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Fig. 1.2 shows a simple single spool turbojet engine. When the air in the

combustor isheated, it expands and is forced through the turbine blades which, in

turn, drive thecompressor. Air is drawn into the compressor and the pressure is

increased as it enters thecombustion chamber. The cycle is continuous.

Approximately 90% of the energy produced by the expansion of air in the

combustionchamber is used to drive the compressor and the remaining 10% goes

out the exhaustnozzle to produce thrust. Most of the fuel burned in the engine is

usedto drive the compressor.

Fig. 1.2Single Spool Turbojet Engine

Fig.1.3 shows a dual spool turbojet engine. In this engine a turbine wheel

is placed behindthe primary turbine and is used to drive the first stage compressor.

This engine has theadvantage of being capable of producing much higher

compression ratios since the firststage (low pressure section) forces a large

amount of air into the high pressure section.This type of turbojet engine produces

more thrust for a given diameter than a single spoolengine and is desirable for

fuselage-mounted engines.

Fig. 1.3 - Dual Spool Turbojet Engine

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CHAPTER 2

DESCRIPTION OF WORK

2.1 SCHEME

Fig. 2.1Schematic Design

The scheme adopted for making turbojet engine is shown in Fig. 2.1. Ituses the compressor and turbine from a common turbocharger. The turbocharger

compressor serves the same function as the compressor on a commercial jet

engine. The turbine on the turbocharger drives the compressor and the excess

energy is expelled out the exhaust nozzle to provide thrust. The lower portion of

the drawing shows the combustion chamber attached to the turbocharger. Fuel is

injected through the bottom of the combustion chamber into the flame tube. A

spark plug is also connected at the bottom the combustion chamber to ignite the

fuelair mixture. Enough air is allowed to go into the burner to allow the correct

fuel to air ratio and the rest is used as cooling air in the turbine. Without this

cooling air, the turbine would get too hot and melt the blades. Also oil is supplied

into the region around the shaft which connects the turbine and compressor. This

serves as a lubricant as well as a cooling agent that takes away the heat generated

in the turbocharger. The blades are generally made from Hastalloy, a nickel alloy,

and can handle temperatures in excess of 2,000 deg. F. without damage.

Inlet Duct

Airflow

Compressor

Turbine

Exhaust

Flame tube

Combustion Chamber

Fuel InjectorSpark Plug

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2.2 CONSTRUCTION

2.2.1 Selecting the Turbocharger

Check the unit very carefully. Make sure that the turbine and compressor

turn freely. If the unit has been overheated there will be signs of heat

discoloration on the turbine wheel and turbine housing, Check the castings for

cracks or lumps. If a foreign object has entered the compressor and broken a

blade, it will likely fly apart and damage the case. The compressor housing is

made from aluminum alloy and is easily broken. The turbine housing is made

from malleable cast iron and is quite tough. They are rarely damaged. The

turbocharger used for this project is shown below. The turbocharger was

manufactured by Garret Turbochargers. GTC 1241 VZ used in Volkswagen cars.

Fig. 2.2Garret GTC 1241 VZ Turbocharger

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point is about 1800 deg.F. The turbine wheel is usually cast from Hastalloy or

some other nickel alloy.

The thrust bearing on the turbine end rides on a layer of oil and is cooled by

oil. The turbine end bearing runs extremely hot, usually about 1,800 deg.F .Large

quantities of oil must be supplied to provide adequate cooling.

The Drive Shaft and Bearings

The turbine drives the compressor by means of a drive shaft; usually a very

small diameter shaft that is friction welded to the turbine wheel and bolted to the

compressor. The shaft runs through an aluminum bearing. Most modern

turbochargers use hydrodynamic bearings. This an alloy sleeve bearing with design

tolerances that allow a layer of oil between the shaft and the bearing. When the

turbocharger is running, the oil supply is under pressure and the shaft rides on a

layer of oil and does not touch the alloy bearing. The shaft is suspended on a layer

of oil.

