Alternative Aviation Fuels Research Articles

Развитие технологий и перспективы внедрения авиационного биотоплива

An overview of the current state of production technologies of biojet fuels in the world and in Russia is presented. The contribution of the aviation sector to climate change processes and the likelihood of achieving global environmental goals in the event of large-scale production of alternative aviation fuels are assessed. The level of commercialization, constraining factors and possible measures to support synthetic kerosene production technologies are reviewed. Special attention is paid to the current international certification procedure for aviation biofuels. aviation biofuel, biojet fuels, synthetic kerosene, global warming, climate change, greenhouse gases emission, sustainable biofuel, ASTM certification, biomass conversion, photosynthetic microorganisms, microalgae. The review was financially supported by the Ministry of Science and Higher Education of the Russian Federation, project no. 14.574.21.0139 (Unique Project Identifier RFMEFI57417X0139).

Life cycle environmental analysis of ‘drop in’ alternative aviation fuels: a review

Alternative aviation fuels possess significant potential to reduce the environmental burdens of the aviation industry.

Future Fuels—Analyses of the Future Prospects of Renewable Synthetic Fuels

The Future Fuels project combines research in several institutes of the German Aerospace Center (DLR) on the production and use of synthetic fuels for space, energy, transportation, and aviation. This article gives an overview of the research questions considered and results achieved so far and also provides insight into the multidimensional and interdisciplinary project approach. Various methods and models were used which are embedded in the research context and based on established approaches. The prospects for large-scale fuel production using renewable electricity and solar radiation played a key role in the project. Empirical and model-based investigations of the technological and cost-related aspects were supplemented by modelling of the integration into a future electricity system. The composition, properties, and the related performance and emissions of synthetic fuels play an important role both for potential oxygenated drop-in fuels in road transport and for the design and certification of alternative aviation fuels. In addition, possible green synthetic fuels as an alternative to highly toxic hydrazine were investigated with different tools and experiments using combustion chambers. The results provide new answers to many research questions. The experiences with the interdisciplinary approach of Future Fuels are relevant for the further development of research topics and co-operations in this field.

Nonreacting Spray Characteristics for Alternative Aviation Fuels at Near-Lean Blowout Conditions

The spray characteristics of standard and alternative aviation fuels generated by a hybrid pressure-swirl airblast atomizer were studied at conditions corresponding to near-lean blowout conditions: ambient gas pressure , fuel temperature , and atomizing gas temperature . The candidate alternative fuels (C-1, C-5, C-7, and, C-8 synthetic blends) were compared to Jet-A (A-2). The drop size and drop velocity were measured using phase Doppler anemometry at three measurement planes downstream of the swirler exit. The representative diameters [, , and the mass mean diameter (MMD)] were used to characterize the drop size. The drop velocity was characterized using the arithmetic mean and the root mean square. An increase in the swirler pressure drop () showed a decrease in the mean drop size and an increase in the magnitude of the axial drop velocity. Comparing the different fuels generally showed an increase in for higher fuel viscosity. However, definitive trends in and the MMD were not observed, based on fuel physical properties such as viscosity, surface tension, or density. A variation of the fuel injection pressure showed no significant effect for both the standard and alternative fuels. The full cone angle (obtained using shadowgraph images) was found to not vary significantly with or .

Measurement of laminar burning velocity of high performance alternative aviation fuels

