Power Plant Engineering

Fig. 9.8. Combustion Chamber with Upstream Injection with Bluff-body Flame Holder.
Fuel
Primary
Zone
Air from
Compressor
Swirl Type
Flame Holder
Secondary Zone
Tertiary
Zone
To
Turbine
Fig. 9.9. Combustion Chamber with Downstream Injection and Swirl Holder.
The common methods of flame stabilization used in practice are bluff body method and swirl
flow method. Two types of combustion chambers using bluff body and swirl for flame stabilization are
shown in Fig. 9.8 and Fig. 9.9. The major difference between two is the use of different methods to
create pilot zone for flame stabilization.
Nearly 15 to 20% of the total air is passed around the jet of fuel providing rich mixture in the
primary zone. This mixture burns continuously in the primary (pilot) zone and produces high tempera-
ture gases. About 30% of the total air is supplied in the secondary zone through the annuals around the
flame tube to complete the combustion. The secondary air must be admitted at right points in the com-
bustion chamber otherwise the cold injected air may chill the flame locally thereby reducing the rate of

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POWER PLANT ENGINEERING
reaction. The secondary air helps to complete the combustion as well as helps to cool the flame tube.
The remaining 50% air is mixed with burnt gases in the “tertiary zone” to cool the gases down to the
temperature suited to the turbine blade materials.
By inserting a bluff body in mainstream, a low-pressure zone is created downstream side that
causes the reversal of flow along the axis of the combustion chamber to stabilize the flame.
In case of swirl stabilization, the primary air is passed through the swirler, which produces a
vortex motion creating a low-pressure zone along the axis of the chamber to cause the reversal of flow.
Sufficient turbulence must be created in all three zones of combustion and uniform mixing of hot and
cold bases to give uniform temperature gas stream at the outlet of the combustion chamber.