At the end of 2023, at a flight test site in Northwest China, the Industrial Technology Research Institute of Chongqing University organized an engine test test. A small unmanned verification aircraft equipped with an FB-1 detonation engine successfully ignited and flew under the strong thrust brought by continuous deflagration.
The results of this test have caused a sensation in public opinion at home and abroad, because the detonation engine is the key breakthrough direction of the current aerospace engine research and one of the aerospace power with the most application potential.
China started late in the field of aviation, but this time undoubtedly shows that the independent research and development of continental engines is no longer subject to the technological monopoly of other countries, and has reached the level of the world's first echelon.
How does it work?
So, what is a detonation engine, and what new possibilities can the use of this engine bring to China's aerospace technology?
The detonation engine is a propulsion device based on a new combustion mode, and the key lies in the word "detonation". The engines that use detonation combustion mainly include rotary detonation engines, pulse detonation engines and oblique detonation engines. Here we focus on how a rotary detonation engine works.
A rotary detonation engine usually consists of an annular combustion chamber, an initiating device, an injector, a tail nozzle and other parts. The combustion chamber is closed at one end and open at the other.
When the engine is working, the fuel and oxidizer are injected into the combustion chamber by the injector at the closed end of the combustion chamber, and then ignited by the spark plug and other detonation devices to form a detonation wave that rotates and propagates in the circumferential direction, and the high-temperature and high-pressure detonation products are accelerated by the tail nozzle and discharged at high speed to generate thrust.
When it comes to the phenomenon of "detonation", combustion in nature is generally divided into two types, slow combustion and deflagration. In the combustion of daily life and the traditional aerospace power, energy is basically provided in the form of slow combustion. Deflagration, on the other hand, is a combustion mode in which the combustion wave propagates at subsonic speed in a high-temperature and high-pressure environment, accompanied by the detonation phenomenon.
Detonation produces a detonation wave that moves at supersonic speed, and at the same time forms a detonation product of high temperature and pressure. Because of the high-speed movement of the detonation wave, the thermal cycle efficiency of the deflagration mode is higher, the heat energy release speed is fast, and the detonation engine can provide more sufficient energy and more economical under the same fuel supply.
As for why the phenomenon of detonation can produce thrust, it is necessary to first introduce the working principle of the aerospace engine. The aerospace engine is a reaction-force engine, which is a mode of operation based on the reaction force.
In layman's terms, it is to mix fuel and oxygen, and use the ignition device to make it burn in the combustion chamber to produce high-temperature and high-pressure gas, and the gas works on the turbine through thermal expansion to make it operate, and releases high-speed gas to the outside - this is the principle of the turbine engine;
Or the gas is accelerated through the propulsion nozzle and injected directly to the outside to do work, thus obtaining a reaction force thrust - this is the principle of a ramjet engine.
The working mode of the rotary detonation engine is more similar to that of a ramjet engine, that is, the internal energy of the combustion product is directly converted into the kinetic energy of the external thrust through interaction. The high-temperature and high-pressure products generated by the detonation phenomenon are further accelerated through the tail nozzle and then projectile to the outside, so as to obtain the reaction force thrust.
What are the benefits?
It is also thanks to the characteristics of high thermal cycle efficiency and low energy loss of detonation phenomenon, the rotary detonation engine can not only reduce fuel consumption, but also be more economical, and far exceed the vast majority of current engines in terms of performance.
Conventional turbine engines, which limit the flight speed due to a complex pressurization mechanism, do not exceed Mach 2.5 for their maximum flight speed. The flight speed of the ramjet engine is also in the range of Mach 3.5-4.0. However, the thrust brought by the rotary detonation engine can drive fighter jets or missiles to fly at hypersonic speeds of more than Mach 5, or even Mach 10.
In addition, because the detonation phenomenon produces high temperature and high pressure products, the pressure in the annular combustion chamber increases, and the injection hole with less pressure automatically stops the fuel input. When the detonation product is discharged from the tail nozzle and the pressure in the combustion chamber is less than that of the injection hole, the fuel is fed in for the next round of deflagration – this is the "self-pressurizing" characteristic.
