The world’s main atmospheric “greenhouse gas” is carbon dioxide (CO2). The CO2 content of the atmosphere continues to rise due to increasing world demand for energy, and thus further means are needed to achieve its abatement. Most gas turbine powered electricity generating plants use hydro-carbon fuels and this inevitably produces CO2 in the engine exhaust. This paper discusses a scheme for concentrating the gas turbine exhaust CO2, thus facilitating its extraction. The scheme is a gas turbine operating synchronously in closed cycle, with CO2 as the working fluid. The additional CO2 and water produced in the combustion process are removed continuously. CO2 and air have substantially different gas properties. This significantly affects the performance of the gas turbine. It is shown that any gas turbine designed to use air, and operating synchronously, would need considerable modifications to its compressor and combustion systems to use carbon dioxide as its working fluid.

The estimation of gas turbine engine weight during the preliminary or conceptual design phase is a key part of a Techno-economic Environmental Risk Analysis (TERA). Several methods that are available in the public domain are analysed and compared, in order to establish the physics driving them and their suitability for the weight estimation of modern gas turbine engines. Among the tested methods, only WATE managed to achieve acceptable accuracy for engine optimisation studies. This work demonstrates that the age and restrictions of existing 'whole engine based' methods, along with their dependency on old engine databases make them unsuitable for future and novel aero engines. A hybrid weight modelling approach is proposed as a solution permitting the creation of simple 'whole engine based' methods that do not depend on the availability of existing engine data, which are also subject to uncertainties and incoherencies.

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The use of hydrogen as an aviation fuel can be beneficial for the reduction of CO2 emissions, if renewable energy sources are used for hydrogen production. Pure hydrogen fuel produces no CO2 in flight. NOx emissions can be significantly lower for hydrogen fuelled combustors than for current kerosene fuelled combustors. Other advantages derive from the high energy content, which reduces the necessary fuel mass, and from the availability of a valuable heat sink, useful to improve cycle performance. The present paper (based on the EU Cryoplane Project) focuses on the use of hydrogen in aero gas turbine engines. It studies the differences in performance produced by of its cryogenic properties in unconventional cycles. Three novel concepts are applied to a turbofan aero engine; for each cycle the improvement in performance at take-off and cruise is presented. An estimation of the weight and size of the engine is then made.

The current situation of fuel supply, fuel price, noise, and other environmental regulations are reviewed. Some current trends in aero engine design for subsonic transport aircraft are considered and their possible impact on fuel economy, airline economics and the environment are assessed.