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A recent review of aviation fuels and sustainable aviation fuels
Abstract
Aviation fuels are essential for flight transportation. The increasing demand for such fuels threatens the present efforts to mitigate global warming. Changing to renewable energy sources and hydrogen to drive airplanes is not ready and will take a few decades. Therefore, alternative fuels such as sustainable aviation fuels (SAFs, also so-called bio-jet fuels) could play an excellent role in mitigating greenhouse emissions. SAFs encompass blends of bio and synthetic fuels. Some SAF pathways have already been certified (such as oil-to-jet, alcohol-to-jet, gas-to-jet, and sugar-to-jet), and some are on the way to being certified. This review starts by providing a detailed overview of the current status of aviation fuels, including their growth, types, and emission trends. After that, it comprehensively delves into a thorough discussion of SAFs, covering various aspects such as their types, combustion properties, production technologies and pathways, cost evolution, and life cycle assessments. The paper discusses the SAFs’ future prospects while providing practical recommendations based on the analysis. It was shown that the oil-to-fuel (HEFA) pathway is more mature with less carbon emissions. SAFs face challenges, including high costs, limited production scale, feedstock availability, energy-intensive production methods, land-use competition, potential indirect environmental impacts, certification standards, infrastructure, and public acceptance. Much research is needed to reduce SAF costs substantially less than conventional aviation fuels.
... • Alcohol-to-Jet (ATJ-SPK) technology extracts polymeric sugars from biomass feedstocks and then involves their saccharification to obtain glucose and fermentation to obtain an alcohol platform molecule that is then dehydrated, oligomerized, and hydrogenated to produce large paraffin and iso-paraffins. Ethanol and isobutanol are some of the raw materials studied for this technology [10][11][12][13]. • Fischer-Tropsch (FT-SPK) involves the transformation of synthesis gas (syngas) into liquid hydrocarbons as the main technology, for which the biomass must be transformed into syngas through high-temperature gasification and then reformed to adjust the H 2 and CO ratio for final synthetic fuel production [14]. ...
The production of sustainable aviation fuel (SAF) has gained more attention in recent years due to the initiative to implement new technologies to improve the decarbonization of the energy and transport industry, especially the aviation sector, in different countries. In Mexico, the production of SAF has been promoted as a sustainable initiative to boost the agro-industrial sector, the nation’s self-sufficiency, and compliance with national and international CO2 emission reduction goals. Nowadays, there are two technologies with a high level of technological readiness ready to be implemented as a solution to produce SAF, which are hydrotreating esters and fatty acids (HEFA) and Alcohol to Jet (ATJ). These technologies use biomass as a source of feedstock and are described as possible sustainable solutions to reduce the CO2 emissions from conventional aviation fuels. This work analyses the feasibility of implementing these two technologies as a strategy to promote the use of SAF in Mexico from the biomass available in the country based on a techno-economic analysis and a life cycle assessment of each technology. Based on this study on SAF production, a return on investment of 10.2% for HEFA-SPK technology and 13.7% for ATJ-SPK technology was obtained.
... Though safe and efficient, aviation is facing more and more pressure due to its relatively high passenger-to-emission ratio: though aviation-related emissions only constitute approximately 2.5% of global anthropogenic CO2 emissions, the percentage is not proportional to the total number of travelers by means of transport (Bergero et al., 2023, and references therein). The introduction of Sustainable Aviation Fuel (SAF) is now expected to turn the odds in aviation's favor (Qasem et al., 2024), with an estimated reduction of up to 80% in CO2 emissions and some estimates providing even higher yields (Prussi et al., 2021). Carbon dioxide (CO2) is a powerful climate-altering agent due to its GWP (Global Warming Potential), which essentially indicates its capacity to perform a radiative forcing effect on Earth's atmosphere, and therefore alter the climate of our planet (Liu et al., 2017). ...
Mounting pressure on emissions strictly connected to aviation has led to the development of SAF or Sustainable Aviation Fuel, an efficient tool by which aircraft operations are expected to cut emissions of climate altering agents considerably. According to several estimates, CO2 (carbon dioxide) emissions could be cut significantly, and the emission of sulfur compounds into the atmosphere could also be vastly reduced via SAF. Though this form of alternative fuel is still somehow challenged by costs, production availability and related concerns, it’s still expected to lead to considerable reductions in terms of aviation-related emissions over the course of forthcoming years. As of today, the attention is almost entirely focused on reduced emissions and how to make the implementation of SAF more efficient, but there’s a remarkable side effect of SAF’s replacement of conventional fossil fuels – namely, its characteristic carbon isotope fingerprint – which could be used to improve estimates and other models at least on local scales.
... International agreements, such as the Paris Agreement, outline carbon emission reduction targets to mitigate the effects of climate change [1]. To address the increasing demand from the aviation and transport sectors, the implementation of alternative fuels is essential for reducing pollution and promoting environmental sustainability [2]. The use of biofuels in combustion at low temperatures shows great potential to reduce the emissions of CO, THC, and NO x [3]. ...
This work presents an experimental study of the performance and emissions of an internal combustion engine operating in the Otto cycle with a high volumetric compression ratio (17:1). The engine was initially fueled with the standard ethanol used in Brazil, with 7% distilled water (E93W07); we then studied the effects of using different ethanol-in-water mixtures, or ‘wet ethanol’, with 17%, 27%, 37%, and 47% distilled water concentrations. The tests were carried out with power loads of 5.0–25.0 kW at 5.0 kW intervals and with power loads of 27.5–35.0 kW at 2.5 kW intervals, whether by adding up the loads or by taking them away. The ignition timing was changed to evaluate each load imposed on the engine to avoid knocking. Specific fuel consumption (SFC), brake thermal efficiency (BTE), carbon dioxide emissions (CO2), carbon monoxide (CO), nitrogen oxides (NOx), and total hydrocarbon content (THC), as well as the internal pressure in the cylinder and the heat release rate, were measured, and the results are compared. The results show a reduction in CO and NOx and an increase in THC emissions. However, there were no significant changes in CO2 emissions when the distilled water percentage in ethanol increased. Regarding the brake thermal efficiency, it was observed that it remained approximately constant for all blends, with the same load being applied to the engine shaft, reaching a maximum value of 35%. The results obtained confirm the technical feasibility of operating an internal combustion engine in the Otto cycle with a high volumetric compression ratio using ethanol with up to 47% distilled water without significant loss of performance.
... Although the use of SAF has grown, alternative fuels account for less than 0.1% of jet fuel consumption and cost up to twice as much as its traditional pathways [44]. There are many barriers to the broader use and development of these technologies, such as economic viability, development difficulties, and legal and bureaucratic issues. ...
The use of biofuels represents a promising means of achieving a sustainable future and offers considerable economic and environmental benefits. Since they are derived from organic sources, such as vegetable oils and animal fats, biofuels can mitigate the effects of greenhouse gas emissions, improve air quality, support local agriculture, create employment opportunities, and enhance energy security by reducing dependence on fossil fuels. However, introducing these alternative fuels to the aviation sector remains a significant challenge. Thus, it is vital to investigate the potential of sustainable aviation fuel (SAF) and discover how to overcome the technological obstacles to its integration into mainstream aviation to attain broader decarbonization objectives. This article seeks to contribute to a discussion about SAF by examining how it has evolved and its connections to related patents. This article is a comprehensive study of biofuel innovation, highlighting the complex relationships between academia, industry, and other stakeholders. It is hoped that the findings from this study will provide a clearer understanding of the catalysts involved in SAF innovation and provide valuable insights for policymakers, academics, and professionals in the field who are committed to shaping the trajectory of sustainable energy technologies in the future.
With the aviation industry facing increasing environmental and energy challenges, there has been a growing demand for sustainable aviation fuel (SAF). Previous studies have shown the role of ice accretion, release and blockage in aviation-related incidents and accidents with conventional jet fuel. However, there is no available data that establishes the magnitude of influence new fuel compositions will pose on ice formation and accretion in aircraft fuel systems. A recirculating fuel test rig capable of cooling fuel from ambient to −30°C within 4h was built by Airbus to simulate conditions in an aircraft wing tank and allow characterisation of ice accretion. The key characteristic was the pressure drop across an inline fuel strainer for the different SAF explored but visual analysis of ice accretion on the strainer mesh (filters used in protecting fuel feed pumps) was also performed for individual experimental runs for comparison. Measurements revealed that 100% conventional fuel exhibited a higher propensity to strainer blockage compared to the SAF tested. However, all SAF blends behaved differently as the blending ratio with Jet A-1 fuel had an impact on the pressure differential at different temperatures. Data from this work are essential to establish confidence in the safe operation of future aircraft fuel systems that will potentially be compatible with 100 % SAF.
