1. A method of extracting more power from Internal Combustion Engines
JET ENGINE PROPULSION
Chapter 9
Thrust Augmentation System
A method of extracting more power from Internal Combustion Engines

2. Thrust Augmentation Piston engines:- Supercharging or turbo charging
Forced air aspiration
Higher Octane fuels
More power per bang
Gas turbines engines:-
Booster engines
HS121 Trident and early V/STOL a/c
Water injection + more fuel
Methanol – Argosy and Brittannia
Water injection
Argosy and Brittannia
Afterburning
Mainly military but also Concorde
Other methods
Rocket boosters
RATO – Rocket Assisted Take-Off
Single use only
Hercules

3. Thrust Augmentation
C130 Hercules JATO Take-Off

4. Thrust Augmentation Water Methanol Injection
Older style engines lacked power at high ambient temperature and therefore
required some way of boosting power to be able to take-off.
Modern engines do not require this as they are designed to cope with high
ambient temperatures.
The limiting factor in achieving maximum thrust is the maximum burner temperature.
Once this is reached no more power is available.
But by injecting water into the airflow it cools the airflow and increases pressure and therefore density.
This reduces the burner temperature so more fuel (can be methanol mixed with
the water) can be added to regain maximum burner temperature and so achieve
more power.
Using water injection continuously would damage the engine as it changes the
combustion characteristics of the engine.
Also water weighs more than fuel and the extra weight needs more power to
overcome it.
A small amount of water is carried to be used just for take-off and initial climb.

5. Thrust Augmentation Water Methanol Injection Dart Engine Series
Water Methanol Tank and Pump
Dart Engine Series
How is it injected?
Prop Shaft Torque (ENGINE POWER)
Torque Pressure (ENGINE POWER)
Water Methanol Control Unit
In the Dart engine, more power means coarser propeller pitch = more thrust.
Use limited because of combustion characteristics

6. Thrust Augmentation Water Injection Rolls-Royce Spey Series
Increased Primary Fuel flow
Primary Fuel flow
Water flow
Take a closer look here
Water cools the burner which drops the burner temperature.
This allows the maximum temperature control system to add more fuel to regain maximum
burner temperature
This will allow RPM to increase and therefore the airflow so producing more power.

7. Reheat System (Afterburner)
Thrust Augmentation
Engine Rear End
Reheat System (Afterburner)
Heat Shields
Variable Nozzle
Vapour Gutters
Spray Tubes

8. Thrust Augmentation

9. Engine Gas Stream without Reheat
Thrust Augmentation
Engine Gas Stream without Reheat
Variable Nozzle ‘Closed’

10. Reheat Starts with Vapour Gutters Spraying Fuel
Thrust Augmentation
Reheat Starts with Vapour Gutters Spraying Fuel

11. Then Spray Tubes add more fuel to combustion process
Thrust Augmentation
Then Spray Tubes add more fuel to combustion process
And Variable Nozzle ‘Opens’
This is to prevent higher jet pipe pressure
to ensure that reheat has no effect on jet engine

12. Thrust Augmentation Typical Reheat System
Rolls-Royce Phantom Spey and Jaguar Adour series

13. MacDonald Douglas F4 Phantom – Reheat Lit
Thrust Augmentation
MacDonald Douglas F4 Phantom – Reheat Lit
Visible ‘Shock’ waves appear in exhaust plume!
FA18 Hornet on Carrier Take-off – Reheat Lit
Does the Afterburner get hot?
Just a little bit!!
Use of the afterburner is restricted to take-off and combat only (except Concorde of course) due to the extremely high fuel consumption rate

14. Thrust Augmentation
Typhoon