combustion chamber 3/5

Ignition Ignition & & Fuel SupplyFuel Supply

*** Some gas turbines are “bi-fuel”. They may burn a mixture of gas and liquid fuel.

Ignition occurs during the start cycle

FUEL is injected at the upstream end of the

burner.

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The igniter plug(s) is (are) located

in the combustion liner adjacent

to the start fuel nozzle.

TWO is a typical number

The flame lights off the can closest the igniter

and cross tubes rapidly conduct the flame

to the other combustion cans.

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On engine shutdown, or, if start failure occurs,

the combustion chamber drain pressure-actuated valve

automatically DRAINS any raw fuel from the

combustion chamber

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Fuel NozzlesFuel must be atomised or

vaporised

Function: inject the fuel into the combustion chamber

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Common Types

•Vaporiser •Atomiser

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VAPORISER TYPE

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ATOMISING TYPE

Swirl Atomiser

• consists of a small cylindrical or conical cavity into which a number of streams of fuel enter through tangential holes.

• The direction of fuel entry into the cavity creates a vortex and the swirling fuel leaves in atomised form from a single orifice.

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SIMPLEX

provides good atomisation at HIGH fuel pressures

• unsatisfactory at LOW fuel pressures and at LOW engine

rpm, especially at high altitudes.

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DUPLE & DUPLEX

• two sets of atomisers, one for low flows and both combined for high flows

• two manifolds, the primary and the main,

supply fuel to the nozzles• each nozzle has two swirl chambers, one for the primary flow and the other

for the main flow

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Spill Type

• supply fuel to the swirl chamber at a high pressure all the time

• ADVANTAGE: satisfactory swirl providing constant and efficient fuel atomisation (even at the extremely low fuel flows that occur at high altitude)

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Rotary Atomizer

• feeds fuel into the centre of the main shaft

• fuel is atomised by the CENTRIFUGAL action of the shaft.

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Spray Nozzle

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• Primary air is introduced with the injected fuel. Aerating the spray in

this manner achieves greater burning efficiency, therefore

reducing both carbon formation and exhaust smoke. The comparatively

low pressures required for atomisation also makes it possible to

use the lighter gear-type pump.

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