Engine Systems and Fuel Management

Fuel System Overview

• Engine fuel system is essential for aircraft operation
• System components are mostly installed on the left side of the fan compartment
• It consists of a primary fuel system connected to the airframe and a secondary fuel system connected to the engine

Main Functions of the Engine Fuel System

• Function One: Provide fuel flow to combustion chamber and sustain combustion for engine thrust.
  • This involves fuel flow from the main tanks via the LP pump, heating, filtering, and pressurization by HP pump.
  • Metered fuel passes through the FMV to the nozzle and combustion chamber.
• Function Two: Servo fuel (pressurized fuel) actuates compressor airflow control, turbine clearance control, and the FMV.
  • Servo fuel passes through a wash screen filter and servo fuel heater to remove ice particles.
  • Servo fuel drives the actuators (TBV, VSV, VBV, LPTACC, HPTACC) controlled by the ECU.
• Function Three: Heat Management
  • Engine oil is cooled using the oil/fuel heat exchanger.
  • Integrated drive generator (IDG) oil is cooled using the IDG cooler
  • Bypass valve in the Hydro Mechanical Unit (HMU) redirects servo fuel to cool IDG oil.
  • Fuel return valve (FRV) is controlled by the ECU and uses servo fuel to mix hot return fuel with cold fuel to reduce thermal stress.

Engine Protection

• Overspeed Protection:
  • Mechanically controlled by governor, flywheel, and bypass valve.
  • Independent of FADEC.
  • Bypasses fuel to reduce fuel flow in case of increased speed.
  • FADEC receives a signal if N2 exceeds 45%.
• Emergency Shutdown:
  • Fire push button closes the LP shutoff valve to shut down the engine.
• High Pressure Shut Off Valve:
  • Supplied by pilots and controlled by pressure, it shuts off fuel to the combustion chamber.
• Normal Shutdown:
  • The engine master switch turns off the LP and HP fuel shutoff valves and FRV.
  • ECU drives the FRV to close.

FADEC System

• Full Authority Digital Engine Control (FADEC): Regulates and schedules engine systems for thrust control and engine optimization.
  • Interfaces with aircraft signals.
• FADEC System:
  • Consists of two channels of electronic control units (ECUs) per engine.
  • ECU is the FADEC computer, located on the engine fan case.
• Power Supply:
  • ECUs are powered by a three-phase permanent magnet alternator when N2 > 15%.
  • The FADEC control alternator provides independent power to both ECU channels.

FADEC System Functions

- Power management control
- Variable Bleed Valves (VBVs) control

• Other Components
  • Hydro Mechanical Unit (HMU)
  • Fuel Control Unit (FCU)
  • Fuel metering valve (FMV)
  • LP pump
  • HP pump
  • Oil/fuel heat exchanger