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A US Navy F/A-18 Hornet being launched from the catapult at maximum power

An afterburner (or reheat in British English) is an additional combustion component used on some jet engines, mostly those on military supersonic aircraft. Its purpose is to increase thrust, usually for supersonic flight, takeoff, and combat. The afterburning process injects additional fuel into a combustor ("burner") in the jet pipe behind (i.e., "after") the turbine, "reheating" the exhaust gas. Afterburning significantly increases thrust as an alternative to using a bigger engine with its added weight penalty, but at the cost of increased fuel consumption (decreased fuel efficiency) which limits its use to short periods. This aircraft application of "reheat" contrasts with the meaning and implementation of "reheat" applicable to gas turbines driving electrical generators and which reduces fuel consumption.[1]

SR-71 Blackbird in flight with J58 engines at maximum power, with numerous shock diamonds visible in the exhaust

Jet engines are referred to as operating wet when afterburning and dry when not.[2] An engine producing maximum thrust wet is at maximum power, while an engine producing maximum thrust dry is at military power.[3]

Principle

[edit]

The first jet engine with after-burner was the E variant of Jumo 004.[4]

Rear part of a sectioned Rolls-Royce Turbomeca Adour. The afterburner with its four combustion rings is clearly seen at the center.

Jet-engine thrust is an application of Newton's reaction principle, in which the engine generates thrust because it increases the momentum of the air passing through it.[5] Thrust depends on two things: the velocity of the exhaust gas and the mass of the gas exiting the nozzle. A jet engine can produce more thrust by either accelerating the gas to a higher velocity or ejecting a greater mass of gas from the engine.[6] Designing a basic turbojet engine around the second principle produces the turbofan engine, which creates slower gas, but more of it. Turbofans are highly fuel efficient and can deliver high thrust for long periods of time, but the design tradeoff is a large size relative to the power output. Generating increased power with a more compact engine for short periods can be achieved using an afterburner. The afterburner increases thrust primarily by accelerating the exhaust gas to a higher velocity.[7]

The following values and parameters are for an early jet engine, the Pratt & Whitney J57, stationary on the runway,[8] and illustrate the high values of afterburner fuel flow, gas temperature and thrust compared to those for the engine operating within the temperature limitations for its turbine.

The highest temperature in the engine (about 3,700 °F (2,040 °C)[9]) occurs in the combustion chamber, where fuel is burned (at an approximate rate of 8,520 lb/h (3,860 kg/h)) in a relatively small proportion of the air entering the engine. The combustion products have to be diluted with air from the compressor to bring the gas temperature down to a specific value, known as the Turbine Entry Temperature (TET) (1,570 °F (850 °C)), which gives the turbine an acceptable life.[10] Having to reduce the temperature of the combustion products by a large amount is one of the primary limitations on how much thrust can be generated (10,200 lbf (45,000 N)). Burning all the oxygen delivered by the compressor stages would create temperatures (3,700 °F (2,040 °C)) high enough to significantly weaken the internal structure of the engine, but by mixing the combustion products with unburned air from the compressor at (600 °F (316 °C)) a substantial amount of oxygen (fuel/air ratio 0.014 compared to a no-oxygen-remaining value 0.0687) is still available for burning large quantities of fuel (25,000 lb/h (11,000 kg/h)) in an afterburner. The gas temperature decreases as it passes through the turbine (to 1,013 °F (545 °C)). The afterburner combustor reheats the gas, but to a much higher temperature (2,540 °F (1,390 °C)) than the TET (1,570 °F (850 °C)). As a result of the temperature rise in the afterburner combustor, the gas is accelerated, firstly by the heat addition, known as Rayleigh flow, then by the nozzle to a higher exit velocity than that which occurs without the afterburner. The mass flow is also slightly increased by the addition of the afterburner fuel. The thrust with afterburning is 16,000 lbf (71,000 N).

The visible exhaust may show shock diamonds, which are caused by shock waves formed due to slight differences between ambient pressure and the exhaust pressure. This interaction causes oscillations in the exhaust jet diameter over a short distance and causes visible banding where pressure and temperature are highest.

Thrust augmentation by heating bypass air

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The plenum-chamber-burning Bristol Siddeley BS100 engine had thrust augmentation at the front nozzles only.

Thrust may be increased by burning fuel in a turbofan's cold bypass air, instead of the mixed cold and hot flows as in most afterburning turbofans.