The VGT disc

The VGT disc controls the airflow into the inlet manifold based on the

speed of the engine. At high speeds the vanes on the disc closes and allows less air

into the manifold, and at low speeds the vanes open and allows more air.

LOW SPEED HIGH SPEED

Fig. 2.3VGT disc variations during low speed and high speed.

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For maximizing the thrust force in this project we have removed the VGT

disc so that more air will be forced out of the turbine side creating more thrust.

Fig. 2.4Turbine housing with VGT disc removed.

2.2.3 Construction of the Combustion Chamber

The combustion chamber is the key element of the engine. This is where

fuel is mixed with compressed air and burned, causing the air to expand and drive

the turbine wheel. The combustion chamber used in this project is mainly divided

into four parts - a cylindrical section which houses majority of the flame tube, a

tapered conical section which converges into the turbine inlet size, a bend pipe

section and a base plate which covers one end of the chamber and supports the

fuel nozzle and spark plug. A shield called a combustion liner or flame tube is

kept inside the combustion chamber to allow some air to mix with the fuel and

burn, while the remainder of the air is used to cool the steel parts.

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Fig 2.5Base plate with nozzle and spark plug

The holes in the combustion liner are adjusted to allow the right amount of

air to mix with the fuel so that combustion can occur. If the holes are too large, the

incoming pressurized air will blow out the flame. If the holes are too small, there

will not be enough oxygen to support combustion. If the holes at the fuel inlet end

are too small, the flame will have to travel along the combustion liner until enough

oxygen has entered to support combustion. This will cause the combustion to occur

in the inlet to the turbine and overheat the turbine.

Fig 2.6Combustion Chamber Assembly

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Flame tube/Combustion liner

Flame tube hole pattern is most important in the design of combustion

chamber and it is the essential part of the entire system. There are three different

zones in the hole pattern. Primary zone with small holes supply air needed to start

the combustion, without blowing out the flame. The secondary zone supplies air

needed to sustain the flame and finally tertiary zone or dilution zone provides

remainder of air to cools the exhaust gases before reaching the turbine blades.

Fig 2.7Flame tube

2.2.4 Lubrication System

Most turbochargers are equipped with hydrodynamic bearings. The

bearing itself is a sleeve made from an aluminum alloy. The bearings are designed

to have an excess of clearance on the turbine shaft. The bearing is flooded, under

pressure, with light oil. The oil provides lubrication as well as cooling. When the

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turbocharger is running, the oil fills the gap between the bearing and shaft and the

metal parts do not touch. This is an excellent bearing for this particular application

since the turbine runs at extremely high temperatures and some sort of mechanism

is needed to carry the heat away from the bearings. The oil gets very hot though.

The system consist a high pressure oil pump from a diesel automobile, a

0.25HP motor coupled to the oil pump via chain, oil sump, banjo fittings for the

oil line and an oil pressure guage. The oil used was SAE 15W40 which is

commonly used in turbocharged trucks.

Fig. 2.8High pressure oil pump

The pump was a belt driven one and it was modified into a chain driven by

attaching a sprocket. The maximum allowed oil pressure to the turbo was around

70psi. The oil pump delivers oil upto 200 psi. So inorder to reduce high pressure

going to the turbocharger shaft, the oil relief of the pump was modified so that the

limit was set to 100psi.

.

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Fig. 2.9Banjo fittings used in oil lines

2.2.5 Fuel System

We are using LPG as fuel because it is very easy to install and there is no

need for any injection systems or fuel pumps. LPG is stored in a 2 Kg capacity

cylinder. The cylinder is connected to two valves, one stop valve and other control

valve, that regulate the flow of gas. The valve is followed by high pressure

flexible tubes used in gas welding. The other end is connected to the fuel nozzle

made from mild steel, which is welded to the base plate of the combustion

chamber. A pressure gauge was also connected to know the cylinder pressure.

