A comprehensive well-to-wake climate impact assessment of sustainable aviation fuel

This work presents a transpacific airliner designed for minimal climate impact, incorporating several novel design features. These include open rotor engines, sustainable aviation fuels, natural laminar flow airfoils, and riblets. The design’s configuration and mission have been optimised simultaneously using a combination of standard preliminary techniques, experimental data, a multi-point mission analysis, and a model of average temperature response. It is demonstrated that, on an 8000 km mission, the design offers an 89.8% reduction in average temperature response relative to an Airbus A330-200, at the expense of a 7.3% increase in direct operating cost. The sensitivity of these results is investigated by comparing the performance over a range of operating conditions. In addition, several alternative designs incorporating only some of the above-mentioned features are analysed, allowing for an assessment of their individual contribution. Finally, a life-cycle average temperature response analysis is presented to place the climate impact of operation, manufacturing and end-of-life procedures in context.

<div class="section abstract"><div class="htmlview paragraph">Sustainable Aviation Fuels (SAFs) offer great promises towards decarbonizing the aviation sector. Due to the high safety standards and global scale of the aviation industry, SAFs pose challenges to aircraft engines and combustion processes, which must be thoroughly understood. Soot emissions from aircrafts play a crucial role, acting as ice nuclei and contributing to the formation of contrail cirrus clouds, which, in turn, may account for a substantial portion of the net radiative climate forcing. This study focuses on utilizing detailed kinetic simulations and soot modeling to investigate soot particle generation in aero-engines operating on SAFs. Differences in soot yield were investigated for different fuel components, including n-alkanes, iso-alkanes, cycloalkanes, and aromatics. A 0-D simulation framework was developed and utilized in conjunction with advanced soot models to predict and assess soot processes under conditions relevant to aero-engine combustion. The simulations, conducted under combustion and inert conditions, revealed that aromatic fuels significantly enhance soot yield, exhibiting accelerated growth toward larger aromatics under both combustion and pyrolysis conditions. The results also highlight the necessity for higher gas temperatures for PAHs to grow, in agreement with pyrolysis experiments indicating soot onset temperatures between 1400 and 1500K. Furthermore, the study assessed the influence of precursors on soot formation, challenging the appropriateness of using C<sub>2</sub>H<sub>2</sub> or mono-aromatics as precursors with the tested soot models. The simulation results indicate that such precursors lead to large errors, advocating for the use of larger PAHs as precursor in these soot models, as suggested by the models’ validation space. Finally, this work also explores the impact of fuel structure on soot formation, contributing to ongoing efforts to replace aromatics with cycloalkanes in jet fuels through examining reference fuel blends representative of petroleum-based jet fuel and cycloalkane-based SAFs. The “SAF” blends result in a reduced soot yield compared to the jet fuel surrogate, underscoring SAFs’ capability to diminish emissions in the aviation industry.</div></div>

The aviation industry’s efforts to reduce carbon emissions have driven the rapid development and scale-up of sustainable aviation fuels (SAFs). SAFs have the potential to significantly reduce CO2 lifecycle emissions by up to 80% in comparison to Jet A and other conventional fossil-derived jet fuels. For multiple logistical and practical reasons, it is preferable to ensure that SAFs are ‘essentially identical’ (also referred to as ‘drop-in SAF’) to conventional jet fuel in terms of their performance, durability and compatibility with existing hardware systems. Because the majority of SAFs are not identical (non-drop-in) to conventional jet fuel, they have not been approved for use in their neat (100%) form. Instead, these non-identical SAFs are named synthetic blend components (SBC) as they are blended with conventional fuels to different extents per ASTM D7566-23a. It should be noted that there are on-going efforts to develop non-drop in SAF specifications to broaden their proliferation and maximise the aviation industries’ ability to reduce CO2 lifecycle emissions. One very important area of focus is the compatibility of SAFs with engine and fuel system seals, specifically understanding the dynamics of elastomeric seals. To address this, a novel approach has been developed to measure seal dynamics in flowing fuel. This technique has been applied to study the dynamic seal behaviour of four industrially relevant elastomer seals commonly employed in aviation fuel systems. The study involved three test fuels: (i) conventional fossil-derived Jet A, neat hydroprocessed esters and fatty acids (HEFA) SAF, and neat alcohol to jet (ATJ) SAF. Notably, both HEFA and ATJ fuels contain 0% aromatics, in contrast to Jet A, which typically contains around 17% aromatics by volume. The novel fuel-elastomer test rig used in this study was designed to simulate a practical scenario in which fuel flows through the inner surface of a pre-loaded static O-ring. The results of these tests demonstrate that the behaviour of different nitrile elastomers is unique to their formulation, and in all cases, the behaviour in HEFA and ATJ SAF differs significantly from that in Jet A. However, new fuel approval tests may only list one type of elastomer for evaluation, for example the ‘Fit-for-Purpose’ test in ASTM D4054-22 Tier 2 lists one specific nitrile. The findings of this study highlight the complexities of fuel-elastomer interactions within nominally identical chemical families and emphasise the potential risks of assessing compatibility based on tests conducted with a single member of a chemical family.