An early augmented turbofan, the Pratt & Whitney TF30, used separate burning zones for the bypass and core flows with three of seven concentric spray rings in the bypass flow.[11] In comparison, the afterburning Rolls-Royce Spey used a twenty chute mixer before the fuel manifolds.

Plenum chamber burning (PCB) was partially developed for the vectored thrust Bristol Siddeley BS100 engine for the Hawker Siddeley P.1154 until the program was cancelled in 1965. The cold bypass and hot core flows were split between two pairs of nozzles, front and rear, in the same manner as the Rolls-Royce Pegasus, and fuel was burned in the fan air before it left the front nozzles. It would have given greater thrust for take-off and supersonic performance in an aircraft similar to, but bigger than, the Hawker Siddeley Harrier.[12]

Duct heating was used by Pratt & Whitney for their JTF17 turbofan proposal for the U.S. Supersonic Transport Program in 1964 and a demonstrator engine was run.[13] The duct heater used an annular combustor and would be used for takeoff, climb and cruise at Mach 2.7 with different amounts of augmentation depending on aircraft weight.[14]

Design

[edit]
Afterburners on a British Eurofighter Typhoon

A jet engine afterburner is an extended exhaust section containing extra fuel injectors. Since the jet engine upstream (i.e., before the turbine) will use little of the oxygen it ingests, additional fuel can be burned after the gas flow has left the turbines. When the afterburner is turned on, fuel is injected and igniters are fired. The resulting combustion process increases the afterburner exit (nozzle entry) temperature, resulting in a significant increase in engine thrust. In addition to the increase in afterburner exit stagnation temperature, there is also an increase in nozzle mass flow (i.e. afterburner entry mass flow plus the effective afterburner fuel flow), but a decrease in afterburner exit stagnation pressure (owing to a fundamental loss due to heating plus friction and turbulence losses).

The resulting increase in afterburner exit volume flow is accommodated by increasing the throat area of the exit nozzle. Otherwise, if pressure is not released, the gas can flow upstream and re-ignite, possibly causing a compressor stall (or fan surge in a turbofan application). The first designs, e.g. Solar afterburners used on the F7U Cutlass, F-94 Starfire and F-89 Scorpion, had 2-position eyelid nozzles.[15] Modern designs incorporate not only variable-geometry (VG) nozzles but multiple stages of augmentation via separate spray bars.

To a first order, the gross thrust ratio (afterburning/dry) is directly proportional to the root of the stagnation temperature ratio across the afterburner (i.e. exit/entry).

Limitations

[edit]
An F-4K Phantom of the Royal Navy on a catapult aboard an aircraft carrier deploys full afterburner prior to launch

Due to their high fuel consumption, afterburners are only used for short-duration, high-thrust requirements. These include heavy-weight or short-runway take-offs, assisting catapult launches from aircraft carriers, and during air combat. A notable exception is the Pratt & Whitney J58 engine used in the SR-71 Blackbird which used its afterburner for prolonged periods and was refueled in-flight as part of every reconnaissance mission.

An afterburner has a limited life to match its intermittent use. The J58 was an exception with a continuous rating. This was achieved with thermal barrier coatings on the liner and flame holders[16] and by cooling the liner and nozzle with compressor bleed air[17] instead of turbine exhaust gas.

Efficiency

[edit]
Main article: Propulsive efficiency

In heat engines such as jet engines, efficiency is highest when combustion occurs at the highest pressure and temperature possible, and expanded down to ambient pressure (see Carnot cycle).

Since the exhaust gas already has a reduced oxygen content, owing to previous combustion, and since the fuel is not burning in a highly compressed air column, the afterburner is generally inefficient in comparison to the main combustion process. Afterburner efficiency also declines significantly if, as is usually the case, the inlet and tailpipe pressure decreases with increasing altitude.[citation needed]

This limitation applies only to turbojets. In a military turbofan combat engine, the bypass air is added into the exhaust, thereby increasing the core and afterburner efficiency. In turbojets the gain is limited to 50%, whereas in a turbofan it depends on the bypass ratio and can be as much as 70%.[18]

However, as a counterexample, the SR-71 had reasonable efficiency at high altitude in afterburning ("wet") mode owing to its high speed (Mach 3.2) and correspondingly high pressure due to ram intake.

Influence on cycle choice

[edit]

Afterburning has a significant influence upon engine cycle choice.

