Lecture on Aircraft Engine Fuel Systems

Introduction

• Topic: Fuel systems in internal combustion, gas turbine, and rocket engines.
• Importance: Ensures engines run safely and efficiently.
• Focus: Fuel systems required for engines using fossil fuels.

Key Characteristics of Fuel Systems

• Primary Task: Deliver appropriate amount of fuel to the combustion chamber safely.
• Danger: Fuel is highly ignitable.
• General Purposes:
  • Increase fuel pressure
  • Heat fuel
  • Adjust fuel flow
  • Filter impurities
  • Deliver fuel to nozzles

Comparison to Automobile Fuel Systems

• Similarity: Fuel adjustment akin to pressing the accelerator pedal in cars.
• Difference: Aircraft systems are more complex due to atmospheric conditions.

CFM 56-7 Engine Fuel System

• Fuel Pump: First unit fuel enters; attached to gearbox; increases fuel pressure.
  • Contains low and high-pressure elements and filters.
  • Task: Supply pressurized fuel to HMU and nozzles.
• HMU (Hydromechanical Unit): Adjusts fuel flow to combustion chamber.
  • High-pressure shut-off valve: Stops fuel flow when throttle is off.
• Fuel Flow Transmitter: Measures fuel amount passing through.
• Fuel Nozzle Filter: Further cleans fuel.
• Fuel Nozzles: Atomize fuel for efficient combustion.

Fuel System Operation

• Fuel Journey:
  • From aircraft fuel system (main and wing tanks) to engine fuel pump.
  • Centrifugal Flow Low Pressure Pump: Pressurizes fuel.
  • IDG Oil Cooler & Main Oil Fuel Heat Exchanger: Heat exchange between oil and fuel to achieve ideal combustion temperature.
  • Filters: Purify fuel from foreign substances.
  • High-Pressure Pump: Further increases fuel pressure.
  • Servo Washer Filter: Cleans fuel for HMU servo section.
  • Servo Fuel Heater: Heats fuel for servo system.
  • Fuel Metering Valve & Flow Transmitter: Adjust fuel rate and measure flow.
  • Fuel Nozzle Filter & Nozzles: Final filtration and atomization for combustion.

Additional Notes

• Bypass Fuel: Excess fuel from HMU returns to IDG oil cooler and then back to fuel pump.
• Fuel Flow Transmitter: Sends fuel consumption data to EEC and informs pilot.
• Hydromechanical Unit Functions: Controls fuel metering, transient bleed valve, active clearance control valves, variable bleed valves, and stator vanes.

Conclusion

• Understanding Fuel Systems: Important for pilots and technicians to comprehend engine operation and troubleshoot issues.
• Similarity Across Systems: Despite differences, fundamental tasks remain consistent.
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