Technical analysis of the role, components, and limitations of an afterburner in a modern fighter jet.

The principle of afterburning

Afterburning is a power boost phase integrated into military turbojet engines. It is found in almost all modern supersonic fighter jets. Its purpose is clear: to provide a short-term boost by injecting fuel into the hot gases at the turbine outlet, just before the nozzle.

The operation is based on a simple phenomenon: some of the oxygen contained in the gases leaving the combustion chamber has not been consumed. This residual oxygen allows for additional combustion if fuel is injected into the rear of the engine. This mixture ignites on contact with the oxygen, causing a sudden increase in the temperature and volume of the gases. The result is an increase in thrust of around 40 to 70%, depending on the engine.

However, an afterburner engine remains inefficient during cruise flight. Kerosene consumption increases exponentially. For example, an F110-GE-129 used on F-16s consumes up to 180 liters per minute in afterburner mode, compared to 60 liters/min in dry mode.

Afterburning is therefore a temporary system. It is used for short takeoffs, rapid climbs, air combat, or to break the sound barrier. The phase is not continuous: on some aircraft, such as the Rafale, fractional or intermittent afterburning allows thrust to be modulated without remaining in full afterburning.

Modern fighter aircraft incorporate afterburning as a tactical option, not as a permanent flight mode. It is activated by the pilot via the throttle lever or automatically on certain flight profiles.

A set of components dedicated to secondary combustion

An afterburner system consists of several precise components located in the rear section of the turbojet engine. Their role is to ensure stable combustion without disrupting the gas flow or creating destructive turbulence.

The main component is the fuel injector located after the turbine. It sprays the fuel (often JP-8 or F-44) in a pulverized form. This fuel mixes with the hot gases leaving the turbine.

The flame stabilizer grid, or flame holder, is essential. It slows down the flow of gases locally to keep the flame alive. This device is often shaped like an inverted V, perforated, and made of an alloy resistant to temperatures exceeding 1,200°C.

The system also includes an igniter, often plasma or high-voltage spark, capable of initiating secondary combustion. In general, this system assists in starting the afterburner for a few seconds.

Finally, the critical section is the variable nozzle. To contain the increase in pressure and temperature, the nozzle opens mechanically (between 15 and 35% more depending on the operating mode). This system, composed of movable titanium petals, is controlled by hydraulic actuators and thermal sensors.

The nozzle is the nerve center. If its opening is incorrectly calibrated, the excess pressure will destroy the engine. In afterburner mode, the exhaust temperature can reach 1,800 to 2,200°C, compared to 950°C in dry mode.

Some engines, such as the Russian Saturn AL-31F and the Pratt & Whitney F119, incorporate a steerable vector nozzle, which improves maneuverability without losing thrust. These systems further complicate thermal and mechanical management.

An essential but energy-intensive performance gain

Afterburning offers an immediate performance gain that is essential in certain phases of flight. In particular, it enables aircraft to break the sound barrier, climb vertically at high speed, and engage in close combat.

On the Rafale, the M88-2 engine develops 50 kilonewtons in dry mode, but 75 kN with afterburner. On the F-22, the two F119-PW-100 engines go from 116 kN to 156 kN each with afterburner.

This extra power is achieved without complex architecture, unlike civil turbofan engines. On the other hand, fuel consumption skyrockets. At full afterburner, an aircraft can consume up to 2 tons of fuel in less than 10 minutes.

This directly affects the range. An F-16C with external fuel tanks can fly 3,200 km in economy mode. With frequent afterburner use, this range drops to less than 1,500 km.

Thermal constraints are also severe. Titanium and ceramic components must withstand high expansion. The engine’s service life is reduced: frequent use of afterburners shortens maintenance cycles. An F110-GE-129 engine has a maintenance interval of 4,000 hours in normal use, reduced to 1,000 hours in intensive use.

For this reason, afterburner training is limited to what is strictly necessary. Simulators or dry runs are preferred to preserve the equipment. In actual operation, every minute of afterburner use is planned, as it has a direct impact on the mission’s logistics.

Technology now facing competition from supersonic dry thrust engines

The use of afterburners remains a temporary technical solution to the demands of supersonic flight. Recent fighter aircraft programs aim to eliminate it by providing sufficient dry thrust. The term supercruise refers to this ability to maintain supersonic flight without afterburners.

The F-22 Raptor is capable of flying at Mach 1.6 without firing its afterburners. This reduces the infrared signature, conserves fuel, and increases tactical discretion. Conversely, a Su-35S or Eurofighter Typhoon reaches Mach 1.2 to 1.3 in dry mode, and only exceeds this speed with afterburners.

Current research into sixth-generation engines, such as General Electric’s XA100, aims to integrate adaptive cycles: variable flow, optimized efficiency, and reduced afterburning. These engines are expected to achieve more than 180 kN of dry thrust with improved energy efficiency.

At the same time, thermal constraints remain a limitation. Ultra-resistant alloys and ceramics are expensive. The price of a modern afterburner engine exceeds $12 million per unit for aircraft such as the F-35.

Finally, on a strategic level, some countries are abandoning afterburners for reasons of discretion. The thermal signature of an aircraft with afterburners can be detected by infrared sensors from 80 kilometers away, even without active radar.

The logical evolution is therefore towards more fuel-efficient engines capable of maintaining supersonic speeds without resorting to secondary fuel injection. However, this transition remains limited by industrial constraints, immediate tactical needs, and development costs.

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