Browse Topic: Aviation fuels

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Analysis and Experimental Research on The Impact of the BangBang Valve Switch on the Flow Rate of the Storage and Supply System2026-99-1615To be published on 07/24/2026
This article focuses on a wide range of high-precision storage and supply systems. Under the rated flow rate of 2.928 mg / s of the proportional flow controller, the instantaneous flow fluctuation range of the BangBang valve reaches 2.963 mg / s, exceeding the control accuracy requirement of 1% for the proportional flow controller. By establishing mathematical models of the BangBang valve, proportional valve, and proportional flow controller for simulation analysis, the trend of the simulation results is consistent with the experimental results. Furthermore, considering the spatial layout and weight of the storage and supply system, this paper proposes a method to improve the accuracy of flow output by adding 180 mL of air capacity between the proportional valve and the proportional flow controller. Ultimately, the maximum flow fluctuation of the proportional flow controller at the moment of the BangBang valve opening and closing is 2.941 mg / s, which meets the control accuracy of the proportional flow controller. Moreover, the error between the output flow rate of the proportional flow controller and the rated working flow rate is minor after increasing the air capacity.
Li, Zhong, Yan, Zelong, Huang, Tiankun
Design and Application of A Pressure Measurement System Based on Spacecraft Chemical Propellant Engine Plume Test2026-99-1623To be published on 07/24/2026
Spacecraft with chemical propellant engines, especially spacecraft for exploring extraterrestrial objects, need to carry out plume tests on the ground in order to determine the influence of engine plumes on spacecraft. An important purpose of the plume test is to accurately measure the pressure field in key parts of the spacecraft. In this paper, according to the pressure measurement requirements of the spacecraft plume test, the design of a pressure measurement system is carried out, which mainly includes a pressure measurement sensor, a pressure difference measurement sensor, a pipeline, a cable, a measuring instrument, a data acquisition instrument, upper measurement software, and so on. The designed pressure measurement system was successfully applied to the plume impact test of Chang'e VII, which provided important technical support for the development of the spacecraft.
Wu, Yue, Guo, Qinliang, Wu, Dongliang, Liu, Xiaoning, Tao, Dongxing, Lin, Boying, Xie, Zheng, Wei, Xi, Niu, Tong
Alcohol-Based Energy Carriers in Transportation: Status, Standards, and Outlook2026-37-00426/9/2026
The global transport sector accounts for approximately 30 % of total final energy consumption and 15.9 % of worldwide greenhouse gas (GHG) emissions, with road transport alone accounting for the largest share at 11.8 %. Decarbonizing this sector requires energy sources that combine scalable generation from renewable sources with compatibility with various modes of transportation and existing infrastructure. Methanol and ethanol emerge as promising alternative energy carriers that can leverage existing logistics infrastructure while reducing dependence on fossil fuels. Global methanol production reached 112 million metric tons, and global ethanol production totaled approximately 93.5 million metric tons in 2024, compared to more than 2 billion metric tons of gasoline and diesel produced annually. The review assesses production pathways and cost trajectories for both alcohols, evaluates fuel requirements across multiple transport modes, including passenger vehicles, light- and heavy-duty vehicles, maritime shipping, aviation, and rail, and provides regulatory frameworks governing fuel standards in six major markets, the European Union, the USA, Brazil, China, Japan, and India. From a technical perspective, the internal combustion engine is examined in greater detail as the energy conversion system, synthesizing current combustion research on engine performance, emissions characteristics, and cold-start behavior. Current standards predominantly accommodate ethanol blending for spark-ignition (SI) engines in passenger vehicle applications, with permitted concentration limits ranging from 3 % in Japan to nearly pure ethanol in Brazil. Methanol applications remain more limited in road applications. In the maritime sector, recent ISO 8217:2024 specifications and International Maritime Organization (IMO) interim guidelines have established frameworks for the use of methanol and ethanol as marine fuels. Aviation remains the most restrictive sector, with alcohol fuels explicitly prohibited in certified aviation fuels due to material compatibility and safety concerns. To unlock the decarbonization potential of methanol and ethanol in the transport sector, coordinated policy support and continued technological innovation will be essential. As production scales and regulatory frameworks mature, both alcohol fuels may play an increasingly central role in the transition toward sustainable mobility.
Fitz, Patrick, Fellner, Felix, Rößlhuemer, Raphael, Härtl, Martin, Jaensch, Malte
Thermal Management System in Commercial Aircraft: A Case Study on Passenger Egress System2026-26-07606/1/2026
It is known fact that Thermal management systems are essential to the safety, operational efficiency, and structural integrity of present-day commercial aircraft. Very critical insulation and thermal protection materials are utilized across various aircraft zones to mitigate extreme temperature challenges, ranging from cryogenic conditions at high altitude to pyrotechnic conditions at low altitude/ sea level. Some of the examples where specific materials at their functional role are, In engine pylons and nacelles, high temperature alloys such as Titanium and Inconel, along with ceramic Matrix composites (CMCs) serve as firewalls and heat shields, which are designed to contain fires and protect primary structures. In bleed air ducting, fiberglass or silica insulations blankets are employed to prevent thermal degradation of surrounding aluminum and composite components, when air at temperatures above 200 degree C flows. This paper focuses on the critical insulation and thermal protection materials on passenger Egress system utilized to mitigate pyrotechnic events. The focused case study on passenger egress system highlights a unique application of thermal protection. As these system, as mandated by FAA TSO-C69c, must ensure the system remains deployable and structurally stable for at least 90 seconds under intense heat exposure, preserving a workable egress path for passengers. The passenger egress system surface functions as a heat resistance barrier, resisting thermal energy from potential post-crash jet fuel fire. The heat barrier materials are polymer coated with woven nylon, impregnated with a metallic/ Ceramic layer. This study will emphasize how tailored material coating solutions are fundamental to addressing the diverse and extreme thermal demands in aerospace design, directly contributing to passenger’s safety and aircraft survivability.
Govindaraju, Parthasarathy, Nanjundegowda, Harshavardhana
Weight Estimation of Novel Aircraft Configurations in Early Design Phase2026-26-07736/1/2026
Initial weight estimation from Top Level Aircraft Requirements (TLAR) is a critical first step in aircraft design, yet existing empirical methods are inadequate for novel configurations such as those using Liquid Hydrogen (LH2) or Sustainable Aviation Fuels (SAF). This paper presents a hybrid methodology for top-level weight estimation of such unconventional aircraft. The approach is based on modifying a conventional baseline aircraft, integrating a new statistical model with component-specific weight estimations. A multivariate regression model to estimate the empty weight fraction (We/W0) was developed from a dataset of 44 conventional aircraft, yielding an R-squared value of 0.833. This statistical model was integrated with physics-based models for novel components, including cryogenic fuel tanks and fuel systems. The methodology accounts for iterative changes to fuselage structure and parasitic drag. Four configurations were analyzed: fuel types being Jet A1, SAF, LH2 with aft-fuselage tanks, and LH2 with under-wing podded tanks. The results demonstrate that while LH2 configurations introduce weight penalties for tanks and systems, these are significantly offset by a reduction in fuel weight, resulting in a final Maximum Takeoff Weight (MTOW) comparable to or lower than the conventional baseline. The modular nature of this methodology makes it a viable tool for exploring the design space in early-stage conceptual design.
Goyal, Tushar
Conceptual Design of Hydrogen Fuel-Cell-Based Utility Aircraft2026-26-07836/1/2026
The aviation industry contributes to around 2% of global carbon dioxide emissions. As various sectors of the economy look to reduce their global carbon footprint, the aviation industry is positively acknowledging alternatives to jet fuel. Hydrogen proves to be one such alternative having a high energy density and producing zero carbon emissions on combustion. Hydrogen when used in a jet engine produces water vapour and NOx emissions. In order to reduce the effect of GHGs, the current study aims to develop aircraft concepts suitable with hydrogen propulsion through fuel cells for a short-haul commercial mission profile. Aircrafts such as Metro-23 and Dornier 228-212 were referenced for the requirements of a utility turboprop aircraft. The weight estimation was done to obtain the take-off weight of 10,863 kg following the optimization of thrust to weight ratio and wing loading to calculate the initial dimensions. OpenVSP was used to model the initial structure of the aircraft. For the propulsion system, the PEM fuel cell was sized for the aircraft to achieve a range of 2,065 km and endurance of 6 hours in two configurations. Also, various configurations of fuel tanks and their positions were analyzed. The design was able to achieve a reduction of up to 18% in the propulsion system weight through fuel stack configuration. Iterations were performed to achieve static stability and CG was estimated to be 31% of root chord. The final configuration layout with cabin seats, propellers, fuel tank and fuel cells were analysed for static stability. The flight performance of the aircraft is comparable to the reference aircrafts. The proposed design leads towards the path of sustainable aviation.
