Experimental and Numerical Investigation of the Mechanisms of Local Extinction Using Flame Kernel-Vortex Interactions

本研究的目的是利用一种新的火焰核涡结构，从实验和计算两方面研究预混火焰中的局部消光过程。核涡相互作用提供了丰富的配置来研究至少两个重要的机制负责消光：火焰流场拓扑（曲率和应变）；和火焰-火焰相互作用（或相互火焰湮灭过程）。在同一相互作用下，可以同时产生正非定常应变率和负非定常曲率的条件，为比较火焰对不同类型火焰拉伸的响应提供了理想条件。此外，膨胀核对涡旋的相对大小决定了涡旋在核演化过程中对火焰起皱及其平流的贡献。这两种互补的（实验和计算）方法进行了协调，以提供对火焰和流场拓扑（主要是非定常应变和曲率效应）和相互火焰湮灭对局部火焰熄灭的作用的更好理解，并确定了测量预混碳氢化合物火焰局部燃烧强度的实验观测值。三个重要的因素代表了这项工作的主要推力及其技术优点：(1)火焰核涡相互作用中消光过程的实验研究。该研究依赖于广泛的实验条件，跨越不同的火焰和涡旋强度。同时测量中间物质、温度和速度，在火焰和流场拓扑和局部火焰响应之间提供了更强大的联系；(2)火焰核中受非定常应变淬灭或火焰相互湮灭作用的一般结构和两个重要区域的结构的数值研究。数值研究用于确定相关的实验条件，并利用详细的化学方法探索灭绝过程中涉及的化学机制。选取的实验条件为详细的化学模拟提供了初始条件；(3)综合方法为确定局部灭绝的条件和机制提供了补充信息。一个同样重要的努力是利用模拟来确定候选的实验观测值，这些观测值可用于量化非定常和熄灭条件下碳氢化合物预混火焰的燃烧强度。更广泛的影响核涡提供了一个现实的和有利的配置，以开发火焰熄灭模型，这将是有价值的，我们的理解湍流火焰一般和湍流核，特别是，如在火花点燃的内燃机和其他实际燃烧装置中观察到的。所提出的方法可以对燃烧科学和相关研究领域的类似问题产生广泛的影响，其中单独的计算或实验方法都不能充分解释观察结果。协调实验-计算方法的范例为项目要求的两种方法的研究生教育提供了独特的机会。

Project SummaryThe objective of this research is to investigate, both experimentally and computationally, the local extinction processes occurring in premixed flames using a novel flame kernel-vortex configuration. The kernel-vortex interaction provides a rich configuration to study at least two important mechanisms responsible for extinction: flame-flow field topologies (curvature and strain); and flame-flame interactions (or mutual flame annihilation processes). Conditions of positive and negative unsteady strain rate and curvature may be generated simultaneously within the same interaction, providing the ideal condition for comparing the flame's response to different types of flame stretch. Moreover, the relative size of the expanding kernel to the vortex results in an evolving contribution of the vortex to flame wrinkling and its advection during the kernel evolution. The two complementary (experimental and computational) approaches are coordinated to provide improved understanding of the role of flame and flow field topologies (mainly unsteady strain and curvature effects) and mutual flame annihilations on local flame extinction, and to identify experimental observables that measure the local burning intensity in premixed hydrocarbon flames. Three important elements represent the main thrusts of thework and its technical merit: (1) An experimental study of extinction processes during flame kernel-vortex interactions. The study relies on a broad range of experimental conditions that span different flame and vortex strengths. Simultaneous measurements of intermediate species, temperature, and velocity provide a more robust link between flame and flow-field topologies and the local flame response; (2) Numerical studies of the general structure as well as the structure of two important regions in the flame kernels that are subject to quenching by unsteady strain or mutual flame annihilation. The numerical studies are used to identify relevant experimental conditions and explore, using detailed chemistry, the chemical mechanisms involved during extinction. Initial conditions for the detailed chemistry simulations are provided by the selected experimental conditions; and (3) The combined approaches provide complementary information to identify conditions and mechanisms for local extinction. An equally important endeavor is to use the simulations to identify candidate experimental observables that may be used to quantify the burning intensity of hydrocarbon premixed flames for unsteady and extinction conditions.Broader impactThe kernel-vortex offers a realistic and advantageous configuration to develop models for flame extinction that will be of value to our understanding of turbulent flames in general and turbulent kernels specifically, such as those observed in spark-ignited internal combustion engines and other practical combustion devices. The methodology proposed can have a broad impact on similar problems in combustion science and related areas of research where neither computational nor experimental approaches alone can adequately explain observations. The paradigm of coordinated experimental-computational approaches provides unique opportunities for the education of graduate students in both approaches as the project requires.