In other engines, oxygen is pressurized by a compressor and fed into the combustion chamber to fully mix the fuel with oxygen and achieve a fast-acting high-temperature and high-pressure state. However, the high-pressure products produced by the combustion chamber can hinder the continuous flow of oxygen. The self-pressurization of the rotary detonation engine solves this problem well, without pressurizing the fuel and oxidizer, and as the detonation products are generated and ejected, a duty cycle can be formed.
At the same time, because of the self-pressurization characteristics, the rotary detonation engine does not need to introduce compressor and other designs, and does not need to process the air in multiple stages, which is simpler and more compact than the traditional engine, and also reduces the overall quality.
The engine ejects the combustion products outward to obtain a reaction force, and the combustion products also have a certain mass, which is carried by the aircraft. Usually the mass of fuel is 36 times higher than the payload of the aircraft. Therefore, the lightweight and compact characteristics of the rotary detonation engine enable the aircraft to increase the load, carry more fuel, thereby increasing the range, and also enable it to have more application scenarios, such as small unmanned aerial vehicles.
What are the prospects?
Based on the advantages of the rotary detonation engine, this engine is very suitable for the development of the sixth generation fighter of the continental.
In mid-2023, CCTV's seven sets of national defense and military "Sharpening the Sword" program "Sharpening the Blade" exposed a simulated new fighter, which adopts the tailless layout of the French "Mirage" 2000 and is similar to the J-20.
However, the air intake is in the abdomen, and the structural layout of the fuselage can be changed according to actual needs, and the position of the wing and tail can be switched to the form of a forward-swept wing. In addition, in addition to the innovative design of the fuselage, in terms of aerospace power, it is equipped with the most advanced rotary detonation engine at the moment.
According to reports, under the propulsion of the rotary detonation engine, this fighter can achieve hypersonic cruise in the atmosphere, and even fly out of the atmosphere to cruise to the space station. That is to say, the working nature of the rotary detonation engine can meet the application scenarios of aviation and aerospace at the same time, covering the flight speed from low speed of Mach 0-2 to ultra-hypersonic speed, that is, wide speed range and cross-airspace.
Now we have completed the test flight of a small UAV equipped with this engine, and it is likely that it will continue to be used on unmanned aircraft, target aircraft, and target missiles for a period of time in the future. With further load enhancement and optimized stability, it can also be used as a power plant for aerospace aircraft, warplanes, and even rockets.
According to the characteristics of different engines and specific application requirements, the engine can also form a combined cycle engine with turbine engines and ramjet engines to expand its working range.
According to the South China Morning Post, researchers are developing a new combined engine that combines rotary detonation technology with oblique detonation technology to meet the needs of different speed ranges, allowing the aircraft to accelerate directly from 0 to 16 times the speed of sound.
Among them, the two engines work in series, when Mach 0-7, the rotary detonation engine of the first half is used, and after Mach 7, the oblique detonation engine is enabled, and the maximum speed can reach Mach 14-17.
At the 2017 Global Space Exploration Conference, the China Aerospace Science and Industry Corporation proposed the "Tengyun Project", the main goal of this project is to create an "aerospace aircraft" that can take off and land horizontally directly, and repeatedly travel back and forth to the atmosphere until low earth orbit before 2030.
Judging from the research trend of detonation engines, perhaps the successful completion of the Tengyun project and the scientific and technological miracle of human beings traveling back and forth between space and land are just around the corner.
Bibliography:
Ju Meina,Yuan Cheng,Cao Junwei.Review of research progress of rotary detonation engine[J].Aeronautical Science and Technology.2023(34):1-9;
Chen Zhenyi.Luo Feiteng.Chen Wenjuan.Research overview and key technical problems analysis of rotary detonation rocket engine[J].Special and New Propulsion Related Technologies.2023(12):1145-1163;
Qin Yaxin.New progress in the development of rotary detonation engine.Aviation Power[J].2022(3):16-19
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