Bhattacharya, Anisha, Seetha Ramu, Sree Valli, C N, Lakshmi Manasa, Rohit, Benjamin
Advanced Silicone Materials for Harsh Aerospace Environments26AERP06_016/1/2026
Aerospace and defense systems demand materials capable of maintaining performance under extreme environmental and operational stressors, including wide thermal cycling ranges, exposure to hydrocarbon fuels, vacuum conditions, and repeated mechanical strain. Silicone-based materials have become essential in these environments because they can retain elasticity, stability, and functionality where many traditional materials fail. Silicones are widely used as coatings, adhesives, sealants, and elastomers in aircraft and spacecraft applications. Their chemical structure enables resistance to both high and low temperatures, while also providing durability against solvents and fuels such as jet fuel. In contrast, many conventional elastomers degrade under prolonged thermal exposure or become brittle at cryogenic temperatures.
Potential of an In-Cylinder Pressure–Based Combustion Control for Compression Ignition Aviation Engines Operated with Sustainable Aviation Fuels2026-01-50285/29/2026
The aviation industry represents a significant greenhouse gas emitter and aims to reduce net CO2 emissions to zero by 2050. The deployment of sustainable aviation fuel (SAF), alongside measures such as increasing engine efficiency and enhancing ground handling processes, represents a key driver to reach this ambitious goal. SAF exhibits significantly different physical and chemical properties compared to conventional kerosene. The corresponding fuel specification (ASTM D7566 [1]) currently only defines fuel parameters relevant for the use in jet engines. To assess the suitability of SAF for the use in compression ignition (CI) aviation engines, a collaborative project was conducted at TU Wien—Institute of Powertrain and Automotive Technology, together with Austro Engine. ASTM D7566-certified fuels like Hydrotreated Vegetable Oil (HVO), Fischer–Tropsch–Kerosene (FTK), and Alcohol-to-Jet (AtJ) have been investigated on the engine test bench at TU Wien. The core contribution of this study is the experimental evaluation of a real-time capable in-cylinder pressure–based combustion control strategy that enables fuel-flexible and optimized CI engine operation across a wide range of SAF while accounting for mechanical constraints such as peak cylinder pressure and pressure rise rate. To evaluate the potential of such a control system, optimized engine operation was compared to operation with conventional ECU (Engine Control Unit) mapping. Furthermore, the influence of such a real-time combustion process optimization on critical emissions like NOx or soot has been evaluated. Through the implementation of an in-cylinder pressure–based combustion control, a considerable fuel-saving potential could be demonstrated across the entire fuel range. As combustion phasing is optimized toward early crank angle positions, a slight increase in NOx, with a corresponding decrease in soot is observed. Additionally, the use of automotive, piezoresistive pressure sensors was examined regarding a potential serial application. It has been shown that piezoresistive sensors (standard serial parts—calibrated for automotive application) are well-suited for determination of combustion phasing, while in-cylinder peak pressure and its position can only be determined with insufficient accuracy.
Kleissner, Florian, Hofmann, Peter
Combustion Characterization of Hydroprocessed Esters and Fatty Acids (HEFA) as an Alternative Fuel for Use in IC Engines2026-01-03174/7/2026
In the endeavors to reduce reliance on fossil fuels and reduce greenhouse gas emissions, synthetic fuels from less carbon intensive feedstocks have emerged as a promising alternative to conventional fuels. These synthetic fuels have gained traction in the aviation industry as sustainable aviation fuels (SAFs). One such fuel is a synthetic paraffinic kerosene derived from hydroprocessed esters and fatty acids (HEFA). Preliminary research has also suggested that this fuel may also be favorable for use in IC engines. This investigation will explore the combustion characteristics of HEFA in an IC engine in more detail. The thermophysical properties of HEFA were investigated and found comparable to or improving upon those of ULSD. Spray atomization analysis revealed more than 25% smaller SMD compared to ULSD, and lower span factor indicating a more uniform spray which can promote faster formation of a homogenous mixture. A tribological analysis using a pin-on-disk tribometer revealed comparable lubricity compared to ULSD, without requiring any additives. A CVCC was used to investigate the autoignition characteristics of the fuels. HEFA was found to have a DCN of 58 compared to ULSD at 48. Resultingly, the ignition delay for HEFA was notably shorter compared to the baseline of ULSD. Fired engine testing was conducted using a single-cylinder CRDI experimental engine. Emissions were measured using a FTIR and Microsoot sensor. Combustion characteristics such as ignition delay, LTHR, pressure rise rate, peak pressure, ringing intensity, CA50, and combustion duration were compared to ULSD at matched operating modes. HEFA was observed to have a shorter ignition delay and smaller premixed combustion event, releasing more of its energy in mixing controlled combustion. This caused CA50 and overall combustion duration to be extended compared to ULSD. The combustion behavior of HEFA contributed to significant reductions in NOx and Soot emissions compared to ULSD. Cycle variability was reduced by half for HEFA, indicating smoother engine operation and combustion stability. These results showcase the versatility of this SAF to be used in IC engines with conventional combustion strategies.
Soloiu, Valentin, Willis, James, Norton, Coleman, Davis, Zachary, Peralta Lopez, Guillermo, Rahman, Mosfequr
Fundamentals of Sustainable Aviation FuelsR-5471/22/2026
As global energy demands rise and environmental challenges intensify, the aviation industry faces a critical need to redefine how it powers the skies. Fundamentals of Sustainable Aviation Fuels presents a comprehensive, research-driven exploration of the transition from fossil-based fuels to renewable alternatives that promise to reshape the future of air transportation. This book bridges the gap between academic knowledge and industrial application, offering a detailed overview of the science, technology, and policy driving the adoption of Sustainable Aviation Fuels (SAFs). From understanding feedstocks and conversion pathways to evaluating production technologies, emissions performance, and life-cycle impacts, the text equips readers with a holistic understanding of SAFs within today’s global energy landscape. Across five insightful chapters, readers will find a clear roadmap: the evolution and importance of SAFs; production methods and technological foundations; environmental performance and emissions reduction potential; safety, certification, and market integration; and future projections supported by international initiatives and regulatory frameworks. By combining technical depth with practical relevance, Fundamentals of Sustainable Aviation Fuels serves as both a foundational reference and a forward-looking guide for researchers, policymakers, industry professionals, and students. It underscores that achieving sustainability in aviation depends not only on innovation but also on global collaboration, paving the way toward cleaner skies and a resilient, low-carbon future for air travel.
Yilmaz, Nadir
Architecting ATA 28 with Model-Based Systems Engineering: Center of Gravity Balance and System Performance01-18-03-00151/7/2026
The fuel management system for a fixed-wing aircraft has been developed and explored with the model-based systems engineering (MBSE) methodology for maintaining the center of gravity (CoG) and analyzing flight safety. The system incorporates high-level modeling abstractions that exploit a mix of behaviors and physical detail resembling real-world components. This approach enables analysis for a multitude of system requirements, verification, and failure scenarios at high simulation speed, which is necessary during system definition. Initially, the CoG is maintained by directly accessing the flight deck valves and pumps in both wings and controlling them through the bang-bang control law. In the refinement phase of the fuel system controller, the manual and individual controls of the valves and pumps are replaced with an autonomous fuel transfer scheme. The autonomous scheme achieves no more than a 20 kg difference in fuel between the wings during normal conditions. In the event of failures, the controller achieves no more than a 100 kg difference in fuel between the wings. The difference returns to 20 kg within a settling time of 5 sec and a maximum allowable overshoot safety margin of 10% of the 20 kg difference in normal conditions (±2 kg). The specification 20 kg/5 sec band varies with pump and valve parameters. Although this specification is sufficient for a system-level model, it can be refined with pump and valve parameters and nonlinear effects in the network. The system identification method is also trialed to control an individual engine by estimating a proportional integrator derivative (PID) controller of the engine plant. The safety tests are initiated in a user interface enabling error detection and injection. The fuel system model is used for analyzing refueling, defueling, and jettison scenarios with appropriate flow rates. Besides the CoG maintenance, several aspects of configurations of the system’s functional and logical architecture, considering increasing component redundancy and activities for MBSE framework, have been conducted. The logical and temporal verification of system requirements is performed in simulation. To ensure traceability and coverage, the requirements and the associated verification artifacts are digitally linked to the implementing blocks. Test scenarios are implemented for investigating resultant and emergent behaviors at various levels of system hierarchy by isolating either the subsystem or the components that have been performed. To further check out the MBSE workflow, the fuel system controller code has been directly emitted from the controller model for DO-178C objectives. At the mission-level validation, a jettison scenario is developed for a mission and flight plan in the digital mission engineering and systems analysis environment of Systems Tool Kit (STK) Aviator. The aircraft fuel system configuration is set using the fuel system model. The power of MBSE methodology supported by a modeling and simulation framework provides plenty of opportunities for through-life analysis in the early design lifecycle phase.
