Gas turbine theory


Basic information for gas turbine  CLICK

Gas Turbine Theory
A simple gas turbine is comprised of three main sections a compressor, a combustor, and a power turbine. The gas-turbine operates on the principle of the Brayton cycle, where compressed air is mixed with fuel, and burned under constant pressure conditions. The resulting hot gas is allowed to expand through a turbine to perform work. In a 33% efficient gas-turbine approximately two / thirds of this work is spent compressing the air, the rest is available for other work ie.( mechanical drive, electrical generation).

Refer : http://massengineers.com/Documents/gasturbinetheory.htm

Gas Turbine For the Best Performance

GAS TURBINE(AIRCRAFT ENGINE)

It is flow cycle engine. Air is compressed  and heated by burning  fuel after which it passes through the turbine which drive the comprssor and fan

Basically a gas turbine contain 2 section
 i core section produce power to drive the propulsor section
ii Propulsor section  that produce the thrust

Thrust is force created by the acceleration of air
                                Thrust = airflow x change in velocity

This is basically from newtons second law
                 Force = Mass x Acceleration(This force propelles the Aircraft)

Working Principle :

Intake of air in the low compressor  It passes through the rotary blades in between stationary blade.

After it enter in to the high pressure  compressor where the pressure raise to 70% at the end the of high pressure is 35 times high pressure and 1000° C  hotter  than outside air. 

Air (air  it is now  in right pressure to ignited but it is moving too fast to efficient to ignited )leaves the compressor  and passes through the diffuser where it converts  the velocity energy into pressure energy  and   to remaining optimum temperature and pressure.

Total massive air passes through the combustion chamber  is primary air and enter in to the flame tube (flame tube orifice) for combustion  remaining air passes along the outside of the flame tubes entering through dilution holes in the side of the tubes and is used for cooling.

Each combustion chamber containing a burner containing swirl type atomizer. Through the atomizer fuel  is injected under pressure by the fuel pump inside the combustion chamber . where the fuel is mixes the fine droplets incoming primary air. Combustion mixture is formed is ignited by the ignitors by 2 or 3 of the combustion chamber depends on the design of the engine .

On completion of the starting cycle ignitors  are cut off  at this stage we have “light off’

From this point combustion is continuous and pressure inside the combustion chamber for the given fuel flow is constant .

Residual of the secondary air which passes through the dilution hole in to the flame tube mixes with the main  massive burning gas and cools  it sufficient  committed  to pass through the turbine at a temperature with the safe limits of the turbine material with in the combustion chamber . going to the added heat   energy  fuel  the gas rises in temperature  and increases in volume

After the hot gases pass through the combustion chamber hot gasses enter into the nozzle guide ways which direct them increases the velocity on to the turbine  blades. Causing  the turbine disc to rotate. Which turn drives the compressor of the total energy approximately 60% is used to drive the compressor so that it is considerable  drop in gas.

Remaining 40% of energy after deriving the turbine and the compressor used to form high speed

 Jet which has substancely residual pressure  this jet passes exhaust   cone  to merge at the cluster  atmospheric pressure at the orifice.

Jet not only produce the kinetic energy going to its velocity  but also has heat energy

Heat energy released to atmosphere and consequently wasted

This heat energy which is wasted to the atmosphere is more than 800° C this heat can be used in some other way to some useful  energy  for the aircraft   

                                Three main condition in the engine working condition
i During Compression work is done to increase the pressure & decrease
  the volume of air which will corresponding increase in the temperature.

ii During the Combustion when fuel is added to the air and burned to increase
  the temperature there is corresponding increases in volume while the
   pressure remains almost constant.

iii During the expansion when work is taken from the gas stream by the turbine
  assembly there is decrease  in temperature and pressure with corresponding
   increase in volume.