Lowering the fan pressure ratio decreases specific thrust (both dry and wet afterburning), but results in a lower temperature entering the afterburner. Since the afterburning exit temperature is effectively fixed,[why?] the temperature rise across the unit increases, raising the afterburner fuel flow. The total fuel flow tends to increase faster than the net thrust, resulting in a higher specific fuel consumption (SFC). However, the corresponding dry power SFC improves (i.e. lower specific thrust). The high temperature ratio across the afterburner results in a good thrust boost.

If the aircraft burns a large percentage of its fuel with the afterburner alight, it pays to select an engine cycle with a high specific thrust (i.e. high fan pressure ratio/low bypass ratio). The resulting engine is relatively fuel efficient with afterburning (i.e. Combat/Take-off), but thirsty in dry power. If, however, the afterburner is to be hardly used, a low specific thrust (low fan pressure ratio/high bypass ratio) cycle will be favored. Such an engine has a good dry SFC, but a poor afterburning SFC at Combat/Take-off.

Often the engine designer is faced with a compromise between these two extremes.

History

[edit]
MiG-23 afterburner

The Caproni Campini C.C.2 motorjet, designed by the Italian engineer Secondo Campini, was the first aircraft to incorporate an afterburner. The first flight of a C.C.2, with its afterburners operating, took place on 11 April 1941.[19][20]

Early British afterburner ("reheat") work included flight tests on a Rolls-Royce W2/B23 in a Gloster Meteor I in late 1944 and ground tests on a Power Jets W2/700 engine in mid-1945. This engine was destined for the Miles M.52 supersonic aircraft project.[21]

Early American research on the concept was done by NACA, in Cleveland, Ohio, leading to the publication of the paper "Theoretical Investigation of Thrust Augmentation of Turbojet Engines by Tail-pipe Burning" in January 1947.[22]

American work on afterburners in 1948 resulted in installations on early straight-wing jets such as the Pirate, Starfire and Scorpion.[23]

The new Pratt & Whitney J48 turbojet, at 8,000 lbf (36 kN) thrust with afterburners, would power the Grumman swept-wing fighter F9F-6, which was about to go into production. Other new Navy fighters with afterburners included the Chance Vought F7U-3 Cutlass, powered by two 6,000 lbf (27 kN) thrust Westinghouse J46 engines.

In the 1950s, several large afterburning engines were developed, such as the Orenda Iroquois and the British de Havilland Gyron and Rolls-Royce Avon RB.146 variants. The Avon and its variants powered the English Electric Lightning, the first supersonic aircraft in RAF service. The Bristol-Siddeley/Rolls-Royce Olympus was fitted with afterburners for use with the BAC TSR-2. This system was designed and developed jointly by Bristol-Siddeley and Solar of San Diego.[24] The afterburner system for the Concorde was developed by Snecma.

Afterburners are generally used only in military aircraft, and are considered standard equipment on fighter aircraft. The handful of civilian planes that have used them include some NASA research aircraft, the Tupolev Tu-144, Concorde and the White Knight of Scaled Composites. Concorde flew long distances at supersonic speeds. Sustained high speeds would be impossible with the high fuel consumption of afterburner, and the plane used afterburners at takeoff and to minimize time spent in the high-drag transonic flight regime. Supersonic flight without afterburners is referred to as supercruise.

A turbojet engine equipped with an afterburner is called an "afterburning turbojet", whereas a turbofan engine similarly equipped is sometimes called an "augmented turbofan".[citation needed]

A "dump-and-burn" is an airshow display feature where fuel is jettisoned, then intentionally ignited using the afterburner. A spectacular flame combined with high speed makes this a popular display for airshows, or as a finale to fireworks. Fuel dumping is used primarily to reduce the weight of an aircraft to avoid a heavy, high-speed landing. Other than for safety or emergency reasons, fuel dumping does not have a practical use.