Ambitious fossil-free targets imposed on the aviation industry worldwide demand a large volumetric supply of sustainable aviation fuel (SAF) to meet. Sweden's commitment to a 30% volume SAF blending target by 2030 attracts interest in local production. However, the sustainability of local production is largely unknown. Addressing this gap, we aim to explore potential SAF technology pathways and assess their environmental performances in Sweden. To do so, we utilize a socio-technical system (STS) approach for pathways selection and prospective life cycle assessment (LCA) for environmental impact assessment. As a result, we identify two lignocellulosic-based and two electrofuel-based pathways and evaluate their global warming potential, mineral depletion potential, ionizing radiation, land use, freshwater ecotoxicity and human toxicity impact in comparison to jet fuel. Our findings show that the well-to-wake global warming potential (100 years) of 30% SAF is on average 20% lower than that of jet fuel, with non-carbon dioxide species emitted in flight being the major contributors, prompting the need for urgent research efforts to mitigate their potential impacts. Under the assumption that no burdens are allocated to waste material used as feedstock, lignocellulosic-based 100% SAF has a well-to-pump climate impact (100 years) ranging from 0.6 to 1.5 g CO2−eq/MJ compared to jet fuel's 10.5 g CO2−eq/MJ. In contrast, the well-to-pump climate impact (100 years) of electrofuel-based 100% SAF (ranging from 7.8 to 8.2 g CO2−eq/MJ) is only marginally lower than that of jet fuel, mainly attributed to emissions from steel and concrete produced for wind turbine manufacturing. In general, the use of electricity generated by wind power could shift the potential environmental burden associated with jet fuel from global warming to mineral depletion, land use, freshwater ecotoxicity and human toxicity. The STS approach underscores the need to prioritize changes in systems underpinning SAF production, in turn supporting policy and investment decision making.

Non-CO2 emissions are the major factor that contributes to the climatic impact of the aviation sector. In addition to reducing net-CO2 emissions, drop-in sustainable aviation fuels (SAF) can lead to a reduction in particulate emissions. The latter may act as condensation nuclei for water vapor to form condensation trails (contrails). However, studies have shown that the differences in particulate emissions of both total soot particle mass and number density between conventional jet fuel and SAF depend on the aero engine operating point. A more detailed assessment of soot emissions along a flight mission requires modeling the soot particle formation including the particle size distribution (PSD), incorporating detailed thermodynamic information of the aero engine and chemical fuel characteristics within reasonable computational time and accuracy. This study applies a chemical reactor network with finite-rate chemistry and a sectional soot model combined with an aero engine performance model to evaluate the soot particle mass, particle number and PSD along with further combustion emissions at various aero engine operating points. Simulations are carried out for different SAF types and compared to conventional Jet-A fuel. The model results show a reduction in soot mass of up to 73% and the formation of fewer large soot particles when using SAF surrogates.

Global energy business is shifting towards more sustainable alternatives fuels due to climate change issue. Countries, companies, and associations start to adopt energy sources with less emission and carbon footprints in their business portfolio, including the introduction of Sustainable Aviation Fuel (SAF) in the aviation industry. Indonesia had created regulation in SAF utilization as blend component in Jet Fuel by the Energy & Mineral Resources Ministry Regulation No.12/2015: 2% (2016), 3% (2020) and 5% (2025). Considering the projected domestic demand of Jet Fuel 6.730.000 KL in 2030, requirement of SAF in Indonesia will reach 337.000 KL. In the contrary, there is no current SAF production in Indonesia despite of its potential feedstock for SAF such as Crude Palm Oil (CPO) Refined Bleached Deodorized Palm Kernel Oil (RBDPKO), or Used Coking Oil (UCO). The research analyzed the business aspect of SAF product development, especially bio-feedstock selection. This paper selected the most optimum feedstock for SAF by Analytical Hierarchy Process (AHP) method with 5 selection criterias: feedstock availability, feedstock price, required capital expenditure (CAPEX), profitability and SAF marketability. A base scenario of “highly regulated and fastly adopted SAF” is selected as the reference of developing the strategy. This scenario is indicated by early warning signs such as establishment of GHG emission reduction framework, establishment of incentives framework and high SAF demand from airlines.

