Technology vision

Challenges in new age of gas turbine engines

The highly complex gas turbine engines work on a simple principle of compression, combustion, expansion and exhaust; and have spanned applications in civil and military aircraft, naval and commercial ships, electricity production, gas compression and oil pumping for over 70 years as an important source of power.

Manufacturers of gas turbine have generally adopted an evolutionary approach to engine design due to engineering and commercial reasons. Progress is often incremental, and once a technology is proven, it is deployed in as many areas as possible. Future development, however, is now likely to involve fundamental changes. Civil aerospace is at a crossroads, on the brink of a new era where environmental and social factors will take on a far greater importance than ever before. The defence sector also enters uncharted territory with the emergence of remotely piloted vehicles. The marine sector is using gas turbines to drive propulsion systems and vessels very different from the conventional propeller driven ship, and energy applications, with their emphasis on efficiency and emission control, will have a major impact this century. The propulsion system requirements of civil and military aerospace are moving in quite different directions, although the underlying technologies remain largely common. Advances in materials, more digital/electric technologies, sophisticated design methods, environmentally cleaner and quieter technologies, and the intelligent engine will all influence further developments of the gas turbine. Because of the commonality of the aeroderivative engine, most of these advances made in aerospace may also be applied to energy and marine products using the Rolls-Royce philosophy of ‘design once, use many times’.1

Major challenges thought to be in the future for the gas turbine engine are categorised in terms of capability (performance, operability and durability); affordability (development cost, production cost and maintenance cost); safety (reliability, robustness and inflight shutdowns); and environmental compatibility (fuel consumption, NO_x emissions and noise). The focus will always be on environmental compatibility and high operational flexibility while maintaining a very high level of efficiency at low operation costs.2

Numerous parameters have to be optimised in order to achieve these challenging targets and this is further complicated by interdependencies between some of these. In recent years, two design requirements have received even higher priority: the reduction of noise and reduction of emissions. Considerable research and development is going into the reduction of these emissions even though significant improvements have been achieved historically.1 However, challenging requirements for the future mean that much still remains to be done.

In order to meet the low emission challenge for the industrial gas turbines, one of the projects co-funded by the European Union, is H₂-integrated gasification combined cycle (IGCC). The full scale demonstration of this technology is expected in 2014 and it will be commercially available by 2020. The overall objective of H₂-IGCC project is to provide and demonstrate technical solutions which will allow the use of state-of-the-art, highly efficient, reliable industrial gas turbines in the next generation of IGCC plants. The goal is to enable combustion of undiluted hydrogen rich syngas with low NOx emissions and also allow for high fuel flexibility. The challenge is to operate a stable and controllable gas turbine on hydrogen rich syngas with emissions and processes similar to current state-of-the-art natural gas turbine engines. The H₂-IGCC project aims to tackle this challenge as well as fuel flexibility, by enabling the burning of back-up fuels, such as natural gas, without adversely affecting reliability and availability. The technical challenges are in the area of combustion, materials, turbo-machinery and system analysis.3

Reduced specific fuel consumption in modern subsonic turbo fan engines requires increased thermal efficiency, albeit increased compression system pressure ratio coupled with high by-pass ratio. Also, increased thrust to weight in high performance gas turbine engines requires increased specific core power. In either case, air cooled gas turbines with higher gas temperature capability are the key. It has been shown that high temperature materials, improved cooling effectiveness, increased aero efficiency, and reduced leakage have been instrumental in enabling an increasing turbine rotor inlet temperature. Improved cooling has provided the bulk of the increase in turbine rotor inlet temperature. In order to meet the above requirement, breakthrough manufacturing technologies for complex internal cooling is needed that in turn will enable material integrity at high temperatures. In essence, with these types of technologies, stoichiometric gas temperature capability in the gas turbine can be met.

Although gas has a significant role to play in the future energy mix, the extent of that role depends on gas prices and how tough governments get on climate change. Future energy policies will have an impact on gas turbine technology. Gas turbine manufacturers are already working on solutions that will increase turbine efficiency to enhance emissions to be cut from gas fired generation. Environmental policy and CO₂ prices will impact users’ technology choices and how gas turbine developers react to user needs. Therefore, how will CO₂ prices affect technology development? How will increasing pressure on emissions drive turbine efficiency? Will technology advances jeopardize reliability? With users needing to arbitrage between fuel, emissions and electricity production, is there a greater need for a focus on both fuel and operational flexibility? If so, what is being done by the manufacturers?4 We have more questions than answers for challenges in the new age of gas turbine engines.

As the complexity of technology and design increases, it leads to increase in cost of development, production and maintenance. In the face of increased complexity, business must also explore opportunities to reduce cost to remain competitive. The major gas turbine engine cost comes from materials, labour and manufacturing. There is a need to develop high performing materials at affordable prices and with a reduction in the number of parts to be assembled in order to reduce the total manufacturing cost. The developments in direct digital manufacturing and higher level of parts’ integration are quite promising in order to have reduced cost that will enhance affordability for customers and provide better product and service at same or lower cost. Rolls-Royce takes an ‘integrated systems’ approach to addressing many of the challenges detailed above.