But the process is not as small as the blade parts low pressures

The reactors remain among the most complex objects designed by the man and a nightmare for the engineer. These rotating machines combine infernal temperatures, outbreaks of several tonnes, a strong oxidation, intense mechanical abrasion, of complicated aerodynamic flows, all dusted vibration. These multiple equations, engineers must juggle with regulatory and economic constraints very strong and promised to incessant hardening. No wonder therefore that the progress of the engines will be carefully. The engine manufacturers and their aircraft manufacturers like to explain that the consumption of an engine is now 70 lower than in 1950. The whole with 90 less noise. However, these successes are more, enough all industrial sectors being summoned to drastically reduce their carbon footprint. However, unlike automobile, energy, building, aviation has no alternative to oil, both technical and regulatory constraints (security) are strong. And then the decades of research have exhausted the margins of operating temperatures had engineers. "The progress of the aeronautical engine always came operating temperatures increase to boost the performance of combustion." "But we are very far from the limit that can withstand the materials," explains Pierre Thouraud, technical director of Snecma.

The challenge of materials

The 1.600C furnace in combustion chamber has pushed the science of materials and Metallurgy in his deletions. Decades of work gave birth of single-crystal superalloys titanium-based which have no rival in the hot parts. Most exposed blades are equipped in addition to thermal shields in composite and equipped with cooling systems with microchannels moulded within the blade.

But the high-performance alloys are more, sufficient density of the order of 9 in terms of heavy materials. Supporters of the composite materials, much lighter, there are a great gap to impose their sector. If the composite long since invaded the fuselage of the aircraft, they have failed to settle that some fixed pieces of engines. The challenge now is to test the composite in the most critical parts: blades that turn and push the air.

Snecma is placed in advanced on this subject with his experience of composites in the space. In recent years, he studied a transfer in the area of the floors low pressures (blower, compressor and turbine low pressure) of the engine. These works are motivated by the preparation of the replacement of the CFM56 bestseller, including who will equip the successors of the single-aisle Airbus or Boeing. The Leap-X 2 billions of dollars of investment project will be a demonstrator in 2012. It is in this range that engineers believe introduce first blades in carbon fibre composites. The first floor of the engine sucking cold air from the sky and suffers no high temperatures. The group uses production by weaving process that boosts the performance of the blades. Bruno Dambrine, expert in mechanics of materials in the French engine manufacturer began the first works in 2000: "Traditionally, it is realized in carbon fibre parts stacking layers of composite taken in resin." But the process is not as small as the blade parts low pressures. The key to this technology is to use a Jacquard Loom that weaves fiber in 3 dimensions. Some 300 prototypes of blades has already been made and we already have 6 patents on the subject. "Thanks to the carbon composite, a dawn of fan from 100 to 20 grams and its geometry, more easily adaptable, allows an aerodynamic gain. In total, this will reduce the weight of the engine of about 180 kg.

The experience of missile

The technology is not also ready for the hottest parts of the engine. To alleviate low pressure blades which see temperatures of over 1,000 C, engineers must resort to other composite, this time in ceramic matrix. Snecma and several research centres French, as the laboratory of composite thermostructuraux in Bordeaux, have experience at the global level through their work on nuclear missiles. A first generation has been developed at Snecma Propulsion solid (SPS) for the nozzle of the M51 missile. Then, engineers tested the manufacture of a huge rear piece of reactor, mixer. This component in the form of Tulip is used to dilute the hot gases emitted by the turbine with the cold gas of the blower. The next step, these are the blades. So far the use of these materials in mechanical functions base on their high vulnerability to manufacturing defects and cracks. The silicon carbide used to produce fibers and matrix autour is oxidized at high temperature. The lesser fault causes a corrosive attack of oxygen, fatal aviation. The French scientists, abroad, others have found a parade by adding silicon carbide material comparable to the glass becomes liquid for crack and immediately stops the fragility, protecting the ceramic oxidation.

Tasadduq Khan, Senior Advisor to the Onera and specialist materials, superalloys cede their place within several years, but, for him the competition remains widely open. "The cost of ceramics is 3 or 4 times more than a metal solution," he said. For him, AC material as niumbum silicide made large progress over the past five years. It offers the qualities of superalloys for a 30 weight gain and fits the economic processes (casting). Another track followed by researchers: eutectic materials, an old technology which is topical. "The titanium Aluminide which will make its appearance on the next GE engine studied thirty years ago and had been abandoned before a new youth," says Tasadduq Khan.