Lecture 25

Question 1

How is turbine engine ignition different from piston engine ignition?

Answer 1

Turbine engines use an untimed continuous combustion process
High-energy sparks only during engine start
Igniters are also not prone to carbon fouling due to the high-energy spark blasting off any deposits

Piston engines have timed magnetos
Low-energy spark every other revolution of the crankshaft
Ignition in pistons is constant while ignition in turbine engines only happens at start-up

Question 2

How is heat energy in turbine engine fuel different from piston engine fuel?

Answer 2

Turbine engine fuel has less heat energy in it and requires a much hotter spark for ignition than piston engine fuel

Question 3

When is ignition needed in a turbine engine?*

Why?

Answer 3

Only needed during the start sequence

Pressurized flammable gas, don’t have to keep lighting the fuel

Question 4

What are the parts of a turbine engine ignition system?*

What combination makes up a typical turbine engine ignition system?

Answer 4

Excitor box
Lead
Igniter

2 Ignition Exciters
2 High-Tension Leads
2 Igniters

Question 5

Turbine engine ignition systems have a _____ rate of current and a _____ voltage to produce a _____.

Answer 5

high

high

spark

Question 6

Why is it beneficial to have an extremely short spark time?

Answer 6

Ignition systems can be small and light

Question 7

When is the ignition system turned on?

Answer 7

Takeoff
Landing
Flight into turbulent conditions
Turbine engine flameout

Question 8

Cooling-down period for the ignition system is called a _____.

Answer 8

duty cycle

Question 9

What are the two types of duty systems?

Answer 9

Intermittent
Continuous

Question 10

When are intermittent-duty systems used?

What is the operating time limit? How much cool down must follow the first operation and second operation?

Answer 10

Main ignition

2 minutes of operation
3 minutes of cool down
2 minutes of operation
20 minutes of cool down

Question 11

Where does a continuous-duty system provide energy?

Do they have a operating time limit?

Answer 11

One igniter

No operating time limit

Question 12

What is the purpose of igniters?

Answer 12

Ignite the fuel-air mixture

Question 13

What are the two types of igniters?

Answer 13

Spark
Glow plug

Question 14

What is the main goal of turbine engine start systems?*

Answer 14

Get air flowing through the combustor so we can mix it with fuel and burn it

Question 15

Describe air starters*

Answer 15

Used in large engines
Light weight with good amount of torque produced
Requires large volumes of low pressure compressed air
APU, GPU, and cross-flow of compressor bleed air

Question 16

Describe electrical starters

Answer 16

Used in small engines
Series-wound electric starters
Connected to the engine through a ratcheting starter jaw similar to reciprocating engines
Starter jaw engages a mating jaw on the engine starter drive

Question 17

Describe a starter generator

Answer 17

Used for smaller engines on business jets
A combination of starter and generator
Once engine is running is automatically switches off

Question 18

Describe an air impingement starter

Answer 18

Low-pressure air is ducted through the turbine blades
Once engine reaches self-sustaining speed, check-valve closes the air path

Question 19

Describe auxiliary power units (APU)*

Answer 19

Self-contained gas-turbine-powered unit in the tail
Provides electric power, compressed air when main engines are not running