The document discusses the design and operation of a turbojet engine. A turbojet engine consists of an air intake, compressor, combustion chamber, turbine, and propelling nozzle. The compressor increases the air pressure and temperature before it enters the combustion chamber where fuel is added and ignited. The hot gases then expand through the turbine, which extracts energy to power the compressor. The remaining high-speed gases are accelerated through the nozzle to produce thrust. Turbojet engines are efficient at high speeds and have been used primarily in aircraft, though occasionally in land vehicles seeking speed records. Improvements involve raising pressure ratios and turbine temperatures but must balance efficiency gains against higher jet velocities.

1. PRESENTATION
ON
TURBOJET
Prepared by:
Gokarna basnet
B.tech( ME 4TH sem)
Ansal university.

2. What is turbojet?
 The turbojet is an airbreathing 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

3. INTRODUCTION
•

4. DESIGN OF A TURBOJET
Air intake - An intake, or tube, is needed in front of the compressor to help direct the
incoming air smoothly into the moving compressor blades. The intake is shaped to minimise
any flow losses when the compressor is accelerating the air through the intake at zero and
low aircraft speeds, and to slow the flow down for the compressor when the aircraft is
operating above Mach 1. The air flowing into a turbojet engine must always be subsonic,
regardless of the speed of the aircraft itself.
Compressor:
 The compressor is driven by the turbine. It rotates at high speed, adding energy to the
airflow and at the same time squeezing (compressing) it into a smaller space.
Compressing the air increases its pressure and temperature. The smaller the compressor
the faster it turns.

5.  Turbine:
 Hot gases leaving the combustor expand through the turbine. The turbine vanes and blades
have internal cooling passages. Air from the compressor is passed through these to keep the
metal temperature within limits.
 In the first stage the turbine is largely an impulse turbine and rotates because of the impact of
the hot gas stream. Later stages are convergent ducts that accelerate the gas. Energy is
transferred into the shaft through momentum exchange in the opposite way to energy
transfer in the compressor. The power developed by the turbine drives the compressor as well
as accessories, like fuel, oil, and hydraulic pumps that are driven by the accessory gearbox.

6. OPERATION OF TURBOJET

7. WORKING OF TURBOJET
 Large amounts of surrounding air are continuously brought into the
engine inlet.
 At the rear of the inlet, the air enters the compressor.
 The compressor acts like many rows of airfoils, with each row producing a small
jump in pressure.
 At the exit of the compressor, the air is at a much higher pressure than free
stream.
 In the burner a small amount of fuel is combined with the air and ignited.
 Leaving the burner, the hot exhaust is passed through the turbine. The turbine
works like a windmill and extracts energy from a flow of gas by making the
blades spin in the flow.
 The turbine takes some energy out of the hot exhaust, but there is enough energy
left over to provide thrust to the jet engine by increasing the velocity through the
nozzle.
 Because the exit velocity is greater than the free stream velocity, thrust is
created . For a jet engine, the exit mass flow is nearly equal to the free stream
mass flow, since very little fuel is added to the stream

8. APPLICATION
 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.

9.  Cycle improvements
 The operation of a typical turbojet is modelled approximately by
the Brayton Cycle.
 The efficiency of a gas turbine is increased by raising the overall
pressure ratio, requiring higher temperature compressor
materials, and raising the turbine entry temperature, requiring
better turbine materials and/or improved vane/blade cooling.
However, when used in a turbojet application, where the output
from the gas turbine is used in a propelling nozzle, raising the
turbine temperature increases the jet velocity. This reduces the
propulsive efficiency giving a loss in overall efficiency, as
reflected by the higher fuel consumption, or SFC.