Fig. 2.10Fuel Supply unit

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2.2.6 Ignition System

The ignition system consists of an ignition coil of Maruti 800, a capacitor

of 12.5 F, 400V and a 400W light dimmer. Capacitor and dimmer are connected

in series to the primary terminal ignition coil. The high tension secondary terminal

is connected to a spark plug that is welded to the combustion chamber through a

high voltage wire and the body of the spark plug is connected to the neutral

terminal.

230V mains are connected to the ignition coil through dimmer and

capacitor. The ignition coil increases input voltage many times, the dimmer

synchronizes with the frequency of the main supply and creates a continuous

spark between the terminals of the spark plug. The dimmer together with the

capacitor serves the function of distributor in the car that triggers the creation of

spark. By controlling the dimmer we can change the characteristics of the spark.

Fig. 2.11Circuit Diagram for the Ignition System

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Fig. 2.12Ignition System

2.2.7 Final Assembly

Turbojet Engine

Flanges were made for both turbine inlet and compressor outlet. So the

combustion chamber was bolted onto the turbocharger. The turbocharger was

supported using a frame made of steel anglers. The frame was minimized so that

testing of thrust will be easier. All units were arranged in a very compact manner

so as to reduce the overall size. A tray with wheels was used to identify any

noticeable thrust.

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Fig. 2.13Final Assembly

2.3 OPERATION PROCEDURE AND SAFETY PRECAUTIONS

Engine Starting Procedure:

Ensure the blades are spinning (or not stuck) by keeping the blower to thecompressor inlet.

Start oil pump and keep it for a few minutes. Turn the igniter (spark plug) on. Open fuel valve to pre-ignite cold engine. You will hear a rumbling sound

at this moment.

Confirm fuel ignition. Allow engine to accelerate. Turn igniter off. Flame will self-sustain. The engine can be accelerated, reduced, or idled with the fuel control.

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Safety Precautions

If the turbine blades or exhaust nozzle appears to be red-hot shut fuel offimmediately. Or else it may damage the turbine wheel.

If excess smoke is coming from the turbocharger stop the engineimmediately. The smoke is due to the burning of oil which is supplied for

lubrication.

The operation of the fuel control should be done in a safe distance from theengine. Sufficient length is provided for the fuel line for this.

Always keep one hand on the shut off valve while the other hand controlsthe throttling valve.

Do not touch parts such as turbine housing, combustion chamber etc. as itwill be very hot after working the engine.

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CHAPTER 3

CALCULATIONS

3.1 FLAME TUBE

Flame tube dimensions

Diameter = Compressor inducer dia x 3= 29 x 3 mm

= 87 mm

3 inch (76.2 mm)

Length = Compressor inducer dia x 3= 29 x 6 mm

= 174 mm

7 inch (177.8 mm)

Hole Pattern

Inducer area = sum of area of all the holes in the flame tubeInducer area = 660.52 mm

2

Primary zone = 30% of Inducer area = 198.16 mm2 Secondary zone = 20% of Inducer area = 132.1 mm2 Tertiary zone = 50% of Inducer area = 330.26 mm2

Table 3.1Flame tube pattern

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3.2 SELF SUSTAINABILITY

Velocity of air from the blower, v1 = 10 m/s

(when blower is at its lowest speed)

Diameter of blower end = 28 mm

Area of blower end, a1 = 615.75 mm2

Diameter of compressor inlet = 46 mm

Area of compressor inlet, a2 = 1661.9 mm2

Using equation of continuity, a1v1=a2v2

Velocity of compressor inlet, v2 = 3.7 m/s

ie, if the compressor (engine itself) is moving at a speed of 3.7 m/s (13.32

km/hr) the engine will self sustain.

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CHAPTER 4

RESULTS AND DISCUSSION

4.1 TESTING RESULTS

Once the engine starts, the expanded air from the combustion chamberstarts rotating the turbine and which in turn will rotate the compressor. So

the engine should work smoothly even if the blower is removed from the

compressor inlet after the engine has started. But from testing it is found

that the engine will turn off once the blower is removed.