Towards drop-in sustainable aviation fuels in aero engine combustors: Fuel effects on combustion performance

<div class="section abstract"><div class="htmlview paragraph">Aviation industry currently accounts for almost 3% of worldwide greenhouse gas (GHG) emissions. Despite the continuous efforts to reduce this environmental footprint, with the use of technological efficiency driven solutions and operational changes to reduce climatic effects, such as engine improvements, fleet renewals and navigation operational improvements, the industry, which is permanently challenged by the continuously stringent standards, is aware of the need of additional measures to tackle, and even reduce, the GHG emissions, by decoupling the world's industry average growth (almost 4.1% annually) to the aviation's carbon emissions. Given its inherent operational features, the aviation sector requires fuels with high specific energy and energy density. This technical requirement makes the well known clean and efficient electrical propulsion technology to be limited to niche aviation segments (short range and low capacity airplanes) in the short and medium terms. In this scenario, the so called Sustainable Aviation Fuels(SAF) - non fossil hydrocarbons, manufactured with renewable & sustainable feedstocks - appear as the big bet for the carbon footprint reduction for the medium and long range aviation. The biofuel SAF pathway, i.e. that which relies on biological feedstocks (crops and waste), already certified and produced to be used in blends with fossil jet fuel, into a drop-in fuel concept, has some environmental limitations associated with GHG net emissions, cost, and natural resources (land use and water) requirements. These limitations might set sustainable challenges to a massive future biofuel based SAF approach. In this context, the so called Power to Liquids (PtL) fuels, which comprises the production of synthetic liquid hydrocarbon fuels, using renewable electricity (for hydrogen generation with water electrolysis) and non fossil carbon dioxide (CO<sub>2</sub>) as the main feedstocks, is seen as a promising SAF pathway. Compared to biofuels, PtL SAF reaches higher area-related yields, with the intensive use of renewable electricity, such as photovoltaic and wind energy. The PtL's SAF water requirement is also significantly lower, compared to the biofuel production. Hence, the PtL SAF technology is seen as an important SAF pathway to enable a non fossil and fully sustainable fuel supply for aviation in the long run, avoiding the risks and adverse effects potentially associated with biomass based pathways. This work presents, based on an assessment of the researched technical literature, an overview of the PtL SAF technology, with a focus on the production methods and the required inputs, followed by an assessment of operational effects and costs for the aviation sector. The analysis shows that the PtL SAF appears as a promising sustainable SAF pathway, with a lower GHG footprint (into a Lyfecycle basis) and reduced water requirement, as well as a higher yield, compared to the plant-based SAF pathways (biofuels). Moreover, PtL SAF does not raise the demand for arable land, avoiding the so called food & fuel conflict. From a technical perspective, the PtL SAF might produce fuels suitable for even a net fossil fuel substitution (no blends). Nevertheless, the PtL SAF costs, which relies strongly on the renewable electricity price, are still a challenge to enable the competition with fossil jet fuel. This might initially require regulatory actions as well as further technological improvements, mainly associated with renewable electricity - fuel conversion and CO<sub>2</sub> supply alternatives.</div></div>

The aviation industry is challenged to reduce its climate impact. The introduction of sustainable aviation fuels (SAF) is, among other policy instruments such as the European Emissions Trading Scheme, an option favored by policymakers in Europe to achieve this objective. These fuels feature substantially reduced carbon life-cycle emissions in comparison to fossil fuels. In Europe, a mandatory quota for the use of sustainable fuels will most likely be introduced, starting in the year 2025. The introduction of a blending mandate by governments and the European Commission is associated with a range of challenges. The purpose of this paper is to discuss the economics of climate change mitigation in aviation and the role SAFs can play. The economic issues associated with the introduction of SAFs are analyzed, with a particular focus on the European Commission’s proposal for a blending mandate. Several suggestions for improvement are discussed. Furthermore, alternatives to SAFs are presented and evaluated.

