An afterburner is a secondary combustion system in a jet engine that injects extra fuel directly into the hot exhaust stream, producing a dramatic boost in thrust. It’s the component responsible for the long visible flame you see trailing behind fighter jets during takeoff or high-speed maneuvers. Afterburners are simple in concept but demanding in engineering, and they come with significant tradeoffs in fuel consumption and heat management.
How Afterburners Work
In a standard jet engine, fuel burns inside a combustion chamber surrounded by a large volume of air pulled in by the compressor. Not all the oxygen in that air gets used during combustion. By the time the exhaust gases pass through the turbine and head toward the back of the engine, there’s still enough unburned oxygen to support a second round of combustion.
An afterburner exploits this leftover oxygen. Fuel is sprayed through ring-shaped injectors (called spray bars or hoops) directly into the hot exhaust stream behind the turbine. That fuel ignites and burns, adding energy to the exhaust and accelerating it to much higher velocities. The result is a substantial jump in thrust, though the process is less efficient than the primary combustion inside the engine’s main chamber. You’re getting more push, but you’re burning through fuel at a much faster rate to get it.
In engines with a bypass design, where some air flows around the core rather than through it, the bypass and core exhaust streams are typically mixed together before afterburner fuel is injected. This gives the afterburner a larger volume of oxygen-rich gas to work with.
Keeping the Flame Lit at 1,500 MPH
One of the core engineering challenges is keeping a flame burning inside a stream of gas moving at extremely high speed. At those velocities, a flame would simply blow out, the same way wind extinguishes a candle. Afterburners solve this with components called flameholders, which are metal structures shaped to deliberately create pockets of turbulence and slow-moving recirculating air. These recirculation zones act as sheltered anchoring points where the flame can burn stably, even as the surrounding exhaust rushes past at high velocity. The design of these flameholders, including variations like V-shaped gutters and double-wall struts, is one of the most carefully engineered aspects of an afterburner system.
Why the Nozzle Has to Change Shape
When an afterburner kicks on, the exhaust gas temperature and volume spike dramatically. If the exhaust nozzle stayed the same size, that sudden pressure increase would back up into the engine and force the compressor into a stall, effectively choking the engine. To prevent this, afterburner-equipped engines use a variable-area nozzle: a ring of overlapping metal petals at the tail of the engine that can open wider or close tighter depending on conditions.
When the afterburner ignites, the nozzle opens to accommodate the larger volume of hot gas. This also ensures the exhaust fully expands to match the surrounding air pressure before it exits, which maximizes the thrust produced. At different altitudes and flight speeds, the nozzle adjusts continuously to maintain optimal expansion. If you watch footage of a fighter jet engaging its afterburner, you can often see the nozzle petals flare open just before the flame appears.
Surviving 3,500°F Exhaust
The gas temperature at the afterburner outlet can reach roughly 2,200 Kelvin (about 3,500°F), which far exceeds the melting point of the metals used to build the engine’s tailpipe. Without protection, the afterburner would destroy itself within seconds.
Engineers address this with heat shields, thin-walled structures installed inside the afterburner duct. The most common protection method is film cooling, where a thin layer of cooler air is directed along the inner surface of the liner to insulate it from the scorching exhaust. More advanced designs use a technique called impingement/effusion cooling, where cool air is first jetted against the back side of the heat shield (impingement) and then seeps through tiny holes to form a protective film on the hot side (effusion). These layered cooling systems allow the afterburner to operate at temperatures that would otherwise be impossible for any known structural material to withstand.
When Pilots Actually Use Them
Afterburners are not meant for sustained use. Because they burn fuel so rapidly, they’re reserved for situations where a short burst of maximum thrust is worth the cost. The most common scenarios include takeoff from short runways or aircraft carriers, rapid acceleration to intercept a target, breaking through the transonic speed range (the drag-heavy zone around Mach 1), and emergency combat maneuvers where raw speed is a matter of survival.
Most supersonic military aircraft can only sustain speeds above Mach 1 in short bursts with afterburners engaged. Once the afterburner is switched off, they slow back below the sound barrier. A small number of aircraft can maintain supersonic flight on normal engine power alone, a capability called supercruise. The F-22 Raptor is the most well-known example. This distinction matters tactically because supercruise allows sustained high speed without the massive fuel penalty or the heat signature that afterburners create.
Concorde, the famous supersonic airliner, used afterburners during takeoff to handle weight increases that came after its initial design phase. It also used them to push through the high-drag transonic range, not because it strictly needed the extra thrust at cruise, but because it was available and improved the economics of the flight profile.
A Brief History
The first commercially built afterburner in the United States was produced by Ryan Aeronautical and demonstrated on April 25, 1946. It was fitted to a General Electric I-16 engine, the same powerplant used in the Ryan FR-1 Fireball, which was the Navy’s first aircraft to incorporate a jet engine. From that point, afterburner technology became standard equipment on nearly every generation of military fighter and interceptor. The SR-71 Blackbird, which entered service in the 1960s, was designed to cruise continuously at supersonic speed with afterburners running, a unique operational profile that demanded extraordinary advances in materials, cooling, and fuel systems.
Today, afterburners remain essential for combat aircraft, where the ability to generate sudden, overwhelming thrust in critical moments outweighs the cost in fuel and engine wear. They are not used in commercial aviation (Concorde being the notable exception) because the fuel consumption makes them economically impractical for routine passenger flights.