turbofan jet engine

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                                 ANUJ KAUSHAL
what is a turbofan jet
A turbofan is a air breathing ,turbine powered engine which is
the most widely used engine on modern aircraft today. It uses a
fan or a series of fans to compress the air.

                   Fig -shows the turbofan engine
 There are a large number of different types of Turbofan Engines,
  all of which achieve forward thrust from the principle of jet

 “Jet propulsion is motion produced by passing a jet of fluid (e.g.
  air or water) in the opposite direction to the direction of motion”.

 Jet propulsion is the thrust imparting forward motion to an

 This thrusting action is similar to the recoil of a gun.
Main components of a
turbofan jet engine
  There are five main components of a turbofan jet engine-

 FAN – The propulsion process begins with the fan at the
  front of the engine. It draws in a large volume of air. As the
  air leaves the fan it separates into two streams. The larger
  stream, typically about 85% of the total, is called bypass air.
  The smaller stream, typically about 15% of total, is called
  primary air.

   BYPASS AIR – Because of the huge volume only needs to
  accelerate , a small amount to produce an enormous kick of
  thrust and has added benefits of keeping the engine cooler,
  quieter and more fuel efficient.
 COMPRESSORS - Primary air enters the first of the
  two compressors that are spinning in the same
  direction as the fan itself . As this air passes through
  the compressor, both its temperature and pressure
  rises significantly.

 COMBUSTION CHAMBER - When the compression
  is complete , the pressure of air becomes 30 times
  higher and 1100 *F hotter. This high pressure and high
  temperature air is forced through the combustor ,
  where the fuel is added and burned. The air’s
  temperature soars even higher and reaches well
  beyond 2000* F.
 TURBINES – The hot air then blasts through the blades
  of the two turbines. The whirling turbine turns the shafts
  that drive both the compressors and the fan at the front
  of the engine. This process, in which the engine extracts
  the energy from the air it has just captured, is what allows
  the modern jets to operate with such high fuel efficiency.

 EXHAUST NOZZLE- After passing through the turbines,
  the hot air is forced through the exhaust opening at the
  back of the engine. The narrowing walls of the nozzle
  force the air to accelerate. The weight of the air, combined
  with its acceleration, drives the engine forward.
Together, these five components of a turbofan jet
engine enables today’s aircraft to fly with a greater
speed and fuel efficiency, as well as lower exhaust
emissions and noise, than ever before
              1. Inlet
              2. Fan and
              3. Combustor
              4. Turbine blades
              5. nozzle
 The air travels through the engine from left to
right, starting at the fan and progressing
towards the exhaust nozzle. There are various
stages in which a turbofan jet engine works
and are given below.

1. Air Intake/Ingestion - The fan is
responsible for producing the majority of the thrust
generated by a turbofan engine. Ambient air enters
the engine by passing through the fan. Most of the
air that passes through the fan travels around the
core of the engine. This air that travels around the
core is known as bypass air. Bypass air is accelerated
out of the back of the engine by the fan thereby
creating thrust. It never interacts with the
compressor, combustor, turbine, or exhaust nozzle.
2. Compression - The purpose of
  compression is to prepare the air for
  combustion by adding energy in the
  form of pressure and heat. The
  compressor is divided into two portions:
  the low pressure compressor and the
  high pressure compressor.

   The Low Pressure Compressor(LPC) -
  The LPC is directly connected to the fan
  and the low pressure turbine (LPT) by
  the low pressure shaft. The LPC has rows
  of spinning blades which push the air
  further back into the engine. As the air is
  being forced rearward, the LPC’s cross
  sectional area decreases, causing the
  volume of air to decrease. From the ideal
  gas law, this implies that the air is
  becoming pressurized and the
  temperature is increasing. Immediately
  after the air passes through the LPC, it
  enters the high pressure compressor.
   The High Pressure Compressor (HPC) -The high pressure
  compressor, or HPC, is located directly downstream of the
  LPC and directly upstream of the combustor. The HPC is
  connected directly to the high pressure turbine by the high
  pressure shaft. Like the LPC, the HPC has rows of spinning
  blades which force the air flow rearward into a higher pressure
  and higher temperature state due to a decrease in volume. The
  HPC typically has more rows of blades when compared to the
  LPC. Air exiting the HPC has a high temperature and pressure
  and is now ready for combustion.
3. Combustion - The combustor is directly downstream of the
  HPC and directly upstream of the high pressure turbine. The
  purpose of the combustor is to add even more energy to the air
  flow by way of heat addition. Within the combustor, fuel is
  injected and mixed with the air. This fuel-air mixture is then
  ignited, creating a dramatic increase in temperature and
  energizing the flow, propelling it rearward towards the high
  pressure turbine.
                         4. Expansion- Expansion occurs within the
                           high pressure and low pressure turbines. The
                           purpose of the turbines is to extract energy from
Rows of turbine blades     the flow which is then used to spin the
                           compressors and the fan.

                           The High Pressure Turbine(HPT)- The high
                           pressure turbine is located directly downstream of
                           the combustor and directly upstream of the low
                           pressure turbine. The HPT is driven by the high
                           pressure air that passes through it. The HPT’s cross
                           sectional area is initially small and then increases
                           downstream. This change in area allows the air to
                           expand, increasing in volume thereby decreasing in
                           pressure and temperature. This decrease in
                           pressure and temperature, along with the energy
                           used to spin the turbine, correspond to a decrease
                           in the overall energy in the air flow. Air exiting the
                           HPT is significantly cooler and less pressurized
                           than the air entering; however, it still has viable
                           energy which will be extracted by the low pressure
  The Low Pressure Turbine (LPT) - The low pressure turbine, or LPT, is
 located directly downstream of the HPT and directly upstream of the
 exhaust nozzle. The LPT functions exactly as the HPT does; however,
 it is connected to the LPC and the fan via the low pressure shaft.
 Therefore, when the LPT is driven by the air passing through it, is also
 drives the LPC and the fan. When the LPC is spinning, it provides the
 HPC with air to feed to the combustor. When the fan is spinning, it
 provides the LPC with air to feed to the HPC, and it produces thrust
 by accelerating bypass air out of the engine.
5. Exhaust- The exhaust nozzle is located directly downstream of
 the LPT and it is the last component that the air flow touches before
 exiting the engine. The purpose of the exhaust nozzle is to propel the
 core flow out of the engine, providing additional thrust.
      Applications and
      manufacturers of
      turbofan jet engine
 Turbofan jet engines are widely used in all airliners and are
 used by the jet fighters. Different type of turbofan engines
 are used according to the thrust requirement. For example
 the engine used in jet fighter planes is low bypass turbofan
 engine and engine used by commercial flights are the high
 bypass turbofan engine.
  The leading manufacturers of the turbofan engines are:
 General electric
 CFM International
 Rolls- Royce
 Pratt & Whitney
Turbofan thrust
Thermodynamics of a jet engine are modeled approximately by a
Brayton Cycle. The Brayton cycle is a thermodynamic cycle that
describes the workings of the gas turbine engine, basis of the
Turbofan engine and others.

             Simple Open Cycle Gas Turbine

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Description: gives you the detail study of each and every part of turbofan jet engine
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