Greenhouse gas emissions from the global aviation industry are still rising rapidly, which is based on the emissions from developed economies and driven by the rapid growth of developing economies. China’s aviation industry became the world’s second largest aviation market after the US, with emissions of 94.9 million tons in 2018, equivalent to more than 30 million tons of aviation fuel. However, China’s per capita passenger traffic is still significantly lower than that of developed countries. By 2050, China’s aviation emissions will increase by 130–400%. Although with the growth of the national fleet, Chinese airlines have purchased new and more energy-efficient aircraft, major innovations are still needed in order to avoid uncontrolled growth of emissions in this field. With the rapid development of aviation industry, Chinese President Xi Jinping recently announced at the United Nations General Assembly that China plans to reach the peak of carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060. Although the details are still under study, it is obvious that every sector of China’s economy, including the aviation department, needs to take major actions to decarbonize. In addition, as the international pressure to reduce emissions from the aviation industry is increasing and the international emission reduction plan frameworks, including Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), gradually come into effect, China needs to formulate a plan. The International Air Transport Association (IATA) estimates that in order to achieve carbon neutrality by 2050, the global civil aviation departments will need to significantly increase sustainable aviation fuel (SAF) to replace fossil aviation fuel. With the implementation of new technologies, the use of SAF will account for more than half of the total aviation emission reduction. As one of the largest aviation fuel consumers, China also needs its own methods to develop and expand its SAF production capacity. In this paper, the main opportunities and problems surrounding the development of SAF were summarized, and the main stakeholder groups were identified. It is suggested that the stakeholders in China work out a comprehensive and achievable roadmap to greatly increase the production and application scale of SAF in China, so as to support China’s goal of achieving carbon neutrality by 2060. By learning from the experience of other countries and regions in SAF industry development, policies and formulation of SAF roadmap, China now has the opportunity to promote the development of SAF technology, supply chain and industry in China by combining the needs and interests of government, aviation industry, energy industry, environmental protection and people. In the end, some commercial and policy suggestions were put forward to promote the sustainable development of China's aviation industry in the future.KeywordsSAFBiofuelCORSIAFeedstockCertificationRoadmap

The extensive utilization of fossil fuels by humanity has led to notable ecological degradation alongside a surge in productivity. The ensuing climate change, a result of global warming, poses a grave threat to human survival. A significant contributor to global warming is the emission of abundant greenhouse gases, with carbon dioxide being the most prevalent. Addressing global warming necessitates the identification and adoption of cleaner, alternative fuels to diminish carbon dioxide emissions. Sustainable Aviation Fuel (SAF) emerges as a prime alternative in this context. Chemically akin to conventional and fossil fuels, SAF originates from cleaner sources, offering a reduction in carbon dioxide emissions upon combustion. This paper highlights the importance of SAF as a viable strategy to mitigate CO2 emissions resulting from fossil fuel combustion. The paper also examines different SAF synthesis approaches, such as Fischer-Tropsch, Hydrogenated fatty acid esters and fatty acids (HEFA), and Alcohol-to-Jet (ATJ) processes. In summary, challenges such as high production costs, raw material price fluctuations, and the need for supportive policies hinder SAF's widespread adoption. To address climate change and reduce aviation emissions, further research, technological advancements, government incentives, and collaborative efforts within the aviation industry are crucial.

Comparative assessment of pyrolysis and Gasification-Fischer Tropsch for sustainable aviation fuel production from waste tires

