Aviation Fuel Research Articles

A nonlinear dynamic analysis of skidding behavior in rolling bearings using lubricant traction coefficients and cage flexibility

Skidding is a primary cause of rolling element bearing (REB) failure, which is influenced by operating conditions, lubricant properties, and bearing design. This paper presents an improved nonlinear dynamic model of REBs to analyze the impact of lubricant characteristics on REB skidding at different speed states. The model considers time-varying traction coefficient, cage flexibility, and cage pocket clearance. The selected tested lubricants include lithium grease (LGT2), compound calcium sulfonate (CCS) grease, and 4109 Chinese aviation oil. Simulation results show that CCS grease effectively reduces cage skidding, with the lowest load limits (300 N at 2000 RPM) under constant speed conditions and the highest stable limit (2932 RPM) during acceleration. LGT2 grease exhibits minimal sensitivity to acceleration and fluctuation speed parameters change.

Alternative climate metrics to the Global Warming Potential are more suitable for assessing aviation non-CO2 effects

A growing body of research has highlighted the major contribution of aviation non-CO2 emissions and effects to anthropogenic climate change. Regulation of these emissions, for example in the EU Emissions Trading System, requires the use of a climate metric. However, choosing a suitable climate metric is challenging due to the high uncertainties of aviation non-CO2 climate impacts, their variability in atmospheric lifetimes and their dependence on emission location and altitude. Here we use AirClim to explore alternatives to the conventional Global Warming Potential (GWP) by analysing the neutrality, temporal stability, compatibility and simplicity of existing climate metrics and perform a trade-off. We find that using the temperature-based Average Temperature Response (ATR) or using an Efficacy-weighted GWP (EGWP) would enable a more accurate assessment of existing as well as future aircraft powered by novel aviation fuels.

Life cycle emissions and unit production cost of sustainable aviation fuel from logging residues in Georgia, United States

Production of Sustainable Aviation Fuel (SAF) has gained popularity for reducing carbon emissions from the aviation sector. To evaluate the environmental and economic tradeoffs related to SAF production and its potential use, this study estimates the life cycle carbon emissions and unit production cost of SAF produced from logging residues generated during harvest and thinning operations in Georgia, a major roundwood producing state in the Southern United States. We considered two production pathways, i.e., Ethanol-to-Jet (ETJ) and Iso-Butanol-to-Jet (Iso-BTJ), to compute the carbon savings and unit production costs. A sensitivity analysis was performed to identify significant factors contributing to the overall carbon savings and unit production costs for the selected pathways. After considering revenues generated from co-products, the minimum aviation fuel selling price (MASP) was $2.71 L-1 and $2.44 L-1 for ETJ and Iso-BTJ pathways, respectively. Capital investment cost at biorefinery accounted for most of the MASP, followed by the minimum haul rate for transporting biomass and variable cost for alcohol intermediate production. Finally, after considering tax credit from the Inflation Reduction Act of 2022 and RIN (Renewable Identification Number) credit along with co-product revenue, the MASP ranged between $2.29 L-1 and 0.83 L-1 for the ETJ pathway and between $2.04 L-1 and $0.59 L-1 for the Iso-BTJ pathway. In addition, the carbon intensity of both the ETJ and Iso-BTJ pathways were 758 g CO2e L−1 and 976 g CO2e L−1, with relative carbon savings of 70.6 % and 62.1 % compared to conventional aviation fuel. The production cost suggests a minimum abatement cost of $59 t CO2e−1 for the ETJ and -$59.3 t CO2e−1 for the Iso-BTJ pathways in the presence of federal incentives. Our study shows that logging residues-based SAF could reduce the overall carbon footprint of the aviation sector; however, policy support is needed to support its production in light of higher production costs.