See also

[edit]

References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Afterburner

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from Grokipedia
An afterburner, also known as reheat in , is an additional combustion component integrated into certain and engines, predominantly those powering military , designed to temporarily augment by injecting fuel into the engine's exhaust stream downstream of the , where it combusts with residual oxygen to accelerate the gases and increase . The working principle of an afterburner exploits the unburned oxygen in the exhaust—typically 10-20% of the total airflow in a —by spraying fuel through into this hot stream, igniting it via holders or the residual heat, which expands the gases and boosts exhaust , often increasing by 50% to over 100% compared to dry without afterburning. This produces a visible from the during operation, especially at night, and is controlled variably in modern to optimize performance. Afterburners trace their origins to , when engineers in , the , and the independently developed the concept to enhance early power; the first American afterburner was built by the (NACA) in 1944, while a British reheat system underwent flight tests on a jet in late 1944. Postwar advancements refined the technology for sustained supersonic flight, with widespread adoption in military aviation during the . Primarily employed in fighter aircraft such as the F-16 Fighting Falcon, F-22 Raptor, and F-35 Lightning II for rapid acceleration, dogfighting, and short takeoffs from carriers, afterburners also powered the supersonic passenger airliner Concorde during takeoff and transonic acceleration, though civilian use is rare due to efficiency concerns. Despite their effectiveness in providing burst thrust—enabling speeds exceeding Mach 2 in some cases—they dramatically elevate fuel consumption, often by a factor of 4 to 10 times the normal rate, limiting operation to mere minutes (typically 5-15) to avoid rapid depletion of onboard fuel reserves. This high inefficiency, coupled with increased engine wear and infrared signature for heat-seeking missile vulnerability, confines afterburners to tactical, high-performance scenarios rather than routine cruising.

Principles of Operation

Basic Principle

An afterburner serves as a post-combustor device in or engines, where additional is injected directly into the hot exhaust stream downstream of the to reheat the gases and promote further expansion. This process occurs without modifying the core engine's compression or primary combustion stages, allowing for selective augmentation during high-demand operations such as takeoff or supersonic flight. The afterburner effectively extends the standard Brayton by incorporating a reheat stage, which adds a second constant-pressure heat addition process after the expansion. In the temperature- (T-s) diagram for this augmented cycle, the core Brayton processes—isentropic compression (1-2), constant-pressure heat addition in the (2-3), isentropic expansion in the (3-4), and constant-pressure heat rejection—are followed by the reheat (4-5), where increases at constant pressure due to fuel combustion, elevating the gas temperature significantly. This elevated temperature then undergoes further isentropic expansion in the (5-6), resulting in higher exhaust and velocity compared to the non-afterburning case. The thrust augmentation arises primarily from the increased exhaust velocity, quantified by the equation for the thrust increase: ΔT=m˙(Ve,after−Ve,core)\Delta T = \dot{m} (V_{e,after} - V_{e,core}) where m˙\dot{m} is the mass flow rate through the engine, Ve,afterV_{e,after} is the exhaust velocity with the afterburner active, and Ve,coreV_{e,core} is the exhaust velocity without it. This difference in velocities stems from the reheated gases achieving higher thermal energy, which converts to greater momentum upon nozzle expansion, while the mass flow rate remains largely unchanged. Afterburner operation leverages the high-velocity exhaust from the , which provides inherent ram recovery in the form of that promotes rapid fuel-air mixing and supports stability by sustaining high flow velocities and temperatures conducive to sustained propagation.

Thrust Augmentation Mechanisms

In afterburners, additional is injected into the exhaust stream downstream of the through spray rings, where it atomizes into a fine spray to facilitate rapid mixing with the oxygen-rich core exhaust gases. This mixing process relies on the high-velocity turbulent flow in the exhaust duct to ensure even distribution, promoting complete and maximizing augmentation. The injected , typically kerosene-based, evaporates quickly due to the elevated temperatures (around 1000-1200 K from the turbine exit), allowing it to blend with the core flow before ignition. Ignition of the fuel-air mixture in the afterburner is achieved through methods such as hot-streak ignition or pilot flames. In the hot-streak approach, an enriched fuel-air mixture is temporarily introduced into one of the primary combustors to generate a high-temperature gas jet that propagates downstream to light the afterburner fuel without requiring separate igniters. Alternatively, pilot flames—sustained by small continuous burners—provide a stable ignition source in the afterburner duct, ensuring reliable light-off under varying conditions. These techniques leverage the residual heat and oxygen from the core flow to initiate efficiently. In low-bypass engines, bypass air plays a in afterburner operation by mixing with the hot core exhaust prior to , which cools the core flow to protect components from excessive temperatures while supplying additional oxygen for . This mixing enhances overall augmentation by increasing the total mass flow through the afterburner, though it must be balanced to avoid reducing exhaust velocity. Afterburners typically boost by 50-100% in engines; for instance, the F100-PW-200 in the F-16 achieves approximately 63% additional in afterburner mode compared to military power. Combustion efficiency in the afterburner is influenced by factors including —the duration the mixture spends in the combustion zone, typically 1-5 milliseconds—and the equivalence ratio (φ), which represents the fuel-to-air ratio relative to stoichiometric conditions. Optimal is achieved at φ ≈ 0.8-1.2, where is near-complete (efficiencies of 90-98%), balancing heat release with minimal unburned hydrocarbons. Shorter s at high Mach numbers can reduce , necessitating duct length designs that provide sufficient reaction time without excessive loss.

