POWER PLANT
18-4
For Training Purposes Only
May 03
P I L O T T R A I N I N G G U I D E
Engine Fuel System
Description
Fuel is delivered to the fuel injectors at pressures and flow rates required to maintain
the desired engine thrust. The engine fuel system, in addition to providing fuel for
combustion, is used for:
•
controlling and actuating the VG compressor linkage
•
cooling the engine oil (heat exchange)
•
actuating and lubricating servos within the Fuel Control Unit (FCU)
•
providing motive flow for the main ejector and scavenge ejector pumps
Combustion fuel can be interrupted by moving the thrust lever to SHUTOFF or by
selecting the engine FIRE PUSH switch/light. The SHUTOFF position shuts off the
fuel at the FCU. The FIRE PUSH switch/light closes the fuel shutoff valve.
Components and Operation
Engine-Driven Fuel Pump
The accessory gearbox-mounted fuel pump is comprised of three separate pumps
contained within a single housing. The engine-driven fuel pump provides high-
pressure fuel at a flow rate that exceeds the requirements of the engine at any power
setting. Fuel pump pressure is used to generate motive flow for the scavenge and main
ejectors of the aircraft fuel system.
Fuel/Oil Heat Exchanger and Fuel Filter
A fuel/oil heat exchanger is used to warm engine fuel and cool engine oil. The fuel
temperature at the fuel filter is indicated on the EICAS status page. A fuel filter is used
to remove solid contaminants from the fuel. If the filter becomes clogged, the fuel
bypasses the filter to ensure continued operation. A clogged filter is indicated by the
L(R) FUEL FILTER caution EICAS message.
Fuel Control Unit (FCU)
The fuel control unit is a hydromechanical metering device that supplies fuel in
response to mechanical inputs from the thrust levers. In addition, the FCU controls and
actuates the VG inlet guide vanes and stator vanes of the engine compressor.
During start and at low power, the FCU hydromechanically schedules the fuel.
