turbine 2 fuel week 2

function of fuel control system

• provide engine with proper amount of metered fuel

• automatically adjust fuel flow for changes in temp and pressure settings 

types of fuel control systems

• hydro mechanical

• hydro pneumatic

• electronic hydro mechanical

• FADEC

another name for shutoff valve

spar valve

what controls shutoff valve

fire handle

function of fuel pump

delivers unmetered fuel to FCU

where does EDP receive fuel

from the tank boost pump(s) through the open shutoff valve

where is the fuel pump installed

AGB

two stage fuel pump assembly

1st stage - impeller type pump; low pressure

2nd stage - positive displacement gear pump; high pressure

some aircraft tap fuel from the pumps to provide

motive flow for ejector pumps in the fuel tanks

function of fuel heater

heat cold fuel from the tanks to prevent ice formation

heating medium for fuel

engine bleed air and engine oil

primary heat exchanger is used to 

heat fuel

secondary heat exchanger is used to

cool oil

fuel temperature sensor

maintains stable fuel temp at the outlet

restricts or bypasses heating medium

function of fuel filter

remove debris and ice formation

locations of fuel filter

• Fuel supply to the pump

• Between pump stages

• Between pump and FCU

• In fuel nozzles

differential pressure switch on fuel filter

provide clogging indication

bypass if there is a clog

types of fuel filter

• micron

• wafer screen

• plain mesh

wafer screen

consists of layers of metal screen discs

plain mesh

wire screen formed into a cone

used where filtering is not as critical

FCU function

delivers metered fuel to fuel nozzles for combustion

3 functions of FCU

• computing

• metering

• governing

how does FCU receive input commands

from flight deck

FCU commands from flight deck are

power and fuel shutoff

how does FCU control engine rpm

providing the proper amount of metered fuel

how does the FCU maintain selected power command

requires speed, temp, pressure info

minimizes the need for flight crew to adjust throttle levers for changing operating conditions

FCU location

attached to pump on AGB

another name for fuel pressurizing and dump valve

flow divider

function of P&D valve

schedules primary and secondary fuel flow to fuel nozzles

provides fuel cutoff at engine shutdown so fuel can drain from the manifold

P&D valve operation during engine start

control signal from FCU closes dump valve > fuel flows through primary manifold to nozzles > fuel pressure is high enough > pressurizing valve opens > fuel flows through secondary (main) manifold

P&D valve operation during engine shutdown

no control from FCU > dump valve opens > shutoff fuel > fuel is drained from both manifolds through open dump valve > prevents potential tailpipe fires and fuel nozzle carbonization

fuel manifold function

delivers fuel to nozzles for combustion

types of fuel manifold

single and dual

where is the fuel divider in a single fuel manifold with dual nozzles

flow divider is built into fuel nozzles

where is the fuel divider in a dual fuel manifold

flow divider is separated upstream of fuel nozzles

fuel nozzle function

atomizes fuel to provide efficient combustion

types of fuel nozzle

simplex and duplex

simplex fuel nozzle

single fuel path to nozzle to produce single spray pattern

has internal spin/swirl chamber to swirl fuel

duplex fuel nozzle

primary and secondary (main) flow spray patterns

primary flow sprays at a wide angle from engine start to idle (inner)

secondary flow opens at a preset pressure (outer)

drain valve function

ensures all fuel is removed after engine shutdown to prevent risk of tailpipe fire and prevents carbon buildup

where does drained fuel end up

drain tank or through P&D valve where fuel is recovered during next engine start

types of drain valve

manifold dump valve - located at low point of fuel manifolds

combustor drain valve

hydromechanical system

input from flight deck is mechanical (cables and linkages)

input levers hydromechanical system

controls thrust and fuel shutoff

hydropneumatic system

uses 2 governors

• Ng governor for compressor turbine speed

• Nf (prop) governor for power turbine speed

EEC system (electronic engine control)

operates as a limiter engine parameters from being exceeded

FADEC system (full authority digital engine control)

electrically controls engine operation (fly by wire)

consists of EEC and hydromechanical unit

FADEC - HMU

performs FADEC control functions commanded by EEC

FADEC - HMU control functions

fuel metering

servo control

low pressure cooling