Numerical investigation and cause-and-effect analysis of cyclic fluctuations and their effect on auto-ignition in hydrogen combustion

在资助期1，采用尺度分辨模拟（LES）来研究循环波动对烃基燃料爆震燃烧发展的影响。结果表明，在紊流自燃模型中，必须考虑多组分燃料的复杂点火动力学。特别是在负温度系数（NTC）状态下，点火延迟时间对温度的强烈非线性依赖直接影响发动机的自动点火。NTC系统的两级自动点火特性可以用更先进的自动点火模型来建模。在使用TP 2的直接数值模拟（DNS）数据进行验证后，对引擎LES进行了实现。利用多循环LES分析表明，NTC体系中的自燃化学与影响局部自燃过程的循环燃烧波动之间存在很强的相互作用。快速燃烧与大的压力上升率和强压缩的最终气体导致早期爆震发生。LES进一步表明，自燃质量与实验观察到的爆震幅值之间存在很强的相关性。在第二个资助期内，将研究氢燃料发动机中异常燃烧现象的发生。爆震和预点火都可归因于湍流和热表面的自燃。在发动机工况下，氢气表现出非常复杂的点火行为，不仅受到动力学的影响，还受到强烈的微分扩散效应的影响。在少数关于氢发动机的研究中，迄今主要研究的是全局变量；在本项目中，重点分析了发动机工况下的局部点火过程。对输运、氢化学的局部相互作用，以及在表面点火的情况下，对壁面的相互作用将有更好的理解。资助期1的模型将扩展到氢点火，并将首先对TP 2的一般火焰和DNS数据进行验证。发动机的应用将与TP 6密切合作进行调查。点火将首先在具有温度控制表面的高压室中进行，然后在氢发动机中进行。在因果链分析中，将研究局部自燃与流量、残余气体分数和燃烧的循环变化的相互作用。

In funding period 1, scale-resolved simulations (LES) were used to investigate the influence of cyclic fluctuations on the development of knocking combustion for hydrocarbon-based fuels. It was shown that the complex kinetics of ignition of multicomponent fuels must be taken into account for modeling turbulent auto-ignition. In particular, the strongly nonlinear dependence of the ignition delay time on temperature in the Negative Temperature Coefficient (NTC) regime has a direct impact on auto-ignition under engine conditions. The two-stage auto-ignition that is characteristic of the NTC regime could be modeled using a more advanced auto-ignition model. After validation using data from a direct numerical simulation (DNS) from TP 2, the implementation for the engine LES was carried out. Using a multi-cycle LES, it was shown that there is a strong interaction between the auto-ignition chemistry in the NTC regime and the cyclic combustion fluctuations that affect local auto-ignition processes. Rapid combustion with large pressure rise rates and strong compression of the end gas resulted in earlier knock onset. LES further showed a strong correlation between auto-igniting mass and experimentally observed knock amplitudes. In the second funding period, the occurrence of abnormal combustion phenomena in hydrogen-fueled engines will be investigated. Both knocking and pre-ignition can be attributed to auto-ignition in turbulent flows and at hot surfaces. Under engine conditions, hydrogen exhibits very complex ignition behavior, which is influenced not only by kinetics but also by strong differential diffusion effects. In the few studies on hydrogen engines, mainly global variables have been investigated so far; in this project, the focus is on the analysis of the local ignition processes under engine conditions. A better understanding of the local interaction of transport, hydrogen chemistry and, in the case of surface ignition, the wall will be achieved. The models of funding period 1 will be extended for hydrogen ignition, and validation will initially be performed on generic flames and DNS data from TP 2. The engine application will be investigated in close cooperation with TP 6. Ignition will be considered first in a high-pressure chamber with temperature-controlled surfaces, then in the hydrogen engine. In a cause-and-effect chain analysis, the interaction of local auto-ignition with cyclic variations of the flow, the residual gas fraction and the combustion will be investigated.