Turbine Engine Starting: Ignition; Relight And Shutdown Flashcards
Describe the general precautions and safety checks prior to starting and ground running a turbine engine.
Check both turbines are clear front and rear.
For turbo prop, make sure engine turns by hand before attempting a start. With a single shaft turbines a seized engine could lead to a hung start and over temperature leading to engine damage.
What are requirements to start an engine.
Compressor must be rotated done by an electric starter motor, a ground air start unit blowing air over the compressor or by bleed air from another engine.
Sparks and fuel are added to produce combustion to achieve a light up.
Describe general procedures for starting and shutting down a turbine engine.
Engine core rotated, from there, ignitors are activated first and fuel is introduced last. Rest is automatic (compressor turn, ignitors spark and fuel introduced at correct time) but RPM, temp and fuel flow should be monitored.
Turboprop requires pilot to introduce fuel manually.
Shutdown - prior to shut down needs to be run for a short period of time to enable temps to stabilise, basically bring it to idle power and then cutting the fuel supply. Deprived of fuel engine will wind down decreasing in RPM until spools stop.
Describe the positive cockpit indications of light-up during start.
Point which combustion occurs. Rising fuel flow, EGT and continuation of turbine RPM increasing.
Describe what is meant by self-sustaining rpm and how this is achieved.
This is the RPM at which the starter has automatically cut out and the engine will continue to accelerate on its own.
This is achieved by accelerating the engine to a torque that will drive the compressor sufficiently to supply the combustor with sufficiently compressed/heated air to burn without any assistance.
Describe why it is important to accelerate an engine up to sustaining rpm as quickly and uniformly as possible.
To avoid hung start leading to a hot start. Also over time excessively long starts wear the starter components.
Describe the causes, indications, effects and remedial actions for the following start defects—
hung start
RPM not increasing at rate expected.
Causes - result of starter cutting out too early due to a fault or caused by insufficient fuel flow or very occasionally variable inlet guide vanes or bleed valves not responding to start command.
Indications - engine rpm stop increasing, EGT too high for that RPM and continue increasing
Actions - cut off fuel and continue turning engine (dry motoring)
Describe the causes, indications, effects and remedial actions for the following start defects—
hot start
When engine temp exceeds the limits imposed by the manufacturer.
Causes - not enough airflow through compressor or too much fuel for airflow. Can occur if tailwind is strong enough which can blow the exhaust gasses back into engine.
Indications - EGT rises beyond limit, slow rising engine RPM.
Actions - cutting off fuel supply to engine, motoring engine without fuel to return engine temp to a normal range.
Describe the causes, indications, effects and remedial actions for the following start defects—
Wet start.
When engine fails to start after fuel is introduced
Causes - ignitors aren’t functioning correctly (not working or working at low power to ignite).
Indications - no EGT rise, fuel vapour coming from tailpipe, RPM, will be same as starter motor.
Actions - cut off fuel supply to engine, motoring engine without fuel to purge fuel from combustion chamber.
Describe the causes, indications, effects and remedial actions for the following start defects—
Bleed band or bleed valve stuck in open or closed position.
If stuck in closed position, over pressure is likely which may occur which can result in compressor stall or surge.
If stuck open, compressed air will vent out the engine meaning the compressor won’t be able to attain its normal operating pressure. Reducing efficiency
Describe the causes, indications, effects and remedial actions for the following start defects—
Stall and surging
Causes - rotors and stators don’t deliver a smooth progression of air through the compressor, turbulent airflow into engine and disruption of airflow by contaminated or damaged blades.
Indications - fluctuating RPM, fuel flow, vibration and popping or banging noises.
Actions - shut down engine.
Describe the causes, indications, effects and remedial actions for the following start defects—
Tail pipe fire
Caused by fuel pooling in the tail pipe and there being too much fuel in the combustion chamber, has no cockpit indications and quickest way to remedy the situation is to cut fuel and dry motor the engine
Describe why turbine engines are often fitted with separate low and high energy ignition systems.
the high energy system is used whenever a high altitude (and thus low temperature) re-light may be required (a very uncommon occurrence), or a start at very low temperatures is required.
The low energy ignition system may only be required for a start under warm conditions. Additionally, it is often used as a precaution when encountering turbulence, icing conditions or on take off.
Describe the conditions under which the ignition system(s) should be turned on.
During the start cycle, once the fuel air mixture is ignited an if stable conditions remain , the flame in the combustion chamber becomes self sustaining.
The igniters can also be used during takeoff or during heavy rain snow or turbulence.
Describe the requirement and general procedures for an engine relight in the air.
Must put aircraft in the relight envelope of an airspeed vs time graph. This will assure relight unless aircraft is damaged. the engine can be relight usually by not engaging the starter mechanism.
