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SECTION 7
CESSNA
AIRPLANE AND SYSTEMS DESCRIPTION
MODEL 208B 867 SHP
GARMIN G1000
ENGINE FUEL SYSTEM
(Continued)
The fuel control unit consists of a fuel metering section, a temperature
compensating section, and a gas generator (N
) pneumatic governor.
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The fuel control unit determines the proper fuel schedule to provide the
power required as established by the power lever input. This is
accomplished by controlling the speed of the compressor turbine. The
temperature compensating section alters the acceleration fuel schedule
to compensate for fuel density differences at different fuel
temperatures, especially during engine start. The power turbine
governor, located in the propeller governor housing, provides power
turbine overspeed protection in the event of propeller governor failure.
This is accomplished by limiting fuel to the gas generator. During
reverse thrust operation, maximum power turbine speed is controlled
by the power turbine governor. The temperature compensator alters the
acceleration fuel schedule of the fuel control unit to compensate for
variations in compressor inlet air temperature. Engine characteristics
vary with changes in inlet air temperature, and the acceleration fuel
schedule must, in turn, be altered to prevent compressor stall and/or
excessive turbine temperatures.
The flow divider schedules the metered fuel, from the fuel control unit,
between the primary and secondary fuel manifolds. The fuel manifold
and nozzle assemblies supply fuel to the combustion chamber through
10 primary and 4 secondary fuel nozzles, with the secondary nozzles
cutting in above a preset value. All nozzles are operative at idle and
above.
When the fuel cutoff valve in the fuel control unit closes during engine
shutdown, both primary and secondary manifolds are connected to a
dump valve port and residual fuel in the manifolds is allowed to drain
into the fuel can attached to the firewall where it can be drained daily.
COOLING SYSTEM
No external cooling provisions are provided for the PT6A-140 engine in
this installation. However, the engine incorporates an extensive internal
air system which provides for bearing compartment sealing and for
compressor and power turbine disk cooling. For additional information
on internal engine air systems, refer to the engine maintenance manual
for the airplane.
7-66
208BPHCUS-00
U.S.
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