Towards drop-in sustainable aviation fuels in aero engine combustors: Fuel effects on combustion performance

The application of sustainable aviation fuels (SAFs) in aviation industry has emerged as a key strategy for reducing the net carbon oxide (CO₂) emissions while minimizing modifications to the current aircraft and engine systems. SAFs, which are derived from sustainable feedstocks through biological, thermal and chemical (or their combinations) conversion pathways, can be used in current aero engines, however, at a maximum blending ratio of 50 % with conventional fossil-based jet fuels due to their distinct physical and chemical properties. To enable the use of 100 % ‘drop-in’ SAFs, extensive research has been conducted to obtain a better understanding of the fuel effects on the combustion performance of aero engine combustors, especially the comparison between SAFs and conventional jet fuels. The present paper aims to provide a comprehensive review on this topic by firstly introducing the production pathways of both conventional jet fuels and SAFs, which serve as the root cause of the distinct physiochemical properties among the fuels of interest. Then, the relationship between fundamental combustion properties (atomization, ignition and flame speed) and fuel peculiarities is explored and discussed. This is followed by a summary of the currently available component- and engine-level tests/simulations which compare the emissions, lean blowout (LBO) limit and combustion instabilities of conventional jet fuels and SAFs. Finally, representative flight tests fueled by SAFs ranging from 2006 to the most recent 2023 are summarized and discussed. The paper closes with key conclusions and future directions for the development of SAFs.