Can China produce aircraft engines?

Accurately speaking, China can produce aircraft engines, but it cannot produce advanced aero engines.

Modern advanced aero-engines, modern fighters, military transport planes, civil aviation trunk passenger planes, etc. Both use turbofan engines. Simply put, the turbofan engine has two concentric ducts, which consist of five parts: fan, compressor, combustion chamber, turbine and nozzle. Among them, compressor, combustion chamber and turbine are often collectively referred to as core engines. The main difference between turbofan engines for fighter planes and transport planes and civil airliners lies in fans. Large-diameter fans are generally used in the engines of passenger planes, which can reduce fuel consumption. The engine fan diameter of fighter aircraft is generally relatively small, suitable for supersonic flight. Air flows in from the air inlet of turbofan engine, compressed by compressor, mixed with kerosene in combustion chamber, high temperature and high pressure gas expands through turbine and nozzle, and finally is ejected from tail nozzle at high speed. Part of the thrust of turbofan engine comes from the reaction force generated by jet; The other part is a turbine-driven fan, which rotates to drive air, and the reaction force is ejected through the external duct of the engine.

Turbofan engine and turbojet engine

Why is turbofan engine so difficult? Imagine that the maximum afterburning thrust of the Su -27' s AL-3 1 turbofan engine is 12.5 tons, and two AL-3 1 s can propel the Su -27 with more than 20 tons to fly at more than twice the speed of sound. But the fan diameter of AL-3 1 is less than 900 mm, and the turbine diameter is less than 300mm；; According to the basic principle of physics, the forces are interactive, that is to say, the fan and turbine with such a small size have to bear the force of 12.5 tons all the time. In addition, a turbofan engine for supersonic fighter is generally only about 1 m in diameter and about 4 meters in length. Take AL-3 1 as an example. Such a small cylindrical object should be stuffed into a four-stage fan, a nine-stage compressor, a two-stage turbine, a convergent-divergent nozzle, a combustion chamber and an afterburner. A cooling duct should be arranged between them, and a fuel control system should be installed around them. Therefore, it is extremely difficult to design and manufacture high-performance turbofan engines. Only Rolls-Royce of Britain, Pratt & Whitney of America and General Motors have mastered the first-class turbofan engine manufacturing technology in the world. Both Russia and France are second-rate, and China should be outside the second-rate. This is a real monopoly industry.

In order to work normally at such a high temperature, the turbine of F- 1 19 adopts the third generation single crystal hollow blades. Single crystal hollow blade has a large number of free-form surfaces and complex cavities (used for intake cooling) in a blade with an area of only a few square centimeters, and it needs to control the continuous production of alloy crystals, which requires extremely high precision casting technology. Russian and China have not yet or just started the industrial manufacture of single crystal hollow turbine blades. Professionally speaking, in order to achieve greater thrust and lower fuel consumption, the first thing to do for turbofan engines is to improve pressure ratio and thermal efficiency. The temperature in front of the turbine is an important index to measure the thermal efficiency. For example, the pre-turbine temperature of the AL-3 1 engine of the third generation Su -27 is 1665K, while the F-19 engine of the fourth generation F-22 improves this index to1977 K; The pre-turbine temperature of AL-3 1 is still lower than the melting point of ordinary steel, but the pre-turbine temperature of F- 1 19 is over 200 degrees. The engine should increase the ratio of thrust to its own weight, and the compressor and turbine should be lighter. The traditional manufacturing technology of compressor and turbine is to connect the blade with the bladed disk through mortise and tenon locking, but the advanced engines in the west have begun to adopt the integral bladed disk. That is, the single crystal hollow precision casting blade is fixed on the blade disk by electron beam welding, which can reduce the weight by 30% compared with the blade manufactured by traditional technology. There are more than 10 manufacturing technologies for integral bladed disks, but other countries have not applied them to mass production except the three aviation giants mentioned above.