The Paris Agreement’s objectives related to climate change put aviation under great pressure and environmental inspection. In particular, the aviation industry is committed to achieving a 50% reduction in CO2 emissions by 2050 compared to 2005 levels. A shift to alternative aviation fuels seems imperative. The International Air Transport Association (IATA) has identified the production of drop-in sustainable liquid fuels (SAFs) as the most promising strategy, at least short term, to reduce the environmental impact of the sector. Within this review, a critical summary of the current alternative aviation fuels/pathways is presented and a comparative analysis of the dominant technologies is performed considering techno-economic assessment, environmental evaluation, and future projections. The impact of the ‘ReFuelEU Aviation’ initiative on the current dominant policies and market incentives is assessed. Hydroprocessed esters and fatty acids (HEFA), Fischer–Tropsch (FT) synthesis, alcohol-to-jet (AtJ) conversion, and e-fuel pathways are put under the microscope. A wide range of potential fuel selling prices (0.81–5.00 EUR/L) was observed due to the presence of multiple routes, while some pathways seem able to secure more than 90% emission savings compared to the fossil jet reference. The accelerated scale-up of SAF production is a reasonable demand for the aviation industry. The establishment of a sustainable scale-up framework and the alignment of all of the involved aviation stakeholders is an immediate challenge.
Concerns have been raised about the effects of fossil fuel combustion on global warming and climate change. Fuel consumer behavior is also heavily influenced by factors such as fluctuating fuel prices and the need for a consistent and reliable fuel supply. Microalgae fuel is gaining popularity in the aviation industry as a potential source of energy diversification. Microalgae can grow in saltwater or wastewater, capture CO2 from the atmosphere and produce lipids without requiring a large amount of land. As a result, the production of oil from microalgae poses no threat to food availability. The low carbon footprint of microalgae-derived fuels has the potential to mitigate the impact of traditional aviation fuels derived from petroleum on climate change and global warming. Therefore, aviation fuels derived from microalgae have the potential to be a more environmentally friendly and sustainable alternative to conventional fuels. Gathering microalgal species with a high lipid content, drying them, and turning them into aviation fuel is an expensive process. The use of biofuels derived from microalgae in the aviation industry is still in its infancy, but there is room for growth. This study analyses the potential routes already researched, their drawbacks in implementation, and the many different conceptual approaches that can be used to produce sustainable aviation fuel from microalgal lipids. Microalgae species with fast-growing rates require less space and generate lipids that can be converted into biofuel without imperiling food security. The key challenges in algal-based aviation biofuel include decreased lipid content, harvesting expenses, and drying procedure that should be enhanced and optimized to increase process viability.
Aviation produces a net climate warming contribution that comprises multiple forcing terms of mixed sign. Aircraft NOx emissions are associated with both warming and cooling terms, with the short-term increase in O3 induced by NOx emissions being the dominant warming effect. The uncertainty associated with the magnitude of this climate forcer is amongst the highest out of all contributors from aviation and is owed to the nonlinearity of the NOx–O3 chemistry and the large dependency of the response on space and time, i.e., on the meteorological condition and background atmospheric composition. This study addresses how transport patterns of emitted NOx and their climate effects vary with respect to regions (North America, South America, Africa, Eurasia and Australasia) and seasons (January–March and July–September in 2014) by employing global-scale simulations. We quantify the climate effects from NOx emissions released at a representative aircraft cruise altitude of 250 hPa (∼10400 m) in terms of radiative forcing resulting from their induced short-term contributions to O3. The emitted NOx is transported with Lagrangian air parcels within the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model. To identify the main global transport patterns and associated climate impacts of the 14 000 simulated air parcel trajectories, the unsupervised QuickBundles clustering algorithm is adapted and applied. Results reveal a strong seasonal dependence of the contribution of NOx emissions to O3. For most regions, an inverse relationship is found between an air parcel's downward transport and its mean contribution to O3. NOx emitted in the northern regions (North America and Eurasia) experience the longest residence times in the upper midlatitudes (40 %–45 % of their lifetime), while those beginning in the south (South America, Africa and Australasia) remain mostly in the Tropics (45 %–50 % of their lifetime). Due to elevated O3 sensitivities, emissions in Australasia induce the highest overall radiative forcing, attaining values that are larger by factors of 2.7 and 1.2 relative to Eurasia during January and July, respectively. The location of the emissions does not necessarily correspond to the region that will be most affected – for instance, NOx over North America in July will induce the largest radiative forcing in Europe. Overall, this study highlights the spatially and temporally heterogeneous nature of the NOx–O3 chemistry from a global perspective, which needs to be accounted for in efforts to minimize aviation's climate impact, given the sector's resilient growth.
This paper examines the potential of suitable second-generation feedstocks for sustainable aviation fuel production, theoretically based on fatty acid-based fuel properties. The fatty acid composition of 38 s-generation feedstocks was collected from the literature. The fuel properties of these feedstocks were then calculated using empirical formula and assessed according to international fuel standards including American and European standards. The selected feedstocks were assessed and ranked using a multi-criteria decision analysis (MCDA) tool, i.e., PROMETHEE GAIA, to identify the suitability of the sources based on kinematic viscosity (KV), density (D), higher heating value (HHV), cetane number (CN), iodine value (IV), oxidation stability (OS), and cold filter plugging point (CFPP). It was found that 20 of the 38 feedstocks meet international fuel standards. The utilisation of the MCDA tool indicates that Ricinus communis is the highest-ranked feedstock for sustainable aviation fuel production, followed by the Azadirachta indica feedstock, with Sterculia feotida L. the lowest-ranked feedstock. The assessment of the properties of ranked feedstock against aviation fuel standards, including Jet A and Jet A1, reveals that the kinematic viscosity of all the feedstocks meets both these standards. However, fatty acid-based fuel properties could not satisfy the international aviation fuel standards for D, HHV, and freezing points. Further experimental work is recommended, including improvements in the processing and modification of biofuel produced from second-generation feedstocks. It is recommended that a comprehensive action plan is required to facilitate the introduction of sustainable biofuel from non-edible sources for the aviation industry, such as the adjustment of the current jet fuel standards.
As the push for carbon-neutral transport continues, the aviation sector is facing increasing pressure to reduce its carbon footprint. Furthermore, commercial air traffic is expected to resume the continuous growth experienced until the pandemic, highlighting the need for reduced emissions. The use of alternative fuels plays a key role in achieving future emission goals, while also lowering the dependency on fossil fuels. The so-called sustainable aviation fuels (SAF), which encompass bio and synthetic fuels, are currently the most viable option, but hydrogen is also being considered as a long-term solution. The present paper reviews the production methods, logistical and technological barriers, and potential for future mass implementation of these alternative fuels. In general, biofuels currently present higher technological readiness levels than other alternatives. Sustainable mass production faces critical feedstock-related challenges that synthetic fuels, together with other solutions, can overcome. All conventional fuel replacements, though with different scopes, will be important in meeting long-term goals. Government support will play an important role in accelerating and facilitating the transition towards sustainable aviation.
Presented work has an overview character and is focused on perspectives of sustainable aviation fuels application in civil aviation sector. The mean role of SAF application is to ensure reduction of greenhouse gas emissions and aviation footprint on environment. Paper describe the combustion proces of hydrocarbon fuels and problem related to the emission of carbon dioxide to the atmosphere. Fuel consumption, CO2 emission and SAF production data was presented on the graphs. The sustainalbe aviation fuel has been characterized. Certified conversion technologies with potential feedstock used for SAF production was described. Literature studies indicate that sustainable aviation fuel is successfully used in air transport.