Zaidi, Yaseen, Michalek, Ota
Sustainable Aviation Fuels – A Review of the Challenges Associated to the Aviation’s Net Zero Commitment2025-36-021812/18/2025
The aviation sector currently accounts for 2-3% of global Greenhouse Gas (GHG) emissions, while the projected increased air travel demand (average 3.4% per year), might surge the aviation fuel use. This increase in jet fuel demand, associated with the current decarbonization pathway of other sectors might increase the aviation’s absolute emissions, as well as its relative global GHG share. This scenario has driven the aviation stakeholders into a decarbonization strategy, focused on an immediate and gradual GHG reduction effort associated with a net-zero commitment by 2050. Meanwhile, the aviation sector is known as one that set most difficulties to use alternative fuels and/or powertrains, such as battery electric or sustainable hydrogen fueled propulsion systems, already used on some road and rail applications, but still restricted to the aviation, due to the inherent weight and volume tight requirements. In this context, the sustainable aviation fuels (SAF) are set as the most promising short and medium term aviation decarbonization tool, due to their drop-in feature, which ultimately allows its use on the current aircraft fleet, as well as the fuel storage and distribution systems, provided the certified blends. The prominent SAF role brings increasing demand volumes in the foreseeable future. However, the SAF scaling process from the current 0.1% share of the global jet fuel market faces an array of challenges (technical, regulatory – including the sustainability associated with the feedstocks and the production pathways and economic), requiring collective efforts to boost the technology deployment, address demand reliability and set an efficient regulatory frameworks. Different regulatory approaches have been proposed, with the so called mandates, adopted, for instance, in the European Union and to be adopted in Brazil (from 2027), to encourage investments for SAF production, while the United States (U.S.), the larger jet fuel market in the world, has adopted the use of incentives, to foster the SAF production capacity. This work presents, in a review format, a chronological timeline of the challenges associated with the implementation and scale use of SAF. It highlights the technical, regulatory and economic topics associated with the aviation’s net zero commitment, as well as sets the required roles of the associated stakeholders to make SAF a feasible alternative.
Barbosa, Fábio Coelho
In-Flight Evaluation of Sustainable Hydrocarbon Fuels in Compression Ignition Aircraft Engines2025-01-053311/25/2025
As global air traffic is expected to increase significantly in the coming decades, reducing the associated climate impact requires scalable solutions. While alternative propulsion technologies such as electric and hybrid-electric systems might offer long-term potential, their current applicability remains limited due to low energy density, limited range and scalability, and system complexity. Consequently, thermodynamic propulsion systems – such as gas turbines and piston engines – are expected to remain dominant in the medium term. In this context, sustainable hydrocarbon-based aviation fuels represent a practical and necessary solution. Certified sustainable aviation fuel (SAF) pathways are currently approved exclusively for use in gas turbines, with certification standards tailored to turbine-specific requirements. Consequently, fuel properties such as cetane number and evaporation behavior are not included in existing specifications. However, when SAF-kerosene blends are used in compression ignition engines, the impact of these properties on ignition quality, combustion behavior, and emissions must be specifically evaluated. For this purpose, a flight test campaign was conducted using a fully instrumented Diamond DA42 aircraft, configured as a flying laboratory and equipped with serial-production piston engines. Two synthetic fuel variants were evaluated: one certified according to ASTM D7566-23a Annex A2 (HEFA SPK) and a second, Tall Oil derived fuel with a distinctly different molecular composition – characterized by an increased content of cycloparaffins and low aromatics content. The aircraft as a flying air lab was equipped with special engine measurement technology including high-pressure in-cylinder indication to analyze the impact of these differing fuel compositions on engine efficiency and combustion characteristics, including ignition delay and peak pressure. Furthermore, a mobile emission and particle number measurement system enabled the assessment of environmental performance under real flight conditions. Both fuels demonstrated significant reductions in thermal NOx formation due to their low aromatics content. However, no clear benefit was observed in total particle number (PN), likely due to a shift in the particle size distribution towards the nanoparticle regime.
Kleissner, Florian, Hofmann, Peter, Vogd, Philipp, Vauhkonen, Ville, Käkölä, Jaana, Greve, Alina
Glossary of Terms - Aircraft Ground Refueling and DefuelingAIR4783B (Current)11/18/2025
This SAE Aerospace Information Report presents a glossary of terms commonly used in the ground delivery of fuel to an aircraft and pertinent terms relating to the aircraft being refueled.
AE-5A Aerospace Fuel, Inerting and Lubrication Sys Committee
Establishing a Sustainability Certification System for Aviation Fuel in China01-18-03-001211/7/2025
Amid escalating global warming challenges, the aviation industry must adopt low-carbon and green practices. China, aiming to meet its dual carbon goals, urgently requires enhanced research and development in sustainable aviation fuels (SAF), including their sustainability certification. However, China’s regulatory framework and limited research foundation in biofuels exacerbate this endeavor. This article summarizes the development status of SAF sustainability certification internationally and within China, encompassing the indicator framework, full life cycle greenhouse gas (GHG) calculation methodologies, and emission reduction thresholds. It also highlights issues encountered in the application of current international sustainability certification systems in China, such as high certification costs and inadequate data security. Advancement in domestic sustainability certification in China faces obstacles related to the incomplete foundational database, despite possessing life cycle assessment (LCA) calculation capabilities. To address these challenges, it is imperative to expedite the development of SAF certification systems, research in big data tracking systems, and establish targeted international mutual recognition data tracking platforms. Furthermore, enhancing GHG reduction thresholds in SAF sustainability certification is crucial. These steps will expedite SAF adoption in China, significantly contributing to global decarbonization efforts.
Zhang, Shuping, He, Yin, Jia, Quanxing, Jia, Qin, Tao, Zan, Miao, Jiahe, Shi, Yao, Zhang, Xiangping, Wang, Siyu
The Aircraft nvPM Mission Emissions Estimation Methodology, Version 2 (MEEM2)2025-01-600010/13/2025
The nvPM Mission Emissions Estimation Methodology (MEEM) was previously developed to estimate nonvolatile particulate matter (nvPM) emissions from ground certification data using the publicly available data from the International Civil Aviation Organization (ICAO) Aircraft Engine Emissions Databank (EEDB). In order to potentially improve the accuracy of nvPM emissions estimation and to enhance its usefulness to modelers, the method was revised to make use of fuel flow correlations and similar altitude corrections as used in the Boeing Fuel Flow Method 2 (BFFM2). The new fuel flow approach allows for improved trade-off-type assessments between nvPM and gaseous emissions—i.e., less relative uncertainties when assessing results from the two methods. Like the former MEEM, the new method, MEEM2, can be used with just publicly available data such as nvPM emissions indices (EI) from the EEDB as well as predicted fuel flows from publicly available aircraft performance models. MEEM2 has been validated against proprietary original equipment manufacturer (OEM) data and methods, helping to understand prediction uncertainties of nvPM emissions, thus supporting environmental impact assessments, including those related to climate impacts from commercial aviation’s non-CO2 components as well as the use of sustainable aviation fuels (SAF).
Ahrens, Denise, Kim, Brian, Méry, Yoann, Zelina, Joseph, Dudebout, Rudolph, Miake-Lye, Richard C.
Optimal Sets of Molecules to Predict Aviation Fuel Properties2025-01-039510/7/2025
The complexity and variability of modern aviation fuels necessitate the development of robust and efficient tools to assess their properties accurately, particularly within the certification framework established by the American Society for Testing and Materials (ASTM). Therefore, previous research has developed predictive models to reduce the experimental burden by predicting aviation fuel properties from broad chemical classes. While two-dimensional Gas Chromatography (GC×GC) provides detailed compositional information, it only identifies the weight of hydrocarbon families (aromatics, cycloalkanes, n-alkanes, iso-alkanes), not individual molecules. Aviation fuels are complex, and their composition can contain more than 60 key classes, the majority of which are isomeric. As a result, an exceptionally high number of possible molecule combinations makes random selection prone to high errors in property prediction. To this end, we used a Monte Carlo approach to search for the optimal combination of 64 hydrocarbon molecules from this vast combinatorial space. By exploring up to 500 million combinations, we aim to determine the molecule set that best predicts mass density, kinematic viscosity, and distillation temperature using linear mixing rules. These rules calculate the properties of molecule mixtures using the weight of each molecule in the mixture and the pure molecules’ properties. We used experimental data for various aviation fuels, including conventional jet fuels, sustainable aviation fuels, and rocket propulsion fuels. Results showed that the isomeric effect has a substantial role in predicting mass density, kinematic viscosity, and the distillation temperature. Results showed that the linear mixing rules could outperform machine learning that overlooks the isomeric effect for the three properties. This research benefits the surrogate fuel analysis, which requires defining a surrogate mixture of hydrocarbon molecules, and will provide insights into the best isomers or molecules to choose to predict aviation fuel properties with the least error. This work will help deliver aviation fuel producers with a relatively accurate pre-screening tool for property prediction, minimizing the need for iterative experimental processes.