Though this is similar to the previous work done, it was found that theengine could work at the least possible airflow of the blower, unlike

before. This minimum limit was identified as 15% of max blower air flow

rate , compared to 73% of max blower air flow rate of the previous work.

In usual jet engine applications the body to which the engine is attachedwill have a sufficient velocity that will force more air into the compressor

wheels. Hence the minimum air flow rate supplied by the blower is

equivalent to the air flow rate at compressor inlet if the engine wasactually moving at a certain amount of speed.

By knowing the values of the compressor inlet and blower outlet areas, aswell as min velocity of air exiting the blower, this speed equivalence of the

engine was found out using equation of continuity. If the compressor

(engine itself) is moving at a speed of 3.7 m/s (13.32 km/hr) the engine

will self sustain.

This is a very small velocity value compared to the usual valuesencountered in jet engine with thrust output applications.

In the previous work, the engine cannot be run for long durations of timeas it will start to smoke after a few minutes of operation. This was because

the oil getting burned due to high temperature developed. The oil pump we

used then was not able to supply oil at very high pressures which is needed

for the smooth working of the engine.

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By using an automobile oil pump, coupled to a 180W AC motor(1440rpm), along with a dimmer for speed control, the above problem was

completely solved. Also reduced the size of oil sump from 5litres to a mere

1.8litres.

Use of oil and fuel pressure gauges helped us to attain combustion quiteeasily and it was guaranteed unlike the previous work. Anemometers was

used to measure blower velocities.

The frame was made much compact than before, though a much largerturbocharger and combustion chamber used. This was achieved mainly due

to the use of a compact high pressure lubrication system.

Anemometers that were available cannot withstand the heat of the exhaustgases. Hence exhaust velocity calculations could not be made and

theoretical thrust could not be calculated. This stopped us from the

possibility of measuring theoretical efficiency also, as a function of turbo

shaft speed, intake air flow rate, fuel supply pressure and flow rate,

correlations between lubrication pressures and thrust etc.

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CHAPTER 5

CONCLUSIONS AND SCOPE FOR FUTURE WORK

5.1 CONCLUSIONS

Turbojet engines are widely used in aircrafts, even though land based

applications are minimal. But jet engine designs allow conversion into gas turbine

engines, which are used in a wide variety of industrial applications such as

electrical power generations, to power water, natural gas or oil pumps, propulsion

for ships and locomotives etc. Industrial gas turbines can create up to 50,000 shaft

horse power.

Turbocharger turbojet engines can be utilized to power miniature aircrafts,

unmanned aerial vehicles for surveying or espionage, model rocketry often they

are used in drag racing calls, go karts, skate boards, and even in two wheelers.

And these turbojet engines made from turbochargers can be utilized for

educational purposes too.

As the main raw material for construction is old or unused turbocharger,

we can construct lots of turbojet engines easily and economically and these arepowerful for their size and weight. Also these turbojet engines work on LPG or

propane, rather than ATF or other liquid fuels. Its emissions are very low. Hence

further research and development is needed for effectively utilizing these turbojet

engines.

5.2 SCOPE FOR FUTURE WORK

Using liquid fuel like kerosene or petrol, along with fuel injectors and afuel pump will definitely help to achieve measurable thrust, i.e the engine

will move under its own power.

Using anemometers capable of withstanding the heat produced by ourturbojet engine (temperatures in excess of 700 deg Celsius) or with similar

arrangements, exhaust gas velocity can be calculated.

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REFERENCES

[1]Edwin H. Springer , Constructing a Turbocharger Turbojet Engine[2] V. Ganesan, Gas turbines, Tata Mcgraw Hill (2004)[3]Hugh MacInnes, Turbochargers, Price Stern Sloan, Inc. 1984[4]Lauren Tsa,Design and Performance of a Gas-Turbine Engine from an

Automobile Turbocharger, 2005

[5]Kurt Schreckling, Gas Turbine Engines for Model Aircraft, 1994