Aviation fuels of the future − A techno-economic assessment of distribution, fueling and utilizing electricity-based LH2, LCH4 and kerosene (SAF)

This paper investigates the techno-economic implications on air travel when fossil-based kerosene is phased out of the market, specifically focusing on the comparison between liquid hydrogen, liquid methane and renewable kerosene for ten exemplary flight routes to estimate the cost of air travel per passenger and 100 km distance travelled €2020PAX100km for every fuel type. By considering the entire supply chain, including hydrogen production from renewable sources, synthesis, oversea transport, domestic distribution, and utilization, this study addresses the overarching question of whether it is more economical to change the fuel source or the fuel itself to reduce fossil kerosene usage in the aviation industry. It is demonstrated that aircraft acquisition costs play a minor role compared to fuel supply costs and specific fuel demand. The study shows that for electricity-based fuels, liquid hydrogen is the most economic option, even with a potential energy penalty, followed by liquid methane and renewable kerosene. The results for an aircraft with a capacity 180 passengers are 3.08, 4.57 and 5.11 €PAX100km for liquid hydrogen, liquid methane and renewable kerosene, respectively. Challenges regarding storage and isolation requirements for cryogenic fuels in aviation are discussed, with assumptions made that these obstacles can be overcome to realize economic benefits. Additionally, the study suggests potential shifts in aircraft size selection by airlines to mitigate rising fuel prices in the future. The study advocates for the aviation industry's openness to new fuels like liquid hydrogen and liquid methane to alleviate the cost increase associated with phasing out fossil kerosene.

Volatility Measurements of Sustainable Aviation Fuels: A Comparative Study of D86 and D2887 Methods

Volatility Measurements of Sustainable Aviation Fuels: A Comparative Study of D86 and D2887 Methods

Impact of Internal Baffle Designs on Liquid Hydrogen Sloshing in Cryogenic Aircraft Fuel Tanks

Hydrogen because of its zero carbon emissions and highly energy-dense nature has a strong potential to be used as an aviation fuel. There are currently two main ways that hydrogen is being considered for use in aircraft: it can be vaporized and mixed with air before being burned in the jet engine, or it can be used to power fuel cells that generate electricity, which can be used to power electric motors. Both these scenarios would require storing liquid hydrogen (LH2) in cryogenic tanks on board as it minimizes the tank size. But a major challenge with cryogenic hydrogen storage is the dynamic movement of the fuel which can lead to fuel boil off and bubble formation. In the current paper, the sloshing motion of LH2 in a CHEETA type thin-walled composite fuel tank, under acceleration data obtained from an Airbus A-320 in cruising conditions, is investigated. The dynamic fluid structure interaction problem is solved numerically using the Coupled Eulerian-Lagrangian (CEL) technique in ABAQUS. The developed modelling strategy is then employed to study the impact of various internal baffle designs on the sloshing behavior of the fuel under different fill levels. This study not only establishes that sloshing is a major cause for concern when it comes to LH2 aircraft fuel storage, but also advances our understanding in devising potential mitigative strategies.

An Engine-Level Safety Assessment Approach of Sustainable Aviation Fuel Based on a Multi-Fidelity Aerodynamic Model

Safety is essential for sustainable aviation fuels (SAFs). However, evaluating SAFs’ impacts on aero-engine safety is challenging because it involves multiple space scales and the strongly coupled relationships of aero-engine components. Aiming at addressing this problem, a model-based approach is proposed to establish the relationship between the fuel-level physical properties and engine-level safety parameters. Firstly, a unified modeling criterion is proposed to consider the interrelations of aero-engine components. Under this criterion, aero-engine secondary air system (SAS) components are included in SAF safety assessment, since they have non-neglectable influences on aero-engine safety. Secondly, this paper proposes a surrogate-based iteration strategy to embed the combustor’s high-dimensional computational fluid dynamics (CFD) model into the aero-engine flow network model. Then, the proposed model-based safety assessment approach is applied to a Fischer–Tropsch hydro-processed synthesized paraffinic kerosine (F-T SPK) safety assessment case. The effects of fuel flow and blending ratio are considered. The results indicate the necessity to evaluate SAFs’ safety at the aero-engine level and consider the influences of SAS components. The proposed model-based approach may provide a preliminary screening before SAFs’ certification tests. This convenience may be beneficial for reducing the cost and accelerating SAFs’ application.

