*
Cleans the fuel (filter)
*
Controls the fuel pressure (pressure regulator)
*
Controls fuel flow (fuel metering valve and fuel shutoff solenoid valve)
*
Divides the fuel flow (fuel flow divider)
*
Monitors the fuel temperature (fuel temperature sensor).
APUC Control
The APUC has the logic to control the fuel solenoid valve and the fuel metering valve.
EFFECTIVITY
BEJ ALL
During APU start, the APUC energizes the fuel shutoff solenoid valve when the APU engine RPM is more than 7 percent. The APUC also controls the fuel metering valve when the RPM is more than 7 percent.
The APUC uses start-up control logic to control the fuel metering valve when the RPM is less than 95 percent. This logic schedules fuel flow to start the APU quickly and to keep the EGT low. Start-up fuel flow logic uses these inputs:
*
APU RPM (N)
*
Inlet pressure (P2)
*
Inlet temperature (T2)
*
Turbine inlet temperature (T4)
*
Exhaust gas temperature (EGT)
*
ATS command
*
Fuel temperature.
The APUC uses on-speed control logic to control the fuel metering valve when the RPM is more than 95 percent. This logic schedules fuel flow to keep APU speed at 100 percent RPM or at the correct speed for no-break power transfers. During no-break power transfers between the APU generator and external power, the APUC adjusts the APU speed between 96.25 percent and 104.5 percent.
The on-speed control logic uses these inputs:
*
APU RPM
*
Fuel temperature
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APU FUEL SYSTEM -FUNCTIONAL DESCRIPTION
* Frequency trim.
Fuel Manifolds
The fuel cluster supplies metered fuel to the primary and secondary fuel manifolds for combustion.
Only the primary manifold gets fuel at low engine speeds during engine start. Both manifolds get fuel when the engine speed is more than 50 percent RPM.
Servo Fuel
The fuel cluster also supplies pressurized fuel to operate the inlet guide vane and surge control valve actuators.
Return fuel from these actuators goes back to the pump in the fuel cluster.
APUC Monitoring
The APUC monitors these APU fuel system components:
*
Fuel temperature sensor
*
Fuel filter differential pressure switch
*
Fuel metering valve
*
Fuel shutoff valve.
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APU FUEL SYSTEM -FUNCTIONAL DESCRIPTION
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BOEING PROPRIETARY -Copyright # -Unpublished Work -See title page for details.
APU IGNITION/STARTING -INTRODUCTION
General
The APU ignition/starting system has these systems:
*
Ignition system
*
Air turbine starter system
*
Electric starter system.
Ignition System
The ignition system starts the APU combustion during APU start. These components are part of the ignition cluster on the right side of the APU:
*
Ignition unit
*
Ignition lead (2)
*
Igniter plug (2).
The APUC controls the ignition system.
Start Systems
There are two starter motors: one pneumatic and one electric. They are on the front of the APU.
The air turbine starter system starts the APU when pneumatic pressure is available. The air turbine starter system uses an air turbine starter control valve (ATSCV) to control pneumatic flow to the air turbine starter.
The electric starter system starts the APU only when the pneumatic system is not pressurized or if there is a failure in the air turbine starter system.
The APUC controls both start systems and automatically selects between the starters.
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APU IGNITION/STARTING -INTRODUCTION
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APU IGNITION/STARTING -APU IGNITION SYSTEM -GENERAL DESCRIPTION
General
The ignition system starts the combustion of the fuel-air mixture during engine start. The APU controller controls the ignition system.
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