How does an afterburner work?

What is an afterburner?

An afterburner (often called reheat) is a supplementary combustion system located downstream of the turbine in many military jet engines. Its purpose is straightforward: deliver a massive, short-duration thrust boost.

By dumping jet fuel directly into the hot exhaust stream and igniting it, the engine shifts from standard dry thrust to augmented thrust. This rapid shift improves acceleration during critical flight phases.

How does an afterburner work?

The system works by introducing additional thermal energy just after the turbine stage. Once activated, it sprays a large volume of fuel straight into the hot exhaust.

Standard jet engine combustion leaves plenty of unburnt oxygen behind, so this secondary fuel ignites almost instantly. The resulting combustion heats and expands the gases, spiking their stagnation temperature and exit velocity as they pass through the nozzle.

Why does thrust increase?

Thrust surges primarily because the afterburner accelerates exhaust gas to a much higher velocity. The added fuel mass contributes slightly, but the real driving force is the expansion of heated gases.

This expansion depends on the temperature ratio inside the jet pipe before and after secondary combustion, pushing momentum higher at the nozzle exit. The result is a 40-70% thrust gain, without any need for a larger engine core.

What parts make it work?

Several components work together to maintain stable secondary combustion. Fuel injectors spray aviation fuel directly into the exhaust stream.

Because that air travels at extreme velocities, flame holders create localized pockets of turbulence and lower speed, keeping the flame lit so it doesn’t blow out. Heat-resistant liners and cooling air gaps protect the engine structure from the thermal loads before the expanding gases exit through the adjustable rear nozzle.

Why do afterburners need variable nozzles?

A variable-geometry nozzle is essential for managing exhaust flow during thrust augmentation. As temperatures rise during reheat, the nozzle area must expand to prevent high-pressure gases from backing up into the engine.

If the nozzle stayed fixed, that pressure backflow could cause a compressor stall. By mechanically opening the nozzle, the engine transitions smoothly between dry and augmented thrust.

How much fuel does it use?

Fuel consumption during afterburner use is enormous, often more than doubling the specific fuel consumption compared to dry thrust. Injecting raw fuel into the exhaust bypasses the efficient core combustion process entirely, creating a direct tradeoff between thrust and fuel economy.

The M88 engine, for instance, reaches a specific fuel consumption of roughly 47.11 g/(kn·s) with the afterburner on, compared to around 21-23 g/(kn·s) in dry operation. That burn rate is why pilots use afterburners only in brief spurts.

When are afterburners used?

Because of the fuel penalty, military aircraft limit afterburner use to short bursts. They’re critical for short-runway and carrier takeoffs, getting heavy jets to lift-off speed in seconds.

Pilots also use them for supersonic dashes and demanding air combat maneuvers. Afterburners are rare in civilian aircraft, with the Concorde and Tupolev Tu-144 being the well-known exceptions.

What temperatures do they reach?

During secondary combustion, flame temperatures inside the jet pipe quickly exceed 1,700°C.

Keeping the jet pipe and nozzle intact under that kind of heat requires advanced metallurgy, heat shields, and specialized impingement cooling techniques.

What are shock diamonds?

Watch a military jet at full power, and you might notice bright, repeating geometric shapes glowing in the exhaust plume.

These are shock diamonds, and they form from pressure gradients and standing shock waves in the supersonic exhaust. As gases exit the nozzle, they expand and compress repeatedly while trying to match ambient atmospheric pressure, producing that glowing, diamond-shaped trail behind the aircraft.

How do afterburners compare to super cruise?

Afterburners deliver acceleration quickly, but at a steep cost to range. Super cruise takes a different approach, letting an aircraft sustain supersonic flight on dry thrust alone, with no fuel dumped into the exhaust.

The F-22 Raptor can reach high supersonic speeds this way, without touching the afterburner. That means no fuel penalties and none of the strict time limits that come with reheat.