An experimental study was conducted on the measurement of the laminar burning velocity of alternative aviation fuels, in order to assess the feasibility of using the newly developed fuels in aviation applications. Two kinds of high performance hydrocarbon fuels (HPF-1 and 2), having higher density but moderate viscosity as compared with existing conventional aviation fuels, were created, and a Bunsen burner was manufactured to measure their laminar burning velocities at an elevated temperature of 550 K and atmospheric pressure. The measured laminar burning velocity of HPF-1 and 2 at the preheating temperature shows that the peak burning velocity of HPF-1 is approximately 125 cm/s, which is very close to that of the reference fuel (RF) and higher than Jet A-1, while the maximum laminar burning velocity of HPF-2 is shown to be approximately 130 cm/s, which is slightly higher (5–6 cm/s) than those of HPF-1 and RF. Compared with RF and Jet A-1, furthermore, the laminar burning velocity curves of HPFs shift to the fuel-rich side, with a corresponding decrease in the burning velocity on the lean side and an increase on the rich side. Therefore, the equivalence ratio where the laminar burning velocity reaches maximum (Φmax) increases slightly for the HPFs; Φmax for Jet A-1 and RF are around 1.07 and 1.08, respectively, while those for HPF-1 and 2 are 1.12 and 1.14, respectively. These fundamental data can be used to develop and validate combustion models to enable quantitative performance predictions in engine design for the newly developed fuels.

Characterization of the Fine Particle Emissions from the Use of Two Fischer-Tropsch Fuels in a CFM56-2C1 Commercial Aircraft Engine.

The fine particulate matter (PM) emissions from the use of two types of Fischer-Tropsch aviation fuels and their 50:50 blends with military JP-8 were quantified as part of the first Alternative Aviation Fuel Experiment (AAFEX). Measurements were made at 30-m downstream of a CFM56-2C1 engine for PM mass and number, particle size distribution, black carbon (BC), and volatile PM (sulfate + organics) using selected on-line instrumentation. The PM number emission index (EI N ) ranged from ~ 2 × 1015 to 7 × 1016 particles/kg fuel burned depending on fuel flow, fuel composition, and sampling temperature with the magnitude of the emissions inversely correlated to fuel flow. The PM mass emissions (EI M ) measured in the study varied from ~ 5 to 680 mg/kg fuel again depending on fuel flow, fuel type, and sampling temperature with a characteristic U-shaped curve of EI M with respect to fuel flow observed from the data. At low fuel flow (corresponding to low engine power), particle number and volume size distributions contained a single mode whereas at higher engine power, a bi-modal distribution was observed. The BC emissions varied from ~ 3 to 415 mg/kg fuel depending on fuel type and were found to exponentially increase with engine power (fuel flow). The volatile PM varied with sample temperature, fuel type, and increasing fuel flow within the range of EIs from ~ 0.4 to 11 mg/kg fuel with the highest values being at low fuel flow. Finally, the use of the two neat alternative fuels reduced the EI N by a median value of 70-73% and the EI M by ~ 94% as compared to JP-8 across all power conditions tested.

Lean flammability limits of alternative aviation fuels

Alternative fuels are being certified to be used in aircraft. However, the fire-safety properties of these fuels are unknown. The present work focused on measurements of the lean flammability limits (LFLs) of three alternative aviation fuels including Hydroprocessed Esters and Fatty Acids (HEFA), Synthesized Iso-Paraffins (SIP), and Fischer-Tropsch Iso-Paraffinic Kerosene (FT-IPK). The results were compared to that of conventional petroleum-based Jet A. The results showed that only FT-IPK had higher LFLs than that of Jet A. Additionally, the LFLs of four pure hydrocarbons including n-heptane, iso-octane, n-decane, and n-dodecane were measured since they are the major components of transportation fuels. The LFLs were within the range of 0.032–0.040 in terms of the fuel-air mass ratio for all four aviation fuels in the temperature range of 350–420 K. Unlike temperature, pressure had a minor influence on the lean flammability limit. For all measured samples (pure hydrocarbons and fuels), the lean limit decreases with increasing molecular weight.

LES of a swirl-stabilized kerosene spray flame with a multi-component vaporization model and detailed chemistry

