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

本研究的目的是从实验和计算两方面研究预混火焰中的局部熄灭过程，采用一种新的火核-旋涡结构。核-涡相互作用为研究至少两种重要的消光机制提供了丰富的构型：火焰-流场拓扑(曲率和应变)和火焰-火焰相互作用(或相互火焰湮没过程)。在相同的相互作用中，可以同时产生正负非定常应变率和曲率的条件，为比较火焰对不同类型火焰拉伸的响应提供了理想的条件。此外，膨胀核与涡旋的相对大小导致了涡旋在核演化过程中对火焰起皱及其平流的演化贡献。这两种互补的(实验和计算)方法相互协调，以更好地理解火焰和流场拓扑(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，并确定测量预混碳氢火焰局部燃烧强度的实验观测数据。三个重要部分代表了这项工作的主要内容及其技术优点：(1)火核-旋涡相互作用过程的实验研究。这项研究依赖于广泛的实验条件，这些条件跨越不同的火焰和涡旋强度。对中间组分、温度和速度的同时测量在火焰和流场拓扑与局部火焰响应之间提供了更牢固的联系；(2)对火焰核中的两个重要区域的一般结构以及结构进行了数值研究，这两个区域受到非稳定应变或相互火焰湮灭的影响。数值研究被用来确定相关的实验条件，并用详细的化学方法探索灭绝过程中涉及的化学机制。所选实验条件为详细的化学模拟提供了初始条件；(3)组合方法提供了补充信息，以确定局部灭绝的条件和机制。另一项同样重要的工作是利用模拟来确定候选的实验观测数据，这些实验观测数据可以用来量化碳氢化合物预混火焰在非稳定和熄灭条件下的燃烧强度。广泛影响核涡提供了一个现实和有利的结构来发展火焰熄灭模型，这将对我们理解总体上的湍流火焰和特别是湍流内核有价值，例如在火花点火内燃机和其他实际燃烧装置中观察到的那些。所提出的方法可以对燃烧科学和相关研究领域中的类似问题产生广泛影响，在这些领域中，仅靠计算或实验方法都不能充分解释观测结果。协调实验-计算方法的范例为这两种方法的研究生教育提供了独特的机会，这是项目需要的。

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.