Investigation and modeling of the early flame kernel development in hydrogen spark-ignition engines

氢火花点火发动机早期火焰核心发展的研究和建模

• 批准号: 422970818
• 负责人: Professor Dr.-Ing. Heinz Pitsch
• 金额: --
• 依托单位: Institut für Technische Verbrennung (ITV)
• 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/422970818?language=en
• 关键词: Investigation; modeling; early; flame; kernel

The transition from the ignited laminar flame kernel to turbulent flames is crucial for cycle-to-cycle variations in spark ignition engines. For mixtures with non-unity Lewis numbers, this transition can be significantly affected by differential diffusion effects due to the strong curvature of the small flame kernel. In the second funding period, hydrogen will be used as a fuel. In contrast to the iso-octane flames studied in the first funding period, which have an effective Lewis number larger than unity, lean hydrogen flames have an effective Lewis number lower than unity. As a result, in contrast to iso-octane, for hydrogen, the local burning rate in strongly convexly curved flame kernels increases due to differential diffusion. This can lead to thermodiffusive instabilities, and thus a significant increase in turbulent flame speed. Therefore, the transition from laminar flame kernels to turbulent flames is significantly different for hydrogen flames compared to iso-octane. This subproject aims to investigate and model the cycle-to-cycle variations of early flame propagation in hydrogen-fueled engines. For this purpose, Direct Numerical Simulations (DNS) of the early flame kernels as well as Large Eddy Simulations (LES) of the hydrogen-fueled engine in TP 1 will be performed. DNS will be performed for a simplified engine geometry, but for the first time under engine-relevant conditions considering the spark plug, interactions of the spark channel with the flow, and a mean velocity caused by the tumble motion. Simulations will first be carried out for a homogeneous fuel distribution using conditions derived from the experiments in TP 1. Using the mixture distribution conditions obtained from the experiments in TP 3 and the LES in TP 5, DNS with inhomogeneous fuel distribution will also be performed. Furthermore, 2D-DNS of auto-ignition in hydrogen/air mixtures will be carried out, which will be used by TP 7 for knock modeling. The resulting data will be compared with measurements from TP 1 and TP 3. Investigations and modelling of the interactions between the intrinsic instabilities and turbulence, as well as the influences of relative velocity and spark plug, will be carried out based on the optimal estimator and dissipation element analysis. DNS data with inhomogeneous fuel distribution will be used by TP 5 for model development. Here, the influence of the mixture inhomogeneities on the intrinsic instabilities is of particular interest. Models will be validated in LES of the engine in TP 1. Backward analysis of the cycle-to-cycle variations will be performed in TP 1 using LES and experiments.

从点燃的层流火焰核心到湍流火焰的转变对于火花点火发动机的循环变化至关重要。对于具有非统一路易斯数的混合物，由于小火焰核的强曲率，这种转变可能会受到微分扩散效应的显着影响。在第二个资助期，氢气将被用作燃料。与第一个资助期研究的异辛烷火焰相比，其有效路易斯数大于1，贫氢火焰的有效路易斯数低于1。因此，与异辛烷相比，对于氢来说，由于扩散差异，强烈凸弯曲的火焰核心中的局部燃烧速率增加。这可能导致热扩散不稳定性，从而导致湍流火焰速度显着增加。因此，与异辛烷相比，氢火焰从层流火焰核心到湍流火焰的转变显着不同。该子项目旨在研究氢燃料发动机中早期火焰传播的循环变化并对其进行建模。为此，将对 TP 1 中的早期火焰内核进行直接数值模拟 (DNS) 以及氢燃料发动机的大涡模拟 (LES)。 DNS 将针对简化的发动机几何形状进行，但首次在发动机相关条件下考虑火花塞、火花通道与流动的相互作用以及翻滚运动引起的平均速度。首先将使用从 TP 1 中的实验得出的条件对均匀燃料分布进行模拟。使用从 TP 3 中的实验和 TP 5 中的 LES 中获得的混合分布条件，还将执行具有不均匀燃料分布的 DNS。此外，还将进行氢气/空气混合物中自燃的 2D-DNS，TP 7 将使用该方法进行爆震建模。所得数据将与 TP 1 和 TP 3 的测量结果进行比较。将基于最佳估计器和耗散元素分析，对固有不稳定性和湍流之间的相互作用以及相对速度和火花塞的影响进行调查和建模。 TP 5 将使用燃料分布不均匀的 DNS 数据进行模型开发。在这里，混合物不均匀性对内在不稳定性的影响特别令人感兴趣。模型将在 TP 1 中的发动机 LES 中进行验证。循环间变化的向后分析将在 TP 1 中使用 LES 和实验进行。