Much is said about post combustion engines and what they are used for, but little is heard about how the engine is arranged, what makes it work, how it is activated and what tests it es before being released.
Post combustion in reaction engines became almost a rule in the 60s so that fighters could maintain supersonic flight or overcome the sound barrier, nowadays we have the presence of fighters such as the Gripen NG and the F-22 that are capable of maintaining this same type of flight but with the dry cycle as they say in aviation.
One of the great disadvantages and inefficiencies of the afterburner is its very high fuel consumption, which can drastically reduce the aircraft's autonomy, something that must be considered by the pilot when imposing a faster cruising pace or quickly evading a conflict area.
Fuel injection takes place through several circular tubes that inject the fuel directly, unlike the engine's combustion chamber which contains injector nozzles. The result of burning air + kerosene comes straight from the combustion chamber at a very high temperature and because of this temperature the mixture is able to burn again at the exhaust outlet. Notable in an afterburner engine is its huge tube just after the reaction engine sections.
This hoop-shaped tube (pictured above) is made of an ultra-resistant material and controlled by valves that release additional kerosene when the pilot commands the afterburner to turn on, generally used during takeoff or in quick stealth maneuvers, also known in the field. military as Dogflight, widely used by postmodern aircraft to have a stealth effect in an era of little technology involved in combat. The main feature that this afterburner gives the hood is an exhaust outlet that contains fire. A pressurizing pump also participates in the system, which is responsible for sending kerosene separately to the injecting tubes and also a distributor that keeps the burning of hot gases uniform, thus making better use of the injection to improve burning and the overall efficiency of the set.
Another feature is an exhaust outlet which is the opposite of what is found in normal reaction engines, instead of fixed fins directing the air outlet it contains movable fins that internally regulate the pressure of the explosion which ends up regulating the air output speed. burned inside the engine, which may further increase the differential between the initial and final air speed, responsible for generating the thrust of the reaction engines. In some aircraft such as the F-35, the engine is also composed of a movable mouth that can direct the post combustion air to different angles in order to obtain greater efficiency during critical operations, such as takeoff and go-around, or even to overcome high drag. generated when it is close to breaking the sound barrier.
Because the air that comes out of the burn no longer contains much oxygen, it takes a lot of fuel for optimal burning to occur. Just as it is an easy-to-implement project aimed at instantly increasing the engine's power, its disadvantages are related to the high fuel consumption and the engine's behavior level, which can represent different behaviors in relation to its use with or without an afterburner.
In this image above provided by NASA about afterburners is represented the main relationship that this system causes in the operation of the engine. The force exerted by the engine conserves Newton's 3rd law of action in reaction, so the force with which the engine manages to throw that air backwards is reflected in the movement of the aircraft forward. What causes this engine strength in such a configuration is the difference in the speed with which the air enters and the air leaves, which is why we commonly see large air intakes in modern reaction engines, but with a smaller output. This difference in size causes a narrowing of the engine output, imposing more speed on the air, otherwise it would gain pressure. Try to do this at home, take a funnel and right after an object with no restricted air outlet, blow on both and see the difference in speed with which the air comes out of the funnel.
The afterburner further increases the air output velocity compared to the normal jet engine through the principle of air combustion. the piston engine, in which the combustion was responsible for the air pushing the piston downwards, yes, here we have the same principle, the combustion ends up energizing the engine gases even more, throwing them at a much higher speed in the exit. That's why it's a system often used to break the sound barrier, especially in older aircraft where the engine had a lower power sophistication when operating dry.
More current aircraft such as the F-22, F-35 and the Gripen NG manage to reach super cruise without the need for an afterburner, thus saving a large amount of fuel and increasing their range of attack, which in design generates an advantage over other aircraft. competitors, both in of range of attack (also called range) and cost to put such an aircraft in the sky.