Purpose Sustainable Aviation Fuel (SAF) is crucial for aviation decarbonization, but its current pre-blending process at refineries presents challenges, including fixed blending ratios, higher transportation costs and long lead times. This study explores the potential of an innovative technology that enables on-site SAF blending at airports. By postponing blending to the point of use, this approach offers customization opportunities. However, the precise benefits and trade-offs of this concept remain unclear. The research aims to assess the impact of on-site blending on fuel price, lead time, carbon emissions and supply chain costs. Design/methodology/approach This empirical study evaluates the effects of SAF postponement using case analyses of Singapore-Seletar and Maastricht airports. The analysis incorporates cost modeling, lead time assessment and carbon impact calculations to quantify the implications of shifting blending downstream to airport sites. Data sources include industry reports, airport-specific logistics information and SAF supply chain parameters. A comparative analysis is conducted to determine optimal airport conditions for SAF postponement, highlighting key enablers and barriers to implementation. Findings The results indicate that on-site SAF blending can create competitive advantages by reducing supply chain costs and lowering carbon emissions. The benefits are contingent on airport-specific factors, such as Hydroprocessed Esters and Fatty Acids availability, logistics infrastructure and regulatory conditions. The findings suggest that certain airports, particularly those with strategic locations and favorable cost structures, are better suited for adopting SAF postponement. By shifting production downstream, airports can achieve greater flexibility in SAF blending ratios while minimizing logistical inefficiencies. Originality/value To the best of the authors’ knowledge, this study is among the first to empirically examine the feasibility of postponing SAF blending to the airport level. While existing literature focuses on SAF production and distribution, the concept of downstream blending has not been systematically analyzed. The research provides new insights into how mass customization principles can be applied to SAF supply chains, potentially reshaping fuel logistics in the aviation industry. By identifying critical factors for successful implementation, this study contributes to both academic discussions and practical decision-making in sustainable aviation fuel management.

In order to achieve the International Air Transport Association’s (IATA) goal of achieving net-zero emissions in the aviation industry by 2050, there has been a growing emphasis globally on the technological development and practical application of sustainable aviation fuels (SAFs). Discrepancies in feedstock and production processes result in differences in composition between SAFs and traditional aviation fuels, ultimately affecting the emission performance of the two types of fuel. This paper discusses the impact of CO2/NOx/SO2/CO/PM/UHC emissions from the aviation industry on the natural environment and human health by comparing the two types of fuel under the same conditions. Fuel combustion is a complex process in the combustor of an engine, which transfers chemical energy into heat energy. The completeness of combustion is related to the fuel properties, including spray, evaporation, and flammability. Therefore, engine performance is not only affected by fuel performance, but also interacts with engine structure and control laws. The CO2 emissions of SAFs differ significantly from traditional aviation fuels from a lifecycle analysis perspective, and most SAFs can reduce CO2 emissions by 41–89%. Compared with traditional aviation fuels, SAFs and blended fuels can significantly reduce SO2 and PM emissions. Pure Fischer–Tropsch hydroprocessed synthesized paraffinic kerosine (FT-SPK) can reduce SO2 and PM emissions by 92% and 70–95% respectively, owing to its extremely low sulfur and aromatic compound content. In contrast, the differences in NOx emissions between the two types of fuel are not significant, as their generation mechanisms largely stem from thermal drive and turbulent flow in the combustor, with emissions performance being correlated to power output and flame temperature profile in engine testing. CO and UHC emissions are related to engine operating conditions and the physical/chemical properties of the SAFs, with no significant upward or downward trend. Therefore, SAFs have significant advantages over conventional aviation fuels in terms of CO2, SO2, and PM emissions, and can effectively reduce the hazards of aviation to the environment and human health.

It is hard to decarbonize a passenger jet. The aviation industry contributes to approximately 2.5% of global greenhouse gas emissions, underscoring the need for decarbonization to achieve net-zero emissions by 2050. Sustainable aviation fuels (SAFs) derived from conventional biomass, i.e., agricultural residues, forestry by-products, and organic waste, present a scalable solution. Conventional biomass has the potential to produce 60 to 80 billion liters of SAF annually, meeting up to 20% of current jet fuel demand. Lifecycle assessments indicate GHG emission reductions of 70 to 85% compared to fossil fuels. Advanced conversion technologies such as gasification and fermentation have achieved efficiencies exceeding 65%, demonstrating commercial viability. Case studies highlight significant CO2 reductions of 50 to 70% per flight using SAFs. Despite its promise, biomass-based SAFs are costlier, ranging from USD 1.10 to USD 2.40 per liter. However, policy instruments such as the U.S. SAF Grand Challenge and the EU’s RED II are accelerating adoption. Beyond environmental benefits, SAFs support socio-economic development, potentially creating 1.2 million green jobs globally while addressing waste management challenges. To realize this potential, challenges in technology, economics, and policy need to be addressed. Coordinated efforts in policy, research, and investment are essential to scale SAF deployment, enabling the aviation sector to significantly reduce lifecycle emissions and achieve its net-zero ambitions.