Contrail cirrus account for the major share of aviation’s climate impact. Yet, the links between jet fuel composition, contrail microphysics and climate impact remain unresolved. Here we present unique observations from two DLR-NASA aircraft campaigns that measured exhaust and contrail characteristics of an Airbus A320 burning either standard jet fuels or low aromatic sustainable aviation fuel blends. Our results show that soot particles can regulate the number of contrail cirrus ice crystals for current emission levels. We provide experimental evidence that burning low aromatic sustainable aviation fuel can result in a 50 to 70% reduction in soot and ice number concentrations and an increase in ice crystal size. Reduced contrail ice numbers cause less energy deposition in the atmosphere and less warming. Meaningful reductions in aviation’s climate impact could therefore be obtained from the widespread adoptation of low aromatic fuels, and from regulations to lower the maximum aromatic fuel content.
Machine Learning (ML) models are increasingly applied in the field of jet fuel property predictions due to their ability of modelling a high number of complex composition-property relationships directly on measurement data. Their applicability is still limited as for safety relevant use cases like synthetic fuel approval or aircraft design consequences of prediction errors might be too severe to be acceptable. For Machine Learning algorithms the predictive capability strongly depends on the data utilized for the training for the models. Predictions for fuels that that differ from the training data might have uncertainties that need to be systematically considered. We present an approach of utilizing the probabilistic ML algorithm Gaussian Process Regression to model jet fuel density over a range of -40 to 140 °C and estimating the uncertainty that results from limited training data. To assess the influence of synthetic fuels on the predictive capability two models are studied, one trained exclusively on conventional fuels data and the other one trained on the same conventional fuels and additional synthetic fuels. The predictive capability of the models is assessed using metrics to rate the accuracy and precision of the prediction, as well as the validity and reliability of the estimated prediction interval. Results show that prediction intervals can correctly be estimated by both models and a valid estimation of the predictive capability is possible. Furthermore, the addition of synthetic fuels data drastically improves the accuracy, reduces the uncertainty, and is necessary to achieve adequate predictions for the considered hold-out fuels. The presented method is transferable and can be applied for different probabilistic models and jet fuel properties
A demonstrative Fischer-Tropsch fuel without any cost intensive post-processing treatment has been investigated for its application potential as a synthetic blending component with conventional petroleum-derived aviation fuels. As a first step, the focus of the analysis was purely on combustion related properties. The Fischer-Tropsch fuel was obtained via a specific Power-to-Liquid Fischer-Tropsch process, developed by Ineratec. Whereas the already approved Fischer-Tropsch-SPK process (ASTM D7566 Annex A1) utilizes hydrotreatment and is applied in large-scale plants, the herein presented plant features a unique and compact container-scale set-up, with no further downstream hydrotreatment, which allows for a significant reduction of production time and costs. Main objective of this paper is to provide the fuel producer with fast feedback to find the minimum complexity of fuel processing technology to achieve a synthetic blending component for aviation fuels directly from a container plant. As a first step in the ongoing process, the combustion properties of the non-hydroprocessed Fischer-Tropsch fuels are assessed regarding their suitability for aviation purposes.Fuel characterization was carried out regarding the physiochemical properties of the fuels and their chemical composition to monitor selected "fit-for-purpose" properties for aviation with regard to combustion properties. Additional combustion experiments were conducted in a high-temperature flow-reactor with coupled molecular beam mass spectrometer (MBMS) for two stoichiometries to map lean and rich combustion (Φ = 0.8 and 1.2), allowing quantitative access to the chemical reaction species formed within the combustion. The general combustion chemistry and reaction temperature regime was found similar to Jet A-1 and pure n-alkane decane. This indicates the dominant species for the observed combustion process are aliphatic hydrocarbons. The detailed evaluation of relevant intermediates allows for an observation on typical soot precursors (e.g. benzene, naphthalene) in the combustion process and enables the estimation on the pollutant reduction potential of the Fischer-Tropsch fuel when used as blending component to Jet A-1.Blending analysis has been performed utilizing the data from the CRC world fuel survey to evaluate the range of blending ratios of the Fischer-Tropsch fuel with conventional jet fuels determined by identified limiting factors. The presented evaluations demonstrate the potential of the Fischer-Tropsch fuel as a blending component with conventional jet fuels considering the combustion behavior only.
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