A GHG reduction obligation for sustainable aviation fuels (SAF) in the EU and in Germany

Techno-Economic Analysis (TEA) of Civilian Sustainable Aviation Fuel (SAF) – A systematic review of Hydrotreated Esters and Fatty Acids (HEFA) and Lignocellulosic Biomass Conversion (LCBC) Strategies

The U.S. Bioeconomy: Charting a Course for a Resilient and Competitive Future

<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 global aviation industry adopted a set of targets to mitigate CO2 emissions resulting from air transportation in 2009. The engine fuel burn is the main driver of CO2 emission; hence it will be the focus of this study. Rotorcraft are designed for supporting different types of missions or operations that are different from fixed wing aircraft. For this reason, the rotorcraft strategy for addressing the carbon impact should mainly target the new emerging technologies that will assist in reducing the fuel consumption and the deployment of Sustainable Aviation Fuels (SAF). This paper presents a forecast of the contribution level that could be achieved by rotorcraft industry in CO2 emission reduction in the period up to 2050. A projection of growth in civil rotorcraft fleet worldwide is provided as the starting point. Several new emerging technologies for both rotorcraft and engine together with the implementation scheme and their projected positive net impact on CO2 emission level are considered. Further, the contribution from SAF deployment in rotorcraft operation is analyzed. It is generally recognized that as much as 80% reduction in overall CO2 life cycle emission can be achieved from SAF relative to the fossil-based fuels or Conventional Aviation Fuels (CAF). However, some critical parameters used in predicting the SAF benefits remain uncertain. These pertain to fuel resources, economy, investment and policies. Therefore, consistent with previous studies, several fuel substitution scenarios are considered ranging from the most conservative to an optimistic projection.

The aviation industry is responsible for approximately 2–3% of worldwide CO2 emissions and is increasingly subjected to demands for the attainment of net-zero emissions targets by the year 2050. Traditional fossil jet fuels, which exhibit lifecycle emissions of approximately 89 kg CO2-eq/GJ, play a substantial role in exacerbating climate change, contributing to local air pollution, and fostering energy insecurity. In contrast, Sustainable Aviation Fuels (SAFs) derived from renewable feedstocks, including biomass, municipal solid waste, algae, or through CO2- and H2-based power-to-liquid (PtL) represent a pivotal solution for the immediate future. SAFs generally accomplish lifecycle greenhouse gas (GHG) reductions of 50–80% (≈20–30 kg CO2-eq/GJ), possess reduced sulfur and aromatic content, and markedly diminish particulate emissions, thus alleviating both climatic and health-related repercussions. In addition to their environmental advantages, SAFs promote energy diversification, lessen reliance on unstable fossil fuel markets, and invigorate regional economies, with projections indicating the creation of up to one million green jobs by 2030. This comprehensive review synthesizes current knowledge on SAF sustainability advantages compared to conventional aviation fuels, identifying critical barriers to large-scale deployment and proposing integrated solutions that combine technological innovation, supportive policy frameworks, and international collaboration to accelerate the aviation industry’s sustainable transformation.

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.

Aiming to reduce greenhouse gas emission in the aviation sector, enhance energy security, and create value from domestic, non-food feedstocks, Thailand has set the Sustainable Aviation Fuel (SAF) blending targets to increase from 1% in 2026 to 8% by 2037. This study examines the potential of non-food-based SAF co-products to supplement the road transport fuel supply. Thailand’s SAF deployment will primarily rely on Hydro-processed Esters and Fatty Acids (HEFA) and Alcohol-to-Jet (AtJ) pathways, utilizing non-food feedstocks such as Used Cooking Oil (UCO), Palm Fatty Acid Distillate (PFAD), and molasses-derived ethanol. Therefore, this study estimated the quantity of co-products from considered pathways from literature based on the feedstock availability expected from the SAF targets in the Thailand energy plan. Based on projected feedstock availability, the study estimates that by 2026, HEFA-derived SAF could produce approximately 0.13 million liters per day (ML/D) of diesel and 0.04 ML/D of gasoline-range co-products. With the addition of molasses-based AtJ by 2030, these volumes could rise to 0.74 ML/D of diesel and 0.32 ML/D of gasoline. These co-product volumes contribute significantly to Thailand’s AEDP goals, providing an additional 37.68% beyond biodiesel targets for renewable diesel, and 34.37% beyond ethanol targets for renewable gasoline. These findings indicate that SAF deployment not only supports decarbonization in the aviation sector but also provides co-benefits for the land transport sector by enhancing the supply of renewable diesel and gasoline. This dual-sector impact can help reduce fossil fuel consumption and support Thailand’s greenhouse gas (GHG) reduction targets under the Nationally Determined Contribution (NDC). By quantifying the contribution of SAF co-products to road transport fuels, this study addresses a critical research gap—an area that has received limited attention in the Thai context. However, the support actions are needed to ensured that the utilization of SAF co-products for transport sector can sustainably decarbonizations such as cooperation of relevant industry sector needs, process improvement, emission factor analysis.