This article presents a preliminary suitable sizing methodology for the design process of the powertrain architecture for a hybrid-electric propulsion system for ultra-light and general aviation aircraft. The main objective of this activity is to design and realize a prototype of a hybrid-electric propulsion system for Cessna 337 aircraft with a maximum take-off power of 134 kW. At the same mission, two operating strategies have been chosen, max recharge and max efficiency. The first one consists of the engine running at wide-open throttle to quickly charge the battery, while the second runs at minimum specific consumption to reduce consumption. The primary energy assessment has been conducted in all proposed propulsion configurations with the same aircraft, mission, and maximum take-off weight. The results also indicated that parallel hybrid propulsion shows a better compromise in terms of 10% energy saving, 4% CO
2
reduction, and mission duration.
Advanced biofuels are required to facilitate the energy transition away from fossil fuels and lower the accompanied CO2 emissions. Particularly, jet fuel needs a renewable substitute, for which novel production routes and technology are needed that are more efficient and economically viable. The direct conversion of bio-syngas into fuel is one such development that could improve the efficiency of biomass for jet fuel processes. In this work, bifunctional catalysts based on hierarchical zeolites are prepared, tested and evaluated for their potential use in the production of actual jet fuel. The bifunctional catalysts Co/H-mesoZSM-5, Co/H-mesoBETA and Co/H-mesoY have been applied, and their performance is compared with their microporous zeolite-based counterparts and two conventional Fischer–Tropsch Co catalysts. Co/H-mesoZSM-5 and Co/H-mesoBETA showed great potential for the direct production of jet fuel as bifunctional catalysts. Besides the high jet fuel yields under Fischer–Tropsch synthesis conditions at, respectively, 30.4% and 41.0%, the product also contained the high branched/linear hydrocarbon ratio desired to reach jet fuel specifications. This reveals the great potential for the direct conversion of syngas into jet fuel using catalysts that can be prepared in few steps from commercially available materials.
Front‐end design decisions for a process to produce sustainable aviation turbine fuel from waste materials were presented. The design employs distributed conversion of wastes to oils, which are then transported to a central facility for gasification, syngas cleaning, Fischer–Tropsch synthesis and refining, that is, a spoke‐and‐hub approach. Different aspects of the front‐end design, that is, the steps up to syngas cleaning, were evaluated. The evaluation employed a combination of case studies, calculations, experimental investigations, and literature review. The supply of sustainable aviation fuel (SAF) as a 50:50 mixture of waste‐derived and petroleum‐derived kerosene to meet the demand of an international airport (Pearson, Toronto) was employed as case study. The amount of raw material required made it impractical to make use of only one type of waste. Using the same set of assumptions, it was shown that in terms of cumulative transport distance required, a spoke‐and‐hub approach was twice as efficient as centralized processing only. Technologies for decentralized production of oils were assessed, and oils produced by pyrolysis and hydrothermal liquefaction (HTL) in pilot‐scale and larger facilities were procured and characterized. These oils were within the broader compositional space of pyrolysis oils and HTL oils reported in laboratory studies. The oil compositions were employed to study the impact of oil composition on entrained flow gasification. Thermodynamic equilibrium calculations of pyrolysis and HTL oil entrained flow gasification resulted in H2/CO ratios of syngas and O2 consumption rates in a narrow range, despite the diversity of feeds. At the same time, to produce an equal molar amount of syngas (H2 + CO), less HTL oil than pyrolysis oil was required as feed. Gas cleaning technologies were reviewed to ascertain types of contaminants anticipated after gasification, their removal effectiveness, and Fischer–Tropsch catalyst poisoning potential. Raw syngas cleaning requirements were comparable to that from coal gasification.
A policy change in the European Union's Emissions Trading Scheme (EU ETS) provides us with a unique opportunity to measure the impact of carbon pricing on aviation, the most climate-intensive mode of transport. We implement a difference-in-differences strategy on a sample based on all flights within Europe from 2010 to 2016 to examine the causal impact of the EU ETS on emissions and supply. We find that the EU ETS reduced emissions by 4.7% in the regulated routes relative to the counterfactual. When we restrict the sample to short-haul flights, routes on which competition from other means of transport may exist (less than 1,000 km), the reduction in emissions is 10.7%. Finally, the reduction in emissions is also high for low-cost airlines (−11%) but it is not statistically significant for network airlines. In sum, the EU ETS has helped to mitigate emission growth by 3 Mt CO2 per year during the period analyzed, but not to reduce absolute emissions in the sector, as needed.
The coronavirus 2019 (COVID 19, or SARS-CoV-2) pandemic that started in December 2019 has caused an unprecedented impact in most countries globally and continues to threaten human lives worldwide. The COVID-19 and strict lockdown measures have had adverse effects on human health and national economies. These lockdown measures have played a critical role in improving air quality, water quality, and the ozone layer and reducing greenhouse gas emissions. Using Soil Moisture Active Passive (SMAP) Level 4 carbon (SMAP LC4) satellite products, this study investigated the impacts of COVID-19 lockdown measures on annual carbon emissions globally, focusing on 47 greatly affected countries and their 105 cities by December 2020. It is shown that while the lockdown measures significantly reduced carbon emissions globally, several countries and cities observed this reduction as temporary because strict lockdown measures were not imposed for extended periods in 2020. Overall, the total carbon emissions of select 184 countries reduced by 438 Mt in 2020 than in 2019. Since the global economic activities are slowly expected to return to the non-COVID-19 state, the reduction in carbon emissions during the pandemic will not be sustainable in the long run. For sustainability, concerned authorities have to put significant efforts to change transportation, climate, and environmental policies globally that fuel carbon emissions. Overall, the presented results provide directions to the stakeholders and policymakers to develop and implement measures to control carbon emissions for a sustainable environment.
Near-term decarbonization of aviation requires energy-dense, renewable liquid fuels. Biomass-derived 1,4-dimethylcyclooctane (DMCO), a cyclic alkane with a volumetric net heat of combustion up to 9.2% higher than Jet A, has the potential to serve as a low-carbon, high-performance jet fuel blendstock that may enable paraffinic bio-jet fuels to operate without aromatic compounds. DMCO can be produced from bio-derived isoprenol (3-methyl-3-buten-1-ol) through a multistep upgrading process. This study presents detailed process configurations for DMCO production to estimate the minimum selling price and life-cycle greenhouse gas (GHG) footprint considering three different hydrogenation catalysts and two bioconversion pathways. The platinum-based catalyst offers the lowest production cost and GHG footprint of 1.5/L-Jet-Aeq cost and 18.3 gCO2e/MJ GHG footprint if biomass sorghum is the feedstock. This price point requires dramatic improvements, including 28 metric-ton/ha sorghum yield and 95–98% of the theoretical maximum conversion of biomass-to-sugars, sugars-to-isoprenol, isoprenol-to-isoprene, and isoprene-to-DMCO. Because increased gravimetric energy density of jet fuels translates to reduced aircraft weight, DMCO also has the potential to improve aircraft efficiency, particularly on long-haul flights.
Since fast-growing emissions from the aviation sector have become a major contributor to climate change, global efforts have been undertaken to reduce them effectively. The European Union Emissions Trading System (EU ETS) and the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) are two existing market-based measures (MBMs) for addressing aviation emissions, whose implementation has been affected by the Coronavirus 2019 (COVID-19) pandemic. This article aims to examine challenges that the pandemic has posed on both systems by assessing the policy options for revising the EU ETS provisions on aviation, as well as the political debates regarding amendment to the CORSIA design in June 2020.
Key policy insights
• From the environmental, economic and international perspectives, none of the six policy options proposed in the Inception Impact Assessment regarding future implementation of CORSIA alongside the EU ETS is optimal to achieving the EU’s multiple goals in revising its ETS.
• This article recommends the adoption of a hybrid option, which would help maintain international intra-EU/European Free Trade Association (EFTA) flights under the EU ETS scope to achieve EU climate targets and at the same time still integrate some features of CORSIA’s design in implementation. Concerning the reduction of free allowances for aviation, the swift phase-out option should be considered in conjunction with plans to develop sustainable aviation fuels (SAFs).
• While long-term effects of the pandemic on the effectiveness of CORSIA remain to be seen, its immediate impacts can be noticed in the weakening of this scheme’s credibility and stability in implementation.
