Coordination Funds

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The significant improvement of present-day combustion systems used for mobility is an important aspect for the reduction of greenhouse gas emissions. The overarching goal of the Research Unit is to provide, based on systematic analysis of cyclic variations, the foundations for a further optimization of modern spark-ignition (SI) combustion concepts, which lead to considerable improvements of efficiency and the reduction of pollutant emissions. Presently, the operation range of highly optimized SI-engines is limited by the occurrence of unwanted combustion phenomena, such as misfire, incomplete fuel conversion, and engine knock, which are all significantly impacted by cyclic variations. Strategies to minimize the appearance of these phenomena exist, but they typically lead to reduced thermal efficiency and hence increased emissions of carbon dioxide. For a further optimization of SI-engines, it is therefore necessary to extend the operation range either by the reduction of cyclic variations or by their targeted exploitation in a way that ensures stable operation at high efficiency. Accomplishing this goal requires a fundamental understanding of the root causes, the development, and the effects of cyclic variations. However, at present, these are neither completely understood nor can they be predictively described. Using novel experimental techniques combined with innovative modeling and simulation technology, a detailed understanding of these phenomena will be established by performing forward and backward analysis of the multi-scale causal chain, and predictive simulation methods will be developed. For this, data for analysis and validation will be generated from experiments and direct numerical simulations for a hierarchy of different configurations from simple flows all the way to full engine cycles. The experimental data, which will be acquired with highly-accurate laser-based methods, will be unique compared with conventional engine experiments, since special attention will be devoted to initial and boundary conditions, which are of critical importance for numerical simulations. Only this level of detail will enable development and validation of new and highly accurate modeling approaches. On the basis of these data, predictive models for mixing and combustion will be developed and validated. Finally, cause and effect of cyclic variations both for idealized port-fuel-injected and for direct-injected SI-engines will be investigated by a combination of experimental studies and numerical analyses using large-eddy simulations (LES). The goal is the systematic forward and backward analysis of the causal chain to characterize cyclic variations and to identify their various causes in a close interaction of experiment and simulation.