Radaideh, Mohammed I., Kim, Doohyun, Radaideh, Majdi, Violi, Angela
A Life Cycle Assessment of Potential Pathways to Increase Sustainable Aviation Fuel Yields through CO 2 Upgrading Co-located with Corn Ethanol Production13-06-03-00239/4/2025
Alcohol-to-jet (ATJ) upcycling of ethanol to sustainable aviation fuel (SAF) is an attractive emerging pathway for SAF production, especially in the US Midwest with large-scale corn ethanol production. Only 39% of the corn carbon is converted to ethanol, 20% is emitted as CO2. Capturing the CO2 to produce additional ethanol or SAF directly can increase the carbon yield. To guide technology selection, this work used life cycle assessment for several CO2-to-SAF production pathways. Additionally, improvements for corn ethanol production were explored by replacing natural gas burners with heat pumps for corn drying, which reduced the carbon intensity of corn ethanol by nearly 16%. But subsequent upgrading of the ethanol to SAF is only 4.5–20% better than conventional aviation fuel. By contrast, CO2-based alternative routes to SAF fared better, reducing carbon intensities between 83% and 90%. Gas fermentation of CO2 to ethanol with subsequent ATJ upcycling to SAF was contrasted to Fischer–Tropsch conversion of CO2 to SAF. Both streams require CO2 conversion to CO, which can be produced using reverse water–gas shift or solid oxide electrolyzer cells. The Fischer–Tropsch synthesis shows a higher reduction in carbon intensity (up to 90%) compared to ATJ (up to 84.4%). For other impact categories, such as ozone depletion, ecotoxicity, and the like, the differences are of similar magnitude. Capturing CO2 locally at the bioethanol factory and converting that CO2 to ethanol might overall be preferable with a fermentation process that is quite like bioethanol production compared to Fischer–Tropsch synthesis for which products require a new transportation infrastructure. The aviation fuel yield from ATJ can reach 90%, higher than the 50–70% yield from Fischer–Tropsch synthesis, with gasoline and diesel fuel as major by-products for which markets will shrink in the future. Overall, ATJ appears to be the best choice for CO2-to-SAF using the synergy with corn ethanol factories for quick launch.
McCord, Stephen, Talsma, Sam, Bouchard, Jessey, Zavaleta, Victor Gordillo, He, Xin, Sick, Volker
Converting Waste Streams into BiofuelTBMG-535528/1/2025
Made from renewable materials like biomass and agricultural waste, sustainable aviation fuel has enormous potential to decarbonize the aviation industry. But widespread adoption has yet to take off.
Aerospace Fuel System Specifications and StandardsAIR1408B (Current)7/16/2025
This report lists documents that aid and govern the design of aircraft and missile fuel systems. The report lists the military and industry specifications and standards and the most notable design handbooks that are commonly used in fuel system design. Note that only the principle fuel specifications for the U.S. and Europe (Military Specifications, ASTM, and Def Stan) have been included within this report. The specifications and standards section has been divided into two parts: a master list arranged numerically of all industry and military specifications and standards, and a component list that provides a functional breakdown and a cross-reference of these documents. It is intended that this report be a supplement to specifications ARP8615, MIL-F-17874, and JSSG 2009. Revisions and amendments which are correct for the specifications and standards are not listed. The fuel system design handbooks are listed for fuels and for system and component design.
AE-5A Aerospace Fuel, Inerting and Lubrication Sys Committee
Fuel Versus Oxygen: Evaluations and ConsiderationsAIR5648B (Current)7/9/2025
Current regulations (e.g., Title 14 of the United States Code of Federal Regulations, or 14 CFR) define design requirements for oxygen system provisions for protection of crewmembers and passengers following emergency events such as in-flight decompression. This aerospace information report (AIR) addresses the operational oxygen system requirements for a decompression incident that may occur at any point during a long-range flight, with an emphasis for a decompression at the equal time point (ETP). This AIR identifies fuel and oxygen management contingencies and presents possible solutions for the efficient, safe, and optimum fuel/oxygen flight continuation. Oxygen management is a critical concern for all aircraft, ranging from single-engine types operating above 10000 feet to complex, high-performance aircraft equipped with supplemental oxygen systems. Proper planning ensures compliance with regulations and supports pilot and passenger safety at higher altitudes. This document provides a method which can help guide users in developing an oxygen solution for their aircraft. This document is not intended to change, modify, or alter any existing design or installation procedure and has been mostly developed for flight operations.
A-10 Aircraft Oxygen Equipment Committee
Application of Sustainable Aviation Fuels in Compression Ignition Aviation Engines: In-Flight Investigations2025-01-03177/2/2025
To achieve a significant reduction in net CO₂ emissions in the aviation sector, sustainable aviation fuels (SAFs) are considered a key factor. Current research efforts are therefore focused on SAFs, which exhibit properties that differ from conventional kerosene, particularly in aspects critical to compression-ignition (CI) engines, such as cetane number, evaporation behavior or lubricity. These differences necessitate dedicated investigations to assess their suitability and performance in such engines. However, real operating conditions — such as intake air- and exhaust- pressure levels during flight — cannot be fully replicated on standard engine test benches. For this reason, real flight experiments were conducted to address these limitations. Notably, this work marks the first instance of in-flight testing of SAFs in CI aviation engines, constituting a significant milestone in this research area. In the course of these investigations, ASTM D7566 Annex A2-compliant HEFA (hydroprocessed esters and fatty acids) was tested across a wide range of blend ratios, including pure HEFA. The in-flight tests were performed, using a DA42 aircraft from Diamond Aircraft Industries (DAI), equipped with two AE330 engines from Austro Engine (AE). For safety reasons, one engine was left in its original configuration, while the other one was outfitted with advanced measurement systems, including in-cylinder pressure sensors, a mobile exhaust gas analysis system (portable emission measurement system - PEMS), and various pressure and temperature probes. This setup enabled precise measurement of gaseous emissions, particle number (PN), efficiency, and combustion parameters. The operation of the test engine with HEFA blends, up to and including pure HEFA, was successfully demonstrated. The flight campaign highlighted the emission potential of this aromatics-free fuel. Additional test bench investigations confirmed the findings from the initial flight campaign: while soot mass emission decreased significantly with increased HEFA-share, particle number (PN) remains on a constant level, indicating a shift in the particle size distribution. This emphasizes the importance of understanding the trade-offs and adapting engine calibration when using SAF in CI (aviation) engines.
Kleissner, Florian, Reitmayr, Christian, Hofmann, Peter
Aircraft Fuel System and Component Icing TestARP1401C (Current)6/27/2025
This SAE Aerospace Recommended Practice (ARP) covers a brief discussion of the icing problem in aircraft fuel systems and the different means that have been used to test for icing. Fuel preparation and icing test procedures for aircraft fuel systems and components are proposed herein as a recommended practice to be used for fixed wing and rotary-wing aircraft within their operational environment. This ARP mostly addresses aircraft fuel system level testing and provides a means to address the requirements of FAR 14 CFR § 23.951(c), § 25.951(c), § 27.951(c), and § 29.951(c). In the context of this ARP, the engine and the auxiliary power unit (APU) are not considered to be components of the aircraft fuel system. However, some of the methods described in this document can be applied to the engine, APU, and other aircraft (system or component level) icing tests. This revision does not completely address new developments in ice accretion and release resulting from internal flow in tubing (see 2.3.6). This will be addressed in a different document when more experimental data is available.
AE-5A Aerospace Fuel, Inerting and Lubrication Sys Committee
Evaluation of Jet Fuels on Thermal Efficiency, NO X Emissions, Particulate Matter, and Particle Size Distribution in a Heavy-Duty Compression Ignition Engine2025-01-02446/16/2025
Alternative fuels such as Fischer-Tropsch Synthesized Paraffinic Kerosene (FT-SPK) and Catalytic Hydrothermal Conversion Jet (CHCJ) are among the important sustainable aviation fuels (SAFs) for future transportation. However, these alternative fuels often vary in their characteristics, depending on their feedstock and fuel production processes. Therefore, a detailed analysis of these alternative fuels' combustion, emissions, and efficiency must be performed under controlled experiments to understand the impact of fuel properties and operating conditions. This study used a single-cylinder research engine (SCE) with a compression ratio of 17:1. Extensive operating conditions were performed to determine the effect of each fuel on the engine performance, which can be fundamentally understood by fuel properties (e.g., cetane number, heat of combustion, and density) in comparison with Jet-A fuel. The experimental setup includes high-speed data acquisition for combustion analysis and gaseous and solid emissions benches for nitrogen oxides (NOX). Results suggested that an engine control management (ECM) strategy can potentially optimize the performance of these alternative jet fuels by compensating for differences in their fuel properties. This study aims to provide insights for future work on exploring different SAF fuels that are more environmentally friendly while meeting the required performance.
