The Aeronautical Journal December 2024 Vol 128 No 1330

Global air transport is a significant contributor to anthropogenic environmental impact. The use of kerosene for propulsion produces carbon dioxide and water vapour, both greenhouse gases, plus a mixture of nitric oxide and nitrogen dioxide that changes the levels of atmospheric, ozone and methane, also greenhouse gases. Furthermore, the exhaust gases are hot and contain particulates. Under the right conditions, water vapour in the exhaust condenses on the particles, freezes and may form contrails. Some contrails dissipate quickly, whilst others persist for many hours and can, in some cases, develop into cirrus cloud. Both contrails and the associated clouds have a large, direct impact atmospheric warming.

To develop a better understand of these effects, the atmospheric science community needs increasingly detailed and increasingly accurate data on aircraft performance. Unfortunately, such information is generally known only to the manufacturers and the airlines and is often commercially sensitive.

As a contribution to the improved understanding of aviation’s role, a novel, open, transparent and independently verifiable performance model has been under development by Poll and Schumann for several years. Currently, it provides fuel flow rate for gaseous emission estimation and engine overall efficiency to predict the likelihood of contrail formation, but only for cruise. This is because it models the product of the engine overall efficiency and airframe lift-to-drag ratio, η_oL/D, which is the parameter that controls fuel flow rate. In cruise, thrust is always approximately equal to drag and so η_o and L/D both change together in response to changes in drag. However, if the method is to be extended to other phases of flight, where thrust will not always be equal to drag, η_o and L/D must be modelled separately. A method for obtaining L/D at any flight condition has been given in a previous paper and the focus of the present work is to develop a complimentary method for the estimation of η_o under any flight condition.

In books on aircraft design, engine performance is usually represented as either charts for specific, often very old, engines, or curves giving vague trends for groups of, again usually old, engines. Rarely are any fundamental, physics based, relations provided. By contrast, texts on engine design tend to concentrate on the thermodynamic characteristics of components and their integration. There is usually very little information on complete engines and such information that does appear is either anonymised, incomplete, or merely qualitative. Recently, software packages that can be used to build detailed engine models have become available. However, to be reliable, these still need to be calibrated with real engine data. This leaves an important gap in the literature.

However, the overall behaviour of the turbofan engine is constrained by the laws of physics and there are some useful and open sources of data available. This admits a line of development that has the potential to close the current gap and this is the approach adopted in this paper.

Read the Special Issue of The Aeronautical Journal, featuring a curated selection of peer-reviewed papers from Volume 128 – Issue 1330 of The Aeronautical Journal.

The Royal Aeronautical Society is the world’s only professional body dedicated to the entire aerospace community. Established in 1866 to further the art, science and engineering of aeronautics, the Society has been at the forefront of developments ever since.

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