ATA 73 - ENGINE FUEL AND CONTROL

• When the engine oil temperature exceeds 90°C (200°F) the ECU sends a signal to open the Fuel Return Valve (FRV).

• ADIRUs are directly linked to ECU (hard linked, no EIU).

• IDG oil is cooled down by return servo fuel or metering bypass fuel.

• The LP and HP Fuel shut off valves closes when the ENG MASTER lever is set to OFF.

• The ECU sends electrical signals to the torque motor servo-valves of both the HMU and the fuel return valve.

• The fuel filter differential pressure switch is located on the fan case. The switch sends a signal to the SDACs when the differential pressure increases to a certain level when the fuel filter clogs. Fuel Filter clogs when differential pressure above 11.5 PSI.

• It receives electrical signals from the electronic control unit (ECU) and converts these electrical input signals through torque motors/servo valves into engine-fuel flow and hydraulic signals to various external systems.

• The fuel metering valve is hydraulically driven through a torque motor/servo valve by the ECU.

• The Valve (HP) closed/not closed position is indicated to the ECU by two electrical limit switches.

• The fuel shut off valve shuts off fuel flow to the engine commanded by the master switch (in OFF solenoid is energized) (solenoid energized by aircraft 28 VDC from bus bar 3PP).

• It has to be noted that the HP fuel shut off valve shut off signal by the Master switch also closes the LP fuel valve.

• HP valve in HMU is controlled directly from the MASTER control switch in OFF position (hard wired)

• The IDG oil shall be cooled by engine fuel through an oil/fuel heat exchanger which is installed in the fuel bypass line.

• The purpose of the Burner Staging Valve (BSV) is to shutoff 10 of the 20 fuel nozzles as commanded by the ECU.

• The BSV (Burner Staging Valve) is a poppet type shutoff valve that is opened or closed by fuel pressure (PC or PCR) from the HMU based on ECU logic.

• The fuel nozzles contain both primary and secondary fuel flow passages.

• The fuel flow transmitter is installed in the fuel line between the HMU and the burner staging valve.

• The overspeed governor is hydro-mechanical (flyweights) and independent of the ECU.

• The FRV (Fuel Return Valve) is electrically controlled by the ECU, and hydraulically operated by the servo fuel.

• Combustion chambers types:

- DAC = Dual Annular (Combustion) Chamber

- SAC = Short Annular (Combustion) Chamber

• Engine’s HP Fuel Pump is directly connected to AGB (Accessory Gear Box), HP Fuel Pump is also connected to HMU (Hydro-mechanical Unit).

• HP Fuel Pumps are rated to provide more fuel that the amount of engines actually need at any flight phase, there’s always some fuel returning back to tanks.

• HP FUEL SOV closes when energized.