Cung, Khanh, Miganakallu Narasimhamurthy, Niranjan, Khalek, Imad, Hansen, Greg
Impact of Copper Contamination on the Thermal Stability of Jet FuelsAIR6443A (Current)5/27/2025
This SAE Aerospace Information Report (AIR) discusses the sources of copper in aviation jet fuels, the impact of copper on thermal stability of jet fuels and the resultant impact on aircraft turbine engine performance, and potential methods for measurement of copper contamination and reduction of the catalytic activity of copper contamination in jet fuels. This document is an information report and does not provide recommendations or stipulate limits for copper concentrations in jet fuels.
AE-5B Aircraft and Engine Fuel and Lubricant Sys Components
A Conjugate Heat Transfer Numerical Framework Applied to Energy-Assisted Ignition of Jet Fuel in a Rapid Compression Machine2025-01-83524/1/2025
Airborne compression ignition engines operating with aviation fuels are a promising option for reducing fuel consumption and increasing the range of hybrid-electric aircraft. However, the consistent ignition of Jet fuels at high-altitude conditions can be challenging. A potential solution to this problem is to ignite the fuel sprays by means of a glow-plug-based ignition assistant (IA) device. The interaction between the IA and the spray, and the subsequent combustion event result in thermal cycles that can significantly affect the IA’s durability. Therefore, designing an efficient and durable IA requires detailed understanding of the influence that the IA temperature and insertion depth have on the complex physics of fuel-air mixture ignition and flame propagation. The objective of this study is to design a conjugate heat transfer (CHT) modeling framework that can numerically replicate F-24 Jet fuel spray ignition using a glow-plug-based IA device in a rapid compression machine (RCM). A new phenomenological energy source model has been introduced to simulate the heat generation inside the heating element of the IA. The thermodynamic state prior to the spray injection is accurately modeled by simulating the RCM compression process. The ignition and combustion events were simulated using two different approaches, i.e., via a multi-component surrogate fuel and single-species surrogate fuel reaction mechanisms. Comparisons against experimental data of time evolution of the IA’s temperature showed that the CHT framework accurately predicts the IA’s transient heating process prior to spray injection. This approach avoids the need for ad-hoc, case-by-case calibration of the IA preheating duration in numerical simulations. Also, comparisons against available experimental data for reacting sprays showed that the multi-component surrogate fuel approach not only correctly predicts the volumetric and spray ignition modes but also captures the IA temperature for which the transition between the two combustion modes occurs.
Oruganti, Surya Kaundinya, Lien, Hao-Pin, Torelli, Roberto, Motily, Austen, Lee, Tonghun, Kim, Kenneth, Mayhew, Eric, Kweon, Chol-Bum
Impacts of Injection Pressure on Split-Injection Energy-Assisted Compression-Ignition Combustion of Low Cetane Number SAFs with a Gaussian-Shaped Ribbed Piston Bowl Design2025-01-83504/1/2025
The impact of injection pressure on a split-injection energy-assisted compression-ignition (EACI) combustion strategy was studied in an optically accessible engine with a custom ribbed piston bowl design. Three injection pressures (600, 800, and 1000 bar) were investigated for three split-injection dwells (1.5, 2.0, and 2.5 ms) with a fixed second injection timing of -5.0 CAD. The Gaussian-shaped ribbed piston bowl design was employed to position hot combustion gases from the first injection near the centrally located injector to enable rapid ignition and mixing-controlled combustion of the second injection. At 600-bar injection pressure, as injection dwell was shortened, relocation of hot combustion gases near the injector became increasingly more difficult due to less available time for relocation and due to the higher in-cylinder densities at the start-of-injection (SOI) for the first injection. Increased injection pressure (800 and 1000 bar) improved the relocation of the first injection combusted gases and increased the number of fuel jets rapidly igniting and undergoing mixing-controlled combustion during the second injection. Injection pressures of 800 and 1000 bar for a 2.0-ms injection dwell resulted in a greater number of fuel jets rapidly igniting than for the 600-bar injection pressure with a 2.5-ms injection dwell. These results suggest there is potential to achieve EACI operation at more application-relevant engine speeds through the utilization of custom piston bowl designs which allow for stable engine operation with higher injection pressures.
Amezcua, Eri, Stafford, Jacob, Kim, Kenneth, Kweon, Chol-Bum, Rothamer, David
Morphologies and Structures of Liquid Fragments Derived from the Near-Field Zone of a Twin-Orifice Swirl Atomizer2025-01-84614/1/2025
Aviation gas turbine engines typically utilize twin-orifice swirl atomizers to achieve a fine spray, widen the spray cone angle, and shorten spray penetration. However, using twin-orifice atomizers complicates the spray structure, and knowledge of the spray, especially in the near-field nozzle zone, remains limited. This study experimentally investigates the morphologies and structure of liquid fragments in the near-field nozzle of a twin-orifice atomizer. A high-speed backlit experimental system was developed to examine the liquid fragment morphologies and structures. The fragments are classified into spherical droplets, ligaments, and other irregular structural fragments. Results show that with increasing the pressure in the near field of the nozzle, the proportion of nearly round fragments decreases with increasing pressure. In contrast, the proportion of ligament-like fragments tends to increase. Besides, the particle size distribution did not change significantly within the 10 to 50-bar pressure range. Understanding these morphologies and structures could aid in developing a secondary atomization model suitable for predicting the droplet size distribution generated by twin-orifice atomizers.
Pham Vu, Nam, Manh, Vu, Pham, Phuong Xuan, Nguyen, Kien Trung
Comprehensive Investigation of Combustion Characteristics, Emissions, and Tribological Properties of Synthetic Kerosene (S8) in a CVCC and CRDI Research Engine2025-01-84434/1/2025
There is a need to reduce both the greenhouse gas emissions of internal combustion engines, and the reliance on traditional fossil fuels like Ultra Low Sulfur Diesel (ULSD). In this research, a synthetic paraffinic kerosene fuel, designated S8 and created from natural gas feedstocks using the Fischer-Tropsch process was investigated to determine its autoignition and combustion characteristics, emissions, and tribological properties. This fuel, S8, was found to have a Derived Cetane Number (DCN) of 62, which reflects a shorter Ignition Delay (ID), and Combustion Delay (CD) compared to ULSD, which has a DCN of 48. However, due to the chemical properties of S8, it lacks sufficient lubrication qualities in comparison to ULSD, so addition of 3% methyl oleate by mass was used to improve lubricity. The shorter ignition delay of S8, initially observed in a Constant Volume Combustion Chamber (CVCC) and confirmed in a fired Common Rail Direct Injection (CRDI) experimental engine. Investigations with Mie scattering He-Ne laser instrument, revealed the superior atomization of S8, which resulted in a Sauter Mean Diameter (SMD) of 19.2 μm, 8% smaller than that of ULSD. The combined effect of the superior atomization and shorter ID of S8 resulted in a reduction of the premixed combustion event for S8, with smoother engine operation due to the greater proportion of mixing-controlled combustion. This characteristic was also reflected in the comparison of the Low Temperature Heat Release (LTHR) region of S8 with that of ULSD. In LTHR, S8 released more energy during the low temperature cool flame formation region and entered High Temperature Heat Release (HTHR) sooner than ULSD. Analysis of the emissions of the CRDI engine when operated with S8 was conducted with the engine under a sustained load at 5.4 bar Indicated Mean Effective Pressure (IMEP), and the results were compared with identical operating parameters using ULSD. A 14% reduction in NOx emissions and a 33% reduction in soot was achieved compared to ULSD.
Soloiu, Valentin, Willis, James, Norton, Coleman, Davis, Zachary, Graham, Tristan, Nobis, Austin
SAE TOMORROW TODAY: A Breakthrough in Sustainable Aviation Fuel135022/17/2025
We often hear about sustainable fuel options when it comes to vehicles, but what about aerospace? With aviation fuel demand expected to rise to 160 billion gallons per year by 2050, new and innovative Sustainable Aviation Fuel (SAF) pathways are certainly needed. In response, CleanJoule has developed a proprietary manufacturing process that produces SAF with 10% higher energy density than average Jet A fuel. This process utilizes abundant biomass residue to create a cost-effective, drop-in replacement for conventional jet fuel. To learn more, we sat down with Mukund Karanjikar CEO, to discuss CleanJoule's mission is to create accessible, affordable and abundant SAF and reduce the aerospace industry's reliance on fossil fuels. We'd love to hear from you. Share your comments, questions and ideas for future topics and guests to podcast@sae.org. Don't forget to take a moment to follow SAE Tomorrow Today--a podcast where we discuss emerging technology and trends in mobility with the leaders, innovators and strategists making it all happen--and give us a review on your preferred podcasting platform. Follow SAE on LinkedIn, Instagram, Facebook, Twitter, and YouTube. Follow host Grayson Brulte on LinkedIn, Twitter, and Instagram.
