Reaction mechanism validation for nitrogen diluted ethane/nitrous oxide mixtures at stoichiometric conditions has been performed using ignition delay time measurements at p = 1, 4 and 16 bar as well as laminar flame speed measurements at p = 1 and 3 bar. The predictive capability of the public domain mechanism GRI 3.0 was improved considerably by adapting some reactions within the nitrogen-subsystem and optimizing the most sensitive reactions with respect to selected optimization targets, i.e. ignition delay time and selected laminar flame speed measurements, within the published error bounds.
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.Synthetic fuels based on renewable energies (RE) are widely seen as a key element to achieving climate-neutral transport (e.g., [1,2]). As liquid hydrocarbons have a high energy and power density, they are primarily discussed as fuels for (heavy) road vehicles, ships, and aircraft. Due to their low storage and transport losses, they are also conceivable as a complementary long-term electricity storage option [3]. The challenges of producing and implementing these fuels are manifold. Chemical processes and renewable electrical or thermal energy can be used to produce liquid hydrocarbons from various carbon sources and hydrogen (and sometimes oxygen). Synthetic fuels have several advantages: they can be easily integrated into our existing energy and mobility infrastructures, can be used in all areas of the transport sector, and they can be optimized with regard to their chemical properties. The main disadvantages are the high energy losses and production costs.In this research context, eleven research groups at the German Aerospace Center (DLR) are working together on the Future Fuels project on synthetic fuels. The aim of the interdisciplinary approach is to realize synergies and joint research activities, as well as new research impulses through different perspectives. The scientists and engineers are investigating how synthetic fuels can be produced using solar energy and electrolysis processes (Solar Fuels), and are developing concepts for the re-conversion of these fuels into electricity. They are working on emission-optimized fuels for transport and aviation (Designer Fuels), as well as advanced space ap...
In this study a novel model for the analysis and optimisation of numerical and experimental chemical kinetics is developed. Concentration time profiles of non-diffusive chemical kinetic processes and flame speed profiles of fuel oxidiser mixtures can be described by certain characteristic points, so that relations between the coordinates of these points and input parameters of chemical kinetic models become almost linear. This linear transformation model simplifies the analysis of chemical kinetic models, hence creating a robust global sensitivity analysis and allowing a quick optimisation and reduction of these models. Firstly, in this study the model is extensively validated by the optimisation of a syngas combustion model with a large data set of imitated ignition experiments. The optimisation with the linear transformation model is quick and accurate, revealing the potential to decrease numerical costs of the optimisation process by at least one order of magnitude, compared to established methods. Additionally, the optimisation on this data set demonstrates the capability of predicting reaction rate coefficients, more accurately than by currently known confidence intervals. In a first application, methane combustion models are optimised with a small experimental set, consisting of OH(A) and CH(A) concentration profiles from shock tube ignition experiments, species profiles from flow reactor experiments and laminar flame speeds. With the optimised models, especially the predictability for the flame speeds of mixtures of hydrogen, carbon monoxide and methane can be increased compared to established models. With the analysis of the optimised models, new information for the low pressure reaction coefficient of the fall-off reaction H+CH 3 (+M)<=>CH 4 (+M) is determined. In addition, the optimised combustion model is quickly and efficiently reduced to validate a new rapid reduction scheme for chemical kinetic models.
In the last years, the development of synthetic aviation jet fuels has attracted much interest, to provide alternatives to crude-oil based kerosene. Synthetic jet fuels can be produced from a variety of feedstocks and processes. To limit possible harmful effects on the environment when burning a jet fuel, discussions are attributed to the effects of the specific composition of a synthetic fuel on its performance and its emission pattern. A numerical tool, if available, would also be helpful within the specification process any aviation jet fuel must pass. The present work contributes to the studies and efforts how to design a synthetic jet fuel to match predefined properties, e.g. the energy content or a less harmful emission characteristics compared to Jet A-1. The approach of a generic fuel will be followed in order to design a synthetic jet fuel with pre-defined chemical properties: A chemical kinetic reaction mechanism will be elaborated capable predicting the fundamental combustion properties of the generic fuel for each possible mixing ratio of the components included. In this work, a generic mixture serving as an innovative synthetic jet fuel was studied, with n-dodecane, cyclohexane, and iso-octane chosen as single fuel components; no aromatics were added to reduce the concentration of soot precursors. Then, their fundamental combustion properties, i.e. laminar burning velocity and ignition delay time, were measured in a burner test rig and applying the shock tube technique, respectively. These experimental data were used for the validation of the reaction mechanisms developed for each single fuel component, which were then combined to the reaction mechanism for the generic fuel under consideration. To allow a comparison of the combustion behavior of the synthetic jet fuel directly, with the same reaction mechanism, to Jet A-1, toluene was added as a model component for aromatics. A reduced surrogate reaction model was produced, too. All the reaction mechanisms elaborated are shown to reasonably predict the fundamental combustion properties within the parameter range considered. The compact reduced surrogate model can serve as a virtual jet fuel within numerical simulations. Thus, ultimately, an estimation of the suitability of an innovative synthetic jet fuel as a blending component to crude-oil kerosene is enabled. As a result, CFD simulations can be run efficiently tackling the combustion of a synthetic fuel in a jet engine under practical conditions and by taking into account the interaction between turbulence and chemistry.
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