Design and Implementation

Key Components

The afterburner system in jet engines relies on several critical hardware components to facilitate controlled of additional in the high-velocity exhaust stream downstream of the . Central to this are holders, which stabilize the against the rapid airflow. These are typically bluff bodies, such as V-gutters or other aerodynamic shapes, designed to create low-velocity recirculation zones that anchor the process. The aerodynamic profile of V-gutters, often triangular in cross-section and arranged in annular arrays, minimizes total pressure loss by optimizing wake formation and reducing drag while ensuring stability across a wide range of Mach numbers up to 0.5 in the afterburner duct. Fuel delivery in the afterburner is handled by specialized injectors and nozzles that ensure efficient atomization and mixing of with the hot exhaust gases. These systems can employ discrete spray bars, each with multiple orifices positioned circumferentially around the duct, or annular manifolds that distribute uniformly through a ring of ports. Discrete designs, common in older turbojets, allow for targeted injection but may introduce uneven mixing, whereas annular configurations promote better radial distribution and reduce hotspots, enhancing efficiency. is injected at pressures exceeding 1.7 MPa (250 psi) to achieve droplet sizes under 50 micrometers for rapid vaporization in the 1000–1500 K environment. To manage the expansion of the heated exhaust and maximize , afterburners incorporate convergent-divergent with variable geometry. These adjust their and exit areas to maintain optimal expansion ratios—typically ranging from 1.5:1 to 2:1 depending on operating conditions—preventing over- or underexpansion that could reduce . Hydraulic actuators, operating at pressures around 6.2 MPa (900 psi), drive the movement of flaps or petals to vary the geometry, enabling seamless transitions between subsonic dry operation and supersonic afterburning modes. Protecting the afterburner liner from extreme loads is essential, as combustion temperatures can reach up to 2000 , far exceeding material limits. Cooling is primarily achieved through film cooling, where cooler air—often sourced from the engine's stream or residual discharge—is injected through slots or holes along the liner to form a protective that shields the walls from direct hot gas impingement. This method can reduce wall temperatures by 300–500 , with cooling air flow rates comprising 2–5% of the total engine , balancing with minimal impact on overall performance.

Integration in Jet Engines

In pure engines, the afterburner is integrated directly into the exhaust duct immediately downstream of the , where is injected into the high-velocity core flow for , augmenting without the complication of bypass streams. This straightforward configuration allows for efficient mixing and within a compact augmentor section, optimized for high-speed military applications. In contrast, engines require more complex integration, particularly in low-bypass designs where the fan airflow is mixed with the exhaust prior to entering the afterburner to provide cooling and dilution for stable . For example, the , a low-bypass afterburning with a of approximately 0.3:1, incorporates this mixing in its augmentor duct to balance augmentation with thermal management, enabling capabilities in like the F-22 Raptor. The nozzle and augmentor duct in afterburner systems are sized to match the core flow characteristics, ensuring adequate residence time for fuel-air mixing and complete combustion while minimizing pressure losses. Typically, the augmentor duct employs a length-to-diameter ratio of 2 to 4:1 to achieve high combustion efficiency, as shorter ratios may lead to incomplete burning and longer ones increase drag and weight. For instance, the J71-A2 turbojet afterburner features a duct length of 11 feet and diameter of 40 inches, yielding an L/D ratio of about 3.3, which supports efficient flame stabilization under varying operating conditions. Nozzle area is variably controlled to maintain optimal exhaust velocity, often converging-diverging in afterburning mode to handle the increased mass flow and temperature. Afterburners are rarely integrated into high-bypass engines due to significant efficiency losses at supersonic speeds, where the large fan airflow generates excessive drag and reduces overall propulsive effectiveness compared to the core's augmented output. However, in variable-cycle designs, afterburners are employed to enable by dynamically adjusting bypass ratios, allowing the engine to shift between high-efficiency subsonic modes and high-thrust supersonic operation without excessive fuel penalty. Such configurations, as explored in advanced prototypes like the General Electric YF120, optimize thrust-to-weight ratios for sustained Mach 1+ flight. Control systems for afterburners ensure seamless transitions between dry (non-afterburning) and wet (afterburning) modes, primarily through full authority digital engine controls () that integrate sensor data for precise fuel scheduling, positioning, and ignition timing. In the F119 engine, the dual-redundant manages afterburner light-off and modulation, preventing stalls or surges by continuously adjusting parameters like exhaust area to maintain inlet temperature limits during mode shifts. This electronic oversight enhances operational reliability and pilot workload reduction across the engine's thrust spectrum.

