Breakthroughs in aerospace industry to drive turbo-engine efficiency

 A series of breakthroughs in materials science are helping to drive efficiency in aerospace manufacturing, by improving material properties and reducing aircraft production times, whilst maintaining a low overall weight

Much of this is due to the use of advanced composites, which are now widely used in many parts of modern aircraft design – from the fuselage to the wings and control surfaces, and even cabin interiors.

One area of modern aircraft design that has changed comparatively little since its development in the early 1900s, is the jet engine. This is largely due to the extreme pressure and temperature constraints that apply when testing materials for use in this application.

Now, the latest ceramic matrix composites (CMCs) are beginning to demonstrate their suitability for turbo-engine applications and promising to bring significant gains. From an intellectual property (IP) perspective, a patent search has revealed some of the manufacturers leading the way.

Driving this innovation activity is the push from governments around the world to improve fuel efficiency and reduce air pollution, which is in part a response to growing consumer concern for environmental protection.

The EU’s Strategic Research and Innovation Agenda (SRIA 2050) has set a target to achieve a 75% reduction in aviation CO2 emissions by 2050, compared to 2000 levels. This needs to be achieved whilst reducing NOx emissions by 90% and reducing noise pollution by 6% over the same time period. To date, the main focus for innovators has been reducing the overall weight of the turbojet engine, whilst maintaining its reliability and enhancing its thrust per fuel consumption.

Currently, turbojet engines use a wide variety of materials. Fan blades are typically made from aluminium, titanium or stainless steel, whereas compressors are mainly made from nickel-, cobalt- or iron-based alloys. Superalloys made using refractory metals such as tungsten, molybdenum, niobium and tantalum tend to be used in the combustion chamber, where temperatures can reach 1,700 degrees centigrade.

Turbine blades are commonly made from a nickel-based superalloy, where the temperatures and pressures are so high that the turbine blades need internal cooling channels in order to operate at temperatures that exceed the melting temperature of the superalloy.

Despite the obvious strengths of nickel-based superalloys, there is always a drive to develop lighter materials that perform better, and this has resulted in the generation of new ceramic matrix composite (CMC) turbine blades.

However, these materials can be extremely difficult to manufacture, due to their complex architecture, and until recently, they were only used on static parts of the engine, such as the turbine shroud.

However, engine manufacturers such as GE Aviation and Rolls-Royce have begun exploring their use in even more demanding applications, such as turbine blades.

The redesign of turbine blades, from nickel-based superalloys to CMCs, brings with it many challenges that need to be overcome before we are likely to see the widespread adoption of this technology in the moving parts of aero engines. For instance, despite being able to withstand higher temperatures than nickel-based superalloys, CMCs have a lower thermal conductivity that requires new methods of cooling to be developed.

As a result, Siemens Energy has recently applied for patent protection for an innovative hybrid turbine blade comprising a ceramic composite leading edge and a nickel-based superalloy trailing edge, which is lighter and stiffer than a non-hybrid design, whilst tackling difficulties in cooling the blade.

Typically, these material systems involve enveloping the ceramic portion to create a permanent interlock. A further patent application by Siemens Energy for a mechanical interlock system is currently pending, which allows these two components to be joined, whilst still allowing future retrofitting and repairs to be undertaken. This hybrid approach is a great compromise that allows the two materials to complement each other.