Aviation fuel pump health state assessment based on evidential reasoning and random forests

AbstractAs the power source of the engine, the Fuel Pump(FP) plays a vital role in the safe operation of the aircraft. Due to the complexity of the working mechanism of Aviation Fuel Pumps (AFP) and the strong correlation between the components, the assessment model cannot reflect the health state of the FPs better, while the initial parameters in the assessment model will affect the assessment effect of the model. Therefore, this paper proposes a health status assessment model that can fully integrate monitoring data. To improve the accuracy of the model parameters, the Random Forest algorithm is used to give the feature weights to make up for the limitation of relying on expert knowledge, and the model parameters are optimized by the Covariance Matrix Adaptive Evolutionary Strategy algorithm, which achieves an accurate assessment of the state. Finally, the AFP test bed was built and the AFP was tested. Compared with other methods, the accuracy of the proposed method in this question reaches 96%, which is greatly superior to other methods and verifies the effectiveness of the proposed method. It also provides an outlook on future research directions for health state assessment.

Preliminary Envelope for Large Transport Aircrafts Operating with Non-Primary Fuels AVGAS, MOGAS and F76-Dieso

This study explores the operational implications and safety considerations of using non-primary fuels—AVGAS, MOGAS, and F76 Dieso—in military transport aircraft, against the backdrop of standard aviation fuels. Through an analysis of fuel properties such as vapor pressure, density, viscosity, freeze temperature, water solubility, and thermal conductivity, this work outlines the operational envelopes for the mentioned non-primary fuels, highlighting the temperature and altitude limitations inherent to their use. The evaluation underscores the necessity of relevant testing, certification, and adherence to operational guidelines and constrains to ensure aircraft safety and reliability when standard fuels are unavailable, and hence, non-primary fuels may be required in special missions under emergency. Key findings include the specific altitude and temperature limitations for AVGAS and MOGAS to prevent fuel freezing and boiling, as well as the operational challenges posed by F76 Dieso due to its higher density and viscosity. The study also addresses the importance of managing water content in the fuel system, the flammability range of the non-primary fuels, and the considerations for fuel mixing to maintain aircraft performance and safety standards. This analysis aims to enhance the understanding of non-primary fuel usage in military transport aircraft, providing insights for system design, performance assessment, and the development of operational procedures to support military aviation in diverse operational scenarios.

Experimental Evaluation of Methanol/Jet-A Blends as Sustainable Aviation Fuels for Turbo-Engines: Performance and Environmental Impact Analysis

This study offers a comprehensive examination, both theoretically and experimentally, of the potential of methanol (M) as a sustainable aviation fuel (SAF) assessed in combination with kerosene (Ke—Jet-A aviation fuel + 5% Aeroshell oil). Different blends of methanol and kerosene (10%, 20%, and 30% vol. of (M) was added to Ke) were tested in an aviation micro turbo-engine under various operating regimes, such as idle, cruise, and maximum. Key engine parameters, including combustion temperature, fuel consumption, and thrust, were closely monitored during these trials. Essential performance indicators such as combustion efficiency, thermal efficiency, and specific consumption for all fuel blends under maximum operating conditions are also presented. Physical and chemical characteristics, such as viscosity, density, calorific value and flash point, were determined for each blend. Moreover, elemental analysis and FTIR spectroscopy were utilized to evaluate the chemical composition of the fuels. This study further investigated the air requirements for stoichiometric combustion and computed the resulting CO2 and H2O emissions. Experimental tests were conducted on the Jet Cat P80® micro turbo-engine, covering assessments of starting procedures, acceleration, deceleration, and pollutant emissions (CO and SO2) during various engine operating conditions. The results suggest that the examined fuel blends demonstrate stable engine performance at concentrations of 10% and 20% methanol. However, observations indicate that with an increase in methanol concentration, particularly at 30%, the stability of the engine at idle and, notably, at maximum speed decreases significantly. Specifically, at a 30% methanol concentration, the engine no longer operates stably, exhibiting significant rpm fluctuations, leading to the decision not to explore higher concentrations.