The fan of turbofan engine is far away from the combustion chamber, so the heat load is low, but the aerodynamic efficiency is also improving. The fans of F- 1 19 and Lorida 900 engines all use wide chord blades. The processing method is to cut the titanium alloy blank into two halves, weld it into a whole hollow blade body by vacuum diffusion welding, and finally superplasticize it into an extremely complicated curved surface. This is a brand-new processing technology.

Take the F- 1 19 turbofan engine used by the U.S. F-22A stealth fighter as an example. The 6-stage compressor and 2-stage turbine all adopt hollow single-crystal blades, and the 3-stage fan adopts wide-chord blades, so the thrust-to-weight ratio reaches 10, and the maximum afterburning thrust exceeds 15 ton under the condition of small windward area. Therefore, the American F-22A stealth fighter can cruise at supersonic speed of 1.7 times the speed of sound. The fourth-generation J-20 and T-50 in China and Russia can only temporarily use the third-generation turbofan engine, and the aircraft can only be truly developed after the fourth-generation engine is successfully developed.

Many netizens still think titanium alloy processing is very high-tech, but in order to further reduce weight, the fourth generation engine in the west has begun to use resin-based composite materials as low-temperature components. For example, the external bypass casing and intake casing of F- 1 19 engine generally have a heat-resistant temperature of about 300 to 350 degrees Celsius, and the upper limit of the temperature resistance of resin-based composites with more advanced performance is higher, which can break through the 400 degrees Celsius mark.

China's military industry started with the technical assistance of the Soviet Union, and it is good at reverse imitation. In the past, it solved the problem of "existence" in many fields, and even some light weapons experts called themselves "the king of the cottage". For many common devices, reverse imitation can at least "know why" even if "I don't know why". However, the "industrial crown" of turbofan engine has been applied with various new theories, materials and technologies. It's hard to know what it is, so it can't be simply copied. Even if there is no operation manual, it is difficult to disassemble the turbofan engine correctly. For example, CFM-56, which we are very familiar with, is one of the most widely used turbofan engines in the world, such as Boeing 737 and Airbus A320. However, it is still very difficult to disassemble CFM-56. There are many small holes in the leaves of several square centimeters, which are used to dissipate heat. The position of the small hole is very special, depending on the direction of the gas path ... so CFM-56. Even if various types of engine parts can be manufactured, they still need technical and technological support in assembly. Different batches of engines manufactured on the same production line are different, and the difference of thrust-to-weight ratio can even reach 0.2. With the development of engines with thrust ratio above 15 and the wide application of various new materials, the engine structure is becoming more and more complex and the requirements for processing technology are higher. Copying someone else's new engine may take more time than developing it from scratch, and the performance of the copied product is probably not as good as that of the prototype. China has learned this lesson. For example, the core engine of "Taihang" turbofan engine originated from CFM-56. Taihang engine was designed and finalized in 2005, but eight years later, there are still problems, and it is only used on the twin-engine J- 1 1 fighter. The J- 10 fighter with single engine requires high engine reliability. Before the mass production of J- 10B, J- 10 series fighters can only use Russian-made AL-3 1FN engines.

From the perspective of scientific research system, the research and development of aero-engines in China used to follow the model, that is, to develop an aircraft, it is necessary to develop a supporting engine; If the plane is unloaded, the engine will also be unloaded. In developed countries such as the United States and Britain, the research and development of engines and aircraft are basically separated, and the research and development of engine core machines is much ahead of schedule. For example, the F- 1 19 engine used in the American F-22 fighter belongs to the fourth generation engine, but the core engine technology of the United States has been developed to the sixth generation, and the core engine of the fifth generation engine used to replace F- 1 19 has also been manufactured.

It is very difficult to develop a turbofan engine, and it is precisely because of the difficulty that there is no shortcut. Must be completely independent research and development, and spend a lot of money on pre-research. In recent years, China's industry also had an epiphany and began to invest heavily in independent research and development. However, the gap before was too big, and it may take decades of efforts to catch up with the world's advanced level.