Hineman, Marcie
Aerospace & Defense Technology: February 202525AERP022/6/2025
The Art of Reverse Engineering Yesteryear for Aerospace and Defense Data Storage Drives Manufacturing Spotlight: Machining Complex Parts and Materials for Space Flight and Exploration Notre Dame's New Boundary Breaking Mach 10 Quiet Wind Tunnel Shape-Shifting Antenna Poised to Transform Communications British Army Completes First Test of Drone Killing Radio Frequency Weapon A Swarm of Sensors, Rovers and Astronauts Explore the 'Moon' Researchers at the German Aerospace Center have developed a new approach to networked communications that could theoretically occur on the Moon or in environments on Earth where conventional communications are unavailable. Army Researchers Examine Nanotechnology for Climate Solutions Army scientists are joining forces with experts from across the nation to tackle the climate crisis using the power of nanotechnology Airman Brings Fuel Sampling Innovation to Eglin, Possibly Air Force The U.S. Air Force is testing a new prototype single point nozzle adapter that drastically reduces the time required for jet fuel quality sampling. Atomic Fountain for Research in Quantum Sensing Nears Completion of First Phase Naval Postgraduate School (NPS) physicists are on track to bring the institution's new atomic fountain online - the largest of its kind in the world - for applications to quantum sensing experiments in precise navigation and timekeeping. Revolutionizing the Waves: A Breakthrough in Surf Observation Technology for Sailors and Marines A team of Army and Navy scientists and engineers have developed a real-time sensing technology for deciding whether conditions are suitable for landing troops on enemy shores.
Experimental Evaluation of Binary Iso-Dodecane/n-Dodecane Blends for Emulating Sooting Characteristics of Sustainable Aviation Fuels01-18-01-00032/6/2025
Sustainable aviation fuels (SAFs) derived from renewable sources are promising solutions for achieving carbon neutrality and further controlling aircraft engine emissions, operating costs, and energy security. These SAFs, primarily consist of branched and normal paraffins and exhibit significantly reduced sooting tendencies compared to conventional petroleum-based jet fuels, due to their lack of aromatics content. Our previous study investigated soot formation in non-premixed combustion for three ASTM-approved alternative jet fuels, namely Fischer–Tropsch synthetic paraffinic kerosene (FT-SPK), hydroprocessed esters and fatty acids from camelina (HEFA-Camelina), and alcohol-to-jet (ATJ), and demonstrated that the varying paraffinic composition within SAFs results in diverse sooting propensities, in the order of ATJ > FT-SPK > HEFA-Camelina. To evaluate the impact of iso-paraffins on sooting tendency and validate the suitability of utilizing binary blends of iso-dodecane (iC12) and normal dodecane (nC12) as surrogates for emulating sooting characteristics of SAFs, an experimental study was conducted to measure the soot volume fraction profiles of iC12/nC12 blends with varying blending ratios in the counterflow non-premixed flame configuration using laser-induced incandescence technique. It is shown that ATJ and HEFA-Camelina can be well-represented by pure iC12 and the blend of 25% iC12 and 75% nC12 (in liquid volume), respectively. At high (low) reactant concentrations, the blend of 75% iC12/25% nC12 (90% iC12/10% nC12) exhibits similar sooting characteristics of FT-SPK. The present experimental results indicate that binary blends of iC12 and nC12 have the potential to serve as effective surrogates for SAFs, as they are predominantly composed of these two types of paraffinic components. Furthermore, it is found that when the iC12 blending ratio exceeds 90%, the maximum soot volume fraction exhibits a stronger nonlinear increase. This experimentally observed nonlinearity in maximum soot volume fraction with increasing alkane branching in the binary fuel blend signifies the importance of fuel molecular structure effects on soot formation pathways in counterflow non-premixed flames.
Xue, Xin, Sung, Chih-Jen, Wang, Xiaofeng
Blended-Wing Body Airplane Tradeoffs: H2 vs. Jet FuelSM_H2_2025-54132/2/2025
Blended-Wing Body Airplane Tradeoffs: H2 vs. Jet Fuel
Kerr, Ryan
Aircraft Safety: Jet Fuel vs. HydrogenSM_H2_2025-54082/2/2025
Aircraft Safety: Jet Fuel vs. Hydrogen
Damazo, Jason, Simitz, Lauren
Airman Brings Fuel Sampling Innovation to Eglin, Possibly Air ForceTBMG-525212/1/2025
With a few of snaps, turns and clicks, a new fuel innovation is sealed in place to an Air Force R-11 fuel truck. After that five-second attachment, it is ready to gather a required fuel sample for evaluation to ensure aircraft fuel is free of water or any other contamination.
Sustainable Aviation Fuel – An Effective Tool for Complying with the Aviation’s Global Environmental Commitment2024-36-006612/20/2024
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 (CO2) 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 CO2, accounting for 2% of the global energy related CO2 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. 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. 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. 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. 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.
Barbosa, Fábio Coelho
Effect of Fuel Chemical Structure on Soot Formation in Sustainable Aviation Fuels2024-01-431011/5/2024
Sustainable Aviation Fuels (SAFs) offer great promises towards decarbonizing the aviation sector. Due to the high safety standards and global scale of the aviation industry, SAFs pose challenges to aircraft engines and combustion processes, which must be thoroughly understood. Soot emissions from aircrafts play a crucial role, acting as ice nuclei and contributing to the formation of contrail cirrus clouds, which, in turn, may account for a substantial portion of the net radiative climate forcing. This study focuses on utilizing detailed kinetic simulations and soot modeling to investigate soot particle generation in aero-engines operating on SAFs. Differences in soot yield were investigated for different fuel components, including n-alkanes, iso-alkanes, cycloalkanes, and aromatics. A 0-D simulation framework was developed and utilized in conjunction with advanced soot models to predict and assess soot processes under conditions relevant to aero-engine combustion. The simulations, conducted under combustion and inert conditions, revealed that aromatic fuels significantly enhance soot yield, exhibiting accelerated growth toward larger aromatics under both combustion and pyrolysis conditions. The results also highlight the necessity for higher gas temperatures for PAHs to grow, in agreement with pyrolysis experiments indicating soot onset temperatures between 1400 and 1500K. Furthermore, the study assessed the influence of precursors on soot formation, challenging the appropriateness of using C2H2 or mono-aromatics as precursors with the tested soot models. The simulation results indicate that such precursors lead to large errors, advocating for the use of larger PAHs as precursor in these soot models, as suggested by the models’ validation space. Finally, this work also explores the impact of fuel structure on soot formation, contributing to ongoing efforts to replace aromatics with cycloalkanes in jet fuels through examining reference fuel blends representative of petroleum-based jet fuel and cycloalkane-based SAFs. The “SAF” blends result in a reduced soot yield compared to the jet fuel surrogate, underscoring SAFs’ capability to diminish emissions in the aviation industry.
Yi, Junghwa, Manin, Julien, Wan, Kevin, Lopez Pintor, Dario, Nguyen, Tuan, Dempsey, Adam
Operation of a Compression-Ignition Kerosene Aviation Engine with Sustainable Aviation Fuel: An Experimental Study2024-01-600510/28/2024
The aviation industry is undergoing environmental scrutiny due to its significant greenhouse gas emissions. Sustainable aviation fuels (SAFs) are a vital solution for reducing carbon emissions and pollutants, aligning with global efforts for carbon-neutral aviation growth. SAFs can be produced via multiple production routes from different feedstock, resulting in significantly different physical and chemical fuel properties. Their suitability in a compression-ignition (CI) aircraft engine was evaluated through test bench investigations at TU Wien - Institute of Powertrain and Automotive Technology in partnership with Austro Engine. ASTM D7566-certified fuels like Hydrotreated Vegetable Oil (HVO), Fischer–Tropsch–Kerosene (FTK) or Alcohol to Jet (AtJ), but also an oxygen containing biodiesel have been tested extensively. Gaseous emissions, soot emissions, indication measurement data, efficiencies, and the like were acquired and comprehensively analyzed for engine operation with different fuels and fuel blends. Operation with all investigated fuels could be demonstrated successfully at three representative operating points with the original engine setup. At constant boundary conditions, neither maximum permitted in-cylinder pressure, pressure gradient, or exhaust gas temperature were exceeded (nevertheless, an adaption of the injection strategy is recommended). Ignition delay and combustion duration—dependent on fuel properties—greatly influence the formation of incomplete combustion products like HC and CO as well as NOx and soot emissions. Especially the extremely low cetane number of AtJ leads to a substantial increase in premixed combustion, which significantly influences NOx and soot emissions, depending on operating conditions. A low aromatic content (as found in HVO) is beneficial for reducing HC, CO, and soot due to the absence of ring-like molecule structures. Also, a reduced adiabatic flame temperature contributes to a decreased NOx concentration. The high oxygen content of the biodiesel is known to be beneficial for reducing HC, CO, and soot, while it contributes to increased NOx emissions. At comparable air/fuel ratios within a specific operating point, all tested fuels and fuel blends exhibit comparable CO2 emissions.
