Engines 2: Gas Turbine & Reciprocating Engines

Question 1

What is the purpose of an inlet duct?

Answer 1

To provide the proper amount of high pressure, turbulent-free air to the compressor

Question 2

What are the two basic inlet designs?

Answer 2

Single entrance
Divided entrance

Question 3

What shape is a subsonic inlet?

Answer 3

Divergent

Question 4

What shape is a supersonic inlet?

Answer 4

Convergent-Divergent

The convergent shape initially reduces the airflow velocity to subsonic speeds (and increases pressure) and then the divergent shape increases pressure

Question 5

What is the purpose of the compressor section?

Answer 5

• Supply high pressure air to the combustion chamber to satisfy combustion

Question 6

Why doesn’t the Bernoulli Principle apply to the compressor section?

Answer 6

The compressor section is not a closed system so both airflow velocity and pressure increases

Question 7

What are the three types of compressors?

Answer 7

Centrifugal
Axial
Axial-centrifugal

Question 8

What are the three main parts to a centrifugal compressor? What does each part do?

Answer 8

Impeller - increase velocity, pressure, and total pressure
Diffuser - decreases velocity and increases pressure
Manifold - routes the air to the burner section

Question 9

What are the two main parts to an axial compressor?

Answer 9

Rotors
Stators

Question 10

What is the purpose of the burner section?

Answer 10

To ensure the proper mixing of air and fuel for good combustion

Question 11

How is air entering the burner section (from the compressor) split up (percentages)?

Answer 11

Primary Air - 25%
Secondary Air - 75%

Question 12

What is primary air used for?

Answer 12

To mix fuel and air for combustion

Question 13

What is secondary air used for?

Answer 13

Cooling
Afterburning
Control of the flames

Question 14

What is engine creep?

Answer 14

The elongation and deformation of turbine blades due to repeated heating over long periods of time

Question 15

How can engine creep be minimized?

Answer 15

The “fir tree” method

The turbine blades are attached to the shaft in a fir tree shape that allows for expansion when heated

Question 16

What is the purpose of the exhaust section?

Answer 16

To direct the flow of gases rearward to create high exit velocity and minimize turbulence

Question 17

What are the main parts of the exhaust section?

Answer 17

Exhaust outer duct
Exhaust inner cone
Radial hollow struts (about 3 - 4)

Question 18

What are the two types of exhaust nozzles?

Answer 18

Convergent
Variable exhaust nozzle

Remember, nozzles always increase velocity and that is the purpose of the exhaust section

Question 19

What type of airflow does a convergent exhaust nozzle work for?

Answer 19

Subsonic airflow

Question 20

What type of airflow does a variable geometry convergent-divergent nozzle work for?

Answer 20

Supersonic airflow

Question 21

What is afterburning?

Answer 21

A method to increase max thrust available from an engine by 50% or more

Question 22

Which air from the compressor is used for afterburning?

Answer 22

Secondary air

Question 23

What are the four parts of the afterburner section?

Answer 23

Spray bars
Flame holders
Screech liner
Variable exhaust nozzle

Question 24

What does a screech liner do?

Answer 24

Acts as a shock absorber to reduce pressure fluctuations and vibrations due to afterburner operations

Question 25

What are the parts of a reciprocating engine?

Answer 25

Crankcase
Cylinders
Pistons
Connecting rods
Valves
Valve-operating mechanism
Crankshaft

Question 26

How does the turbine use the heat energy from the burner section?

Answer 26

75% of the heat energy is turned into mechanical energy to drive the compressor/accessories

25% of the heat energy is used for thrust