<div class="section abstract"><div class="htmlview paragraph">The (commercial) aviation sector (passenger and freight), which is strongly engaged with the world efforts to mitigate the carbon emissions and their inherent climate change effects, has accounted in 2018 for 2.4 % of global carbon dioxide (CO<sub>2</sub>) emissions (pre-pandemic levels). Despite the reductions in air travel demand during the 2020 pandemic, with a reduction of up to 80% in passenger travel during the peak pandemic period, the air travel demand has already recovered to around 80% of the pre-pandemic level, with aviation emissions in 2022 reaching around 800 Mt CO<sub>2</sub>, accounting for 2% of the global energy related CO<sub>2</sub> emissions. Moreover, the demand for air travel is expected to double by 2040, growing at an annual average rate of 3.4%, which means that. despite the efficiency improvement trend (average 2%/year), will almost double the aviation’s greenhouse (GHG) emissions, with a significant increase in its relative GHG share, compared to the other transport modes.</div><div class="htmlview paragraph">Meanwhile the aviation sector is one of the hardest to decarbonize, with few and costly pathways available. Zero emissions technologies, such hydrogen fuel and electric batteries are currently far from commercially ready for aviation use in the short to medium term, due to the technical challenges, such as aircraft onboard liquid hydrogen storage difficulties, as well as battery weight and volume, and are unlikely ever to be able to power large or long-haul flights.</div><div class="htmlview paragraph">In this scenario, the so called sustainable aviation fuel (SAF), a drop-in fuel concept, already available in modest amounts on a commercial scale, are seen as a promising short to medium term alternative to tackle aviation emissions, by using existing aircraft designs and infrastructure. As a drop-in fuel, the SAF enables the replacement for the fossil jet fuel by using the existing fuel delivery and storage infrastructure and existing aircraft engines, with lifespan that still ranges from 20 to 30 years. From a chemical perspective, the SAF is the liquid aviation fuel derived from non fossil carbon resources, such as biomass or organic derived waste feedstocks, as well as synthetic fuels produced from carbon capture and renewable energy sources. They might be currently used in blends with fossil jet fuel, with current blending limits ranging from 5% to 50%, depending on the feedstock and production pathway. It is estimated from the International Air Transport Association (IATA) that to reach the net zero emission commitment, by 2050, around 65% of emission reductions should be reached by replacing conventional jet fuel with SAF.</div><div class="htmlview paragraph">Despite its important role in the aviation decarbonization, the SAF share currently makes up only 0.1% of aviation fuel demand, which requires a huge increase in the production capacity, which might face challenges, such as feedstock availability, fuel sustainability and cost competitiveness.</div><div class="htmlview paragraph">This work presents a review of the SAF technology, with a focus on the production pathways and their environmental footprint, their use on current aircraft engines and the associated required blends, as well as the challenges associated with SAF production increase and cost reductions, still required to make it a realistic aviation decarbonization tool.</div></div>

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.

International governments and the airline industry have set goals to progressively replace aviation fossil fuels with sustainable aviation fuel (SAF). SAF is presently less than 0.1 % of the global aviation fuel supply but projected to be greater than 50% by 2050. SAF is kerosene synthetically produced from sustainable agriculture and recycled waste. SAF has lower contrail-forming particulates and has substantial benefit of lifecycle CO2 reduction from using sustainable feedstocks rather than petroleum. The rotorcraft industry consumes less than 1% of the global aviation fuel supply and is not driving the transition to SAF but will need to have compatibility with SAF. The American Society of Testing and Materials (ASTM) has developed a process in conjunction with the FAA and original equipment manufacturers (OEMs) whereby SAF blends are approved as drop-in equivalent to ASTM D1655 Jet A/A1 fuel and can then be seamlessly distributed and utilized under existing aircraft approvals for Jet A/A1. SAF candidates are comprehensively evaluated by an OEM task group. Global aviation industry, certification agencies, and military are harmonizing around this approach. The FAA has encouraged rotorcraft manufacturers to monitor OEM task group proceedings and provide input for concerns to rotorcraft. A unique rotorcraft concern regarding suction lift fuel systems is explained as an example.