Performance Characteristics

Efficiency Analysis

The (TSFC) serves as a key metric for assessing afterburner performance, quantifying the required per unit of produced. For engines employing afterburners, the overall TSFC incorporates both the core engine's dry TSFC and the additional injected in the afterburner. This formula highlights how the afterburner's low-pressure contributes disproportionately to use relative to the thrust gain. The of an afterburning experiences a notable decline compared to dry operation, primarily due to incomplete expansion in the and elevated exhaust temperatures that limit . This results in lower in non-afterburning mode, as the afterburner's heat addition occurs at lower , reducing the cycle's overall thermodynamic effectiveness. Such losses underscore the afterburner's role as a short-duration boost rather than a sustained solution. Additionally, decreases because the higher exhaust velocity in afterburner mode is less matched to typical flight speeds. Specific impulse (I_sp), which measures per unit of consumed, further illustrates afterburner inefficiencies, with values ranging from 1000 to 1500 seconds during operation—substantially below the 3000+ seconds achievable by core engines in dry mode. This disparity arises from the afterburner's reliance on high flows for modest increments, yielding lower effective exhaust velocities per unit . For context, a representative core might deliver I_sp around 4000 seconds dry, dropping to approximately 1800 seconds with full afterburner engagement. Thrust augmentation ratios vary by engine type, with afterburners providing 50-100% increases in turbojets but up to 70% in low-bypass s, depending on and operating conditions. Accompanying this is a sharp rise in fuel burn rates, often 3-5 times higher than dry operation, as total fuel flow escalates to sustain the elevated temperatures and mass flows. For instance, in military applications, afterburner activation can elevate fuel consumption from baseline levels of 0.7-0.9 lb/hr/lbf to 2.5-3.5 lb/hr/lbf, emphasizing its use for transient high- demands like takeoff or combat maneuvers.

Operational Limitations

Afterburners impose significant operational constraints on due to their extraordinarily high fuel consumption rates, which can surpass 64,000 pounds per hour in fighters like the F-16 at low altitudes and full power. This rapid depletion limits continuous afterburner usage to typically 5-10 minutes in military fighters to prevent exhausting internal reserves, as exemplified by the F/A-18 Hornet, where internal would be consumed in under 10 minutes at full afterburner. Such brevity restricts afterburners to short-duration, high-thrust scenarios like takeoff, combat maneuvers, or supersonic dashes, after which pilots must revert to dry thrust to conserve for mission completion. Thermal and structural limitations further constrain afterburner operation, as the combustion process elevates temperatures (EGT) beyond 1800 , often reaching 1500–2000°C in the exhaust plume. These extreme conditions demand sophisticated systems, such as cooling or , to protect the afterburner liner and from burnout and thermal fatigue; without such measures, sustained exposure risks structural failure, as evidenced in high-temperature tests where temperatures alone approached 1255 (982°C), with exit temperatures far higher. The heightened thermal output from afterburners dramatically increases the aircraft's infrared (IR) signature, primarily through the hot exhaust plume, which enhances detectability by enemy IR-guided missiles and sensors at extended ranges. In modern stealth aircraft, this vulnerability is addressed via exhaust suppression techniques, including the mixing of hot core flow with cooler bypass or ambient air to dilute and lower plume temperatures, thereby reducing the overall IR emissivity and line-of-sight visibility of the heat source. Afterburner engagement also exacerbates noise and emissions challenges, generating jet levels 5–10 dB higher than military power settings due to intensified turbulent mixing and shock cell structures in the exhaust. This contributes to sonic booms during supersonic operations, where the amplified exhaust velocity propagates pressure waves over large areas. Additionally, the high-temperature, fuel-rich combustion produces elevated emissions compared to non-afterburning modes, as measured in tests where NOx concentrations varied significantly with power level and afterburner activation. Although afterburners are predominantly , their rare use in civilian supersonic transports like the falls under strict regulatory limits from ICAO and FAA on takeoff/landing (e.g., Chapter 14 standards) and emissions (e.g., CAEP/8 limits of 15–20 g/kN), which constrain deployment to minimize environmental impact.

