15.14 Ignition Flashcards
What do these stand for?
EGT
TIT
TGT
ITT
TOT
Exhaust gas temperature
Turbine inlet temperature
Turbine gas temperature
Inter stage turbine temperature
Turbine outlet temperature
Where would you find the highest temperature on the engine?
And what is used to measure this?
Directly behind the combustion chamber where hot gas hits HP turbine (turbine inlet guide vanes)
TIT
Where is the EGT measurement taken from?
Either between the HPLP turbine or directly behind the LP turbine
What are all of the indications relative to?
The temperature of gases entering first stage turbine inlet guide vanes
Where are thermocouples placed?
Turbine discharge as it’s impractical to measure at turbine IGV
What does the EGT indicate?
And where are they located?
The average temperature measured by the individual thermocouples
Placed at intervals around perimeter of engine turbine casing or exhaust duct
How is the EGT indicator sealed?
Hermetically sealed
How does TIT operate?
And what happens if it reaches a predetermined limit?
By using duel thermocouple system that has two electrically independent junctions providing dual system reliability
And over temp warning light in the indicator illuminates
What are the three groups engine thrust indications?
Performance indications (primary)
System indications (secondary)
Engine trend monitoring
What is the purpose of the primary indications?
To monitor performance and limits and sets thrust for flight phases
What is the purpose of system indications? (Secondary)
To monitor operation of oil and fuel systems and to detect malfunctions quickly
What can be used to give thrust indication?
Either N1 or EPR
Under what conditions can warnings and cautions be displayed?
When indication exceeds a limit
Low oil pressure
Filter clogged
When an unlocked thrust reverser detected
What is trend monitoring?
Used to detect early stages of problems
Done in a workshop by analysing engine data and recorded in flight deck by ACM
What are the three analysis performed in trend monitoring?
Thermodynamic
Mechanic dynamic
Oil consumption
How is the EPR displayed?
Actual EPR shown by pointer or digital valve
Amber or red line shows EPR for Max available thrust
Blue circle shows the EPR that corresponds to actual throttle position
What are the two types of pressure transmitters?
Bourdon tube
Strain gauge
How does the boarding tube pressure transmitter work?
Pressure media will enter the tube causing it to extend the helical sea shaped. Closed-end is attached to a movement that moves a needle as the helical extends
What is the Borden tube made from?
Copper, brass, aluminium or nickel alloy (Monel)
What is a strand gauge used to measure?
The resistance change when a material deformed undergoes strain
What configuration does the strain gauge use? And what’s the principle?
Wheat stone bridge configuration where resistance changes as the length of active arms changes when under strain
Resistance causes output voltage to change, which is amplified and filtered before the data can be read and analysed
What warnings will be given if oil temp exceeds its limits?
Both visual and audible warnings
What two indications does fuel flow provide?
And what is the unit of measurement?
Actual fuel flow to engine engines
Fuel used since engine start
KG, LBS, tons
What do all fuel indications require to provide a measurement?
Fuel flow transmitter
Which measure the force supplied by the flow of fuel (F = M x a)
What is the principle behind synchronous mass flow?
Fuel mass turns a turbine against a spring and deflection angle is measured
An impeller driven by an electric motor accelerate fuel flow
Acceleration of the fuel is constant so massive fuel is proportional to turbine angle
What is the principle behind motorless mass flow?
And how is it measured?
The fuel itself generates acceleration
The angle is measured between rotating drum and rotating impeller
Mass of fuels proportional to an angle between drum and impeller
Using two coins and four magnets 2 at drum and 2 at impeller
What happens as magnetic reluctance as the air gap increases in a variable reluctance sensor?
Magnetic reluctance increases
What does a variable reluctance sensor detect?
Changes in magnetic flux between a magnet and a ferromagnet target
What is a tachometer?
Permanent magnet driven by a gearbox with a speed proportional to N2 rotor speed
It also supplies power to the computer
What are the three types of speed indications?
Display clock type scale
Display with moving vertical bar
Classical electromagnetic indicator
What is the red line limit?
Max permitted rotor speed
Exceeding the red line can cause severe engine damage from over speed
Where are the two sensors usually located for accelerometer?
One located in compressor area near N1 Road A Shift and One located in turbine area (turbine frame)
What are the two types of accelerometers?
Accelerometer - (electromagnet)
Piezoelectric - crystal accelerometer
What happens if N1 or N2 speed signal fails?
Rotor identification shows broadband (BB)
When would we see white on black secondary engine display?
When vibration is equal to or more than 4.0
How does an electrical torque meter operate?
Measures angular displacement relative to that on the driveshaft
It is comprised of two concentric shafts
How does a hydraulic torque meter operate?
Engine pressure metered through a valve with a helical gear that moves in response to applied torque
Measured in lbs/ft or percentage horsepower
What can the hydraulic torque meter also be used?
Set power settings
What is a power assurance test?
And when must this be carried out
Checks engine can accelerate from idle to given EPR value within a specific time, and back to idle within a specific time
Carried out after maintenance or installing a new engine
What are the first three steps in a power assurance test?
1- operate at idle for five minutes
2- identify Max EPR for the day
3- anti-ice and bleed air switches off for better acceleration
What is the time permitted for the engine to reach the same EPR Max value in a para insurance test?
Seven seconds or less
What must be done at the end of a power assurance test before shutting down?
Operate at minimum idle for 10 minutes to safely reduce temperature
