A technoeconomic risk assessment of conventional aero-gas turbines: technological limits and future directions

Increasing environmental awareness, uncertain economic climates and fluctuating fuel prices have led to airlines investigating the means to lower aircraft fuel burn, emissions and noise, while maintaining the highest possible safety standards. This is done in order to reduce operating costs as well as a desire to offer customers more environmentally responsible transport options. The jet engine has been a fundamental part of passenger aircraft travel and has evolved to become more efficient and quiet. With an aim to improve the overall efficiency of the gas turbine, the industry has consistently sought to improve thermal and propulsive efficiency. Higher thermal efficiencies have been achieved through increased overall pressure ratios and the turbine entry temperatures, while higher propulsive efficiencies has been achieved through increase in bypass ratios. Conventional technology is however reaching the limits of any further improvements. This study seeks to investigate these design limits for the conventional aero gas turbine and focusses on the propulsion system of short to medium range jet aircraft, specifically catering to low cost airline operations in Europe. A techno-economic risk analysis approach was followed through the utilisation of a flexible multi-disciplinary framework. This allows a multitude of critical parameters and factors to be investigated and their effects established. Some of the key parameters investigated include the effect of design optimisation on SFC, mission fuel burn, engine sizes and weights. By first quantifying the current design parameters and associated constraints for the selected conventional propulsion system, an optimisation study is carried out to identify the possible design limits to which the conventional technology may be pushed. It is therefore possible to then quantify the maximum benefit available to this mature technology and also to further identify which future technologies may offer the most benefits for a particular airline market strategy. The key contribution to knowledge from this study is to therefore provide a techno-economic risk assessment of an optimised conventional high bypass ratio turbofan and establish the design limits that may be needed to achieve further benefits from conventional designs. The study is undertaken from an operator/airline perspective and further quantifies the point at which the investment opportunity of a novel technology justifies the risks associated with it. This study has shown that there is still potential for fuel burn improvement from the evolution of the conventional turbofan. This improvement could be up to 15-20% when compared to technology of the year 2000. This is shown to be achieved through improvement material and design of the high pressure compressor spool, aimed at essentially reducing weight and diameters. The study also includes a qualitative discussion on novel, disruptive technologies, and the risks associated with their introduction as future propulsion systems.