Due to the introduction of alternative aviation fuels, new methods and models are necessary which have the capability to predict the performance of combustors dependent on the fuel composition. Towards this target, a multi-component vaporization model is coupled to a direct, detailed chemistry solver in the context of Eulerian–Lagrangian LES. By means of the computational platform, a lab-scale, swirl-stabilized spray flame is computed. The burner exhibits some of the key features of current aero-engine combustors. Global features like the measured spray distribution and the position of the reaction zone are well reproduced by the LES. The comparison of droplet size, droplet velocity and liquid volume flux profiles with experimental data also show a good agreement. However, discrepancies in the temperature profiles in the central mixing zone exist. The computational results show that evaporation and mixing are the rate-controlling steps in the flame zone. In this zone, chemistry can be assumed to be infinitely fast. However, other zones exist where finite rate chemistry effects prevail. For these states, the direct computation of the elementary reactions by means of Arrhenius equations and the transport of all individual species are beneficial. Furthermore, the finite rate chemistry approach demonstrates a great potential with respect to pollutant formation, as precursors can be directly computed. Additionally, the example of benzene forming from one specific chemical class in the fuel suggests that a multi-component description of the liquid phase and the evaporation process is required to correctly predict soot emissions.

Experimental and Analytical Characterization of Alternative Aviation Fuel Sprays Under Realistic Operating Conditions

The National Jet Fuel Combustion Program (NJFCP) is an initiative being led by the Office of Environment & Energy at the FAA, to streamline the ASTM jet fuels certification process for alternative aviation fuels. To accomplish this, the program has identified specific applied research tasks in several areas. The National Research Council of Canada (NRC) is contributing to the NJFCP in the areas of sprays and atomization and high altitude engine performance. This paper describes work pertaining to atomization tests using a reference injection system. The work involves characterization of the injection nozzle, comparison of sprays and atomization quality of various conventional and alternative fuels, and uses the experimental data to validate spray correlations. The paper also briefly explores the application viability of a new diagnostic system that has the potential to reduce test time in characterizing sprays. Measurements were made from ambient up to 10 bar pressures in NRC's High Pressure Spray Facility using optical diagnostics including laser diffraction, phase Doppler anemometry (PDA), LIF/Mie imaging and laser sheet imaging to assess differences in the atomization characteristics of the test fuels. A total of nine test fluids including six NJFCP fuels and three calibration fluids were used. The experimental data were then used to validate semi-empirical models, developed through years of experience by engine original equipment manufacturers, and modified under the NJFCP, for predicting droplet size and distribution. The work offers effective tools for developing advanced fuel injectors, and generating data that can be used to significantly enhance multidimensional combustor simulation capabilities.

Impact of Alternative Fuel Blending Components on Fuel Composition and Properties in Blends with Jet A

One challenge in the deployment of alternative aviation fuels is the lengthy “fuel approval process”, which costs millions of dollars and can take many years as the exact effect of these alternative options on engine and framework is still an unknown. A candidate aviation fuel needs to pass the tests as deemed necessary by the ASTM D4054 Standard Practice. The fuel manufacturer faces the risk of not receiving the ASTM certification after significant financial and time investment, which currently acts as a considerable hindrance to broadening the alternative aviation fuel options in commercial and military aircraft. Approval tests are based on the fuel properties and fuel performance as there is currently a knowledge gap on fuel chemical composition–property correlations. Therefore, the aim of this study was to accomplish the first step in this target, i.e., to obtain a detailed chemical composition of four approved blending components (FT-SPK, HEFA, SIP, and ATJ) and their mixtures with Jet A using GC × GC-TOF/MS and GC × GC-FID. Infrared spectroscopy and principal components analysis were utilized as additional techniques to demonstrate the differences among the blending components and Jet A, further utilizing their infrared spectral features. Moreover, the main physiochemical properties were measured, such as distillation profile, density, viscosity, flash point, freezing point, and net heat of combustion. Lastly, the impact of the differences in chemical composition on these main fuel properties was discussed.

