On afterburner of fighter engine

Since you are talking about the afterburner of the fighter, there are two problems, fuel consumption and endurance.

First of all, in general, afterburner refers to jet engine, whether it is turbofan or turbojet (turboprop engine can be regarded as a variant of turbofan engine). Piston engines also have the theory of afterburner, that is, injecting alcohol or water into the combustion chamber, but the active fighters are basically jet fighters, so it is beyond the scope of this paper.

The structure of turbojet engine is compressor section (low pressure section plus high pressure section), combustion chamber, working turbine and exhaust section. The entire airflow path becomes an internal duct. Compared with turbojet engine, turbofan engine has an outer duct outside the inner duct, which generates backward compressed air thrust by increasing the diameter of low-pressure compressor blades. Therefore, under the same fuel consumption, greater thrust can be obtained than that of turbojet. Or conversely, it is more economical under the same thrust. Disadvantages are more complicated structure, larger diameter and weight. However, with the help of modern advanced metallurgical technology and manufacturing technology, the advantages of turbofan engine (fuel saving and large thrust) far exceed its disadvantages. At present, the thrust-to-weight ratio of the most advanced turbofan engine F119-PW-100 has reached more than10. In other words, the engine can generate thrust ten times its own weight.

In combat, fighters sometimes need to reach the war zone at maximum speed or quickly seize high-energy points because of tactical needs. Therefore, in addition to the maximum military thrust, it is also necessary to obtain the instantaneous speed through the opening force. Every jet engine has the function of afterburner when it is designed. The principle of afterburner is that when the jet engine is running, additional atomized fuel is injected into the inner duct behind the combustor and in front of the working turbine, and it is ignited by the gas discharged from the combustor. Because of its combustion and expansion, it generates additional thrust, which accelerates the working turbine, thus driving the front two-stage compressor to suck more air. Because the afterburner does work behind the combustion chamber, it is commonly called afterburner or afterburner. This section of the engine structure is often reinforced, also known as the afterburner section.

When the jet engine is turned on, its fuel consumption is at least twice that under normal conditions, and the range of the corresponding fighter will also be reduced. Take the f119-pw-100 mentioned above as an example, the non-afterburner fuel consumption is 0.75-0.8Kg/ hr Kg thrust, and the afterburner fuel consumption is 1.8Kg/ hr Kg thrust. At the same time, afterburning will dramatically increase the temperature and pressure in the internal combustion section and the speed of the core turbine, so afterburning will shorten the life of the engine. Generally speaking, the maximum afterburner time allowed by Russian jet engines is no more than two minutes, and that of western jet engines is no more than five minutes. If the stress exceeds the yield strength, serious problems such as cracks and fractures may occur. And check the turbine blades and combustion chamber in detail after landing. Therefore, fighters generally only apply afterburner when they take off with heavy load (especially carrier-based fighters) or are fighting. You don't need to apply afterburner completely at once, but decide according to your needs. The electronic control system of modern aircraft can accurately control the opening force according to the needs, that is, the fuel utilization efficiency is higher.

Third-generation and below jets can't reach supersonic speed with the maximum thrust of the military, that is to say, even a twin-engine heavy fighter like F 15 needs afterburner to exceed the speed of sound. The fourth generation aircraft benefited from the improvement of the thrust-to-weight ratio of the equipped jet engine, and it can reach the supersonic level of 1.5M by relying on military thrust without afterburner. This is also one of the important indicators of the fourth generation machine.