Gas Turbine Combustion System

Question 1

In the combuster the following gas states can be found

Answer 1

~high static pressure -fed from the compressor
~a exponential rise temperature wihtin the primary zone
~velocity increases towards mach 1 in the combuster outlet
~dilution air (or also called secondary air) cools the exhaust gases ready for the turbine stage

Question 2

Combustor

Answer 2

Air enters via the diffuser and separates in to 80/20
80% secondary air ,dilution airflow
20%primary ,burner air,hottest part of the engine 2100 C

The dilution airflow reduces the primary airflow temperature ensuring it’s safe fort he turbine
~velocity remains at around 110m/s
~outlet temperature varies ,but is usually 1000-1700 C

The primary airflow feeds the combustion flmae via swirler vane and a recirculating vortex
~this reduces the primary air forward velocity to the correct 3 m/s
~kerosene burns with a flame rate of 3m/s

This also creates a torodial flame
The stability element holds the flame away from combustion chamber preventing it contacting the material

Question 3

Air/fuel ratio

Answer 3

Air engines are based on 15:1

Due to the interaction of the primary and secondary airflow,in the primary zone is rapidly diluted and it can operate between 45:1 and 130:1

This allows an efficent fuel burm at also reducing emission specially oxides of nitrogen

Question 4

Fuel nozles

Answer 4

~vaporizers - prone to black smoke
~simplex nozzles - only useful at high rpm
~duplex nozzles -adaptation of the sipmplex to create a combined fuel flow -primary and main

With advent of FADEC most engines utilities the air spray injector
Incorporates a swirler and vortex genrator to create a toroidal flame in the primary zone

Advantage of air spray injector is effiecnt air.fuel mixing
~lower carbon emission
~lower pollution

Question 5

Ignition

Answer 5

For redundancy system is dupicated
~2 x ignition units
~2 x high tension leads
~2 x igniter plugs,arrange diametrically opposite

During heavy rain ,snow ,hail or wet runway ,operation sys can enter in continuous :
~both igniter at a reduce power settings

HEIU(high energy ignition units)

Question 6

Gas turbine engines

Answer 6

Gas turbine engines are constant pressure engines

Internal combustion engines are constant volume engines