Life-cycle assessment of Greenhouse Gas emissions from alternative jet fuels

Abstract

The key motivation for this work was the potential impact of alternative jet fuel use on emissions that contribute to global climate change. This work focused on one specific aspect in examining the feasibility of using alternative jet fuels - their life-cycle Greenhouse Gas (GHG) emissions relative to conventional jet fuel. This involved the quantification of the overall GHG emissions of potential alternative jet fuels, from feedstock recovery and transportation, to the production, transportation and utilization of the fuels. The fuels examined in this work included jet fuel and ultra-low sulfur jet fuel from conventional crude, jet fuel from oil sands and oil shale, Fischer-Tropsch jet fuel from natural gas, coal and biomass, and biojet from soy oil and palm oil. By identifying and varying important input parameters, a range of life-cycle GHG emissions for each fuel pathway was derived. From the analyses in this work, only alternative jet fuels from biomass offer substantial life-cycle GHG emissions reductions compared to conventional jet fuel, and that is true only if land use change emissions were negligible. Direct or indirect land use changes from the use of biomass feedstocks (particularly food crops) could potentially increase life-cycle GHG emissions to levels several times above that of conventional jet fuel. A scenario analysis was conducted to examine the amount of biofuel needed to displace conventional jet fuel in 2025 to maintain U.S. aviation GHG emissions at baseline 2006 levels. It was found that the large-scale deployment of biofuels to achieve carbon-neutral U.S. aviation growth through 2025 was limited by feedstock and land availability if current generation biofuels (particularly those made from food crops) were used. Hence, it is important to explore the use of next generation non-food, high yield feedstocks (e.g. algae) that use little land and result in little or no land use change emissions for large-scale biofuel production.