China Aims For Gas Turbine Catch-up

By Bradley Perrett
If there is one area in which China has had persistent difficulty catching up with Western aerospace technology, it is aviation gas turbines. Chinese aero-engines are known for poor efficiency and low reliability, and it would well suit China’s neighbors and the U.S. if they kept that reputation.

So the prospect of MTU Aero Engines and Avio working on a major Chinese commercial turbofan program prompts a critical question: will technology transfer be strictly contained?

According to MTU, yes, it will. If the German company joins the program of Avic Commercial Aircraft Engine Co. Ltd. (ACAE), it will follow the same secrecy procedures that it has long used in collaborative developments with General Electric, Pratt & Whitney and Rolls-Royce, says a company spokesman. Quite apart from any question of withholding military-civil dual-use technology, MTU has its own strong commercial reasons not to share its know-how with ACAE.

MTU is doing preliminary work with ACAE on the CJ1000 Changjiang engine, which is supposed to go into service in the next decade on the Comac C919 six-abreast airliner. The airframe program has adopted the CFM International Leap-X1C as its initial engine in recognition that developing a competitive commercial turbofan will be even harder than producing an adequate airframe.

MTU says it could develop the low-pressure turbine or the high-pressure compressor. Since the technology of the high-pressure spool of a commercial turbofan can be transferred to a combat-aircraft engine, it is the compressor that will arouse the most concern in Washington—and in Tokyo, New Delhi, Seoul, Taipei and Canberra.

Italy’s Avio will work with another part of the Avic conglomerate, Xian Aero Engine, to make the combustor of the CJ1000. They will do this in a joint company, Xian Avio XAE Aero Engine Components. Again, the combustor is a critically sensitive element of the engine core. Avio did not immediately respond to Aviation Week’s question on how technology transfer would be controlled.

“Production processes and technologies applied in the Chinese industrial plants will be in line with extremely high standards achieved by Avio in Italy and Poland,” Avio says in a statement.

No major Western manufacturer appears to be helping ACAE with the other main part of the hot section, the high-pressure turbine, but the Chinese company is negotiating with more potential partners, including some from Russia. The big three Anglo-American engine houses and France’s Snecma have declined to help.

Even if critical technologies are withheld from the CJ1000 development, China will be pleased with whatever it can get, says aerospace analyst Sash Tusa of Echelon Research and Advisory, likening the process to putting together a mosaic: “If you get enough pieces, it may not be that hard to finish the mosaic.”

Beyond the challenges in developing individual technologies for the CJ1000, ACAE has negligible experience in integrating designs—getting everything to work together optimally. It might be receiving some help there, however. It held job fairs in Britain and the U.S. this year with the aim of hiring experienced engineers. It seems to have succeeded, since experts who previously worked for General Electric and Rolls-Royce have joined the program, says an official of the Chinese company. Many of them are newly retired from their Western jobs. Their numbers and areas of expertise are unknown. It is also unclear how effectively those individuals are restricted by their governments’ regulations on trade in military technology.

Moreover, ACAE can be expected to seek as much integration advice as it can from partners MTU and Avio, even if giving it is not strictly part of their role—just as Comac has sought such help from Western partners making systems for the C919. Partners will have a strong interest in contributing beyond the scope of their contract because they want the project to succeed.

But success will not be easily attained, executives of foreign engine companies say. “I expect them [ACAE] to spend a great deal of money, to run into a great many problems and to eventually build an engine that is not very competitive,” says one senior Western industry executive. “But in the process, they will learn a lot. Every time they hit a problem, they will learn something important.”

An executive at one of the major Western engine companies doubts that the CJ1000, as the first commercial engine from China, will turn into much of a threat.

The CJ1000 is a direct competitor to the Leap-X, since it is to be developed to the same specification from Comac. A few scant details suggest it will not match the performance of that GE-Snecma engine, however, nor that of the Pratt & Whitney PW1127G on the Airbus A320NEO.

Thrust-specific fuel consumption, measuring fuel burned in generating cruise thrust over time, will be 10-12% better than the current CFM56 and International Aero Engines V2500, says an industry official familiar with ACAE’s studies. Western manufacturers are aiming to go a few percentage points further than that in their new engines.

The overall pressure ratio of the CJ1000—a critical parameter measuring the work done by the fan, core-boosting low-pressure compressor and, above all, the high-pressure compressor—will be in the range of 35-40:1. The Leap-X will have an overall pressure ratio above 40.

The Chinese engine’s bypass ratio is expected to be below 10:1, though perhaps not much below that, compared with the 11:1 CFM executives now say the Leap-X will achieve. Thrust will be about 30,000 lb., in line with engines for the Airbus A320 and Boeing 737.

The exact configuration of the CJ1000 is not yet set. The number of fan blades and stages in the low-pressure turbine and both compressors remains to be determined. But in their concept studies, the designers have consistently chosen two stages for the high-pressure turbine, as has become normal for engines of this size, so that feature looks unlikely to change. Counter-rotation of the spools has been studied but only as an alternative to the conventional and probable configuration of two spools rotating in the same direction—in this case, clockwise, when viewed from the front.

The fan blades will be hollow and made of titanium. An engineer not involved in the project supposes that the ideal choice, carbon-fiber-reinforced composite, would have been technically too difficult for ACAE. The choice will affect the containment structure, but that part of the engine has not yet been closely studied—showing that the program really is at quite an early stage. Weight and dimensions should be similar to those of the Leap-X.

ACAE plans to have a demonstrator engine that meets initial performance targets in 2016, which suggests that it would have to begin running it in 2015. The formal target for entry into service is 2020, but that date could easily slip.

MTU is not yet a confirmed partner on the CJ1000. It and ACAE now “intend to jointly prepare the development phase of this engine,” including a “feasibility study as well as further partner discussions for the indigenous Chinese aero-engine.”

The two partners will complete a joint definition study by next month.

“The Chinese aviation market is very dynamic and we intend to participate in this expected growth through our business expertise and know-how,” says MTU CEO Egon Behle, who signed the agreement with ACAE President Wang Zhilin.

The market assessment must depend heavily on an assumption that the Chinese government will direct its airlines to buy the engine, as it is directing them to buy the C919.

With the moniker Changjiang, ACAE’s engine is named after a river, following Rolls-Royce tradition. The Changjiang, also called the Yangtze, is the longest river in Asia, flowing from Tibet to Shanghai.


With Leithen Francis in Beijing.

Photo Credit: Bradley Perrett/Aviation Week

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