Algae to HEFA: Economics and potential deployment in the United States

AbstractTo reach the goals set by the US Department of Energy's Sustainable Aviation Fuel (SAF) Grand Challenge, currently available feedstocks may be insufficient. Giving priority to developing, prototyping and reducing the cost of algal feedstock before investing and lining up locations is important. As the production of algal feedstocks advances, a simplified conversion approach using more mature technologies can help reduce the investment risk for algae‐based fuels. Reducing process complexity to the steps described here [namely, conversion of lipids to HEFA (hydroprocessed esters and fatty acids) fuels and relegating the remainder of the biomass to anaerobic digestion or food/feed production] enables the near‐term production of algal SAF but presents challenging economics depending on achievable cultivation costs and compositional quality. However, these economics can be improved by present‐day policy incentives. With these incentives, the modeled algae‐to‐HEFA pathway could reach a minimum fuel selling price as low as $4.7 per gasoline gallon equivalent depending on the carbon intensity reduction that can be achieved compared with petroleum. Uncertainty about algal feedstock production maturity in the current state of technology and the future will play a large role in determining the economic feasibility of building algae‐to‐HEFA facilities. For example, if immaturity increases the feedstock price by even 10%, SAF production in 2050 is about 58% of the production which could have been achieved with mature feedstock. Additionally, growth in this conversion pathway can be notably boosted through the inclusion of subsidies, and also through higher‐value coproducts or higher lipid yields beyond the scope of the process considered here.

Life-Cycle Assessment of Sustainable Aviation Fuel Derived from Paper Sludge

Life-Cycle Assessment of Sustainable Aviation Fuel Derived from Paper Sludge

Microwave-assisted pyrolysis of plastics for aviation oil production: energy and economic analyses

Microwave-assisted pyrolysis of plastics for aviation oil production: energy and economic analyses

Sustainable Aviation Fuel from High-Strength Wastewater via Membrane-Assisted Volatile Fatty Acid Production: Experimental Evaluation, Techno-economic, and Life-Cycle Analyses

Sustainable Aviation Fuel from High-Strength Wastewater via Membrane-Assisted Volatile Fatty Acid Production: Experimental Evaluation, Techno-economic, and Life-Cycle Analyses

Optimization of the Caustic Treatment of Jet-Fuel to Reduce the Consumption of Caustic Soda in an Oil Refinery

Jet-Fuel desulfurization is one of the most important processes in the petroleum industries due to the high quality required for aviation fuels. In the pre-sent work, the desulfurization of Jet-Fuel with a content of sulfurous compounds was studied using a process assisted with sodium hydroxide. It was considered that the composition of the turbo fuel varies because different blends of crude oil are processed in the refinery under study. The effects of operating conditions, such as reaction time (15 to 30 min) and the amount of caustic soda (NaOH) in its solution (0.024 to 0.2 mol/L) were investigated. The objective functions (responses) were the NaOH consumption and the total cost of production while the acidity and the total sulfur content of Jet-A1 were considered as restrictions. The optimal conditions of the proposed model were obtained using the optimization with the fmincon function of the MATLAB software. These optimal conditions were found to vary according to the content of sulfur compounds present in the process feed. From the optimal points obtained, it was possible to determine the frequency of change of the NaOH solution that allows its maximum use.

Critical interplay between ruthenium oxide and water for the catalytic conversion of lignin to sustainable aviation fuel

The production of renewable drop-in fuels from lignocellulosic biomass is desirable for achieving net-zero carbon emissions in the transportation sector. However, the high irregularity of lignin and its resistance to complete ring saturation and deoxygenation hinder its conversion to sustainable aviation fuels (SAFs) such as C7–C16 isoparaffins and alkylated cycloalkanes. In this study, we achieve the direct production of SAFs from lignin-derived oil over a nonacidic Ru/C catalyst in water. Hydrogen atoms generated by H2 dissociation combine with neighboring water molecules to produce hydronium ions, which are then transferred via H-shuttling to attack the double bonds and cyclic –OH groups of adsorbed reactants and intermediates. Density functional theory calculations suggest that hydrodeoxygenation in water decreases the activation energy for the direct hydrogenolysis of cyclic –OH groups over oxygen-vacant ruthenium oxide sites. The critical interplay between oxygen-vacant ruthenium oxide and water results in the almost-complete conversion of lignin-derived monomers, dimers, and bio-oils to desirable SAF components.

