Considerations on GHG emissions and energy balances of promising aviation biofuel pathways

This article presents results of a European Commission Joint Research Centre study to analyse the Greenhouse Gas (GHG) emissions and energy efficiency of various options for alternative aviation fuels. Interest in alternative aviation fuels is growing, as the sector seeks viable options to reduce increasing GHG emissions. For biofuels non-biogenic emissions arise from cultivation, harvesting and transport of the feedstock, as well as from their conversion into biofuel. It is important to consider whether any emissions reductions benefits are justified by the energy efficiency of each alternative. This article is focussed on American Society for Testing and Materials (ASTM) certifiable alternative drop-in biojet fuels [1], i.e. non-fossil hydrocarbon fuels which have (i) the same chemical structure and (ii) can be blended with conventional jet fuels, (iii) can use the same jet fuel supply infrastructure, and (iv) do not require modification of the aircraft. The results indicate that the biofuels studied tended to exhibit lower GHG than conventional jet fuels although indirect effects or existing uses of materials were not included in this study. Some biofuels performed better at reducing GHG than others (for example biofuels from wastes and residues). A large and important effect on emissions is seen due to land type used for cultivation and whether methane capture is used for certain pathways. GHG savings results vary due to the Life Cycle Analysis (LCA) methodology chosen for dealing with emissions and co-products. Certain pathways are notably more energy intensive than others and strong GHG reduction does not always coincide with high energy efficiency. An overview of industry initiatives and critical EU legislation relating to aviation biofuels is given. The insights from this work are expected to be of use for decision-makers considering investment options in this sector.