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

直接喷射产生的不均匀混合物中的火焰传播 â 大涡模拟、模型验证和分析

• 批准号: 423192870
• 负责人: Professor Dr.-Ing. Andreas Kempf
• 金额: --
• 依托单位: Lehrstuhl für Fluiddynamik
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/423192870?language=en
• 关键词: Flame; propagation; inhomogeneous; mixtures; resulting

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.

在这个项目中，将对直喷式氢气发动机的流动、混合气形成和燃烧进行详细的模拟。这些大涡模拟(LES)考虑了非定常湍流场、混合气的不均匀以及强卷曲火焰的传播，具有很高的时空分辨率，因此可以模拟多个连续的周期，这些周期因周期变化而不同。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。采用反向分析方法，通过各种统计方法和记录的颗粒轨迹，可以识别早期流动和混合场的特殊特征，这些特征导致在(稍后)点火时间及之后火焰传播特别强或特别弱。在这种情况下，必须考虑氢发动机的特殊性，特别是(I)超音速直喷对流场的强烈影响和(Ii)热扩散不稳定性的影响，热扩散不稳定性伸展、折叠，从而扩大火焰(表面积)，导致强烈加速燃烧。本项目旨在回答以下问题：a)发动机在氢气直接喷射过程中如何发生循环波动，以及如何有效地预测这些波动？B)氢燃烧的热扩散不稳定性对循环波动有什么影响？如何对其进行建模？C)燃烧室中燃料(和废气)不均匀的影响是什么？该模拟使用了详细的边界条件，用于氢喷射、反应和火焰传播模型，以及实验验证数据。相反，模拟可以对实验中测量的数据进行验证、分析和解释，还可以对模型进行测试，并可以追溯到喷嘴和喷嘴。该实验提供了大量循环的快速、经济高效的测量点，而模拟仅限于较少的循环，并受模型假设的限制，但允许在任何时间和燃烧室的任何位置详细访问所有状态。通过实验和模拟相结合的方法，建立了相关的、有效的和完整的数据集，作为详细的反向分析的基础，这些影响链导致了具有内部混合气形成的氢发动机的循环波动。