A convolutional neural network prediction model for aviation nitrogen oxides emissions throughout all flight phases

In recent years, there has been an increasing amount of research on nitrogen oxides (NOx) emissions, and the environmental impact of aviation NOx emissions at cruising altitudes has received widespread attention. NOx may play a crucial role in altering the composition of the atmosphere, particularly regarding ozone formation in the upper troposphere. At present, the ground emission database based on the landing and takeoff (LTO) cycle is more comprehensive, while high-altitude emission data is scarce due to the prohibitively high cost and the inevitable measurement uncertainty associated with in-flight sampling. Therefore, it is necessary to establish a comprehensive NOx emission database for the entire flight envelope, encompassing both ground and cruise phases. This will enable a thorough assessment of the impact of aviation NOx emissions on climate and air quality. In this study, a prediction model has been developed via convolutional neural network (CNN) technology. This model can predict the ground and cruise NOx emission index for turbofan engines and mixed turbofan engines fueled by either conventional aviation kerosene or sustainable aviation fuels (SAFs). The model utilizes data from the engine emission database (EEDB) released by the International Civil Aviation Organization (ICAO) and results obtained from several in-situ emission measurements conducted during ground and cruise phases. The model has been validated by comparing measured and predicted data, and the results demonstrate its high prediction accuracy for both the ground (R2 > 0.95) and cruise phases (R2 > 0.9). This surpasses traditional prediction models that rely on fuel flow rate, such as the Boeing Fuel Flow Method 2 (BFFM2). Furthermore, the model can predict NOx emissions from aircrafts burning SAFs with satisfactory accuracy, facilitating the development of a more complete and accurate aviation NOx emission inventory, which can serve as a basis for aviation environmental and climatic research. SynopsisThe utilization of the ANOEPM-CNN offers a foundation for establishing more precise emission inventories, thereby reducing inaccuracies in assessing the impact of aviation NOx emissions on climate and air quality.

Rapid assessment of jet engine-like soot from combustion of conventional and sustainable aviation fuels using flame spray pyrolysis

Rapid assessment of jet engine-like soot from combustion of conventional and sustainable aviation fuels using flame spray pyrolysis

Geospatially explicit technoeconomic assessment of sustainable aviation fuel production: A regional case study in Virginia

There is strong interest in sustainable aviation fuels (SAF) to decarbonize aviation; however, local decision-makers will need to consider what additional incentives could stimulate SAF commercialization within their own jurisdictions. This study analyzed SAF production in Virginia, evaluating two biomass-to-energy platforms (gasification Fischer Tropsch [GFT] and pyrolysis) and two regionally abundant feedstocks (woody wastes and municipal solid wastes). A suite of open-access modeling tools were applied to possible SAF supply chains encompassing feedstock collection and transportation, conversion, and fuel upgrading and transport. Key modeling outputs were minimum product selling price (MPSP) ($/gallon) and life-cycle global warming potential (GWP) (g CO2eq/MJ). Results suggest that early SAF production via GFT will require local incentives of approximately $3.61 per gallon compared to $0.75 per gallon for pilot-scale pyrolysis. Location of production facility (by county) influences economic and environmental metrics but is not nearly as important as facility size (tonnes/year). Different formats of financial incentives (i.e., tax credits, loan forgiveness, etc.) offer markedly different reductions in SAF MPSP. Finally, under current federal incentives in the US, it is still more economically efficient to use pyrolysis (with higher GWP) than GFT (with lower GWP). Therefore, regional stakeholders will need to navigate the tradeoff between economic and environmental performances of these platforms. Though Virginia was used as a case study, the methodology is replicable for other jurisdictions, insofar it can be adapted for use in other locations without decision-makers having to completely build their own TEA models.

Experimental and data-driven chemical kinetic modeling study of alcohol-to-jet (ATJ) synthetic biofuel for sustainable aviation fuels

This work assesses the chemical ignition delay behavior of an isoparaffinic alcohol-to-jet (ATJ) fuel, one of the certified sustainable aviation fuels (SAFs). Chemical ignition delay measurements of ATJ were performed at a compressed pressure of PC = 2 MPa and three equivalence ratios (phi = 0.5, 1.0, & 1.3) in synthetic dry air, between 667 K and 1250 K. The unique chemical structures of isoalkanes result in high thermal decomposition rate, but low chemical oxidation reactivity. The new lumped mechanism (ARLMech-HC-ATJ) is developed using a genetic algorithm based on empirical ignition delays. The mechanism shows good performance over the temperature range from 667 K to 1250 K and varied equivalence ratios. Using the suggested mechanism, this study presents sensitivity analysis for the temperature range to understand chemical kinetics of ATJ fuel. The results show the impact of using ATJ modeling to design and optimize propulsion systems operating in the negative temperature coefficient (NTC) or low temperature chemistry (LTC) regime in the future and a methodology that can be adapted to other novel fuels.