Biojet Fuel - A Tool for a Sustainable Aviation Industry - A Technical Assessment

Abstract

The aviation industry currently holds a share of 2% global greenhouse gas (GHG) emissions. Although relatively small, estimated demand increase indicates an up to 350% emission rise in 2050, in the so called “no action scenario”. These emissions are injected into the upper atmosphere, with a potentialized stronger greenhouse effect than at ground level. In this context, ambitious emission reduction targets have been proposed into a global commitment, focused into a long term carbon emission reduction strategy, which would lead to net GHG emissions to peak in 2020, and then halves by 2050, based on 2005 levels, while accommodating increased air transport demand. To achieve this challenging goal, a multifaceted approach is required, ranging from technology oriented actions, like revolutionary aerodynamically driven design, new composite lightweight material and engine technology improvement, as well as improved ground and flight operational practices. However, such an ambitious target cannot be achieved solely by technology and operational improvements within the aviation industry alone. In this context, the so called Sustainable Aviation Fuels (SAF), most particularly biofuels (biojet fuels), have been identified as having the potential to make a significant contribution to a carbon emission reduction pathway in the aviation industry, as they allow a 50 to 80 percent GHG reduction into a lifecycle basis, compared to fossil fuel emissions, as well as a reduction in sulfur, soot and particulate emissions. Biojet fuel, the generic term that describes biofuel for jet engines, made from renewable, biologically derived material, is basically a liquid fuel produced through chemical processes/conversion pathways, with the same or better performance properties available on conventional jet fuel (petroleum based). They may be used in the so called drop-in fuel concept, which allows compatibility with existing engines, aircraft, fuel storage and distribution system, as well as be blended with existing tradition (petroleum based) jet fuel in increasing quantities (currently up to 50%). From a technical perspective, biojet fuels perform as well as or better than traditional petroleum based jet fuel. Nevertheless, current availability of aviation biofuels is limited and their costs are still higher than petroleum based jet fuels, basically due to production processes’ technology immaturity and small scale production. However, there are currently ongoing efforts from the aviation industry focused on identifying sustainable and economically feasible biologically derived feedstocks, conversion process and supply chains, to make biojet fuel competitive with fossil based jet fuel in the medium term. Moreover, as crude oil supply and pricing become less predictable, conventional jet fuel prices will trend upward. This work is supposed to present an overview of the current state of the art of biojet fuel technical knowledge (from feedstock, conversion methods to in use performance analysis), associated with an economic assessment, followed by some illustrative case studies, into a unique document, to make available to the reader the current most relevant available biojet fuel technology knowledge into a review format.