Aviation is currently one of the strongest growing transport sectors, and this trend is predicted to continue. In the period up to 2030, global aviation is expected to grow by 5% annually according to the International Air Transport Association (IATA). Its effects on the climate change process are not large but not negligible either. Recent estimates indicate that aviation accounts for approximately 2.6% of total anthropogenic CO2 (main greenhouse gas (GHG) produced by human activities) emissions, but this figure is expected to grow up to 3% by 2050. Adding up other flight emissions, like different nitrogen oxides (NOx), particles and water vapor, the total effect reaches approximately 5% of total anthropogenic radiative forcing (RF), the parameter normally used to evaluate the comparable instantaneous effect of all the sources.

While this amount is small compared with other industry sectors, such as energy production and ground transport, these industries have viable alternative energy sources currently available. For example, the power generation industry can turn to wind, hydro, nuclear and solar technologies to produce electricity with low CO2 emissions. In the case of aviation, while solar and electric aircraft are being researched, they are still a long way from commercial versions due to aviation need for high power-to-weight ratio and globally compatible infrastructure. Thus the aviation sector will still be largely dependent on alternative liquid hydrocarbons by 2050.

ICAO predicts that without mitigation measures, total GHG emissions will be 400 to 600% higher in 2050 than in 2010, driven by a sevenfold increase in air traffic [8]. With this perspective, the use of sustainable fuels, with a lower carbon footprint than the fossil-origin kerosene, is generally accepted as the most efficient way to reduce air transport impact on climate change in short-medium term.

Both governments and industry are widely supporting the development and the introduction of sustainable fuels that are able to decrease the carbon footprint of aviation. The EU Directive 2009/28/EC requires a 10% share of renewable energy in the transport sector in every Member State by 2020, and the EU energy roadmap for 2050 aims at a 75% share of renewables in the gross energy consumption. Taking in to account the characteristics of the aviation sector, to achieve this goal it will require a 40% target share of low carbon sustainable fuels to achieve this goal. Aeronautics sector stakeholders have defined as priority “to address key scientific and technical challenges that inhibit development, production and use of economically viable alternative aviation fuels”.

The airline industry is fully committed to this path. For example, the International Air Transport Association (IATA) has established a goal for total global airline operations to emit 50% less GHG emissions by the year 2050 than in the year 2005. Existing analyses indicate, that the GHG emission intensity of aviation would need to decrease by more than 80% in order to achieve this goal.

The aviation community is following this direction by improving aircraft operations, airport and air traffic management, by accelerating the development and deployment airframe and engine technologies, and by aiming for large-scale introduction of alternative jet fuels (AJF) with significantly lower GHG emissions on a lifecycle basis than petroleum-derived jet fuel.

On the policy side, carbon-neutral growth in the short-term and substantial emissions reduction in the medium to long-term are aimed to be incentivized by a mix of policy-measures targeting both Research & Development on mitigation options and their deployment. EU domestic aviation is part of the EU CO2 emissions trading scheme (ETS) and the CO2 offsetting scheme for international aviation (CORSIA) is currently in the last phase of implementation at ICAO.

AJF hold significant promises as a key contributor for mitigating the climate impact of aviation. Contrary to operational measures, AJF can (depending on feedstock and production pathway) reduce the GHG emission intensity of aviation significantly (with the potential of negative emissions for certain pathways), while contrary to other technological measures such as airframe and engine improvement they are not inhibited in their effectiveness by slow fleet turnover. In other words: AJF could be deployed relatively fast and could yield high GHG emissions benefits under the condition of having a specification very close to the one of the fossil-origin kerosene. In this way, it can be blended, using all the existing infrastructure and not requiring aircraft or engines modifications. All AJF complying with those conditions are usually named as “drop-in” fuels.

However, despite significant research and commercialization efforts, there are still significant unknowns pertaining to the environmental benefits of using specific AJF pathways, especially with regard to indirect effects of their use, but also with regard to the impact of “emissions accounting” (e.g. choices being made within the LCA analysis on their perceived benefits). In addition, given that climate impacts of AJF cannot be observed, but only be modelled, there are significant uncertainties involved in key input and output parameters that have to be appropriately captured. Moreover, the economic implications of using AJF have to be studied and compared to the potential environmental benefits. AJF will remain more costly than petroleum-derived jet fuel, which not only has consequences for airline costs and ticket prices, but might make market and policy incentives necessary in order to increase market penetration.

So far, five conversion pathways are approved as alternative blend stocks: Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK), Fischer-Tropsch Synthetic Paraffinic Kerosene with aromatics (FT-SKA), Hydroprocessed Esters and fatty Acids – Synthetic Paraffinic Kerosene (HEFA-SPK), Synthesized Iso- Paraffinic (SIP) and Alcohol-to-Jet – Synthetic Paraffinic Kerosene (AtJ-SPK). However, there are only two facilities worldwide dedicated to the production of alternative fuels, the AltAir fuel refinery in USA California, and Neste oil Porvoo plant, in Finland. It has to be noted that the Neste oil plant only produced HEFA-SPK batch wise. The alternative fuel industry faces different problems to be competitive to petroleum industry. The selection and availability of feedstocks is one of these problems. Alternative fuels are not yet available in volumes sufficient to meet the needs of the aviation industry. In addition, the certification process for alternative fuel is long and expensive, for example, the development of one of the approved pathways mentioned above took up to four years and more than 10M€. Therefore, reducing time, cost and uncertainties of the fuel testing will benefit to additional conversion processes currently under development. Indeed, aviation stakeholders have identified the research to be put in place as “regulatory enablers and a streamlined certification approval process”. The point of departure of the proposed research project is, therefore, the need to reduce the unknowns with regard to AJF’s actual environmental and economic viability, in order to help leverage AJF’s unique promise for a rapid and large-scale decarbonization of the aviation sector. This European and Chinese cooperation proposal aims to enlarge the aviation sustainable fuel framework, in both technical and economic areas, starting with the possible use of more feedstocks and sustainable production pathways than the existing ones. New fuel candidates will be evaluated according to improved modelling methods, considering LCA optimization, climate change effects and technical, economic and environmental consequences of their use. New advanced certification procedures will be proposed and tested to simplify and make more accurate the alternative fuel certification process. On the basis of those results, an evaluation of some possible ways to introduce a relevant amount of sustainable fuels in the air transport market will be done, aiming to formulate specific recommendations for stakeholders on optimising the flight planning system and the use of those sustainable fuels.