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

从点燃的层流火焰核心到湍流火焰的过渡对于火花点火发动机的循环变化是至关重要的。对于非统一的刘易斯数的混合物，这种转变可以显着影响微分扩散效应，由于小火焰核的强曲率。在第二个供资期，氢将被用作燃料。在第一个资助期研究的异辛烷火焰的有效刘易斯数大于1，而贫氢火焰的有效刘易斯数低于1。因此，与异辛烷相反，对于氢，由于微分扩散，强烈凸形弯曲火焰核的局部燃烧速率增加。这会导致热扩散不稳定性，从而显著增加湍流火焰速度。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是显著不同的。这个子计划的目的是研究和模拟氢燃料发动机早期火焰传播的循环变化。为此，将进行TP 1中氢燃料发动机早期火焰核心的直接数值模拟（DNS）以及大涡模拟（LES）。DNS将在简化的发动机几何形状下进行，但这是第一次在考虑火花塞、火花通道与气流的相互作用以及滚流运动引起的平均速度的发动机相关条件下进行。首先将使用TP 1中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中获得的混合物分布条件，还将执行具有不均匀燃料分布的DNS。此外，将进行氢气/空气混合物中自燃的2D-DNS，其将被TP 7用于爆震建模。将所得数据与TP 1和TP 3的测量值进行比较。基于最优估计器和耗散元分析，将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将使用具有不均匀燃料分布的DNS数据进行模型开发。在这里，混合物的不均匀性对固有的不稳定性的影响是特别感兴趣的。模型将在TP 1中的发动机LES中进行验证。将在TP 1中使用LES和实验对循环间变化进行反向分析。

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.