accessory, starter, and ignition systems A

two categories for accessories driven by the turbine

driven by bleed air

driven mechanically

dual-axial compressor engines have three separate bleed air system

high pressure

low pressure

interstage bleed-air

high and low pressure systems are used to drive

aircraft and engine components or accessories

interstage bleed valves are required

to ensure compressor stability

on dual/split spool axial compressors, low pressure bleed air is extracted

extracted between the low pressure and high pressure spools

dual-axial compressor engines have two accessory drive gear boxes connected to

the low pressure compressor and the other to the high pressure compressor

starter system purpose

accelerate the engine until the turbine is producing enough power to continue engine acceleration by itself

starting cycle

as the compressor has been accelerated enough, fuel flow occurs when engine has reached 30%, ignition occurs when sufficient airflow supports combustion of fuel air mixture

different abnormal starts

hot start

hung start

false start

wet start

hot start

exceeding the maximum allowable temperature for the turbine section during start

hung start

temperature within the turbine section continues to rise, and the compressor stabilizes below normal

false start

compressor rpm stabilizes below normal, and turbine temperature remains within limits

wet start

fuel-air mixture does not light off initially, but has the capability to eventually ignite

most dangerous abnormal start

wet start

two different types of starters

DC electric motor

air turbine starter

what type of ignition system is normally used for gas turbine engines

high energy capacitor-type ignition system

why is the high energy capacitor-type ignition system used

ensures ignition of the low volatile fuel at all temperatures and high altitudes

how many ignitor plugs is a gas turbine engine provided with

2

annular gap plug

protrudes slightly into the combustion chambers liner to provide effective spark

constrained-gap plug

the spark does not closely follow the face of the plug and jumps in an arc which carries beyond the face of the chamber liner

two types of ignitor plugs used

annular gap

constrained-gap