Why do afterburners have flames?

Answered by Jason Smith

Afterburners are a fascinating component of jet engines that play a crucial role in boosting the thrust of the aircraft. One might wonder why afterburners have flames and what purpose these flames serve. To understand this, let’s delve into the working principle of afterburners.

An afterburner is essentially a supplementary combustion chamber located at the rear of a jet engine. Its purpose is to extract the remaining oxygen from the exhaust gases and burn additional fuel in this oxygen-rich environment. By injecting fuel directly into the exhaust stream and igniting it, afterburners generate intense flames.

The primary reason for afterburners to have flames is to maximize thrust. By burning additional fuel in the exhaust gases, the afterburner significantly increases the temperature and pressure of the exhaust stream. This expansion of hot gases provides a substantial boost in thrust, enabling the aircraft to achieve higher speeds or accelerate rapidly.

The flames in an afterburner result from the combustion process taking place in the presence of the remaining oxygen in the exhaust gases. When the fuel is injected and ignited, it reacts with this oxygen, releasing a large amount of energy in the form of heat and light. This energy is responsible for the flames that are visible at the back of the engine.

It is important to note that afterburners are only used in specific situations, such as during takeoff, supersonic flight, or combat maneuvers. The use of afterburners is typically limited due to the significant increase in fuel consumption associated with their operation. However, when the extra thrust is needed, the afterburner provides a substantial performance boost.

To further understand why afterburners have flames, let’s consider the basic principles of combustion. Combustion occurs when fuel, oxygen, and heat are present in the right proportions. In a conventional jet engine, the combustion process takes place in the primary combustion chamber, where fuel is mixed with compressed air and ignited. The resulting high-pressure and high-velocity gases pass through the turbine, producing thrust.

In an afterburner, the exhaust gases leaving the turbine still contain a considerable amount of oxygen, as not all of it was consumed during the initial combustion process. By introducing additional fuel into this oxygen-rich environment and igniting it, the afterburner creates a secondary combustion process. This combustion releases additional heat and energy, resulting in a significant increase in thrust.

The flames in an afterburner are a visible manifestation of this intense combustion process. The high temperatures reached during afterburner operation cause the fuel to burn rapidly and produce flames that are often visible even in broad daylight. These flames serve as a visual indicator of the afterburner’s active operation.

Afterburners have flames because they inject fuel directly into the exhaust stream and burn it using the remaining oxygen present in the exhaust gases. This combustion process generates intense flames that signify the afterburner’s operation. The flames play a crucial role in heating and expanding the exhaust gases, resulting in a substantial increase in thrust, often exceeding 50% of the engine’s normal output.