Numerical Modeling of Flame Propagation in the Flamelet Regime

奖项建议编号：CTS-0552140首席研究员：马塔隆，莫什研究所：西北大学提案题目：火焰传播的数值模拟燃烧是一个非常经济和社会关注的课题。尽管人们在继续寻找替代能源，但燃烧仍然提供了当今所消耗的大部分能源。因此，必须确保以最有效的方式利用燃烧过程，并将对环境的不良影响降至最低。拟议的活动旨在提高我们对燃烧现象的理解，从而为更好的工程设计提供建议。其具体目标是对复杂的火焰传播问题进行建模和模拟，类似于实际应用中遇到的问题。基于这些模型的预测可能会导致燃烧设备效率的提高，燃料消耗的节省，以及污染物和不需要的再燃烧产物的排放的减少。拟议工作的更广泛影响将通过技术和科学界的出版物和专题介绍以及培训和教育在学术界和工业界从事职业的新一代科学家来实现。燃烧问题包括在不同的时间和长度尺度上发生的现象的相互作用。在所有尺度上解决这些问题，无论大小，都是一项具有数学挑战性和计算密集型的任务。提出利用复杂火焰传播问题的多尺度特性对其进行数值模拟。火焰理论的渐近进展将被用来简化数学描述。由于火焰被限制在一个表面上，数学公式简化为一个自由边界问题，并补充了一些条件，这些条件说明了发生在较小尺度上的过程的影响。简化的问题仍然是非线性的，具有相当的挑战性；但它的相对简单性使得能够在跨越广泛的物理参数的同时处理大规模多维火焰的动力学。对于本项目中提出的一些问题的描述，目前的水动力模型是足够的。该模型综合了热膨胀、差异和优先扩散、混合物强度、非统一反应级数、依赖温度的传输和体积热损失(辐射损失)的影响，并可能包括使用简化的化学机制的详细动力学。利用该框架，对流体动力不稳定火焰的非线性发展、火焰起皱和火焰加速以及外部随机噪声对传播的影响进行了数值模拟。有时，需要修改流体动力学描述，例如，允许沿火焰表面创建孔洞及其后果。所提出的工作具有许多潜在的应用，包括湍流火焰，特别是在火焰区，最小的相关尺度大于火焰厚度，因此不影响内部火焰结构。这种制度包括许多实际应用，例如火花点火发动机和涡轮喷气式发动机。

Award AbstractProposal Number: CTS-0552140Principal Investigator: Matalon, MosheInstitution: Northwestern University Proposal Title: Numerical Modeling of Flame Propagation in the Flamelet RegimeCombustion is a subject of great economical and societal concern. Despite the continuing search for alternative energy sources, combustion still provides the majority of the energy consumed today. It is therefore important to ensure that combustion processes are utilized in the most efficient way and in such a way as to minimize undesirable effects on the environment. The proposed activity is directed towards improving our understanding of combustion phenomena, which may consequently lead to suggestions for better engineering design. The specific objective is to model and simulate complex flame propagation problems similar to the one encountered in practical applications. Predictions based on such models may lead to improvement in the efficiency of combustion devices, saving in fuel consumption, and reduction in the emission of pollutants and unwanted after-burning products. The broader impact of the proposed work will occur through publications and presentations in the technical and scientific community and by training and educating a new generation of scientists for careers in academia and industry. Combustion problems encompass the interaction of phenomena that take place on different time and length scales. Resolving such problems on all scales, small and large, poses a mathematically challenging and computationally intensive task. It is proposed to numerically simulate complex flame propagation problems by exploiting their multi-scale nature. The asymptotic advances in flame theory will be used to simplify the mathematical description. With the flame confined to a surface, the mathematical formulation reduces to a free-boundary problem supplemented by conditions that account for the influences of the processes occurring on the smaller scales. The simplified problem, still nonlinear, is quite challenging; but its relative simplicity enables addressing the dynamics of large-scale multi-dimensional flames while spanning a wide range of the physical parameters. For the description of some of the problems proposed in this project, the hydrodynamic model in its present state is adequate. The model incorporates effects of thermal expansion, differential and preferential diffusion, mixture strength, non-unity reaction orders, temperature-dependent transport and volumetric heat losses (radiative losses), and can potentially include detailed kinetics using reduced chemistry mechanisms. Using this framework, it is proposed to numerically simulate the nonlinear development of hydrodynamically unstable flames, flame wrinkling and flame acceleration, and the effect of external random noise on the propagation. Occasionally, the hydrodynamic description needs to be modified, for example by allowing for the creation of holes along the flame surface and its consequences. The proposed work has many potential applications including turbulent flames, particularly in the flamelet regime, where the smallest relevant scales are larger than the flame thickness and therefore do not affect the internal flame structure. Such regime encompasses many practical applications, for example spark-ignition engines and turbojets.