Transcript Thrust Augmentation

JET ENGINE PROPULSION
Chapter 9
Thrust Augmentation System
A method of extracting more power from Internal Combustion Engines
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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
Hercules
Single use only
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C130 Hercules JATO Take-Off
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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.
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Water Methanol Injection
Dart Engine Series
Water Methanol
Tank and Pump
How is it injected?
Prop
Torque
Shaft
Pressure
Torque
(ENGINE
POWER)
Water Methanol Control Unit
In the Dart engine, more power means coarser propeller pitch = more thrust.
Use limited because of combustion characteristics
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Water Injection
Increased
Primary
Primary
Fuel flow
Fuel flow
Rolls-Royce Spey Series
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.
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Engine
Rear End
Reheat System
(Afterburner)
Variable
Nozzle
Spray Tubes
Vapour Gutters
Heat
Shields
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Engine Gas Stream without Reheat
Variable Nozzle ‘Closed’
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Reheat Starts with Vapour Gutters Spraying Fuel
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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
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Typical Reheat System
Rolls-Royce Phantom Spey and Jaguar Adour series
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MacDonald Douglas F4 Phantom – Reheat Lit
Visible ‘Shock’ waves appear in exhaust plume!
Does the Afterburner get hot?
FA18 Hornet on Carrier
Take-off – Reheat Lit
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
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Typhoon