Why are aero engines so difficult? Can't the Chinese build advanced aircraft engines?

Let's first get acquainted with modern advanced aero engines, modern fighter jets, military transport aircraft, civil aviation trunk airliners, etc. are all turbofan engines.

To put it simply, a turbofan engine has 2 concentric circle ducts, which are composed of 5 parts: fan, compressor, combustion chamber, turbine, and nozzle.

Among them, the compressor, combustion chamber and turbine are often collectively referred to as the core engine of the engine. The main difference between the turbofan engine used in fighter aircraft and transport aircraft and civil airliners is the fan, and the engine of the passenger aircraft generally uses a large-diameter fan, which can reduce the fuel consumption rate; Fighter jets generally have smaller engine fan diameters for supersonic flight.

Air flows in from the intake of the turbofan engine, compresses by the compressor, mixes with kerosene in the combustion chamber, expands through the turbine and nozzle, and finally sprays out of the tail nozzle at high speed.

Part of the thrust of the turbofan engine comes from the reaction force generated by the injection of gas; The other part is the turbine drive fan, which rotates to drive the air and the reaction force that is ejected through the engine duct.

Why are turbofan engines so difficult? Imagine that the maximum afterburner thrust of the AL-31 turbofan engine of the Su-27 is 12.5 tons, and 2 AL-31s can propel the Su-27 of more than 20 tons to fly at more than 2 times the speed of sound. But the AL-31 has a fan diameter of less than 900 mm and a turbine diameter of less than 300 mm.

According to the basic principles of physics, forces interact with each other, which means that such a small size fan and turbine in turn have to bear a force of 12.5 tons at all times.

Figuratively speaking, everyone should have seen the performance of a strong man pushing a car with a steel gun against his throat, and the turbofan engine is probably the same, but the strong man pushes the car slowly, and the turbofan engine pushes the aircraft to fly at 2 times the speed of sound, and all parts have to withstand the extremely harsh high temperature and high pressure test.

Other than that. A turbofan engine used in a supersonic fighter is generally only about 1 meter in diameter and about 4 meters in length. Taking the AL-31 as an example, such a small cylindrical object should be stuffed into a 4-stage fan, a 9-stage compressor, a 2-stage turbine, a convergent-expandable nozzle, a combustion chamber, an afterburner, a cooling air channel in between, and a fuel control system installed around it.

Therefore, design and manufacture a high-performance turbofan engine. It can be said that 'making a dojo in a snail shell' is extremely difficult. In the world, the only one who has mastered the first-class turbofan engine manufacturing technology is the British Luo? Romania, Pratt & Whitney and General Motors, Russia and France are all second-rate, and this is a real monopoly industry.

To describe it professionally, in order to achieve greater thrust and lower fuel consumption of turbofan engines, the most important thing is to improve the boost ratio and improve thermal efficiency, and the temperature before the turbine is an important indicator to measure thermal efficiency.

For example, the pre-turbine temperature of the AL-27 engine of the third generation Su-31 is 1665K. And the F-22 engine of the fourth-generation F-119 raised this indicator to 1977K; The pre-turbine temperature of the AL-31 is below the melting point of ordinary steel, but the F-119's has exceeded about 200 degrees.

The pre-turbine temperature of Tianfeng Technology's turboshaft D and turboshaft E engines is still below 2000K, while the turbofan engine under development has reached a high temperature of 2100K before the turbine.

In order to operate normally at such high temperatures, the third generation of monocrystalline hollow blades must be used. It is difficult to describe what a monocrystalline hollow blade is here, but it can only be said that a blade with an area of only a few square centimeters has a large number of free-form surfaces and complex internal cavities (for inlet air cooling). It is also necessary to control the continuous production of alloy crystals, which requires a very high precision casting process.

Li Tianfeng spent two days at the helicopter factory. Considering that there are many things in his company, especially the turbofan engine being developed, which is now at a critical juncture, Li Tianfeng returned to Tianfeng Technology Company two days later.

………

China Commercial Aircraft Co., Ltd.

This is a professional civil airliner manufacturer, speaking of Xiang-Feng regional airliner, everyone may be more familiar. This civilian regional airliner is a great product of this company (not to be tied to reality).

Xiang-Feng regional airliner is known as "a new generation of regional aircraft in the 21st century". It is a regional aircraft developed by China Commercial Aircraft Co., Ltd. In addition to the aircraft engine provided by General Electric, the Xiang-Feng is the first regional jet designed and manufactured entirely in-house in China.

The aircraft underwent its first test flight in 2008 and will be delivered to customers for commercial operation after obtaining its airworthiness certificate in 2009. There are four types of Xiang-Feng regional airliners with different capacities, and the passenger models can be set up with about 70~100 seats.

As a vice president and one of the executives of COMAC, Shen Wensheng is frowning and smoking, whenever he encounters tricky things or annoying things, Shen Wensheng will do this.

