Turbine Theory

Question 1

How do turbine engines work?

Answer 1

By taking advantage of Newton’s third law: “Every action has an equal and opposite force”. We’re converting the potential energy in fuel into the force that propels us forward. Using the expansion of fuel, we push out air, which creates the thrust that propels us forward

Question 2

What does the anatomy of a turbine engine look like?

Answer 2

-Fan at the front that takes air in
-Air goes through the compressor (which compresses the air)
-The compressed air moves to the combustion chamber, which receives fuel from the fuel injector
-The combustion pushes the air through the back, rotating the turbine, which goes back to turn the fan
-Air passes through the turbine and gets expelled at the back

Question 3

Instead of strokes, turbine engines have sections. Why is that?

Answer 3

Turbine engines have sections instead of strokes because the intake, compression, combustion, and exhaust stages all happen at the same time and at all times

Question 4

What turns the fan and compressors in a turbine engine?

Answer 4

The turbine at the back of the engine that is connected to the fan

Question 5

How do centrifugal-flow compressors work?

Answer 5

They spin, pushing the air outwards by exerting centrifugal force on it. As it exits the centrifugal flow compressor, the air meets with a diffuser, which slows it down and increases and maintains density (slowing it down and increasing pressure even more)

Question 6

What’s another word for centrifugal-flow compressors?

Answer 6

Impeller flow compressor

Question 7

How do axial flow compressors work?

Answer 7

They are huge, powerful fans that speed up the air and push it backwards

Question 8

What do stator vanes do?

Answer 8

They are stationary blades that stop the rotation of the air in axial flow engines and keep it moving back parallel to the longitudinal axis

Question 9

Between each row of stator vanes is a row of_____?

Answer 9

Compressors

Question 10

What are the pros of Axial flow compressors?

Answer 10

(+)More efficient
(-)Less durable
Pushes air back
Larger circumference
Higher compression ratio
Big airliners

Question 11

Pros & cons of Centrifugal flow compressor

Answer 11

(-)Less efficient
(+)More durable
Pushes air out
Long and skinny engines (less drag)
Less thrust to weight
Turbo props and corporate jets

Question 12

What does a stage mean when referring to compressors?

Answer 12

A row of either rotor or stator blades, aka each compressor in a row

Question 13

How are compressors numbered?

Answer 13

By stage. The first compressor is the one closest to the intake, and the last compressor is the one closest to the combustion chamber

Question 14

What is the goal of every stage of the compressor?

Answer 14

Each stage increases air pressure a little more than the previous one

Question 15

What is the spool?

Answer 15

The pipe that connects the compressor to the turbines

Question 16

Why do we sometimes see a spool in a spool or a pipe in a pipe?

Answer 16

Because at times, the axial flow and centrifugal flow compressors have to spin at different speeds

Question 17

What is a turbine engine also called?

Answer 17

Gas generator or core engine turbine

Question 18

What is a turbofan engine?

Answer 18

Basically, like a turbojet engine, but it has a large “shrouded fan” at the front of the engine. The fan is connected to the turbine of the engine and creates more thrust than the turbine itself. The fan acts similarly to a propeller

Question 19

Why is the fan of turbofan engines shrouded?

Answer 19

Because the shroud prevents the disruption of airflow over the wing

Question 20

How does the shroud make turbofan engines quieter?

Answer 20

It does so by speeding up the air immediately outside of the engine, which lessens the difference in speed between air coming from the engine and the surrounding air. This provides a barrier to wind shear coming out of the exhaust of the engine

Question 21

What is a turboprop engine?

Answer 21

A turbine engine that has a propeller mounted at the front

Question 22

What are the 2 types of turboprop engines?

Answer 22

-Direct Drive
-Free Turbine

Question 23

What is a direct drive turboprop engine?

Answer 23

The propeller, through a reduction gearbox, is directly connected to the turbine

Question 24

What is a free turbine turboprop engine?

Answer 24

Where the air intake flows from back to front, there is no physical connection between the turbine and the free turbine; the free turbine turns from the air that the turbine blows onto it. The free turbine then rotates the propeller

Question 25

How many turbine sections does a free turbine engine have?

Answer 25

Two. 1 turbine connected to the engine and 1 turbine connected to the propeller, but free from physical connection with the engine

Question 26

What is the difference between power and thrust?

Answer 26

Turboprop pilots set power via torque settings Jet pilots set thrust, which is the engine pressure ratio

Question 27

How can we measure thrust?

Answer 27

-By measuring the difference between the air pressure at intake and the increased pressure at the exhaust of the engine -By measuring the power created by different spools in the engine. This is given in a % of the maximum because the number is too large

Question 28

Why do we have to monitor the Exhaust Gas temperature (EGT) and Interstage Turbine temperature(ITT)?

Answer 28

To monitor the performance of the engine

Question 29

How do we control a turbine engine?

Answer 29

By controlling the fuel being fed to it (adding or removing fuel)

Question 30

How do we shut down a turbine engine?

Answer 30

By cutting the fuel we feed it

Question 31

How do we start a turbine engine?

Answer 31

1) Rotate the compressor section to prevent gases from moving forward out of he combustion chamber. In big engines, they usually use the alternate power unit to do so 2) Add fuel to the combustion chamber once the pressure has built up enough 3) Light the fuel-air mixture. This is achieved with igniters (which are plugs similar to a spark plug). Once the mixture is lit, it does not need to be re-ignited because it keeps burning like a candle

Question 32

What does APU stand for?

Answer 32

Alternate Power Unit

Question 33

What does the GPU stand for?

Answer 33

Ground Power Unit

Question 34

What is a hot start?

Answer 34

An issue with starting the engine. It is when the compressor is not running fast enough, but the engine is started regardless. This makes the hot gases from combustion move forward instead of backwards

Question 35

What is a hung start?

Answer 35

An issue with starting the engine. It is when the starter doesn't spin the engine fast enough

Question 36

What are clamshell doors, and what do they do?

Answer 36

Doors that go over the back of the engine that divert the air from the exhaust forward to stop the plane

Question 37

What are cascade doors, and what do they do?

Answer 37

Doors on the side of the engine divert the air from the fan forward

Question 38

What is the difference between stator blades and rotor blades?

Answer 38

Stator blades are stationary blades that direct the airflow parallel to the longitudinal axis, while the rotor blades are the moving parts (the compressors themselves)

Question 39

In a high bypass engine, what part produces the most thrust?

Answer 39

In a high bypass engine, more thrust is generated by the fan than the engine

Question 40

What does the EPR measure?

Answer 40

Engine pressure ratio. Measures the difference between the total pressure at engine inlet and at turbine exhaust

Question 41

Which is louder, turbofan or turbojets?

Answer 41

Turbojets are louder

Question 42

What do N1 and N2 measure?

Answer 42

The rotational speed of the high pressure and low pressure spools

Question 43

When are igniters lit?

Answer 43

During start-up and in times of precipitation

Question 44

Why do we have different spools?

Answer 44

Because we need to spin different components at different speeds. One spins the extra prop and the other spins the compressors