Enabling alternate fuels for commercial aircraft

Abstract

The following reports on the past four years of work to examine the feasibility, sustainability and economic viability of developing a renewable, greenhouse-gas-neutral, liquid biofuel for commercial aircraft. The sharp increase in environmental concerns, such as global warming, as well as the volatile price fluctuations of fossil fuels, has ignited a search for alternative transportation fuels. However, commercial aircraft can not use present alternative fuels that are designed for ground transportation. Aircraft also have much longer service lives, are capital intensive to purchase, require a complex refueling infrastructure, and are specifically designed to use petroleum-type liquid jet fuels. Synthetic jet fuel, manufactured using a Fischer-Tropsch process from coal, is currently the only alternative jet fuel commercially available to aviation, but it presently experiences environmental challenges. Biojet fuels are currently not commercially available for aviation, but have the potential to become quite acceptable If passenger growth increases at 5%/year, it appears the only way that the aviation industry can meets its environmental goals of reducing CO2 emissions would be through commercialization of carbon-neutral fuels. This research shows that biojet fuels can be developed that do not compete with food or fresh water resources, will not lead to deforestation and will not cause other adverse environmental or social impacts. The approach of using a “drop in” jet fuel replacement, which would consist of a blend of kerosene and up to 50% biofuel will be possible for use in existing and future aircraft. A 60-80% lifecycle CO2 emission reduction is calculated for the biofuel portion with no performance degradation. New biofuel processing techniques (i.e. hydroprocessing, isomerization & distillation) and next generation feedstock sources (e.g. halophyte and algal biomass) appear to be the best pathways to enable the large scale deployment of sustainable and economically competitive biojet fuels in the near future.