Brussels, 29 Jun 2004
The STR project developed new components and production processes that will make future generations of gas turbine engine more affordable to produce, and much more efficient to operate than current models.
The large power-to-weight ratio of gas turbines revolutionised air travel when they replaced the internal combustion engine. Although the turbine has had a relatively short but extremely busy development history, aerothermal and mechanical design, coupled with advanced manufacturing techniques, has helped make the turbine's highly efficient components robust and reliable. Such engines require very little maintenance.
However, research and development into smaller turbomachine components – turbomachinery refers to turbine driven systems for propulsion, power generation and energy conversion – has been a different story. Use of small turbomachines in air processing, turbochargers and small gas turbines has been hindered by poor performance. Design know-how specifically tailored for small turbomachines is desperately needed if they are to be made efficiently and work just as successfully as their much larger cousins.
For transport applications, where efficiency is paramount, the pressure is therefore on to develop better ways of designing components for small, 30 to 200 kW gas turbine engines.
Mass manufacturing at low cost
The Fifth Framework Programme (FP5) STR project was aimed at developing methodologies so that small turbomachine components can be suitably designed for a wide range of applications. It carried out research into structural and aerothermal analysis, the main techniques used in turbomachine design, to work out how to mass manufacture such technologies at a low enough cost, but reliably and efficiently.
STR contained a proof-of-concept phase, and set itself a number of targets compared with existing machines of a similar size and power:
- Make components more efficient;
- Cut fuel consumption and CO2 emissions by 10%; and
- Reduce the size of engines producing 50 kW of power by 12%.
Seven partners signed up for STR. These included Prvni Brnenska Strojirna Velka Bites (PBS) – a gas turbine manufacturing company from the Czech Republic – and French air cycle machine manufacturer Liebherr Aerospace Toulouse (LTS). Two manufacturing partners brought their particular expertise to the project: UK casting specialist Castings Technology International and Turbocam Europe, a UK-based, five-axis milling company, which provided the material and processing know-how.
Aerothermal research and development was carried out at the National Technical University of Athens (NTUA) and France's Ecole Nationale Superieure d'Ingenieurs de Constructions Aeronautique (ENSICA), with mechanical design by Imperial College London, the latter acting as the project's coordinator – Imperial also developed a new fuel gas compressor. The overall success of this application depended on developing new kinds of turbomachine components and a high-speed magnetic motor with insulated gate bipolar transistor (IGBT) drive.
A gas turbine consists of a compressor, combustor and the turbine. The more efficient, higher capacity axial flow compressors are used in most gas turbines. An axial compressor is made up of a relatively large number of stages, each one consisting of one row of rotating blades (airfoils) and another of stationary blades (stators), arranged so that the air is compressed as it passes through each stage.
Project partners completed the design of two sets of axial turbine components for small gas turbines. These were manufactured and evaluated in the actual gas turbine engine. Results show substantial performance improvements for both sets of hardware.
"Such step improvements in axial turbomachine design have not been recorded before and pave the way for high efficiency turbine engines for the power and transportation industries," says project coordinator Dr Shahram Etemad. "The turbine manufacture within the project has formed specific follow-on activities to exploit the developed know-how."
Similar efforts were also directed towards designing and manufacturing radial turbomachinery, and the resulting components also showed big performance improvements. Radial turbomachines are used extensively in engineering. Centrifugal compressors are found in petrol and diesel engine turbochargers and small gas turbines such as those used in helicopters. The movement of any fluid usually involves the use of a centrifugal pump; millions of them are in use in our homes, vehicles and industries.
Ready to meet global competition
STR managed to reduce gas turbine component manufacturing costs by 30-fold by developing designs suitable for mass manufacture as precision castings instead of being fully machined. The project also produced small turbomachine components for the gas turbine engine to make it as efficient as a conventional diesel engine. It has already shown it can be less polluting.
Once these components are mass manufactured they should make a big impact on the European transportation, and deregulated electricity-generating markets. The market for sub-250 kW electrical generating units also shows worldwide demand for approximately 1.5 million units annually. Even a small market share would make this environmentally friendly technology highly exploitable, and impact employment in the engineering/ manufacturing sector that has suffered in Europe due to lack of technological competitiveness with the USA and Far Eastern based companies.