OVERALL EFFICIENCY= (Propulsive Power (or) Thrust Power)/(Power Input To the Engine)
Propulsive Power = Mass of Air Fuel mixture[speed of existing gas from the engine - flight speed]                
                                 flight speed  

Power Input To The engine = Mass flow of Fuel  x  Calorific Value of Fuel  

                                                                 (OR)
OVERALL EFFICIENCY =  Propulsive Efficiency   x   Thermal Efficiency

     COMPARISON OF GAS TURBINE AND IC ENGINE 

Arrangement of internal parts , pressure and temperature at various point of JT8D Engine(Pratt & Whitney) 

Exploded view of the GE80C2 high bypass turbofan engine

 Gas Turbine Engines - Fan Blades

Blade Materials

Fan blades for high by pass aero-engines were, for many  years, manufactured from solid titanium alloy forgings  and were designed with mid span snubbers to control vibration. However, snubbers impeded airflow and reduced aerodynamic efficiency, penalising fuel consumption. Modern designs have deleted the snubber to provide a more aerodynamically efficient aerofoil, and increased the blade chord for mechanical stability, reducing the number of blades by approximately one third. This has been achieved at reduced weight with a hollow construction and an internal core. For both snubbered and wide chord blades, a conventional fine grain titanium alloy - 6% aluminium and 4% vanadium (Ti6Al4V) is used. It is simple in terms of chemistry, with the aluminium offering strengthening and low density, and the vanadium making hot working of the material easier. It is used for discs and compressor blades up to about 350°C, but excellent superplastic forming and solid state diffusion bonding capabilities make it particularly suitable for the wide chord blade. The low density core for the hollow design is an integral part of the structure. The two external skins are separated by either honeycomb filler or a superplastically formed corrugation which carries a share of the centrifugal load. Both panel-to-panel and core-to-panel joints must achieve parent material properties to withstand the effects of foreign body impact and fatigue. For the first generation design the joints are made by a transient liquid phase diffusion bonding process, whereas the second generation employs solid state diffusion bonding in association with superplastic forming of the assembly. The cavity of the bonded construction is inflated at elevated temperatures between contoured metal dies using an inert gas to expand the core and simultaneously develop the blade's external aerodynamic profile. The reliability of these wide chord blades has been second to none. The step in technology produced a major competitive advantage and ten years passed before an equivalent design appeared from a manufacturer other than Rolls Royce. This service record was the result of thorough development testing. Fatigue testing in both low and high cycle modes was essential. Groups of blades were repeatedly accelerated to maximum speed in vacuum to establish low cycle endurance, and high cycle fatigue was investigated on a static vibration rig up to the maximum stress levels likely to be encountered in service. With a large forward facing area, resistance to bird ingestion is required. Ingestion of a number of medium size birds has to be demonstrated by running an engine at take-off power and requiring it to ingest four birds within the space of one second. The engine continued to deliver power, accelerating and decelerating for a total period of thirty minutes to simulate the likely operating procedure following a severe ingestion incident. In the very unlikely event of a blade mechanical failure, the engine has to be shown to be structurally sound and to contain all the debris, even if the failure occurs at maximum power. Containment in modern engines is achieved with aluminium or titanium casings through which the blade fragments can penetrate, to be caught in external windings of Kevlar. As an indication of the benefits of materials development and design enhancements, engines incorporating the wide chord blade have fan modules that are approximately 24% lighter and an engine which is 7% lighter (typically the Trent 800 engine as used in the Boeing 777).  Gas Turbine Engines - Combustor

Big Giants in the Evolution of Gas Turbine

   

                                         

     HONDA Makes light engine for small aircraft  

HF120  ENGINE FOR LIGHT JET ENGINE-GE & HONDA COLLABORATION MAKE 

NEW INVENTION WITH TURBINE 

 

                                                                           

                                                                   

INVENTOR

Sir Frank Whittle (1907–1996) was an English aeronautical engineer who invented the turbojet engine in 1930 (the first application of the gas turbine to jet propulsion).

Sir Frank Whittle patented the design for a gas turbine for jet propulsion in 1930