Kleissner, Florian, Hofmann, Peter
Optical Equipment Safety in Aircraft Fuel TanksARP7977 (Current)8/1/2024
The recommended practices of this document are intended for optical devices and associated optical cables and connectors installed inside transport category aircraft or environments of equivalent ignitability. This document covers optical radiation in the wavelength range from 380 nm to 10 μm. As explained in this document, wavelengths below this range are capable of igniting fuel-air mixtures through an ignition mechanism not considered at this issue of ARP7977. Use of wavelengths outside the range 380 nm to 10 μm should be discussed with the relevant Certification Authority.
AE-5A Aerospace Fuel, Inerting and Lubrication Sys Committee
Experimental and Numerical Investigations of a Dual-Fuel Hydrogen–Kerosene Engine for Sustainable General Aviation2024-01-60016/17/2024
Reducing CO2 emissions is an increasingly important issue. In aviation, approaches such as e-propulsion only represent a solution for special applications due to the low energy density of batteries. Because of the low-cost and robust design of combustion engines, this concept is still the most suitable for general aviation. For defossilization, besides e-fuels and bio-fuels, which represent the so-called sustainable aviation fuels (SAF), hydrogen can serve as a promising energy carrier for CO2 reduction. For this purpose, the combustion process of a dual-fuel hydrogen–kerosene (Jet A-1) engine was developed and investigated for use in small aircrafts. This study explores the influence of hydrogen addition on combustion parameters, emissions, and efficiency. An advantage of this special design as dual-fuel engine (hydrogen and kerosene) is the possibility of redundancy operation in the event of a H2 fuel system failure as well as full operational capability of the aircraft in the event of hydrogen supply difficulties at various airports. Besides test bench investigations, 3D CFD simulations were performed to optimize hydrogen injector position, ensure backfire-free operation, and improve mixture formation. In addition to a low load and high load point, a high-altitude point was investigated based on real flight data. The maximum achievable hydrogen energy shares, limited by abnormal combustion, and the respective CO2 reductions are shown. Furthermore, the influence of the hydrogen mass distribution in the inlet ports was investigated to achieve an advantage in the homogenization of the hydrogen–air mixture. Finally, the efficiency losses in hydrogen dual-fuel mode compared to base kerosene operation are shown in a detailed analysis.
Reitmayr, Christian, Wiesmann, Frederik, Gotthard, Thomas, Hofmann, Peter
Electrification and Autonomy: Vol. 1EPRCOMPV3320235/10/2024
David, Aharon, Muelaner, Jody E., Rezende, Rene Nardi
Manufacturing of Thermoplastic Composite Parts with Press Forming TechnologyF-0080-2024-13625/7/2024
Thermoplastic composites are serious competitor for classic epoxy composites. They have comparable properties to epoxy composites, but characterize much lower processing costs. There are several methods of manufacturing the components from thermoplastic composites. One of the most interesting method in terms of efficiency is thermoforming on a press. This technology allows to product of the aircraft parts such as: ribs, brackets, covers, stiffeners. Thermoplastic composites are resistant to most solvents such as grease, oil and aviation fuel. They are also non-flammable and heat-resistant. This all makes them suitable for use in aircraft as upholstery, casing or elements around the tank. PZL Mielec has been developing press thermoforming technologies since 2016 and is the owner of the several patents in this area.
Głodzik, Marcin, Wojtuszewski, Radosław, Farbaniec, Konrad, Sienicki, Jarosław, Banaś, Aleksander, Gałaczyński, Tomasz
Impact of a Split-Injection Strategy on Energy-Assisted Compression-Ignition Combustion with Low Cetane Number Sustainable Aviation Fuels2024-01-26984/9/2024
The influence of a split-injection strategy on energy-assisted compression-ignition (EACI) combustion of low-cetane number sustainable aviation fuels was investigated in a single-cylinder direct-injection compression-ignition engine using a ceramic ignition assistant (IA). Two low-cetane number fuels were studied: a low-cetane number alcohol-to-jet (ATJ) sustainable aviation fuel (SAF) with a derived cetane number (DCN) of 17.4 and a binary blend of ATJ with F24 (Jet-A fuel with military additives, DCN 45.8) with a blend DCN of 25.9 (25 vol.% F24, 75 vol.% ATJ). A pilot injection mass sweep (3.5-7.0 mg) with constant total injection mass and an injection dwell sweep (1.5-3.0 ms) with fixed main injection timing was performed. Increasing pilot injection mass was found to reduce cycle-to-cycle combustion phasing variability by promoting a shorter and more repeatable combustion event for the main injection with a shorter ignition delay. For both fuels, dwells between 2.0 and 2.5 ms resulted in the lowest variability. For these dwells, the pilot injection cumulative heat release at the main injection timing is maximized, resulting in more rapid ignition of the main injection. Emissions results suggest that mixing-controlled combustion of the main injection is achievable with higher pilot masses at injection dwells between 2.0 and 2.5 ms as indicated by an increase in filter smoke number at these conditions.
Stafford, Jacob, Amezcua, Eri, Miganakallu Narasimhamurthy, Niranjan, Kim, Kenneth, Kweon, Chol-Bum, Rothamer, David
Compression Ignition Engine Smoke Emissions at Reduced Ambient Pressures and Temperatures2024-01-23804/9/2024
Smoke emission from compression ignition (CI) engines is directly tied to fuel atomization, vaporization, mixing and combustion processes. Engine boundary conditions such as ambient pressures and temperatures, particularly at higher altitudes, have significant impacts on both available ignition energy and on the mixing-controlled combustion process. However, the effects of boundary conditions are difficult to explore without thorough pressure and temperature control of the engine intake air and exhaust gas at higher altitude conditions. The objective of this research is to investigate the relationship between engine smoke emission and engine power in a CI engine fueled with jet fuel at various ambient conditions including higher altitudes. A multi-cylinder compression-ignition engine was operated on a jet fuel at various ambient pressure and temperature conditions, as low as 60 kPa and -12°C, respectively. Single and multi-injection strategies were applied depending on engine power. Detailed analysis was made on in-cylinder pressure, heat release, and the ratio of premixed combustion to mixing-controlled combustion as indicated by the heat release rate. Smoke opacity and filtered smoke number (FSN) measurements were made using an AVL Opacimeter and an AVL Smoke Meter, respectively, at sea level conditions as well as at reduced ambient temperatures and pressures. Depending on the engine power, a shift between premixed and mixing-controlled combustion occurred which significantly impacted the engine-out smoke. Further, the smoke emission was dependent on the injection strategies. Smoke emissions for the jet-fueled engine were examined with respect to heat release behavior and equivalence ratio. The capabilities and challenges of measuring smoke at higher altitude conditions are discussed.
