Aviation gas turbine alternative fuels: A review

The development of kerosene-like drop-in alternative aircraft fuels is currently receiving increased attention. Using a range payload approach the need for drop in fuels is justified. The alternative fuels available can be categorised into two groups; depending on whether the product increases supply security of supply or provides a reduced environmental footprint. This paper uncovers this relationship through a review of commercially available process technologies (Transesterfication, Fischer-Tropsch (FT) and hydroprocessing (HRJ)) to produce alternative fuels. The lifecycle assessments available are reviewed to identify what are actually clean fuels or have the potential to be one. A summary of the recent alternative fuel flight test campaigns is given and there results evaluated along with ground based results. A review of combustion characteristics available for the alternative fuels including ignition characteristics are presented to demonstrate the effect the distillation curve has on combustion and how too narrow a distribution of components in the fuel could generate problems with high altitude relight. The effect alternative fuels have on gaseous emissions regulated by the International Civil Aviation Organisation (ICAO) Committee on Aviation Environmental Protection (CAEP) is discussed and shown to be engine hardware dependant. Experimental data, from an Auxiliary Power Unit (APU) engine, are provided showing how, although the Gas to Liquid (GtL) and Coal to Liquid (CtL) FT fuels may not reduce GHG emissions, even with Carbon Capture and Sequestration (CCS), the local air quality around airports will benefit through reduced particulate emissions. Finally the prospects for future fuel development are discussed.