Influence on Engine Design

Impact on Cycle Choices

The inclusion of an afterburner in jet engines strongly favors low-bypass or pure cycles over high-bypass configurations, primarily because these cycles maintain higher core flow temperatures and better align the bypass and core streams for effective afterburner operation. In low-bypass designs, the reduced fan airflow allows for mixing with the hotter exhaust prior to , enabling stable and thrust augmentation without excessive cooling of the exhaust gases. High-bypass engines, by contrast, produce cooler bypass air that would dilute the afterburner flame, reducing and requiring complex mixing systems. Afterburner integration introduces key trade-offs in compressor and turbine design, particularly regarding turbine inlet temperature (TIT). Elevating TIT enhances dry (non-afterburning) thrust by increasing overall cycle efficiency and power extraction in the turbine, but it also raises the exhaust temperature entering the afterburner, which can limit the available temperature margin for additional fuel injection and combustion without exceeding material limits. This necessitates careful balancing in compressor pressure ratios and turbine cooling strategies to optimize baseline performance while preserving afterburner capability, as higher TIT reduces the delta-T available for reheat. Afterburners particularly suit Brayton cycles with high overall pressure ratios, typically exceeding 20:1, which compress air more effectively to support the elevated temperatures and mass flows required for significant gains. For instance, the engine, powering the , achieves an overall pressure ratio of 26:1 in its low-bypass configuration, enabling efficient operation across subsonic and supersonic regimes. In terms of overall , afterburning shifts the optimal toward higher exhaust velocities, which is essential for supersonic flight where flight speeds approach or exceed Mach 1. This adjustment improves the matching between exhaust and flight velocities, thereby enhancing compared to subsonic-optimized cycles that prioritize lower velocities for fuel economy. Such designs are critical for applications demanding rapid and sustained high-speed .

Advanced Configurations

Advanced configurations of afterburners have evolved to mitigate limitations such as high fuel consumption and signatures, incorporating variable and adaptive systems that optimize performance across flight regimes. cycle engines, exemplified by General Electric's XA100 adaptive cycle demonstrator, employ a three-stream to dynamically adjust airflow between the core, bypass, and a , enabling partial thrust augmentation without relying on full afterburner activation. This design facilitates —sustained supersonic flight—by blending high-thrust modes for acceleration with efficient partial augmentation, reducing fuel burn compared to traditional fixed-geometry afterburners. The XA100 achieves up to 30% greater range and 20% increased thrust over legacy engines while supporting at Mach 1.2 or higher without afterburner, as demonstrated in ground tests. In stealth-oriented designs, augmented turbofans integrate serpentine ducts to conceal engine components and minimize cross-section (RCS). These S-shaped inlets, common in afterburning turbofans like those powering the F-22 Raptor and F-35 Lightning II, block direct line-of-sight to the blades and fan, scattering incoming waves and significantly reducing frontal RCS in key frequency bands. The ducts also incorporate radar-absorbent materials on internal surfaces to further attenuate reflections, balancing aerodynamic losses with stealth gains; pressure recovery remains above 95% at subsonic speeds despite the curvature. This configuration addresses afterburner plume visibility indirectly by shielding the hot core, though exhaust treatments are still required for reduction. As of 2025, adaptive cycle engine technology from programs like 's XA101, originally developed under the U.S. Air Force's Adaptive Engine Transition Program (AETP), is advancing under the Next Generation Adaptive Propulsion (NGAP) program. This includes variable bypass ratios for optimized fuel-air mixing in augmentors, delivering demonstrated goals of 10% greater and 25% improved compared to legacy engines, with ground tests validating stable partial afterburning modes reducing specific fuel consumption by 15-20% during high-speed operations. In February 2025, both GE and completed detailed design reviews for NGAP engines, focusing on applications such as the NGAD. Emerging concepts focus on and plasma ignition systems to overcome ignition delays and emissions challenges in afterburners. ignition, using focused pulses to create plasma kernels, enables faster light-off times—under 1 —compared to traditional spark systems, allowing leaner fuel mixtures that cut emissions by up to 50% while improving relight reliability at high altitudes. Plasma-assisted ignition further enhances flame stability in variable cycle setups by generating non-thermal plasma to accelerate kinetics, potentially reducing afterburner response time by 30% and enabling operation in vitiated environments. These technologies, explored in aerospace propulsion reviews, represent high-impact future directions for reducing environmental impact and boosting operational flexibility in next-generation engines.

