Starting Flashcards
What is a Hot Start?
Its a failure to establish sufficient cooling air while starting a gas turbine engine, often caused by adding more fuel than the rpm is suitable for
Indicated by high EGT
An engine that runs perfectly might, one out of every thousand starts, have a hot start
Shut it down immiediatly let it cool down
Two hot starts in a row something is wrong, probably the fuel control.
When should the igniters be on, do the they stay on all flight?
Igniters are used during engine start and are normally used again only for takeoff, landing or cruising in heavy precipitation or icing conditions.
Describe how a Jet Turbine starts.
In order for a Jet engine to start, high pressure air must be introduced into the system, the APU is usually in charge of this task. The flow of high pressure air is controlled by a start valve, based on inputs from the cockpit.
After the start valve, the air is sent to the accessory gear box, usually located near the bottom of the engine cowling. The AGB houses different pumps and an air starter unit. The air starter unit is consisted of a turbine which is linked to a radial drive shaft, this shaft from the air starter unit is connected to the N2 shaft (high pressure shaft). Once the air reaches the air starter turbine the radial drive shaft begins to rotate and the N2 shaft with it, aiding in compression of air.
As the N2 shaft rotates, the igniters come on inside the combuster, the fuel is then introduced through the fuel nozzles to create fuel a air mixture, this causes the N2 shafts rotation speed to increase further.
Slowly the N1 shaft starts to rotate. This aids in the increased speed for both shafts. The ignition is cutoff since the flame becomes self sustaining. As speed is increased the radial drive shaft from the air starter unit is disengaged, the starter valve can now be closed.
What systems are available to help start a Jet Engine?
APU
Huffer Cart
Other Engine bleed air (if running)
What is a Hung Start?
A Hung start is due to lack of power of the starter usually due to a problem with the air valve
EGT is accelerating slower than normal
What is a “No light off”
Fuel is introduced into the combustion chamber but fails to ignite properly or at the correct time. This can lead to an accumulation of unburned fuel within the engine, posing a risk of a sudden and potentially violent ignition if the fuel eventually does ignite. It could become a Bomb.
