Turbine Engine Fuel System Fundamentals

021-08-02Pablo Asensio Martínez2026-03-242 min

Turbine aircraft fuel systems are designed to handle high flow rates, widely varying temperatures, and critical weight management. They use specific types of kerosene-based fuels.

Jet Fuel Characteristics

  • Jet A:
    • Freezing point: -40°C
    • Flash point: +38°C
    • Common in the USA.
  • Jet A-1:
    • Freezing point: -47°C
    • Flash point: +38°C
    • Density: Approx 0.8 kg/l (Specific Gravity ~0.8).
    • The standard fuel for international commercial aviation.
  • Jet B:
    • "Wide-cut" fuel (mixture of gasoline and kerosene).
    • Freezing point: -60°C (Ideal for extremely cold climates).
    • Flash point: -20°C (Highly flammable/volatile).
    • Comparison: Jet A has a higher freezing point and a higher flash point than Jet B.
  • Additives:
    • FSII (Fuel System Icing Inhibitors): Prevent water freezing/ice crystals. Mandatory in military jets; civil jets usually use fuel heaters instead.

System Components

  • Pumps:
    • LP Booster Pumps (AC): Centrifugal pumps located in the tanks. They pressurize the fuel lines to preventing vapor lock and cavitation at the engine-driven HP pump inlet.
    • HP Pump: Engine-driven. If booster pumps fail, the HP pump can often "suck" fuel (gravity feed), but operations are restricted.
    • DC Pump: Primarily used to supply fuel to the APU for starting.
  • Crossfeed Valve:
    • Purpose: Allows any fuel tank to feed any engine. It maintains aircraft stability and balance.
    • Operation for Balancing: To correct an imbalance (e.g., Low fuel in Left tank), the pilot opens the crossfeed valve and turns OFF the pumps in the low (Left) tank. The engines will then feed from the high (Right) tank pumps.
  • Vents:
    • Allow air to replace consumed fuel to prevent a vacuum.
    • Often use ram air to provide a small positive pressure head to the pumps.
  • Baffles:
    • Internal barriers to prevent fuel "sloshing" during maneuvers, which could cause rapid CG shifts or unporting of pumps.

Advanced Features

  • Trim Tanks:
    • Located in the tail (horizontal stabilizer).
    • Fuel is transferred aft to move the CG rearward during cruise.
    • Benefit: Reduces the aerodynamic downforce required from the tail, thereby reducing trim drag and fuel consumption.
  • Fuel Jettison (Dumping):
    • Allows the crew to reduce aircraft weight to the Maximum Landing Mass quickly in an emergency (e.g., engine failure shortly after takeoff).