The diffuser receives high velocity air from the tip of the
centrifugal impeller. The function of the diffuser is the decrease
velocity and increase air pressure in this area. Air pressure at the
diffuser discharge is at its highest value, with air temperature in
the vicinity of 500 F. The diffuser also provides a means for
bleeding a portion of the high temperature air for required engine
and airframe use, such as engine antiicing and cockpit heat. Later
versions have an external air manifold, known as a piggyback
diffuser, where air is extracted for use as required.
Externally, the diffuser provides engine mounting points at
the four, eight, and twelve o'clock positions. Hoisting provisions
are incorporated in the top or twelve o'clock mount. A port for
extracting pressurized air for use as the pneumatic force for
operation of an interstage bleed system actuator is provided at the
three o'clock position. Mounting points for required engine
accessories are provided on the external housing.
4.14.
COMBUSTOR TURBINE ASSEMBLY
Located aft of the diffuser housing, the combustor turbine
assembly consists of the combustion chamber housing and liner, gas
producer turbines, power turbines, and exhaust diffuser. The
combustor assembly is an external annular reverseflow type.
Although this design increases the diameter of the engine to a
degree, it significantly reduces its overall length. It is
classified an external annular reverseflow type, in that the
circular combustion chamber is located outside of and encloses the
turbine area.
As shown back in figure 4.2, compressed air flowing aft from
the diffuser enters the combustor (25 percent primary air) and mixes
with fuel and supports combustion, within the combustion liner. The
hot expanding gas flows forward within the liner; it is diluted and
cooled by the remaining compressed air (75 percent secondary air).
Flow direction is changed again to the rear by the stationary
deflector mounted within the diffuser inner housing. The gases then
flow through the gas producer nozzles which greatly accelerate the
gas stream and direct it onto the gas producer turbine (N1). The N1
turbine extracts approximately 60 percent of the energy to rotate the
compressor assembly. The gases still possessing energy are again
accelerated as they pass through the power turbine N2 nozzles. The
gas stream is then directed onto the power turbines where most of the
remaining gas energy is extracted to rotate the N2 power shaft.
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