15.13 Start And Ignition Flashcards
Where is the engine turbine ignition system normally used?
Short period during the engine starter sequence and in the combustion chamber to ignite fuel
When would continuous ignition mode be used?
Uses at lower voltage and energy level, is used during certain flight conditions i.e if there is a possibility of an engine flame out, to relight the fuel and keep the engine from stopping
How do you start a GTE
Accelerate the high pressure compressor to provide sufficient airflow for combustion
Give some examples of when continuous ignition could be used?
Take off, landing and some abnormal or emergency situations, such as flying through a hailstorm or volcanic clouds
What are most turbine aircraft ignition system?
A high energy, capacitor-type ignition system and air cooled by a fan airflow
What is the order of starting a GTE
Ignition on, fuel, engine lights up, engine attains self-accelerating speed, ignition off, starter cuts out, engine reaches idle rpm
Why can working on a starter motor be dangerous ?
Starter motors generate high amounts of torque and are very heavy
What other ignition systems could turbine engines be equipped with?
Electronic type of ignition system
What can be left behind on the ignition exciter (igniter)?
High voltage and current, so it should not be touched if circuit breakers aren’t pulled or is the igniter lead is not connected
What tools should be used when disconnecting igniter leads?
Insulated tools and never bare hands
What should you always follow when or king on ignition systems ?
Manufacturer’s instructions and / or the AMM
What should be ensured before working on the ignition systems ?
There is no electricity left in the igniters
Should fuel be sprayed before ignition is on
No, ignition should be on before fuel
identical independent ignition units operating from a common low voltage (DC) electrical power source what are they?
Aircraft battery, 115 AC, permanent magnet generator
identical independent ignition units operating from a common low voltage (DC) electrical power source what are they?
Aircraft battery, 115 AC, permanent magnet generator
What is the generator turned by?
Directly by the engine through the accessory gearbox and produces power any time the engine is turning
Why is it imperative that the system can supply a high heat intensity spark?
Because they they often operate in low temp of high altitudes
What does a typical ignition system include?
Two exciter units two transformers, two intermediate ignition leads and two high tension leads. As a safety factor, the ignition system is a goal system designed to fire two igniter plugs
Before electrical energy reaches the exciter unit what does it pass through?
A filter that prevents noise voltage from being induced into the aircraft electrical system
What measures throttle position
Resolver (Boeing)
Potentiometer (Airbus)
From breaker points where do rapidly interrupted currents get delivered to?
Auto transformer
What are advantages of cartridge starting
Quick independent engine start by using compressed gas
What happens when the breaker closes and when it opens?
When closing the flow of current through the primary winding of the transformers establishes magnetic field. When breaker opens, flow of current stops and the collapse of the field induces a voltage in the secondary of the transformer
What are disadvantages of cartridge
Single use so need replacing
How is the cartridge ignited
By applying a voltage through the connector at the end of the breech handle
1 joule per second = … watts?
1 watt
All high voltage in the triggering circuits is completely what from the primary circuits?
Isolated
How is the complete exciter sealed?
Hermetically
What does hermetically seal also ensure?
Shielding against leakage of high-frequency voltage interfering with the radio reception of the aircraft
What is the advantages of air starting
Lightweight and simple and economical
What does an air starter transmit power through
Reduction gear and clutch
Where does air from an air starter come from
External ground supply or APU or via a cross feed from the other engine
What does the capacitor type system provide?
Ignition for turbine engines
How is energy stored?
In capacitors
What pressure air is used to start an engine
30-50psi
How many capacitors are in each discharge unit?
Each discharge circuit incorporates two storage capacitors; both are in the exciter unit
What pressure air is used to start an engine
30-50psi
How many capacitors are in each discharge unit?
Each discharge circuit incorporates two storage capacitors; both are in the exciter unit
What type of clutch is used in air starting
Sprag clutch
What is an igniter plug?
Its electrode must be capable of withstanding a current of much higher energy than the electrode of a conventional spark plug. This high energy current can quickly cause electrode erosion, but the short periods of operation minimise this
Explain a typical annular gap igniter plug?
sometimes referred to as a long-reach igniter because it projects slightly into the combustion chamber liner to produce a more effective spark
What is a constrained gap plug?
It operates at a much cooler temperature because it does not project into the combustion chamber liner. This is possible because the spark does not remain close to the plug, but arcs beyond the face of the combustion chamber liner
What is the typical maintenance of a turbine engine ignition system?
inspection, testing, troubleshooting, removal, and installation
How long should you wait after shutdown of the capacitor?
20 mins
What does the inspection of ignition systems consist of?
Ignition lead terminal inspection - ceramic terminal should be free of arcing, carbon tracking, and cracks.
The grommet seal should be free of flashover and carbon tracking.
The wire insulation should remain flexible with no evidence of arcing through the insulation.
Inspect the complete system for security of component mounting, shorts or high voltage arcing, and loose connections.
How should you inspect ignition leads?
Remove clamps
Remove the safety locking wire and disconnect electrical connectors from exciter units and disconnect the lead from the igniter plug
Discharge any electrical charge
Clean leads
Inspect connectors
Inspect leads
Perform a continuity check of ignition leads
Reinstall leads, reversing the removal procedure
What is the purpose of the magnetic drain plug on the transmission housing for
Removing any ferrous particles in the oil
How do you inspect plugs?
Disconnect ignition leads
Remove igniter plugs
Inspect igniter plug gap
Inspect for fretting
Replace dirty or carbonised igniter plugs
Install igniter plugs in mounting pads
Check for proper clearance
Tighten igniter plugs to the manufacturer’s specified torque
Safety wire igniter plugs
What are the two types of electrical starting
- Direct cranking electrical system
-Starter-generator systems
What are the two types of electrical starting
- Direct cranking electrical system
-Starter-generator systems
What current is used in a direct cranking electric starter
DC
How long should be left before working on the igniters after pulling CB’s ?
At least three minutes
