Flame-propagation in inhomogeneous mixtures resulting from direct injection – large-eddy-simulation, model validation and analysis

在本计画中，将对直接喷射式氢引擎的流动、混合气形成与燃烧进行详细的模拟。这些大涡模拟（LES）考虑到不稳定的湍流场，混合物的不均匀性和传播的强回旋火焰具有高的空间和时间分辨率，使许多连续的周期可以模拟，这是不同的彼此的周期变化。首先使用实验数据检查（验证）模拟结果的正确性，然后进行分析。向后分析使用，与各种统计方法和记录的粒子轨迹，使得有可能识别的特殊功能，在早期的流动和混合领域，导致特别强或特别弱的火焰传播在（后来）点火时间和其后。在这种情况下，氢发动机的特殊性必须考虑在内，特别是（i）（超音速）直接喷射对流场的强烈影响和（ii）热扩散不稳定性的影响，它拉伸，折叠，从而扩大火焰（表面积），导致强烈加速燃烧。该项目旨在回答以下问题：a）在氢直接喷射期间，发动机中如何发生循环波动，以及如何有效地预测它们？B）氢燃烧的热扩散不稳定性对循环波动有什么影响，如何模拟它？c）燃烧室中燃料（和烟气）不均匀性的影响是什么？ 模拟使用详细的边界条件，氢气喷射，反应和火焰传播模型，以及实验验证数据。相反，模拟允许验证、分析和解释在实验中测量的数据，测试模型以及追溯到喷射射流和喷射器。该实验提供了快速和具有成本效益的测量点，从大量的循环，而模拟是有限的，以较少的循环，并受到模型假设，但允许详细访问所有状态在任何时间和在燃烧室中的任何位置。通过结合实验和模拟，相关的，验证和完整的数据集创建的基础上，详细的反向分析链的影响，导致循环波动的氢发动机与内部混合物的形成。

In this project, detailed simulations of flow, mixture formation and combustion in the hydrogen engine with direct injection are to be carried out. These large-eddy simulations (LES) take into account the unsteady turbulence fields, the mixture inhomogeneities and the propagation of the strongly convoluted flame with high spatial and temporal resolution, so that many successive cycles can be simulated, which differ from each other by cyclic variations. The results of the simulations are first checked (validated) for correctness using experimental data and then analysed. A backward analysis is used which, with various statistical methods and logged particle trajectories, makes it possible to identify special features in early flow and mixing fields which lead to particularly strong or particularly weak flame propagation at the (later) ignition time and thereafter. In this context, the particularities of hydrogen engines have to be taken into account, especially (i) the strong influence of the (supersonic) direct injection on the flow field and (ii) the effect of the thermodiffusive instability, which stretches, folds and thus enlarges the flame (surface area), leading to a strongly accel-erated combustion. This project aims to answer the following questions: a) How do cyclic fluctuations occur in the engine during hydrogen direct injection and how can they be efficiently predicted? b) What effects does the thermodiffusive instability of hydrogen combustion have on the cyclic fluctuations and how can it be modelled? c) What is the effect of fuel (and flue gas) inhomogeneities in the combustion chamber? The simulation uses detailed boundary conditions for hydrogen injection, reaction and flame propagation models, as well as experimental validation data. Conversely, the simulation allows the verification, analysis and interpretation of the data meas-ured in the experiment, the testing of the models as well as the tracing back into the injection jet and the injector. The experiment provides fast and cost-efficient measurement points from a large number of cycles, whereas the simulation is limited to fewer cycles and is subject to model assumptions, but allows detailed access to all states at any time and at any location in the combustion chamber. By combining experiment and simulation, relevant, validated and complete data sets are created as a basis for the detailed backward analysis of the chains of effects that lead to cyclic fluctuations in the hydrogen engine with internal mixture formation.