Climate change and the aviation sector: A focus on the Victoria Falls tourism route

This study examined the environmental impacts of the aviation industry on the Victoria Falls tourism route and sustainability measures being put in place to deal with aviation’s impact on climate change. Primary data that includes an online survey of 370 tourists and secondary data from IATA Schedule Reference Analyzer among other sources were used in establishing the carbon footprint of the sector and an assessment of measures being undertaken to cut back on greenhouse gas (GHG) emissions in this case study. The study revealed that there is a correlation between the aviation industry and climate change. Despite efforts to cut back on carbon emissions, such efforts are not sufficient to result in meaningful cutbacks in GHG emissions owing to the inadequate regulatory framework and capacity challenges. Currently, the tourism sector on the Victoria Falls route outpaces technological gains aimed at achieving carbon-neutral growth. It is in African aviation’s best interests to cut back on carbon emissions, which can be done through public and private partnerships by taking advantage of available research. In such efforts, transparency and accountability will assist in steering the aviation industry towards the green path. Further research is recommended on how Africa can tap into alternative aviation fuels as a measure of achieving sustainable development goals.

Considerations on GHG emissions and energy balances of promising aviation biofuel pathways

This article presents results of a European Commission Joint Research Centre study to analyse the Greenhouse Gas (GHG) emissions and energy efficiency of various options for alternative aviation fuels. Interest in alternative aviation fuels is growing, as the sector seeks viable options to reduce increasing GHG emissions. For biofuels non-biogenic emissions arise from cultivation, harvesting and transport of the feedstock, as well as from their conversion into biofuel. It is important to consider whether any emissions reductions benefits are justified by the energy efficiency of each alternative. This article is focussed on American Society for Testing and Materials (ASTM) certifiable alternative drop-in biojet fuels [1], i.e. non-fossil hydrocarbon fuels which have (i) the same chemical structure and (ii) can be blended with conventional jet fuels, (iii) can use the same jet fuel supply infrastructure, and (iv) do not require modification of the aircraft. The results indicate that the biofuels studied tended to exhibit lower GHG than conventional jet fuels although indirect effects or existing uses of materials were not included in this study. Some biofuels performed better at reducing GHG than others (for example biofuels from wastes and residues). A large and important effect on emissions is seen due to land type used for cultivation and whether methane capture is used for certain pathways. GHG savings results vary due to the Life Cycle Analysis (LCA) methodology chosen for dealing with emissions and co-products. Certain pathways are notably more energy intensive than others and strong GHG reduction does not always coincide with high energy efficiency. An overview of industry initiatives and critical EU legislation relating to aviation biofuels is given. The insights from this work are expected to be of use for decision-makers considering investment options in this sector.

Impact of HEFA Feedstocks on Fuel Composition and Properties in Blends with Jet A

Alternative aviation fuels and their approval process contribute to one of the biggest challenges in deployment of an enhanced volume of aviation fuels. One of the approved fuel blending components is hydroprocessed esters and fatty acids (HEFAs) for mixing with petroleum-derived fuel (Jet A/A-1) up to 50 vol %. As the ASTM fuel specification (D7566) is merely based on the performance expected, the final blend concentration of HEFA in Jet A/A-1 can vary depending on the resultant fuel properties. Currently, there is a lack of information on how these properties are affected by the constituent chemical composition. The aim of this study was to compare three HEFAs sourced from different feedstocks (camelina, tallow, and mixed fat) and their blends with Jet A (10–60 vol %) based on the detailed chemical composition. The chemical composition was obtained using two-dimensional gas chromatography with mass spectrometry and flame ionization detector. The properties of interest were the distillation profile, dens...

Refining drop-in jet fuel coupling GHGs reduction in LCA with airworthiness in aero-engine and aircraft

Abstract The current challenge of drop-in jet fuel should couple the reduction of GHGs emission in whole life cycle with economic competitiveness and achieving performance as same as traditional jet fuel without reducing safe service life in engine and aircraft. From the insight of GHGs reduction, the whole life cycle, including sustainable feedstock, refining process integration and low emission in combustion are optimized for reduction in energy input and emission output. From the insight of airworthiness in aero-engine and aircraft, a certification process is achieved by extracting safety criteria from the “history experience” of petroleum-based jet fuel as the source and to predict the aero-engine safety implications of alternative aviation fuels as the target by “similar analogy”. The critical key parameters have been extracted by fundamental process related with safety and performance on achieving the duty of engine in the whole flight envelop. Alternative jet fuel can be qualified for certifying drop-in jet fuel and accordingly confirm with identical safe service life in engine and aircraft by analogizing the boundaries of critical key parameters with petroleum-based jet fuel. The critical parameters thereof, including carbon distribution and classification as well as C/H ratio, can conduct directly for feedstock choice and refining process modification. Accordingly, a process of refining algae-based jet fuel was modified coupling the requirement of GHGs reduction in life cycle with airworthiness in aero-engine and aircraft. Based on process integration to connect upstream feedstock to downstream combustion outcomes of alternative jet biofuel and co-product, GHGs in fuel stage deduced further by co-product and nutrient recovery in spite of additional separation process.

