nozzle cluster. These nozzles are the dual-orifice
mechanical energy to drive the compressor and
necessary accessories. This is the sole purpose of
(duplex) type that require the use of a flow-divider
(pressurizing valve), as mentioned above in the
the turbine. This function absorbs about 60 to 80
percent of the total pressure energy from the
can-type combustion chamber. Preswirl vanes are
located around each of the nozzles for imparting
exhaust gases. The exact amount of energy
a swirling motion to the fuel spray. This results
absorption at the turbine is determined by the load
in better atomization of the fuel, thus better
the turbine is driving. The compressor size, type,
burning and efficiency.
if the engine is a turbo-propeller type also effect
The swirl vanes perform two important
functions imperative to proper flame propagation:
absorption.
The turbine section of a turbojet engine is
1. High flame speed: Better mixing of air and
located aft, or downstream, of the combustion
fuel, ensuring spontaneous burning.
chamber section. Specifically, it is directly behind
2. Swirling prevents the flame from moving
the combustion chamber outlet.
rapidly rearward.
The turbine assembly consists of two basic
The swirl vanes greatly aid flame propagation,
elements, the stator and the rotor, as does the
since a high degree of turbulence in the early
compressor unit. These two elements are shown
combustion and cooling stages is desirable. The
in figures 1-30 and 1-31.
vigorous mechanical mixing of the fuel vapor with
The stator element is known by a variety of
the primary air is necessary, since mixing by
names. Turbine nozzle vanes, turbine guide vanes,
diffusion alone is too slow. This same mechanical
mixing is also established by other means, such
as placing coarse screens in the diffuser outlet,
as is the case in most axial-flow engines.
The can-annular combustion chambers also
must have the required fuel drain valves, located
in two or more of the bottom chambers, thereby
assuring proper drainage and eliminating the
possibility of residual fuel burning during the next
start cycle.
The flow of air through the holes and louvers
of the can-annular chambers is the same as the
flow through other types of burners. Figure 1-29
shows the flow of combustion air, metal-cooling
air, and the diluent or gas-cooling air. Pay
particular attention to the direction of airflow,
indicated by the arrows.
TURBINE SECTION
The turbine transforms a portion of the kinetic
Figure 1-30.-Stator element of the turbine assembly.
(velocity) energy of the exhaust gases into
Figure 1-31.-Rotor element of the turbine assembly.
Figure 1-29.-Airflow through a can-annular chamber.
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