The aviation sector has grown at a significant pace in recent years, and despite improvements in aircraft effi
ciency, the sector’s impact on climate change is a growing concern. To address this concern, the International
Civil Aviation Organization (ICAO) established the Carbon Offsetting and Reduction Scheme for International
Aviation (CORSIA) to help reduce aviation greenhouse gas (GHG) emissions. This paper presents a methodology
agreed by the 193 ICAO member states to evaluate the life-cycle GHG emissions of sustainable aviation fuels
(SAFs), in the CORSIA system. The core life-cycle assessment and induced land use change values of SAFs are
presented to determine the GHG savings of certified pathways. The paper aims to present that a number of SAFs
can yield significant life-cycle emission reductions compared to petroleum-derived jet fuel. This implies the
potentially major role of SAFs in reducing aviation’s carbon footprint.
Over the coming years, the world is projected to witness an upsurge in “drop-in” aviation biofuel production as part of the renewable energy and bioeconomy developments. This paper presents a comprehensive review of the current status of biojet fuel development and uptake in global commercial aviation industry, including state-of-the-art certified technologies (i.e. Fischer-Tropsch (FT); hydroprocessed esters and fatty acids (HEFA); alcohol-to-jet (ATJ); and hydroprocessing of fermented sugars (HFS)); potential feedstock that can be deployed; a comparison of techno-economic and environmental performances of biojet fuel production routes; airlines’ commitment in promoting higher biofuel uptake; and global initiatives and policies. This review shows that the HEFA route using oil-based crops is best performing in terms of lowest production cost and greenhouse gas emissions, however it is in competition with the existing road transport biofuel market. Lignocellulosic biomass and waste feedstock should be promoted in view of replacing food/feed crops which have high indirect land use change emissions. Therefore, further improvement should be focused on FT, ATJ and HFS routes to enhance the cost effectiveness of biojet fuel production and promote commercialisation of these technologies. The selection of feedstock and technologies for SAF production should be justified based on production cost and environmental footprint, while avoiding competition with the existing road transport biofuel market. The shortcomings in the SAF policies such as blending mandate and multiplier in RED II should be addressed to reduce the negative impacts of feedstock competition between the road and aviation biofuel sectors and to meet the decarbonisation targets.
This study assesses an integrated biorefinery model's efficiency for biojet fuel production as Jet A1 blending component through the Alcohol-to-Jet (ATJ) and Hydroprocessed Esters and Fatty Acids (HEFA) thermochemical routes, employing lignocellulosic biomass from oleaginous crops. The ATJ process involved cellulosic ethanol production through steam explosion hydrolysis, simultaneous saccharification and co-fermentation. The anhy-drous ethanol was sequentially dehydrated, oligomerized, and hydrotreated. On the other hand, the HEFA process upgraded vegetable oil from residues and fatty acid distillates. The vegetable oil was thermally hydro-lyzed, decarboxylated and hydrotreated. The models were simulated in AspenPlus® v.11, achieving a specific biojet fuel production of 48 wt% for the ATJ and 87 wt% for the HEFA. In both cases, a biojet fuel mixture primarily composed of C 9 to C 12 isoalkanes was produced. The minimum selling price ranged between 1.01 €/kg to 1.43 €/kg. The studied routes were evaluated through exergetic and thermoeconomic analyses for optimizing. The life cycle assessment was carried out in SimaPro® v.9.0. The estimated net GHG emissions were 75 gCO 2eq / MJ for the ATJ and 18 gCO 2eq /MJ for the HEFA; nevertheless, significant improvements were achieved from by-product displacement credits. In both cases, the GHG emissions are under those from petroleum-derived Jet A1 production. Finally, the physico-chemical properties fulfilled the ASTM D7566 specifications, and the calculated payload vs range showed a better performance for an intermediate-range flight.
PurposeBio-jet fuel derived from energy crops has been promoted by governments around the world through policies such as the Carbon Offsetting and Reduction Scheme for International Aviation. The environmental impact and techno-economic analysis of bio-jet fuel are particularly pertinent to China because China is under huge pressure to reduce emissions, endeavouring to meet bio-economic goals.Methods
An LCA study was conducted on the production of bio-jet fuel from jatropha and castor by estimating the well-to-wake emissions and its economic impact. The functional unit was 1 MJ of bio-jet fuel, and field survey data was used in inventory analysis. A scenario analysis was performed to measure diverse conditions, including the planting conditions, planting regions, allocation methods, and hydrogen sources. A techno-economic analysis that combined the production costs and co-product credits was performed to calculate the minimum bio-jet fuel selling price (MJSP) based on a plant capacity of 2400 metric tonnes of feedstock per day.Results and discussionCompared to the environmental impacts to the fossil jet fuel, the use of biofuel would reduce the majority environmental impacts by 36–85%, when a 1:1 displacement of fossil jet fuel is considered, though the human toxicity potential impact was 100% higher. The scenario analysis indicated that (i) planting castor in harsh and unevenly distributed conditions and jatropha in stable or fertile conditions can leverage their respective advantage; (ii) the global warming potential (GWP) from castor planting in the region of north-east China ranges from 34 to 48 g CO2 eq/MJ; (iii) the GWP produced through the steam methane reforming process can be reduced by 16–17%, using advances in technological processes. The MJSP for fuel produced from jatropha and castor under the basic scenario is estimated to be 5.68 and 4.66 CNY/kg, respectively, which falls within the current market price range of 4.5–7.5 CNY/kg.Conclusions
Bio-jet fuel from jatropha and castor oilseeds offers potential environmental benefits if they can reduce fossil jet fuel on an energy-equivalent basis. However, these benefits are likely to be reduced by the rebound effect of the fuel market. Future research is needed to better understand the magnitude of the rebound effect in China and what policy interventions can be implemented to alleviate it. Scenario analysis demonstrated the feasibility and potential of bio-jet fuel development from multiple perspectives and technological progress are conducive to the realization of environmental protection policies.
The aviation sector is responsible for at least 2% of the anthropogenic greenhouse gas (GHG) emissions. The production and use of new sustainable aviation fuels (SAFs) appear as the most relevant strategy to achieve significant GHG emissions reductions in aviation industry. Gasification technology has the potential of converting carbonaceous feedstock, as lignocellulosic biomass, in an atmosphere of low oxygen and high temperature into syngas, which can be used for energy production or synthesis of chemical compounds. Well-known technologies, such as Fischer–Tropsch (FT), or developing processes, such as alcohol-to-jet (ATJ) fuel, are being studied for the conversion of gasification syngas into SAF. The term sustainability transcends carbon footprint. This definition should be analyzed considering its three fundamental pillars (environmental, economic, and social). Therefore evaluation tools, such as techno-economic analysis (TEA) and life cycle assessment (LCA), determine whether or not the SAF produced is sustainable. The economic and environmental performance indicators of these assessments allow the comparison of different technologies and feedstocks. Generally, the minimum jet fuel selling price and the global warming are the indicators determined in existing TEA and LCA studies for the SAF from the FT process, and similarly but with less studies for the SAF produced through the ATJ pathway.
COVID-19 has prompted unprecedented government action around the world. We introduce the Oxford COVID-19 Government Response Tracker (OxCGRT), a dataset that addresses the need for continuously updated, readily usable and comparable information on policy measures. From 1 January 2020, the data capture government policies related to closure and containment, health and economic policy for more than 180 countries, plus several countries’ subnational jurisdictions. Policy responses are recorded on ordinal or continuous scales for 19 policy areas, capturing variation in degree of response. We present two motivating applications of the data, highlighting patterns in the timing of policy adoption and subsequent policy easing and reimposition, and illustrating how the data can be combined with behavioural and epidemiological indicators. This database enables researchers and policymakers to explore the empirical effects of policy responses on the spread of COVID-19 cases and deaths, as well as on economic and social welfare. The Oxford COVID-19 Government Response Tracker (OxCGRT) records data on 19 different government COVID-19 policy indicators for over 190 countries. Covering closure and containment, health and economics measures, it creates an evidence base for effective responses.
