Gas turbine combustors and fuels

Question 1

What are the 9 basic requirements of a gas turbine combustor?

Answer 1

High combustor efficiency - fuel burned and heat liberated
Reliable smooth ignition - ground and altitude
Wide stability limits
Free from pressure pulsations and instabilities
Low pressure loss
Good outlet temperature traverse (blade and nozzle life)
Design for min cost and ease of maintenance
Size and shape constrained by engine architecture
Durability

Question 2

What is the simplest form of a combustor and why is it impractical?

Answer 2

A duct which connects the compressor to the turbine

Results in a high pressure loss

Question 3

Where do losses originate from in a diffuser?

Answer 3

Losses originate due to wall frictional losses and separation or stall

Question 4

The optimum diffuser angle lies between…

Answer 4

7 and 12 degrees

Question 5

List 3 types of combustor

Answer 5

Tubular Combustion system
Annular Combustor
Turbo Annular Combustion system

Question 6

What are the advantages (3) and disadvantages (1) of Tubular Combustion system?

Answer 6

+ Mechanically robust
+ Fuel & airflow patterns easily matched
+ Rig testing easy small fraction of engine flow

• Bulky and heavy

Question 7

What are the advantages (4) and disadvantages (4) of Annular Combustor?

Answer 7

+ Minimum length and weight
+ Minimum engine frontal area
+ Minimum pressure loss
+ Easy light around

• Outer liner buckling loads
• Rig test require high airflows
• Difficult to match fuel and air patterns
• Inlet velocity profiles can effect outlet traverse

Question 8

What are the advantages (4) and disadvantages (3) of Turbo Annular Combustion system?

Answer 8

+ Mechanically robust
+ Fuel & airflow patterns easily matched
+ Rig testing easy small fraction of engine flow
+ Low pressure loss

• Less compact than annular
• Requires interconnectors
• Cooling requirements

Question 9

What are the stages of formation of air spray fuel injector?

Answer 9

Dribble stage
Distorted pencil
Onion stage
Tulip stage
Fully developed spray

Question 10

What are the aims of a combustion system?

Answer 10

To maximise combustion efficiency with minimal pressure loss

Provide down stream turbines with an appropriate flow to maximise the life of both the combustor and turbine

Question 11

Why is kerosene an almost perfect fuel for aviation purposes?

Answer 11

It is easy to handle
Stable for very a wide range of temperatures
Highly calorific