Gas Turbines

Question 1

What type of engine is a gas turbine?

Answer 1

internal combustion, constant flow engine

Question 2

What is the main benefit to external combustion chambers on a gas turbine?

Answer 2

allows use of a wider range of fuels (also for ease of maintenance)

Question 3

Describe regeneration in a gas turbine.

Answer 3

Some of the exhaust heat is use to heat the air of combustion.

Question 4

Describe cogeneration in a gas turbine.

Answer 4

Exhaust heat is used to generate steam for power generation of other plant processes.

Question 5

What are the different shaft arrangements available in a gas turbine?

Answer 5

single shaft, split shaft, twin spool shaft

Question 6

Generators for electric power must run at speeds that are multiples of _____ for correct cycle in the power grid (N. America)

Answer 6

60 (60 Hz power grid frequency)

Question 7

What type of blading is found in gas turbines?

Answer 7

reaction blading (although the blading does incorporate some impulse principles)

Question 8

What is the thermal efficiency of an open cycle gas turbine?

Answer 8

15-40%

Question 9

What is the thermal efficiency for a regeneration gas turbine?

Answer 9

up to 60%

Question 10

What is the thermal efficiency for a cogeneration gas turbine?

Answer 10

50 to 90%

Question 11

Are the pressures in a gas turbine higher or lower than a steam turbine?

Answer 11

lower

Question 12

What can happen if the pressure in the combustion chamber becomes higher than the pressure in the diffuser in a gas turbine?

Answer 12

the gases can back up into the compressor and possibly cause a surge or stall (causing severe damage)

Question 13

What are the two main sections of a gas turbine, and what are the three main components of these sections?

Answer 13

Gas generation section, and Power section, the three main components are the compressor, combustion chamber and the turbine

Question 14

What are the two basic types of air compressors found in gas turbines? Which is more efficient in larger gas turbines?

Answer 14

radial flow (centrifugal) and axial flow, the axial flow is more efficient in larger gas turbines

Question 15

What are the two types of rotors in a gas turbine, and which are used in most present-day high-speed gas turbines?

Answer 15

Drum type or disc type rotors, the disc type is used more

Question 16

Name the 3 parts of a combustion chamber.

Answer 16

Primary zone, intermediate zone, and dilution zone

Question 17

How much of the compressed air is used for combustion? What is the rest used for?

Answer 17

35-40% of the compressed air is used for combustion, the rest is used for cooling

Question 18

What connects the combustion chamber to the turbine?

Answer 18

the transition piece

Question 19

Name the 3 styles of combustion chambers. Which has the most igniters?

Answer 19

can type, annular type, can-annular type, the can type has the most igniters (one for each can)

Question 20

What does the can-annular style combustion chamber have that enables the flame to pass to each can during start-up?

Answer 20

crossfire tubes

Question 21

At which speed of rotation should a rotor be dynamically balanced?

Answer 21

3600 rpm and over

Question 22

What material may be used to increase the endurance of the nozzles in the power section of a gas turbine?

Answer 22

ceramic

Question 23

What type of shaft seals are used on both the compressor and turbine in a gas turbine?

Answer 23

labyrinth seals

Question 24

Fuels used in gas turbines can be either gaseous or liquid, name some common fuels used.

Answer 24

natural gas, liquefied petroleum gas, alcohol, kerosene, gasoline, diesel, bunker oil, a gas/diesel blend

Question 25

At what percentage of max speed must a turbine be rotated before fuel is turned on?

Answer 25

20-30%

Question 26

Where is the highest temperature found in a gas turbine?

Answer 26

The point where heated air leaves the combustion chamber.

Question 27

How are gas turbines for aircraft usually constructed?

Answer 27

modular construction

Question 28

How are dirt deposits on compressor blading cleaned in a gas turbine?

Answer 28

first the wash system is used, if this isn't sufficient then ground walnut shells may be introduced into the compressor inlet while the engine is running

Question 29

What may be equipped around the combustion section of a gas turbine to indicate where problems may be if one nozzle or one combustion chamber is malfunctioning?

Answer 29

pyrometers

Question 30

Describe the sequence of an engine wash system on a gas turbine.

Answer 30

With the turbine driven by the starting mechanism or during operation, a soak cleaning fluid is sprayed on the compressor blades, followed by spraying a wash off fluid, and finally an inhibiting fluid.

Question 31

How much loss in engine power (%) will result from a 1% loss in intake pressure on a gas turbine?

Answer 31

2.5%

Question 32

What is the purpose of a diffuser in a gas turbine?

Answer 32

To lower the velocity/increase the pressure of the air leaving the axial flow compressor to allow combustion

Question 33

What can cause pitting on gas turbine blades?

Answer 33

unburned liquid fuel, ash, dirty air, dirty fuel

Question 34

What is the purpose of the holes that are drilled in some turbine blades from root to tip?

Answer 34

aids in blade cooling

Question 35

Why are there fewer stages in a gas turbine compared to that of a steam turbine?

Answer 35

there are fewer pressure drops available