An afterburner is a system that gives some jet engines a short burst of extra thrust. It is most common on military fighter aircraft, where rapid acceleration, steep climbs, or supersonic flight may be needed. The idea is simple: burn more fuel in the fast, hot exhaust after it leaves the main turbine.
This creates a dramatic flame and a powerful push, but it uses fuel very quickly.
Inside a jet engine, air is compressed, mixed with fuel, burned, and sent through a turbine before exiting the nozzle. In an afterburner, extra fuel is sprayed into this hot exhaust stream, where there is still enough oxygen to burn. The expanding gases leave through a nozzle at higher speed, increasing thrust according to Newton's third law.
Pilots use afterburners only when the extra performance is worth the high fuel cost and heat stress.
Key Facts
- An afterburner adds fuel behind the turbine, not inside the main combustion chamber.
- Extra fuel burns in the exhaust stream and raises the exhaust gas temperature.
- Thrust increases when exhaust leaves the engine with greater momentum: F = change in momentum per second.
- Jet thrust can be estimated by F = mass flow rate × change in velocity.
- Afterburners can greatly increase thrust, but fuel use can rise several times above normal operation.
- A variable nozzle opens wider during afterburner use to handle the larger volume of hot expanding gas.
Vocabulary
- Afterburner
- A device that injects and burns extra fuel in the exhaust stream of a jet engine to produce more thrust.
- Thrust
- The forward force produced when an engine pushes mass, such as hot exhaust gas, backward.
- Turbine
- A rotating engine section that extracts energy from hot gas to drive the compressor.
- Exhaust nozzle
- The rear opening of a jet engine that shapes and speeds up the escaping exhaust gases.
- Fuel flow rate
- The amount of fuel burned per unit time, often measured in kilograms per second or liters per minute.
Common Mistakes to Avoid
- Thinking the afterburner is a second engine is wrong because it is an added burning section behind the main jet engine, not a separate engine.
- Assuming afterburners are fuel efficient is wrong because they trade a very large fuel burn for a temporary thrust boost.
- Placing the afterburner before the turbine is wrong because afterburning happens downstream of the turbine in the exhaust duct.
- Believing bigger flames always mean higher speed is wrong because aircraft speed also depends on drag, altitude, aircraft mass, and how long the afterburner can be used.
Practice Questions
- 1 A fighter engine produces 80,000 N of thrust without afterburner and 120,000 N with afterburner. What is the percent increase in thrust?
- 2 An aircraft burns 1.5 kg of fuel per second in dry thrust and 6.0 kg per second with afterburner. How much more fuel does it burn during 2 minutes of afterburner use than during 2 minutes of dry thrust?
- 3 Explain why afterburners are useful for takeoff, combat maneuvers, or supersonic flight, but are not used continuously during normal cruising.