Mattson, Jonathan, Gibson, Joseph, Kweon, Chol-Bum, Kim, Kenneth, Schroen, Erik, Hepp, Kyle, Meininger, Rik, Clerkin, Peter, Kruger, Kurt, Musser, Marshall, Pope, Aaron, Kang, Sang-Guk
Zero Carbon Emission Aviation Fuel Technology Review - The Hydrogen Pathway2023-36-00291/8/2024
The commercial aviation currently accounts for roughly 2.5 % of the global CO2 emissions and around 3.5% of world warming emissions, taking into account non CO2 effects on the climate. Its has grown faster in recent decades than the other transport modes (road, rail or shipping), with an average rate of 2.3%/year from 1990 to 2019, prior to the pandemic. Moreover, its share of Greenhouse (GHG) emissions is supposed to grow, with the increasing demand scenario of air trips worldwide. This scenario might threaten the decarbonization targets assumed by the aviation industry, in line with the world efforts to minimize the climate effects caused by the carbon emissions. In this context, hydrogen is set as a promising alternative to the traditional jet fuel, due to its zero carbon emissions. Furthermore, its high energy content makes it suitable for the aviation industry, especially in the short to medium haul flights niche, that currently accounts for around 43.8% of global aviation CO2 emissions. Hydrogen fueled aircrafts might have fewer range limitations, compared with battery electric counterparts, currently restricted to smaller commuter flights, given the low energy density of the batteries. For long range flights, liquid fuels alternatives, such as sustainable aviation (SAF), still have a leading position in the short to medium term environmental agenda. Hydrogen can be burned directly in (modified) gas turbine engines, in fuel cells, to generate electricity to power electric motors, or in hybrid-electric propulsion systems. Nevertheless, despite the environmental benefits, there are great challenges to make hydrogen a viable alternative to the fossil liquid jet fuel. One of the main hurdles is the fuel storage, associated with the much higher volume and storage system complexity required for (liquid) hydrogen, to provide the same amount of energy of liquid jet fuel. These fuel features require aircraft and engine design modifications, as well as a new fuel distribution infrastructure. Another major challenge is the full understanding of the non CO2 related climate impacts of hydrogen combustion, such as H2O emissions at cruise altitudes, which interacts with soot and particles in the atmosphere, to form contrails. Finally, the H2 cost, might be addressed to enable a fair competition with fossil jet fuel. Currently, there is a great research effort, from both the government and academic sectors, as well as from the aircraft manufacturers, which includes the test of demonstration H2 aircraft prototypes. This effort also might include policies to foster environmental friendly fuel alternatives, to make them cost competitive. This work presents a review of the aviation hydrogen technology, with a focus on both the propulsion and onboard storage systems, as well as on the potential environmental benefits and the associated costs of the aviation hydrogen fuel pathway. The review research has been supported on a wide search on the technical literature, by using up to date (mainly published in the last two years) articles, whitepapers and technical reports, available at specialized directories and scientific journals. The search has used key words, such as aviation sustainability, hydrogen for aviation propulsion, aviation environmental footprint (and Greenhouse emissions) reduction, as well as liquid and gaseous hydrogen storage.
Barbosa, Fábio Coelho
Emissions of Aerospace Fuels F-24 and Jet-A in a Jet Engine and Correlation with Combustion Characteristics from a Constant Volume Combustion Chamber2023-01-166610/31/2023
An investigation into emissions differences and their correlations with differing combustion characteristics between F24 and Jet-A was conducted. Raw emissions data was taken from a single stage jet engine by a FTIR gas analyzer. Measurements of H2O, CO2, CO, NOx, and total hydrocarbon emissions (THC) were taken at 60K, 65K, and 70K RPM. At 70K RPM Jet-A and F-24 the emissions were similar at approx.: 4% H2O, 3% CO2, 970 PPM CO, 28 PPM NOx. Jet-A THC emissions were approx.: 1200 PPM THC, F24 THC emissions were lower by over 60%. The significantly lower amount of THC emissions for F24 suggests more complete combustion compared to Jet-A.
Soloiu, Valentin, Rowell, Aidan, Weaver, Amanda, Mcafee, John, Willis, James, O'Brien, Brandon
Comparative Analysis of the Lubrication, Friction, and Wear of Injection System Materials, with Synthetic Paraffinic Kerosene, Jet-A, and ULSD2023-01-163310/31/2023
Alternative fuels are sought after because they produce lower emissions and sometimes, they have feedstock and production advantages over fossil fuels, but their wear effects on engine components are largely unknown. In this study, the lubricity properties of a Fischer-Tropsch Gas-to-Liquid alternative fuel (Synthetic Paraffinic Kerosene-S8) and of Jet-A fuel were investigated and compared to those of Ultra Low Sulphur Diesel (ULSD). A pin-on-disk tribometer was employed to test wear and friction for a material pair of an AISI 316 steel ball on an AISI 1018 steel disk when lubricated by the fuels in this research work. Advanced digital microscopy was used to compare the wear patterns of the disks. Viscosity and density analysis of the tested fluids were also carried out. Tribometry for the fuel showed that S8 fell between Jet-A and ULSD when friction force was calculated and showed higher wear over time and after each test when compared to that of Jet-A and ULSD. An initially higher running-in friction force of 0.35N to 0.38N was observed for all three tested fluids, and then quasi-steady-state lower values of friction force of .310N for S8, 0.320 N for Jet-A and 0.295N for ULSD (the lowest observed).Wear values obtained by mass loss of the tested AISI 108 steel disks show that Jet-A and the reference fuel ULSD may yield lower wear (which is associated to better lubricity) than that of S8, and microscopy images are consistent with the wear results.
Soloiu, Valentin, Davis, Zachary, Molina, Gustavo J., Myrthil, Christopher, Willis, James, Weaver, Amanda
Development of a Laboratory Unit to Study Internal Injector Deposits Formation2023-24-00788/28/2023
The formation of deposits in the fuel systems of heavy-duty engines, using drop-in fuels, has been reported in recent years. Drop-in fuels are of interest because they allow higher levels of alternative fuels to be blended with conventional fuels that are compatible with today’s engines. The precipitation of insolubles in the drop-in fuel can lead to clogging of fuel filters and internal injector deposits, resulting in increased fuel consumption and engine drivability problems. The possible mechanisms for the formation of the deposits in the fuel system are not yet fully understood. Several explanations such as operating conditions, fuel quality and contamination have been reported. To investigate injector deposit formation, several screening laboratory test methods have been developed to avoid the use of more costly and complex engine testing. To further evaluate and understand the formation of internal injector deposits in heavy-duty engines, a thermal laboratory test method has been developed. The test method is called Thermal Deposits Test (TDT) and it is inspired by Jet Fuel Thermal Oxidation Test (JFTOT) method. This test unit can be used to study in applications where a fluid is in contact with a hot surface. The method uses common laboratory hardware and readily available off-the-shelf parts, making it inexpensive to build and very flexible to operate. Deposits are collected on a metal foil, which makes it easier to analyze. This paper describes the construction of the apparatus and its performance. Experimental tests with diesel fuel, doped with soap-type soft particles, which contain typical particles that can form deposits, are performed, and compared with JFTOT results. Analytical techniques, such as Scanning Electron Microscopy with Energy Dispersive X-Ray, Fourier-transform Infrared Spectroscopy, and Pyrolysis coupled with Gas Chromatography-Mass Spectroscopy and Ellipsometry were used. Conclusions about the performance of the doped fuel are drawn from the test. Future plans are to study the mechanisms behind the formation of internal diesel injector deposits.
Pach, Mayte, Hittig, Henrik, Scholle, Tobias, Kusar, Henrik, Engvall, Klas
Experimental and Numerical Investigation of Combustion and Noise, Vibrations, and Harshness Emissions in a Drone Jet Engine Fueled with Synthetic Paraffinic Kerosene01-17-01-00068/14/2023
Emissions and effects of climate change have prompted study into fuels that reduce global dependence on traditional fuels. This study seeks to investigate engine performance, thermochemical properties, emissions, and perform NVH analysis of Jet-A and S8 using a single-stage turbojet engine at three engine speeds. Experimental Jet-A results were used to validate a CFX simulation of the engine. Engine performance was quantified using thermocouples, pressure sensors, tachometers, flow meters, and load cells fitted to the engine. Emissions results were collected using an MKS Multigas Emissions Analyzer that examined CO, CO₂, H₂O, NOx, and THC. NVH analysis was conducted using a multifield, free-field microphone, and triaxial accelerometer. This study found that Jet-A operates at higher temperatures and pressures than S8, and S8 requires higher fuel flow rates than Jet-A, leading to poorer efficiency and thrust. S8 produced stronger vibrations over 5 kHz compared to Jet-A. S8 showed a decrease in all measured emissions. The CFD model was validated, showing an increase in temperature, pressure, and gas velocity as speed increased. The swirl effect of combustion was examined, improving atomization. Emissions contours were validated by experimental results, showing increases in CO₂, H₂O, and NOx, and a decrease in CO as speed increases.
Soloiu, Valentin, Mcafee, John, Ilie, Marcel, Rowell, Aidan, Willis, James, Dillon, Nicholas
On-Board Fuel Sensing for UAS and Ground Vehicle Applications2024-01-41288/10/2023
The variability in fuel, particularly for fuel blends containing sustainable aviation fuels (SAFs), emphasizes the importance of understanding fuel properties for optimizing engine performance. This paper introduces spectroscopic fuel sensors capable of real-time estimation of jet fuel properties, mainly derived cetane number (DCN). While initially developed for unmanned aircraft systems (UAS), the paper explores their potential in ground vehicle applications: enhancing engine performance through sensing for feed-forward control and fuel property monitoring at fuel depots. The fuel sensing technologies are based on spectroscopic techniques coupled with machine learning (ML) approaches. The combination of these techniques demonstrates a promising solution for a wide spectrum of fuel applications.
Patel, Dev B., Sutar, Ashish, Abraham, Abhinav, Ambre, Dhananjay, Brezinsky, Kenneth, Lynch, Patrick T., Okada, Haruna, Stafford, Jacob M., Miganakallu, Niranjan, Sanders, Scott, Rothamer, David, Mayhew, Eric, Kim, Kenneth S.
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