An investigation on flame-front instability in laminar and turbulent flames

现代高性能发动机（如汽车和飞机发动机）的燃烧发生在高压湍流条件下。发动机的效率和可靠性在很大程度上取决于火焰动力学，而在这种极端条件下，火焰动力学本质上是不稳定的。提出的研究将描述在发动机相关条件下火焰前缘不稳定性对火焰传播的作用。这些知识是优化现代发动机所需要的，特别是在高压和高湍流条件下。使用独特的双腔容器，可以进行高压研究，实验的目标是扩展我们目前对层流和湍流火焰火焰前不稳定性的了解。本研究的结果可以推广到其他问题，例如即使在大气压下燃烧也本质上是湍流的野火和城市火灾的大规模火涡动力学，以及具有宇宙强度的超新星爆炸的天体物理现象。该项目将吸引研究生和本科生，他们将在学习基础燃烧物理和化学的同时接触到先进的诊断。该计划旨在了解和量化在静态或明确定义的湍流环境中传播火焰的内在火焰前不稳定性的不同模式的基本动力学。这种认识目前还很不成熟，但这是现代内燃机设计和优化的进一步发展所需要的。该研究包括在高压和恒压条件下使用高速高分辨率光学诊断对火花点燃的球形火焰进行实验。这项研究的独特之处在于控制良好、特征良好的高压环境。在这样的环境中，突出的流体动力细胞/起皱火焰前结构得到了体现，并且可以使用光学诊断以前所未有的细节精确量化。通过获取高保真实验数据以及定量定义和评估各种稳定性参数，有助于理解。这项工作将描述在孤立不稳定、孤立湍流及其耦合影响条件下不同模式火焰传播的全局和局部长度尺度。由于拟议的研究包括实验和理论研究，它将为这两个组成部分的设计和数据解释提供必要的协同经验，从而导致高压湍流燃烧系统知识的进步。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Combustion in modern high-performance engines, such as automotive and aircraft engines, occurs at high-pressure turbulent conditions. Engine efficiency and reliability strongly depend on flame dynamics, which can be intrinsically unstable in such extreme conditions. The proposed research will characterize the role of flame-front instabilities on flame propagation in engine-relevant conditions. This knowledge is needed for optimizing modern engines, especially at high pressures and high turbulent conditions. Using a unique dual-chamber vessel, which allows high-pressure investigations, the experiments will be targeted to extend our current knowledge on flame-front instabilities in both laminar and turbulent flames. Results from this study can be extended to other problems, such as large-scale fire-whirl dynamics in wildland and urbane fires, which are intrinsically turbulent even the combustion is at atmospheric pressure, in addition to the astrophysical phenomena of the supernova explosion with cosmic intensity. This project will engage graduate and undergraduate students who will be exposed to advanced diagnostics while studying the basic combustion physics and chemistry.The proposed program aims to understand and quantify the fundamental dynamics of different modes of intrinsic flame-front instabilities of propagating flames in either quiescent or well-defined turbulent environments. Such an understanding is rather immature at present but is required for the further advance in the design and optimization of modern combustion engines. The investigation includes experimentation on spark-ignited, spherical flames at high- and constant-pressure conditions using high-speed high-resolution optical diagnostics. The uniqueness of this study is the well-controlled, well-characterized, high-pressure environment. In such environments, prominent hydrodynamic cellular/wrinkling flame-front structures are manifested and can be precisely quantified using optical diagnostics in unprecedented details. The understanding is facilitated by acquiring high-fidelity experimental data and by quantitatively defining and assessing various stability parameters. This work will characterize global and local length scales for different modes of flame propagation under conditions of isolated instability, isolated turbulence, and their coupled influences. Since the proposed study includes both experimental and theoretical investigations, it will provide the essential synergistic experience in the design and data interpretation of both components, leading to advances in the knowledge of high-pressure turbulent combustion systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.