Sustainable aviation fuels (SAFs) are vitally important for aviation decarbonization. The laminar burning velocity (LBV), a key parameter reflecting the combustion behavior of fuel/oxidizer mixtures, serves as a fundamental metric for evaluating SAF performance. This paper systematically reviews and evaluates the LBV experiment method and the performance of traditional aviation fuel, SAFs produced via different pathways, and individual components (n-alkanes, iso-alkanes, cycloalkanes, and aromatic hydrocarbons, as well as the impacts of isomers and homologues) in aviation fuels. It is found that LBV values of different SAFs exhibit significant fluctuations, approaching or slightly deviating from those of conventional aviation fuels. Carbon number, branching degree, substituent types, and testing methods in the components all affect LBV performance. Specifically, increased branching in iso-alkanes reduces LBV, cyclohexane and benzene show higher LBV than their methylated counterparts (methylcyclohexane and toluene), and n-alkylcyclohexanes/benzenes with short (C1–C3) side chains demonstrate minimal LBV variation. Spherical flame methods yield more consistent (and generally lower) LBV values than stagnation flame techniques. These findings provide insights for optimizing SAF–conventional fuel blends and enhancing drop-in compatibility while ensuring operational safety and usability.

Evaluation of performance variables to accelerate the deployment of sustainable aviation fuels at a regional scale

Cost-benefit analysis of using sustainable aviation fuels in South America

The net zero emission objective requires urgent carbon reduction from the aviation sector. Sustainable aviation fuel (SAF) is deemed to reduce aviation’s greenhouse gas emissions in the short to medium term due to civil aircraft’s inherent characteristics. Though SAF is considered a low-carbon aviation fuel, its carbon footprint varies substantially depending on raw materials, techniques, regions, etc. Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) has published SAF’s default carbon footprint values; however, the findings only encompass a limited range of raw material categories, techniques, and regions, potentially compromising the evaluation accuracy. We used a thorough review of the literature to reveal the status quo of SAF and its carbon footprint. First, we constructed the process flow for SAF production from different raw materials, creating a network of integrated processes. Next, we reviewed the SAF’s carbon footprint from 194 cases across five continents. At the regional level, the average carbon footprint of SAF production was lower in South and North America. For raw materials, oil-produced SAF had the lowest carbon footprint. For techniques, the catalytic hydrothermolysis jet route has the smallest carbon footprint. Meanwhile, the results demonstrate a significant divergence between the SAF’s carbon footprint made from different raw materials using the same technique. Comparing the literature values with those from CORSIA underscores the need to include more studies in the calculation. The study finally summarizes the factors that may influence the results accuracy and highlights more environmental and socioeconomic dimensions that should be considered in future research.

Global aviation sector contributes nearly 2.5% of global CO2 emissions. Aviation is hard-to-decarbonize sector due to the high energy densities required for aircraft. Commercial aviation is fueled by kerosene-based jet fuel. Alternatives for this carbonbased fuel include electric batteries, hydrogen fuel, and SAF. Electric batteries have very low energy densities. Hydrogen would require a complete change of the aviation system, including fuel & airport infrastructure. SAF is the only viable option in the short to medium term. SAF is produced from sustainable feed-stocks (like agricultural oils), with no embodied carbon. Existing airplanes can use traditional fuel blended with up to 50% SAF, without changing the aviation system. Currently, global SAF production accounts only for 0.5% of global aviation fuel, and costs at least 2 times more than traditional jet fuel. Egypt plans to produce SAF for the first time from UCO using the chemical process known as Hydro-processed Esters and Fatty Acids (HEFA). The contribution of this paper is to highlight some concerns regarding the feedstock availability and quality, the pricing of the product, and the required policies and regulations in order to produce SAF in Egypt successfully. Egypt can benefit from the existing units of its refineries, mainly hydrogenation and isomerization, and the produced SAF can be used for supplying its twenty six airports that operated 365,000 flights in 2023. Surplus SAF production can be exported, hence adding value to the Egyptian economy and contributing to decreasing the carbon emissions from the international aviation sector.