Gas Turbine - Fuel Systems

Question 1

Specific Fuel Consumption for turbojet engine is

Answer 1

The mass of fuel burned per hour divided by the thrust produced

Question 2

Fuel Oil Heat Exchanger or Fuel cooled oil cooler

Answer 2

Hot oil cooled and cold fuel is warmed - could indicate failure if oil contents rising and oil pressure is falling

Question 3

Primary means of determining the thrust of jet engine

Answer 3

Rate of fuel flow

Question 4

Spar Valve in fuel system of gas turbine
(Low pressure shut off valve)

Answer 4

Located in engine pylon isolates the ac fuel supply from the engine

Question 5

Route of fuel into the engine

Answer 5

Enter fuel oil heat exchanger (warm cold fuel) then filtered and delivered under a LP pump to a HP pump. Fed to fuel controller (determined by thrust)

Question 6

Fuel control systems x3

Answer 6

Hydro mechanical unit (mechanical fuel control unit) - old
Hydro mechanical engine controller - basic control of speed core
FADEC - 2 channel engine electronic controller

Question 7

FADEC System - Why do they have two Engine controllers

Answer 7

2 channels for redundancy

Question 8

Fuel System Major Components

Answer 8

Low pressure fuel pump
High pressure fuel pump
High pressure shut off valve (HP Cock)
Pressure raising shut off valve (PRSOV)

Question 9

Low pressure fuel pump

Answer 9

Ensure positive fuel pressure feed to the HP pump

Question 10

HP Fuel Pump x2 types are

Answer 10

Spur Gear fixed volume pump
Variable Volume Type (Swash Plate)

Question 11

Spur Gear Fuel Pump - Spur Gear

Answer 11

Light/simple/minimal heat transfer
Pump supplies excess fuel to fuel metering units

Question 12

Variable Volume - High Pressure Fuel Pump

Answer 12

Swash plate/control piston/governor to control pumps output

Stroke volume limited by angle of swash plate via control piston from inputs from engine over speed governor and the FCU

Question 13

HP Fuel pumps use what liquid for lubrication

Answer 13

Fuel

Question 14

Fuel Oil Heat Exchanger

Answer 14

Heat from oil used to warm the fuel.
Oil is always at a higher pressure than the fuel
Prevents fuel entering the oil system

Question 15

NON FADEC Control - Fuel control unit

Answer 15

Adjust fuel flow to keep engine RPM/temp in limits
Each engine has a dedicated FCU
Ensures correct ratio of fuel and air
Controls piston in HP fuel pump

Question 16

FCU senses

Answer 16

Thrust level
Air temp/pressures
Rapid acceleration/deacceleration
Engine speed
Exhaust gas temperature
Compressor delivery pressure

Question 17

Acceleration Control Unit

Answer 17

Limit fuel flow to prevent over fuelling when thrust lever advanced

Question 18

Altitude sensing unit

Answer 18

Compensates for changes in intake pressure caused by changes of airspeed or variation in pressure

Question 19

FADEC basic principals

Answer 19

EEC engine electronic controllers computers than sense a wide variety of engine parameters and send control commands to FMU which regulates HP pump output pressure to deliver correct fuel to engine

Question 20

FADEC functions

Answer 20

Deliver correct amount of fuel to the engine
Maintain sufficient HP pump output at low RPM to power the FMUs internal components
Fuel shut off when commanded by the pilot
Over speed protection
Control compressor airflow
Ensure manifold fuel draining on shutdown and returning excess fuel to the tanks

Question 21

Fuel used in gas turbines

Answer 21

AVTUR - SG 0.62 to 0.88

Jet A/A1/A-1

Question 22

Jet A

Answer 22

USA
Freezing point -40 degrees

Question 23

JET A1

Answer 23

Most countries - additives to inhibit oxidation/corrosion/anti static/FSII

-47 degrees more suitable for long haul flights

Question 24

Fuel Waxing

Answer 24

Very cold environment leads to clogging filters and pipes
Slowly builds up and fuel does not freeze at one temperature
Slush

Question 25

HP Cock

Answer 25

Shuts off fuel to the combustor

Question 26

Fuel Metering Unit

Answer 26

Regulates HP pump output pressure and flow to fuel nozzles

Question 27

Electronic Engine Controller

Answer 27

FADEC system
Digital computer sending commands to FMU
Also send control commands to engines airflow to control system for preventing compressor stalls

Question 28

Where is fuel measured

Answer 28

Between the fuel control unit and engine burners

Question 29

Where is pressure measured in gas turbine

Answer 29

Between booster pump and engine

Question 30

Auxiliary gearbox

Answer 30

Driven by HP compressor via shaft via an internal gearbox to an external gearbox

AC generator through its constant speed drive
Oil pumps
Hydraulic pumps
High pressure fuel pumps

Question 31

Fuel Oil Heat Exchanger leak

Answer 31

If normal the oil is at higher pressure so would leak into the fuel and be burnt out
- low oil pressure and oil level dropping

If fuel system is at higher pressure than oil then fuel will leak into the oil system.

Rising oil level and low oil pressure

Question 32

Hydro mechanical unit operation

Answer 32

Uses fuel used in combustion as hydraulic fluid
Fuel control system that uses the following signals for FCU

• N2
• Compressor discharge pressure
• Compressor inlet temperature
• Fuel shut off
• Thrust Lever angle

Question 33

Thermal efficiency in jet engine

Answer 33

Around 30%
Describes the efficiency with which fuel energy is converted to kinetic energy

Question 34

Propulsive efficiency

Answer 34

Kinetic energy translated into propulsive force

Question 35

Specific Range

Answer 35

Distance flown per unit of fuel in nautical miles

NM/KG