Paths to alternative fuels for aviation

Almost the complete amount of jet fuel available on the global market is produced from fossil crude oil being an exhaustible raw material. Furthermore its use is inherently connected with emissions of the greenhouse gas CO2. To cope with this, several processes for the production of alternative aviation fuels were developed including the use of biomass as a renewable feedstock. Since biomass from cultivation farming is in competition with food and fodder production, the preferred raw material would be residues from agriculture and forestry or municipal waste, also microalgae can be used. Independent of the raw material, the conversion of biogenic feedstock into alternative jet fuel is based on microbial, thermal and/or chemical breakdown of larger (bio)-molecules into smaller ones, followed by the catalytic formation of fuel molecules and hydrogenation. An overview on the production of different alternative bio-based jet fuels is given including a survey about producers and capacities, focusing on already certificated bio-based jet fuels. In addition to that, a comparison of fundamental combustion properties between Jet A-1 and different alternative jet fuels is presented: Laminar burning velocities and ignition delay times, each measured for two synthetic jet fuels based on fossil resources (coal-to-liquid—CtL and gas-to-liquid—GtL) as well as for two biofuels (farnesane and an Alcohol-to-Jet fuel—AtJ). Measurements of the burning velocities were performed at a preheat temperature of 473 K and pressures of 1 and 3 bar by variation of the fuel–air-equivalence ratios φ. Ignition delay times were determined for φ-values of 0.5, 1.0, and 2.0, at an initial pressure of about 16 bar and temperatures ranging between 800 and 1700 K. It turns out that with respect to the characteristic combustion properties tested the considered alternative fuels have a combustion behavior similar to Jet A-1.

Simulation-Based Analysis of the Potential of Alternative Fuels towards Reducing CO2 Emissions from Aviation

The mid-term framework of global aviation is shaped by air travel demand growth rates of 2–5% p.a. and ambitious targets to reduce aviation-related CO2 emissions by up to 50% until 2050. Alternative jet fuels such as bio- or electrofuels can be considered as a potential means towards low-emission aviation. While these fuels offer significant emission reduction potential, their market success depends on manifold influencing factors like the maturity of the production technology or the development of the price of conventional jet fuel. To study the potential for adoption of alternative jet fuels in aviation and the extent to which alternative fuels can contribute to the reduction targets, we deploy a System Dynamics approach. The results indicate that the adoption of alternative fuels and therefore their potential towards low-emissions aviation is rather limited in most scenarios considered since current production processes do not allow for competitive prices compared to conventional jet fuel. This calls for the development of new production processes that allow for economic feasibility of converting biomass or hydrogen into drop-in fuels as well as political measures to promote the adoption of alternative fuels.

Intensification of the hydrotreating process to produce renewable aviation fuel through reactive distillation

Aviation sector faces great challenges to guarantee its sustainable development. In order to achieve this main objective, several strategies have been proposed being the development of alternative aviation fuels one of the most promissory. The renewable aviation fuel can be generated from all type of biomasses; however, the hydroprocessing of triglyceride feedstock is one of the most mature technologies. In previous works, the hydrotreating process has been modeled considering different renewable raw materials; also, the application of intensification strategies has been proposed, particularly using thermally coupled distillation columns. In this work, the intensification of the hydrotreating process through reactive distillation columns is presented; jatropha curcas oil is considered as renewable raw material. Results show that it is feasible to use this intensification strategy, which allows an increasing of the yield to biojet fuel, decreasing the operation pressure and also the environmental impact.

