A.A.B Engines - Tutorial

Question 1

Draw limiting cycles of ramjet. Include low and top speed limit

Answer 1

T-S graph.

dotted lines showing limiting cycles

Question 2

What are the losses in a real ramjet

Answer 2

1. Intake, combustor and nozzle have pressure losses
2. Losses occur during combustion
3. Compression and expansion are not isentropic
4. Irreversibilities result in flight and exhaust Mn to be different

Question 3

Discuss challenges of SR-71 has when flying at M=2 on ground level

Answer 3

1. Ambient pressure is higher at ground level so higher friction as body moves through air
2. Diffuser performance decreased due to increased pressure of atmosphere
3. Shock waves could interact with ground and reflect back to aircraft causing issues
4. Speed of sound is faster

Question 4

Describe why rocket combustion is more controllable than scramjet combustion

Answer 4

Rocket:

• simple design using solid propellant as fuel
• do not need to control air intake so combustion stays the same no matter the speed
• can be used at any altitude
• can start from initial velocity of 0

Scramjet:

• must be travelling at supersonic speeds
• has to use full aircraft frame to control air intake
• blowout limit issues
• high speeds mean high heating so a lot of cooling required
• highly sensitive system
• thermal management limit

Question 5

Draw scramjet design

Answer 5

PIC

Question 6

Discuss pro’s and con’s of SABRE concept

Answer 6

Pros:

1. Cooling inlet air means higher density
2. Lower temp means lighter alloys can be applied
3. Can transition between air breathing and pure rocket
4. Expansioin deflection nozzle achieves altitude compensation and reduces performance losses
5. Can be tested on the ground

Cons:

1. It has to use cryogenic fuels
2. Complex design and heat exchanger

Question 7

Describe difference between pulse jet and PDEs

Answer 7

• Pulse jet combusts using deflagration, PDEs uses detonation
• PDEs - pressure increases significantly more during combustion
• PDEs is supersonic combustion, Pulse jet is subsonic
• Detonation transfers heat via shock, Pulse jet is conduction

Question 8

Why can pulse jet start from static and ramjets can’t

Answer 8

Pulse jet:
require subsonic air inlet flow which is possible from static

Ramjets:
require supersonic air inlet flow for combustion

Question 9

Draw T-S diagram for pulsejet

Answer 9

stages 3-4 entropy stays constant (vertical line)