Tailored surrogate fuels for the simulation of diesel engine combus- tion of novel biofuels

The finite nature of fossil fuel supply as well as the impact of the combustion of fossil fuels on atmospheric CO2 levels has led to increasing research efforts in the field of renewable fuels. In this context, the cluster of excellence "Tailor Made Fuels from Biomass" at RWTH Aachen University strives to develop and apply novel, third-generation, biomass-derived fuels. Recently, several promising fuels for diesel engines have been identified, produced, and test- ed. Diesel engine experiments at the Institute for Combustion Engines (VKA in the following) con- firmed very low soot and low NOX emissions. With regard to further improvements of the combustion system, it is desirable to complement the diesel engine experiments with numerical simulations. To date, this is hindered by the lack of suitable chemical reaction mechanisms for these novel fuels. Also, in the future, the development of chemical kinetic reaction mechanisms will not be able to keep up with the number of newly proposed bio-derived fuel components. Therefore, a surrogate approach is presented here and applied in CFD simulations. Combus- tion and pollutant formation is simulated using the representative interactive flamelet (RIF) model. By inclusion of detailed reaction chemistry, ignition, combustion, and pollutant formation are described in a consistent manner. Different mixtures of iso-octane, n-heptane, toluene, ethanol, dimethylether, and potentially other components are employed to describe the combustion chemistry of the biofuels. The compositions of the surrogate fuels are compiled according to H/C ratio, oxygen content, and cetane rating of the experimental fuels. Spray, injection, and evaporation properties of the experimental fuels, as obtained from spray vessel experiments, are included in the CFD simulations. By systematic comparison of experimental and numerical results, the surrogate methodology is validated and an improved understanding of the limitations of the current surrogate is achieved. Thus, a methodology for the fast adoption of novel fuels for simulations is proposed that can be used regardless of the availability of specific chemical re- action mechanisms.

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