Aircraft Engine Fuel System Overview

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Questions and Answers

What is the primary function of the engine fuel system in a gas turbine engine?

To control aircraft navigation

To enhance fuel efficiency

To sustain combustion in the combustion chamber (correct)

To manage engine temperature

Which component is responsible for pressurizing the fuel before it enters the hydromechanical unit?

HP pump (correct)

Fuel metering valve

Fuel filter

Hydro-Mechanical Unit (HMU)

What does the servo fuel in the engine fuel system act upon?

Actuating the compressor airflow control (correct)

Maintaining fuel temperature

Regulating engine speed

Filtering impurities from the fuel

Where are the primary components of the fuel system located?

On the left side of the fan compartment Signup and view all the answers

Which unit processes the metered fuel before it enters the combustion chamber?

Fuel metering valve (FMV) Signup and view all the answers

What role does the torque motor play in the engine fuel system?

It drives the hydraulic operation of servo valves Signup and view all the answers

Which component clears ice particles from the fuel before it enters the servo valves?

Servo fuel heater Signup and view all the answers

What does the fuel flow (FF) from the main tanks to the combustion chamber pass through first?

Low-pressure valve Signup and view all the answers

What is the role of the fuel return valve (FRV) in the heat management system?

Allows hot fuel to return to the aircraft tanks and mix with cold fuel. Signup and view all the answers

How does the overspeed protection system signal that it is active?

By sending a signal to the FADEC when N2 exceeds 45%. Signup and view all the answers

What happens when the engine oil and IDG oil become too hot?

The FRV allows some hot fuel to return to the aircraft tanks. Signup and view all the answers

What is the purpose of the Full Authority Digital Engine Control (FADEC)?

To interface with aircraft signals and control engine operations. Signup and view all the answers

What triggers the engine's emergency shutdown process?

Activation of the fire push button by the pilot. Signup and view all the answers

Which component is responsible for the power supply to each ECU of the FADEC system?

The three-phase permanent magnet alternator. Signup and view all the answers

During a normal shutdown of the engine, what happens to the fuel valves?

The LP and HP fuel shutoff valves along with the FRV are closed. Signup and view all the answers

What is the function of the variable bleed valves (VBVs) in the FADEC system?

To regulate airflow based on engine performance requirements. Signup and view all the answers

Study Notes

Introduction

The Engine Fuel System is a crucial component for aircraft operation, responsible for providing fuel to the engine under all flight conditions.
The system's main components are located on the left-hand side of the fan compartment.

Fuel System Subcategory

The fuel system is divided into two parts: the Primary Fuel System located within the airframe and the Secondary Fuel System located within the engine.

Main Functions of the Engine Fuel System

Function One: Supply fuel to the combustion chamber to generate thrust during all engine operation modes. The process involves fuel flowing from the main tanks through the LP valve (driven by the LP pump), being heated by the oil/fuel heat exchanger, filtered, pressurized by the HP pump, and finally passing through a fuel metering valve (FMV) before reaching the combustion chamber.
Function Two: Servo fuel acts as a power source to operate actuators that control airflow, turbine clearance, and fuel flow. After passing through the HP pump, the fuel goes through a wash screen filter and a servo fuel heater to remove ice particles. Servo valves in the HMU are hydraulically driven by torque motors to control these actuators:
- Transient Bleed Valve (TBV)
- Variable Stator Valve (VSV)
- Variable Bleed Valve (VBV)
- Low-Pressure Turbine Active Clearance Control (LPTACC)
- High-Pressure Turbine Active Clearance Control (HPTACC)
- Fuel Metering Valve (FMV)
Function Three: Heat management system, where engine oil is cooled through the oil/fuel heat exchanger, and the Integrated Drive Generator (IDG) oil is cooled through the IDG oil cooler. Servo fuel is also employed to heat the servo fuel heater.
- IDG Oil Cooling: Fuel bypass valve and servo fuel return are used to cool the IDG oil through the IDG cooler.
- Fuel Return Valve (FRV): The FRV is electrically controlled by the ECU and hydraulically operated by servo fuel. It mixes cold fuel from the LP pump with hot return fuel, reducing thermal stresses.

Engine Protection

Overspeed: The engine protects against overspeed through a mechanical governor system that utilizes a flywheel and a bypass valve, independent of the FADEC system. In case of overspeed, the flywheel activates the bypass valve, diverting part of the fuel for recirculation instead of feeding it to the combustion chamber. The FADEC system receives a signal when N2 exceeds 45% to indicate overspeed protection is active.
Emergency Shutdown: In emergencies, a fire push button initiates the closure of the LP shutoff valve, which shuts down the engine.
High-Pressure Shut-Off Valve: Controls fuel flow to the combustion chamber, activated by pilots and operated by fuel pressure.
Normal Shutdown: Setting the engine master switch to OFF closes the LP and HP fuel shutoff valves (LP/HP SOV) and the fuel return valve (FRV). The FRV is closed by the ECU.

FADEC System

General: The Full Authority Digital Engine Control (FADEC) system manages and schedules engine systems to control thrust and optimize engine operation. The system also interfaces with aircraft signals. It consists of two channels of Electronic Control Units (ECUs) located on the engine fan case.
Power Supply: Each ECU is powered by a three-phase permanent magnet alternator when engine N2 exceeds 15%. The FADEC control alternator provides an independent power supply to both ECU channels.
FADEC Functions:
- Power management control
- Variable Bleed Valves (VBVs) control
- ...

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Description

Explore the vital components and functions of the Engine Fuel System in aircraft. This quiz covers the distinction between primary and secondary fuel systems, as well as the fuel supply process to the combustion chamber. Test your knowledge on how fuel interacts with various engine components for optimal performance.