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.

The desired reduction of fossil fuel consumption of the aviation sector requires the introduction of alternative jet fuels from renewable sources. A major hurdle for their introduction is the cost-intensive assessment of fuel effects on combustion performance, which relies on fuel-dependent processes such as atomization, vaporization and chemical reaction. The present work describes results from a newly designed experiment that provides accurate measurements of vaporization of free-falling droplets of realistic size (D≈80 µm) in a vertical laminar flow with temperatures typical of technical combustors. Measurements are performed for a set of systematically chosen conventional and alternative multi-component jet fuels for which detailed compositions are available, and for three single species. The results show that the differences of their vaporization can be accurately resolved and related to physical properties. In particular, it is found that the effect of fuel boiling point on vaporization is largest for ambient gas temperatures T ∞ below ≈1000 K, whereas for higher T ∞ the influence of heat of vaporization is dominant. The well-defined boundary conditions of the experiment further enable a numerical simulation of the ambient flow and the droplet vaporization, where the latter uses a multi-component vaporization model based on a continuous thermodynamic representation of chemical species. Comparisons to measurements show that the present model accurately predicts the temporal evolution of droplet diameters and fuel-dependent effects on vaporization.

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Alternative jet fuels have a high potential to reduce emissions in aviation. A big difficulty for their introduction is the costly and lengthy assessment of fuel effects on combustion performance. In the present work, the evaporation of freefalling droplets of realistic size (D ≈ 80 µm) in a well-defined vertical laminar heated flow is studied experimentally and numerically. Measurements of droplet diameters and velocities using microscopic double-pulse shadowgraphy are conducted for several single species and systematically chosen conventional and alternative multi-component jet fuels.The results show that the experiment is fuel-sensitive with respect to evaporation. In this study, special attention is paid to unknown or uncertain boundary and initial conditions, which serve as input in the validation of the numerical models. Therefore, non-intrusive non-deterministic simulations using Polynomial Chaos Expansion are performed to account for these uncertainties. The uncertainty quantification displays that overall uncertainties are small enough to distinguish between the different fuels and to predict fuel-dependent effects on evaporation. Nevertheless, the uncertainties are not negligible. A sensitivity analysis shows a high sensitivity of the evaporation to the offset of the droplet from the centerline and to the uncertainty of the inflow gas temperature. Reducing the uncertainties of the two above-mentioned conditions is most promising in enhancing the validation experiment.

Alternative jet fuels have a high potential to reduce emissions in aviation and to increase the independence from mineral oil. However, as a safe operation must be guaranteed, new fuels have to pass elaborate and expensive tests to be finally certified. To reduce the costs and time of the certification process, numerical simulations can be used to assess the impact of a new fuel on combustion. Further, the detailed simulations provide an insight into the fuel sensitive sub-processes. The lean blowout (LBO), i.e. the lower stability limit of a gas turbine combustor, is of primary concern for safe operation and the approval of alternative jet fuels. The paper at hand focuses on the formulation of a calculation protocol for the numerical representation of a lab-scale LBO experiment. The test case is a swirl-stabilized spray flame, which mimics several key features of aero-engine combustors. The LBO-limits are determined by a stepwise reduction of the fuel mass flow starting from a stable operation point above the measured blowout limit. Towards extinction, the heat release rate in the combustor drops. Furthermore, fuel is still evaporating, but less fuel is burned, leading to an accumulation of fuel in the combustion chamber. The blow-out is defined by a steep drop in heat release combined with a large increase of the gaseous fuel mass fraction in the computational domain. The semi-automated calculation protocol is able to successfully capture a blowout event at an equivalence ratio of ϕ = 0.32 and can thus be applied to evaluate alternative jet fuels in the future. In addition, a reignition event is observed for equivalence ratios slightly above ϕLBO.