M15.11 Flashcards
What is the job of a primary fuel system?
It is the system of storing fuel
What is the job of a secondary fuel system?
It is the fuel system that goes to the engine
The engine fuel system can be split into two subsystems, what are these?
Fuel distribution and fuel control
The engine fuel distribution system has three main tasks, what are they?
- to safely supply fuel
- to pressurise the fuel to be vaporised
- to heat the fuel
What is the job of the low pressure fuel pump?
To increase the fuel pressure that comes from the tanks
What is the job of the high pressure fuel pump?
Increase the pressure to the high level needed for vaporisation in the combustion chamber
What is the job of a pressure relief valve?
To protect the pump from over pressurisation by releasing pressure
What is the job of a fuel control unit?
To regulate the amount of fuel needed in the combustion chamber. There is also a shut off valve to the fuel nozzles in emergency’s
What is can be added to be absolutely free of ice in the servo fuel?
Servo fuel heater
Why is a fuel flow transmitter used?
It measures the actual fuel flow and sends signals to the cockpit
What is the advantage of having the oil cooler downstream of the high pressure pump?
Less external fuel lines
What pressure does a low pressure fuel pump go up to?
175psi
Why is the low pressure fuel pump pressurised?
So the high pressure stage doesn’t need to suck fuel through and to prevent cavitation
What is the pressure at the high pressure fuel pump at max engine speed?
900psi
At what pressure does the overpressure relief valve open?
1250psi
What can the bypass fuel be used for?
To cool the IDG oil (cold fuel may be need to cool the now hot fuel down to prevent thermo shock)
Where can the fuel control unit of an engine be found?
Usually mounted to the engine fuel pump on the accessory gearbox
What type of component is the fuel control unit?
Hydrochemical (all control functions are done by fluid pressures and mechanical components)
What are the two types of fuel control units?
- speed governed fuel control units (old)
- constant thrust fuel control units (new)
What does a speed governed fuel control units use for steady state fuel metering?
N2 speed
What does a constant thrust fuel control unit use for steady state fuel metering?
N1 speed, ambient pressure and temperature
How is the thrust lever signal out putted?
Rack and pinion or by rods and levers
How is the N2 speed feedback signal transmitted?
Via a mechanical drive shaft from the main fuel pump
How is the N1 speed feedback signal transmitted?
Comes from a hydrochemical N1 speed sensor
Where do temperature signals like CIT or fan inlet temperatures come from?
Hydro mechanical temperature sensors
What does FADEC stand for?
Full authority digital engine control
What is the computer called in a FADEC system?
Electronic control unit or the electronic engine control
What is the second main component of the FADEC system?
Fuel metering unit
What is the fuel metering unit also known as?
Hydro mechanical unit
The fuel metering unit and the hydro mechanical unit don’t have control in them, whys this?
Because they only receive from the electronic control unit not control
Where is the electronic control unit located?
On a fan stator case of the engine
What is needed for correct operation of the electronic control unit?
A demand signal from the thrust lever in the cockpit
