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

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

Thrust Augmentation C130 Hercules JATO Take-Off

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.

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

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.

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

Thrust Augmentation

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

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

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

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

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

Thrust Augmentation Typhoon