Research efforts have investigated a range of system designs for algae growth and conversion into biofuels. The economic feasibility and environmental impact of these systems are frequently evaluated through techno-economic analyses (TEA) and life-cycle assessment (LCA), which typically determine the levelized cost of fuel production in gallons of gasoline equivalent (MFSP, in $-gge⁻¹), global warming potential (GWP, in g CO2-eq-MJfuel⁻¹), and net energy ratio (NER, unitless). While the outputs from these models seem comparable, the results often conceal the impact of a large number of assumptions inherent to the modeling, limiting direct comparisons. As such, a direct comparison of the modeling results as published can be misleading due to differences in critical assumptions and/or foundational methodology. This work applies harmonization methodology to several sustainability assessment studies found in the literature with the goal of enhancing comparability through implementation of a standard set of assumptions. For the economic evaluation, two harmonization efforts were performed: the first focused on harmonizing productivity, economic assumptions, and cost year for the entire growth to product process; the second compared only downstream fuel conversion technologies by fixing the biomass cost, thereby removing the uncertainty of upstream-growth assumptions. For LCA, harmonization focused on productivity and system boundary. The results of these efforts show a decrease of 43% in the range of reported fuel prices and minimal redcution in the range of LCA results. Both TEA and LCA harmonization efforts then investigated the impact of productivity by simulating a range of biomass productivity values (12.5, 25, and 50 g-m⁻² day⁻¹). The work reveals limitations to both the economic and environmental benefits of productivity improvements past approximately 35 g-m⁻² day⁻¹. Results highlight the need to redirect research efforts not only to increase productivities, but also to other areas where investments can make a greater impact in terms of economic viability and environmental impact.
This paper outlines the benefits and procedures for prescreening Sustainable Aviation Fuel (SAF) candidates before entering the official ASTM D4054 evaluation process. Specific properties are identified, that if not met, may result in extensive and costly efforts to correct if not recognized until later in the fuel development process. Hence, an approach with specific techniques that use low fuel volumes is suggested that enable (1) early estimates of critical properties and subsequently (2) direct measurement of these properties to guide fuel processing development prior to formally entering the ASTM evaluation process. The process is demonstrated with two exemplary candidate fuels.
Climate neutrality is becoming a core long-term competitiveness asset within the aviation industry, as demonstrated by the several innovations and targets set within that sector, prior to and especially after the COVID-19 crisis. Ambitious timelines are set, involving important investment decisions to be taken in a 5-years horizon time. Here, we provide an in-depth review of alternative technologies for sustainable aviation revealed to date, which we classified into four main categories, namely i) biofuels, ii) electrofuels, iii) electric (battery-based), and iv) hydrogen aviation. Nine biofuel and nine electrofuel pathways were reviewed, for which we supply the detailed process flow picturing all input, output, and co-products generated. The market uptake and use of these co-products was also investigated, along with the overall international regulations and targets for future aviation. As most of the inventoried pathways require hydrogen, we further reviewed six existing and emerging carbon-free hydrogen production technologies. Our review also details the five key battery technologies available (lithium-ion, advanced lithium-ion, solid-state battery, lithium-sulfur, lithium-air) for aviation. A semi-quantitative ranking covering environmental-, economic-, and technological performance indicators has been established to guide the selection of promising routes. The possible configuration schemes for electric propulsion systems are documented and classified as: i) battery-based, ii) fuel cell-based and iii) turboelectric configurations. Our review studied these four categories of sustainable aviation systems as modular technologies, yet these still have to be used in a hybridized fashion with conventional fossil-based kerosene. This is among others due to an aromatics content below the standardized requirements for biofuels and electrofuels, to a too low energy storage capacity in the case of batteries, or a sub-optimal gas turbine engine in the case of cryogenic hydrogen. Yet, we found that the latter was the only available option, based on the current and emerging technologies reviewed, for long-range aviation completely decoupled of fossil-based hydrocarbon fuels. The various challenges and opportunities associated with all these technologies are summarized in this study.
The present study evaluated the influence of three strategies to improve the economic feasibility of sustainable aviation fuel (SAF) production through gasification and Fischer-Tropsch synthesis (GFT) of lignocellulosic biomass feedstocks in Biomass-to-Liquids (BtL) plants. Apart from the integration with sugarcane ethanol production and the use of economic incentives by the carbon credits market, we evaluated the decentralization of the production chain with fast pyrolysis (FP) units to densify the biomass into bio-oil, aiming to reduce feedstock transportation costs for biofuel production. These analysis made use of process simulation coupled with techno-economic assessment (TEA) and life cycle assessment (LCA).
Carbon credits commercialization alone is not enough to enable the standalone GFT scenario with current prices (up to 30 US/L and achieve over 70 g of CO2 eq avoided/MJ of SAF. The addition of the FP process for decentralization is a better option than a centralized production only for distances above 1,000 km. This is due to expenses with feedstock bio-oil being from 2 to 5 times higher than with the direct use of solid biomass. In conclusion, the path to make SAF production feasible lies in the integration with more mature routes and by relying on incentives from environmental policies, while the decentralization could help markets with highly disperse biomass availability.
Sustainable alternative fuels, or SAFs, are recognized to have lower carbon footprints and emit fewer greenhouse emissions. As a carbon-neutral alternative and intended drop-in fuels, SAFs would be an appropriate path forward for sustainable aviation. Current approved drop-in fuels enable 50% blending of SAFs, which decreases CO2 emissions up to 40%. However, CO2 emissions can be reduced much further by using 100% SAFs or hydrogen. Comprehensive analysis of SAFs in terms of their operational performance, impact on gaseous and particulate emissions, seal swell, engine and fuel systems compatibility, blow-off limits, ignition and relight, vibrations, and noise is essential to move towards 100% SAFs. Furthermore, SAF has been demonstrated to reduce other emissions like NOx, particulate and CO2 emissions subjective to the fuel production pathways. Therefore, engineering novel fuels and innovative production pathways may lower emissions and reduce the costs of aircraft system design and operation, resulting in cheaper air travel. This study thoroughly examined and discussed all the aspects mentioned above. Hydrogen, a potential competitor for SAFs, has also been analyzed in this study in terms of future production capability to meet aviation needs and the impact of hydrogen combustion on design changes, emissions, and fuel systems. Furthermore, to reduce experimental costs related to SAFs, this study explored approaches for modeling and predicting novel fuel performance in the preliminary stages of fuel assessment.
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An increase in jet fuel consumption and its associated emissions across the world have led to the need for alternative technologies to produce sustainable aviation fuels (SAF). One option to produce SAFs is to utilize waste or biomass-based feedstocks that has the potential to reduce greenhouse gas emissions by 50% or more compared to conventional jet fuel. However, there is a lack of understanding of how the synergistic effects of key performance variables could hinder or help the deployment of aviation fuels on a regional scale. Here, we assess the implications of key variables–including type and quantity of waste/biomass feedstock availability near the airport, cost of SAF production, life cycle greenhouse gas (GHG) emissions, policies, and fuel/infrastructure logistics–on the deployment of SAF at Chicago’s O’Hare International Airport. We consider three ASTM International-approved SAF technologies (Hydroprocessed Esters and Fatty Acids, Fischer-Tropsch, and Alcohol to Jet) that can be blended up to 50% with petroleum-based jet fuel. Results from our analysis show that woody biomass-based Fischer-Tropsch technology has the lowest fuel production costs (2.31–2.81/gallon gasoline equivalent) of all pathways, and it reduces life cycle GHG emissions by 86% compared to conventional jet fuel despite the higher availability of crop residues compared to either woody biomass or fats, oils, and greases. Also, infrastructure is available at O’Hare International Airport to blend SAF with Jet A fuel through three terminals directly connected to the airport via pipelines. Our sensitivity analysis shows renewable fuel incentives and feedstock price to be key performance variables affecting the production cost and deployment of SAF.
As one of the fastest-growing carbon emission sources, the aviation sector is severely restricted by carbon emission reduction targets. Sustainable aviation fuel (SAF) has emerged as the most potential alternative to traditional aviation fuel, but harsh production technologies limit its commercialization. Fatty acids photodecarboxylase from Chlorella variabilis NC64A (CvFAP), the latest discovered photoenzyme, provides promising approaches to produce various carbon-neutral biofuels and fine chemicals. This review highlights the state-of-the-art strategies to enhance the application of CvFAP in carbon-neutral biofuel and fine chemicals production, including supplementing alkane as decoy molecular, screening efficient CvFAP variants with directed evolution, constructing genetic strains, employing biphasic catalytic system, and immobilizing CvFAP in an efficient photobioreactor. Furthermore, future opportunities are suggested to enhance photoenzymatic decarboxylation and explore the catalytic mechanism of CvFAP. This review provides a broad context to improve CvFAP catalysis and advance its potential applications.
