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In this work, the potential of laser-induced ignition to improve combustion initiation and heat release in a direct-injection engine is investigated by a combined experimental and numerical investigation. Laser ignition is studied in fuel/air mixtures with homogeneous equivalence ratio fields. The results provide knowledge about minimum ignition energies and the ignition limits of laser-induced ignition. Furthermore, in mixtures with nominally identical conditions, statistical variations of the ignition success are observed experimentally. These variations can be explained, based on numerical simulations, by fluctuations in the strain rate in the turbulent in-cylinder flow. Additionally, laser ignition in engines with a spray-guided combustion mode, with strongly inhomogeneous fuel/air mixtures, was investigated.

To meet future emission standards with gasoline direct injection engines it is important to have a reliable process robustness during stratified charge operation. Especially engines with a wide spacing arrangement of fuel injector and spark plug which operate with an air-guided concept are very sensitive concerning misfire operation caused by cyclic variations of the mixture formation and transport. Primarily the turbulent in-cylinder gas motion and the interaction with the fuel injection indicate these fluctuations. To reduce these cycle-to-cycle variations and to generate a steady flow behavior an adjustable air-guiding system was developed and attached to the inlet port of a single-cylinder DI engine. The following examinations show that the air-guiding system can lead to a significant reduction of the cycle-to-cycle-variation of the in-cylinder air flow. As a result of these improvements, the deviation of imep in the fired engine decreases obviously.

This paper analyses the scavenge process of a conventional two-stroke engine in order to find ways to significantly reduce the scavenge losses by applying a combination of 1D and 3D simulation procedures. A special evaluation method was developed which allows a clear distinction between the main hydrocarbon loss mechanisms. Furthermore, the paper presents an approach to simulate the highly turbulent combustion at a speed of 9000 rpm. The results of the numerical investigations are compared with experimental results. The engine chosen for this purpose was a 64 cm3 four-port production two-stroke engine. The CFD calculations were performed using the finite volume CFD code STAR-CD. The mesh generation process was automated using pro*am. Combustion was modelled with the one-equation Weller flamelet model. The results of the present study show that the combination of 1D and 3D simulation procedures is a powerful tool for further investigations (e.g. stratified charge, GDI).

The main objectives of this investigation are the visualisation of the flame propagation depending on different boundary conditions. Turbulence intensities, wall-temperatures and an air-fuel ratios were varied in a wide range. For the experiments a rapid compression machine with a quadratic piston and a good optical access is used which allows to observe the entire burning. With an additionally integrated turbulence generator it is possible to create a defined turbulence field in the burning chamber.