combustion chamber and then allowed to expand

through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is

accelerated to high speed to provide thrust.[1] Two engineers, Frank Whittle in the United

Kingdom and Hans von Ohlin in Germany, developed the concept independently into

practical engines during the late 1930s.

Turbojets have been replaced in slower aircraft by turboprops which use less fuel. At

medium speeds, where the propeller is no longer efficient, turboprops have been replaced

by turbofans. The turbofan is quieter and uses less fuel than the turbojet. Turbojets are still

common in medium range cruise, due to their high exhaust speed, small frontal area, and

relative simplicity.

The jet engine is only efficient at high vehicle

speeds, which limits their usefulness apart

from aircraft. Turbojet engines have been used

in isolated cases to power vehicles other than

aircraft, typically for attempts on land speed

records. Where vehicles are 'turbine powered'

this is more commonly by use of

a turboshaft engine, a development of the gas turbine engine where an additional turbine is

used to drive a rotating output shaft. These are common in helicopters and hovercraft.

Turbojets have also been used experimentally to clear snow from switches in railyards.

6.2 Ramjet

A ramjet, sometimes referred to as a flying stovepipe or an athodyd (an abbreviation

of aero thermodynamic duct), is a form of air breathing jet engine that uses the engine's

forward motion to compress incoming air without an axial compressor. Ramjets cannot

produce thrust at zero airspeed; they cannot move an aircraft from a standstill. A ramjet-

powered vehicle, therefore, requires

an assisted take-off like a rocket assist to

accelerate it to a speed where it begins to

produce thrust. Ramjets work most efficiently

at supersonic speeds around Mach 3

(2,284 mph; 3,675 km/h). This type of engine

can operate up to speeds of Mach 6

(4,567 mph; 7,350 km/h).

Ramjets can be particularly useful in

applications requiring a small and simple mechanism for high-speed use, such as missiles.

Weapon designers are looking to use ramjet technology in artillery shells to give added

range; a 120 mm mortar shell, if assisted by a ramjet, is thought to be able to attain a range

of 35 km (22 mi).[1] They have also been used successfully, though not efficiently, as tip

jets on the end of helicopter rotors.[2]

Ramjets differ from pulsejets, which use an intermittent combustion; ramjets employ a

continuous combustion process.

As speed increases, the efficiency of a ramjet starts to drop as the air temperature in the

inlet increases due to compression. As the inlet temperature gets closer to the exhaust

temperature, less energy can be extracted in the form of thrust. To produce a usable amount

of thrust at yet higher speeds, the ramjet must be modified so that the incoming air is not

compressed (and therefore heated) nearly as much. This means that the air flowing through

the combustion chamber is still moving very fast (relative to the engine), in fact it will be

supersonic - hence the name Supersonic Combustion Ramjet, or Scramjet.

6.3 Rocket

A rocket engine is a type of jet engine that uses only stored rocket propellant mass for

forming its high speed propulsive jet. Rocket engines are reaction engines, obtaining thrust

in accordance with Newton's third law. Most rocket

engines are internal combustion engines, although non-

combusting forms (such as cold gas thrusters) also

exist. Vehicles propelled by rocket engines are

commonly called rockets. Since they need no external

material to form their jet, rocket engines can perform in

a vacuum and thus can be used to

propel spacecraft and ballistic missiles.

Rocket engines as a group have the highest thrust, are

by far the lightest, but are the least propellant efficient

(have the lowest specific impulse) of all types of jet

engines. The ideal exhaust is hydrogen, the lightest of

all gases, but chemical rockets produce a mix of heavier

species, reducing the exhaust velocity. Rocket engines become more efficient at high

velocities (due to greater propulsive efficiency and Oberth effect). Since they do not benefit

from, or use, air, they are well suited for uses in space and the high atmosphere.

Rocket engines produce thrust by the expulsion of an exhaust fluid which has been

accelerated to a high speed through a propelling nozzle. The fluid is usually a gas created by

high pressure (150-to-2,900-pound-per-square-inch (10 to 200 bar)) combustion of solid or

liquid propellants, consisting of fuel and oxidiser components, within a combustion chamber.

The nozzle uses the heat energy released by expansion of the gas to accelerate the exhaust

to very high (supersonic) speed, and the reaction to this pushes the engine in the opposite

direction. Combustion is most frequently used for practical rockets, as high temperatures

and pressures are desirable for the best performance, permitting a longer nozzle, giving

higher exhaust speeds and better thermodynamic efficiency.

An alternative to combustion is the water rocket, which uses water pressurised by

compressed air, carbon dioxide, nitrogen, or manual pumping, for model rocketry.

Rocket propellant is mass that is stored, usually in some form of propellant tank, prior to

being ejected from a rocket engine in the form of a fluid jet to produce thrust.

Chemical rocket propellants are most commonly used, which undergo exothermic chemical

reactions which produce hot gas which is used by a rocket for propulsive purposes.

Alternatively, a chemically inertreaction mass can be heated using a high-energy power

source via a heat exchanger, and then no combustion chamber is used.

Solid rocket propellants are prepared as a mixture of fuel and oxidising components called

'grain' and the propellant storage casing effectively becomes the combustion

chamber. Liquid-fuelled rockets typically

pump separate fuel and oxidiser

components into the combustion

chamber, where they mix and

burn. Hybrid rocket engines use a

combination of solid and liquid or

gaseous propellants. Both liquid and

hybrid rockets use injectors to introduce

the propellant into the chamber. These

are often an array of simple jets - holes

through which the propellant escapes under pressure; but sometimes may be more complex

spray nozzles. When two or more propellants are injected, the jets usually deliberately cause

the propellants to collide as this breaks up the flow into smaller droplets that burn more

easily.

7. Conclusion

A propulsion system is a machine that produces thrust to push an object forward. On

airplanes, thrust is usually generated through some application of Newton's third law of

action and reaction. A gas, or working fluid, is accelerated by the engine, and the reaction to

this acceleration produces a force on the engine.

The four basic parts of a jet engine are the compressor, turbine, combustion chamber, and

propelling nozzles. Air is compressed, then led through chambers where its volume is

increased by the heat of fuel combustion. On emergence it spins the compression rotors,

which in turn act on the incoming air.

8. References

1- Thermodynamics by P. K. Nag

2- Engineering Thermodynamics by R. K. Rajput

3- http://www.grc.nasa.gov

4- https://spaceflightsystems.grc.nasa.gov

5- https://en.wikipedia.org