This paper investigates options to produce low carbon and renewable aviation fuel through existing commercial first generation biorefineries, which could be strategic given the rapid growth of the electric vehicle market for personal mobility. We evaluate the environmental impact of retrofitting a first generation biorefinery to produce aviation fuel through chemical process simulation. The analysis investigates the potential for reducing greenhouse gas (GHG) emissions and displacing fossil fuel (petroleum-based jet kerosene) in the aviation fuel industry through using corn feedstocks in dry grind biorefineries to convert sugars to 1,4-dimethylcyclooctane (DMCO), which qualifies as renewable jet-A fuel blend and is infrastructure compatible. The average life cycle GHG emissions for a baseline case and a scenario with carbon capture and storage (CCS) of fermentative CO2 are 36 and 5 g CO2 e/MJ DMCO, respectively. Investment in CCS at the biorefinery and adoption of crop best management practices on farms are essential for mitigating the risks of induced land use change GHG emissions for existing corn biorefineries. DMCO as a low-carbon aviation fuel could be a strategic fuel product for retrofitting existing corn dry grind facilities. For aviation fuel supply, corn dry grind facilities could displace about 12 % of jet fuel demand in the near term, which would meet sustainable aviation fuel policy targets. We conclude that corn-to-DMCO shows promise for near-term low-carbon fuel markets in the aviation industry and as a bridge to developing biomass-based jet fuel in the future.
Europe anchored aspiring targets in achieving climate neutrality and this motivates the research communities to analyze, investigate and frame strategies to achieve the goals in the stipulated timeframe. This study reviews the effective decarbonization strategies in the context of Europe's climate neutral vision. Initially, the study analyzes the reasons for ever-increasing emissions and investigates the perception of decarbonization in line with various influencing factors such as population size, economic growth, energy intensity, emission intensity, innovation, affordability and time. Subsequently, an in-depth qualitative analysis is performed to force out the challenges that Europe faces in decarbonizing the heating sector from the aspects, such as using clean energy resources, effective heat energy conversion and management approaches. Sustainable approaches and practices are proposed to mitigate carbonization and to promote carbon sink in line with the major problems associated with various sectors such as building, energy, industry and transportation sector. Furthermore, the roles of digitalization in decarbonization are explored and the inherent challenges are also discussed. This study also reviews various decarbonization policies that can direct the governments' action to effectively make a transition towards a climate-neutral society. The key findings highlight that solar energy utilization in small-scale is relatively not preferable for heat energy conversion in Europe due to climatic conditions, while district heating network with bio- and geothermal energy resource highly favors clean heat transformation scenario. In addition, 3D printing has a prodigious role to reduce building lifecycle emissions and hybrid policies as well as reward-based policies yields better outcomes. Promoting hydrogen utilization and carbon capture storage and utilization technologies can pivot climate neutrality in the sectors that are difficult to decarbonize. On the other hand, it can be observed that more focus is provided to reduce emissions and significantly less attention is focused on carbon sink.
View Video Presentation: https://doi.org/10.2514/6.2022-2048.vid This paper explores the idea of thermally cracking ammonia via shock waves to produce a blend of ammonia-hydrogen as a ‘carbon neutral’ aviation fuel, reducing global carbon dioxide emissions. The method is based on wave rotor technology utilizing the energy contained in the combustor burned gas to compress and heat ammonia to temperatures at which high conversion rates can be achieved on short timescales. Then, the resulting ammonia-hydrogen mixture is fed into the burner as reactant which leads to hydrogen, nitrogen, and water vapor as primary gas products. The shock wave process has been modeled numerically using an in-house quasi-one-dimensional code by Tüchler and Copeland that has been experimentally validated for non-reacting wave rotors. A single-reaction, global kinetic model was developed to approximate the NH3 pyrolysis reaction chemistry across the temperature and pressure conditions of interest, thereby enabling the incorporation of chemistry in the numerical simulations. The computational results provide data used in the prediction of flow fields inside the channels of the wave reformer and at the inflow/outflow ports of the reactor. The data confirm production of a mixture of ammonia and hydrogen using energy harvested from the engine burner exhaust. This study introduces a new application of the shock-wave reforming process as well as another step in the realization of ammonia as an aviation fuel without carbon content.
Aircraft powered by green hydrogen (H2) are a lever for the aviation sector to reduce the climate impact. Previous research already focused on evaluations of H2 aircraft technology, but analyses on infrastructure related cost factors are rarely undertaken.
Therefore, this paper aims to provide a holistic overview of previous efforts and introduces an approach to assess the importance of a H2 infrastructure for aviation. A short- and a medium-range aircraft are modelled and modified for H2 propulsion. Based on these, a detailed cost analysis is used to compare both aircraft and infrastructure related direct operating costs (DOC).
Overall, it is shown that the economy of H2 aviation highly depends on the availability of low-cost, green liquid hydrogen (LH2) supply infrastructure. While total DOC might even slightly decrease in a best LH2 cost case, total DOC could also increase between 10 and 70% (short-range) and 15–102% (medium-range) due to LH2 costs alone.
Besides lower environmental impact, full and hybrid-electric propulsion systems offer an opportunity to set-up a highly redundant powertrain. As safety is one of the important topics for the design of unmanned aircraft systems (UAS), concepts of full-electric and hybrid-electric propulsion have been investigated in terms of meeting: mass, volume, power, energy and safety constraints. In the first step, the powertrain system has been sized according to preliminary design data described in the project Automated Low Altitude Air Delivery (ALAADy) using generic data of state-of-the-art system components. In the next steps the powertrain system has been analyzed and modelled with simulation models to investigate the system performance in more detail. Optimal powertrain system architectures concerning system overall mass and redundancy have been set up especially for the vehicles designed for the ALAADy project. The differences between full-electric and hybrid-electric powertrain systems is discussed as well.
Many existing scenario studies show the need for large amounts of biomass energy with carbon dioxide capture and storage (BECCS) to achieve net-zero emissions, requiring high mitigation costs. This study provides comprehensive and cost-efficient technological portfolios for both energy supply and demand, and reveals the roles of carbon dioxide utilization (CCU) and direct air capture (DAC) for achieving global net-zero emissions by using a technology-rich global energy systems and climate change mitigation model which can assess them comprehensively, while considering several kinds of uncertainties. According to the analyses, DAC will be able to dramatically reduce emission reduction costs and alleviate dependence on BECCS. There are no feasible solutions for temperature increases below 1.5 °C in 2100 with 66% achievability under a temperature overshoot pathway unless DAC is used. Carbon free or nearly carbon free hydrogen plays important roles for net-zero emissions, and CCU helps increase the usability of hydrogen via synthetic fuels, and thus contributes to net-zero emissions. The relationships between DAC and CCU are very complex; the reductions in marginal abatement costs of carbon dioxide (CO2) due to DAC will reduce the roles of CCU around 2050 for many of the pathways to net-zero emissions. Meanwhile, for deeper reductions of CO2 emissions including net negative emissions in 2100, DAC will increase the roles of CCU by providing recovered CO2 from DAC, and also expand the opportunity for the use of recovered CO2 from fossil fuel combustion for synthetic fuels, because the related emissions are offset by larger negative emissions from the combination of DAC and CO2 storage (DACCS).
This study aims to investigate the contribution of aviation related travel restrictions to control the spread of COVID-19 in Europe by using quasi-experiment approaches including the regression discontinuity design and a two-stage spatial Durbin model with an instrumental variable. The study provides concrete evidence that the severe curtailing of flights had a spontaneous impact in controlling the spread of COVID-19. The counterfactual analysis encapsulated the spillover effects deduced that a 1% decrease in flight frequency can decrease the number of confirmed cases by 0.908%. The study also reveals that during the lockdown, the aviation industry cancelled over 795,000 flights, which resulted in averting an additional six million people being from being infected and saving 101,309 lives.
