Chapter 10: Jet Engine Fuel Systems

• Chapter 10 focuses on fuel systems, referencing "The Jet Engine" (Rolls Royce, 1996).

Fuel Facts

• Aviation turbine fuels power jet and turbo-prop engine aircraft.
• The are two main grades of turbine fuel in civil commercial aviation: Jet A-1 and Jet A, kerosene-type fuels.
• Jet B is a wide-cut kerosene (gasoline and kerosene blend) primarily for very cold climates.

Civil / Military Jet Fuels

• Jet A-1 is a kerosene-grade fuel for most turbine engine aircraft meeting stringent international standards.
• It has a flash point above 38°C (100°F) and a maximum freeze point of -47°C, widely available outside the U.S.A.
• Jet A is similar but only available in the U.S.A., meeting ASTM specifications.
• It shares the same flash point as Jet A-1 but has a higher freeze point maximum of -40°C.
• Jet B is a distillate of naphtha and kerosene fractions and used as an alternative to Jet A-1.
• Because it's more difficult to handle, it's utilized in very cold climates due to its better weather performance.
• In Canada, meeting CAN/CGSB 3.23 specifications for supply.
• JP-4, military equivalent of Jet B, has corrosion inhibitors and anti-icing additives.
• JP-5, high flash point kerosene, used by military systems.
• JP-8 , the military equivalent of Jet A-1 with corrosion inhibitor and anti-icing additives

Precautions and Mixed Refueling

• Mixing Jet A-1 and Jet B is very explosive.
• Mixed refueling increases safety distances.
• Three subsequent refuelings need this extra precaution.
• The operator must strictly follow the refueling instructions manual.

Qualities of Aviation Fuel

• The fuel must flow easily under operating conditions.
• It needs to permit engine starting at all ground conditions and give good flight relighting.
• It must give efficient combustion at all conditions wile maintaining a high calorific value.
• The fuel cannot produce harmful effects or corrosion, and provide adequate lubrication.
• It should reduce fire hazards.

Fuel System Overview

• The fuel system provides the engine with fuel for combustion.
• Adjust fuel flow for easy starting, acceleration, and constant engine operation.
• Torque motoring allows airflow regulation of engine operation.

Fuel System Components

• The fuel system consists of:
• Fuel LP & HP Valve / LP & HP Cock
• Fuel Pump
• Fuel Filter (LP & HP)
• Fuel Oil Heat Exchanger (FOHE/FCOC/Fuel Heater)
• Fuel Control Unit / Hydromechanical Unit
• Fuel Flow Transmitter
• Flow Divider
• Fuel Nozzles
• Pressurizing and Dump Valve

Fuel LP & HP Valve (LP & HP Cock)

• LP Valve isolates the aircraft and engine fuel systems.
• It's normally controlled by the Engine Fire Switch or Engine Master Switch.
• HP Valve stops the engine by cutting fuel to the Combustion Chamber.
• The HP Valve cuts off fuel from the HMU to Fuel Nozzles.

Fuel Pump

• The two-stage fuel pump has a centrifugal boost stage and a positive displacement main stage.
• It provides servo fuel (Pf) to engine components.

Fuel Filter

• LP filters are located upstream, subjected to low pressure.
• HP filters are located downstream from the FCU, subjected to high pressure.
• A differential pressure switch/indicator monitors filter clogging.
• A bypass valve allows fuel to bypass if the filter gets clogged.

Fuel Oil Heat Exchanger (FOHE/FCOC/Fuel Heater)

• Helps to cool the oil when fuel flow is high.
• The fuel gets heated by the oil at this heat exchanger..
• An oil tank that smells of fuel may indicate a FOHE leak.

Fuel Control Unit

• The unit "computes" the correct amount of fuel and distributes it.
• Other actions include:
• Fuel shutoff and overspeed protection
• Supplying servo fuel to actuators

Inputs to the Fuel Control Unit

• Thrust lever position
• Inlet total pressure and temperature
• Shaft RPM (N1, N2, N3)
• Burner pressure or Compressor Discharge Pressure
• Exhaust Gas Temperature

Fuel Flow Transmitter

• It sends an electrical signal to display fuel flow in the cockpit which is useful during startup to verify HP shutoff valve conditions.
• It’s a parameter used to prevent high EGT conditions.

Fuel Nozzles

• Inject/aid fuel to the combustion chamber.
• Simplex and Duplex are the two nozzle types
• Proper burning process needs the following:
• Evenly distributed fuel while being well-centered in the combustion chamber to protect the liner.

Duplex Nozzle

• During low engine rpm usage, only the primary manifold is pressurized.
• At high engine rpm, both primary/secondary manifolds are pressurized enabling better atomization.
• The wider uses simplex, since the duplex nozzle usage is better throughout.

Dump Valve

• Dump Valve removes fuel from the fuel manifold downstream/nozzles after engine shutdown which closes and opens the fuel shutoff valve.
• When open, the dump valve will drain the fuel to a drain collector tank to resupply by a get pump inlet to the fuel pump inlet at the next start.

Electronic Engine Control System(EEC)

• The EEC interfaces with the control system, while controlling electrical, hydraulic and pneumatic subsystems.
• It provides the following benefits:
• Improves efficiency by controlling components and functions.
• Enhances basic Engine Control
• Protects the engine by limiting critical factors.
• Improves reliability by fault detection, compensation.
• It Provides easier engine maintenance.
• Improves communication with the flight deck.

EEC Inputs

• Thrust lever position, Ambient pressure
• Inlet/Exhaust total pressure
• Shaft RPM (N1,N2,N3) and Burner pressure
• Start lever/switch position
• Ignition switch selection & VSV position
• EGT and Inlet Temperature

FADEC

• FADEC is a computer-based control system that controls engine operations and acts as the main interface between the engine and aircraft systems.
• FADEC (Full Authority Digital Electronic Control), enhances control, efficiency/reliability and protects both aircraft and engine systems.
• The ECC oversees this system and sends/receives/interprets info, whilst controlling and monitoring everything.
• FADEC aircraft systems include:
• TMC (Thrust Management Computer) and FMC (Flight Management Computer).
• ADC ( Air Data Computer) and (EICAS) Engine Indication Crew Alert system.
• EFIS (Electronic Flight Instrument System)

EEC Redundancy

• Vital parameters of the EEC have dual inputs or redundancy.
• The electrical supply has redundancy, which assists w/ key operations
• All Servo actuators have dual monitors and inputs.

EEC Programming Plug

• Engine thrust and EPR (Engine Pressure Ratio) are programmed during Engine Start.
• Data is cross-wired (A+B), cross-talked at Channels A and B.
• If the EEC programming plug is not installed, the EEC will not permit the engine to start.
• If the Engine control programming plug disconnects, the controls will continue to operate
• Stay consistent/matched in the event of being replaced.

Fuel Uplift

• Calculate average by doing fuel flow rate x (no. of engines) which gives the hourly fuel consumption.
• Calculate overall quantity by doing: trip fuel + reserve fuel + alternate fuel.

Thrust Specific Fuel Consumption (TSFC)

• TSFC=Fuel Flow rate/Thrust
• TSFC measures fuel consumption per unit thrust; the engine is efficient if TSFC is lower.
• Units measure kilograms per hour/newton or pound/hour/ pounds of force.

Explore aviation turbine fuels for jet and turbo-prop engines, focusing on Jet A-1 and Jet A kerosene-type fuels. Jet B, a blend for colder climates, is also examined. Learn about the specifications, flash points, and freeze points of these fuels.