By 2050, the evolutionary approach to aero engine research may no longer provide meaningful returns on investment, whereas more radical approaches to improving thermal efficiency and reducing emissions might still prove cost effective. One such radical concept is the addition of a secondary power cycle that utilizes the otherwise largely wasted residual heat in the core engine's exhaust gases. This could provide additional shaft power. Supercritical carbon dioxide closed-circuit power cycles are currently being investigated primarily for stationary power applications, but their high power density and efficiency, even for modest peak cycle temperatures, makes them credible bottoming cycle options for aero engine applications. Through individual geometric design and performance studies for each of the bottoming cycle's major components, it was determined that a simple combined cycle aero engine could offer a 1.9% mission fuel burn benefit over a state-of-the-art geared turbofan for the year 2050. However, the even greater potential of more complex systems demands further investigation. For example, adding inter-turbine reheat (ITR) to the combined cycle is predicted to significantly improve the fuel burn benefit.

This paper provides design and performance data for two envisaged year-2050 engines: a geared high bypass turbofan for intercontinental missions and a contra-rotating pusher open rotor targeting short to medium range aircraft. It defines component performance and cycle parameters, general arrangements, sizes, and weights. Reduced thrust requirements reflect expected improvements in engine and airframe technologies. Advanced simulation platforms have been developed to model the engines and details of individual components. The engines are optimized and compared with “baseline” year-2000 turbofans and an anticipated year-2025 open rotor to quantify the relative fuel-burn benefits. A preliminary scaling with year-2050 “reference” engines, highlights tradeoffs between reduced specific fuel consumption (SFC) and increased engine weight and diameter. These parameters are converted into mission fuel burn variations using linear and nonlinear trade factors (NLTF). The final turbofan has an optimized design-point bypass ratio (BPR) of 16.8, and a maximum overall pressure ratio (OPR) of 75.4, for a 31.5% TOC thrust reduction and a 46% mission fuel burn reduction per passenger kilometer compared to the respective “baseline” engine–aircraft combination. The open rotor SFC is 9.5% less than the year-2025 open rotor and 39% less than the year-2000 turbofan, while the TOC thrust increases by 8% versus the 2025 open rotor, due to assumed increase in passenger capacity. Combined with airframe improvements, the final open rotor-powered aircraft has a 59% fuel-burn reduction per passenger kilometer relative to its baseline.

New commercial aero engines for 2050 are expected to have lower specific thrusts for reduced noise and improved propulsive efficiency, but meeting the ACARE Flightpath 2050 fuel-burn and emissions targets will also need radical design changes to improve core thermal efficiency. Intercooling, recuperation, inter-turbine combustion and added topping and bottoming cycles all have the potential to improve thermal efficiency. However, these new technologies tend to increase core specific power and reduce core mass flow, giving smaller and less efficient core components. Turbine cooling also gets more difficult as engine cores get smaller. The core-size-dependent performance penalties will become increasingly significant with the development of more aerodynamically efficient and lighter-weight aircraft having lower thrust requirements. In this study the effects of engine thrust and core size on performance are investigated for conventional and intercooled aeroengine cycles. Large intercooled engines could have 3%–4% SFC improvement relative to conventional cycle engines, while smaller engines may only realize half of this benefit. The study provides a foundation for investigations of more complex cycles in the EU Horizon 2020 ULTIMATE programme.

The aviation sector is projected to grow rapidly over the next two decades and beyond. These projections coupled with ever more stringent environmental legislation call for action within the commercial aviation sector to radically reduce greenhouse gas emissions by 2050. It is perceived that by 2050 current state-of the-art direct-drive turbofans will have evolved into geared turbofans and geared open rotor engines for short haul missions. These changes in engine configuration may be attributed to calls from the Advisory Council for Aviation Research and innovation in Europe to dramatically reduce CO2 generation and greenhouse gas emissions by 2050. The geared open rotor architecture is predicted to significantly reduce fuel burn relative to a typical short-range year-2000 aircraft mission, and greatly reduce CO2 emissions per passenger kilometer. Although relative fuel-burn benefits have been estimated in various studies, the economic feasibility of developing the geared open rotor (GOR) engine configuration for potential manufacturers and operators has not been reported. Therefore, this paper describes methodologies employed to estimate the relative fuel burn benefit of a short-range year 2050 GOR engine-aircraft configuration. In addition, it details the financial feasibility of year-2050 short-range engine and aircraft concepts, for manufacturers and operators alike. An overview of the technical specifications of a potential ‘GOR2050’ engine configuration is provided. This paper further describes methods employed to predict the unit cost of a year-2050 engine and aircraft concept that might be offered by the manufacturers, as well as a revenue model for manufacturers in the 2050-timeframe. In order to capture the supplier–customer relationship between the OEMs and their customers, direct operating cost (DOC) and representative revenue models have been constructed for the operators. This paper also analyses the effects that potential future fuel price and taxation policies regarding emissions could have on the operational profitability of such an aircraft and engine combination. Based on a representative set of model inputs, an illustrative test-case for a year-2050 short-haul aircraft and engine combination predicts, with a 50% confidence level, that the minimum number of twin-engine aircraft sales needed to ensure the financial feasibility of the program would be 630 units. Furthermore, with a 50% confidence level, a potential operator could expect an internal rate of return over 7%. The impact of different fuel prices and taxation scenarios are quantified in terms of internal rate of return forecasts.

In the article by Rolt(1), there was an error in Equation (2). The correct equation is republished here. 2$$\begin{equation} {W_c} = \ \frac{{{W_{\it cref}}\left( {{T_{\it grel}} - {T_{\it cref}}} \right){{({W_4}/{W_{\it 4ref}})}^{0.65}}}}{{\left( {{T_{\it gref}} - {T_c}} \right)}}\ \ \ \ \ \ \ \end{equation}$$