Substitution of conventional jet fuel with low-to zero-carbon-emitting alternative aviation fuels is vital for meeting the climate targets for aviation. It is important to understand the technical, environmental, and economic performance of alternative aviation fuels and prospective engine and propulsion technologies for future aircraft. This study reviews alternative fuels and propulsion systems, focusing on costs and technical maturity, and presents conceptual aircraft designs for different aviation fuels. The cost review includes minimum jet fuel selling price (MJFSP) for alternative aviation fuels. Direct operating cost (DOC) is estimated based on the conceptual aircraft designs and the reviewed MJFSP. The DOCs for bio-jet fuel (5.0–9.2 US cent per passenger-kilometer (¢/PAX/km)), fossil and renewable liquefied hydrogen (5.9–10.1 and 8.1–23.9 ¢/PAX/km, respectively), and electro-methane and electro-jet fuel (5.6–16.7 and 9.2–23.7 ¢/PAX/km, respectively) are higher than for conventional jet fuel (3.9–4.8 ¢/PAX/km) and liquefied natural gas (4.2–5.2 ¢/PAX/km). Overall, DOC of renewable aviation fuels is 15–500 % higher than conventional jet fuels. Among the bio-jet fuels, hydroprocessed esters and fatty acids (23–310 /GJ) pathways offer the lowest MJFSPs. The implementation of alternative fuels in existing aircraft engines and the design and development of appropriate propulsion systems and aircraft are challenging. The overall cost is a key factor for future implementation. Bio-jet fuel is most promising in the near term while hydrogen and electrofuels in the long term. The level of carbon tax on fossil jet fuels needed for the latter options to be competitive depend on the hydrogen production cost.
Recognition of the adverse impacts of climate change has led to interest in a transition to renewable, carbon-neutral energy and fuels. Ammonia has been proposed as a renewable transportation fuel,...
The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is the first programme to tackle carbon dioxide (CO2) emissions from a single industry at the global level, to realize the carbon-neutral growth of international flights from 2020 onwards. However, the COVID-19 pandemic has caused a drastic decline in the global aviation industry. The International Civil Aviation Organization (ICAO) has adjusted the CORSIA by removing 2020 emissions from the baseline, which now will only be based on 2019 emissions. We estimate that the total carbon dioxide (CO2) emissions from global international flights decreased by 70% from February to July 2020 compared to those in 2019. Our analysis suggests that the annual CO2 emissions from international flights during the pilot stage of CORSIA (2021-2023) will be far below the revised baseline even if the global aviation industry could embrace an optimistic recovery. The major airline companies will have very limited motivations due to the CORSIA scheme to implement mitigation actions proactively. Therefore, more progressive actions are needed to align the industry recovery of global aviation and climate change mitigation during the post-COVID-19 period.
The mitigation of greenhouse gas (GHG) emissions is a subject of high importance at a global level. The expansion of advanced liquid biofuels use can contribute to increase the sustainable bioenergy deployment while reducing GHG emissions in comparison to fossil fuels. In this study, the economic and environmental performance of a biorefinery involving biomass gasification followed by Fischer-Tropsch (FT) liquid biofuels production associated to sugarcane value chain is explored through a multiobjective optimization approach. The biorefinery configurations investigated include different biomass combinations, and the possibility of integrating the thermochemical processes to a first-generation ethanol distillery or operating it as a stand-alone plant. Different biomass mix considering conventional sugarcane, energy-cane and eucalyptus are considered in the optimization strategy. A Design of Experiments with a second-order polynomial regression technique is used to fit a metamodel from detailed and high-fidelity spreadsheet-based process models. Internal Rate of Return and avoided GHG emissions per agricultural land occupation are used as objective functions. The Pareto-optimal curves show the best performance possibilities and allows to identify the most suitable biorefinery configurations. Results indicate there is an economic benefit from the integration between the thermochemical process and conventional first-generation ethanol mills. An increase in cane and eucalyptus processing capacities tends to improve the economic performance due to the gain of scale. A higher proportion of energy-cane processed leads to better environmental performance as it reduces both the GHG emissions and the demand for agricultural land. In contrast, a greater share of energy-cane present trade-offs on the economic performance in the integrated biorefinery caused by the higher energy demand and lower ethanol production, but a minor effect is observed on the stand-alone configuration.
Commercial production of jet fuel from biobased feedstocks is still encumbering, mainly due to their high production cost and competition with food resources. Pennycress oilseed is a potential jet fuel feedstock which can be supplied at a lower price compared to similar oilseeds, such as soybean and canola. However, the techno-economics of pennycress-based jet fuel production needs to be evaluated. The objective of this study was to assess the technical feasibility and costs of hydroprocessed renewable jet fuel (HRJ) production from pennycress. The production capacity was considered to be 18.9 million L/yr (5 million gal/yr). The analysis considered pennycress grain handling and conditioning, oil extraction and conversion to HRJ and byproducts, i.e., LPG, naphtha and green diesel, through hydroprocessing technology, as well as pennycress meal processing as boiler fuel and wastewater treatment. Total investment for establishing the HRJ biorefinery at the selected capacity was estimated to be 90.8 million USD. Minimum selling price (MSP) of HRJ was estimated to be 1.2 USD/L, which was comparable to the MSP of HRJ from similar oilseeds, including soybean and canola. It could also be further reduced by supplying pennycress grain at a lower price, increasing the oil content and increasing the production capacity of the biorefinery. The outcomes of this research would help establish the performance targets needed to reach the economic viability of HRJ production from pennycress at the commercial scale.
Aviation sector discharges approximately 2% of the global anthropogenic CO 2, and the proportion is growing. The search for cost-effective and environmental-friendly bio-jet fuels derived from natural resources is gaining momentum. The microalgae cultivation conditions including temperature, pH, light intensity and nutrients have shown significant influence on the microalgae growth rate and chemical composition, which create the opportunities to enhance the yield and quality of microalgae bio-jet fuel. This review is focused on the hydroprocessing method for converting microalgae oil into bio-jet fuel, as well as the novel conceptual approaches for bio-jet fuel production such as gasification with Fischer-Tropsch and sugar-to-jet. Fischer-Tropsch synthesis of biomass is one of the best alternative ways to replace natural aviation fuel due to the high maximum energy efficiency and low emission of greenhouse gas. In addition, hydroprocessing with the aid of Ni and zeolites catalysts has successfully converted the microalgae biodiesel to bio-jet fuel with high yield and alkane selectivity. Among these techniques, hydroprocessing used the lowest production cost with the longest duration, whereas the bio-jet fuel with high selectivity (C 8-C 16) could be produced by using gasification with the Fischer-Tropsch process. Consequently, gasification and Fischer-Tropsch and sugar-to-jet can become the future alternative process to convert microalgae to bio-jet fuel. The development of microalgae bio-jet fuel will increase the security of energy supply and reduce the fuel expenses in aviation industry.
Nowadays, concerns about rising emissions and climate change have raised the issue of decarbonization. Several approaches have been promoted in the aeronautical sector to reduce CO2 emissions. The present work provides quantitative data to support decision-making for the first pillar of International Air Transport Association (IATA) strategy to mitigate aviation climate impact. This strategy comprises improving aircraft technology and deploying sustainable low-carbon fuels. The most promising technologies for an imminent application are new engine architecture and natural laminar flow. On the other hand, efforts have been put to produce Sustainable Aviation Fuel (SAF) reaching the point where some methods for the production of alternative jet fuel are already approved by ASTM. Therefore, the present work quantifies the future reduction of CO2 emissions by 2050 in the aeronautical sector with these strategies. For this purpose, two methodologies are used, a numerical model to calculate fuel consumption and CO2 emissions from the global air transport fleet. For the SAF analysis, it is developed an approach that considers, besides the SAF production, the feedstocks, and the production pathway. Two cases and three scenarios represent the technological improvements and quantify the effects of new aircraft concepts and technologies on future CO2 emissions. For the SAF analysis, four scenarios and two conditions assess the different production capacities and feedstocks. The combined effect of technologies with SAF is considered verifying if the goals proposed by IATA, carbon-neutral growth from 2020, and a reduction of 50% in net emissions by 2050 compared to 2005 levels are achieved. The assessment results reveal that the goals cannot be met only with the combined action of imminent aircraft technologies and the use of alternative fuels. Carbon-neutral growth is only reached when it is considered the combined effect of technologies with the scenario where the amount of SAF introduced is higher (an increase of 15% annually between 2030 and 2050). However, this carbon-neutral growth is only possible to start in 2040. Imminent aircraft technologies can reduce up to 15% in CO2 emissions when compared to the Business as Usual scenario. The different feedstocks used in each process to produce SAF do not have a considerable impact on reducing CO2 emissions, the maximum difference registered between each condition was 1.47%.