The smoke was filling, there were already a lot of cigarette butts in the ashtray on the desk, and there was a distinct smell of smoke in the whole office.

"It's so uncomfortable to get stuck in the neck!" While smoking, Shen Wensheng thought so in his heart.

At present, the development momentum of the commercial aviation company is very good, the Xiang-Feng regional passenger aircraft is sold well in the domestic market, and the reputation is also very good, and Shandong Airlines, Shanghai Airlines, Xiamen Airlines and other companies have signed hundreds of orders with the commercial aviation company.

According to this momentum, in a few years, the Xiang-Feng regional airliner may be able to go abroad and enter the international market, and Shen Wensheng, who is only in his 40s, is upright and vigorous, full of energy, and is ready to do a big job.

At this juncture, as a supplier of engines for Xiang-Feng regional airliners, GE of the United States has made it clear that it will cut the supply of engines starting next year, and the price of each engine will rise by 10 percent.

After smoking several cigarettes in a row and thinking about it for a long time, Shen Wensheng didn't have a clue in his heart, and sighed in his heart and thought, it would be nice if the domestic aero engine was powerful, hey, it seems that he can only be honestly stuck in the neck by GE.

"I'm really unwilling!"

Shen Wensheng thought so in his heart, the reduction in the number of engine supplies means that the production of Xiang-Feng regional airliners will not rise but fall, and the hope of doing a big job will be in vain.

After thinking for a long time, Shen Wensheng picked up the phone and called his Minister of Commerce, "Mr. Li, you also know about GE, try to contact Pratt & Whitney and Rolls-Royce to see if there is any hope." ”

Minister Li of the Ministry of Commerce nodded helplessly, knowing that the matter had come to this point, he could only be a dead horse doctor and try to contact these aero-engine giants, but there was definitely little hope.

Minister Li said: "Mr. Shen, I tried to work hard, but I just ......"

Seeing that Minister Li was a little hesitant, Shen Wensheng didn't know what he meant, and waved his hand and said, "Let's try it first, there is no hope." ”

Seeing Minister Li bow his head and retreat, Shen Wensheng sighed again, thinking in his heart, it would be great if a domestic aero engine company could have an excellent turbofan engine.

In his mind, Shen Wensheng went through the domestic national aviation companies one after another, and he really didn't have the aero engine he needed.

At present, even if the domestic national aviation industry enterprises develop turbofan engines, they are also for military aircraft, and besides, the engines of military fighters are not powerful, and their own civilian regional airliners should not try to find excellent and suitable aero engines in China.

After thinking about it for a long time without success, Shen Wensheng could only let out a long sigh again.

Tianfeng Technology Co., Ltd.'s turboshaft D and turboshaft E have been produced in batches, especially the turboshaft D engine, which has produced nearly 1,000 units, and is still being produced at a rate of about 70 or 80 units per month.

These two turboshaft engines are basically known and agreed with by people in the domestic aviation industry, knowing that these are two excellent turboshaft engines. And the turbofan engine that is really being developed is really little known because it is far from being applied for design projects.

Shen Wensheng didn't know that this excellent turbofan engine was normal, even if it was an industry insider in the aviation industry, there were not many people who knew the Tao.

Like Zhang Haiping, Yang Xianfeng and other Li Tianfeng's friends, they only know that Tianfeng Technology Company is developing the fourth-generation turbofan engine, and some very specific things are really not very clear.

…………

Tianfeng Technology Company, Foundry Workshop.

Before casting, Zeng Qinghai specially organized a process review, improved and improved the casting process again, and through guò digital simulation simulation, after determining that there was no problem, the casting of the first batch of compressor casing began.

Because it is the first batch of titanium alloy casing, the batch of casting is not large, and the three-piece casing, and because it is the first batch of casting, considering the difficulty of the process, Li Tianfeng and Zeng Qinghai are both in the casting workshop.

"Mr. Li, Mr. Zeng, the casting preparations have been completed, and the casting can be carried out."

Li Tianfeng waved his hand and said, "Then start casting, and see what will happen to our first batch of titanium alloy casing casting?" ”

This is a titanium alloy casing with a thin-walled complex structure, and it is really hard to say whether it can be successful at one time, and Li Tianfeng is not completely sure.

Precision casting, the preparatory work in the early stage, spends the most effort, such as the design and manufacture of molds, mold making before casting, melting of titanium alloys, and so on.

Of course, the process parameters of casting will also be strictly controlled, not to be sloppy, otherwise, it may cause defective products or even the scrapping of castings, you know, this is a difficult titanium alloy complex thin-walled casing casting, representing the highest level of domestic casting.

Far away, through the glass, watching the titanium alloy molten metal injected into the mold, Li Tianfeng's face was very serious, and the whole scene was quiet, and no one spoke.

…………

Today, we will continue to watch two more, and the second one will be sent! (To be continued......)