This work shows experiments and simulations of the fired operation of a spark ignition engine with port-fueled injection. The test-rig considered is an optically accessible single cylinder engine specifically designed at TU Darmstadt for the detailed investigation of in-cylinder processes and model validation. The engine was operated under lean conditions using isooctane as a substitute for gasoline. Experiments have been conducted to provide a sound database of the combustion process. A planar flame imaging technique has been applied within the swirl and tumble plane to provide statistical information on the combustion process to complement the pressure-based comparison between simulation and experiments. This data is then analyzed and used to assess the Large Eddy Simulation performed within this work. For the simulation, the engine code KIVA has been extended by the dynamically thickened flame model combined with chemistry reduction by means of pressure dependent tabulation. 60 cycles have been simulated to perform a statistical evaluation. Based on a detailed comparison with the experimental data, a systematic study has been conducted to obtain insight into the most crucial modeling uncertainties.
-This work applies Large Eddy Simulation (LES) to the combustion process within a CAI engine. The chemical reaction is treated with a pre-tabulation approach based on homogeneous reactor simulations. At this juncture, a five-dimensional chemistry database is employed where the thermochemical properties are a function of the unburnt gas temperature, the air-fuel ratio, the exhaust gas ratio, the pressure, and the reaction progress variable. Statistical quantities are gathered for 20 simulated cycles and the averaged pressure curves get compared to measurements. The simulation data are then used to provide further insight into the auto-ignition process. It will be shown how thermochemical states are distributed within the cylinder and how the ignition quality depends on them. A statistical analysis is conducted to identify manifolds in the multi-dimensional scalar space along which the conditions leading to ignition evolve. Furthermore the strong influence in between consecutive cycles caused by the exhaust gas is investigated to identify the mechanism of cycle-to-cycle variations.
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