In this study, a life cycle assessment and comparative evaluation is performed for different types of renewable and alternative fuels for aircrafts. The life cycle assessment impacts of both hydrogen and ammonia fuels are primarily investigated considering conventional and renewable energy-based routes. The overall life cycle impacts of several hydrocarbon fuels including kerosene, ethanol, methanol, dimethyl ether, and biodiesel are also studied. The steam methane reforming-based route for hydrogen and ammonia fuels is found to have higher global warming potentials as compared to alternative production routes. High phosphate emissions result in a higher freshwater eutrophication potential for the solar-based route for ammonia fuel. Fossil fuel-based dimethyl ether is found to have a comparatively higher global warming potential of 1.3 kgCO2 equivalent per tonne-km amongst the considered hydrocarbon fuels that include ethanol (1.1 kgCO2 equivalent per tonne-km), kerosene (1.04 kgCO2 equivalent per tonne-km), methanol (1.01 kgCO2 equivalent per tonne-km), and biodiesel (1.07 kgCO2 equivalent per tonne-km). Dimethyl ether is found to entail high toxicity potentials and the reduction of arsenic, barium, cadmium, chromium, cobalt, and lead emissions is recommended. However, higher photochemical ozone formation potentials of 0.0055 and 0.0046 kgNOx equivalent per tonne-km are associated with biodiesel and kerosene fuels respectively.
Investigations and applications of renewable and sustainable energy have become central for addressing the issue of emissions of greenhouse gases from the use of fossil transportation fuels. Triglyceride-based liquid fuels have great potential as substitutes for petroleum and its derivatives. To date, the proven technologies for converting triglycerides into biofuels include transesterification, thermal cracking conversion, and hydrogenation. This paper presents an overview of recent research on these conversion technologies, employing homogeneous, heterogeneous, enzymatic, and photocatalytic catalysts. We focus on technical aspects critical to triglyceride conversion, including feedstock analysis, mechanism research, analysis of technological advantages and disadvantages, and catalyst development and selection. Biodiesel produced by the transesterification process must be blended with diesel before use due to its higher oxide content. The resultant “green diesel” has a broader range of applications, especially when its structure has been upgraded. Life cycle assessment (LCA) and greenhouse gas (GHG) emissions are reviewed to assess the renewability and sustainability of biofuels. We discuss the typical biodiesel production technologies with their development status, as well as the relevant policies and prospects for biofuels, mainly concerning biodiesel and aviation biofuel. It is hoped that our work will be of guiding significance for future biofuel research.
Hydrothermal liquefaction is a promising conversion technology in algae biofuel research due to its ability to agnostically convert proteins, carbohydrates, and lipids to biocrude. The high-temperature conditions that define this conversion process require the material to maintain a subcritical liquid state, which complicates the assessment of accurate thermochemical properties due to the required pressure. To clarify this issue, this work compares the estimated performance of algal hydrothermal liquefaction between different thermodynamic models. A process model was developed in Aspen Plus from a robust assessment of current literature. Techno-economic assessment and life-cycle assessment metrics are derived from this model and used as key performance indicators. The baseline fuel price contribution of hydrothermal liquefaction is 0.07 per liter gasoline equivalent. The baseline global warming potential is +23 g CO2 eq MJ⁻¹ and the net energy ratio is 0.30. Environmental metrics beyond global warming potential and net energy ratio are also discussed for the first time. Uncertainties in conversion performance are bounded through a scenario analysis that manipulates parameters such as product yield and nutrient recycle to produce a range of economic and environmental metrics. The work is supplemented with an open source model to support future hydrothermal liquefaction assessments and accelerate the development of commercial-scale systems.
Purpose
This paper aims to investigate the environmental impact of various pollutant emissions including carbon monoxide (CO), carbon dioxide (CO 2 ), nitrogen oxide (NO x ) and hydrocarbon (HC) from aircraft exhaust gases during the landing and take-off (LTO) cycles at Eskisehir Hasan Polatkan Airport, Turkey, between 2017 and 2018.
Design/methodology/approach
The methodology approach used to calculate the emissions from aircrafts is based on the ICAO databank and the actual data records taken from Presidency of The Republic of Turkey Directorate of Communications (DoC).
Findings
The maximum amount of total fuel burnt during the two years is 80.898 and 70.168 tons in 2017 and 2018, respectively, while the average fuel burnt per year from 2017 to 2018 is approximately 369.773 tons. The highest CO, CO 2 , NO x and HC emissions are found to be 248.3 kg in 2017, 261.380 tons, 1.708 tons and 22.15 kg, during the 2018 year, respectively. Average CO, HC, NO x and CO 2 emissions amount per year are observed to be 1.392 tons, 135 kg, 6.909 tons and 1,143 tons, respectively. Considering the average of total emission amount as an environmental factor, as expected, CO 2 emissions contributed the most to the total emissions while HC emissions contributed the least to the total emissions from the airport.
Practical implications
The study presents the approach in determining the amounts of emissions released into the interannual atmosphere and it explicitly provides researchers and policymakers how to follow emissions from commercial aircraft activities at different airports.
Originality/value
The value of the study lies in the transparent computation of the amounts of pollutants by providing the data directly from the first hand-DoC.
The year 2020 has witnessed the extraordinary impact of the coronavirus (COVID-19) outbreak. Across the globe, countries and cities took drastic measures in the attempt to halt the spread of the virus that led to the sudden cease of major economic and transportation activities. As a result, the temporary lockdown periods prompted sharp declines in daily global CO2 emissions. Moreover, the positive impacts on the local environment were evident from reduced production and movements among cities and regions around the world. While there is a much greater sense of urgency in addressing the fallout of the COVID-19 pandemic, the efforts in curbing global carbon emissions and mitigating the potential irreversible consequences of climate change are as equally important in these times of uncertainty. Taking advantage of the COVID-19 recovery schemes to concurrently boost the climate agenda is regarded as a strategic opportunity to ensure a sustainable path for a post-pandemic world. As governments still grapple with the fallout of the pandemic, implications on future climate change policy remain a subject of further investigation. This review aims to examine the effects of COVID-19-related lockdowns on global CO2 emissions while highlighting the need for synchronized solutions to tackle the double threat caused by the current COVID-19 pandemic and climate change crisis.
The aviation industry has been studying strategies to produce sustainable aviation fuels (SAF) for over ten years. Our objective is to conduct detailed techno-economic analyses (TEA) of six SAF production technologies and to develop a simplified cost estimation method. Triglyceride based Hydroprocessed esters and fatty acids (HEFA) was compared against five lignocellulose-based technologies using standardized criteria. TEA was conducted to determine minimum fuel selling price (MFSP). The base case annual product capacity was fixed at 60 million liters of total fuel, for which SAF MFSPs ranged from 0.88 to 3.86 $ L⁻¹ of fuel. Triglyceride-based HEFA had the best economic performance. Although triglycerides are more expensive than lignocellulose, HEFA is still a very competitive technology due to its high fuel yield (86–91% of feedstock) and low MFSP. Lignocellulosic-based technologies have lower fuel yields (9–23% of feedstock) due to high oxygen content of initial feedstock, resulting in higher fuel cost per unit of fuel. In order to reach a market fuel price, SAF yields from lignocellulosic materials needs to achieve an estimated value of 60%. Such yields are only possible if carbon efficiencies are close to 100%. Therefore, efforts are needed to avoid the removal of oxygen as CO2. Based on these considerations, a new scheme is proposed for SAF production that could result in yields near those needed to achieve cost targets. This proposed integrated biomass/natural gas hybridized concepts to produce inexpensive SAFs should be thoroughly investigated in future work.