Historical and Modern Developments

Early Innovations

The development of the afterburner began during , with German engineers incorporating the technology into prototype versions of the turbojet engine in 1944. Intended for the fighter, the Jumo 004C variant featured auxiliary and an afterburner to boost , marking one of the earliest attempts at practical reheat augmentation in a production-oriented engine, though it remained experimental and was not deployed in operational aircraft. Parallel efforts occurred in the United States, where the National Advisory Committee for Aeronautics (NACA) developed the first American afterburner in 1944 using a General Electric I-A turbojet. In the United Kingdom, a reheat system underwent flight tests on a Gloster Meteor jet in late 1944. Following the war, afterburner technology saw rapid adoption in the United States, exemplified by the General Electric J47 turbojet, which became the first afterburning engine to complete qualification testing in 1948 for the U.S. Navy. This axial-flow engine, with its integrated afterburner, delivered significantly enhanced thrust for supersonic applications and powered early jet fighters like the North American F-86 Sabre variants, establishing afterburners as a standard feature in military turbojets. In the , British engineers advanced afterburner design through the turbojet, introducing improved flame stabilization techniques to ensure reliable ignition and sustained in the exhaust stream. These innovations, tested in experimental configurations on aircraft like the , addressed variability in airflow and fuel mixing, enabling more consistent performance during reheat operation. Early afterburners faced significant challenges, including combustion instability that caused pressure oscillations and flame blowout, as well as extremely short operational life—often under 10 hours—due to material degradation from extreme temperatures exceeding 1,700°C. These issues were progressively resolved in the through metallurgical advancements, such as the development of dispersion-strengthened superalloys like those incorporating yttria (Y₂O₃), which improved heat resistance and extended for sustained use.

Contemporary Applications

In contemporary , afterburners remain a critical component for high-performance fighter jets, enabling short bursts of and enhanced maneuverability. The exemplifies this application, powered by two F119-PW-100 engines equipped with afterburners and two-dimensional nozzles that provide ±20° pitch control for superior agility in combat scenarios. This integration allows the F-22 to achieve capability without afterburners for efficient transit, while engaging afterburners for rapid acceleration and evasion tactics. Recent advancements in fifth-generation stealth fighters continue to incorporate afterburners with stealth-oriented modifications. China's , operational since 2017, utilizes the indigenous WS-10C engine featuring serrated afterburner nozzles designed to reduce signatures and enhance evasion by scattering waves. These nozzles maintain the thrust augmentation necessary for the J-20's Mach 2+ capabilities during intercepts, while prioritizing low-observability in contested . As of 2025, afterburners are increasingly integrated into unmanned aerial systems for autonomous high-speed operations. Turkey's (UCAV) successfully tested an afterburner-integrated engine alternative in March 2025, achieving enhanced takeoff performance and sustained supersonic dash for strike missions, with the AI-322F planned for future integration. Similarly, experimental hypersonic engines, such as GE Aerospace's dual-mode with rotating detonation combustion (RDC) concepts, are under development to enable sustained Mach 5+ flight in air-breathing modes, with ground tests targeting scalability by late 2025. These applications highlight afterburners' role in extending unmanned and hypersonic platforms' tactical envelopes. Despite their utility in military contexts, afterburners have a declining presence in commercial aviation due to their poor fuel efficiency, which can increase consumption by factors of 5 to 10 during operation compared to non-afterburning thrust. Modern supersonic designs, such as Boom Supersonic's Overture prototypes, deliberately omit afterburners to optimize for sustainable aviation fuel and reduce noise, relying instead on medium-bypass turbofans like the Symphony engine for Mach 1.7 cruise without the efficiency penalties of afterburning. This shift underscores a broader trend toward efficiency-driven propulsion in civilian high-speed travel.

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