Radiation Emissions from Turbulent Diffusion Flames Burning Vaporized Jet and Jet-like Fuels

This study measured and compared the size and radiation emissions from turbulent diffusion flames burning large hydrocarbon fuels, including jet fuels. This effort is motivated by the need to understand how burning conventional or alternative jet-like fuels changes radiation emissions. Radiative heat transfer is significant because it is can alter pollutant formation and the lifetime of combustion devices. Eleven fuels were evaluated, consisting of traditional and alternative aviation fuels (e.g., Jet-A) and 1–3 component fuels. The flames were burned on a reduced-scale piloted Sydney turbulent diffusion burner with Reynolds numbers (Re) ranging from 7500 to 45 000. The vaporized fuel exited the burner near 300 °C. The radiative heat flux and the radiation intensity were measured using a radiometer (Medtherm, Model 64-0.2-20) and a mid-infrared camera (FLIR, Model SC6700), respectively. The radiant fraction (χR) is reported for the different fuels. χR typically varied by <15% at similar Re for the different flames, despite the aromatic content ranging from 0% to 31%. The χR had a tendency to be relatively insensitive to aromatic content, but was sensitive to the weight percent of hydrogen in the fuel. Differences in the molecular structure of the fuels, even for fuels with similar hydrogen contents, can significantly affect χR. χR values initially increased as the Re was increased, but then decreased monotonically for Re > 20 000. This trend is attributed to competing effects of flame stretch, entrainment, and surface-to-volume ratio on radiation emissions. The peak radiation intensity occurs near the location of the peak heat flux, which corresponds to the visible flame height. Radiation emitted from soot and unburned hydrocarbons is predominantly observed from within the flame sheet; significant variations in radiation emissions was observed between the different fuels. In contrast, emissions from CO2 for all the fuels varied by <10% and were more broadly distributed across the flame. Fluctuations in radiation emissions have a tendency to be greatest near the flame sheet for CO2 and within the flame sheet for soot and unburned hydrocarbons. Total radiation emissions from these flames have a tendency to be dominated by emissions from gaseous combustion products instead of emissions from soot or unburned hydrocarbons.

Theoretical approach to modeling the combustion process in turbine engines fuelled by alternative aviation fuels containing various components/biocomponents

The aim of this paper is presentation of the possibility of combustion processes modelling so that to better describe the influence of fuels chemistry on fuels combustion. This is important for prediction the behaviour of different alternative fuels in processes in combustion chamber. Currently used mathematical models do not sufficiently take into account the influence of fuels chemical composition on combustion process. The idea of new mathematical model is proposed in this paper. The paper presents the main assumptions of this model and the results of its preliminary verification using MiniJetRig.

Multi-attribute sustainability evaluation of alternative aviation fuels based on fuzzy ANP and fuzzy grey relational analysis

The objective of this study is to develop a multi-attribute sustainability evaluation model for assessing the sustainability of various alternative aviation fuels. Fuzzy Analytic Network Process (ANP) which can incorporate the interdependences and interactions among the criteria was used for weights determination. Fuzzy Grey Relational Analysis (FGRA) was employed to determine the integrated priority of each alternative aviation fuel. Four alternative aviation fuels (petroleum refining -A1, Fischer-Tropsch synthesis based on natural gas -A2, algal-based fuel -A3, and soybean -based fuel -A4) were studied by the model, the sustainability order from the best to the worst determined based on the preferences/opinions of the three groups of stakeholders/decision-makers was Algal-based fuel (A3), soybean -based fuel (A4), petroleum refining (A1), and Fischer-Tropsch synthesis based on natural gas (A2). The method presented in this study was validated by comparing the results determine by the proposed method with that determined fuzzy TOPSIS and fuzzy sum weighted method, and the results in the case study were also validated by a programming based multi-criteria decision-making which partially using the real data to determine the sustainability order of the four aviation fuels. In order to investigate the effects of the weights on the sustainability order, sensitivity analysis was also carried out in this study.