ACCESSORY, STARTER AND IGNITION SYSTEM Flashcards
Accessories for gas turbine engines can be divided into two categories:
1 those driven by bleed air and
2. those driven mechanically
Gas turbines are unique because bleed air is readily available for driving aircraft accessories. Compressor discharge air at high pressure and temperature is bled from the engine through ports or valves at intervals along the compressor case and at the end of the diffuser. It is ducted as a source of power for operating
1
2
3
1 air conditioning units,
2 cockpit pressurization and
3 engine anti-ice
Cockpit or cabin pressurizing and heating units sometimes are operated by a separate air compressor, while in other aircraft, engine compressor bleed air is piped directly to the ____________. The use of a separate compressor guarantees uncontaminated air for aircraft crew and passengers but adds weight and power requirements.
cockpit for pressurization
Dual-axial compressor engines usually have three separate bleed air systems: High pressure, low pressure and interstage bleed-air. The high and low pressure systems are used to drive aircraft and engine components or accessories, while the interstage bleed valves are required to ensure compressor stability. High pressure air is also used to anti-ice the engine air inlet guide vanes and parts of the aircraft air inlet duct.
HIGH AND LOW PRESSURE
The other method of driving accessories is by a mechanical, geared drive taken directly from the main shaft connecting the turbine to the compressor. These can be located in front of the compressor or in various locations around it. This method is used for__________________________________ that must be mounted near or connected directly to the engine. Dual-axial compressor engines usually have two accessory drive gear boxes: one connected to the low pressure _________ and the other to the high pressure__________.
tachometers, hydraulic pumps, generators, alternators and other accessories
compressor
compressor.
STARTER SYTEM:
The purpose of any starter system is to accelerate the engine until the turbine is producing enough power to continue the engine acceleration itself. This is called the self-accelerating speed
STARTER SEQUENCE
Air, ignition, fuel
AIR COULD BE ROTATION
As soon as the starter has accelerated the ______________ to establish airflow through the engine, the ignition is activated and then the fuel is added. The exact sequence of the starting procedure is important because _________ must be sufficient enough through the engine to prevent the danger of an explosion when the fuel-air mixture is ignited
compressor sufficiently
airflow
A “hot start” is defined as exceeding the maximum allowable temperature for the turbine section during start. If the engine experiences more than the usual difficulty accelerating (due to such problems as early ________________________, the engine may spend a considerable time at very low RPM (sub-idle). Normal engine cooling flows will not be effective during sub-idle operation, and turbine temperatures may appear relatively high. This is known as a hot start
starter cut-out, (STARTER CUT OUT EARLY)
fuel mis-scheduling, or
strong tailwinds)
Introducing too much_____ too early in the start process, before enough air is compressed in the combustion chamber, causes the burning gas temperatures to rise extremely rapidly. Airflow through the engine may be insufficient to maintain EGT temperatures within start limits
fuel
HUNG START
A “hung start” describes a situation where the temperature within the turbine section continues to rise, and the compressor rpm stabilizes below normal
A _________ occurs when compressor rpm stabilizes below normal, and the turbine temperature remains within limits
FALSE START
A _______ is a situation in which the fuel-air mixture does not light off initially, but has the capability to eventually ignite
WET START
What start abnormality is indicated by a slight rise in EGT with RPM stabilizing below limit?
Hung Start
